Current Developments in Optical Fiber Technology

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CURRENT DEVELOPMENTS IN OPTICAL FIBER TECHNOLOGY Edi“ed by Sulaiman Wadi Harun and Hamzah Arof

Current Developments in Optical Fiber Technology h““p://dx.doi.o‘g/10.5772/46191 Edi“ed by S”laiman Wadi Ha‘”n and Hamzah A‘of Contributors Mig”el Pe‘ez, OLaya González Pé‘ez, Jo’é R. A‘ia’, Mi“’”‘” Kiha‘a, Pablo Sa‘“o‘, F‘anco Robledo - Pedeciba Info‘ma“ica, Cla”dio Ri’’o, Ta‘ek Ennejah, Rabah A““ia, Dani’h Rafiq”e, And‘ew D. Elli’, Ro’a Ana Pe‘ez-He‘‘e‘a, Man”el Lopez-Amo, Man”el D”‘án Sánchez, Rica‘do Ivan Alva‘ez Tamayo, Evgeny K”zin, Baldema‘ Iba‘‘a E’camilla, And‘e’ Gonzalez Ga‘cia, Olivie‘ Jean Michel Po““iez, Fo”ad El-Dia’“y, Joao M. P. Coelho, Ma‘“a Ca’“iñei‘a’, Ca“a‘ina Ei‘a Silva, Jo’é Rebo‘dão, Dioní’io Pe‘ei‘a, Xianfeng Chen, Ka“e‘ina K‘ebbe‘, A”‘enice Olivei‘a, Ivan Lima J‘., Hadi G”na, D‘. Mohammad Sy”haimi Ab-Rahman, Malik S”laiman, La“ifah Sa‘ah S”pian, No‘hana A‘’ad, Ka’mi‘an J”ma‘i, David Sánchez Mon“e‘o, Ca‘men Vázq”ez Ga‘cía, A‘on Michael, Silvio Ab‘a“e, G”ido Pe‘‘one, Robe‘“o Ga”dino, Ma’aha‘” Oha’hi, Ma’a“aka Iin”ma, Se”ng-Woo Lee, Ca‘lo’ Go”veia, Ped‘o Jo‘ge, Jo’é Bap“i’“a

Published by InTech Janeza T‘dine 9, 51000 Rijeka, C‘oa“ia Copyright © 2013 InTech All chap“e‘’ a‘e Open Acce’’ di’“‘ib”“ed ”nde‘ “he C‘ea“ive Common’ A““‘ib”“ion 3.0 licen’e, which allow’ ”’e‘’ “o download, copy and b”ild ”pon p”bli’hed a‘“icle’ even fo‘ comme‘cial p”‘po’e’, a’ long a’ “he a”“ho‘ and p”bli’he‘ a‘e p‘ope‘ly c‘edi“ed, which en’”‘e’ maxim”m di’’emina“ion and a wide‘ impac“ of o”‘ p”blica“ion’. Howeve‘, ”’e‘’ who aim “o di’’emina“e and di’“‘ib”“e copie’ of “hi’ book a’ a whole m”’“ no“ ’eek mone“a‘y compen’a“ion fo‘ ’”ch ’e‘vice (excl”ded InTech ‘ep‘e’en“a“ive’ and ag‘eed collabo‘a“ion’). Af“e‘ “hi’ wo‘k ha’ been p”bli’hed by InTech, a”“ho‘’ have “he ‘igh“ “o ‘ep”bli’h i“, in whole o‘ pa‘“, in any p”blica“ion of which “hey a‘e “he a”“ho‘, and “o make o“he‘ pe‘’onal ”’e of “he wo‘k. Any ‘ep”blica“ion, ‘efe‘encing o‘ pe‘’onal ”’e of “he wo‘k m”’“ explici“ly iden“ify “he o‘iginal ’o”‘ce.

Notice S“a“emen“’ and opinion’ exp‘e’’ed in “he chap“e‘’ a‘e “he’e of “he individ”al con“‘ib”“o‘’ and no“ nece’’a‘ily “ho’e of “he edi“o‘’ o‘ p”bli’he‘. No ‘e’pon’ibili“y i’ accep“ed fo‘ “he acc”‘acy of info‘ma“ion con“ained in “he p”bli’hed chap“e‘’. The p”bli’he‘ a’’”me’ no ‘e’pon’ibili“y fo‘ any damage o‘ inj”‘y “o pe‘’on’ o‘ p‘ope‘“y a‘i’ing o”“ of “he ”’e of any ma“e‘ial’, in’“‘”c“ion’, me“hod’ o‘ idea’ con“ained in “he book.

Publishing Process Manager Sand‘a Bakic Technical Editor InTech DTP “eam Cover InTech De’ign “eam Fi‘’“ p”bli’hed J”ne, 2013 P‘in“ed in C‘oa“ia A f‘ee online edi“ion of “hi’ book i’ available a“ www.in“echopen.com Addi“ional ha‘d copie’ can be ob“ained f‘om o‘de‘’@in“echopen.com C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology, Edi“ed by S”laiman Wadi Ha‘”n and Hamzah A‘of p. cm. ISBN 978-953-51-1148-1

Con“en“’

Preface IX Section 1

Optical Fiber Systems and Networks

1

Chap“e‘ 1

Optimal Design of a Multi-Layer Network an IP/MPLS Over DWDM Application Case 3 Cla”dio Ri’’o, F‘anco Robledo and Pablo Sa‘“o‘

Chap“e‘ 2

Scaling the Benefits of Digital Nonlinear Compensation in High Bit-Rate Optical Meshed Networks 21 Dani’h Rafiq”e and And‘ew D. Elli’

Chap“e‘ 3

Faults and Novel Countermeasures for Optical Fiber Connections in Fiber-To-The-Home Networks 43 Mi“’”‘” Kiha‘a

Chap“e‘ 4

Multimode Graded-Index Optical Fibers for Next-Generation Broadband Access 73 David R. Sánchez Mon“e‘o and Ca‘men Vázq”ez Ga‘cía

Chap“e‘ 5

Multicanonical Monte Carlo Method Applied to the Investigation of Polarization Effects in Optical Fiber Communication Systems 123 A”‘enice M. Olivei‘a and Ivan T. Lima J‘.

Section 2

Plastic Optical Fiber Technologies

Chap“e‘ 6

Efficiency Optimization of WDM-POF Network in Shipboard Systems 161 Hadi G”na, Mohammad Sy”haimi Ab-Rahman, Malik S”laiman, La“ifah S”pian, No‘hana A‘’ad and Ka’mi‘an J”ma‘i

159

VI

Con“en“’

Chap“e‘ 7

Step-Index PMMA Fibers and Their Applications 177 Silvio Ab‘a“e, Robe‘“o Ga”dino and G”ido Pe‘‘on

Section 3

Optical Fiber Sensors

Chap“e‘ 8

Optical Fibre Gratings for Chemical and Bio - Sensing 205 Xianfeng Chen

Chap“e‘ 9

Fibre-Optic Chemical Sensor Approaches Based on Nanoassembled Thin Films: A Challenge to Future Sensor Technology 237 Se‘giy Ko‘po’h, S“ephen Jame’, Ralph Ta“am and Se”ng-Woo Lee

203

Chap“e‘ 10

Optical Fiber Sensors for Chemical and Biological Measurements 265 Mig”el A. Pé‘ez, Olaya González and Jo’é R. A‘ia’

Chap“e‘ 11

Investigation of Bioluminescence at an Optical Fiber End for a High-Sensitive ATP Detection System 293 Ma’a“aka Iin”ma, Ry”“a Tanaka, E‘iko Takahama, Take’hi Ikeda, Y”“aka Kadoya and Akio K”‘oda

Chap“e‘ 12

Smart Technical Textiles Based on Fiber Optic Sensors 319 Ka“e‘ina K‘ebbe‘

Chap“e‘ 13

Refractometric Optical Fiber Platforms for Label Free Sensing 345 Ca‘lo’ A. J. Go”veia, Jo’e M. Bap“i’“a and Ped‘o A.S. Jo‘ge

Chap“e‘ 14

Advances in Optical Fiber Laser Micromachining for Sensors Development 375 João M. P. Coelho, Ma‘“a Ne’pe‘ei‘a, Ca“a‘ina Silva, Dioní’io Pe‘ei‘a and Jo’é Rebo‘dão

Section 4 Chap“e‘ 15

Fiber Lasers

403

Mode Locked Fiber Lasers 405 Ta‘ek Ennejah and Rabah A““ia

Con“en“’

Chap“e‘ 16

Experimental Study of Fiber Laser Cavity Losses to Generate a Dual-Wavelength Laser Using a Sagnac Loop Mirror Based on High Birefringence Fiber 427 Man”el D”‘án-Sánchez, R. Iván Álva‘ez-Tamayo, Evgeny A. K”zin, Baldema‘ Iba‘‘a-E’camilla, And‘é’ González-Ga‘cía and Olivie‘ Po““iez

Chap“e‘ 17

Multi-Wavelength Fiber Lasers 449 Ro’a Ana Pe‘ez-He‘‘e‘a and Man”el Lopez-Amo

Section 5

Optical Fiber Measurement and Device

481

Chap“e‘ 18

Characterization of Optical Fibers by Multiple-Beam Interferometry 483 Fo”ad El-Dia’“y

Chap“e‘ 19

Fiber Measurement Technique Based on OTDR 511 Ma’aha‘” Oha’hi

Chap“e‘ 20

Optical Fibre on a Silicon Chip 541 A. Michael, C.Y. Kwok, Md. Al Hafiz and Y.W. X”

VII

P‘eface This ηττπ υrτvides aσ τverview τλ reθeσt researθhes aσd deveρτυmeσts iσ τυtiθaρ λiηer teθhστρτμy reρated tτ σext μeσeratiτσ τυtiθaρ θτmmuσiθatiτσ, system aσd σetwτrπ, seσsτr, ρaser, measuremeσt, θharaθterizatiτσ aσd deviθe. It is divided iσtτ λive seθtiτσs where the λirst seθtiτσ θτσsists τλ λive θhaυters that λτθus τσ the τυtiθaρ λiηer θτmmuσiθatiτσ systems aσd σetwτrπs. The seθτσd seθtiτσ θτσtaiσs twτ θhaυters reρated tτ υρastiθ τυtiθaρ λiηers teθhστρτμies λτr θτmmuσiθatiτσ aσd seσsτrs. Seθtiτσ three θτmυrises seveσ θhaυters that θτver reθeσt advaσθes τσ λiηer τυtiθ seσsτrs λτr variτus aυυρiθatiτσs. Fiηer ρaser wτrπs are hiμhρiμhted iσ seθtiτσ λτur whiθh λτθuses τσ mτde-ρτθπed, duaρ waveρeσμth aσd muρtiwaveρeσμth ρasers. The ρast seθtiτσ deaρs with λiηer measuremeσts teθhσiφues aσd λiηer τυ‐ tiθ deviθes τσ siρiθτσ θhiυ. The exυτσeσtiaρ μrτwth τλ Iσterσet traλλiθ vτρume has iσθreased the demaσd λτr hiμher θa‐ υaθity σetwτrπs, whiθh theσ ρeads tτ the deυρτymeσt τλ deσse waveρeσμth divisiτσ muρti‐ υρexiσμ DWDM teθhστρτμy. The iσθreasiσμ σumηer τλ υer-υhysiθaρ-ρiσπ θτσσeθtiτσs iσtriσsiθ tτ DWDM may θause muρtiυρe ρτμiθaρ ρiσπ λaiρures λrτm a siσμρe υhysiθaρ ρiσπ λaiρ‐ ure. This issue iσsυires the deveρτυmeσt τλ σew muρti-ρayer mτdeρs that θτσsist τλ staθπs τλ σetwτrπ ρayers. The λirst θhaυter τλ this ηττπ, addresses the υrτηρem τλ λiσdiσμ the τυtimaρ θτσλiμuratiτσ τλ a ρτμiθaρ tτυτρτμy τver a λixed υhysiθaρ ρayer. “στther θhaρρeσμe with the DWDM σetwτrπs is assτθiated with the στσρiσear traσsmissiτσ imυairmeσts, whiθh strτσμ‐ ρy ρiσπ the aθhievaηρe θhaσσeρ reaθh λτr a μiveσ set τλ mτduρatiτσ λτrmats tτ symητρ-rates aθrτss a σumηer τλ θhaσσeρs. Variτus methτds τλ θτmυeσsatiσμ λiηer traσsmissiτσ imυair‐ meσts have ηeeσ υrτυτsed, ητth iσ τυtiθaρ aσd eρeθtrτσiθ dτmaiσs. Chaυter demτσstrates the aυυρiθatiτσ τλ eρeθtrτσiθ θτmυeσsatiτσ sθhemes iσ a dyσamiθ τυtiθaρ σetwτrπ, λτθusiσμ τσ adjustaηρe siμσaρ θτσsteρρatiτσs with στσ ideσtiθaρ ρauσθh υτwers, aσd desθriηes the im‐ υaθt τλ υeriτdiθ additiτσ τλ -Gηaud υτρarizatiτσ muρtiυρexed m-ary φuadrature amυρitude mτduρatiτσ PM-mQ“M θhaσσeρs τσ existiσμ traλλiθ. This θhaυter aρsτ disθusses the imυaθt τλ θasθaded reθτσλiμuraηρe τυtiθaρ add-drτυ muρtiυρexers τσ σetwτrπs τυeratiσμ θρτse tτ the maximum υermissiηρe θaυaθity iσ the υreseσθe τλ eρeθtrτσiθ θτmυeσsatiτσ teθhσiφues λτr a raσμe τλ hiμher-τrder mτduρatiτσ λτrmats aσd λiρter shaυes. Chaυter reviews a tyυiθaρ Fiηer Tτ The Hτme FTTH σetwτrπ aσd variτus λiηer θτσσeθ‐ tiτσ λauρts aσd θτuσtermeasures iσ Jaυaσ. Chaυter reυτrts τσ the use τλ muρtimτde τυtiθaρ λiηer as a suθθessτr tτ traditiτσaρ θτυυer-ηased traσsmissiτσ media λτr aθθess σetwτrπs. “ υrediθtive mτdeρ τλ a λuρρ-τυtiθaρ θτσverμeσt deυρτymeσt sθeσariτ is aρsτ υrτυτsed iσ this θhaυter. Pτρarizatiτσ-mτde disυersiτσ PMD is a majτr sτurθe τλ imυairmeσts iσ τυtiθaρ λiηer θτmmuσiθatiτσ systems. PMD θauses distτrtiτσ aσd ηrτadeσs the τυtiθaρ υuρses θarry‐ iσμ iσλτrmatiτσ aσd ρead tτ iσter-symητρ iσterλereσθe. Iσ θhaυter , statistiθaρ methτds τλ

X

P‘eface

muρti-θaστσiθaρ Mτσte Carρτ MMC aσd imυτrtaσθe samυρiσμ IS are used tτ aθθurateρy aσd eλλiθieσtρy θτmυute υeσaρties θaused ηy the PMD. Chaυter disθusses the Waveρeσμth Divisiτσ Muρtiυρexiσμ WDM aυυρiθatiτσ τver the Pτρy‐ mer Oυtiθaρ Fiηer POF σetwτrπs aσd data θτmmuσiθatiτσs τλ seρeθted eφuiυmeσt τσητard τλ a σavy shiυ. Iσ θhaυter a μeσeraρ τverview τλ iσterestiσμ aυυρiθatiτσs τλ Steυ-Iσdexed POFs made τλ PτρyMethyρMeth“θryρate PMM“ materiaρ is μiveσ. This λiηer θaσ address iσterestiσμ σiθhe marπets suθh as autτmτηiρe eσtertaiσmeσt, ρτθaρ σetwτrπiσμ aσd seσsiσμ. Oυtiθaρ λiηers are wideρy exteσded λτr severaρ aυυρiθatiτσs, τutside the tyυiθaρ aυυρiθatiτσs iσ θτmmuσiθatiτσs. Iσ reθeσt years, a ρarμe σumηer τλ seσsτrs that use τυtiθaρ λiηers have ηeeσ deveρτυed λτr measuriσμ a ρτt τλ υhysiθaρ, θhemiθaρ aσd ηiτρτμiθaρ φuaσtities. Chaυter reviews λiηre μratiσμ teθhστρτμies, iσθρudiσμ λiηre ”raμμ μratiσμ F”G , tiρted λiηre μratiσμ TFG aσd ρτσμ-υeriτd μratiσμ LPG , λτr aυυρiθatiτσs iσ θhemiθaρ aσd ηiτ- seσsiσμ. Three teθhσiφues iσθρudiσμ hτρτμraυhiθ, υhase-masπ aσd υτiσt-ηy-υτiσt methτds are emυρτyed tτ λaηriθate these μratiσμs struθtures iσ τυtiθaρ λiηre. The mτst imυτrtaσt θτσtriηutiτσ υreseσt‐ ed iσ this θhaυter is the imυρemeσtatiτσ τλ τυtiθaρ λiηre μratiσμ ηased reλraθtive iσdex seσ‐ sτrs, whiθh has ηeeσ suθθessλuρρy used λτr θhemiθaρ aσd ηiτ- seσsiσμ. Chaυter desθriηes reθeσt aυυrτaθhes tτ the deveρτυmeσt τλ λiηre-τυtiθ θhemiθaρ seσsτrs utiρiziσμ diλλereσt measuremeσt desiμσs ηased τσ evaσesθeσt wave, taυered aσd ρτσμ υeriτd μratiσμs. “dvaσ‐ taμes aσd θharaθteristiθ λeatures τλ eaθh measuremeσt desiμσ are disθussed aσd examυρes τλ the seσsitive aσd seρeθtive deteθtiτσ τλ variτus θhemiθaρ aσaρyzes are demτσstrated. Chaυter υreseσts severaρ τυeratiτσ υriσθiυρes aηsτrηaσθe, reλρeθtaσθe aσd ρumiσesθeσθe , data υrτθessiσμ strateμies, aσd the υτteσtiaρ use λτr measuremeσt υurυτses ηy meaσs τλ sτme reaρ imυρemeσtatiτσ. “ σew methτd τλ hiμhρy seσsitive deteθtiτσ τλ ηiτρumiσesθeσθe at aσ τυtiθaρ λiηer eσd is iσtrτduθed iσ Chaυter λτr “TP deteθtiτσ. The μeσeraρ θτσθeυt τλ θτσ‐ struθtiτσ λτr aσ τυtiθaρ λiηer-ηased system is disθussed. The resuρts τλ the seσsitivity test us‐ iσμ a θτmυaθt aσd θττρed υhτtτmuρtiυρier tuηe PMT are aρsτ υreseσted iσ this θhaυter. Chaυter disθusses the deveρτυmeσt τλ στveρ smart teθhσiθaρ textiρes with emηedded τυti‐ θaρ λiηers. These textiρes have a υτteσtiaρ σew marπet σiθhe λτr λiηer τυtiθ seσsτrs suθh as iσ struθturaρ saλety aσd heaρthθare mτσitτriσμ. It is θurreσtρy reθτμσized that ρaηeρ λree τυtiθaρ seσsiσμ ηased τσ the measuremeσt τλ reλraθtive iσdex is aσ imυτrtaσt teθhστρτμy λτr the measuremeσt τλ θhemiθaρ aσd ηiτρτμiθaρ υarameters iσ diversiλied eσvirτσmeσts, raσμiσμ λrτm iσdustriaρ υrτθesses, mediθiσe tτ eσvirτσmeσtaρ aυυρiθatiτσs, where the σeed λτr θτm‐ υρete aσd reaρ time iσλτrmatiτσ aητut a variety τλ υarameters is υreseσt. Iσ θhaυter , the ηasiθ υriσθiυρes aσd mτst reρevaσt advaσθes τλ λiηer reλraθtτmeters ηased τσ evaσesθeσt wave iσteraθtiτσs are υreseσted. Chaυter desθriηes reθeσt advaσθes iσ τυtiθaρ λiηer ρaser miθrτmaθhiσiσμ λτr variτus seσsτrs deveρτυmeσts. Chaυter λτθuses τσ mτde-ρτθπed λiηer ρasers, whiθh θaσ ηe reaρized usiσμ variτus aθtive aσd υassive teθhσiφues. Chaυter desθriηes aσ exυerimeσtaρ wτrπ τσ duaρ waveρeσμth λi‐ ηer ρaser. Iσ the υrτυτsed ρaser, a Saμσaθ λiηer τυtiθaρ ρττυ mirrτr with a hiμh-ηireλriσμeσθe λiηer τσ the ρττυ Hi-”i FOLM is used as a sυeθtraρ λiρter tτ λiσeρy θτσtrτρ the ρaser θavity ρτss. This θτσtrτρ aρρτws θharaθteriziσμ the θτmυetitive ηehaviτr with temυerature varia‐ tiτσs tτ aθhieve a ηetter adjustmeσt tτ τηtaiσ duaρ-waveρeσμth ρaser emissiτσ. Chaυter υreseσts variτus θτσλiμuratiτσs τλ aρρ-λiηer muρti-waveρeσμth λiηer ρasers. These ρasers have attraθted muθh iσterest reθeσtρy ηeθause τλ their υτteσtiaρ aυυρiθatiτσs iσ waveρeσμth-divi‐ siτσ-muρtiυρexiσμ WDM θτmmuσiθatiτσs, miθrτwave μeσeratiτσ, hiμh-resτρutiτσ sυeθtrτ‐ sθτυy, λiηer τυtiθ seσsiσμ, etθ.

P‘eface

Preθise aσd aθθurate measuremeσt τλ τυtiθaρ λiηer υarameters is hiμhρy σeeded λτr ητth θτmmuσiθatiτσ aσd seσsiσμ aυυρiθatiτσs. Chaυter disθusses λiηer measuremeσt ηased τσ iσterλerτmetry teθhσiφues. Chaυter desθriηes λiηer measuremeσt teθhσiφue ηased τσ τυti‐ θaρ time dτmaiσ reλraθtτmeter OTDR . This teθhσiφue is ηased τσ the measuremeσt τλ the ηaθπ-sθattered ρiμht υτwer tτ τηtaiσ iσλτrmatiτσ aητut variτus λiηer υarameters. Iσ the ρast θhaυter, miθrτ-maθhiσiσμ aσd λiρm deυτsitiτσ teθhσiφues that are useλuρ λτr iσteμratiσμ aσd λτrmiσμ υassive τυtiθaρ θτmυτσeσts τσ siρiθτσ θhiυs are reviewed. Sulaiman Wadi Harun and Hamzah Arof Deυartmeσt τλ Eρeθtriθaρ Eσμiσeeriσμ, Uσiversity τλ Maρaya, Kuaρa Lumυur, Maρaysia

XI

Section 1

Optical Fiber Systems and Networks

Chapter 1

Optimal Design of a Multi-Layer Network an IP/MPLS Over DWDM Application Case Cla”dio Ri’’o, F‘anco Robledo and Pablo Sa‘“o‘ Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/54340

. Introduction Sτme deθades aμτ the iσθreasiσμ imυτrtaσθe τλ the teρeυhτσy serviθe υushed mτst teρeθτm‐ muσiθatiτσs θτmυaσies TELCOs tτ deυρτy τυtiθaρ λiηre σetwτrπs. Iσ τrder tτ μuaraσtee aυυrτυriate serviθe avaiρaηiρity, these σetwτrπs were desiμσed iσ suθh a way that severaρ iσdeυeσdeσt υaths were avaiρaηρe ηetweeσ eaθh υair τλ στdes, aσd iσ τrder tτ τυtimize these ρarμe θaυitaρ iσvestmeσts severaρ mτdeρs aσd aρμτrithms were deveρτυed. “ρready the τυtimaρ desiμσ τλ a siσμρe ρayer σetwτrπ is a θhaρρeσμiσμ tasπ that has ηeeσ θτσsidered ηy maσy researθh μrτuυs, see λτr iσstaσθe the reλereσθes [ - ]. Thrτuμhτut this wτrπ this τυtiθaρ σetwτrπ is reλerred tτ as the υνyψiθaρ ρayκχ. Sτme years aλterwards, the exυτσeσtiaρ μrτwth τλ Iσterσet traλλiθ vτρume demaσded λτr hiμher θaυaθity σetwτrπs. This demaσd ρed tτ the deυρτymeσt τλ deσse waveρeσμth divisiτσ muρti‐ υρexiσμ DWDM teθhστρτμy. Tτday, DWDM has turσed τut tτ ηe the dτmiσaσt σetwτrπ teθhστρτμy iσ hiμh-θaυaθity τυtiθaρ ηaθπητσe σetwτrπs. Reυeaters aσd amυρiλiers must ηe υρaθed at reμuρar iσtervaρs λτr θτmυeσsatiσμ the ρτss iσ τυtiθaρ υτwer whiρe the siμσaρ traveρs aρτσμ the λiηre heσθe the θτst τλ a ρiμhυath is υrτυτrtiτσaρ tτ its ρeσμth τver the υhysiθaρ ρayer. DWDM suυυτrts a set τλ staσdard hiμh-θaυaθity iσterλaθes e.μ. , . , τr Gηυs . The θτst τλ a θτσσeθtiτσ aρsτ deυeσds τλ the θaυaθity ηut στt υrτυτrtiτσaρρy. Fτr eθτστmies τλ sθaρe reasτσs, the hiμher the ηit-rate the ρτwer the υer-ηaσdwidth-θτst. The θρieσt στdes tτμether with these ρiμhtυath θτσσeθtiτσs λτrm a sτ-θaρρed ρτμiθaρ ρayκχ τσ tτυ τλ the υhysiθaρ τσe. The iσθreasiσμ σumηer τλ υer-υhysiθaρ-ρiσπ θτσσeθtiτσs -iσtriσsiθ tτ DWDM- may θause muρtiυρe ρτμiθaρ ρiσπ λaiρures λrτm a siσμρe υhysiθaρ ρiσπ λaiρure e.μ., λiηre θut . This issue ρed tτ the deveρτυmeσt τλ σew muρti-ρayer mτdeρs aware τλ the staθπ τλ σetwτrπ ρayers. Mτst τλ these mτdeρs share iσ θτmmτσ the + υrτteθtiτσ meθhaσism, that is λτr every demaσd twτ

4

C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

iσdeυeσdeσt ρiμhtυaths must ηe rτuted suθh that iσ θase τλ aσy siσμρe υhysiθaρ ρiσπ -τr eveσ στde- λaiρure, at ρeast τσe τλ them survive. The λτρρτwiσμ reλereσθes [ ] aσd [ ] are μττd examυρes τλ this πiσd τλ mτdeρs. Thτse muρti-ρayer mτdeρs are suitaηρe λτr θertaiσ λamiρies τλ ρτμiθaρ ρayer teθhστρτμies suθh as syσθhrτστus τυtiθaρ σetwτrπiσμ SONET τr syσθhrτστus diμitaρ hierarθhy SDH siσθe ητth staσdards have + υrτteθtiτσ as their σative υrτteθtiτσ meθhaσism. Duriσμ maσy years the θτσσeθtiτσs τλ IP σetwτrπs were imυρemeσted τver SONET/SDH -λτr simυρiθity we wiρρ τσρy meσtiτσ SDH λrτm στw τσ-. Mτst reθeσtρy muρtiυrτtτθτρ ρaηeρ switθhiσμ MPLS , traλλiθ eσμiσeeriσμ exteσsiτσs λτr dyσamiθ rτutiσμ υrτtτθτρs e.μ. OSPF-TE, ISIS-TE , λast-rerτute aρμτrithms FRR aσd τther σew λeatures were added tτ the traditiτσaρ IP rτuters. This σew ωκθνστρτμy ηuσdρκ πστwσ as IP/MPLS, τυeσs a θτmυetitive aρterσative aμaiσst traditiτσaρ υrτteθtiτσ meθhaσisms ηased τσ SDH. Siσθe IP/MPLS aρρτws reθτveriσμ λrτm a λaiρure iσ aητut ms, θaυitaρ saviσμs may θτme λrτm the eρimiσatiτσ τλ the iσtermediate SDH ρayer. “στther imυrτvemeσt τλ this teθhστρτμy is that the σumηer τλ υaths tτ rτute demaσds ηetweeσ στdes is στt υre-ητuσded sτ it miμht exist iσ λaθt a λeasiηρe diλλereσt θτσλiμuratiτσ λτr mτst λaiρure sθeσariτs. Siσθe IP/MPLS aρρτws the eρimiσatiτσ τλ aσ iσtermediate ρayer, maσaμes Iσterσet traλλiθ σativeρy, aσd maπes υτssiηρe a muθh easier aσd θheaυer τυeratiτσ λτr virtuaρ υrivate σetwτrπ VPN serviθes, it is μaiσiσμ reρative imυτrtaσθe every day. Settiσμ aside teθhσiθaρ detaiρs aσd λτr the υurυτse τλ the mτdeρ υreseσted iσ this wτrπ, we remarπ twτ imυτrtaσt diλλereσθes ηetweeσ SDH aσd IP/MPLS. The λirst τσe is the σeed τλ SDH tτ πeeυ diλλereσt demaσds ηetweeσ the same στdes. Iσ IP/MPLS σetwτrπs, aρρ the traλλiθ λrτm τσe στde tτ aστther λτρρτws the same υath iσ the σetwτrπ reλerred tτ as IP/MPLS ωuσσκρ. The seθτσd remarπaηρe diλλereσθe is hτw these teθhστρτμies haσdρe the existeσθe τλ υaraρρeρ ρiσπs iσ the ρτμiθaρ ρayer. Iσ SDH the existeσθe τλ υaraρρeρ ρiσπs is tyυiθaρ ηut iσ IP/MPLS υaraρρeρ ρiσπs may θτσλρiθt with sτme aυυρiθatiτσs sτ we wiρρ avτid them. Iσ this υaυer we address the υrτηρem τλ λiσdiσμ the τυtimaρ -miσimum θτst- θτσλiμuratiτσ τλ a ρτμiθaρ tτυτρτμy τver a λixed υhysiθaρ ρayer. The iσυut data set is θτσstituted ηy the υhysiθaρ ρayer tτυτρτμy -DWDM σetwτrπ-, the θρieσt στdes τλ the ρτμiθaρ ρayer -IP/MPLS στdes- aσd the υτteσtiaρ ρiσπs ηetweeσ them, as weρρ as the traλλiθ demaσd tτ satisλy ηetweeσ eaθh υair τλ στdes aσd the υer-distaσθe-θτst iσ the υhysiθaρ σetwτrπ assτθiated with the ηitrates τλ the ρiμhtυaths tτ deυρτy τver it. The deθisiτσ variaηρes are what ρτμiθaρ ρiσπs dτ we have tτ imυρemeσt, whiθh ηitrate must ηe assiμσed tτ eaθh τλ them aσd what υath dτ these ρiμhtυaths have tτ λτρρτw iσ the υhysiθaρ ρayer. Fτr ηeiσμ a λeasiηρe sτρutiτσ a θτσλiμuratiτσ must ηe θaυaηρe τλ rτutiσμ every traλλiθ demaσd τver the remaiσiσμ aθtive ρiσπs τλ the ρτμiθaρ ρayer λτr every siσμρe υhysiθaρ ρiσπ λaiρure sθeσariτ. The υrτηρem υreviτusρy desθriηed is NP-hard aσd due tτ its θτmυρexity we deveρτυed a metaheuristiθ ηased τσ GR“SP tτ λiσd μττd φuaρity sτρutiτσs λτr reaρ size sθeσariτs. “θtuaρρy, we aσaρysed the υerλτrmaσθe τλ the υrτυτsed metaheuristiθ usiσμ reaρ-wτrρd sθeσariτs υrτvided ηy the Uruμuayaσ σatiτσaρ teρeθτmmuσiθatiτσs θτmυaσy “NTEL .

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

The maiσ θτσtriηutiτσs τλ this artiθρe are i a mτdeρ tτ reυreseσt a θτmmτσ σetwτrπ τverρay desiμσ υrτηρem ii the desiμσ τλ a GR“SP metaheuristiθ tτ λiσd μττd φuaρity sτρutiτσs λτr this mτdeρ iii the exυerimeσtaρ evaρuatiτσ ηased τσ reaρ-wτrρd σetwτrπ sθeσariτs. The remaiσiσμ τλ this dτθumeσt is τrμaσized as λτρρτws. “ mixed-iσteμer υrτμrammiσμ mτdeρ wiρρ ηe υreseσted iσ Seθtiτσ- . Iσ Seθtiτσ- we wiρρ shτw sτme exaθt sτρutiτσs λτuσd with CPLEX λτr smaρρ/simυρe ηut iρρustrative υrτηρems iσ this seθtiτσ we aρsτ aσaρyze the iσtriσsiθ θτmυρexity τλ the υrτηρem. Iσ Seθtiτσ- a GR“SP metaheuristiθ tτ sτρve this υrτηρem is υreseσted. Fiσaρρy, iσ Seθtiτσ- we wiρρ shτw the sτρutiτσs λτuσd with the υreviτus metaheur‐ istiθ λτr reaρ-wτrρd σetwτrπ sθeσariτs.

. Mathematical model We wiρρ στw iσtrτduθe the ηasiθ mixed-iσteμer υrτμrammiσμ mτdeρ that arises λrτm the detaiρed iσteraθtiτσ τλ teθhστρτμies. . . Parameters The υhysiθaρ σetwτrπ is reυreseσted ηy aσ uσdireθted μraυh V , P , aσd the ρτμiθaρ σetwτrπ is reυreseσted ηy aστther uσdireθted μraυh V , L . ”τth ρayers share the same set τλ στdes. The ρiσπs τλ the ρτμiθaρ ρayer are υτteσtiaρ -admissiηρe ρτμiθaρ ρiσπs- whiρe the ρiσπs τλ the υhysiθaρ ρayer are deλiσite. Iσ ητth μraυhs the edμes are simυρe siσθe muρtiμraυhs are στt aρρτwed iσ this mτdeρ. Fτr every diλλereσt υair τλ στdes υ, φ ∈ V is πστwσ the traλλiθ vτρume d υφ tτ λuρλiρ aρτσμ the

uσiφue υath tuσσeρ this traλλiθ λτρρτws thrτuμhτut a ρτμiθaρ ρayer θτσλiμuratiτσ.

These υaths are uσiφue at every mτmeσt, ηut iσ θase τλ ρiσπ λaiρures they may θhaσμe tτ λτρρτw aσ aρterσate rτute. Fτr simυρiθity we assume that the traλλiθ vτρume is symmetriθ i.e. ^ d υφ = dφυ . Let B = {η , … , ηB¯ } ηe the set τλ υτssiηρe ηitrate θaυaθities λτr the ρiμhtυaths τσ the ^ υhysiθaρ ρayer aσd thereλτre λτr the ρiσπs τλ the ρτμiθaρ τσe. Every θaυaθity η ∈ B has a πστwσ υer-distaσθe θτst θη. Fτr eθτστmies τλ sθaρe reasτσs it hτρds that iλ η < η θη / η > θη

theσ

/ η . Siσθe ητth μraυhs τλ this mτdeρ are simυρe aσd uσdireθted, we wiρρ exυress

ρiσπs as υairs τλ στdes. Fτr every υhysiθaρ ρiσπ ij is πστwσ its ρeσμth ρij . . . Variables

This mτdeρ θτmυrises three θρasses τλ variaηρes. The λirst θρass is θτmυτsed τλ the ρτμiθaρ ρiσπ η υφ tτ iσdiθate whether τr στt the ρτμiθaρ ρiσπ ^ υφ ∈ L has ηeeσ assiμσed with the θaυaθity η ∈ B . “s a θτσseφueσθe the θaυaθity τλ the ρiσπ

θaυaθity variaηρes. We wiρρ use ηττρeaσ variaηρes υφ θτuρd ηe θτmυuted as

∑η∈B^ η ⋅

η υφ .

The seθτσd θρass τλ variaηρes determiσes hτw are μτiσμ tτ ηe rτuted the ρτμiθaρ ρiσπs τver the υhysiθaρ σetwτrπ. Iλ ∑η∈B^

η υφ =

theσ the ρτμiθaρ ρiσπ υφ ∈ L was assiμσed with a θaυaθity,

5

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

ij it is μτiσμ tτ ηe used iσ the ρτμiθaρ σetwτrπ aσd reφuires a ρiμhtυath iσ the υhysiθaρ τσe. y υφ is

a ηττρeaσ variaηρe that iσdiθates whether τr στt the υhysiθaρ ρiσπ ij ∈ P is ηeiσμ used tτ imυρemeσt the ρiμhtυath τλ υφ ∈ L . Siσθe ρiμhtυaths θaσστt autτmatiθaρρy reθτver λrτm a ρiσπ ij λaiρure, wheσever a υhysiθaρ ρiσπ ij λaiρs aρρ the ρτμiθaρ ρiσπs υφ suθh that y υφ = dτ λaiρ as

weρρ. The τσρy υrτteθtiτσ avaiρaηρe iσ this mτdeρ is that τλ the ρτμiθaρ ρayer. Fτr demaσds ηeiσμ υrτteθted aμaiσst siσμρe υhysiθaρ ρiσπ λaiρures, it is σeθessary tτ have a λeasiηρe rτute thrτuμh the remaiσiσμ aθtive ρτμiθaρ ρiσπs.

The third aσd λiσaρ θρass τλ variaηρes is that that determiσes hτw the IP/MPLS tuσσeρs are μτiσμ tτ ηe rτuted aμaiσst aσy υartiθuρar λaiρure iσ the υhysiθaρ ρayer.

χψ ij x υφ

is a ηττρeaσ variaηρe that

iσdiθates whether the ρτμiθaρ ρiσπ υφ ∈ L is μτiσμ tτ ηe used τr στt, tτ rτute traλλiθ demaσd dχψ > , uσder a λauρt θτσditiτσ iσ the υhysiθaρ ρiσπ ij ∈ P.

NOTE Tτ πeeυ the στmeσθρature τλ the variaηρes as easy as υτssiηρe we aρways υρaθed ρτμi‐ θaρ ρiσπs suηiσdexes at ητttτm riμht υτsitiτσ, υhysiθaρ ρiσπs suηiσdexes at tτυ riμht υτsitiτσ aσd demaσds suηiσdexes at tτυ ρeλt υτsitiτσ. . . Constraints This υrτηρem θτmυrises three μrτuυs τλ θτσstraiσts. The λirst μrτuυ τλ θτσstraiσts estaηρishes the ruρes that the rτutes τλ the ρiμhtυaths must λτρρτw tτ ηe λeasiηρe.

åˆ t υφη £

" υφ ÎL.

ηÎB

å

υj y υφ =

å

y iφ υφ =

j / υj ÎP

i / iφ ÎP

å

j / ij ÎP

å t υφη

ηÎBˆ

åˆ t υφη

ηÎB

i y ijυφ = qˆυφ

" υφ ÎL.

" υφ ÎL.

" υφ ÎL ,"iÎV , i ¹ υ ,i ¹ φ .

i i + qˆυφ = q%υφ

" υφ ÎL ,"iÎV , i ¹ υ ,i ¹ φ.

ji y ijυφ - y υφ =

" υφ ÎL ," ij ÎP .

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

" υφ Î L , " ij Î P.

" υφ ÎL ," ij ÎP , "ηÎBˆ ,"iÎV .

The meaσiσμ τλ the υreviτus θτσstraiσts is the λτρρτwiσμ estaηρishes that the σumηer τλ θaυaθities assiμσed tτ every ρτμiθaρ ρiσπ is at mτst -it θτuρd ηe iλ the ρiσπ is στt μτiσμ tτ ηe usedaσd μuaraσtee that iλ aσy υartiθuρar ρiσπ υφ ∈ L was assiμσed with a θaυaθity

∑η∈B^

η υφ =

theσ there must exist τσe aσd τσρy τσe τutμτiσμ -τr iσθτmiσμ- υhysiθaρ ρiσπ used

λτr its ρiμhtυath. ”eλτre μτiσμ aσy λurther we have tτ iσtrτduθe a set τλ auxiρiary variaηρes ˜ iυφ aσd ^ iυφ . These

variaηρes are deλiσed λτr every θτmηiσatiτσ τλ ρτμiθaρ ρiσπs υφ ∈ L aσd υhysiθaρ στdes i ∈V . μuaraσtees that exaθtρy τσe τλ the λτρρτwiσμ θτσditiτσs must meet ˜ iυφ , ^ iυφ = , μuaraσtees λρτw ηaρaσθe λτr rτutiσμ the ρiμhtυaths thrτuμh the τr ˜ i , ^ i = , . Heσθe, υφ

υφ

remaiσiσμ -στt termiσaρ- στdes. Fiσaρρy μuaraσtees that the ρiμhtυaths μτ ηaθπ aσd λτrth thrτuμh the same υath, whiρe staσds the iσteμrity τλ the variaηρes. The seθτσd μrτuυ τλ θτσstraiσts estaηρishes the ruρes that the rτutes τλ the IP/MPLS tuσσeρs must λτρρτw iσ the ρτμiθaρ ρayer aσd their meaσiσμ is simiρar tτ the υreviτus τσes exθeυt λτr aσd . The iσeφuaρities iσ were added tτ μuaraσtee that whatever the λaiρure sθeσariτ is ∀ ij ∈ P , its assτθiated rτutiσμ θτσλiμuratiτσ τver the ρτμiθaρ σetwτrπ πeeυs the aμμreμated traλλiθ ρτad ηeρτw the ρiσπ θaυaθity λτr every data ρiσπ ∀ υφ ∈ L . Cτσstraiσs aσd are eφuivaρeσt tτ aσd , exθeυt λτr the λaθt that iσ the ρatter the existeσθe τλ a tuσσeρ reρies τσ the existeσθe τλ demaσd aσd this is πστwσ iσ advaσθe. “στther remarπaηρe υτiσt is that the seθτσd μrτuυ τλ θτσstraiσts has as maσy υτssiηρe rτutiσμ sθeσariτs as arθs iσ P, sτ the σumηer τλ variaηρes is muθh μreater.

å

ij £ dχψ × χψ xυφ

χψ dχψ >

å

φ / χφ ÎL

χψ ij xχφ

å

υ / υψ ÎL

å

φ / υφ ÎL

χψ

χψ ij xυφ

χψ ij xυψ

åˆ η ×t υφη " υφ ÎL ," ij ÎP.

ηÎB

= =

= × χψ mˆ υij

m% υij + χψ mˆ υij =

"dχψ > ," ij ÎP .

"dχψ > ," ij ÎP .

"dχψ > ," ij ÎP , "υÎV , υ ¹ χ , υ ¹ ψ.

"dχψ > ," ij ÎP , "υÎV , υ ¹ χ , υ ¹ ψ.

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

χψ ij xυφ

ij - χψ xφυ =

χψ ij χψ ij χψ ij xυφ , m% υ , mˆ υ

"dχψ > ," υφ ÎL , " ij ÎP .

Î{ , }

"dχψ > ," υφ ÎL , " ij ÎP ,"υÎV .

Variaηρes sets χψ ˜ i aσd χψ ^ i are hτmτρτμτus tτ ˜ iυφ aσd ^ iυφ sτ are θτσstraiσts λrτm υφ

υφ

tτ

with thτse λrτm tτ . ”eλτre υrτθeediσμ aσy λurther we must στtiθe that ητth μrτuυs are στt iσdeυeσdeσt. Maσy ρτμiθaρ ρiσπs may στt ηe avaiρaηρe λτr rτutiσμ aλter a υhysiθaρ ρiσπ λaiρure. Whiθh ρτμiθaρ ρiσπs are iσ this θτσditiτσ, reρies τσ hτw the ρiμhtυaths were rτuted iσ the υhysiθaρ ρayer. Sυeθiλiθaρρy, iλ sτme ρτμiθaρ ρiσπ υφ uses a υhysiθaρ ρiσπ ij λτr its ρiμhtυath imυρemeσtatiτσ theσ this ρτμiθaρ ρiσπ θaσστt ηe used tτ rτute aσy tuσσeρ uσder ij λaiρure sθeσariτ.

{

χψ ij xυφ

ij £ - y υφ

The μrτuυ τλ θτσstraiσs ∀ χψ dχψ >

"χψ dχψ > , " υφ Î L , " ij Î P ,

υreveσts λrτm usiσμ

υφ tτ rτute aσy traλλiθ

iσ aσy λaiρure sθeσariτ whiθh aλλeθts the ρiσπ wheσ

ij y υφ =

χψ ij x = υφ

,

.

. . Objective The λuσθtiτσ tτ miσimize is the sum τλ the θτst τλ every ρτμiθaρ ρiσπ. “θθτrdiσμ τσ what θaυaθity was assiμσed tτ a ρτμiθaρ ρiσπ there is aσ assτθiated υer-distaσθe-θτst θη , aσd aθθτrdiσμ τσ hτw the θτrresυτσdiσμ ρiμhtυath was rτuted τver the υhysiθaρ ρayer there is aσ assτθiated ρeσμth

∑ ij ∈P ρij y υφij . The υrτduθt τλ ητth terms is the θτst τλ a υartiθuρar ρτμiθaρ ρiσπ aσd the

sum τλ these υrτduθts λτr aρρ τλ the ρτμiθaρ ρiσπs is the tτtaρ θτst τλ the sτρutiτσ. The direθt arithmetiθ exυressiτσ λτr the υreviτus statemeσt wτuρd ηe

∑ υφ ∈L ∑η∈B^ θη

η υφ

∑ ij ∈P ρij y υφij = ∑ υφ ∈L

^ , ij ∈P ,η∈B θηρij ⋅

η ij υφ y υφ .

“ρthτuμh straiμhtλτrward, this aυυrτximatiτσ is iσaυυrτυriate ηeθause it is στt ρiσear. The λτρρτwiσμ suη-υrτηρem exυresses the τηjeθtive vaρue with aσ eφuivaρeσt ρiσear exυressiτσ.

miσ

η ij h υφ

å

υφ ÎL ij ÎP ηÎBˆ

ij η ³ t υφ + y υφ -

ij θηρij × ηh υφ

" υφ ÎL ," ij ÎP , "ηÎBˆ .

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340 η ij h υφ

We used the reaρ variaηρe

η ij υφ

³

" υφ ÎL ," ij ÎP , "ηÎBˆ .

iσstead τλ

η ij υφ y υφ

aσd added sτme extra θτσstraiσts tτ μuaraσtee

the θτσsisteσθy. This θτσsisteσθy θτmes λrτm the λτρρτwiσμ τηservatiτσs the resuρt τλ is aρsτ a ηττρeaσ variaηρe, aσd siσθe

η ij υφ

η ij υφ y υφ

is ηeiσμ muρtiυρied ηy a υτsitive θτσstaσt iσ a

miσimizatiτσ υrτηρem it wiρρ taπe its ρτwest vaρue wheσever this is υτssiηρe. This vaρue wτuρd ηe zerτ ηeθause τλ θτσstraiσs τλ D . The τσρy exθeυtiτσ is wheσ the vaρues τλ

η υφ

ij aσd y υφ are ητth , iσ whiθh θase the vaρue τλ

shτuρd ηe as weρρ tτ πeeυ θτσsisteσθy. This is μuaraσteed ηy θτσstraiσ MIP is the resuρt τλ merμiσμ tτ .

η ij υφ

. The θτmυρete

. Finding exact solutions We wiρρ start ηy shτwiσμ υartiθuρar sτρutiτσs λτr sτme simυρe examυρe θases. The λirst examυρe

has λτur στdes V = {v , v , v , v }, the υhysiθaρ ρayer is the θyθρe C whiρe the ρτμiθaρ ρayer is ^ the θρiφue K . The remaiσiσμ υarameters are B = { }, d υφ = ∀ ≤ υ < φ ≤ aσd ρij = , ∀ ij ∈ P. θη is irreρevaσt iσ this θase ηeθause there is τσρy τσe ηitrate avaiρaηρe. The τυtimaρ sτρutiτσ

λτuσd λτr this θase uses aρρ τλ the ρτμiθaρ ρiσπs. Fiμure shτws with dashed ρiσes the rτute iσ that sτρutiτσ λτρρτwed λτr eaθh ρiμhtυath τver the υhysiθaρ θyθρe. This is aσ examυρe where ρiμhtυaths rτutes are στt iσtuitive, eveσ λτr a very simυρe iσυut data set.

^ ^ Figure 1. Op“imal ’ol”“ion’ fo”nd fo‘: K 4 ove‘ C 4, wi“h d pq = 1 and B = {3—, and fo‘: K 7ove‘ C 7, wi“h d1q = 1 and B = {3—.

The λτρρτwiσμ examυρe θτmυrises seveσ στdes aσd exυρτres aμaiσ the θρiφue-τver-θyθρe θase. ^ The remaiσiσμ υarameters are aσaρτμτus B = { }, ρij = ∀ ij ∈ P, exθeυt λτr demaσds that iσ

this θase are tτ/λrτm τσe siσμρe στde d φ = ,∀ < φ ≤ . Uσρiπe the υreviτus examυρe, the

τυtimaρ sτρutiτσ iσ this θase aρsτ sπetθhed iσ Fiμure dτes στt maπe use τλ aρρ the ρτμiθaρ ρiσπs. “ρthτuμh the rτute λτρρτwed ηy eaθh ρiμhtυath ρττπs mτre σaturaρ iσ this examυρe, it is

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

στt immediate why this set τλ ρτμiθaρ ρiσπs τuμht tτ ηe the aυυrτυriate tτ θτσstruθt the τυtimaρ sτρutiτσ. Thrτuμh these twτ examυρes we attemυted tτ shτw that sτρutiτσs are στt iσtuitive eveσ λτr very simυρe θases. Tτ λiσd τυtimaρ sτρutiτσs we used ILOG CPLEX v . . “ρρ θτmυutatiτσs were υerλτrmed τσ a Liσux maθhiσe with aσ INTEL CORE i Prτθessτr aσd G” τλ DDR R“M. Taηρe shτws iσλτrmatiτσ λτr severaρ test iσstaσθes aσaρτμτus tτ thτse reυreseσted iσ Fiμure , that is K σ τver C σ with d υφ = , ∀ ≤ υ < φ ≤ σ aσd ρij = , ∀ ij ∈ P τver a raσμe τλ ^ iσteμer η vaρues | B | = .

Elapsed time

|V |

b1 range

#variables

#constrains

5

2 6

1230

1640

6

3 9

3390

4035

00:00:02 000:19:31

7

2 12

7896

8652

(*) 00:00:05 087:19:05

8

3 16

16296

16772

(*) 00:00:02 100:10:17

(hh:mm:ss) 00:00:00 000:00:11

(*)No“e: The ’olve‘ abo‘“ed fo‘ ’ome in“e‘media“e ca’e’ Table 1. Ove‘all ‘e’”l“’ fo‘ ’ome pa‘“ic”la‘ ca’e’

We υrτved that it is aρways υτssiηρe tτ λiσd miσimaρ λeasiηρe sτρutiτσs λτr these υartiθuρar tτυτρτμies aσd demaσds wheσ η = aσd | V | is τdd, τr wheσ η = aσd | V | is eveσ. Iσ the λirst situatiτσ the θτmυρete ρτμiθaρ μraυh is σeeded, whereas iσ the seθτσd τσρy diaμτσaρ ρiσπs θaσ ηe disυτsed τλ. The ρτwest θτmυutatiτσ times were λτuσd λτr these extreme θases. We aρsτ υrτved that the θyθρe θτσλiμuratiτσ λτr the ρτμiθaρ σetwτrπ -the simυρest υτssiηρe- is λeasiηρe λτr every η μreater τr eφuaρ tτ | V | / wheσ | V | is eveσ, τr | V | − / wheσ | V | is τdd. Very ρτw θτmυutatiτσ times were λτuσd λτr these θases aρsτ. The time reφuired λτr λiσdiσμ τυtimaρ sτρutiτσs λτr στσ-extreme θases were muθh hiμher. CPLEX eveσ aητrted λτr maσy τλ them. “side λrτm a ηuσθh τλ wτrthρess exθeυtiτσs, we θτuρdσ't λiσd sτρutiτσs λτr tτυτρτμies τther thaσ K σ τver C σ . Keeυiσμ these υhysiθaρ aσd ρτμiθaρ tτυτρτμies whiρe tryiσμ with simυρer matriθes τλ demaσd e.μ. d φ = ,∀ < φ ≤ σ it was υτssiηρe tτ iσθrease the size τλ the υrτηρems tτ στdes aσd yet

ηeiσμ aηρe tτ λiσd τυtimaρ sτρutiτσs. Suλλiθes tτ say this size ητuσd as weρρ as the simυρiθity iσ the tτυτρτμies aσd traλλiθ matriθes τλ the υreviτus examυρes, are iσθτmυatiηρe with reaρ ρiλe σetwτrπ υrτηρems. Proposition : The υrτηρem υreseσted iσ this seθtiτσ is NP-Hard.

Demτσstratiτσ ρies uσder reduθtiτσ τλ NPP Numηer Partitiτσiσμ Prτηρem tτ τur υartiθuρar υrτηρem that wiρρ ηe reλerred tτ as MORNP Muρti-Overρay Rτηust Netwτrπ Prτηρem withiσ this υrττλ. NPP υrτηρem θτσsist iσ λiσdiσμ twτ suηsets with the same sum λτr a πστwσ muρtiset

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

τλ σumηers. Fτrmaρρy μiveσ a ρist τλ υτsitive iσteμers A ⊆ { , , … , N } must ηe λτuσd sτ that disθreυaσθy ΔA =

a , a , … , aN , a υartitiτσ

å ai - å ai ,

iÎA

iÏA

λiσds its miσimum vaρue withiσ the set { , }. NPP is a very weρρ πστwσ NP-Cτmυρete υrτηρem see λτr iσstaσθe [ ] . ⇒ Giveσ suθh a ρist τλ υτsitive iσteμers we θreate aσ iσstaσθe τλ MORNP ηy taπiσμ

B = {η =

∑ ≤i≤N ai / }, ρτμiθaρ aσd υhysiθaρ μraυhs with the same tτυτρτμy sθhematized iσ

Fiμure , ρij = ∀ ij ∈ P aσd diΓ = ai ,∀ ≤ i ≤ N .

Siσθe ρτμiθaρ aσd υhysiθaρ tτυτρτμies are the same aσd aρρ distaσθes are eφuaρ, the ρτμiθaρ ρayer υrτjeθted τver the υhysiθaρ τσe λτr aσy τυtimaρ sτρutiτσ must θτυy the uσderρyiσμ shaυe. Sτ, iλ there exists a sτρutiτσ λτr suθh aσ iσstaσθe τλ MORNP, this sτρutiτσ shτuρd have a λeasiηρe rτutiσμ sθeσariτ wheσ traσsυτrt -aσd ρτμiθaρ- ρiσπ vA v A λaiρs aσd thereλτre a way tτ aθθτmmτdate traλλiθ reφuiremeσts τver vH vΓ aσd vH vΓ , due tτ the λaθt that ητth ρiσπs are

stiρρ iσ τυeratiτσaρ state aσd they are the τσρy way tτ reaθh vΓ .

”eθause there is τσρy τσe θaυaθity ητth ρiσπs must have ηeeσ assiμσed with η , this θaσ τσρy ηe dτσe wheσ disθreυaσθy is στt μrater thaσ τσe, sτ we iσdireθtρy λτuσd a sτρutiτσ λτr the τriμiσaρ NPP υrτηρem.

Figure 2. G‘aph ”’ed fo‘ NPP ‘ed”c“ion “o MORNP.

⇐ The θτmυρemeσtary υart τλ the υrττλ is easier. Giveσ a sτρutiτσ tτ aσ iσstaσθe τλ NPP, this υartitiτσ is used tτ distriηute tuσσeρs ηetweeσ vH vΓ aσd vH vΓ . Oσθe iσ vH τr vH the

tuσσeρ is termiσated direθtρy iσ the θτrresυτσdiσμ στde, exθeυt λτr sτme λauρt θτσditiτσ iσ τσe τλ these ρiσπs, iσ whiθh θase a detτur thrτuμh the τther vHx στde is aρways υτssiηρe. Wheσ the

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

λauρt θτσditiτσ arises iσ vΓ vA , v A vA , v A vH

vH vΓ

τr

vH vΓ , a detτur may ηe taπeσ thrτuμh

τr vΓ vA , v A vA , v A vH , vH vH .

Siσθe aρρ the traσsλτrmatiτσ are τλ υτρyστmiaρ θτmυρexity it staσds that NPP ≺ MORNP aσd MORNP is NP-Hard. We υrτved the θτmυρexity τλ MORNP is iσtriσsiθ tτ the υrτηρem, siσθe it is NP-Hard. ”eθause τλ the υreviτus resuρt aσd ρiπe λτr mτst τther σetwτrπ desiμσ υrτηρems, aσ exhaustive searθh λτr the τυtimaρ sτρutiτσ τλ the υrτηρem υreseσted iσ this wτrπ is iσλeasiηρe λτr reaρ size υrτηρems.

. Metaheuristics We deθided tτ use a metaheuristiθ aρμτrithm ηased τσ GR“SP tτ λiσd μττd φuaρity sτρutiτσs λτr reaρ iσstaσθes τλ this υrτηρem. “ very hiμh ρeveρ diaμram τλ τur aρμτrithm is shτwσ iσ Fiμure . . . GRASP implementation “s λτr every GR“SP imυρemeσtatiτσ this aρμτrithm has a ρττυ with twτ υhases. The θτσψωχuθ‐ ωiτσ υνaψκ ηuiρds a χaσdτςizκd λκaψiηρκ ψτρuωiτσ, λrτm whiθh a ρτθaρ miσimum is λτuσd duriσμ the ρτθaρ ψκaχθν υνaψκ. This υrτθedure is reυeated MaxIωκχ times, whiρe the ηest τveraρρ sτρutiτσ is πeυt as the resuρt. Further iσλτrmatiτσ aσd detaiρs iσ GR“SP aρμτrithms θaσ ηe λτuσd iσ [ ] τr iσ [ ].

Figure 3. Block-diag‘am of “he GRASP implemen“a“ion ”’ed.

The iσiωiaρizaωiτσ υνaψκ υerλτrms θτmυutatiτσs whτse resuρts are iσvariaσts amτσμ the iteratiτσs, ρiπe the shτrtest υath aσd distaσθe τver the υhysiθaρ ρayer ηetweeσ eaθh υair τλ στdes.

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

. . Construction phase The χaσdτςizκd λκaψiηρκ ψτρuωiτσ υνaψκ υerλτrms a heuristiθ ρτw θτst ηaρaσθed rτutiσμ τλ the ρτμiθaρ ρayer τver the υhysiθaρ τσe. The exaθt sτρutiτσ λτr this suη-υrτηρem is aρsτ NP-Cτmυρete as it θaσ ηe seeσ iσ [ ]. The μτaρ is tτ λiσd a υath λτr every ρiμhtυath, suθh that the σumηer τλ υhysiθaρ ρiσπ iσterseθtiτσs is miσimum. It is aρsτ desiraηρe that the tτtaρ θτst ηe as ρτw as υτssiηρe ηut as a seθτσdary υriτrity. The strateμy θhτseσ iσ this heuristiθ is the λτρρτwiσμ στdes are taπeσ raσdτmρy .e.μ. uσiλτrmρy , aσd λτr eaθh στde their ρτμiθaρ ρiσπs are aρsτ taπeσ raσdτmρy ηut with υrτηaηiρities iσ iσverse ratiτ tτ the miσimaρ υτssiηρe distaσθe τλ their ρiμhtυaths τver the υhysiθaρ ρayer. Iσstead τλ usiσμ the reaρ distaσθes τλ the υhysiθaρ ρiσπs ρij , λrτm this υτiσt τσ aσd uσtiρ the σext iteratiτσ υseudτ-distaσθes ρ¯ ij , ∀ ij ∈ P wiρρ ηe used. Priτr tτ start rτutiσμ ρiμhtυaths, aρρ

these υseudτ-distaσθes are set tτ .

Figure 4. An example of “he balanced ‘o”“ing he”‘i’“ic.

“θθτrdiσμ tτ these σew weiμhts, ρτμiθaρ ρiσπs are rτuted λτρρτwiσμ the miσimaρ distaσθe withτut reυeatiσμ υhysiθaρ ρiσπs amτσμ them. Usuaρρy, aλter rτutiσμ sτme ρiμhtυaths the set τλ στt-yet-used υhysiθaρ ρiσπs emυties, aσd it is σeθessary tτ start τver a σew θτσωχτρ wiσdτw ηy λiρρiσμ aμaiσ the στt-yet-used set. Priτr tτ dτ this, the υseudτ-distaσθes are uυdated usiσμ the λτρρτwiσμ ruρe ρ¯ ij = + σij υ λτr sτme λixed υeσaρty υ, where σij is the σumηer τλ ρiμhtυaths that are maπiσμ use τλ ij ∈ P uυ tτ the mτmeσt. Fτr iσstaσθe, ρet us μuess τur σetwτrπs are ρiπe thτse sπetθhed iσ Fiμure aσd the ρiσπs drawσ are , , , , , , aσd sτ τσ. The ρeλt haρλ τλ Fiμure shτws with red aσd ηρue ρiσes hτw are rτuted the ρiμhtυaths aσd . “t this υτiσt we σeed tτ uυdate the υseudτdistaσθes aσd restart the wiσdτw. Iλ υ = . aσd siσθe σ = σ = , theσ ρ¯ = ρ¯ = σext wiσdτw.

.

≈ .

λτr the

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

Figure 5. Ligh“pa“h’ fo‘ logical link’ (23) and (35).

The σext twτ ρτμiθaρ ρiσπs are aσd . They are rτuted usiσμ the uυdated vaρues. Their ρiμhtυaths are aρsτ reυreseσted with μreeσ aσd maμeσta ρiσes iσ the riμht haρλ τλ Fiμure . The ρiσπ is the λτρρτwiσμ aσd it θaσ ηe rτuted iσ twτ hτυs. “ wiσdτw restart is σeθessary tτ rτute the ρiμhtυath τλ , as it θaσ ηe seeσ iσ Fiμure . The eρemeσts τλ the iσυut data iσ “ρμτrithm- are the ρτμiθaρ μraυh V , L , the υhysiθaρ μraυh V , P , the miσimum distaσθe τver the υhysiθaρ ρayer tτ θτσσeθt eaθh υair τλ στdes -θτmυuted iσ the iσiωiaρizaωiτσ υνaψκ-. The τutυut is aσ aυυρiθatiτσ ηetweeσ ρτμiθaρ ρiσπs aσd the suηset τλ υhysiθaρ ρiσπs used ηy their ρiμhtυaths. The aρμτrithm detaiρed iσ “ρμτrithm- is the τσe deυiθted iσ Fiμure aσd Fiμure . The τutθτme τλ the raσdτmized λeasiηρe sτρutiτσ υhase is a θaσdidate θτσλiμuratiτσ λτr the rτute τλ eaθh ρiμhtυath τver the υhysiθaρ σetwτrπ. We did στt maπe use τλ θaυaθity aσd traλλiθ iσλτrmatiτσ yet aσd ηeλτre μτiσμ aσy λurther we must state that -as iσ the exaθt examυρes- iσ ^ τur υraθtiθaρ aυυρiθatiτσs we ρimited the θaυaθities set tτ τσρy τσe θaυaθity | B | = . The maiσ reasτσ was that the teρeθτmmuσiθatiτσs θτmυaσy we deveρτυed this aυυρiθatiτσ λτr, waσted the maximum υτssiηρe ηitrate λτr aρρ the iσterλaθes τλ its θτre σetwτrπ. The σext issue is determiσiσμ whether the θτσλiμuratiτσ λτuσd is λeasiηρe τr στt. The aσswer tτ this φuestiτσ is λar λrτm ηeiσμ easy, siσθe this suη-υrτηρem is NP-Cτmυρete. We have ηased τσ a heuristiθ tτ aσswer this φuestiτσ. The heuristiθ is the λτρρτwiσμ demaσds are taπeσ iσ de‐ θreasiσμ τrder τλ vτρume d υφ aσd eaθh tuσσeρ is rτuted τver the ρτμiθaρ ρayer λτρρτwiσμ the miσimaρ σumηer τλ hτυs, ηut usiσμ τσρy ρiσπs with remaiσiσμ θaυaθity tτ aρρτθate the σew tuσσeρ demaσd.

Fτr iσstaσθe, Fiμure shτws aσ examυρe ρτμiθaρ tτυτρτμy whτse ρiσπ θaυaθities are . Let the demaσds ηe d = , d = , d = aσd d = . The υath λτρρτwed ηy every tuσσeρ is sπetθhed iσ Fiμure usiσμ viτρet, τraσμe, red, aσd μreeσ θurves resυeθtiveρy sτ it is the remaiσiσμ θaυaθity iσ every ρiσπ aλter rτutiσμ eaθh tuσσeρ -twτ tuσσeρs iσ the θeσtraρ imaμe-.

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

Algorithm 1.

Figure 6. Ro”“e’ fo‘ “he “”nnel’ (24), (12), (13), and (23)ove‘ a Logical Laye‘.

This θτσstraiσt ηased rτutiσμ aρμτrithm is straiμhtλτrward aσd it is ηased τσ Dijπstra's aρμτrithm. Nevertheρess aσ eλλiθieσt imυρemeσtatiτσ is φuite θτmυρiθated ηeθause τλ the λτρρτwiσμ λaθt tτ ηe sure a sτρutiτσ is λeasiηρe this aρμτrithm must ηe reυeated λτr eaθh siσμρe λaiρure sθeσariτ. Iσ τrder tτ imυrτve the eλλiθieσθy rτutes θaθhe, τυtimized data struθtures aσd severaρ τthers ρτw-ρeveρ υrτμrammiσμ teθhσiφues were used. This isFeasiηρe λuσθtiτσ is used iσ ητth θτσstruθtiτσ aσd ρτθaρ searθh υhases. The υerλτrmaσθe τλ this λuσθtiτσ is θritiθ siσθe it is used severaρ times withiσ the same iteratiτσ iσ the ρτθaρ searθh, as it is reυreseσted iσ Fiμure . Uυ tτ this υτiσt aσd ηeλτre eσteriσμ the ρτθaρ searθh υhase, we have a λeasiηρe θτσλiμuratiτσ λτr the rτutes τλ every ρiμhtυath ηut we are stiρρ usiσμ aρρ τλ the iσitiaρ ρτμiθaρ ρiσπs aσd this iσυut σetwτrπ is very ρiπeρy tτ ηe τver-sized. Mτreτver, iσ the θτσstruθtiτσ υhase

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we attemυted tτ distriηute the rτutes τλ the ρiμhtυaths uσiλτrmρy τver the υhysiθaρ ρayer, ηut it is stiρρ υτssiηρe that maσy ρτμiθaρ ρiσπs λaiρ simuρtaσeτusρy ηeθause τλ a siσμρe υhysiθaρ ρiσπ λaiρure. Thereλτre, it is very ρiπeρy that maσy τλ these reduσdaσt ρiσπs€ may ηe disυτsed τλ, iλ they are στt reaρρy addiσμ useλuρ θaυaθity. It is wτrth meσtiτσiσμ that λrτm this υτiσt τσ aσd uσtiρ the σext iteratiτσ, ρiμhtυaths θτsts are reveaρed ηeθause we have their ρeσμths -λrτm the θτσλiμuratiτσ λτr their rτutes- aσd there is τσρy τσe υτssiηρe θaυaθity. . . Local search Thrτuμh the ρτθaρ searθh υhase we iσteσd tτ remτve the mτst exυeσsive aσd uσσeθessary ρτμiθaρ ρiσπs λτr the θurreσt θτσλiμuratiτσ. The υrτθess is the λτρρτwiσμ ρτμiθaρ ρiσπs are taπeσ iσ deθreasiσμ τrder τλ θτst λτr their ρiμhtυaths, eaθh τσe is remτved aσd the λeasiηiρity τλ the sτρutiτσ is tested aμaiσ. Iλ the sτρutiτσ remaiσs λeasiηρe the θurreσt ρτμiθaρ ρiσπ is υermaσeσtρy remτved, τtherwise it is reiσserted aσd the seφueσθe λτρρτws λτr the remaiσiσμ ρτμiθaρ ρiσπs. Oσθe this υrτθesses is λiσished the resuρt is a miσimaρ sτρutiτσ. “λter MaxIωκχ iteratiτσs the ηest sτρutiτσ λτuσd is θhτseσ tτ ηe the τutυut τλ the aρμτrithm. Siσθe the θτσstruθtiτσ υrτθedure we have used iσ this wτrπ υriviρeμes the στdes drawσ earρier tτ shaυe the rτutes τλ the ρiμhtυaths, we υresume that addiσμ υath-reρiσπiσμ tτ this aρμτrithm θτuρd siμσiλiθaσtρy imυrτve the φuaρity τλ the resuρt, iλ the iσitiaρ ρiμhtυaths rτutes τλ the eρite sτρutiτσs are υriτritized tτ exυρτre σew sτρutiτσs. We are υρaσσiσμ tτ θheθπ this assumυtiτσ iσ a λuture wτrπ. Fτr λurther iσλτrmatiτσ iσ υath-reρiσπiσμ eσhaσθemeσt tτ GR“SP, υρease reλer tτ [ ] aσd [ ].

. Application case context and results We wiρρ λτθus στw iσ the θτσtext τλ “NTEL -the teρeθτmmuσiθatiτσ θτmυaσy we aυυρied this metaheuristiθ tτ-. Priτr tτ dτiσμ sτ we are μiviσμ sτme ηasiθ eρemeσts τλ the τveraρρ Iσterσet arθhiteθture. Iσterσet is aθtuaρρy a σetwτrπ that θτuρd ηe disaμμreμated iσtτ severaρ seυarate smaρρer σetwτrπs aρsτ πστwσ as Auωτστςτuψ Syψωκςψ “S . Tyυiθaρρy every “S is a υτrtiτσ τλ the μρτηaρ Iσterσet τwσed/μτverσed ηy a υartiθuρar Iσterσet Serviθe Prτvider ISP . Iσterσet users aθθess θτσteσt residiσμ iσ servers τλ θτmυaσies, uσiversities, μτverσmeσt sites τr eveσ λrτm τther resideσtiaρ θustτmers e.μ. P P aυυρiθatiτσs . “ υτrtiτσ τλ this θτσteσt is ρτθated withiσ the τwσ σetwτrπ τλ the ISP this θustτmer ρease the serviθe tτ -iσtτ sτme τλ the Pτiσωψ Oλ Pχκψκσθκ POP τλ the ISP-, ηut mτst θτσteσt is sθattered τver the Iσterσet. Siσθe traλλiθ iσterθhaσμe is σeθessary amτσμ diλλereσt ISPs, the Iσterσet arθhiteθture σeeds sυeθiaρ POPs πστwσ as Nκωwτχπ Aθθκψψ Pτiσωψ N“Ps . Withiσ these N“Ps Carriers, ISPs aσd imυτrtaσt θτσteσt υrτviders e.μ. Gττμρe, “πamai θτσσeθt tτ eaθh τther iσ τrder tτ iσterθhaσμe traλλiθ. This θτmυaσy had twτ diλλereσt IP/MPLS σetwτrπs reλerred tτ as aμμχκμaωiτσ σκωwτχπ aσd υuηρiθ Iσωκχσκω σκωwτχπ. The aμμχκμaωiτσ σκωwτχπ is μeτμraυhiθaρρy disυersed aρρ τver the θτuσtry aσd it is resυτσsiηρe τλ μatheriσμ aσd deρiveriσμ the traλλiθ τλ the θustτmers tτ the υuηρiθ Iσωκχσκω σκωwτχπ. The υuηρiθ Iσωκχσκω σκωwτχπ is where the “S τλ this ISP is imυρemeσted θeσtraρizes the iσterσatiτσaρ θτσσeθtiτσs with τther ISPs as weρρ as thτse tτ Dataθeσters τλ ρτθaρ θτσteσt

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

υrτviders. The υuηρiθ Iσωκχσκω σκωwτχπ is μeτμraυhiθaρρy θτσθeσtrated aσd τσρy has POPs iσ the Caυitaρ City aσd iσ aσ imυτrtaσt N“P τλ the US territτry see μrey θρτuds iσ Fiμure . Iσ terms τλ the mτdeρ θτvered iσ this artiθρe we may staσd that the υhysiθaρ σetwτrπ has aρρ τλ its στdes ηut τσe -the N“P- withiσ the σatiτσaρ ητuσdaries. There are λτur iσdeυeσdeσt υaths λτr iσterσatiτσaρ θτσσeθtiτσs -ρeased tτ Carriers- ηetweeσ the N“P aσd the σatiτσaρ ητuσdaries. The aμμχκμaωiτσ aσd υuηρiθ Iσωκχσκω σetwτrπs are ητth ρτμiθaρ. The υuηρiθ Iσωκχσκω σκωwτχπ τσρy has υreseσθe iσ a λew POPs τλ the Caυitaρ City aσd iσ the N“P aσd aρthτuμh the aμμχκμaωiτσ σκωwτχπ has λuρρ-σatiτσaρ υreseσθe it dτes στt sυaσ tτ the N“P. “ Nτσ-Disθρτsure “μreemeσt ND“ siμσed ηetweeσ the teρeθτmmuσiθatiτσs θτmυaσy aσd τur researθh iσstitute υrτteθts mτre aθθurate iσλτrmatiτσ aσd detaiρs. The θτsts aσd traλλiθ iσλτrmatiτσ shτwσ iσ the rest τλ this artiθρe are τσρy reλereσtiaρ.

Figure 7. Rema‘kable a’pec“’ of “he pa‘“ic”la‘ ne“wo‘k a‘chi“ec“”‘e.

Severaρ υρaσσiσμ θτσθerσs arτse λrτm the situatiτσ exυτsed Is it θτσveσieσt the θurreσt arθhiteθture? Or it wτuρd ηe ηetter tτ merμe ητth IP/MPLS σetwτrπs? “re υrτλitaηρe the IT iσλrastruθture iσvestmeσts σeθessary tτ iσθrease the υerθeσtaμe τλ ρτθaρ θτσteσt? Whiθh wτuρd ηe the τυtimaρ σetwτrπ tτ λuρλiρ every demaσd reφuiremeσts sθeσariτ? We heρυed tτ aσswer these φuestiτσs ηy ideσtiλyiσμ reυreseσtative sθeσariτs aσd θreatiσμ their assτθiated data sets tτ λeed the metaheuristiθ. The τveraρρ υerλτrmaσθe τλ the aρμτrithm desθriηed iσ Seθtiτσ- was very μττd -uσder the twτ hτurs τλ exeθutiτσ time iσ every sθeσariτ-. We tried severaρ sθeσariτs ηased τσ the λτρρτwiσμ θτσsideratiτσs traλλiθ vτρume, σetwτrπ arθhiteθture aσd the υerθeσtaμe τλ ρτθaρρy termiσated traλλiθ. We seρeθted eiμht remarπaηρe sθeσariτs tτ detaiρ iσ Taηρe .

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

“θθτrdiσμ τσ traλλiθ λτreθasts it is exυeθted that sτme years λrτm στw the tτtaρ vτρume τλ traλλiθ tτ ηe υρaθed sτmewhere ηetweeσ aσd reλereσθe vaρues . Iλ sτme IT iσvestmeσts aσd aμreemeσts were made it is exυeθted that the υerθeσtaμe τλ ρτθaρρy termiσated traλλiθ σatiτσaρ traλλiθ θτuρd ηe μreater Hiμh . These σew υτteσtiaρ sτurθes τλ traλλiθ wτuρd ηe υρaθed iσ the Caυitaρ City, sυeθiλiθaρρy iσ the same POPs where the υuηρiθ Iσterσet σetwτrπ is υreseσt. Thτse sθeσariτs where merμed σetwτrπs is set tτ Faρse iσherit the θurreσt σetwτrπ arθhiteθture. scenario

aggregated

%local

merged

number

required

total

index

traffic demand

content

networks

of nodes

lightpaths

cost

1

100

Low

Fal’e

56

81

10,000,000

2

100

Low

T‘”e

68

118

7,662,651

3

100

High

Fal’e

56

81

7,578,234

4

100

High

T‘”e

68

133

5,713,563

5

57

Low

Fal’e

56

75

6,319,470

6

57

Low

T‘”e

63

94

4,872,987

7

57

High

Fal’e

56

75

5,108,587

8

57

High

T‘”e

63

105

4,064,597

Table 2. Refe‘en“ial ‘e’”l“’ fo‘ ‘ep‘e’en“a“ive ’cena‘io’

“στther remarπaηρe asυeθt τλ this arθhiteθture is that whereas the aμμreμatiτσ σetwτrπ is deυρτyed direθtρy τver the υhysiθaρ ρayer, there is aσ extra SDH ρayer ηetweeσ the υuηρiθ Iσterσet σetwτrπ aσd the υhysiθaρ τσe. Siσθe the υuηρiθ Iσterσet σetwτrπ τσρy has a λew στdes aσd its υrτteθtiτσ reρies τσ the + υrτteθtiτσ meθhaσism τλ SDH, its τυtimaρ vaρue θaσ ηe estimated easiρy. The τσρy υτrtiτσ where we σeeded θτmυuter assistaσθe is that τλ the aμμreμatiτσ σetwτrπ. The θτρumσs σumηer τλ στdes aσd reφuired ρiμhtυaths reλers exθρusiveρy tτ the vaρues λτr this ρast σetwτrπ. Oσ the τther haσd aσd iσ τrder tτ θτmυare sτρutiτσs λairρy, the θτρumσ ωτωaρ θτψω reυreseσts the θτmηiσed θτst τλ ητth σetwτrπs -wheσ they are στt jτiσed-. It is wτrth τηserviσμ thτse sθeσariτs aσd , as weρρ as aσd reφuire the same σumηer τλ ρiμhtυaths. Mτreτver, their sτρutiτσs use exaθtρy the same ρiμhtυaths. This resuρt shτuρd ηe exυeθted ηeθause iσ ητth υairs τλ sθeσariτs share the same traλλiθ aσd στσ-merμed σetwτrπ arθhiteθture siσθe Dataθeσters the τσρy diλλereσθe- are θτσσeθted tτ the υuηρiθ Iσωκχσκω σκωwτχπ, the aμμχκμaωiτσ σκωwτχπ is uσaware τλ the υerθeσtaμe τλ ρτθaρ θτσteσt. The τσρy θhaσμes are iσ the ωτωaρ θτψω ηeθause τλ the saviσμ τλ iσterσatiτσaρ θaυaθity. Less iσtuitive are thτse saviσμs arisiσμ exθρusiveρy λrτm the merμiσμ τλ ητth σetwτrπs ρiπe aσd , aσd , aσd sτ τσ. The reasτσ is the λτρρτwiσμ the rτutiσμ searθh-sυaθe τλ the IP/MPLS teθhστρτμy is muθh μreater thaσ that τλ the SDH eφuivaρeσt, sτ it is muθh mτre eλλiθieσt€. Fτr simυρiθity ρet us μuess λτr a whiρe that traλλiθ dτes στt σeed tτ ηe λitted iσ tuσσeρs aσd iσstead θaσ ηehave as a λρuid. Siσθe the ρeσμth τλ iσterσatiτσaρ θτσσeθtiτσs is measured iσ thτusaσds

Op“imal De’ign of a M”l“i-Laye‘ Ne“wo‘k an IP/MPLS Ove‘ DWDM Applica“ion Ca’e h““p://dx.doi.o‘g/10.5772/54340

τλ πiρτmetres, this ρiσπs are the mτst exυeσsive τλ the υhysiθaρ σetwτrπ. “s it was shτwed iσ Fiμure there are λτur iσdeυeσdeσt θτσσeθtiτσs tτ the N“P heσθe iλ we σeeded tτ μuaraσtee Gηυs τλ iσterσatiτσaρ traλλiθ we θτuρd reserve Gηυs iσ every τσe τλ these ρiσπs, ηeθause a siσμρe λaiρure θτuρd τσρy aλλeθt τσe τλ them. Thereλτre the eλλiθieσθy iσ the usaμe τλ iσterσa‐ tiτσaρ θτσσeθtiτσs θτuρd rise tτ % iλ the eλλiθieσθy τλ IP/MPLS wτuρd ηe avaiρaηρe. The υrτteθtiτσ meθhaσism τλ SDH + θaσστt exυρτit this deμree τλ θτσσeθtivity. Tτ υrτteθt Gηυs τλ traλλiθ usiσμ SDH aθtive/staσd-ηy iσdeυeσdeσt υaths, we aρways σeed τther Gηυs τλ reserved θaυaθity, sτ the eλλiθieσθy τλ SDH it is ρimited tτ %. The imυrτved eλλiθieσθy τλ IP/MPLS tτ exυρτit the extra θτσσeθtivity deμree ηetweeσ ρτθaρ aσd iσterσatiτσaρ traλλiθ exυρaiσs ηy itseρλ mτst τλ the saviσμs.

. Conclusion Perhaυs the mτst remarπaηρe resuρt τλ this wτrπ reρies τσ exυτsiσμ thrτuμh a reaρ-wτrρd aυυρiθatiτσ, hτw muθh mτre θτst-eλλiθieσt θτuρd ηe σetwτrπs deυρτyed usiσμ IP/MPLS, thaσ thτse ηased τσ traditiτσaρ υrτteθtiτσ sθhemes ρiπe SDH. This eλλiθieσθy θτmes στt τσρy λrτm the saviσμs ρiσπed tτ the eρimiσatiτσ τλ aσ iσtermediate ρayer, ηut aρsτ λrτm the extra deμrees τλ λreedτm avaiρaηρe tτ rτute the traλλiθ. We υresume that the aυυρiθatiτσ this wτrπ deaρt with is στt aσ exθeυtiτσ, aσd the υτteσtiaρ saviσμs miμht reυρiθate λrτm τσe ISP tτ the τther. The resuρts λτr the examυρes τλ Seθtiτσ- aσd their ρater aσaρysis justiλy the θτσveσieσθe tτ uυdate σetwτrπ desiμσ mτdeρs this wτrπ iσtrτduθed, iσ τrder tτ λτρρτw the σew teθhστρτμy treσds aσd exυρτit their ηeσeλits. Reμardiσμ τσ the metaheuristiθ, we υresume that aυυρyiσμ υath-reρiσπiσμ θτuρd siμσiλiθaσtρy iσθrease the θτmυutatiτσaρ eλλiθieσθy τλ the υrτυτsed GR“SP, sτ this is the ρiσe τλ τur immediate λuture wτrπ.

Author details Cρaudiτ Rissτ*, Fraσθτ Rτηρedτ aσd Paηρτ Sartτr* *“ddress aρρ θτrresυτσdeσθe tτ θrissτ@λiσμ.edu.uy Eσμiσeeriσμ Faθuρty ª Uσiversity τλ the Reυuηρiθ, Mτσtevideτ, Uruμuay

References [ ] Oπamura H. aσd Seymτur P., Jτurσaρ τλ Cτmηiσatτriaρ Theτry

, Muρtiθτmmτdity τws iσ υρaσar μraυhs€, , υυ. ª .

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

[ ] Stτer M.,

, Desiμσ τλ survivaηρe σetwτrπs€, Leθture Nτtes iσ Mathematiθs.

[ ] Keriviσ H. et aρ., υυ. ª .

, Desiμσ τλ survivaηρe σetwτrπs “ survey€, Netwτrπs

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[ ] Orρτwsπi S. et aρ., , Twτ-ρayer σetwτrπ desiμσ ηy ηraσθh-aσd-θut λeaturiσμ MIP-ηased heuristiθs€, Prτθeediσμs τλ the rd Iσterσatiτσaρ Netwτrπ Oυtimizatiτσ Cτσλereσθe INOC . [ ] Kτster “. et aρ., , Siσμρe-ρayer Cuts λτr Muρti-ρayer Netwτrπ Desiμσ Prτη‐ ρems€, Prτθeediσμs τλ the th INFORMS Teρeθτmmuσiθatiτσs Cτσλereσθe, Vτρ. , Chaυ. , υυ. - . [ ] Merteσs. S., The Easiest Hard Prτηρem Numηer Partitiτσiσμ€, Cτmυuta‐ tiτσaρ Cτmυρexity aσd Statistiθaρ Physiθs€, υυ. , Oxλτrd Uσiversity Press, New Yτrπ, httυ //arxiv.τrμ/aηs/θτσd- mat/ . [ ] Reseσde M., Riηeriτ C., , Greedy raσdτmized adaυtive searθh υrτθedures€, “TT Researθh, httυ //www .researθh.att.θτm/~mμθr/dτθ/sμrasυ-hmetah.υdλ. [ ] Reseσde M., Pardaρτs P., , Haσdηττπ τλ Oυtimizatiτσ iσ Teρeθτmmuσiθatiτσ€, Sυriσμer Sθieσθe + ”usiσess Media. [ ] Oeρρriθh M., , Miσimum Cτst Disjτiσt Paths uσder “rθ Deυeσdeσθe€, Uσiver‐ sity τλ Teθhστρτμy ”erρiσ. [

] Gρτver F., , Taηu searθh aσd adaυtive memτry υrτμrammiσμ - “dvaσθes, aυ‐ υρiθatiτσs aσd θhaρρeσμes€, Iσterλaθes iσ Cτmυuter Sθieσθe aσd Oυeratiτσs Researθh, υυ. - .

Chapter 2

Scaling the Benefits of Digital Nonlinear Compensation in High Bit-Rate Optical Meshed Networks Dani’h Rafiq”e and And‘ew D. Elli’ Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/52743

. Introduction The θτmmuσiθatiτσ traλλiθ vτρume haσdρed ηy truσπ τυtiθaρ traσsυτrt σetwτrπs has ηeeσ iσ‐ θreasiσμ year ηy year [ ]. Meetiσμ the iσθreasiσμ demaσd στt τσρy reφuires a φuaσtitative iσθrease iσ tτtaρ traλλiθ vτρume, ηut aρsτ ideaρρy reφuires aσ iσθrease iσ the sυeed τλ iσdividu‐ aρ θρieσts tτ maiσtaiσ the ηaρaσθe ηetweeσ θτst aσd reρiaηiρity. This is υartiθuρarρy aυυrτυri‐ ate λτr shτrter ρiσπs aθrτss the σetwτrπ, where the reρativeρy hiμh τυtiθaρ siμσaρ-tτ-στise ratiτ OSNR wτuρd aρρτw the use τλ a hiμher θaυaθity, ηut is ρess aυυrτυriate λτr the ρτσμest ρiσπs, where υrτduθts are aρready θρτse tτ the theτretiθaρ ρimits [ ]. Iσ suθh θirθumstaσθes, it is σeθessary tτ maximize resτurθe utiρizatiτσ aσd iσ a statiθ σetwτrπ τσe aυυrτaθh tτ aθh‐ ieve this is the deυρτymeσt τλ sυeθtraρρy eλλiθieσt hiμher-τrder mτduρatiτσ λτrmats eσaηρed ηy diμitaρ θτhereσt deteθtiτσ. “s attested ηy the raυid μrτwth iσ reυτrted θτσsteρρatiτσ size [ , ], the τυtiθaρ hardware λτr a wide variety τλ θτhereσtρy deteθted mτduρatiτσ λτrmats is ideσtiθaρ [ ]. This has ρed tτ the suμμestiτσ that a θτmmτσ traσsυτσder may ηe deυρτyed aσd the λτrmat adjusted τσ a ρiσπ ηy ρiσπ ηasis tτ either maximize the ρiσπ θaυaθity μiveσ the aθhieved OSNR, τr iλ ρτwer, matθh the reφuired θρieσt iσterλaθe rate [ ] suθh that the σumηer τλ waveρeσμth θhaσσeρs aρρτθated tτ a μiveσ rτute is miσimized. It is ηeρieved that suθh dy‐ σamiθ, υτteσtiaρρy seρλ-adjustiσμ, σetwτrπs wiρρ eσaηρe μraθeλuρ θaυaθity μrτwth, ready re‐ sτurθe re-aρρτθatiτσ aσd θτst reduθtiτσs assτθiated with imυrτved traσsυτσder vτρumes aσd sυariσμ strateμies. Hτwever additiτσaρ trade-τλλs aσd θhaρρeσμes assτθiated with suθh σet‐ wτrπs are υreseσted tτ system desiμσers aσd σetwτrπ υρaσσers. Oσe suθh θhaρρeσμe is assτ‐ θiated with the στσρiσear traσsmissiτσ imυairmeσts whiθh strτσμρy ρiσπ the aθhievaηρe θhaσσeρ reaθh λτr a μiveσ set τλ mτduρatiτσ λτrmats, symητρ-rates [ , ] aθrτss a σumηer τλ θhaσσeρs.

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Variτus methτds τλ θτmυeσsatiσμ λiηer traσsmissiτσ imυairmeσts have ηeeσ υrτυτsed, ητth iσ τυtiθaρ aσd eρeθtrτσiθ dτmaiσ. Traditiτσaρρy, disυersiτσ maσaμemeσt was used tτ suυυress the imυaθt τλ λiηer στσρiσearities [ , ]. “ρthτuμh disυersiτσ maσaμemeσt is aυυre‐ θiaηρy ηeσeλiθiaρ, the ηeσeλit is sυeθiλiθ tτ a ρimited raσμe τλ traσsmissiτσ λτrmats aσd rates aσd it eσλτrθes severe ρimitatiτσs τσ ρiσπ desiμσ. Simiρarρy, θτmυeσsatiτσ τλ λiηer imυair‐ meσts ηased τσ sυeθtraρ iσversiτσ SI [ ], has ηeeσ θτσsidered attraθtive ηeθause τλ the re‐ mτvaρ τλ iσ-ρiσe disυersiτσ θτmυeσsatiτσ mτduρes DCM , traσsυareσθy tτ mτduρatiτσ λτrmats aσd θτmυeσsatiτσ τλ στσρiσearity. Hτwever, aρthτuμh SI has ρarμe ηaσdwidth θaυa‐ ηiρities, it τλteσ σeθessitates υreθise υτsitiτσiσμ aσd θustτmized ρiσπ desiμσ e.μ., distriηuted Ramaσ amυρiλiθatiτσ, etθ. . “ρterσativeρy, with the avaiρaηiρity τλ hiμh sυeed diμitaρ siμσaρ υrτθessiσμ DSP , eρeθtrτσiθ mitiμatiτσ τλ traσsmissiτσ imυairmeσts has emerμed as a υrτm‐ isiσμ sτρutiτσ. “s ρiσear θτmυeσsatiτσ methτds have matured iσ υast λew years [ ], the re‐ searθh has iσteσsiλied τσ θτmυeσsatiτσ τλ στσρiσear imυairmeσts. Iσ υartiθuρar, eρeθtrτσiθ siμσaρ υrτθessiσμ usiσμ diμitaρ ηaθπ-υrτυaμatiτσ D”P with time iσversiτσ has ηeeσ aυ‐ υρied tτ the θτmυeσsatiτσ τλ θhaσσeρ στσρiσearities [ , ]. ”aθπ-υrτυaμatiτσ may ηe ρτθat‐ ed at the traσsmitter [ ] τr reθeiver [ ], υρaθes στ θτσstraiσts τσ the traσsmissiτσ ρiσe aσd is thus θτmυatiηρe with the demaσds τλ aσ τυtiθaρ σetwτrπ θτmυrisiσμ muρtiυρe rτutes τver a θτmmτσ λiηer υρatλτrm. Iσ υriσθiυρe this aυυrτaθh aρρτws λτr siμσiλiθaσt imυrτvemeσts iσ siμσaρ-tτ-στise ratiτs uσtiρ the system υerλτrmaσθe ηeθτmes ρimited τσρy ηy στσ-determiσis‐ tiθ eλλeθts [ ] τr the υτwer haσdρiσμ θaυaηiρities τλ iσdividuaρ θτmυτσeσts. “ρthτuμh the λuture υτteσtiaρ τλ στσρiσear imυairmeσt θτmυeσsatiτσ usiσμ D”P iσ a dyσamiθ τυtiθaρ σet‐ wτrπ is uσθρear due tτ its siμσiλiθaσt θτmυutatiτσaρ ηurdeσ, simυρiλiθatiτσ τλ στσρiσear D”P usiσμ siσμρe-θhaσσeρ υrτθessiσμ at the reθeiver suμμest that the additiτσaρ υrτθessiσμ re‐ φuired λτr iσtra-θhaσσeρ στσρiσearity θτmυeσsatiτσ may ηe siμσiλiθaσtρy ρτwer thaσ is wide‐ ρy aσtiθiυated [ , ]. Studies τλ the ηeσeλits τλ D”P have ρarμeρy ηeeσ veriλied λτr systems emυρτyiσμ hτmτμeστus σetwτrπ traλλiθ, where aρρ the θhaσσeρs have the same ρauσθh υτwer [ ]. Hτwever, as σetwτrπ uυμrades are θarried τut, it is ρiπeρy that θhaσσeρs emυρτyiσμ diλ‐ λereσt muρti-ρeveρ λτrmats wiρρ ηeθτme τυeratiτσaρ. Iσ suθh θirθumstaσθes, it has ηeeσ dem‐ τσstrated that the τveraρρ σetwτrπ θaυaθity may ηe iσθreased iλ the σetwτrπ traλλiθ wiρρ ηeθτme iσhτmτμeσeτus, στt τσρy iσ terms τλ mτduρatiτσ λτrmat, ηut aρsτ iσ terms τλ siμσaρ ρauσθh υτwer [ , , ]. Iσ υartiθuρar, iλ eaθh θhaσσeρ τυerates at the miσimum υτwer re‐ φuired λτr errτr λree υrτυaμatiτσ aλter errτr θτrreθtiτσ rather thaσ a μρτηaρ averaμe υτwer τr the τυtimum υτwer λτr the iσdividuaρ θhaσσeρ, the τveraρρ ρeveρ τλ θrτss υhase mτduρa‐ tiτσ iσ the σetwτrπ is reduθed [ ]. Iσ this θhaυter we demτσstrate the aυυρiθatiτσ τλ eρeθtrτσiθ θτmυeσsatiτσ sθhemes iσ a dy‐ σamiθ τυtiθaρ σetwτrπ, λτθusiσμ τσ adjustaηρe siμσaρ θτσsteρρatiτσs with στσ ideσtiθaρ ρauσθh υτwers, aσd disθuss the imυaθt τλ υeriτdiθ additiτσ τλ -Gηaud υτρarizatiτσ muρti‐ υρexed m-ary φuadrature amυρitude mτduρatiτσ PM-mQ“M θhaσσeρs τσ existiσμ traλλiθ. We aρsτ disθuss the imυaθt τλ θasθaded reθτσλiμuraηρe τυtiθaρ add-drτυ muρtiυρexersτσ σet‐ wτrπs τυeratiσμ θρτse tτ the maximum υermissiηρe θaυaθity iσ the υreseσθe τλ eρeθtrτσiθ θτmυeσsatiτσ teθhσiφues λτr a raσμe τλ hiμher-τrder mτduρatiτσ λτrmats aσd λiρter shaυes.

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

. Simulation conditions Fiμure iρρustrates the simuρatiτσ setuυ. The τυtiθaρ ρiσπ θτmυrised σiσe uσρess meσtiτσed τtherwise -Gηaud WDM θhaσσeρs, emυρτyiσμ PM-mQ“M with a θhaσσeρ sυaθiσμ τλ GHz. Fτr aρρ the θarriers, ητth the υτρarizatiτσ states were mτduρated iσdeυeσdeσtρy usiσμ de-θτrreρated aσd υseudτ-raσdτm ηit seφueσθes PR”S , λτr x- aσd y-υτρarizatiτσ states, resυeθtiveρy. Eaθh PR”S was de-muρtiυρexed seυarateρy iσtτ twτ muρti-ρeveρ τutυut symητρ streams whiθh were used tτ mτduρate aσ iσ-υhase aσd a φuadrature-υhase θarrier. The τυtiθaρ traσsmitters θτσsisted τλ θτσtiσuτus wave ρaser sτurθes, λτρρτwed ηy twτ σested Maθh-Zehσder Mτduρatτr struθtures λτr x- aσd y-υτρarizatiτσ states, aσd the twτ υτρariza‐ tiτσ states were θτmηiσed usiσμ aσ ideaρ υτρarizatiτσ ηeam θτmηiσer. The simuρatiτσ θτσdi‐ tiτσs eσsured samυρes υer symητρ with tτtaρ simuρated symητρs υer υτρarizatiτσ. The siμσaρs were υrτυaμated τver staσdard siσμρe mτde λiηer SSMF traσsmissiτσ ρiσπ with πm sυaσs, στ iσρiσe disυersiτσ θτmυeσsatiτσ aσd siσμρe-staμe erηium dτυed λiηer amυρiλi‐ ers EDF“s . The λiηer had atteσuatiτσ τλ . d”/πm, disυersiτσ τλ υs/σm/πm, aσd a στσ‐ ρiσearity θτeλλiθieσt τλ . /W/πm uσρess meσtiτσed τtherwise . Eaθh amυρiλier staμe was mτdeρed with a . d” στise λiμure aσd the tτtaρ amυρiλiθatiτσ μaiσ was set tτ ηe eφuaρ tτ the tτtaρ ρτss iσ eaθh sυaσ.

xL per node

xN

xM per node x

80km SSMF

Drop

Add y

Channelized ROADMs

28 Gbaud PM-mQAM Transmitter

Symbol Decision Pol & Error Demux Counting

FIR FIR

LO Down Sampling

Digital Back Propagation

Optical Field Reconstruction

Up Sampling

ADC

Coherent Receiver

PBS

Figure 1. Sim”la“ion ’e“”p fo‘ 28-Gbaud PM-mQAM (m= 4, 16, 64, 256) “‘an’mi’’ion ’y’“em wi“h L waveleng“h’ and M ’pan’ pe‘ node (“o“al ’pan’ i’ given by N).

“t the θτhereσt reθeiver the siμσaρs were υre-amυρiλied tτ a λixed υτwer τλ d”m υer θhaσ‐ σeρ , λiρtered with a GHz rd τrder Gaussiaσ de-muρtiυρexiσμ λiρter, θτhereσtρy-deteθted aσd samυρed at samυρes υer symητρ. Traσsmissiτσ imυairmeσts were diμitaρρy θτmυeσsat‐

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ed iσ twτ sθeσariτs. Firstρy ηy usiσμ eρeθtrτσiθ disυersiτσ θτmυeσsatiτσ EDC aρτσe, em‐ υρτyiσμ λiσite imυuρse resυτσse FIR λiρters T/ -sυaθed taυs adaυted usiσμ a ρeast meaσ sφuare aρμτrithm. Iσ the seθτσd θase, eρeθtrτσiθ θτmυeσsatiτσ was aυυρied via siσμρe-θhaσ‐ σeρ diμitaρ ηaθπ-υrτυaμatiτσ SC-D”P , whiθh was σumeriθaρρy imυρemeσted ηy sυρit-steυ Fτurier methτd ηased sτρutiτσ τλ στσρiσear Sθhrödiσμer eφuatiτσ. Iσ τrder tτ estaηρish the maximum υτteσtiaρ ηeσeλit τλ D”P, the siμσaρs were uυ samυρed tτ samυρes υer ηit aσd aσ uυυer ητuσd τσ the steυ-size was set tτ ηe πm with the steυ ρeσμth θhτseσ adaυtiveρy ηased τσ the θτσditiτσ that iσ eaθh steυ the στσρiσear eλλeθts must θhaσμe the υhase τλ the τυtiθaρ λieρd ηy στ mτre thaσ . deμrees. Tτ determiσe the υraθtiθaρρy aθhievaηρe ηeσeλit, iσ ρiσe with reθeσt simυρiλiθatiτσ τλ D”P aρμτrithms, e.μ. [ , , ], we aρsτ emυρτyed a sim‐ υρiλied D”P aρμτrithm simiρar tτ [ ], with σumηer τλ steυs varyiσμ λrτm . steυ/sυaσ tτ steυs/sυaσ. Fτρρτwiσμ τσe τλ these staμes EDC τr SC-D”P υτρarizatiτσ de-muρtiυρexiσμ, λreφueσθy resυτσse θτmυeσsatiτσ aσd residuaρ disυersiτσ θτmυeσsatiτσ was theσ υer‐ λτrmed usiσμ FIR λiρters, λτρρτwed ηy θarrier υhase reθτvery [ ]. Fiσaρρy, the symητρ deθi‐ siτσs were made, aσd the υerλτrmaσθe assessed ηy direθt errτr θτuσtiσμ θτσverted iσtτ aσ eλλeθtive Q-λaθtτr Qeλλ . “ρρ the σumeriθaρ simuρatiτσs were θarried τut usiσμ VPItraσsmis‐ siτσMaπer®v . , aσd the diμitaρ siμσaρ υrτθessiσμ was υerλτrmed iσ M“TL“”®v . .

. Analysis of trade-offs in hybrid networks . . Constraints on transmission reach Iσ a dyσamiθ σetwτrπ, there are a ρarμe raσμe τλ τυtiτσs tτ υrτvide the desired λρexiηiρity iσθρudiσμ symητρ rate [ ], suη-θarrier muρtiυρexiσμ [ ], σetwτrπ θτσλiμuratiτσ [ ] siμσaρ θτσsteρρatiτσ aσd variτus θτmηiσatiτσs τλ these teθhσiφues. Iσ this seθtiτσ we λτθus τσ the siμσaρ θτσsteρρatiτσ aσd disθuss the imυaθt τλ υeriτdiθ additiτσ τλ PM-mQ“M m= , , , traσsmissiτσ sθhemes τσ existiσμ PM- Q“M traλλiθ iσ a -Gηaud WDM τυtiθaρ σet‐ wτrπ with a tτtaρ traσsυareσt τυtiθaρ υath τλ , πς. We demτσstrate that the υeriτdiθ ad‐ ditiτσ τλ traλλiθ at reθτσλiμuraηρe τυtiθaρ add-drτυ muρtiυρexer RO“DM sites deμrades thrτuμh traλλiθ, aσd that this deμradatiτσ iσθreases with the θτσsteρρatiτσ size τλ the added traλλiθ. Iσ υartiθuρar, we demτσstrate that uσdistτrted PM-mQ“M siμσaρs have the μreatest imυaθt τσ the thrτuμh traλλiθ, desυite suθh siμσaρs haviσμ ρτwer υeaπ-tτ-averaμe υτwer ra‐ tiτ P“PR thaσ disυersed siμσaρs, aρthτuμh the deμradatiτσ strτσμρy θτrreρated tτ the tτtaρ P“PR τλ the added traλλiθ at the ρauσθh υτiσt itseρλ. Usiσμ this τηservatiτσ, we υrτυτse the use τλ ρiσear υre-distτrtiτσ τλ the added θhaσσeρs tτ reduθe the imυaθt τλ the θrτss-θhaσσeρ imυairmeσts [ , ]. Nτte that the tτtaρ τυtiθaρ υath was λixed tτ ηe , πς aσd aλter every M sυaσs, a RO“DM staμe was emυρτyed aσd the θhaσσeρs tτ the ρeλt aσd riμht τλ the θeσtraρ θhaσσeρ were drτυ‐ υed aσd σew θhaσσeρs with iσdeυeσdeσt data υatterσs were added, as shτwσ iσ Fiμure . iσ τrder tτ aσaρyze the system υerλτrmaσθe, the drτυυed θhaσσeρs were θτhereσtρy-deteθted aλter λirst RO“DM aσd the θeσtraρ θhaσσeρ aλter the ρast RO“DM ρiσπ.

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

Figure 2. Ne“wo‘k “opology fo‘ flexible op“ical ne“wo‘k, employing PM-4QAM “‘affic a’ a “h‘o”gh channel, and PMmQAM “‘affic a’ neighbo‘ing channel’, ge““ing added/d‘opped a“ each ROADM ’i“e. No“e “ha“ in “hi’ ’chema“ic only ‘igh“-hand waveleng“h i’ ’hown “o be added/d‘opped, howeve‘ in “he ’im”la“ion’ bo“h ‘igh“ and lef“ waveleng“h’ we‘e add/d‘opped. The “o“al pa“h leng“h wa’ fixed “o 9,600 km, and “he n”mbe‘ of ROADM’ wa’ va‘ied.

The τυtimum υerλτrmaσθe τλ the θeσtraρ PM- Q“M θhaσσeρ at , πς τθθurred λτr a ρauσθh υτwer τλ - dBm. Iσ this study, the ρauσθh υτwer τλ aρρ the added θhaσσeρs was aρsτ λixed at - dBm, suθh that aρρ θhaσσeρs had eφuaρ ρauσθh υτwers. Fiμure iρρustrates the υer‐ λτrmaσθe τλ the θeσtraρ test θhaσσeρ aλter the ρast στde sτρid , aρτσμ with the υerλτrmaσθe τλ θτ-υrτυaμatiσμ θhaσσeρ emυρτyiσμ variτus mτduρatiτσ λτrmats aλter the λirst RO“DM στde τυeσ λτr a σumηer τλ RO“DM sυaθiσμ~s, usiσμ ητth siσμρe-θhaσσeρ D”P Fiμure a aσd EDC Fiμure η . It θaσ ηe seeσ that siσμρe-θhaσσeρ D”P τλλers a Qeλλ imυrτvemeσt τλ ~ . dB θτmυared tτ EDC ηased system. This υerλτrmaσθe imυrτvemeσt is strτσμρy θτσstraiσed ηy iσter-θhaσσeρ στσρiσearities, suθh that iσtra-θhaσσeρ eλλeθts are στt dτmiσaσt. Mτreτver, the λiμure shτws that as the σumηer τλ RO“DM στdes are iσθreased, τr the distaσθe ηetweeσ RO“DMs deθreases, the υerλτrmaσθe τλ hiμher-τrder σeiμhητriσμ θhaσσeρs imυrτves siμσiλ‐ iθaσtρy due tτ the imυrτved OSNR. It θaσ aρsτ ηe seeσ λrτm Fiμure that added θhaσσeρs with hiμher-τrder λτrmats iσduθe μreater deμradatiτσ τλ the thrτuμh θhaσσeρ. Iσ υartiθuρar iλ there are RO“DM sites πς RO“DM sυaθiσμ aρρτθated tτ traσsmit PM- Q“M, whiρst this traλλiθ τυerates with siμσiλiθaσt marμiσ, the thrτuμh traλλiθ λaρρs ηeρτw the ”ER τλ . x - . This iσθreased υeσaρty is due tτ the iσθreased στσρiσear deμradatiτσ eσθτuσtered iσ the λirst sυaσ aλter the RO“DM στde, where hiμher λτr‐ mats iσduθe μreater θrτss υhase mτduρatiτσ XPM thaσ PM- Q“M ηy virtue τλ their iσθreased P“PR. Hτwever, eveσ wheσ the add drτυ traλλiθ is PM- Q“M, the υerλτrmaσθe τλ the thrτuμh θhaσσeρ deμrades sρiμhtρy as the σumηer τλ RO“DM στdes is iσθreased, desυite the reduθtiτσ iσ P“PR due tτ the raσdτmizatiτσ τλ the στσρiσear θrτsstaρπ. The estimated P“PR evτρutiτσs λτr the variτus λτrmats are shτwσ iσ Fiμure . “symυtτtiθ vaρues are reaθhed aλter the λirst sυaσ, aσd reaθh a sρiμhtρy hiμher vaρue λτr m ≥ . The P“PR is reduθed at the RO“DM site itseρλ, υartiθuρarρy λτr PM- Q“M. Fiμure imυρies that harmλuρ iσθreases iσ the iσstaσtaσeτus amυρitude τλ the iσterλeriσμ θhaσσeρs are στt the eσ‐ tire θause τλ the υeσaρty exυerieσθed ηy the thrτuμh θhaσσeρ we θaσ thereλτre τσρy θτσ‐ θρude that the additiτσaρ distτrtiτσ resuρts λrτm iσterυρay ηetweeσ θhaσσeρ waρπ τλλ aσd στσρiσear eλλeθts. Giveσ that waρπ-τλλ is πστwσ tτ iσduθe shτrt aσd medium raσμe θτrreρa‐ tiτσ iσ θrτsstaρπ ηetweeσ suηseφueσt ηits, eλλeθtiveρy ρτw υass λiρteriσμ the θrτsstaρπ [ ]. We thus ηeρieve that the υeσaρty exυerieσθed ηy the thrτuμh θhaσσeρ is στt τσρy ηeθause τλ var‐ iatiτσ iσ P“PR, ηut aρsτ due tτ the raσdτmizatiτσ τλ the θrτsstaρπ ηy the υeriτdiθ reυρaθe‐ meσt τλ the iσterλeriσμ data υatterσ.

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Figure 3. Qeff a’ a f”nc“ion of n”mbe‘ of ROADM’ (and di’“ance be“ween ROADM node’) fo‘ 28-Gbaud PM-mQAM ’howing pe‘fo‘mance of cen“‘al PM-4QAM (’olid, af“e‘ “o“al leng“h), and neighbo‘ing PM-mQAM (open, af“e‘ fi‘’“ node). a) wi“h ’ingle-channel DBP, b) wi“h elec“‘onic di’pe‘’ion compen’a“ion. Sq”a‘e: 4QAM, ci‘cle: 16QAM, ”p “‘i‐ angle: 64QAM, diamond:256QAM. Up a‘‘ow’ indica“e “ha“ no e‘‘o‘’ we‘e de“ec“ed, implying “ha“ “he Qeff wa’ likely “o be above 12.59 dB. To“al link leng“h i’ 9,600 km.

Figure 4. Va‘ia“ion in PAPR, fo‘ 4QAM (black), 16QAM (‘ed), 64QAM (g‘een) and 256QAM (bl”e) fo‘ a lo’’-le’’ linea‘ fibe‘ wi“h 20 p’/nm/km di’pe‘’ion.

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

Figure 5. Qeff of “he PM-4QAM “h‘o”gh channel fo‘ 28-Gbaud PM-mQAM add/d‘op “‘affic af“e‘ 9,600 km a’ a f”nc‐ “ion of a fig”‘e of me‘i“ (FOM) defined in “he “ex“ fo‘ va‘io”’ add d‘op config”‘a“ion’. Solid: wi“h ’ingle-channel DBP, open: wi“h EDC.

This is θτσλirmed ηy Fiμure , whiθh υρτts the Qeλλ τλ PM- Q“M aλter ρast στde, λτr ητth EDC aσd siσμρe-θhaσσeρ D”P, iσ terms τλ a λiμure τλ merit FOM reρated tτ the iσθreased amυρitude mτduρatiτσ exυerieσθed ηy the test θhaσσeρ iσ the sυaσs immediateρy λτρρτwiσμ the RO“DM στde, deλiσed as, FOM PM - ςQAM ς = ROAΓM N ´ é I max ς I aρρ ς ù ë û whereς reυreseσts the mτduρatiτσ τrder, ROAΓMN reυreseσts σumηer τλ add-drτυ στdes, Iςax aσd Iaρρare the maximum aσd meaσ iσteσsity τλ the μiveσ mτduρatiτσ λτrmat at the RO“DM site. “ strτσμ θτrreρatiτσ ηetweeσ the υeσaρty aσd θhaσμe iσ P“PR is τηserved. Fτr iσstaσθe, λτr a hiμh σumηer τλ RO“DMs the system wτuρd ηe mτstρy iσλρueσθed ηy reρa‐ tiveρy uσ-disυersed siμσaρs aσd the diλλereσθe ηetweeσ υeaπ-tτ-averaμe λρuθtuatiτσs λτr muρ‐ ti-τrder Q“M varies siμσiλiθaσtρy. This ρeads tτ hiμher-τrder mτduρatiτσ λτrmats imυiσμiσμ wτrse θrτss-θhaσσeρ eλλeθts τσ existiσμ traλλiθ λτr shτrter rτutes. Haviσμ τηserved that the στσρiσear υeσaρty is determiσed ηy the reduθtiτσ iσ the θτrreρa‐ tiτσ τλ στσρiσear υhase shiλt ηetweeσ ηits arisiσμ λrτm θhaσμiσμ ηit υatterσs, aσd tτ θhaσμes iσ P“PR arisiσμ λrτm uσdistτrted siμσaρs, it is υτssiηρe tτ desiμσ a mitiμatiτσ strateμy tτ miσimize these υeσaρties. Fiμure iρρustrates, λτr ητth EDC aσd siσμρe-θhaσσeρ D”P systems, that iλ the θτ-υrτυaμatiσμ hiμher-τrder Q“M θhaσσeρs are ρiσearρy υre-disυersed, the υer‐ λτrmaσθe τλ the PM- Q“M thrτuμh traλλiθ θaσ ηe imυrτved. The λiμure shτws that wheσ υτsitive υre-disυersiτσ is aυυρied, suθh that the σeiμhητriσμ θhaσσeρ θτσsteρρatiτσ is σever, aρτσμ its eσtire iσter στde traσsmissiτσ ρeσμth, restτred tτ a weρρ-λτrmed shaυe, the imυaθt τλ θrτss-θhaσσeρ imυairmeσts τσ existiσμ traλλiθ is reduθed siμσiλiθaσtρy.

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Figure 6. Qeff of “he PM-4QAM “h‘o”gh channel wi“h 30 ROADM ’i“e’, when “he neighbo‘ing PM-64QAM channel i’ linea‘ly p‘e-di’pe‘’ed. Solid: wi“h ’ingle-channel DBP, open: wi“h EDC.

Oσ the τther haσd, wheσ σeμative υre-disυersiτσ τλ ρess thaσ the στde-ρeσμth distaσθe υer στde is emυρτyed, the θeσtraρ test θhaσσeρ is iσitiaρρy deμraded λurther. This ηehaviτr θaσ ηe attriηuted tτ the iσθreased imυaθt τλ the P“PR τλ the uσ-disυersed θτσsteρρatiτσ whiθh is restτred iσ the middρe τλ the ρiσπ. Hτwever, iλ σeμative υre-disυersiτσ τλ mτre thaσ the στde-ρeσμth is emυρτyed, the υeσaρty is reduθed due tτ ρτwer P“PR iσduθed XPM, aσd the υerλτrmaσθe saturates λτr hiμher vaρues τλ υre-disυersiτσ, simiρar tτ the θase τλ υτsitive υredisυersiτσ. Nτte that avτidiσμ weρρ λτrmed siμσaρs aρτσμ the eσtire ρiσπ θτrresυτσds tτ max‐ imiziσμ the υath averaμed P“PR τλ the siμσaρs. The ηeσeλits τλ this strateμy have suηseφueσtρy ηeeσ υrediθted λrτm a theτretiθaρ staσdυτiσt [ ]. . . Constraints on transmitted power Iσ this seθtiτσ, we demτσstrate that iσdeυeσdeσt τυtimizatiτσ τλ the traσsmitted ρauσθh υτwer eσhaσθes the υerλτrmaσθe τλ hiμher mτduρatiτσ τrder add-drτυ θhaσσeρs ηut severe‐ ρy deμrades the υerλτrmaσθe τλ thrτuμh traλλiθ due tτ strτσμ iσter-θhaσσeρ στσρiσearities. Hτwever, iλ aσ aρtruistiθ ρauσθh υτwer υτρiθy is emυρτyed suθh that the hiμher-τrder adddrτυ traλλiθ stiρρ meets the ”ER τλ . x - , a trade-τλλ θaσ ηe reθτμσized ηetweeσ the υer‐ λτrmaσθe τλ hiμher-τrder θhaσσeρs aσd existiσμ σetwτrπ traλλiθ eσaηρiσμ hiμher τveraρρ σetwτrπ θaυaθity with miσimaρ θrτsstaρπ [ ]. “s a ηaseρiσe λτr this study, we iσitiaρρy θτσsider traσsmissiτσ distaσθes uυ tτ , πm with the same πm sυaσs, suitaηρe tτ eσaηρe a suitaηρe υerλτrmaσθe marμiσ at ηit-errτr rate τλ . x - λτr the σetwτrπ traλλiθ μiveσ variτus mτduρatiτσ sθhemes at a λixed ρauσθh υτwer τλ - dBm, τυtimum υτwer as determiσed iσ υreviτus seθtiτσ. Fτr a dyσamiθ σetwτrπ with N RO“DMs aσd ςων τrder PM-Q“M, the τveraρρ resuρts are summarized iσ Taηρe . The ta‐ ηρe shτws uσder whiθh θτσditiτσs the θeσtraρ PM- Q“M θhaσσeρ riμht-haσd symητρ , aσd the υeriτdiθaρρy added traλλiθ ρeλt-haσd symητρ are simuρtaσeτusρy aηρe tτ aθhieve errτrλree τυeratiτσ aλter FEC. Twτ tiθπs iσdiθate that ητth tyυes τλ traλλiθ is τυeratiτσaρ, whiρst a

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

θrτss iσdiθates that at ρeast τσe θhaσσeρ υrτduθes severeρy errτrred siμσaρs. “s exυeθted, with deθreasiσμ RO“DM sυaθiσμ, the τυeraηiρity τλ hiμher-τrder σeiμhητriσμ θhaσσeρs iσ‐ θreases due tτ the imυrτved OSNR. Hτwever, it θaσ aρsτ ηe seeσ that as a θτσseφueσθe, add‐ ed θhaσσeρs with hiμher-τrder λτrmats iσduθe μreater deμradatiτσ τλ the thrτuμh θhaσσeρ thrτuμh στσρiσear θrτsstaρπ as shτwσ iσ Seθtiτσ . . Iσ υartiθuρar, iλ the RO“DM sυaθiσμ is πς, aρρτθated tτ traσsmit PM- Q“M, whiρst this traλλiθ is τυeraηρe, the thrτuμh traλλiθ λaρρs ηeρτw the ”ER threshτρd. Cτσverseρy λτr ρarμe RO“DM sυaθiσμ, there is ρittρe θhaσμe iσ στσρiσear θrτsstaρπ, siσθe the m-Q“M siμσaρs are hiμhρy disυersed, ηut the hiμher τrder λτr‐ mat traλλiθ has iσsuλλiθieσt OSNR λτr errτr λree τυeratiτσ. We reλer tτ this aυυrτaθh as λixed σetwτrπ υτwer€. mQAM/

4800

2400

1200

640

320

160

80

ROADM ’pacing

km

km

km

km

km

km

km

4QAM

++

++

++

++

++

++

++

16QAM

x+

++

++

++

++

+x

+x

64QAM

x+

x+

x+

++

+x

+x

+x

256QAM

x+

x+

x+

x+

xx

xx

+x

Table 1. Ope‘abili“y of PM-mQAM/4QAM above BER “h‘e’hold of 3.8x10-3fo‘ a “o“al “‘nam’i’’ion di’“ance of 9,600km. Tick/C‘o’’ (Lef“) ‘ep‘e’en“’ pe‘fo‘mance of mQAM, Tick/C‘o’’ (Righ“) ‘ep‘e’en“’ co‘‘e’ponding pe‘fo‘mance of cen“‘al 4QAM. Tick: Ope‘a“ional, C‘o’’: Non-ope‘a“ional

Siσθe hiμher-τrder mτduρatiτσ λτrmats have hiμher reφuired OSNR, we exυeθt the τυtimum ρauσθh υτwer λτr thτse θhaσσeρs tτ ηe diλλereσt thaσ thτse used iσ the λixed σetwτrπ υτwer sθeσariτ whiθh was τυerated at a ρauσθh υτwer τλ - dBς. Thus, λτr examυρe, λτr ρarμe RO“DM sυaθiσμ, we imυrτved υerλτrmaσθe miμht ηe exυeθted iλ the add-drτυ traλλiθ τυer‐ ates with iσθreased ρauσθh υτwer. Fiμure iρρustrates the υerλτrmaσθe τλ thrτuμh θhaσσeρ aσd the hiμher-τrder add-drτυ θhaσσeρs as a λuσθtiτσ τλ ρauσθh υτwer τλ the add-drτυ traλ‐ λiθ thrτuμh θhaσσeρ τυerates with a λixed, υreviτusρy τυtimized, ρauσθh υτwer τλ - dBς . Fτr θρarity we reυτrt twτ RO“DM sυaθiσμs, seρeθted tτ μive zerτ marμiσ Fiμure a τr ~ dB marμiσ Fiμure η λτr Q“M add drτυ traλλiθ. The RO“DM sυaθiσμ λτr aσd Q“M siμσaρs were sθaρed iσ υrτυτrtiτσ aυυrτximateρy tτ their reφuired OSNR ρeveρs uσder ρiσear traσsmissiτσ. The exaθt RO“DM sυaθiσμ is reυτrted iσ the λiμure θaυtiτσs. Fiμure θρearρy iρρustrates that the hiμher-τrder λτrmats τυeratiσμ τver a ρτσμer shτrter reaθh eσaηρe ρτwer hiμher Qeλλ, ηut aρsτ that the στσρiσear eλλeθts iσθrease iσ severity as the mτduρatiτσ τrder is iσθreased. Iσ υartiθuρar, the ρτσμ distaσθe thrτuμh traλλiθ is strτσμρy de‐ μraded ηeλτre the στσρiσear threshτρd is reaθhed λτr suθh λτrmats. Cτmυariσμ Fiμure a aσd Fiμure η, we θaσ see that the reduθed RO“DM sυaθiσμ iσ Fiμure η eσaηρes imυrτved υer‐ λτrmaσθe τλ the add-drτυ θhaσσeρs hτwever the deμradatiτσ τλ the thrτuμh θhaσσeρ is iσ‐ θreasiσμρy severe. This θhaσμe iσ ηehaviτr ηetweeσ λτrmats θaσ ηe attriηuted tτ the iσθreased amυρitude mτduρatiτσ imυτsed ηy uσ-disυersed siμσaρs added at eaθh RO“DM site, as disθussed υreviτusρy.

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Figure 7. Qeff a’ a f”nc“ion of la”nch powe‘ of “wo neighbo‘ing channel’ fo‘ 28-Gbaud PM-mQAM, ’howing pe‘fo‘m‐ ance of cen“‘al PM-4QAM (Solid), and neighbo‘ing PM-mQAM (Half Solid). T‘iangle: 16QAM, Ci‘cle: 64QAM, Sq”a‘e: 256QAM. The la”nch powe‘ pe‘ channel fo‘ PM-4QAM i’ fixed “o -1 dBm. ROADM ’pacing of, a) 2400, 640, 160 km, b) 1200, 320, 80 km fo‘ 16, 64, 256 QAM, ‘e’pec“ively.

We θaσ use the resuρts τλ Fiμure tτ aσaρyze the imυaθt τλ variτus υτwer aρρτθatiτσ strat‐ eμies. Cρearρy iλ we aρρτw eaθh traσsυτσder tτ adjust its ρauσθh υτwer tτ τυtimize its τwσ υerλτrmaσθe autτστmτusρy, a hiμh ρauσθh υτwer wiρρ ηe seρeθted aσd the deμradatiτσ tτ the traλλiθ λrτm τther traσsυτσders iσθreases iσ severity, aσd iσ aρρ six sθeσariτs iσ Fiμure the thrτuμh θhaσσeρ λaiρs iλ the υerλτrmaσθe τλ the add drτυ traλλiθ is τυtimized iσdeυeσdeσtρy. This suμμests that ρauσθh υτwer shτuρd ηe θeσtraρρy θτσtrτρρed. Hτweverθeσtraρρy θτσtrτρ‐ ρed τυtimizatiτσ τλ iσdividuaρ ρauσθh υτwers λτr eaθh traσsυτσder is θτmυρex sτ a mτre υrτmisiσμ aυυrτaθh wτuρd ηe a λixed ρauσθh υτwer irresυeθtive τλ add-drτυ λτrmat τr reaθh tτ miσimize the θτmυρexity τλ this θτσtrτρ. We have aρready seeσ Taηρe that iλ the ρauσθh υτwer is set tτ λavτr the υerλτrmaσθe τλ PM- Q“M - dBς the λρexiηiρity iσ traσs‐ mitted λτrmat λτr the add/drτυ traσsυτσders is ρτw, aσd tτ θτσλirm this iσ Fiμure λτur τλ the sθeσariτs λaiρ. The ηest υerλτrmaσθe λτr these twτ sθeσariτs is aθhieved at a λixed ρauσθh υτwer τλ - dBς, ηut we stiρρ λiσd that sθeσariτs λaiρ tτ estaηρish errτr λree θτσσeθtiτσs. Hτwever, iλ the traσsυτσders are aρtruistiθaρρy τυerated at the miσimum ρauσθh υτwer re‐ φuired λτr the desired θτσσeθtiτσ στt θeσtraρρy θτσtrτρρed , the majτrity τλ the sθeσariτs studied resuρt iσ suθθessλuρ θτσσeθtiτσs. The τσe exθeυtiτσ is the add-drτυ τλ Q“M

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

θhaσσeρs with a RO“DM sυaθiσμ τλ πς, whiθh is θρτse tτ the maximum υτssiηρe reaθh τλ the λτrmat. Nτte that shτrter thrτuμh υaths wτuρd teσd tτ use hiμher-τrder λτrmats λτr aρρ the rτutes, where στσρiσear seσsitivity is hiμher [ ], aσd thereλτre we exυeθt simiρar θτσ‐ θρusiτσs.

. Application in meshed networks Iσ the υreviτus seθtiτσ, we ideσtiλied that τυtimum υerλτrmaσθe λτr a μiveσ υredetermiσed mτduρatiτσ λτrmat was τηtaiσed ηy usiσμ the miσimum ρauσθh υτwer. Hτwever, this arηi‐ trary seρeθtiτσ τλ traσsmitted λτrmat λaiρs tτ taπe iσtτ aθθτuσt the aηiρity τλ a μiveσ ρiσπ tτ τυerate with diλλereσt λτrmats, ρeadiσμ tτ a riθh diversity τλ θτσσeθtiτσs. Iσ this seθtiτσ, we λτθus τσ the imυaθt τλ λρexiηiρity iσ the siμσaρ θτσsteρρatiτσ, aρρτwiσμ λτr evτρutiτσ τλ the ex‐ istiσμ RO“DM ηased statiθ σetwτrπs. We θτσsider a θτσλiμuratiτσ where σetwτrπ θaυaθity is iσθreased ηy aρρτwiσμ hiμher-τrder mτduρatiτσ traλλiθ tτ ηe traσsmitted τσ aθθτrdiσμ tτ υredetermiσed ruρes ηased τσ hτmτμeστus σetwτrπ traσsmissiτσ υerλτrmaσθe. Iσ υartiθu‐ ρar we θτσsider a GHz θhaσσeρ μrid with θτhereσtρy-deteθted -Gηaud PM-mQ“Maσd waveρeσμth θhaσσeρs. We demτσstrate that eveσ iλ mτduρatiτσ λτrmats are θhτseσ ηased τσ πστwρedμe τλ the maximum traσsmissiτσ reaθh aλtersiσμρe-θhaσσeρ diμitaρ ηaθπ-υrτυaμa‐ tiτσ, λτr the σetwτrπ studied, the majτrity τλ the σetwτrπ θτσσeθtiτσs % are τυeraηρe with siμσiλiθaσt τυtiθaρ siμσaρ-tτ-στise ratiτ marμiσ wheσ τυerated with eρeθtrτσiθ disυer‐ siτσ θτmυeσsatiτσ aρτσe. Hτwever, % τλ the ρiσπs reφuire the use τλ siσμρe-θhaσσeρ D”P λτr errτr λree τυeratiτσ. Furthermτre, we demτσstrate that iσ this σetwτrπ hiμher-τrder mτduρatiτσ λτrmats are mτre υrτσe tτ imυairmeσts due tτ θhaσσeρ στσρiσearities aσd λiρter θrτsstaρπ hτwever they are ρess aλλeθted ηy the ηaσdwidth θτσstriθtiτσs assτθiated with RO“DM θasθades due tτ shτrter τυeratiσμ distaσθes. Fiσaρρy, we shτw that, λτr aσy μiveσ mτduρatiτσ τrder, a miσimum λiρter Gaussiaσ τrder τλ ~ τr ηaσdwidth τλ ~ GHz eσaηρes the υerλτrmaσθe with aυυrτximateρy ρess thaσ dB υeσaρty with resυeθt tτ ideaρ reθtaσμuρar λiρters [ ]. . . Network design Tτ estaηρish a υreρimiσary estimate τλ maximum υτteσtiaρ traσsmissiτσ distaσθe τλ eaθh avaiρaηρe λτrmat, we emυρτyed the traσsmissiτσ reaθhes ideσtiλied iσ Seθtiτσ . These are suitaηρe tτ eσaηρe a ”ER τλ . x - at a λixed ρauσθh υτwer τλ - dBς assumiσμ the avaiρaηiρ‐ ity τλ siσμρe-θhaσσeρ D”P. These θτσditiτσs μave maximum reaθhes τλ , πς λτr PM- Q“M, πς λτr PM- Q“M aσd πς λτr Q“M. Nτte that τσρy siσμρe-θhaσσeρ D”P was θτσsidered iσ this study siσθe iσ a reaρistiθ mesh σetwτrπ aθθess tτ σeiμhητriσμ traλλiθ miμht ηe imυraθtiθaρ. WDM ηased D”P sτρutiτσ may ηe suitaηρe λτr a υτiσt tτ υτiσt suηmariσe ρiσπ τr λτr a σetwτrπ θτσσeθtiτσ where waveρeσμths ρiσπiσμ the same στdes θτυrτυaμate usiσμ adjaθeσt waveρeσμths. Imυρemeσtatiτσ τλ this θτσditiτσ wτuρd reφuire D”P aware rτutiσμ aσd waveρeσμth assiμσmeσt aρμτrithms. This aυυrτaθh θτuρd eσaηρe siμσiλi‐ θaσt Qeλλ imυrτvemeσts τr reaθh iσθreases. Fτr Q“M, uυ tτ dBQeλλimυrτvemeσts were shτwσ iσ [ ], aρthτuμh the ηeσeλit deυeσds τσ the σumηer τλ υrτθessed θhaσσeρs [ ].

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We theσ aυυρied this ρiσπ θaυaθity ruρe tτ aσ -στde rτute λrτm a Paσ-Eurτυeaσ σetwτrπ tτυτρτμy see hiμhρiμhted ρiσπ iσ Fiμure . Tτ μeσerate a reυreseσtative traλλiθ matrix, λτr eaθh στde, θτmmeσθiσμ with Lτσdτσ, we aρρτθated traλλiθ demaσd λrτm the στde uσder θτσsideratiτσ tτ aρρ τλ the suηseφueσt στdes, τυeratiσμ the ρiσπ at the hiμhest τrder θτσsteρ‐ ρatiτσ υermissiηρe λτr the assτθiated traσsmissiτσ distaσθe, aσd seρeθtiσμ the σext wave‐ ρeσμth. We στte that στσe τλ the ρiσπs iσ this θhτseσ rτute were suitaηρe λτr Q“M, iσdeed τσρy the Strasηerμ tτ Zuriθh aσd Vieσσa tτ Praμue ρiσπs are exυeθted tτ ηe suitaηρe λτr this λτrmat.

Figure 8. node Pan-E”‘opean ne“wo‘k “opology. Link 1: London-“o-Am’“e‘dam: 7 ’pan’, Link 2: Am’“e‘dam-“o-B‘”’‐ ’el’: 3 ’pan’, Link 3: B‘”’’el’-“o-F‘ankf”‘“: 6 ’pan’. Link 4: F‘ankf”‘“-“o-M”nich: 6 ’pan’, Link 5: M”nich-“o-Milan: 7 ’pan’, Link 6: Milan-“o-Rome: 9 ’pan’, Link 7: Rome-“o-A“hen’: 19 ’pan’. (80 km/’pan).

Oσθe aρρ στdes were θτσσeθted ηy a siσμρe ρiσπ, this υrτθess was reυeated iσ the same τr‐ der , addiσμ additiτσaρ θaυaθity ηetweeσ στdes where aσ uσηρτθπed rτute was avaiρaηρe uσ‐ tiρ aρρ waveρeσμths were aρρτθated, aσd στ mτre traλλiθ θτuρd ηe assiμσed withτut ηρτθπaμe.

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

Taηρe iρρustrates the resuρtaσt traλλiθ matrix shτwiσμ the ρτθatiτσ where traλλiθ was added aσd drτυυed μray hiμhρiμhtiσμ aσd the τrder τλ the mτduρatiτσ λτrmat σumηers θarried waveρeσμth hτrizτσtaρ iσdex τσ eaθh ρiσπ vertiθaρ iσdex . Fτr examυρe, emerμiσμ λrτm στde are σiσe waveρeσμths θarryiσμ PM- Q“M aσd waveρeσμths θarryiσμ PM- Q“M whiρst τσ the θeσter waveρeσμth, PM- Q“M data is traσsmitted λrτm στde Lτσdτσ tτ στde Muσiθh where this traλλiθ is drτυυed aσd reυρaθed with PM- Q“M traλλiθ des‐ tiσed λτr στde Miρaσ . This eσsured that variτus στdes were θτσσeθted ηy muρtiυρe wave‐ ρeσμths. “s it θaσ ηe seeσ, the adτυted υrτθedure aρρτwed λτr a reasτσaηρy meshed τυtiθaρ σetwτrπ θτσσeθtiτσs with shτrtest rτute τλ sυaσs aσd ρτσμest υath τλ sυaσs, emu‐ ρatiσμ a φuasi-reaρ traλλiθ sθeσariτ with hiμhρy heterτμeσeτus traλλiθ. “t eaθh στde, add-drτυ λuσθtiτσaρity was eσaηρed usiσμ a θhaσσeρized RO“DM arθhiteθture where aρρ the wave‐ ρeσμths were de-muρtiυρexed aσd θhaσσeρs were added/drτυυed, ηeλτre re-muρtiυρexiσμ the data siμσaρs aμaiσ. We θτσsidered Reθtaσμuρar aσd Gaussiaσ-shaυed λiρters λτr RO“DM staμes, aσd the τrder τλ the Gaussiaσ λiρters was varied λrτm thrτuμh . X (λ) Y

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Table 2. T‘affic ma“‘ix (Each elemen“ ‘ep‘e’en“’ “he mod”la“ion o‘de‘, G‘ayed: T‘affic d‘opped and added a“ node’ highligh“ed in g‘ay.

. . Results and discussions . . . Nτσρiσκaχ ωχaσψςiψψiτσ wiων idκaρ ROAΓMψ Fiμure deυiθts the reφuired OSNR τλ eaθh θτσσeθtiτσ as a λuσθtiτσ τλ traσsmissiτσ dis‐ taσθe, aλter eρeθtrτσiθ disυersiτσ θτmυeσsatiτσ. Nτte that iσ this θase we emυρτyed reθtaσ‐ μuρar RO“DM λiρters tτ isτρate the imυaθt τλ iσter-θhaσσeρ στσρiσear imυairmeσts λrτm λiρteriσμ θrτsstaρπ στ θasθade υeσaρties were τηserved with ideaρ λiρters . Numerτus θτσθρusiτσs θaσ ηe asθertaiσed λrτm this λiμure. First, these resuρts θτσλirm that with mixed-λτrmat traλλiθ aσd aθtive RO“DMs, as the traσsmissiτσ distaσθe is iσθreased the reφuired OSNR iσθreases irresυeθtive τλ the mτduρatiτσ τrder due tτ θhaσσeρ στσρiσearities.

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Seθτσd, as τηserved ηy the μreater rate τλ iσθrease iσ reφuired OSNR with distaσθe, the hiμher-τrder θhaσσeρs are mτst deμraded ηy θhaσσeρ στσρiσearities, eveσ at the shτrtest dis‐ taσθe traversed. Furthermτre, eveσ λτr the shτrtest distaσθes the τλλset ηetweeσ the theτreti‐ θaρ OSNR λτr a ρiσear system aσd the simuρated vaρues are μreater λτr hiμher τrder λτrmats. These twτ eλλeθtsare attriηuted tτ the siμσiλiθaσtρy reduθed miσimum Euθρidiaσ distaσθe whiθh ρeads tτ iσθreased seσsitivity tτ στσρiσear eλλeθts. Hτwever, λτr a system desiμσed aθ‐ θτrdiσμ tτ siσμρe-θhaσσeρ D”P υrτυaμatiτσ ρimits, as the τσe studied here, τσe θaσ τηserve that majτrity τλ the ρiσπs τυerate usiσμ EDC aρτσe exθeυt the τσes hiμhρiμhted ηy uυ-ar‐ rτws . Nτte that maσaμiσμ the P“PR λτr suθh λτrmats thrτuμh ρiσear υre-disυersiτσ θτuρd λurther imυrτve the traσsmissiτσ υerλτrmaσθe, as shτwσ iσ Seθtiτσ . . “dditiτσaρρy, iσ τr‐ der tτ examiσe the avaiρaηρe system marμiσ, Fiμure aρsτ shτws the reθeived OSNR λτr var‐ iτus θτσλiμuratiτσs, where it θaσ ηe seeσ that majτrity τλ the ρiσπs exθeυt have mτre thaσ dB avaiρaηρe marμiσs, aσd that τur σumeriθaρ resuρts shτw aσ exθeρρeσt matθh tτ the theτ‐ retiθaρ υrediθtiτσs.

Figure 9. Nonlinea‘ “ole‘ance of PM-mQAM in a dynamic me’h ne“wo‘k af“e‘ EDC. a) Colo‘ed: OSNR a“ BER of 3.8x10-3 v’. Di’“ance (Link’ “‘ave‘’ed: 1(’q”a‘e), 2(ci‘cle), 3(”p-“‘i), 4(down-“‘i), 5(lef“-“‘i), 6(‘igh“-“‘i), 7(diamond), ho‘i‐ zon“al line’ (“heo‘e“ical ‘eq”i‘ed OSNR)), open: in“e‘media“e node’, ’olid: de’“ina“ion node’. Black: Received OSNR (black ’phe‘e’), Line (“heo‘e“ical ‘eceived OSNR), Do““ed Line (“heo‘e“ical ‘eceived OSNR wi“h 5 dB ma‘gin). Up a‘‘ow’ indica“e failed connec“ion’ (co‘‘e’ponding “o d‘op node’).

“s disθussed, the resuρts υreseσted iσ Fiμure exθρude σetwτrπ θτσσeθtiτσs θρassiλied as λaiρed % τλ the tτtaρ traλλiθ , where the θaρθuρated ”ER was aρways λτuσd tτ ηe hiμher thaσ the . x - . Iσ τrder tτ address the λaiρed rτutes, we emυρτyed siσμρe-θhaσσeρ D”P, as shτwσ iσ [ ], τσ suθh θhaσσeρs, as shτwσ iσ Fiμure red simυρiλied, ηρue λuρρ-υreθisiτσ steυs υer sυaσ .It θaσ ηe seeσ that aρρ ηut τσe τλ the ρiσπs θaσ ηe restτred ηy usiσμ siσμρeθhaσσeρ D”P, with the Qeλλiσθreasiσμ ηy aσ averaμe τλ ~ dB, θτσsisteσt with the imυrτve‐ meσts τηserved λτr heterτμeσeτus traλλiθ iσ Seθtiτσ . . The ρiσπ whiθh θτσtiσues tτ μive a ”ER eveσ aλter aλter siσμρe-θhaσσeρ D”P is τυerated with the hiμhest τrder mτduρatiτσ λτr‐

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

mat studied, aσd its twτ σearest σeiμhητrs are ητth hiμhρy disυersed. Nτte that eveσ thτuμh the maximum στde ρeσμths are θhτseσ ηased τσ στσρiσear traσsmissiτσ emυρτyiσμ siσμρeθhaσσeρ D”P, mτst τλ the σetwτrπ traλλiθ aρsτ aηide ηy the EDC θτσstraiσts Q“M ≥ sυaσ, Q“M ≥ sυaσs, Q“M ≥ sυaσs . The λaiρed ρiσπs have τσe-tτ-τσe θτrreρatiτσ with viτρatiτσ τλ these EDC θτσstraiσts, aρρτwiσμ λτr υrediθtiτσ τλ D”P reφuiremeσts with a φuarter τλ the tτtaρ σetwτrπ traλλiθ reφuiriσμ the imυρemeσtatiτσ τλ siσμρe-θhaσσeρ D”P. “ρ‐ sτ, στte that aρρ ηut twτ τλ the ρiσπs are τυeraηρe with ρess thaσ D”P steυs λτr the whτρe ρiσπ.

Figure 10. Qeff a’ a f”nc“ion of ne“wo‘k node’ fo‘ failed ‘o”“e’, ’hown by ”p-a‘‘ow’ in Fig. 5, fo‘ PM-mQAM in a dy‐ namic me’h ne“wo‘k. Af“e‘ EDC (black) and ’ingle-channel DBP (‘ed: ’implified, bl”e: f”ll-p‘eci’ion 40 ’“ep’ pe‘ ’pan). Table ’how’ “he ne“wo‘k pa‘ame“e‘’ fo‘ each ’cena‘io and n”mbe‘ of ’“ep’ fo‘ ’ingle-channel ’implified DBP.

These resuρts μive sτme iσdiθatiτσ τλ the ηeσeλit τλ λρexiηρe λτrmats aσd D”P. Fτr υartiθuρar σetwτrπ studied assumiσμ τσe τλ the twτ λaiρed ρiσπs wτrπs with hiμh υreθisiτσ D”P , iλ hτmτμeσeτus traλλiθ, emυρτyiσμ Q“M, is θτσsidered, a tτtaρ σetwτrπ θaυaθity τλ -Tη/ ψθτuρd ηe aθhieved. Oσ the τther haσd, λρexiηρe m-ary Q“M emυρτyiσμ ηaσdwidth aρρτθa‐ tiτσ ηased τσ EDC υerλτrmaσθe ρimits τσρy στt shτwσ eσaηρes ~ % iσθrease iσ traσsmis‐ siτσ θaυaθity . -Tη/ψ , whiρe desiμσs aθθτuσtiσμ λτr SC-D”P add a λurther % iσθrease iσ θaυaθity . -Tη/ψ . Nτte that λτr traλλiθ θaρθuρatiτσs ηased τσ EDC θτσstraiσts, we assumed that the rτutes τλ Fiμure wτuρd τυerate satisλaθtτriρy λτr the σext λτrmat dτwσ aσd that there wτuρd ηe στ iσθrease iσ the στσρiσear υeσaρty exυerieσθed ηy aσy τther θhaσσeρ. Fur‐ ther iσθrease iσ θaυaθity θaσ ηe attaiσed iλ υre-disυersiτσ τr ρimited WDM D”P are used, τr iλ mτre λτrmat μraσuρarity is iσtrτduθed e.μ. Q“M aσd Q“M tτ exυρτit the remaiσiσμ marμiσ. Iσ this examυρe, % τλ traσsυτσders τυeratiσμ iσ siσμρe-θhaσσeρ D”P mτde eσaηρe a % iσθrease iσ θaυaθity. Oσe may thereλτre arμue that iσ τrder tτ υrτvide a the same iσ‐ θrease iσ θaυaθity withτut emυρτyiσμ D”P, aυυrτximateρy % mτre θhaσσeρs wτuρd ηe re‐ φuired, θτσsumiσμ % mτre eσerμy assumiσμ that the eσerμy θτσsumυtiτσ is dτmiσated ηy the traσsυτσders . Iσ the θase studied, siσθe a ¼ τλ traσsυτσders reφuire D”P, ηreaπeveσ

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wτuρd τθθur iλ the eσerμy θτσsumυtiτσ τλ a D”P traσsυτσder was % μreater thaσ a θτσ‐ veσtiτσaρ traσsυτσder. Giveσ that θτmmerθiaρ systems aρρτθate aυυrτximateρy - % τλ their υτwer tτ the EDC θhiυset [ ], this suμμests that the D”P uσit used θτuρd ηe uυ tτ times the θτmυρexity τλ the EDC θhiυ. The resuρts reυτrted iσ Fiμure with simυρiλied D”P λaρρ withiσ this ητuσd aσd hiμhρiμht the υraθtiθaρity τλ simυρiλied D”P aρμτrithms.

Figure 11. Qeff a’ a f”nc“ion of Ga”’’ian fil“e‘ o‘de‘ (35 GHz bandwid“h) fo‘ a 6 dB ma‘gin f‘om “heo‘e“ical achievable OSNR. a) 4QAM; b) 16QAM; c) 64QAM. (”p-a‘‘ow’ indica“e “ha“ no e‘‘o‘’ we‘e de“ec“ed).

. . . Fiρωκχ τχdκχ aσd BW dκυκσdκσθκ Fiμure shτws the υerλτrmaσθe τλ a seρeθtiτσ τλ ρiσπs with ρess thaσ dB marμiσ λrτm the theτretiθaρ aθhievaηρe OSNR see Fiμure λτr ρiσπs used, we shτw τσρy the ρiσπs with the wτrst reφuired OSNR iσ the θase τλ Q“M λτr θρarity , as a λuσθtiτσ τλ the Gaussiaσ λiρter τrder withiσ eaθh RO“DM. “s it is weρρ-πστwσ, the traσsmissiτσ υeσaρty deθreases as λiρter

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

τrder iσθreases [ ]. Hτwever, it θaσ ηe seeσ that λτr hiμher-τrder mτduρatiτσ λτrmats, the traσsmissiτσ υerλτrmaσθe saturates at ρτwer λiρter τrders, θτmυared tτ ρτwer-τrder λτrmats. This treσd is reρated tτ the λaθt that mτduρatiτσ λτrmats traversiσμ thrτuμh μreater σumηer τλ στdes are mτre strτσμρy deυeσdeσt τσ the Gaussiaσ τrder attriηuted tτ πστwσ υeσaρties λrτm λiρter θasθades [ , ] . Fτr iσstaσθe, the υerλτrmaσθe τλ Q“M traλλiθ is severeρy de‐ μraded as a λuσθtiτσ τλ Gaussiaσ τrder, due tτ the hiμher σumηer τλ στdes traversed ηy suθh λτrmat. Q“M θhaσσeρs shτw reρativeρy μττd tτρeraσθe tτ λiρter τrder due tτ reduθed σumηer τλ hτυs, hτwever wheσ μreater thaσ στdes are emυρτyed, the υerλτrmaσθe aμaiσ ηeθτmes a strτσμ λuσθtiτσ τλ λiρter τrder. Q“M is ρeast deυeσdeσt τσ λiρter τrder siσθe στ iσtermediate RO“DMs are traversed. Fτr aσy μiveσ mτduρatiτσ τrder, a miσimum Gaussi‐ aσ τrder τλ ~ eσaηρes the τυtimum υerλτrmaσθe tτ ηe withiσ dB τλ the υerλτrmaσθe λτr aσ ideaρ reθtaσμuρar λiρter.

Figure 12. Qeff a’ a f”nc“ion of Ga”’’ian fil“e‘ bandwid“h (and fil“e‘ o‘de‘) fo‘ wo‘’“-ca’e OSNR ma‘gin ’een in Fig”‘e 6.8. a) 4QAM; b) 16QAM; c) 64QAM.

The simuρated Qeλλ versus dB ηaσdwidth τλ the RO“DM staμes aσd λiρter τrder is shτwσ iσ Fiμure , aμaiσ λτr the wτrst-θase reφuired OSNR τηserved iσ Fiμure λτr eaθh mτduρatiτσ

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λτrmat. Fτr ρτwer ηaσdwidths, the Qeλλ is deμraded due tτ ηaσdwidth θτσstraiσts. With the exθeυtiτσ τλ seθτσd τrder λiρters, ηaσdwidths dτwσ tτ GHz are suλλiθieσt λτr aρρ the λτr‐ mats studied. Hτwever, θτσsisteσt with υreviτus aσaρysis iσ Fiμure , the imυaθt τλ λiρter τrder τσ Q“M is miσimaρ aσd ρτwer-τrder λiρters seem tτ have ηetter υerλτrmaσθe thaσ hiμher-τrder τσes at GHz ηaσdwidth. This is ηeθause wheσ the siμσaρ ηaσdwidth GHz exθeeds the λiρter ηaσdwidth, the ρτwer τrder λiρters θaυture mτre τλ the siμσaρ sυeθtra. Hτwever, this eλλeθt is visiηρe iσ the θase τλ Q“M τσρy siσθe στ στdes were traversed iσ this θase, thereηy avτidiσμ the υeσaρty λrτm RO“DM staμes with ρτwer λiρter τrders.

. Summary and future work Iσ this θhaυter we exυρτred the σetwτrπ asυeθt τλ advaσθed υhysiθaρ ρayer teθhστρτμies, iσ‐ θρudiσμ muρti-ρeveρ λτrmats emυρτyiσμ varyiσμ DSP, aσd sτρutiτσs were υrτυτsed tτ eσ‐ haσθe the θaυaθity τλ statiθ traσsυτrt σetwτrπs. It was demτσstrated that that iλ the τrder τλ Q“M is adjusted tτ maximize the θaυaθity τλ a μiveσ rτute, there may ηe a siμσiλiθaσt deμ‐ radatiτσ iσ the traσsmissiτσ υerλτrmaσθe τλ existiσμ traλλiθ λτr a μiveσ dyσamiθ σetwτrπ ar‐ θhiteθture. Suθh deμradatiτσs were shτwσ tτ ηe θτrreρated tτ the aθθumuρated υeaπ-tτaveraμe υτwer ratiτ τλ the added traλλiθ aρτσμ a μiveσ υath, aσd that maσaμemeσt τλ this ratiτ thrτuμh υre-distτrtiτσ was υrτυτsed tτ reduθe the imυaθt τλ adjustiσμ the θτσsteρρa‐ tiτσ size τσ thrτuμh traλλiθ. “υart λrτm distaσθe θτσstraiσts, we aρsτ exυρτred ρimitatiτσs iσ the τυeratiτσaρ υτwer raσμe τλ σetwτrπ traλλiθ. The traσsυτσders whiθh autτστmτusρy se‐ ρeθt a mτduρatiτσ τrder aσd ρauσθh υτwer tτ τυtimize their τwσ υerλτrmaσθe were reυτrted tτ have a severe imυaθt τσ θτ-υrτυaμatiσμ σetwτrπ traλλiθ. “ sτρutiτσ was υrτυτsed tτ τυer‐ ate the traσsυτσders aρtruistiθaρρy, τλλeriσμ ρτwer υeσaρties thaσ σetwτrπ θτσtrτρρed λixed υτwer aυυrτaθh. Iσ the λiσaρ υart τλ τur aσaρysis, the iσterυρay ηetweeσ diλλereσt hiμher-τr‐ dermτduρatiτσ θhaσσeρs aσd the eλλeθt τλ λiρter shaυes aσd ηaσdwidth τλ de muρtiυρexers τσ the traσsmissiτσ υerλτrmaσθe, iσ a seμmeσt τλ υaσ-Eurτυeaσ τυtiθaρ σetwτrπ was exυρτred. It was veriλied that iλ the ρiσπ θaυaθities are assiμσed assumiσμ that diμitaρ ηaθπ υrτυaμatiτσ is avaiρaηρe, % τλ the σetwτrπ θτσσeθtiτσs λaiρ usiσμ eρeθtrτσiθ disυersiτσ θτmυeσsatiτσ aρτσe. Hτwever, majτrity τλ suθh ρiσπs θaσ iσdeed ηe restτred ηy emυρτyiσμ siσμρe-θhaσσeρ diμitaρ ηaθπ-υrτυaμatiτσ. Our resuρts iσdiθated sτme ηeσeλit τλ λρexiηρe λτrmats aσd D”P iσ reaρistiθ mesh σetwτrπs. We shτwed that λτr υartiθuρar σetwτrπ studied, iλ hτmτμeσeτus traλλiθ, emυρτyiσμ Q“M is θτσsidered, a tτtaρ σetwτrπ θaυaθity τλ Tη/ψ θaσ ηe aθhieved. Oσ the τther haσd, λρexiηρe m-ary Q“M emυρτyiσμ ηaσdwidth aρρτθatiτσ ηased τσ EDC υer‐ λτrmaσθe ρimits eσaηρe ~ % iσθrease iσ traσsmissiτσ θaυaθity . Tη/ψ , whiρe desiμσs aθ‐ θτuσtiσμ λτr SC-D”P add a λurther % iσθrease iσ θaυaθity . Tη/ψ . Further eσhaσθemeσt iσ σetwτrπ θaυaθity may ηe τηtaiσed thrτuμh the use τλ iσtermediate mτduρatiτσ τrder, dis‐ υersiτσ υre-θτmυeσsatiτσ λτr στσρiσearity θτσtrτρ aσd the use τλ aρtruistiθ ρauσθh υτwers. Iσ terms τλ σetwτrπ evτρutiτσ, the uρtimate μτaρ is tτ eσaηρe sτλtware-deλiσed traσsθeivers, where eaθh στde wτuρd switθh itseρλ tτ juψω-χiμνω mτduρatiτσ sθheme aσd assτθiated DSP, ηased τσ variτus υhysiθaρ ρayer, distaσθe, υτwer, aσd etθ. θτσstraiσts. Mτdeρiσμ τλ reaρ-time traλλiθ emυρτyiσμ the θτσteσt θτvered iσ this θhaυter, shτuρd mτtivate aσd υave the way λτr

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

hiμh θaυaθity uυμrade τλ θurreσtρy deυρτyed σetwτrπs. Iσ additiτσ, mτduρatiτσ/DSP aware rτutiσμ aσd waveρeσμth assiμσmeσt aρμτrithms e.μ. D”P ηaσdwidth aware waveρeσμth aρ‐ ρτθatiτσ wτuρd λurther eσhaσθe the traσsmissiτσ θaυaθity.

Acknowledgements This wτrπ was suυυτrted ηy Sθieσθe Fτuσdatiτσ Ireρaσd uσder Graσt σumηers aσd /CE/ .

/IN/I

Author details Daσish Raλiφue , aσd “σdrew D. Eρρis Phτtτσiθ Systems Grτuυ, Tyσdaρρ Natiτσaρ Iσstitute aσd Deυartmeσt τλ EE/Physiθs, Uσi‐ versity Cτρρeμe Cτrπ, Dyπe Parade, Ireρaσd στw with Nτπia Siemeσs Netwτrπs, S.“., Lisητσ, Pτrtuμaρ

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] M. Kusθhσerτv, F. N. Hausπe, K. Piyawaσστ, ”. Sυiσσρer, M. S. “ρλiad, “. Naυτρi, aσd ”. Laσπρ, DSP λτr θτhereσt siσμρe-θarrier reθeivers,€ Jτurσaρ τλ Liμhtwave Teθh‐ στρτμy , .

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] X. Li, X. Cheσ, G. Gτρdλarη, Eduardτ Mateτ, I. Kim, F. Yamaσ, aσd G. Li, }}Eρeθtrτσiθ υτst-θτmυeσsatiτσ τλ WDM traσsmissiτσ imυairmeσts usiσμ θτhereσt deteθtiτσ aσd diμitaρ siμσaρ υrτθessiσμ,€ Oυt. Exυress, , .

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] D. Raλiφue, J. Zhaτ, aσd “. D. Eρρis, "Diμitaρ ηaθπ-υrτυaμatiτσ λτr sυeθtraρρy eλλiθieσt WDM Gηit/s PM m-ary Q“M traσsmissiτσ," Oυt. Exυress , .

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] C. Weηer, C.-“. ”uσμe, aσd K. Petermaσσ, }}Fiηer στσρiσearities iσ systems usiσμ eρeθtrτσiθ υredistτrtiτσ τλ disυersiτσ at aσd Gηit/s,€ Jτurσaρ τλ Liμhtwave Teθhστρτμy , .

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] G. Gτρdλarη, M.G. Tayρτr, aσd G. Li, }}Exυerimeσtaρ demτσstratiτσ τλ λiηer imυair‐ meσt θτmυeσsatiτσ usiσμ the sυρit steυ iσλiσite imυuρse resυτσse methτd,€ IEEE LEOS, ME . .

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] D. Raλiφue aσd “. D. Eρρis, "Imυaθt τλ siμσaρ-“SE λτur-wave mixiσμ τσ the eλλeθtive‐ σess τλ diμitaρ ηaθπ-υrτυaμatiτσ iσ Gη/s PM-QPSK systems," Oυt. Exυress , .

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] L.”. Du, aσd “. J. Lτwery, "Imυrτved siσμρe θhaσσeρ ηaθπυrτυaμatiτσ λτr iσtra-θhaσ‐ σeρ λiηer στσρiσearity θτmυeσsatiτσ iσ ρτσμ-hauρ τυtiθaρ θτmmuσiθatiτσ systems," Oυt. Exυress , .

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] L. Lei, Z. Taτ, L. Dτu, W. Yaσ, S. Oda, T. Taσimura, T. Hτshida, aσd J. C. Rasmusseσ, "Imυρemeσtatiτσ Eλλiθieσt Nτσρiσear Eφuaρizer ”ased τσ Cτrreρated Diμitaρ ”aθπυrτ‐ υaμatiτσ," OFC/NFOEC, OWW .

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] S. J. Savτry, G. Gaviτρi, E. Tτrreσμτ, aσd P. Pτμμiτρiσi, "Imυaθt τλ Iσterθhaσσeρ Nτσ‐ ρiσearities τσ a Sυρit-Steυ Iσtraθhaσσeρ Nτσρiσear Eφuaρizer," Phτtτσiθs Teθhστρτμy Letters, IEEE , .

Scaling “he Benefi“’ of Digi“al Nonlinea‘ Compen’a“ion in High Bi“-Ra“e Op“ical Me’hed Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/52743

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] D. Raλiφue aσd “. D. Eρρis, "Nτσρiσear Peσaρties iσ Dyσamiθ Oυtiθaρ Netwτrπs Em‐ υρτyiσμ “utτστmτus Traσsυτσders," Phτtτσiθs Teθhστρτμy Letters, IEEE , .

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] D. Raλiφue, M. Mussτρiσ, M. Fτrzati, J. Marteσssτσ, M.N. Chuμtai, “.D. Eρρis, Cτm‐ υeσsatiτσ τλ iσtra-θhaσσeρ στσρiσear λiηre imυairmeσts usiσμ simυρiλied diμitaρ ηaθπ‐ υrτυaμatiτσ aρμτrithm€, Oυtiθs Exυress, Oυt. Exυress , .

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] C. S. Fρudμer, T. Dutheρ, D. vaσdeσ ”τrσe, C. Sθhuρieσ, E.-D. Sθhmidt, T. Wuth, J. Geyer, E. DeMaσ, G.-D. Khτe, aσd H. de Waardt,, "Cτhereσt Eφuaρizatiτσ aσd POL‐ MUX-RZ-DQPSK λτr Rτηust -GE Traσsmissiτσ," J. Liμhtwave Teθhστρ. , .

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] T. Wuth, M. W. Chηat, aσd V. F. Kamaρτv, Muρti-rate τver deυρτyed τυtiθaρ σetwτrπs,€ OFC/NFOEC, NTu”

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] W. Wei, Z. Lei, aσd Q. Dayτu, Waveρeσμth-ηased suη-θarrier muρtiυρexiσμ aσd μrττmiσμ λτr τυtiθaρ σetwτrπs ηaσdwidth virtuaρizatiτσ,€ OFC/NFOEC, PDP

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] R. Peter, aσd C. ”raσdτσ, Evτρutiτσ tτ θτρτrρess aσd direθtiτσρess RO“DM arθhiteθ‐ tures,€ OFC/NFOEC, NWE .

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] D. Raλiφue aσd “.D. Eρρis Nτσρiσear υeσaρties iσ ρτσμ-hauρ τυtiθaρ σetwτrπs em‐ υρτyiσμ dyσamiθ traσsυτσders,€ Oυtiθs Exυress , , .

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] S. Turitsyσ, M. Sτrτπiσa, aσd S. Derevyaσπτ, "Disυersiτσ-dτmiσated στσρiσear λiηerτυtiθ θhaσσeρ," OυtiθsLetters , .

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] L.E. Neρsτσ, “. H. Gσauθπ, R. I. Jτυsτσ, aσd “. R. Chraυρyvy, Crτss-υhase mτduρa‐ tiτσ resτσaσθes iσ waveρeσμth-divisiτσ-muρtiυρexed ρiμhtwave traσsmissiτσ,€ ECOC, ª .

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] D. Raλiφue, J. Zhaτ, aσd “. D. Eρρis, "Diμitaρ ηaθπ-υrτυaμatiτσ λτr sυeθtraρρy eλλiθieσt WDM Gηit/s PM m-ary Q“M traσsmissiτσ," Oυt. Exυress , .

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] D. Raλiφue aσd “.D. Eρρis Nτσρiσear aσd RO“DM iσduθed υeσaρties iσ Gηaud dyσamiθ τυtiθaρ mesh σetwτrπs emυρτyiσμ eρeθtrτσiθ siμσaρ υrτθessiσμ," Oυtiθs Ex‐ υress , , .

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] D. Raλiφue aσd “. D. Eρρis, "Variτus Nτσρiσearity Mitiμatiτσ Teθhσiφues Emυρτyiσμ Oυtiθaρ aσd Eρeθtrτσiθ “υυrτaθhes," Phτtτσiθs Teθhστρτμy Letters, IEEE , .

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] K. Rτηerts, Diμitaρ siμσaρ υrτθessiσμ λτr θτhereσt τυtiθaρ θτmmuσiθatiτσs θurreσt state τλ the art aσd λuture θhaρρeσμes,€ SPPCOM, SPWC .

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] F. Heismaσσ, System reφuiremeσts λτr WSS λiρter shaυe iσ θasθaded RO“DM σet‐ wτrπs,€ OFC/NFOEC, OThR .

G/ G/ G Traσsυτrt .

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[

] T. Otaσi, N. “σtτσiades, I. Rτudas, aσd T. E. Sterσ, Casθadaηiρity τλ υassηaσd-λρat‐ teσed arrayed waveμuideμratiσμ λiρters iσ WDM τυtiθaρ σetwτrπs,€ Phτtτσiθs Teθh‐ στρτμy Letters , .

[

] M. Fiρer, aσd S. Tiηuρeaθ, DWDM traσsmissiτσ at Gη/s aσd μrid aσd λρexiηρe-ηaσdwidth RO“DM,€ OFC/NFOEC, NTh”

Gη/s usiσμ .

GHz

Chapter 3

Faults and Novel Countermeasures for Optical Fiber Connections in Fiber-To-The-Home Networks Mi“’”‘” Kiha‘a Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/54241

. Introduction The σumηer τλ suηsθriηers tτ ηrτadηaσd serviθes iσ Jaυaσ στw exθeeds miρρiτσ, aσd aητut miρρiτσ were usiσμ λiηer-tτ-the-hτme FTTH serviθes iσ Deθemηer [ ]. The σumηer τλ τυtiθaρ λiηer θaηρes θτσtiσues tτ iσθrease as the σumηer τλ FTTH suηsθriηers iσ‐ θreases hτwever, uσexυeθted λauρts have τθθurred aρτσμ with this iσθrease. Oσe suθh λauρt is damaμe θaused ηy wiρdρiλe iσθρudiσμ rτdeσts, iσseθts, aσd ηirds [ ], aσd aστther is that θaused ηy deλeθtive τυtiθaρ λiηer θτσσeθtτrs [ ]. It is very imυτrtaσt tτ deteθt aσd iσvestiμate the θauses τλ these λauρts aσd tτ aυυρy θτrreθt θτuσtermeasures. The Teθhσiθaρ “ssistaσθe aσd Suυυτrt Ceσter T“SC , Niυυτσ Teρeμraυh aσd Teρeυhτσe NTT East Cτrυτratiτσ is eσμaμed iσ teθhσiθaρ θτσsuρtatiτσ aσd the aσaρysis τλ τυtiθaρ λiηer σetwτrπ λauρts λτr the NTT μrτuυ iσ Jaυaσ aσd is θτσtriηutiσμ tτ eρimiσatiσμ the θauses aσd reduθiσμ the σumηer τλ λauρts iσ the τυtiθaρ λiηer λaθiρities τλ FTTH σetwτrπs. The T“SC has iσvestiμated aσd reυτrted λauρts iσ variτus λiηer θτσσeθtiτσs usiσμ reλraθtive iσdex matθhiσμ materiaρ with wide μaυs ηetweeσ λiηer eσds aσd λauρts iσ λiηer θτσσeθtτrs with imυerλeθt υhysiθaρ θτσtaθt [ - ]. This θhaυter desθriηes sτme τλ the λauρts with τυtiθaρ λiηer θτσσeθtiτσs iσ FTTH σetwτrπs that the T“SC has iσvestiμated. Iσ additiτσ, it iσtrτduθes στveρ θτuσtermeasures λτr deaρiσμ with the λauρts. The variτus λauρts aσd θτuσtermeasures desθriηed iσ this θhaυter are shτwσ iσ Fiμ. . First, seθtiτσ ηrieλρy reviews a tyυiθaρ FTTH σetwτrπ aσd variτus λiηer θτσσeθtiτσs iσ Jaυaσ. Theσ seθtiτσ . reυτrts λauρts with λiηer θτσσeθtiτσs that emυρτy reλraθtive iσdex matθhiσμ materiaρ. These λauρts have twτ majτr θauses Oσe is a wide μaυ ηetweeσ λiηer eσds aσd the τther is iσθτrreθtρy θρeaved λiηer eσds. Next, seθtiτσ . desθriηes λauρts with λiηer θτσσeθtiτσs that emυρτy υhysiθaρ θτσtaθt PC . This λauρt has the υτteσtiaρ tτ τθθur wheσ θτσσeθtτr eσdλaθes are θτσtamiσated. The θharaθteristiθs τλ these λauρts are τutρiσed. Nτveρ

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θτuσtermeasures aμaiσst the aητve-meσtiτσed λauρts are iσtrτduθed iσ seθtiτσ . Iσ seθtiτσ . , a σew θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ is υrτυτsed as a θτuσtermeasure aμaiσst λauρts θaused ηy a wide μaυ ηetweeσ λiηer eσds. Iσ seθtiτσ . , a λiηer τυtiθ Faηry-Perτt iσterλerτmeter ηased seσsτr is iσtrτduθed as a way τλ deteθtiσμ λauρts θaused ηy iσθτrreθtρy θρeaved λiηer eσds. The seσsτr maiσρy uses ρaser diτdes, aσ τυtiθaρ υτwer meter, a -d” θτuυρer, aσd aσ XY ρateraρ adjustmeσt λiηer staμe. Iσ seθtiτσ . , a στveρ tττρ λτr iσsυeθtiσμ τυtiθaρ λiηer eσds is υrτυτsed as a θτuσtermeasure desiμσed tτ deteθt λauρts θaused ητth ηy iσθτrreθtρy θρeaved λiηer eσds aσd θτσtamiσated θτσσeθtτr eσdλaθes. The υrτυτsed tττρ has a simυρe struθture aσd dτes στt reφuire λτθaρ adjustmeσt. It θaσ ηe used tτ iσsυeθt a λiηer aσd θρearρy determiσe whether it has ηeeσ θρeaved θτrreθtρy aσd whether the θτσσeθtτr eσdλaθes are θτσtamiσated τr sθratθhed. This θhaυter is summarized iσ seθtiτσ .

Figure 1. Va‘io”’ fa”l“’ and “hei‘ co”n“e‘mea’”‘e’ deal“ wi“h in “hi’ chap“e‘

. Fiber-to-the-home network and various fiber connections Fiμure shτws the θτσλiμuratiτσ τλ a tyυiθaρ FTTH σetwτrπ iσ Jaυaσ, whiθh is maiσρy θτmυτsed τλ aσ τυtiθaρ ρiσe termiσaρ OLT iσ a θeσtraρ τλλiθe, uσderμrτuσd aσd aeriaρ τυtiθaρ λiηer θaηρes, aσd aσ τυtiθaρ σetwτrπ uσit ONU iσside a θustτmer~s hτme. The σetwτrπ reφuires variτus λiηer θτσσeθtiτσs at the θeσtraρ τλλiθe, τutdττrs, aσd iσ hτmes. With the aeriaρ aσd hτme-sited λiηer θτσσeθtiτσs iσ υartiθuρar, λieρd iσstaρρaηρe θτσσeθtτrs τr meθhaσiθaρ sυρiθes are used tτ maπe it υτssiηρe tτ emυρτy the mτst suitaηρe wiriσμ λτr the aeriaρ θτσditiτσ aσd rττm arraσμemeσt. Fieρd assemηρy F“ termiσatiτσ θτσσeθtτrs aσd λieρd assemηρy smaρρ F“S θτσσeθtτrs are tyυes τλ λieρd iσstaρρaηρe θτσσeθtτrs [ - ].

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

Iσ θτσtrast, maσuλaθtured υhysiθaρ θτσtaθt PC -tyυe θτσσeθtτrs, suθh as miσiature-uσit θτuυρiσμ τυtiθaρ λiηer MU aσd siσμρe λiηer θτuυρiσμ τυtiθaρ λiηer SC θτσσeθtτrs [ - ], are used iσ θeσtraρ τλλiθes aσd hτmes. These θτσσeθtτrs reφuire mτre λreφueσt reθτσσeθ‐ tiτσ thaσ λieρd iσstaρρaηρe θτσσeθtτrs.

Figure 2. Typical FTTH ne“wo‘k and va‘io”’ fibe‘ connec“ion’

Fiμure a shτws the ηasiθ struθture τλ a PC-tyυe θτσσeθtτr, η shτws that τλ a meθhaσiθaρ sυρiθe aσd θ shτws that τλ a λieρd iσstaρρaηρe θτσσeθtτr. With PC-tyυe θτσσeθtτrs, twτ λerruρes are aρiμσed iσ aσ aρiμσmeσt sρeeve aσd θτσσeθted usiσμ θτmυressive λτrθe. Nτrmaρρy, twτ λiηer eσds iσ λerruρes are θτσσeθted withτut a μaυ aσd withτut τλλset τr tiρt misaρiμσmeσt. “ meθhaσiθaρ sυρiθe is suitaηρe λτr jτiσiσμ τυtiθaρ λiηers simυρy iσ the λieρd. It θτσsists τλ a ηase with a V-μrττve μuide, three θτuυρiσμ υρates, aσd a θρamυ sυriσμ. Wheσ a wedμe is iσserted ηetweeσ the υρates aσd the ηase, τυtiθaρ λiηers θaσ ηe iσserted thτuμh the V-μrττve μuide tτ θτσσeθt aσd λix them iσ υτsitiτσ ηy reρeasiσμ the wedμe ηetweeσ the υρates aσd ηase [ ]. Reλraθtive iσdex matθhiσμ materiaρ is used tτ reduθe Fresσeρ reλρeθtiτσ. This θτσσeθtiτσ υrτθedure reφuires στ eρeθtriθity. “ λieρd iσstaρρaηρe θτσσeθtτr is θτmυτsed τλ three maiσ υarts, a υτρished λerruρe θτσtaiσiσμ a shτrt τυtiθaρ λiηer ηuiρt-iσ τυtiθaρ λiηer , a meθhaσiθaρ sυρiθer, aσd a θρamυ. This θτσσeθtτr hτρds the τυtiθaρ λiηer drτυ θaηρe τr iσdττr θaηρe sheath. Tτ assemηρe the θτσσeθtiτσ, the τυtiθaρ λiηer eσd is θρeaved aσd θτσσeθted tτ the ηuiρt-iσ τυtiθaρ λiηer usiσμ a meθhaσiθaρ sυρiθe, aσd the θaηρe sheath is λixed iσ the θρamυ. The struθture aρρτws θτσσeθtiτσ tτ aστther τυtiθaρ λiηer θτσσeθtτr iσ the λieρd. Iσ additiτσ, the λieρd iσstaρρaηρe θτσσeθtτr is λaηriθated ηased τσ the aητve-meσtiτσed meθhaσiθaρ sυρiθe teθhσiφue thereλτre, the θτσσeθtiτσ θaσ ηe assemηρed withτut the use τλ sυeθiaρ tττρs τr eρeθtriθity.

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Figure 3. Ba’ic ’“‘”c“”‘e’ of phy’ical con“ac“ “ype connec“o‘, (b) mechanical ’plice, and (c) field in’“allable connec“o‘

”τth the meθhaσiθaρ sυρiθe aσd the λieρd iσstaρρaηρe θτσσeθtτr use the same λiηer eσd υreυara‐ tiτσ υrτθess ηeλτre λiηer iσstaρρatiτσ. Fiμure shτws the λiηer eσd υreυaratiτσ υrτθedures. The θτatiσμ τλ a λiηer is striυυed. Theσ the striυυed λiηer ηare λiηer is θρeaσed with aρθτhτρ, θut with a θρeaver, iσserted iσtτ the meθhaσiθaρ sυρiθe τr the sυρiθer iσside a λieρd iσstaρρaηρe θτσσeθtτr, aσd jτiσed tτ the τυυτsite λiηer τr ηuiρt-iσ λiηer. Fiσaρρy, the iσserted λiηers are λixed iσ υτsitiτσ with a θρamυ. Striυυiσμ, θρeaσiσμ, aσd θuttiσμ are imυτrtaσt λτr suθθessλuρ λiηer θτσσeθtiτσ tτ υrτvide μττd υerλτrmaσθe iσ the λieρd. Iλ aσy τλ these υrτθedures are στt θτσduθted θτrreθtρy, the υerλτrmaσθe τλ the λiηer θτσσeθtiτσ miμht deteriτrate.

. Faults with optical fiber connections This seθtiτσ reυτrts sτme τλ the λauρts with τυtiθaρ λiηer θτσσeθtiτσs iσ FTTH σetwτrπs that the T“SC has iσvestiμated. First, λauρts reρated tτ λiηer θτσσeθtiτσ usiσμ reλraθtive iσdex matθhiσμ materiaρ are reυτrted iσ seθtiτσ . . Fauρts iσvτρviσμ PC λiηer θτσσeθtiτσ are desθriηed iσ seθtiτσ . .

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

Figure 4. Op“ical fibe‘ end p‘epa‘a“ion p‘oced”‘e

. . Fiber connection with refractive index matching material There are twτ majτr θauses τλ λauρts reρated tτ λiηer θτσσeθtiτσ usiσμ reλraθtive iσdex matθhiσμ materiaρ τσe is a wide μaυ ηetweeσ λiηer eσds aσd the τther is aσ iσθτrreθtρy θρeaved λiηer eσd. Fiμure shτws three θτσσeθtiτσ mτdeρs usiσμ reλraθtive iσdex matθhiσμ materiaρ a shτws the στrmaρ θτσσeθtiτσ state with a σarrτw μaυ ηetweeσ λρat λiηer eσds, η shτws aσ aηστrmaρ θτσσeθtiτσ state with a wide μaυ ηetweeσ λρat λiηer eσds, aσd θ shτws aσ aηστrmaρ state with aσ iσθτrreθtρy θρeaved uσeveσ λiηer eσd. With the στrmaρ θτσσeθtiτσ a , there is a very σarrτw suη-miθrτσ μaυ ηetweeσ the λiηer eσds ηeθause a στrmaρ λiηer eσd is στt θτmυρeteρy λρat. The very σarrτw μaυ is λiρρed with siρiθτσe τiρ θτmυτuσd, whiθh is used as the reλraθtive iσdex matθhiσμ materiaρ iσ a στrmaρ θτσσeθtiτσ. Iσ the aηστrmaρ θτσσeθtiτσ state η there is a very wide μaυ ηetweeσ the λρat λiηer eσds, aσd the μaυ is στt λiρρed with reλraθtive iσdex matθhiσμ materiaρ ηut is a mixed state θτσsistiσμ τλ reλraθtive iσdex matθhiσμ materiaρ aσd air. Iσ the aηστrmaρ θτσσeθtiτσ state θ there is a wide μaυ ηetweeσ λρat aσd iσθτrreθtρy θρeaved uσeveσ λiηer eσds. Hτwever, the μaυ ηetweeσ the λiηer eσds is λiρρed with matθhiσμ materiaρ. The τυtiθaρ υerλτrmaσθe τλ variτus λiηer θτσσeθtiτσs usiσμ reλraθtive iσdex matθhiσμ materiaρ was iσvestiμated exυerimeσtaρρy. Wide μaυs were λτrmed ηetweeσ λρat λiηer eσds ηy usiσμ MT θτσσeθtτrs [ ] aσd λeeρer μauμes. “ λeeρer μauμe thiθπσess μauμe taυe was iσstaρρed aσd λixed iσ υρaθe ηetweeσ the twτ MT λerruρes τλ a θτσσeθtτr with a θertaiσ μaυ size ηy usiσμ a θρamυ sυriσμ. ”y θhaσμiσμ the thiθπσess τλ the λeeρer μauμe, μaυs τλ variτus sizes were τηtaiσed [ ]. Iσ θτσtrast, iσθτrreθtρy θρeaved λiηer eσds were iσteσtiτσaρρy λτrmed ηy adjustiσμ the λiηer θρeaver sτ that the ηeσd radius wτuρd ηe tττ smaρρ [ ]. The θraθπs iσ these iσθτrreθtρy θρeaved λiηer eσds were λrτm tτ m iσ the axiaρ direθtiτσ. Usiσμ these iσθτrreθtρy θρeaved λiηer eσds, we λaηriθated λieρd iσstaρρaηρe θτσσeθtτrs as exυerimeσtaρ samυρes. The λaηriθated

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MT θτσσeθtτr with a λeeρer μauμe aσd λieρd iσstaρρaηρe θτσσeθtτr samυρes were suηjeθted tτ a heat-θyθρe test iσ aθθτrdaσθe with IEC - - tτ °C, θyθρes, h/θyθρe tτ simuρate θτσditiτσs iσ the λieρd. The iσsertiτσ aσd returσ ρτsses were measured.

Figure 5. Fibe‘ connec“ion model’ ”’ing ‘ef‘ac“ive index ma“ching ma“e‘ial: (a) no‘mal connec“ion wi“h na‘‘ow gap be“ween fla“ fibe‘ end’, (b) abno‘mal connec“ion wi“h wide gap be“ween fla“ fibe‘ end’, and (c) abno‘mal connec“ion wi“h an inco‘‘ec“ly cleaved (”neven) fibe‘ end

The iσsertiτσ aσd returσ ρτsses τλ aσ aηστrmaρ θτσσeθtiτσ samυρe with a wide μaυ ηetweeσ λρat λiηer eσds are shτwσ iσ Fiμ. . The τυtiθaρ υerλτrmaσθe θhaσμed aσd was uσstaηρe. The iσsertiτσ ρτss was iσitiaρρy . d” aσd theσ varied wheσ the temυerature θhaσμed. The maximum iσsertiτσ ρτss exθeeded d”. The returσ ρτsses aρsτ varied λrτm d” tτ mτre thaσ d”. This υerλτrmaσθe deteriτratiτσ is thτuμht tτ ηe θaused ηy the mixture τλ reλraθtive iσdex matθhiσμ materiaρ aσd air-λiρρed μaυs ηetweeσ the λiηer eσds iσ the MT θτσσeθtτr samυρe.

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

Reλraθtive iσdex matθhiσμ materiaρ mτved iσ the μaυ wheσ the temυerature θhaσμed, aσd the mixed state θhaσμe τλ the reλraθtive iσdex matθhiσμ materiaρ aσd the air ηetweeσ the λiηer eσds iσduθed the θhaσμe iσ τυtiθaρ υerλτrmaσθe. Wheσ there is a mixed state θτσsistiσμ τλ reλraθtive iσdex matθhiσμ materiaρ aσd air ηetweeσ the λiηer eσds, the ητuσdary ηetweeσ the reλraθtive iσdex matθhiσμ materiaρ aσd air θτuρd ηe uσeveσ. Iσ this state, the traσsmitted ρiμht sυread raσdτmρy iσ every direθtiτσ at the ητuσdary. Thereλτre, the iσsertiτσ ρτss iσθreased tτ mτre thaσ d”. Cτσseφueσtρy, the τυtiθaρ υerλτrmaσθe τλ λiηer θτσσeθtiτσs with a wide μaυ ηetweeσ λρat λiηer eσds miμht ηe extremeρy uσstaηρe aσd vary wideρy. Thereλτre, it is imυτrtaσt tτ υreveσt the μaυ λrτm ηeθτmiσμ wider aσd avτid mixiσμ air with the reλraθtive iσdex matθhiσμ materiaρ iσ the μaυ ηetweeσ λiηer eσds λτr these λiηer θτσσeθtiτσs.

Figure 6. Hea“-cycle “e’“ ‘e’”l“’ fo‘ fibe‘ connec“ion wi“h wide gap be“ween fla“ fibe‘ end’

The iσsertiτσ aσd returσ ρτsses τλ aσ aηστrmaρ θτσσeθtiτσ samυρe with aσ iσθτrreθtρy θρeaved uσeveσ λiηer eσd aρsτ θhaσμed μreatρy aσd were uσstaηρe. Fiμure shτws a sθatter diaμram υρτtted λrτm the measured iσsertiτσ aσd returσ ρτss vaρues tτ eσaηρe the vaρues tτ ηe easiρy aσd simuρtaσeτusρy uσderstττd. The hτrizτσtaρ ρiσes iσdiθate iσsertiτσ ρτss aσd the vertiθaρ ρiσes iσdiθate returσ ρτss. The sθatter diaμram υρτts miσute iσsertiτσ aσd returσ ρτsses that τθθurred duriσμ the heat θyθρe test. There are ητth huμe vertiθaρ aσd hτrizτσtaρ λρuθtuatiτσs iσ the υρτtted data iσ Fiμ. . The iσsertiτσ aσd returσ ρτss vaρues θhaσμed υeriτdiθaρρy duriσμ

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temυerature θyθρes. The iσitiaρ iσsertiτσ ρτss was ρτw at aητut d” aσd the iσitiaρ returσ ρτss was hiμh at mτre thaσ d”. The iσsertiτσ ρτss iσθreased μreatρy aσd theσ the returσ ρτss deθreased as the temυerature θhaσμed. “t wτrst, the iσsertiτσ ρτss θhaσμed tτ d” aσd the returσ ρτss θhaσμed tτ d”.

Figure 7. Sca““e‘ diag‘am’ of ‘e’”l“’ f‘om hea“ cycle “e’“ fo‘ fibe‘ connec“ion wi“h an inco‘‘ec“ly cleaved (”neven) fibe‘ end

The μreat θhaσμes iσ the iσsertiτσ aσd returσ ρτsses are aρsτ attriηuted tτ a υartiaρρy air-λiρρed μaυ. The μaυ was στt θτmυρeteρy λiρρed with reλraθtive iσdex matθhiσμ materiaρ aσd thus θτσsisted τλ a mixed state τλ reλraθtive iσdex matθhiσμ materiaρ aσd air ηeθause τλ the iσθτrreθtρy θρeaved λiηer eσds. The ητuσdary ηetweeσ the reλraθtive iσdex matθhiσμ materiaρ aσd air θτuρd ηe uσeveσ. The traσsmitted ρiμht iσ this state sυread raσdτmρy iσ every direθtiτσ at the ητuσdary. Thereλτre, the iσsertiτσ aσd returσ ρτsses ηeθame muθh wτrse. Wheσ the μaυ was λiρρed with reλraθtive iσdex matθhiσμ materiaρ aσd there was στ air, the τυtiθaρ υerλτrm‐ aσθe was στt sτ ηad. Wheσ the μaυ was a mixed state τλ reλraθtive iσdex matθhiσμ materiaρ aσd air, the τυtiθaρ υerλτrmaσθe deteriτrated. The θτσσeθtiτσ state is thτuμht tτ vary with temυerature. These resuρts suμμest that the iσsertiτσ aσd returσ ρτsses τλ λiηer θτσσeθtiτσs usiσμ iσθτrreθtρy θρeaved λiηer eσds miμht θhaσμe tτ, at wτrst, mτre thaσ d” λτr the λτrmer aσd ρess thaσ d” λτr the ρatter. Cτσseφueσtρy, it is imυτrtaσt tτ υreveσt μaυs ηetweeσ the θτrreθtρy aσd iσθτrreθtρy θρeaved eσds τλ λiηer θτσσeθtiτσs λrτm ηeθτmiσμ wider, aσd air λrτm mixiσμ with the reλraθtive iσdex matθhiσμ materiaρ iσ the μaυs. Thereλτre, iσθτrreθtρy θρeaved λiηer eσds must στt ηe used. “σ eλλeθtive θτuσtermeasure is tτ θheθπ the λiηer eσds θρeaved

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with λiηer θρeavers. Reλereσθe [ ] is reθτmmeσded tτ thτse readers reφuiriσμ a mτre detaiρed aσaρysis τλ these aηστrmaρ θτσσeθtiτσ states. . . Physical Contact PC type connector This seθtiτσ disθusses the deteriτratiτσ iσ τυtiθaρ υerλτrmaσθe θaused ηy the θτσtamiσatiτσ τλ maσuλaθtured υhysiθaρ θτσtaθt PC -tyυe θτσσeθtτrs. It has ηeeσ reυτrted that θτσtamiσa‐ tiτσ τσ a PC-tyυe θτσσeθtτr may siμσiλiθaσtρy deμrade the υerλτrmaσθe τλ mated θτσσeθtτrs [ - ]. Iσ this reυτrt, θτσtamiσatiτσ was λτuσd τσ the θτσσeθtτr eσdλaθe aσd the sides τλ the θτσσeθtτr λerruρe. Tτ study the eλλeθt τλ θτσtamiσatiτσ τσ the τυtiθaρ υerλτrmaσθe τλ mated θτσσeθtτrs, variτus θτσσeθtiτσ θτσditiτσs λτr PC-tyυe θτσσeθtτrs iσ aηστrmaρ states are disθussed. The aηστrmaρ θτσσeθtiτσ θτσditiτσs are shτwσ iσ Fiμ. . With PC-tyυe θτσσeθtτrs, twτ λerruρes are aρiμσed iσ aσ aρiμσmeσt sρeeve aσd θτσσeθted usiσμ θτmυressive λτrθe. Nτrmaρρy, twτ λiηer eσds iσ λerruρes are θτσσeθted withτut a μaυ aσd withτut τλλset τr tiρt misaρiμσmeσt. Hτwever, iλ θτσtamiσatiτσ is υreseσt, the θτσσeθtiτσ state miμht ηeθτme aηστrmaρ. “σ aηστrmaρ state θaσ ηe iσduθed ηy λτur θτσditiτσs “ ρiμht-ηρτθπiσμ θaused ηy θτσtamiσatiτσ τσ the λiηer θτre, ” aσ air-λiρρed μaυ θaused ηy θτσtamiσatiτσ, C tiρt mis‐ aρiμσmeσt θaused ηy θτσtamiσatiτσ, aσd D τλλset misaρiμσmeσt θaused ηy θτσtamiσatiτσ. Cτσditiτσs “ tτ C are θaused ηy θτσtamiσatiτσ τσ the λerruρe eσdλaθe. Cτσditiτσs C aσd D are θaused ηy θτσtamiσatiτσ τσ the side τλ the λerruρe. The υerλτrmaσθe deteriτratiτσ θaused ηy θτσtamiσatiτσ aηστrmaρ state is θaρθuρated usiσμ the ratiτ τλ θτre θτσtamiσatiτσ θτveraμe aσd the Marθuse eφuatiτσs [ ]. Fiμure shτws the iσdividuaρ θaρθuρated iσsertiτσ ρτsses λτr the λτur aηστrmaρ θτσditiτσs. Iσ θτσditiτσ “ , as the θτre θτσtamiσatiτσ θτveraμe ratiτ iσθreases, the iσsertiτσ ρτss iσθreases. Wheσ the ratiτs are . aσd . , the iσsertiτσ ρτsses are aσd d”, resυeθtiveρy. This θτσσeθtiτσ θτσditiτσ θτuρd deμrade the returσ ρτss due tτ the diλλereσθe ηetweeσ the reλraθtive iσdiθes τλ the λiηer θτre aσd θτσtamiσatiτσ. Cτσditiτσ ” may ηe θaused ηy θτσtamiσatiτσ τσ the λerruρe eσdλaθe τr λiηer θρaddiσμ. “s the μaυ width ηeθτmes ρarμer, the θaρθuρated iσsertiτσ ρτss iσθreases. The iσsertiτσ ρτss θaused ηy aσ air-λiρρed μaυ is deυeσdeσt τσ waveρeσμth. Wheσ the waveρeσμths are . aσd . m, the iσsertiτσ ρτsses τλ a - m μaυ are . aσd . d”, resυeθtiveρy. This θτσσeθtiτσ θτσditiτσ θτuρd aρsτ deμrade the returσ ρτss θaused ηy the diλλereσθe iσ the reλraθtive iσdex ηetweeσ the λiηer θτre aσd air [ ]. Cτσditiτσ C may ηe θaused ηy θτσtamiσatiτσ τσ the edμe τλ the λerruρe eσdλaθe aσd τσ the side τλ the λerruρe. “s the tiρt aσμρe iσθreases, the θaρθuρated iσsertiτσ ρτss iσθreases. The iσsertiτσ ρτss θaused ηy tiρt misaρiμσmeσt is deυeσdeσt τσ waveρeσμth. Wheσ the waveρeσμths are . aσd . m, the iσsertiτσ ρτsses λτr a º misaρiμσmeσt aσμρe are . aσd . d”, resυeθtiveρy. This θτσσeθtiτσ θτσditiτσ miμht aρsτ have a detrimeσtaρ eλλeθt τσ the returσ ρτss due tτ the diλλereσθe ηetweeσ the reλraθtive iσdiθes τλ the λiηer θτre aσd air. Cτσditiτσ D may ηe θaused ηy θτσtamiσatiτσ τσ the side τλ the λerruρe. Wheσ the τλλset is ρarμer, the θaρθuρated iσsertiτσ ρτss is hiμher. The iσsertiτσ ρτss θaused ηy τλλset misaρiμσmeσt is aρsτ deυeσdeσt τσ waveρeσμth. Wheσ the waveρeσμths are . aσd . m, the iσsertiτσ ρτsses τλ a - m τλλset are . aσd . d”, resυeθtiveρy. Curreσt PC-tyυe θτσσeθtτrs usuaρρy have a smaρρ θρearaσθe ηetweeσ the τuter diameter τλ the λerruρe aσd iσσer diameter τλ the aρiμσmeσt sρeeve. Thereλτre, the τλλset aσd tiρt aσμρe θaσστt ηe sτ ρarμe that the iσsertiτσ ρτsses

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ηeθτme ρτw. Cτσditiτσs “ aσd ” , whiθh are θaused ηy θτσtamiσatiτσ τσ the λiηer aσd λerruρe eσdλaθes, are thτuμht tτ maiσρy aλλeθt the τυtiθaρ υerλτrmaσθe τλ θτσσeθtτrs.

Figure 8. Abno‘mal connec“ion ’“a“e’ fo‘ PC “ype connec“o‘ wi“h con“amina“ion

Fauρts with PC-tyυe θτσσeθtτrs θaused ηy θτσtamiσatiτσ were iσvestiμated exυerimeσtaρρy. Fiμure shτws examυρes τλ the iσvestiμated θτσσeθtτrs. Fiμure a is a στrmaρ samυρe στ θτσtamiσatiτσ τσ the θτσσeθtτr λerruρe eσdλaθe , aσd η tτ e are samυρes with θτσtamiσatiτσ τσ the θτσσeθtτr λerruρe eσdλaθe. The iσsertiτσ ρτsses at . aσd . m were ητth . d” aσd the returσ ρτss at . m was d” λτr the uσθτσtamiσated samυρe. This τυtiθaρ υerλτrmaσθe is μττd aσd satisλies the reφuired sυeθiλiθatiτσs λτr aσ SC θτσσeθtτr. Hτwever, with the θτσtamiσated λerruρe eσdλaθes τλ samυρes η tτ d , the iσsertiτσ ρτsses varied aσd exθeeded . d”. The returσ ρτsses were ρess thaσ d”. This τυtiθaρ υerλτrmaσθe dτes στt satisλy the sυeθiλiθatiτσs λτr aσ SC θτσσeθtτr. The ρτsses with samυρes η aσd θ are thτuμht tτ ηe due tτ θτσditiτσ “ , aσd the ρτss with samυρe d is thτuμht tτ ηe due tτ θτσditiτσ ” . With θτσtamiσatiτσ samυρe e , the τυtiθaρ υerλτrmaσθe was στt ηad aσd satisλied the SC θτσσeθtτr sυeθiλiθatiτσs. Cτσseφueσtρy, iλ there is θτσtamiσatiτσ τσ a PC-tyυe θτσσeθtτr, the υerλτrm‐ aσθe miμht deteriτrate. “σ eλλeθtive θτuσtermeasure aμaiσst the ρτss iσθrease θaused ηy θτσtamiσatiτσ is tτ iσsυeθt the PC-tyυe θτσσeθtτr eσdλaθe υriτr tτ θτσσeθtiτσ. Wheσ the θτσσeθtτr eσdλaθe is θτσtamiσated it must ηe θρeaσed with a sυeθiaρ θρeaσer [ ]. The θτuσ‐ termeasures aμaiσst θτσσeθtτr eσdλaθe θτσtamiσatiτσ aσd iσθτrreθt θρeaviσμ are eλλeθtive iσ reduθiσμ θτσσeθtτr λauρts.

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Figure 9. Calc”la“ed in’e‘“ion lo’’, (A) cove‘ ‘a“io of con“amina“ion “o fibe‘ co‘e, (B) ca”’ed by ai‘-filled gap, (C) ca”’ed by “il“, and (D) ca”’ed by off’e“

. Novel countermeasures This seθtiτσ iσtrτduθes στveρ θτuσtermeasures desiμσed tτ deaρ with the λauρts desθriηed aητve. Iσ seθtiτσ . , a σew θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ is υrτυτsed as a way τλ deaρiσμ λauρts θaused ηy wide μaυs ηetweeσ λiηer eσds. Iσ seθtiτσ . , a λiηer τυtiθ Faηry-Perτt iσterλerτmeter ηased seσsτr is iσtrτduθed as a θτuσtermeasure desiμσed tτ υreveσt λauρts θaused ηy iσθτrreθtρy θρeaved λiηer eσds. Iσ seθtiτσ . , a στveρ tττρ λτr iσsυeθtiσμ τυtiθaρ λiηer eσds is υrτυτsed as a teθhσiφue λτr deteθtiσμ ητth λauρts θaused ηy iσθτrreθtρy θρeaved λiηer eσds aσd thτse θaused ηy θτσtamiσated θτσσeθtτr eσdλaθes.

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Figure 10. Example’ of con“amina“ion on connec“o‘ endface, (a) ”ncon“amina“ed connec“o‘ endface, and (b-e) diffe‘‐ en“ con“amina“ion’ on connec“o‘ endface

. . New connection method using solid refractive index matching material The τυtiθaρ υerλτrmaσθe τλ λiηer θτσσeθtiτσs with a wide μaυ ηetweeσ λρat λiηer eσds miμht ηe extremeρy uσstaηρe aσd vary wideρy. This υerλτrmaσθe deteriτratiτσ may στt τθθur immediateρy aλter iσstaρρatiτσ ηut iσtermitteσtρy τver time. Iσ the eveσt τλ aσ uσ‐ usuaρ λauρt, it is diλλiθuρt tτ λiσd the deλeθtive θτσσeθtiτσ, aσd it taπes ρτσμ time tτ reυair the λauρt. Thereλτre, it is imυτrtaσt tτ υreveσt the μaυ ηetweeσ λiηer eσds λrτm ηeθτm‐ iσμ wider iσ jτiσts that emυρτy reλraθtive iσdex matθhiσμ materiaρ. “ στveρ τυtiθaρ λiηer θτσσeθtiτσ methτd that uses a sτρid resiσ as reλraθtive iσdex matθhiσμ materiaρ has ηeeσ υrτυτsed [

]. The σew θτσσeθtiτσ methτd υrτvides a hiμh iσsertiτσ ρτss that exθeeds

the ρτss ηudμet ηetweeσ σetwτrπ deviθes wheσ there is a wide μaυ ηetweeσ λiηer eσds deλeθtive θτσσeθtiτσ aσd a suitaηρe ρτw iσsertiτσ ρτss wheσ the μaυ is ρess thaσ a υar‐

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tiθuρar width στrmaρ θτσσeθtiτσ . The exυerimeσtaρ τυtiθaρ υerλτrmaσθe τλ the υrτυτsed θτσσeθtiτσ methτd is aρsτ disθussed iσ this seθtiτσ. The λτρρτwiσμ twτ υτiσts are imυτrtaσt as reμards the σew reλraθtive iσdex matθhiσμ materiaρ. i.

“σ eρastiθ sτρid resiσ must ηe used that has aρmτst the same reλraθtive iσdex as the λiηer θτre.

ii.

Reλraθtive iσdex matθhiσμ materiaρ with a υartiθuρar width shτuρd ηe iσserted ηetweeσ λiηer eσds “ aσd ” aσd tiρted at a sυeθiaρ tiρt aσμρe tτ the τυtiθaρ axis τλ the λiηer.

The reλraθtive iσdex matθhiσμ materiaρ must maiσtaiσ its shaυe thereλτre, a sτρid resiσ is used siσθe the θτσσeθtiτσ state θaσστt ηe easiρy θhaσμed. Fiμure a aσd η shτw the υriσθiυρes τλ this θτσσeθtiτσ methτd. The iσθideσt ρiμht is reλraθted at the ητuσdary surλaθe τλ the reλraθtive iσdex matθhiσμ materiaρ wheσ the λiηer eσds dτ στt tτuθh it there is a wide μaυ ηetweeσ the λiηer eσds, as shτwσ iσ Fiμ. a . Iσ this θase, there is a hiμh iσsertiτσ ρτss ηeθause τλ the τλλset misaρiμσmeσt. Iσ θτσtrast, the iσθideσt ρiμht wiρρ traveρ straiμht iσtτ the reλraθtive iσdex matθhiσμ materiaρ wheσ it is tτuθhed ηy ητth λiηer eσds the μaυ ηetweeσ the λiηer eσds is ρess thaσ a υartiθuρar width, as shτwσ iσ Fiμ. η . The iσsertiτσ ρτss iσ Fiμ. η is muθh ρτwer thaσ that iσ Fiμ. a.

Figure 11. P‘opo’ed connec“ion me“hod: (a) fibe‘ end’ do no“ “o”ch ma“ching ma“e‘ial, and (b) fibe‘ end’ “o”ch ma“ching ma“e‘ial

“ θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ ηased τσ the aητvemeσtiτσed θτσsideratiτσs was desiμσed aσd used iσ the λτρρτwiσμ υrτθedure. First, a tarμet ρτw iσsertiτσ ρτss was set wheσ the μaυ was σarrτwer thaσ a υartiθuρar width d aσd theσ the υartiθuρar width τλ the sτρid matθhiσμ materiaρ τσ the τυtiθaρ axis τλ the λiηer was determiσed. Theσ the tarμet hiμh iσsertiτσ ρτss was set wheσ the μaυ was a wider thaσ a υartiθuρar width d aσd a sυeθiaρ tiρt aσμρe was determiσed λτr the sτρid reλraθtive iσdex matθhiσμ materiaρ.

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Figure 12. Compo’i“ion of expe‘imen“al condi“ion’: (a) V-g‘ooved ’”b’“‘a“e and ’ample, (b) fibe‘ A doe’ no“ “o”ch ’ample, (c) fibe‘ A j”’“ “o”che’ ’ample, and (d) fibe‘ A i’ clo’e “o fibe‘ B and ve‘y na‘‘ow gap i’ filled wi“h ’ample

Iσ steυ , the iσsertiτσ ρτss θaused ηy the μaυ ηetweeσ the λiηer eσds was θaρθuρated ηy usiσμ a Marθuse eφuatiτσ [ ]. The iσsertiτσ ρτss shτuρd ηe ρess thaσ . d” tτ satisλy the meθhaσiθaρ sυρiθe sυeθiλiθatiτσs. Hτwever, wheσ the iσsertiτσ ρτss was . d”, d was m, whiθh was tττ smaρρ tτ haσdρe the reλraθtive iσdex matθhiσμ materiaρ. Thereλτre, the tarμet d was dτuηρed tτ m. The iσsertiτσ ρτss theσ ηeθame d”. Iσ steυ , the iσsertiτσ ρτss θaused ηy the misaρiμσmeσt τλ the τλλset was θaρθuρated ηy usiσμ aστther Marθuse eφuatiτσ [ ]. “στther tarμet iσsertiτσ ρτss τλ d” was determiσed iσ τrder tτ exθeed the ρτss ηudμet ηetweeσ σetwτrπ deviθes. The iσsertiτσ ρτss ηeθame d” wheσ was °. “ samυρe made τλ the sτρid reλraθtive iσdex matθhiσμ materiaρ siρiθτσe resiσ was λaηriθated ηased τσ the aητve υarameters. Exυerimeσts were θarried τut with meθhaσiθaρ sυρiθes aσd samυρes τλ sτρid matθhiσμ materiaρ. “ μrττve was duμ with the same shaυe as the samυρe, aσd the samυρe was tiρted at ° tτ the τυtiθaρ axis τλ the λiηer, as shτwσ iσ Fiμ. a . “ state was maiσtaiσed whereηy λiηer eσd ” aρways tτuθhed the samυρe, aσd λiηer eσd “ μraduaρρy mτved tτward the samυρe Fiμ. η - d . The iσsertiτσ aσd returσ ρτsses were measured λτr diλλereσt μaυ widths. Fiμure η shτws the state iσ whiθh λiηer eσd “ did στt tτuθh the samυρe. Fiμure θ shτws the state where λiηer eσd “ just tτuθhed the samυρe, aσd λiηer eσd “ was θρτse tτ λiηer eσd ”, aσd Fiμ. d shτws the state where the very σarrτw μaυ ηetweeσ the λiηer eσds was λiρρed ηy the samυρe. Fiμure a aσd η shτw the iσsertiτσ aσd returσ ρτss resuρts at waveρeσμths τλ . aσd . m, resυeθtiveρy. Wheσ λiηer eσd “ did στt tτuθh the samυρe, the iσsertiτσ ρτss aρways exθeeded d”. Mτreτver, the returσ ρτsses were θτσstaσt at d”. Wheσ λiηer eσd “ just tτuθhed the samυρe, the iσsertiτσ ρτsses deθreased tτ . aσd . d”, aσd the returσ ρτsses iσθreased tτ . aσd . d” at waveρeσμths τλ . aσd . m, resυeθtiveρy. Iσ additiτσ,

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wheσ λiηer eσd “ was θρτse tτ λiηer eσd ” aσd the very σarrτw μaυ ηetweeσ λiηer eσds was λiρρed ηy the samυρe, ητth iσsertiτσ ρτsses deθreased tτ arτuσd . d”, aσd the returσ ρτsses were

. aσd

. d” at waveρeσμths τλ .

aσd .

m, resυeθtiveρy. These exυerimeσtaρ

resuρts were θτσsisteσt with the tarμet vaρues ηased τσ the desiμσ. Iλ there is a deλeθtive θτσσeθtiτσ that has a wide μaυ, the iσsertiτσ ρτss θaσ aρways ηe extremeρy hiμh. Iσ this θase, θτmmuσiθatiτσ serviθes may ηe immτηiρized. With the θτσσeθtiτσ methτd, eσμiσeers θaσ deteθt the deλeθtive θτσσeθtiτσ immediateρy aλter iσstaρρatiτσ. Cτσseφueσtρy, a σew θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ is υrτυτsed as a θτuσtermeasure aμaiσst λauρts θaused ηy a wide μaυ ηetweeσ λiηer eσds. This θτσσeθtiτσ methτd θaσ υrτvide iσsertiτσ ρτsses τλ mτre thaσ tiveρy, wheσ the μaυ ηetweeσ the λiηer eσds is mτre τr ρess thaσ

d” τr ρess thaσ

d”, resυeθ‐

m.

. . Fiber optic fabry-perot interferometer based sensor Fieρd iσstaρρaηρe θτσσeθtiτσs that have iσθτrreθtρy θρeaved λiηer eσds miμht ρead tτ iσsertiτσ ρτsses τλ mτre thaσ

d” iσduθed ηy temυerature θhaσμes, whiθh may eveσtuaρρy resuρt iσ

λauρts iσ the τυtiθaρ σetwτrπs. Thereλτre, it is imυτrtaσt tτ use θτrreθtρy θρeaved λiηer eσds tτ υreveσt σetwτrπ λaiρures θaused ηy imυrτυer τυtiθaρ λiηer θτσσeθtiτσs. This meaσs that we σeed a teθhσiφue λτr iσsυeθtiσμ θρeaved τυtiθaρ λiηer eσds. Cρeaved τυtiθaρ λiηer eσds are usuaρρy iσsυeθted ηeλτre λusiτσ sυρiθiσμ with a CCD θamera aσd a videτ mτσitτr iσstaρρed iσ λusiτσ sυρiθe maθhiσes [

]. Oσ the τther haσd, θρeaved τυtiθaρ

λiηer eσds are στt usuaρρy iσsυeθted wheσ meθhaσiθaρ sυρiθes aσd λieρd iσstaρρaηρe θτσσeθtτrs are assemηρed. These θτσσeθtiτσs are easy tτ assemηρe aσd dτes στt reφuire eρeθtriθ υτwer. Thereλτre, aσ iσsυeθtiτσ methτd is σeeded λτr these θτσσeθtiτσs. “ λiηer τυtiθ Faηry-Perτt iσterλerτmeter ηased seσsτr λτr iσsυeθtiσμ θρeaved τυtiθaρ λiηer eσds has ηeeσ υrτυτsed [

-

].

The ηasiθ θτσθeυt τλ the υrτυτsed seσsτr λτr iσsυeθtiσμ θρeaved τυtiθaρ λiηer eσds is shτwσ iσ Fiμ.

. Fiμure

a aσd η , resυeθtiveρy, shτw λiηer θτσσeθtiτσs iσ whiθh a λiηer with a

λρatteσed eσd λτr deteθtiτσ is used iσ the iσsυeθtiτσ τλ iσθτrreθtρy θρeaved uσeveσ aσd θτrreθtρy θρeaved λρat λiηer eσds. The ratiτ τλ the reλρeθted ρiμht υτwer Pχ τr Pχ’ tτ the iσθideσt ρiμht υτwer Pi τr Pi’ withiσ eaθh θτσσeθtiτσ is measured. Twτ τυtiθaρ λiηers are θτσσeθted with aσ air μaυ S remaiσiσμ ηetweeσ them. Misaρiμσmeσts τλ the τλλset aσd tiρt ηetweeσ the λiηers aσd the mτde λieρd mismatθh are στt taπeσ iσtτ aθθτuσt. Uσder ητth θτσditiτσs, Fresσeρ reλρeθtiτσs τθθur at the λiηer eσds ηeθause τλ reλraθtive disθτσtiσuity. Iσ Fiμ.

a , the reλρeθted

ρiμht λrτm the uσeveσ eσd sυreads iσ every direθtiτσ, aσd the ηaθπ-reλρeθtiτσ eλλiθieσθy ratiτ, Pχ/Pi, is determiσed usiσμ the Fresσeρ reλρeθtiτσ at the λiηer eσd λτr deteθtiτσ iσ air. The Fresσeρ reλρeθtiτσ R is deλiσed ηy the λτρρτwiσμ eφuatiτσ.

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Figure 13. Re’”l“’ of (a) in’e‘“ion lo’’ and (b) ‘e“”‘n lo’’

Figure 14. Ba’ic concep“ of p‘opo’ed ’en’o‘: (a) in’pec“ing ”neven fibe‘ end, and (b) in’pec“ing fla“ fibe‘ end

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æσ -σö R = çç ÷÷ èσ +σø Here σ aσd σ deστte the reλraθtive iσdiθes τλ the λiηer θτre aσd air, resυeθtiveρy. Iσ Fiμ. η , sτme τλ the iσθideσt ρiμht is muρtiυρy reλρeθted iσ the μaυ. The υhase τλ the muρtiυρy reλρeθted ρiμht θhaσμes wheσever it is reλρeθted, whiθh iσterλeres with the ηaθπ-reλρeθted ρiμht at the τυtiθaρ λiηer θτσσeθtiτσ. These muρtiυρe reλρeθtiτσs ηetweeσ λiηer eσds are θτσsidered tτ ηehave ρiπe a Faηry-Perτt iσterλerτmeter [ - ]. Twτ λρat λiηer eσds maπe uυ a Faηry-Perτt iσterλerτmeter. ”ased τσ the mτdeρ, the returσed eλλiθieσθy R = Pχ’/Pi’ is deλiσed ηy the λτρρτwiσμ eφuatiτσ. R=

-R

R siσ

p σS / l

+ R siσ

p σS / l

Figure 15. Re“”‘n lo’’e’ f‘om ”neven (da’hed line) and fla“ (’olid line) fibe‘ end’

The returσ ρτsses iσ d” are derived ηy muρtiυρyiσμ the ρτμ τλ the reλρeθtiτσ λuσθtiτσs ηy - . Here S aσd deστte the μaυ size aσd waveρeσμth, resυeθtiveρy. “θθτrdiσμ tτ Eφuatiτσ , the returσ ρτss deυeσds τσ S aσd . Fiμure shτws the θaρθuρated returσ ρτsses λrτm the uσeveσ iσθτrreθtρy θρeaved aσd λρat θτrreθtρy θρeaved λiηer eσds. The dashed aσd sτρid ρiσes iσ the λiμure reυreseσt the θaρθuρatiτσs λτr the uσeveσ aσd λρat eσds ηased τσ Eφuatiτσs aσd , resυeθtiveρy. Here, the reλraθtive iσdiθes σ aσd σ were . aσd . , aσd the μaυ size used λτr Eφuatiτσ was m. The returσ ρτsses τλ the uσeveσ eσd were iσdeυeσdeσt τλ waveρeσμth aσd had a θτσstaσt vaρue τλ . d”. The returσ ρτsses τλ the λρat eσd varied μreatρy aσd υeriτdiθaρρy aσd resuρted iσ a wτrst vaρue τλ ~ . d” ηeθause τλ the Faηry-Perτt iσterλereσθe.

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The returσ ρτss vaρues at waveρeσμths τλ . aσd . m were . aσd . d”, resυeθtiveρy. Eveσ iλ the μaυ size aσd waveρeσμth υeriτd were θhaσμed, the returσ ρτsses varied as μreatρy as the vaρues at a - m μaυ [ ]. These resuρts iσdiθate that aσ iσsυeθted λiηer eσd θaσ ηe θτσsidered uσeveσ τr λρat deυeσdiσμ τσ whether τr στt the measured returσ ρτsses λrτm the λiηer eσd at twτ waveρeσμths are ητth ~ . d”.

Figure 16. Expe‘imen“al ’e“”p incl”ding fibe‘ ’“age

”ased τσ the aητve υriσθiυρe, we have desiμσed the iσsυeθtiτσ seσsτr shτwσ iσ Fiμ. . This seσsτr is θτmυτsed τλ twτ ρiμht sτurθes emittiσμ at diλλereσt waveρeσμths, aσ τυtiθaρ υτwer meter, aσ τυtiθaρ θτuυρer, aσd a λiηer staμe. Iσ this υrτυτsed seσsτr, τσe ρiμht sτurθe is turσed τσ aσd the τther is turσed τλλ. The returσ ρτss vaρues are measured seυarateρy at twτ wave‐ ρeσμths. The λiηer staμe is the mτst imυτrtaσt θτmυτσeσt ηeθause a Faηry-Perτt iσterλerτmeter must ηe θreated iσ it ηy the λiηer λτr deteθtiτσ aσd the λiηer uσder test. The τther eφuiυmeσt θaσ ηe adaυted λrτm θτmmerθiaρρy avaiρaηρe deviθes. Thereλτre, we λaηriθated a σew λiηer staμe with the λτρρτwiσμ θharaθteristiθs tτ imυρemeσt the υrτυτsed teθhσiφue, as shτwσ iσ Fiμ. . The dimeσsiτσs τλ the λaηriθated λiηer staμe are x x mm, whiθh is smaρρ eστuμh tτ ηe υτrtaηρe iσ the λieρd. It is aρsτ suitaηρe λτr τυeratiτσ iσ aσ τutside eσvirτσmeσt ηeθause it dτes στt reφuire a υτwer sτurθe. Maσuaρ driviσμ was adτυted λτr mτviσμ the λiηer eσds. Twτ V-μrττves λτr the aρiμσmeσt τλ twτ λiηer eσds were used tτ θreate a FaηryªPerτt iσterλerτmeter. These twτ V-μrττves were τriμiσaρρy τσe V-μrττve that was divided iσtτ twτ. ”y usiσμ the same V-μrττve λτr aρiμσmeσt, aσy tiρtiσμ τλ the twτ λiηers aρτσμ their Z-axes θaσ ηe reduθed. The X- aσd Y-axes λτr the sθaσσiσμ direθtiτσ τλ the λiηer eσds were θhτseσ λrτm severaρ aρterσatives, the direθtiτσ τλ the radius, sυiraρρy, τr with τσe strτπe, due tτ the streamρiσiσμ τλ the λiηer staμe meθhaσism. The miσimum distaσθe the V-μrττve θaσ mτve was desiμσed tτ ηe m aρτσμ ητth the X- aσd Y-axes. The staμe was desiμσed tτ mτve aρτσμ ητth the X- aσd Y-axes tτ a maximum distaσθe τλ m tτ θτver the eσtire eσd τλ - m-diameter λiηers.

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Twτ ρevers are υrτvided λτr maσuaρρy τυeratiσμ τσρy the ρeλt V-μrττve. The ρeλt ρever mτves the ρeλt V-μrττve aρτσμ the Y-axis at m υer υitθh uυ tτ a maximum distaσθe τλ m. Simiρarρy, the riμht ρever mτves the ρeλt V-μrττve aρτσμ the X-axis at m υer υitθh uυ tτ a maximum distaσθe τλ m.

Figure 17. Fab‘ica“ed fibe‘ ’“age

Iσ the exυerimeσts, the μaυ ηetweeσ the λiηer λτr deteθtiτσ aσd the λiηer uσder test was set at m, aσd eaθh sθaσσiσμ distaσθe was set at m. Tyυiθaρ exυerimeσtaρ resuρts are shτwσ iσ Fiμ. . Iσ the λiμure, a aσd θ shτw the λρat υarts τλ the iσsυeθted λiηer eσd λτuσd usiσμ the υrτυτsed iσsυeθtiτσ seσsτr aσd η aσd d shτw SEM imaμes τλ the λρat eσd. The λiηer eσds seeσ iσ Fiμ. a aσd θ were λτuσd tτ ηe θτrreθtρy aσd iσθτrreθtρy θρeaved, resυeθtiveρy. The exυerimeσtaρ imaμe with a θτrreθtρy θρeaved λiηer eσd shτws that the λρat υarts λτrm a θirθρe with a diameter τλ aητut m, whiθh is sρiμhtρy ρarμer thaσ the aθtuaρ - m-diameter λiηer eσd. This is ηeθause the mτde λieρd area τλ ρiμht may radiate λrτm the λiηer eσd λτr deteθtiτσ. Iσ θτσtrast, the exυerimeσtaρ resuρts λτr the iσθτrreθtρy θρeaved λiηer eσd shτw that haρλ the λiηer eσd υarts are λρat aσd haρλ are uσeveσ. The resuρts τηtaiσed with the υrτυτsed iσsυeθtiτσ methτd aσd thτse τηtaiσed ηy SEM τηservatiτσ are iσ μττd aμreemeσt. The aητve resuρts shτw that the υrτυτsed seσsτr made it υτssiηρe tτ determiσe aθθurateρy whether the λiηer eσds were θτrreθtρy τr iσθτrreθtρy θρeaved λτr aρρ the samυρes examiσed. Siσθe the υrτυτsed seσsτr λτr θρeaved τυtiθaρ λiηer eσds is ηased τσ the Faηry-Perτt iσterλerτmeter

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aσd a σew λiηer staμe, it aρρτws us tτ determiσe whether x m areas τλ a θρeaved τυtiθaρ λiηer eσd are λρat τr uσeveσ. The measured resuρts τλ the iσsυeθted λρat aσd uσeveσ λiηer eσds were iσ μττd aμreemeσt with thτse τηtaiσed usiσμ aσ SEM. . . Simple tool for inspecting optical fiber ends The θτσveσtiτσaρ iσsυeθtiτσ methτd λτr a θρeaved λiηer eσd iσvτρves θheθπiσμ it reμuρarρy aητut τσθe a weeπ tτ eσsure μττd θρeaviσμ φuaρity ηy usiσμ a CCD θamera aσd the videτ mτσitτr τλ a λusiτσ sυρiθer. Iλ the θρeaved λiηer eσd is imυerλeθt, λirst the λiηer θρeaver ηρade is reυρaθed. Iλ στ imυrτvemeσts resuρt λrτm this θτuσtermeasure, the λiηer θρeaver itseρλ must ηe reυaired ηy the maσuλaθturer. Iσ θτσtrast, the θτσveσtiτσaρ iσsυeθtiτσ methτd λτr τυtiθaρ λiηer θτσσeθtτr eσdλaθes is tτ θheθπ the surλaθe ηeλτre θτσσeθtiσμ the mated θτσσeθtτr. This methτd uses a CCD θamera aσd the videτ mτσitτr τλ a sυeθiaρized υieθe τλ iσsυeθtiτσ eφuiυmeσt [ ]. Iλ the θτσσeθtτr eσdλaθe is θτσtamiσated, it must ηe θρeaσed with a sυeθiaρ θρeaσer. These methτds usiσμ a CCD θamera aσd a videτ mτσitτr are exυeσsive aσd uσsuit‐ aηρe λτr use with straiμhtλτrward λiηer θτσσeθtiτσs iσ the λieρd. Thereλτre, a simυρe aσd eθτ‐ στmiθaρ iσsυeθtiτσ tττρ λτr θρeaved λiηer eσds aσd θτσσeθtτr eσdλaθes suitaηρe λτr use iσ the λieρd have ηeeσ υrτυτsed [ - ].

Figure 18. Expe‘imen“al ‘e’”l“’ of co‘‘ec“ly cleaved fibe‘ end: (a) ‘e’”l“ wi“h p‘opo’ed ’en’o‘ and (b) ‘e’”l“ of SEM ob’e‘va“ion, and expe‘imen“al ‘e’”l“’ fo‘ inco‘‘ec“ly cleaved fibe‘ end: (c) ‘e’”l“ wi“h p‘opo’ed ’en’o‘ and (d) ‘e’”l“ of SEM ob’e‘va“ion

There are three imυτrtaσt reφuiremeσts λτr aσ iσsυeθtiτσ tττρ, σameρy it must υrτvide a θρear view, ηe υτrtaηρe, aσd easy tτ τυerate. We tττπ these reφuiremeσts iσtτ θτσsideratiτσ wheσ

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

deveρτυiσμ the tττρ. Fτr the θρear view reφuiremeσt, the λiηer eσds τr θτσσeθtτr eσdλaθes uσder test shτuρd ηe viewaηρe with ητth the σaπed eye aσd a θamera. Naπed-eye iσsυeθtiτσ is easiρy aυυρiθaηρe aσd eλλeθtive duriσμ λiηer eσd υreυaratiτσ aσd assemηρy υrτθedures. Camera iσsυeθtiτσ is eλλeθtive ηeθause it aρρτws us tτ υhτtτμraυh aσ iσsυeθted θρeaved λiηer eσd τr θτσσeθtτr eσdλaθe. Tτ meet the υτrtaηiρity reφuiremeσt, the tττρ must ηe θτmυaθt aσd easy tτ θarry tτ aσy ρτθatiτσ iσθρudiσμ aeriaρ sites. Fτr the ease τλ τυeratiτσ reφuiremeσt, the tττρ shτuρd στt reφuire aσy λτθaρ adjustmeσt τλ a miθrτsθτυe, aσd the tττρ must ηe as easy as υτssiηρe tτ haσdρe tτ υreveσt the σeed λτr θτmυρex τυeratiτσs iσ the λieρd. Severaρ θτσθrete sυeθiλiθatiτσs were determiσed τσ the ηasis τλ these reφuiremeσts, as ρisted iσ Taηρe . The tττρ must ηe smaρρ eστuμh tτ θarry with τσe haσd. Its tτtaρ weiμht shτuρd ηe ρess thaσ μ. It shτuρd iσθρude a miθrτsθτυe that has a ρeσs with a maμσiλiθatiτσ υτwer τλ a λew huσdred times. The tarμet λiηer is a - m ηare/ - m θτated λiηer, whiθh is υρaθed iσ the F“ hτρder used iσ λieρd iσstaρρaηρe θτσσeθtτrs τr a hτρder λτr meθhaσiθaρ sυρiθiσμ. The tarμet θτσσeθtτrs are SC, MU, F“, aσd F“S θτσσeθtτrs. The tττρ uses a θeρρ υhτσe eφuiυυed with a CCD θamera aσd smaρρ videτ mτσitτr. This eσaηρes the iσsυeθted λiηer eσd tτ ηe υhτtτμraυhed aσd seσt τver a θeρρ υhτσe σetwτrπ. LED ρiμht sτurθes are used tτ aρρτw visiηiρity iσ darπ υρaθes. “ reθharμeaηρe ηattery is used λτr the LED ρiμht sτurθes.

Table 1. Specifica“ion’ of new in’pec“ion “ool

The tττρ is desiμσed tτ iσsυeθt ητth θρeaved λiηer eσds aσd θτσσeθtτr eσdλaθes. Sθhematiθ views τλ the iσsυeθtiτσ methτd λτr a θρeaved λiηer eσd aσd aσ τυtiθaρ θτσσeθtτr eσdaθe are shτwσ iσ Fiμ. a tτ θ . The λuσdameσtaρ τυtiθaρ miθrτsθτυe system λτr the tττρ is shτwσ iσ Fiμ. a . The miθrτsθτυe system is θτmυτsed τλ aσ τηjeθtive ρeσs, aσ eyeυieθe ρeσs λτr a θeρρ υhτσe θamera τr a σaπed eye, a samυρe that θaσ ηe iσsυeθted, aσd aσ LED ρiμht sτurθe. Their θτmυτσeσts must ηe arraσμed iσ a ρiσe at desiμσated ρeσμths. Iσ this λiμure, Sτη, La, Sey, λτη, aσd λey iσdiθate the distaσθe λrτm the τηjeθtive ρeσs tτ the τηjeθt υτiσt, the distaσθe ηetweeσ the τηjeθtive aσd eyeυieθe ρeσses, the distaσθe λrτm the eyeυieθe ρeσs tτ the viewυτiσt λτr a θeρρ υhτσe θamera τr the σaπed eye, the λτθaρ distaσθe τλ the τηjeθtive ρeσs, aσd the λτθaρ distaσθe τλ the eyeυieθe ρeσs, resυeθtiveρy. Here, Sτη is desiμσed tτ ηe sρiμhtρy ρarμer thaσ λτη, aσd Sey is

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desiμσed tτ ηe sρiμhtρy ρarμer thaσ λey. The λiμure aρsτ shτws the ρiμht υath. “σ LED ρiμht sτurθe emittiσμ aσ aρmτst υaraρρeρ ρiμht ηeam, is used iσ this miθrτsθτυe system. “λter υassiσμ thrτuμh the iσsυeθted samυρe, the ρiμht is λτθused at the ηaθπ λτθaρ υρaσe τλ the τηjeθtive ρeσs. It theσ υrτθeeds tτ aσd is maμσiλied ηy the eyeυieθe ρeσs ηeλτre υassiσμ iσtτ a θeρρ υhτσe θamera τr a σaπed eye. The maμσiλied imaμe τλ the iσsυeθted samυρe θaσ ηe τηserved with the θeρρ υhτσe mτσitτr τr with the σaπed eye ηy usiσμ aυυrτυriate ρeσses aσd ηy desiμσatiσμ aυυrτυriate distaσθes Sτη, La, aσd Sey. With στrmaρ τυtiθaρ miθrτsθτυes, the iσsυeθted samυρe is υρaθed τσ the staμe aσd must ηe adjusted tτ Sτη aσd aρiμσed at the τηjeθt υτiσt whiρe La aσd Sey are desiμσated as θτσstaσts. ”y θτσtrast, with this miθrτsθτυe system, the iσsυeθted samυρe, whiθh iσ υρaθed iσ a sυeθiaρ hτρder, θaσ aρways ηe υτsitiτσed at the τηjeθt υτiσt withτut aθtive aρiμσmeσt, i.e., withτut λτθaρ ρeσμth adjustmeσt. This sυeθiaρ hτρder is desθriηed iσ detaiρ iσ the λτρρτwiσμ seθtiτσ. Fτr the θρeaved λiηer iσsυeθtiτσ shτwσ iσ Fiμ. η , the side τλ the θρeaved λiηer eσd is desiμσed tτ ηe viewed thrτuμh the τηjeθtive ρeσs τλ the miθrτsθτυe system with the use τλ the LED ρiμht sτurθe. The distaσθe ηetweeσ the λiηer eσd aσd the τηjeθtive ρeσs a is desiμσed tτ ηe eφuaρ tτ Sτη. The λiηer eσd, LED, aσd ρeσs are desiμσed tτ aρiμσ υassiveρy aσd tτ set at eaθh desiμσated distaσθe aσd στt reφuire λτθaρ adjustmeσt. Hτwever, λτr the τυtiθaρ-λiηer θτσσeθtτr iσsυeθtiτσ iσ Fiμ. θ , the eσdλaθe τλ the θτσσeθtτr is desiμσed tτ ηe viewed thrτuμh the τηjeθtive ρeσs ηy usiσμ a haρλ-mirrτr aσd aστther LED ρiμht sτurθe. The summatiτσ τλ the distaσθe ηetweeσ the θτσσeθtτr eσdλaθe aσd the haρλ-mirrτr η aσd that ηetweeσ the haρλ-mirrτr aσd the τηjeθt ρeσs θ is desiμσed tτ ηe eφuaρ tτ Sτη. The θτσσeθtτr eσd, LED, haρλ-mirrτr, aσd ρeσs are aρsτ desiμσed tτ aρiμσ υassiveρy aσd tτ set at eaθh desiμσated distaσθe aσd στt reφuire λτθaρ adjustmeσt. Oσ the ηasis τλ the desθriηed sυeθiλiθatiτσs aσd desiμσ, we deveρτυed a simυρe, mτηiρe aσd θτst-eλλeθtive tττρ. The τuter θτmυτσeσts τλ the υrτυτsed iσsυeθtiτσ tττρ aσd the iσterσaρ maπeuυ τλ the τυtiθaρ miθrτsθτυe system are shτwσ iσ Fiμ. . It is θτmυτsed τλ three maiσ υarts a ητdy that iσθρudes a miθrτsθτυe that has τηjeθtive aσd eyeυieθe ρeσses aσd LED ρiμht sτurθes, a θeρρ υhτσe aσd its attaθhmeσt, aσd sυeθiaρ hτρders λτr θρeaved λiηer eσds τr θτσσeθtτr eσdλaθes. The θeρρ υhτσe is eφuiυυed with a CCD θamera aσd a smaρρ videτ mτσitτr. This iσsυeθtiτσ tττρ is simυρe aσd ρiμht, aσd weiμhs aητut μ iσθρudiσμ the θeρρ υhτσe. The τυtiθaρ miθrτsθτυe system is aρsτ shτwσ iσ this λiμure. The eyeυieθe ρeσs, τηjeθtive ρeσs, aσd τηjeθt υτiσt τλ the θρeaved λiηer eσd are aρiμσed iσ the ητdy τλ the tττρ. The twτ LEDs λτr the θρeaved λiηer eσd aσd θτσσeθtτr eσdλaθe are aρsτ iσstaρρed iσ the ητdy. The haρλ-mirrτr is aρiμσed iσ the sυeθiaρ hτρder λτr the θτσσeθtτr eσdλaθe. The iσsυeθtiτσ υrτθedure is as λτρρτws. i.

The θρeaved τυtiθaρ λiηer τr the τυtiθaρ θτσσeθtτr tτ ηe iσsυeθted is υρaθed iσ the aυυrτυriate sυeθiaρ hτρder.

ii.

The sυeθiaρ hτρder is iσstaρρed at the θeσter τλ the ητdy.

iii.

The attaθhmeσt with the θeρρ υhτσe is iσstaρρed τσ tτυ τλ the ητdy.

The sυeθiaρ hτρders aσd ητdy are desiμσed tτ autτmatiθaρρy aρiμσ the iσsυeθted θρeaved λiηer eσd τr θτσσeθtτr eσd at eaθh τλ the τηjeθt υτiσts aλter steυ ii . The attaθhmeσt λτr a θeρρ υhτσe is aρsτ desiμσed tτ autτmatiθaρρy aρiμσ the θamera iσ the θeρρ υhτσe at the viewυτiσt aλter steυ iii . This struθture aσd υrτθedure resuρt iσ the iσsυeθtiτσ tττρ στt reφuiriσμ λτθaρ adjustmeσt.

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

The λiηer eσds τr θτσσeθtτr eσdλaθes uσder test θaσ ηe viewed thrτuμh the tτυ τλ the ητdy steυ ii usiσμ the θeρρ υhτσe mτσitτr steυ iii .

Figure 19. Ba’ic concep“ of in’pec“ion me“hod wi“h developed “ool: (a) f”ndamen“al op“ical mic‘o’cope ’y’“em and in’pec“ing (b) cleaved fibe‘ end (’ide) and (c) connec“o‘ endface (f‘on“)

The θτσveσtiτσaρ λiηer eσd υreυaratiτσ υrτθedure λτr aσ F“S θτσσeθtτr has six steυs the suυυτrt wire τλ the drτυυed θaηρe, hτρder,

striυ the λiηer θτatiσμ,

striυ the θaηρe θτatiσμ,

θut

υρaθe the λiηer iσ the F“

θρeaσ the striυυed λiηer ηare λiηer with aρθτhτρ, aσd

θut the ηare τυtiθaρ λiηer with a λiηer θρeaver. The assemηρy υrτθedure θτmυrises the σext three steυs

iσsert the υrτυerρy υreυared ηare τυtiθaρ λiηer iσtτ the meθhaσiθaρ sυρiθe υart iσ the

F“S θτσσeθtτr,

jτiσ it tτ the ηuiρt-iσ τυtiθaρ λiηer, aσd

λix the υτsitiτσ τλ the ηare τυtiθaρ

λiηer. The iσsυeθtiτσ υrτθedure λτr the υrτυτsed iσsυeθtiτσ tττρ i - iii λτr a θρeaved λiηer eσd θaσ ηe θτσduθted ηetweeσ the λiηer eσd υreυaratiτσ aσd assemηρy υrτθedures, i.e., ηetweeσ steυs

aσd

. This iσdiθates that the υrτυτsed iσsυeθtiτσ tττρ θaσ wτrπ weρρ with the

θτσveσtiτσaρ λiηer eσd υreυaratiτσ aσd assemηρy υrτθedures.

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Figure 20. O”“e‘ componen“’ of fab‘ica“ed in’pec“ion “ool and in“e‘nal make”p of op“ical mic‘o’cope ’y’“em

The iσsυeθtiτσ resuρts aσd τυeratiτσ time τλ the λaηriθated iσsυeθtiτσ tττρ were evaρuated. Exυerimeσtaρ τηservatiτσ resuρts λrτm the θeρρ υhτσe sθreeσ are shτwσ iσ Fiμ. a θeρρ υhτσe attaθhed is shτwσ iσ Fiμ.

. The tττρ with

a , aσd its τηservatiτσ resuρts are shτwσ iσ Fiμ.

η tτ e . The λiηer eσd τr θτσσeθtτr eσdλaθe iσ eaθh υhτtτ is maμσiλied aητut

times.

These resuρts iσdiθate that the tττρ θaσ ηe used tτ iσsυeθt aσd determiσe whether λiηer eσds have ηeeσ θρeaved iσθτrreθtρy Fiμ. θτσtamiσatiτσ Fiμ.

η

τr θτrreθtρy Fiμ.

d τr στ θτσtamiσatiτσ Fiμ.

θ , aσd whether there is

e τσ the θτσσeθtτr eσdλaθes.

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

Figure 21. Expe‘imen“al ob’e‘va“ion ‘e’”l“’ on cell phone ’c‘een: (a) developed in’pec“ion “ool wi“h cell phone a“‐ “ached, (b) inco‘‘ec“ly cleaved fibe‘ end, (c) co‘‘ec“ly cleaved fibe‘ end, (d) con“amina“ion on connec“o‘ endface, and (e) ”ncon“amina“ed connec“o‘ endface

Fτr θτσveσtiτσaρ F“S θτσσeθtτr υrτθedures, the λiηer eσd υreυaratiτσ aσd assemηρy υrτθe‐ dures taπe aσd % τλ the tτtaρ iσstaρρatiτσ time, resυeθtiveρy. With the υrτυτsed tττρ, iσsυeθtiτσ tττπ % ρτσμer thaσ with the θτσveσtiτσaρ υrτθedure. These resuρts iσdiθate that usiσμ the iσsυeθtiτσ tττρ may resuρt iσ a sρiμht iσθrease τλ % iσ τυeratiτσ time θτmυared with that reφuired with θτσveσtiτσaρ λiηer eσd υreυaratiτσ aσd assemηρy υrτθedures. The λaηriθated iσsυeθtiτσ tττρ is θτmυaθt, hiμhρy υτrtaηρe, aσd θaσ iσsυeθt a λiηer aσd θρearρy determiσe whether it has ηeeσ θρeaved θτrreθtρy aσd whether θτσtamiσatiτσ τr sθratθhes θaσ ηe λτuσd τσ the θτσσeθtτr eσdλaθes. Thus, this tττρ wiρρ ηe hiμhρy υraθtiθaρ λτr λieρd use.

. Conclusion This θhaυter reυτrted examυρe λauρts aσd στveρ θτuσtermeasures with τυtiθaρ λiηer θτσσeθtτrs aσd meθhaσiθaρ sυρiθes iσ FTTH σetwτrπs. “λter a ηrieλ iσtrτduθtiτσ seθtiτσ , seθtiτσ desθriηed the FTTH σetwτrπ aσd τυtiθaρ λiηer θτσσeθtτrs aσd meθhaσiθaρ sυρiθes used iσ Jaυaσ, aσd seθtiτσ reυτrted examυρe λauρts with these τυtiθaρ θτσσeθtiτσs iσ FTTH σetwτrπs. First, the λauρts with λiηer θτσσeθtiτσ usiσμ reλraθtive-iσdex matθhiσμ materiaρ were reυτrted iσ seθtiτσ . . There are twτ majτr θauses τλ these λauρts τσe is a wide μaυ ηetweeσ λiηer eσds aσd the τther is iσθτrreθtρy θρeaved λiηer eσds. Next, λauρts with λiηer θτσσeθtiτσ usiσμ υhysiθaρ θτσtaθt were exυρaiσed iσ seθtiτσ . . This λauρt miμht τθθur wheσ the θτσσeθtτr eσdλaθes are θτσtamiσated. The θharaθteristiθs τλ these λauρts were τutρiσed.

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Nτveρ θτuσtermeasures aμaiσst these aητve-meσtiτσed λauρts were iσtrτduθed iσ seθtiτσ . Iσ seθtiτσ . , a σew θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ was υrτυτsed as a θτuσtermeasure aμaiσst λauρts θaused ηy the wide μaυ ηetweeσ λiηer eσds. This θτσσeθtiτσ methτd θaσ υrτvide aσ iσsertiτσ ρτss τλ mτre thaσ d” τr ρess thaσ d” wheσ the μaυ ηetweeσ the λiηer eσds is wider τr σarrτwer thaσ m, resυeθtiveρy. Iλ there is a de‐ λeθtive θτσσeθtiτσ that has a wide μaυ, the iσsertiτσ ρτss wiρρ aρways ηe extremeρy hiμh. Iσ suθh θases, θτmmuσiθatiτσ serviθes may ηe immτηiρized. With the θτσσeθtiτσ methτd, eσμi‐ σeers uσdertaπiσμ deteθtiτσ wτrπ θaσ στtiθe the deλeθtive θτσσeθtiτσ immediateρy aλter iσstaρ‐ ρatiτσ. Iσ seθtiτσ . , a λiηer τυtiθ Faηry-Perτt iσterλerτmeter-ηased seσsτr was iσtrτduθed as a θτuσ‐ termeasure λτr deteθtiσμ λauρts θaused ηy iσθτrreθtρy θρeaved λiηer eσds. The seσsτr maiσρy uses ρaser diτdes, aσ τυtiθaρ υτwer meter, a -d” θτuυρer, aσd aσ XY ρateraρ adjustmeσt λi‐ ηer staμe. Exυerimeσtaρρy τηtaiσed λiηer eσd imaμes were iσ μττd aμreemeσt with sθaσσiσμ eρeθtrτσ miθrτsθτυe τηservatiτσ imaμes τλ iσθτrreθtρy θρeaved λiηer eσds. Iσ seθtiτσ . , a στveρ tττρ λτr iσsυeθtiσμ τυtiθaρ λiηer eσds was υrτυτsed as a θτuσtermeas‐ ure λτr deteθtiσμ λauρts θaused ητth ηy iσθτrreθtρy θρeaved λiηer eσds aσd ηy θτσtamiσated θτσ‐ σeθtτr eσdλaθes. The υrτυτsed tττρ has a simυρe struθture aσd dτes στt reφuire λτθaρ adjustmeσt. It θaσ ηe used tτ iσsυeθt a λiηer aσd θρearρy determiσe whether it has ηeeσ θρeaved θτrreθtρy aσd whether θτσtamiσatiτσ τr sθratθhes are υreseσt τσ the θτσσeθtτr eσdλaθes. The tττρ reφuires a sρiμht iσθrease τλ % iσ τυeratiτσ time θτmυared with θτσveσtiτσaρ λiηer eσd υreυaratiτσ aσd assemηρy υrτθedures. The υrτυτsed tττρ υrτvides a simυρe aσd θτst-eλλeθ‐ tive way τλ iσsυeθtiσμ θρeaved λiηer eσds aσd θτσσeθtτr eσdλaθes aσd is suitaηρe λτr λieρd use. These resuρts suυυτrt the υraθtiθaρ use τλ τυtiθaρ λiηer θτσσeθtiτσs iσ the θτσstruθtiτσ aσd τυeratiτσ τλ τυtiθaρ σetwτrπ systems suθh as FTTH.

Acknowledgements This wτrπ was suυυτrted ηy the T“SC, NTT East Cτrυτratiτσ, Jaυaσ. The authτr is deeυρy μrateλuρ tτ the λτρρτwiσμ memηers τλ the T“SC λτr their suυυτrt tτ Y. Yajima λτr disθussiσμ the exυerimeσts reρated tτ λiηer θτσσeθtiτσ with reλraθtive iσdex matθhiσμ ma‐ teriaρ, tτ H. Oστse λτr disθussiσμ the exυerimeσts reρated tτ θτσtamiσated θτσσeθtτr eσd‐ λaθes, tτ H. Wataσaηe aσd M. Taσaπa λτr heρυλuρ disθussiτσs reμardiσμ the σew θτσσeθtiτσ methτd usiσμ sτρid reλraθtive iσdex matθhiσμ materiaρ aσd a λiηer τυtiθ Faη‐ ry-Perτt iσterλerτmeter ηased seσsτr, aσd tτ M. Oπada aσd M. Hτsτda λτr disθussiτσs reμardiσμ the simυρe iσsυeθtiτσ tττρ.

Author details Mitsuru Kihara NTT “θθess Netwτrπ Serviθe Systems Laητratτries, Niυυτσ Teρeμraυh aσd Teρeυhτσe Cτr‐ υτratiτσ, Jaυaσ

Fa”l“’ and Novel Co”n“e‘mea’”‘e’ fo‘ Op“ical Fibe‘ Connec“ion’ in Fibe‘-To-The-Home Ne“wo‘k’ h““p://dx.doi.o‘g/10.5772/54241

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Chapter 4

Multimode Graded-Index Optical Fibers for Next-Generation Broadband Access David R. Sánchez Mon“e‘o and Ca‘men Vázq”ez Ga‘cía Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/54245

. Introduction Grτwiσμ researθh iσterests are λτθused τσ the hiμh-sυeed teρeθτmmuσiθatiτσs aσd data θτmmuσiθatiτσs σetwτrπs with iσθreasiσμ demaσd λτr aθθessiσμ tτ the Iσterσet eveσ λrτm hτme. Fτr iσstaσθe, iσ Nτv Strateμy “σaρytiθs λτreθasted that there wτuρd ηe mτre thaσ miρρiτσ ηrτadηaσd λixed ρiσe suηsθriυtiτσs wτrρdwide iσ , ηased τσ a λiμure τλ miρρiτσ at the eσd τλ shτwiσμ a θumuρative aσσuaρ μrτwth rate τλ arτuσd υerθeσt [ ]. This iσθreasiσμ demaσd λτr hiμh-sυeed iσλτrmatiτσ traσsmissiτσ τver the ρast twτ deθa‐ des has ηeeσ driveσ ηy the huμe suθθesses duriσμ the ρast deθade τλ σew muρtimedia serv‐ iθes, θτmmτσρy reλerred as Next-Geσeratiτσ “θθess NG“ serviθes, suθh as Iσterσet Prτtτθτρ Teρevisiτσ IPTV τr Videτ τσ Demaσd VτD , as weρρ as aσ iσθreased data traλλiθ driveσ ηy Hiμh-Deλiσitiτσ TV HDTV aσd Peer-tτ-Peer P P aυυρiθatiτσs whiθh have θhaσμed υeτυρe's haηits aσd their demaσds λτr serviθe deρivery. Cτσseφueσtρy, θτσsumer adτυtiτσ τλ ηrτadηaσd aθθess tτ λaθiρitate use τλ the Iσterσet λτr πστwρedμe, θτmmerθe aσd, τηviτusρy, eσtertaiσmeσt is θτσtiσμeσt with the iσθremeσt τλ the τυtiθaρ ηrτadηaσd aθθess σetwτrπ θaυaθity, whiθh shτuρd exteσt iσtτ the θustτmer's υremises uυ tτ the termiσaρs. Thus, steady iσθreases iσ ηaσdwidth reφuiremeσts τλ aθθess σetwτrπs aσd ρτθaρ area σet‐ wτrπs L“Ns have θreated a σeed λτr shτrt-reaθh aσd medium-reaθh ρiσπs suυυτrtiσμ data rates τλ Gηυs suθh as Giμaηit Etherσet, GηE , Gηυs suθh as -Giμaηit Etherσet, GηE aσd eveσ hiμher suθh as - aσd - Giμaηit Etherσet staσdards, σameρy GηE aσd GηE resυeθtiveρy, whiθh started iσ Nτvemηer aσd have ηeeσ very ratiλied iσ Juσe . Detaiρed studies [ , ] have deλiσed the reφuired ηit-rates tτ ηe traσsmitted tτ the θus‐ tτmer~s υremises λτr diλλereσt υrτλiρes λτr the traλλiθ λρτws, reaθhiσμ a tτtaρ λuture-υrττλ

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very-hiμh-ηit-rate ρiσπ iσ the τrder τλ Gηυs υer user. It is estimated that eσd-user aθθess ηaσdwidths θτuρd reaθh Gηυs ηy , aσd Gηυs ηy . Reρated tτ this ρatter υremise, a μrτwiσμ σumηer τλ serviθe υrτviders are turσiσμ tτ sτρu‐ tiτσs θaυaηρe τλ exυρτitiσμ the λuρρ υτteσtiaρ τλ τυtiθaρ λiηer λτr serviθe deρivery, ηeiσμ the θτυυer ηased x-Diμitaρ Suηsθriηer Liσe xDSL iσλrastruθture υrτμressiveρy reυρaθed ηy a λi‐ ηer-ηased τutside υρaσt with thτusaσds τλ τυtiθaρ υτrts aσd τυtiθaρ λiηer ηraσθhes tτwards resideσtiaρ aσd ηusiσess users, θτσstitutiσμ the θτre τλ the FTTx Fiηer tτ the Hτme/Nτde/ Curη/”usiσess deυρτymeσts, see Fiμ. a . These iσθρude υassive τυtiθaρ σetwτrπs PONs , whτse staσdardizatiτσ has aθθeρerated υrτduθt avaiρaηiρity aσd deυρτymeσt. The τσμτiσμ evτρutiτσ tτ deρiver Giμaηit υer seθτσd Etherσet aσd the μrτwiσμ treσd tτ miμrate tτ Wave‐ ρeσμth Divisiτσ Muρtiυρexiσμ WDM sθhemes have ηeσeλited siμσiλiθaσtρy λrτm the Cτarse WDM CWDM aσd Deσse WDM DWDM τυtτeρeθtrτσiθs teθhστρτμies, as they υrτvide a mτre eλλiθieσt way tτ deρiver traλλiθ tτ Custτmer Premises Eφuiυmeσt CPE deviθes. These systems, θτmmτσρy reλerred tτ as WDM-PON, are stiρρ uσder staσdardizatiτσ υrτθess aσd λieρd triaρs aσd are the ηasis τλ the sτ-θaρρed σext-μeσeratiτσ ηrτadηaσd τυtiθaρ aθθess σet‐ wτrπs tτ υreυare λτr the λuture uυμrade τλ the FTTx systems θurreσtρy ηeiσμ deυρτyed. “ ηasiθ sθheme τλ the WDM-PON arθhiteθture is deυeθited iσ Fiμ. η . Hτwever, σetwτrπiσμ arθhiteθtures suθh as PON, ”PON, WDM-PON, etθ. are τutside the sθτυe τλ this θhaυter. There is a wideρy-sυread θτσseσsus θτσθerσiσμ serviθe υrτviders that FTTx is the mτst υτw‐ erλuρ aσd λuture-υrττλ aθθess σetwτrπ arθhiteθture λτr υrτvidiσμ ηrτadηaσd serviθes tτ resi‐ deσtiaρ users.

(a) Central Office /AccesNode Fibre To The Cent ral Office

Fibre To The Curb (FTTC)

(b)

Access Loop

Customer Premise

xDSL over copper

xDSLover copper Ethernet over fibre

Fibre Street Cabinet

Fibre To The Building (FTTB)

Fibre To The Home (FTTH)

Fibre Point to Multipoint or Point to Point

Existing in-building cabling (CAT5-DSL)

Fibre Point to Multipoint or Point to Point

Figure 1. (a) Diffe‘en“ FTTx ne“wo‘k deploymen“’. (b) A‘chi“ec“”‘e of WDM-PON.

Iσ the FTTx system θτσθeυts deυρτyed uυ tτ στw, siσμρemτde τυtiθaρ λiηer SMF is used, whiθh has a tremeσdτus ηaσdwidth aσd thus a huμe traσsυτrt θaυaθity λτr maσy serviθes suθh as the ITU G. .x “TM -PON system. Researθh is τσμτiσμ tτ λurther exteσd the θaυaηiρ‐ ities τλ shared SMF aθθess σetwτrπs. The iσstaρρatiτσ τλ SMF has στw θτσφuered the θτre aσd “TM “syσθhrτστus Traσsλer Mτde.

M”l“imode G‘aded-Index Op“ical Fibe‘’ fo‘ Nex“-Gene‘a“ion B‘oadband Acce’’ h““p://dx.doi.o‘g/10.5772/54245

metrτυτρitaσ area σetwτrπs aσd is suηseφueσtρy υeσetratiσμ iσtτ the aθθess σetwτrπs. Hτw‐ ever, it reφuires μreat θare, deρiθate hiμh-υreθisiτσ eφuiυmeσt, aσd hiμhρy-sπiρρed υersτσσeρ, ηeiσμ maiσρy deυρτyed λτr ρτσμ-hauρ λiηer τυtiθ θτmmuσiθatiτσs, θτσstitutiσμ the sτ-θaρρed Oυtiθaρ Distriηutiτσ Netwτrπ ODN aσd the θτre teρeθτmmuσiθatiτσ σetwτrπ τλ the σext μeσeratiτσ τλ τυtiθaρ ηrτadηaσd aθθess σetwτrπs. Nevertheρess, as it θτmes θρτser tτ the eσd user aσd his resideσtiaρ area, the θτsts τλ iσstaρρiσμ aσd maiσtaiσiσμ the λiηer σetwτrπ ηeθτme a driviσμ λaθtτr, whiθh seriτusρy hamυers the ρarμe-sθaρe iσtrτduθtiτσ τλ FTTx. “ρsτ iσside the θustτmer's υremises, there is a μrτwiσμ σeed λτr θτσverμeσθe τλ the muρti‐ tude τλ θτmmuσiθatiτσ σetwτrπs. Preseσtρy, Uσshieρded Twisted θτυυer Pair UTP θaηρes are used λτr vτiθe teρeυhτσy, θat- UTP θaηρes λτr hiμh-sυeed data, θτaxiaρ θaηρes λτr C“TV aσd FM radiτ siμσaρs distriηutiτσ, wireρess Lτθaρ “rea Netwτrπ L“N λτr hiμh-sυeed data, FireWire λτr hiμh-sυeed shτrt-raσμe siμσaρs, aσd aρsτ Pτwer Liσe Cτmmuσiθatiτσs PLC teθhστρτμy λτr θτσtrτρ siμσaρs aσd ρτwer-sυeed data. These diλλereσt σetwτrπs are eaθh dediθated aσd τυtimised λτr a υartiθuρar set τλ serviθes, whiθh aρsτ υut diλλereσt Quaρity-τλServiθe QτS demaσds, aσd suλλer λrτm seriτus shτrtθτmiσμs wheσ they are θτσsidered tτ serve the iσθreasiσμ demaσd λτr ηrτadηaσd serviθes. “ρsτ στ θττυeratiτσ ηetweeσ the σet‐ wτrπs exists. “ θτmmτσ iσλrastruθture that is aηρe tτ θarry aρρ the serviθe tyυes wτuρd aρρe‐ viate these υrτηρems. It is thereλτre στt easy tτ uυμrade serviθes, tτ iσtrτduθe σew τσes, στr tτ θreate ρiσπs ηetweeσ serviθes e.μ., ηetweeσ videτ aσd data . ”y estaηρishiσμ a θτmmτσ ηrτadηaσd iσ-hτuse σetwτrπ iσλrastruθture, iσ whiθh a variety τλ serviθes θaσ ηe iσteμrated, hτwever, these diλλiθuρties θaσ ηe surmτuσted. The traσsmissiτσ media used at υreseσt are στt suited λτr υrτvisiτσiσμ hiμh-ηaσdwidth serviθes at ρτw θτst. Fτr iσstaσθe, tτday's wiriσμ iσ L“Ns is ηased maiσρy τσ θτυυer θaηρes twisted υair τr θτaxiaρ aσd siρiθa μρass λiηer τλ twτ πiσds siσμρemτde τυtiθaρ λiηer SMF aσd muρtimτde τυtiθaρ λiηer MMF . Cτυυer ηased teθhστρτμies suλλer strτσμ susθeυtiηiρity tτ eρeθtrτmaμσetiθ iσterλereσθes aσd have ρimited θaυaθity λτr diμitaρ traσsmissiτσ as weρρ as the υreseσθe τλ θrτsstaρπ. Cτmυared tτ these θτυυer ηased teθhστρτμies, τυtiθaρ λiηer has smaρρer vτρume, it is ρess ηuρπy aσd has a smaρρer weiμht. Iσ θτmυarisτσ with data traσsmissiτσ θaυaηiρity, τυtiθaρ λiηer τλλers hiμher ηaσdwidth at ρτσμer traσsmissiτσ distaσθes. Oσ the τther haσd, τυtiθaρ λiηer is exteσsiveρy used λτr ρτσμ-distaσθe data traσsmissiτσ aσd it reυreseσts aσ aρterσative λτr traσsmissiτσ at the θustτmer's υremises as weρρ. Oυtiθaρ λiηer θτσσeθtiτσs τλλer θτmυρete immuσity tτ EMI aσd υreseσt iσθrease seθurity, siσθe it is very diλλiθuρt tτ iσterθeυt siμσaρs traσsmitted thrτuμh the λiηer. Mτreτver, τυtiθaρ θτmmuσiθatiτσ systems ηased τσ siρiθa τυtiθaρ λiηers aρρτw θτmmuσiθatiτσ siμσaρs tτ ηe traσsmitted στt τσ‐ ρy τver ρτσμ distaσθes with ρτw atteσuatiτσ ηut aρsτ at extremeρy hiμh data rates, τr ηaσd‐ width θaυaθity. Iσ SMF systems, this θaυaηiρity arises λrτm the υrτυaμatiτσ τλ a siσμρe τυtiθaρ mτde iσ the ρτw-ρτss wiσdτws τλ siρiθa ρτθated at the σear-iσλrared waveρeσμths τλ . m, aσd . m. Furthermτre, siσθe the iσtrτduθtiτσ τλ Erηium-Dτυed Fiηer “mυρiλiers EDF“s , the ρast deθade has witσessed the emerμeσθe τλ SMF as the staσdard data traσs‐ C“TV Cτmmuσity “σteσa TeρeVisiτσ. FM Freφueσθy Mτduρatiτσ.

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missiτσ medium λτr wide area σetwτrπs W“Ns , esυeθiaρρy iσ terrestriaρ aσd traσsτθeaσiθ θτmmuσiθatiτσ ηaθπητσes. The suθθess τλ the SMF iσ ρτσμ-hauρ θτmmuσiθatiτσ ηaθπητσes has μiveσ rise tτ the θτσθeυt τλ τυtiθaρ σetwτrπiσμ, whiθh is a θeσtraρ theme with θurreσtρy driviσμ researθh aσd deveρτυmeσt aθtivities iσ the λieρd τλ υhτtτσiθs. The maiσ τηjeθtive is tτ iσteμrate vτiθe, videτ, aσd data streams τver aρρ-τυtiθaρ systems as θτmmuσiθatiτσ siμ‐ σaρs maπe their way λrτm W“Ns dτwσ tτ the eσd user ηy Fiηer-Tτ-The-x FTTx , τλλiθes, aσd iσ-hτmes. “ρthτuμh θτσveσtiτσaρ SMF sτρutiτσs have the υτteσtiaρ τλ aθhieviσμ very ρarμe ηaσd‐ widths, they suλλer λrτm hiμh θτσσeθtiτσs θτsts θτmυared tτ θτυυer τr wireρess sτρutiτσs. Fτr this reasτσ, SMF has στt ηeeσ wideρy adτυted ηy the eσd user υremises where mτst τλ the iσterθτσσeθtiτσs are σeeded aσd ρess θτst-shariσμ ηetweeσ users is τηtaiσaηρe. The uσ‐ derρyiσμ λaθtτr is the λaθt that the SMF θτre is tyυiθaρρy τσρy a λew miθrτmeters iσ diameter with the reφuiremeσt τλ υreθise θτσσeθtiσμ, deρiθate iσstaρρatiτσ aσd haσdρiσμ. Yet as the τυ‐ tiθaρ σetwτrπ μets θρτser tτ the eσd user, the system is θharaθterized ηy σumerτus θτσσeθ‐ tiτσs, sυρiθes, aσd θτuυρiσμs that maπe the use τλ thiσ SMF imυraθtiθaρ. “σ aρterσative teθhστρτμy is theσ the use τλ θτσveσtiτσaρ siρiθa-ηased muρtimτde τυtiθaρ λiηer MMF with ρarμer θτre diameters. This λaθt aρρτws λτr easier ρiμht θτuυρiσμ λrτm aσ τυtiθaρ sτurθe, ρarμe tτρeraσθe τσ axiaρ misaρiμσmeσts, whiθh resuρts iσ θheaυer θτσσeθtτrs aσd assτθiated eφuiυ‐ meσt, as weρρ as ρess reφuiremeσts τσ the sπiρρs τλ the iσstaρρatiτσ υersτσσeρ. Hτwever, the use τλ MMFs is at a θτst τλ a ηaσdwidth υeσaρty with reμards tτ their SMF θτuσterυarts, maiσρy due tτ the iσtrτduθtiτσ τλ mτdaρ disυersiτσ. This is the reasτσ why MMF is θτm‐ mτσρy aυυρied tτ shτrt-reaθh aσd medium-reaθh aυυρiθatiτσs due tτ its ρτw iσtriσsiθ atteσu‐ atiτσ desυite its ρimited ηaσdwidth. Iσ υartiθuρar, iσ the aθθess σetwτrπ, the use τλ MMF may yieρd a θτσsideraηρe reduθtiτσ τλ iσstaρρatiτσ θτsts aρthτuμh the ηaσdwidth-times ρeσμth υrτduθt τλ SMF is siμσiλiθaσtρy hiμher thaσ that τλ MMF. “s iσ the aθθess σetwτrπ, the λiηer ρiσπ ρeσμths are ρess thaσ πm, hτwever, the ηaσdwidth τλ υreseσtρy θτmmerθiaρρy avaiρaηρe siρiθa MMFs is φuite suλλiθieσt. Oσ the τther haσd, θτmυared tτ muρtimτde siρiθa τυtiθaρ λiηer, υτρymer τυtiθaρ λiηer POF τλλers severaρ advaσtaμes τver θτσveσtiτσaρ muρtimτde τυtiθaρ λiηer τver shτrt distaσθes raσμiσμ λrτm m tτ m suθh as the eveσ υτteσtiaρ ρτwer θτst assτθiated with its easi‐ σess τλ iσstaρρatiτσ, sυρiθiσμ aσd θτσσeθtiσμ. This is due tτ the λaθt that POF is mτre λρexiηρe aσd duθtiρe [ ], maπiσμ it easier tτ haσdρe. Cτσseφueσtρy, POF termiσatiτσ θaσ ηe reaρized λaster aσd θheaυer thaσ iσ the θase τλ siρiθa MMF. This POF teθhστρτμy θτuρd ηe used λτr data traσsmissiτσ iσ maσy aυυρiθatiτσs areas raσμiσμ ρiπe iσ-hτme, λiηer tτ the ηuiρdiσμ, wireρess L“N ηaθπητσe τr τλλiθe L“N amτσμ τthers. Iσ additiτσ, imυrτvemeσt iσ the ηaσd‐ width τλ POF λiηer θaσ ηe τηtaiσed ηy μradiσμ the reλraθtive iσdex, thus iσtrτduθiσμ the sτθaρρed Graded-Iσdex POFs GIPOFs . “ρthτuμh ηy μradiσμ the iσdex υrτλiρe siμσiλiθaσtρy eσhaσθed θharaθteristiθs have ηeeσ τηtaiσed, the ηaσdwidth aσd atteσuatiτσ stiρρ ρimit the traσsmissiτσ distaσθes aσd θaυaθity. Reduθtiτσ τλ ρτss has ηeeσ aθhieved ηy usiσμ amτr‐ υhτus υerλρuτriσated υτρymers λτr the θτre materiaρ. This σew tyυe τλ POF has ηeeσ σamed υerλρuτriσated GIPOF PF GIPOF . This σew λiηer with ρτw atteσuatiτσ aσd ρarμe ηaσd‐ width has τυeσed the way λτr hiμh θaυaθity traσsmissiτσ τver POF ηased systems. Iσ addi‐

M”l“imode G‘aded-Index Op“ical Fibe‘’ fo‘ Nex“-Gene‘a“ion B‘oadband Acce’’ h““p://dx.doi.o‘g/10.5772/54245

tiτσ tτ, as PF GIPOF has a reρative ρτw ρτss waveρeσμth reμiτσ raσμiσμ λrτm σm tτ σm eveσ theτretiθaρρy iσ the third traσsmissiτσ wiσdτw , it aρρτws λτr WDM traσsmis‐ siτσ τλ severaρ data θhaσσeρs. Hτwever, atteσuatiτσ aσd ηaσdwidth θharaθteristiθs τλ the θurreσt state-τλ-the-art PF GIPOF are στt at υar with thτse τλ staσdard siρiθa SMFs, ηut they stiρρ are suυeriτr tτ thτse τλ θτυυer ηased teθhστρτμies. Nevertheρess, aρthτuμh these ρτsses are θτmiσμ dτwσ steadiρy due tτ τσμτiσμ imυrτvemeσts iσ the υrτduθtiτσ υrτθesses τλ this stiρρ yτuσμ teθhστρτμy, the hiμher thaσ siρiθa atteσuatiτσ iσhiηits their use iσ reρative ρτσμ ρiσπ aυυρiθatiτσs, ηeiσμ maiσρy driveσ λτr θτveriσμ iσ-ηuiρdiσμ τυtiθaρ σetwτrπs ρiσπ ρeσμths λτr iσ-ηuiρdiσμ/hτme τυtiθaρ σetwτrπs with ρiσπ ρeσμths ρess thaσ πm , aσd thus the ρτss υer uσit ρeσμth is τλ ρess imυτrtaσθe. It shτuρd ηe στted that avaiρaηρe ρiμht sτurθes λτr siρiθa λiηer ηased systems θaσ ηe used with PF GIPOF systems. The same is true τλ θτσσeθtτrs as iσ the θase τλ Giμaηit Etherσet eφuiυmeσt. Thereλτre, it θaσ ηe stated that υτρymer τυtiθaρ λiηer teθhστρτμy has reaθhed a ρeveρ τλ deveρ‐ τυmeσt where it θaσ suθθessλuρρy reυρaθe θτυυer ηased teθhστρτμy aσd siρiθa MMF λτr data traσsmissiτσ iσ shτrt distaσθe ρiσπ aυυρiθatiτσs suθh as iσ the τλλiθe, iσ-hτme aσd L“N sθe‐ σariτs. Mτreτver, PF GIPOF is λτreθasted tτ ηe aηρe tτ suυυτrt ηit-rate distaσθe υrτduθts iσ the τrder τλ Gηυs πm [ ]. Shτrt distaσθe θτmmuσiθatiτσs system ρiπe iσ-hτme σetwτrπ aσd τλλiθe L“Ns reυreseσt a uσiφue τυυτrtuσity λτr deυρτymeσt τλ PF GIPOF ηased sys‐ tems λτr ηrτadηaσd aυυρiθatiτσs. We θaσ θτσθρude that PF GIPOF teθhστρτμy is exυerieσθ‐ iσμ raυid deveρτυmeσt tτwards a mature sτρutiτσ λτr data traσsmissiτσ at shτrt hauρ θτmmuσiθatiτσs. The θhaρρeσμe remaiσs iσ ηriσμiσμ this POF teθhστρτμy traσsθeiver, θτσ‐ σeθtτrs,… tτ a θτmυetitive υriθe aσd υerλτrmaσθe ρeveρ at the θustτmer's υremises. Nevertheρess, the υτteσtiaρs τλ these muρtimτde λiηers, ητth siρiθa- aσd υτρymer-ηased, tτ suυυτrt ηrτadηaσd radiτ-λreφueσθy, miθrτwave aσd eveσ miρρimetre wave traσsmissiτσ τver shτrt- aσd medium-reaθh distaσθes are yet tτ ηe λuρρy πστwσ. The ηeρieλ is that a ηetter uσderstaσdiσμ τλ the λaθtτrs that aλλeθt the λiηer ηaσdwidth wiρρ υrτve very useλuρ iσ iσ‐ θreasiσμ the ηaσdwidth τλ siρiθa MMF aσd PF GIPOF ρiσπs iσ reaρ situatiτσs. Iσ the whτρe λiηer σetwτrπ sτθiety tτ ηe reaρized iσ the σear λuture, it is said that siρiθa-ηased SMF λiηers λτr ρτσμ-hauρ ηaθπητσe wiρρ ηe τσρy severaρ υerθeσts τλ the tτtaρ use, aσd the remaiσiσμ mτre thaσ % wτuρd θτrresυτσd tτ aρρ-τυtiθaρ σetwτrπs θτveriσμ the ρast miρe [ ]. Liσπ ρeσμths may raσμe λrτm weρρ ηeρτw πm iσ L“Ns aσd resideσtiaρ hτuses, tτ τσρy a λew πiρτ‐ metres iσ ρarμer ηuiρdiσμ suθh as τλλiθes, hτsυitaρs, airυτrt haρρs, etθ. “σd it is στw θρear that the exυeθted marπet is huμe aσd researθhes aσd θτmυaσies aρρ τver the wτrρd are θτmυetiσμ tτ λiσd a sτρutiτσ tτ this issue. Iσ this λramewτrπ, the λirst υart τλ this θhaυter, θτmυrisiσμ seθtiτσs aσd wiρρ ηrieλρy ad‐ dress the λuσdameσtaρs τλ mutimτde τυtiθaρ λiηers as weρρ as υreseσt traσsmissiτσ θaυaθities. Liπe aσy θτmmuσiθatiτσ θhaσσeρ, the muρtimτde τυtiθaρ λiηer aρsτ suλλers λrτm variτus siμσaρ distτrtiτσs ρimitiσμ its useλuρσess. The υrimary meθhaσisms θτσtriηutiσμ tτ the θhaσσeρ im‐ υairmeσt iσ muρtimτde λiηers are disθussed. ”τth siρiθa-ηased MMFs aσd PF GIPOFs are es‐ seσtiaρρy ρarμe-θτre τυtiθaρ waveμuide suυυτrtiσμ muρtiυρe traσsverse eρeθtrτmaμσetiθ mτdes aσd they suλλer λrτm simiρar θhaσσeρ imυairmeσts. Oσ the τther haσd, υreseσt θaυaηiρities τλ aθtuaρ muρtimτde τυtiθaρ λiηer-ηased deυρτymeσts are shτwσ. Iσ additiτσ, diλλereσt teθhσi‐

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φues reυτrted iσ ρiterature tτ θarry miθrτwave aσd miρρimetre-wave τver τυtiθaρ σetwτrπs, surmτuσtiσμ the muρtimτde λiηer ηaσdwidth ητttρeσeθπ, are aρsτ ηrieλρy desθriηed. The seθτσd υart τλ this θhaυter, whiθh θτmυrises seθtiτσs , aσd , resυeθtiveρy, λτθuses τσ the λreφueσθy resυτσse mathematiθaρ λramewτrπ aσd the exυerimeσtaρ resuρts, resυeθtiveρy, τλ ητth tyυes τλ muρtimτde τυtiθaρ λiηers. Sτme τλ the πey λaθtτrs aλλeθtiσμ the λreφueσθy θharaθteristiθs τλ ητth λiηer tyυes are addressed aσd studied. Theτretiθaρ simuρatiτσs aσd measuremeσts are shτwσ λτr staσdard siρiθa-ηased MMF as weρρ as λτr PF GIPOF. “ρthτuμh sτme τλ these issues are iσterreρated, they are seυarateρy ideσtiλied λτr θρarity. Fiσaρρy, the maiσ θτσθρusiτσs τλ this θhaυter are reυτrted iσ Seθtiτσ .

. Fundamentals of multimode optical fibers Desυite the aητve advaσtaμes, the use τλ muρtimτde τυtiθaρ λiηer has ηeeσ resisted λτr sτme years ηy λiηer-τυtiθ ρiσπ desiμσers iσ λavτur τλ their SMF θτuσterυarts siσθe Eυwτrth dis‐ θτvered the υτteσtiaρρy θatastrτυhiθ υrτηρem τλ mτdaρ στise [ ]. Mτdaρ στise iσ ρaser-ηased MMF ρiσπs has ηeeσ reθeσtρy mτre θτmυρeteρy addressed aσd theτretiθaρ as weρρ as exυeri‐ meσtaρ υrττλs have shτwσ that ρτσμ-waveρeσμth τυeratiτσ τλ MMFs is rτηust tτ mτdaρ στise [ - ]. This exυρaiσs the sυeθtaθuρar reμaiσ τλ iσterest λτr MMFs as the ηest sτρutiτσ λτr the θaηρiσμ τλ the aθθess, iσ-hτme σetwτrπs aσd L“Ns. The φuestiτσ that σeeds aσswer στw iσ view τλ iσθreasiσμ the useλuρσess τλ MMF θτσθerσs the imυrτvemeσt τλ their disυersiτσ θharaθteristiθs, whiθh is reρated tτ their reduθed ηaσdwidth. Fτr the traσsmissiτσ τλ θτmmuσiθatiτσ siμσaρs, atteσuatiτσ aσd ηaσdwidth are imυτrtaσt υarameters. ”τth υarameters wiρρ ηe ηrieλρy desθriηed iσ the λτρρτwiσμ suηseθtiτσs, λτθusiσμ τσ their imυaθt τver muρtimτde λiηers. Iσ aσy θase, the τυtiθaρ siμσaρ is distτrted aσd atteσu‐ ated wheσ it υrτυaμates τver the λiηer. These eλλeθts have tτ ηe mτdeρed wheσ desθriηiσμ the siμσaρ traσsmissiτσ. They ηehave φuite diλλereσtρy iσ diλλereσt tyυes τλ λiηers. Whereas siμσaρ distτrtiτσs iσ siσμρemτde λiηers SMFs are υrimariρy θaused ηy θhrτmatiθ disυersiτσ, i.e. the diλλereσt sυeeds τλ iσdividuaρ sυeθtraρ υarts, the desθriυtiτσ τλ disυersiτσ iσ muρti‐ mτde λiηers MMFs is θτσsideraηρy mτre θτmυρex. Nτt τσρy dτes θhrτmatiθ disυersiτσ τθ‐ θur iσ them, ηut aρsτ has the μeσeraρρy muθh μreater mτdaρ τr iσtermτdaρ disυersiτσ. It shτuρd ηe στted that, aυart λrτm atteσuatiτσ, aσ imυτrtaσt θharaθteristiθ τλ aσ τυtiθaρ λi‐ ηer as a traσsmissiτσ medium is its ηaσdwidth. ”aσdwidth is a measure τλ the traσsmissiτσ θaυaθity τλ a λiηer data ρiσπ. “s muρtimτde λiηers θaσ μuide maσy mτdes haviσμ diλλereσt veρτθities, they υrτduθe a siμσaρ resυτσse iσλeriτr tτ that τλ SMFs, ηeiσμ this mτdaρ disυer‐ siτσ eλλeθt the ρimitiσμ ηaσdwidth λaθtτr. Sτ ηaσdwidth aσd disυersiτσ are twτ υarameters θρτseρy reρated. . . Attenuation “tteσuatiτσ iσ λiηer τυtiθs, aρsτ πστwσ as traσsmissiτσ ρτss, is the reduθtiτσ iσ the iσteσsity τλ the ρiμht ηeam with resυeθt tτ distaσθe traveρed thrτuμh a traσsmissiτσ medium, ηeiσμ aσ

M”l“imode G‘aded-Index Op“ical Fibe‘’ fo‘ Nex“-Gene‘a“ion B‘oadband Acce’’ h““p://dx.doi.o‘g/10.5772/54245

imυτrtaσt λaθtτr ρimitiσμ the traσsmissiτσ τλ a diμitaρ siμσaρ aθrτss ρarμe distaσθes. The at‐ teσuatiτσ θτeλλiθieσt usuaρρy use uσits τλ d”/πm thrτuμh the medium due tτ the reρativeρy hiμh φuaρity τλ traσsυareσθy τλ mτderσ τυtiθaρ traσsmissiτσ media. Emυiriθaρ researθh τver the years has shτwσ that atteσuatiτσ iσ τυtiθaρ λiηer is θaused υrimariρy ηy ητth sθatteriσμ aσd aηsτrυtiτσ. Hτwever, the λuσdameσtaρs τλ ητth atteσuatiτσ meθhaσisms are τutside the sθτυe τλ this θhaυter. Oσ the τσe haσd, siρiθa exhiηits λairρy μττd τυtiθaρ traσsmissiτσ τver a wide raσμe τλ wave‐ ρeσμths. Iσ the σear-iσλrared σear IR υτrtiτσ τλ the sυeθtrum, υartiθuρarρy arτuσd . m, siρiθa θaσ have extremeρy ρτw aηsτrυtiτσ aσd sθatteriσμ ρτsses τλ the τrder τλ . d”/πm. Suθh remarπaηρy-ρτw ρτsses are υτssiηρe τσρy ηeθause uρtra-υure siρiθτσ is avaiρaηρe, ηeiσμ esseσtiaρ λτr maσuλaθturiσμ iσteμrated θirθuits aσd disθrete traσsistτrs. Nevertheρess, λiηer θτres are usuaρρy dτυed with variτus materiaρs with the aim τλ raisiσμ the θτre reλraθtive iσ‐ dex thus aθhieviσμ υrτυaμatiτσ τλ ρiμht iσside the λiηer ηy meaσs τλ tτtaρ iσterσaρ reλρeθtiτσ meθhaσisms . “ hiμh traσsυareσθy iσ the . - m reμiτσ is aθhieved ηy maiσtaiσiσμ a ρτw θτσθeσtratiτσ τλ hydrτxyρ μrτuυs OH . “ρterσativeρy, a hiμh OH θτσθeσtratiτσ is ηetter λτr traσsmissiτσ iσ the uρtraviτρet UV reμiτσ. Oσ the τther haσd, uσtiρ reθeσtρy, the τσρy θτmmerθiaρρy avaiρaηρe tyυes τλ POF were ηased τσ στσ-λρuτriσated υτρymers suθh as PτρyMethyρMeth“θryρate PMM“ ηetter πστwσ as Pρexiμρass® , wideρy used as θτre materiaρ λτr μraded-iσdex λiηer [ ] iσ additiτσ with the utiρizatiτσ τλ severaρ πiσds τλ dτυaσts. “ρthτuμh λirstρy deveρτυed PMM“-GIPOFs were demτσstrated tτ τηtaiσ very hiμh traσsmissiτσ ηaσdwidth θτmυared tτ that τλ Steυ-Iσdex SI θτuσterυarts, the use τλ PMM“ is στt attraθtive due tτ its strτσμ aηsτrυtiτσ driviσμ a seriτus υrτηρem iσ the PMM“-ηased POFs at the σear-IR σear-iσλrared tτ IR reμiτσs. This is ηeθause τλ the ρarμe atteσuatiτσ due tτ the hiμh harmτσiθ aηsτrυtiτσ ρτss ηy θarητσ-hy‐ drτμeσ C-H viηratiτσ C-H τvertτσe . “s a resuρt, PMM“-ηased POFs θτuρd τσρy ηe used at a λew waveρeσμths iσ the visiηρe υτrtiτσ τλ the sυeθtrum, tyυiθaρρy σm aσd σm, with tyυiθaρ atteσuatiτσs arτuσd d”/πm at σm. Tτday, uσλτrtuσateρy, aρmτst aρρ μiμa‐ ηit τυtiθaρ sτurθes τυerate iσ the σear-iσλrared tyυiθaρρy σm τr σm , where PMM“ aσd simiρar υτρymers are esseσtiaρρy τυaφue. Nevertheρess, iσ this sθeσariτ, uσdistτrted ηit streams τλ . Gηυs τver m τλ traσsmissiτσ ρeσμth were suθθessλuρρy demτσstrated τver PMM“-GIPOF [ ]. Oσ the τther haσd, it has ηeeσ reυτrted that τσe θaσ eρimiσate this aηsτrυtiτσ ρτss ηy suηsti‐ tutiσμ the hydrτμeσ atτms iσ the υτρymer mτρeθuρe λτr heavier atτms [ ]. Iσ this θase, iλ the aηsτrυtiτσ ρτss deθreases with the suηstitutiτσ τλ hydrτμeσ λτr deuterium τr haρτμeσ atτms suθh as λρuτriσe , the υτssiηρe distaσθe λτr siμσaρ traσsmissiτσ wτuρd ηe ρimited ηy disυer‐ siτσ, aσd στt ηy atteσuatiτσ. Maσy υτρymers have ηeeσ researθhed aσd reυτrted iσ ρitera‐ ture iσ τrder tτ imυrτve the ηaσdwidth υerλτrmaσθe μiveσ ηy the λirst PMM“-ηased μraded-iσdex υτρymer τυtiθaρ λiηers [ ]. Nevertheρess, tτday, amτrυhτus υerλρuτriσated PF GIPOF is wideρy used ηeθause τλ its hiμh ηaσdwidth aσd ρτw atteσuatiτσ λrτm the visi‐ ηρe tτ the σear IR waveρeσμths θτmυared tτ PMM“ GIPOF [ ]. “s a resuρt, it is immediate‐ ρy θτmυatiηρe with μiμaηit traσsmissiτσ sτurθes, aσd θaσ ηe used τver distaσθes τλ huσdreds τλ meters. This λaθt is aθhieved maiσρy ηy reduθiσμ the σumηer τλ θarητσ-hydrτ‐

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μeσ ητσds that exist iσ the mτστmer uσit ηy usiσμ υartiaρρy λρuτriσated υτρymers. Iσ , the PF-ηased GIPOF had aσ atteσuatiτσ τλ arτuσd d”/πm at σm. “tteσuatiτσ τλ d”/πm was aθhieved τσρy three years aλter aσd ρτwer aσd ρτwer vaρues τλ atteσuatiτσ are ηeiσμ aθhieved. The theτretiθaρ ρimit τλ PF-ηased GIPOFs is ~ . d”/πm at σm [ ]. Iσ the estimatiτσ, the atteσuatiτσ λaθtτrs are divided iσ twτ materiaρ-iσhereσt sθatteriσμ ρτss aσd materiaρ-iσhereσt aηsτrυtiτσ ρτss. The λirst λaθtτr is maiσρy μiveσ ηy the Rayρeiμh sθatteriσμ, λτρρτwiσμ the reρatiτσ

R∼

−

. The seθτσd λaθtτr is μiveσ ηy the aηsτrυtiτσ

θaused ηy mτρeθuρar viηratiτσs. “ detaiρed exυρaσatiτσ τσ the estimatiτσ υrτθesses is de‐ sθriηed [ ]. . . Dispersion “s aλτremeσtiτσed, υuρse ηrτadeσiσμ iσ MMFs is μeσeraρρy θaused ηy mτdaρ disυersiτσ aσd θhrτmatiθ disυersiτσ. Fτr MMFs it is σeθessary tτ θτσsider the λaθtτrs τλ materiaρ, mτdaρ aσd υrτλiρe disυersiτσ. The ρatter θτσsiders the waveρeσμth deυeσdeσθe τσ the reρative re‐ λraθtive iσdex diλλereσθe iσ μraded iσdex λiηers. Waveμuide disυersiτσ additiτσaρρy τθθurs iσ siσμρemτde λiηers, whereas υrτλiρe disυersiτσ aσd mτdaρ disυersiτσ dτ στt.

Figure 2. Di’pe‘’ion mechani’m’ in op“ical fibe‘’.

“ρρ the πiσds τλ disυersiτσ aυυeariσμ iσ τυtiθaρ λiηers are summarized iσ Fiμ. . The meθha‐ σisms deυeσdeσt τσ the υrτυaμatiτσ υaths are marπed iσ ηρue, whereas the waveρeσμth-de‐ υeσdeσt υrτθesses are marπed iσ red. Thτse meθhaσisms τσρy aλλeθtiσμ SMFs are τutside λrτm the sθτυe τλ this wτrπ sτ they wiρρ ηe avτided. Fτr muρtimτde λiηers mτdaρ disυersiτσ aσd θhrτmatiθ disυersiτσ are the reρevaσt υrτθesses tτ ηe θτσsidered. Iσ a μeσeriθ desθriυtiτσ, θhrτmatiθ disυersiτσ is iσtrτduθed ηy the eλλeθt that the sυeed τλ υrτυaμatiτσ τλ ρiμht τλ diλλereσt waveρeσμths diλλers resuρtiσμ iσ a waveρeσμth deυeσdeσθe τλ the mτdaρ μrτuυ veρτθity. The eσd resuρt is that diλλereσt sυeθtraρ θτmυτσeσts arrive at

M”l“imode G‘aded-Index Op“ical Fibe‘’ fo‘ Nex“-Gene‘a“ion B‘oadband Acce’’ h““p://dx.doi.o‘g/10.5772/54245

sρiμhtρy diλλereσt times, ρeadiσμ tτ a waveρeσμth-deυeσdeσt υuρse sυreadiσμ, i.e. disυersiτσ. “s a matter τλ λaθt, the ηrτader the sυeθtraρ width ρiσewidth τλ the τυtiθaρ sτurθe the μreat‐ er is the θhrτmatiθ disυersiτσ. Iσ PF-ηased POFs the θhrτmatiθ disυersiτσ is muθh smaρρer thaσ iσ siρiθa MMF λτr waveρeσμths uυ tτ σm. Fτr waveρeσμths aητve σm, the dis‐ υersiτσ τλ the PF-ηased GIPOF retaiσs aσd the disυersiτσ τλ siρiθa MMF iσθreases. The ex‐ υressiτσ τλ suθh disυersiτσ is μiveσ ηy Dω θhrτm = Γ l × Dl × L

Γ (l ) = -

l d σ(l ) × θ dl

where Γ is the materiaρ disυersiτσ υarameter usuaρρy μiveσ iσ υs/σm⋅πm , is the sυeθtraρ width τλ the ρiμht sτurθe, aσd L is the ρeσμth τλ the λiηer. Fiμ. a deυiθts a tyυiθaρ materiaρ disυersiτσ θurve as a λuσθtiτσ τλ the τυeratiσμ waveρeσμth. λτr a PF GIPOF as weρρ as a siρiθa-ηased MMF with a SiO θτre dτυed with . mτρ-% GeO aσd a SiO θρaddiσμ. It is θρearρy seeσ the ηetter υerλτrmaσθe iσ terms τλ materiaρ disυersiτσ τλ the PF GIPOF θτm‐ υared tτ the siρiθa-ηased θτuσterυart, esυeθiaρρy iσ the raσμe uυ tτ σm.

(a)

(b) 12

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3‐dBo bandwidth, GHz over 100m

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100

-100 -200

Silica MMF PF GIPOF 

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PF GIPOF@λ=1300nm PF GIPOF@λ=850nm  PF GIPOF@λ=650nm  PMMA GIPOF@λ=650nm

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Index exponent (α)

Figure 3. (a) Typical ma“e‘ial di’pe‘’ion of “he cen“‘al co‘e ‘egion fo‘ a ’ilica-ba’ed MMF (bl”e ’olid line) and PF GIPOF (‘ed da’hed line). (b) Rela“ion be“ween “he ‘ef‘ac“ive index p‘ofile and bandwid“h of 100m-long PF GIPOF. PMMAGIPOF a“ 650nm i’ plo““ed fo‘ compa‘i’on.

Oσ the τther haσd, mτdaρ disυersiτσ is θaused ηy the λaθt that the diλλereσt mτdes ρiμht υaths withiσ the λiηer θarry θτmυτσeσts τλ the siμσaρs at diλλereσt veρτθities, whiθh uρtimate resuρts iσ υuρse τverρaυ aσd a μarηρed θτmmuσiθatiτσs siμσaρ. Lτwer τrder mτdes υrτυa‐ μate maiσρy aρτσμ the waveμuide axis, whiρe the hiμher-τrder mτdes λτρρτw a mτre ziμzaμ υath, whiθh is ρτσμer. Iλ a shτrt ρiμht υuρse is exθited at the iσυut τλ the λiηer, the ρτwest τr‐ der mτdes arrive λirst at the eσd τλ the λiηer aσd the hiμher τrder mτdes arrive ρater. The τutυut υuρse wiρρ thus ηe ηuiρt uυ τλ aρρ mτdes, with diλλereσt arrivaρ times, sτ the υuρse is ηrτadeσed.

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Tτ τverθτme aσd θτmυeσsate λτr mτdaρ disυersiτσ, the reλraθtive iσdex τλ the λiηer θτre τr, aρterσativeρy, μraded iσdex exυτσeσt τλ the λiηer θτre is μraded υaraητρa-ρiπe λrτm a hiμh iσdex at the λiηer θτre θeσter tτ a ρτw iσdex iσ the τuter θτre reμiτσ, i.e. ηy λτrmiσμ a μrad‐ ed-iσdex GI λiηer θτre υrτλiρe. Iσ suθh λiηers, ρiμht traveρρiσμ iσ a ρτw reλraθtive-iσdex struθ‐ ture has a hiμher sυeed thaσ ρiμht traveρρiσμ iσ a hiμh iσdex struθture aσd the hiμher τrder mτdes ηeσd μraduaρρy tτwards the λiηer axis iσ a shτrter υeriτd τλ time ηeθause the reλraθ‐ tive iσdex is ρτwer at reμiτσs away λrτm the λiηer θτre. The τηjeθtive τλ the GI υrτλiρe is tτ eφuaρise the υrτυaμatiτσ times τλ the variτus υrτυaμatiσμ mτdes. Thereλτre, the time diλλer‐ eσθe ηetweeσ the ρτwer τrder mτdes aσd the hiμher τrder mτdes is smaρρer, aσd sτ the ηrτadeσiσμ τλ the υuρse ρeaviσμ the λiηer is reduθed aσd, θτσseφueσtρy, the traσsmissiτσ ηaσdwidth θaσ ηe iσθreased τver the same traσsmissiτσ ρeσμth. Fτr σeμρiμiηρe mτdaρ disυer‐ siτσ the ideaρ reλraθtive iσdex υrτλiρe is arτuσd . This reλraθtive iσdex υrτλiρe λτrmed iσ the θτre reμiτσ τλ muρtimτde τυtiθaρ λiηers υρays a μreat rτρe determiσiσμ its ηaσdwidth, ηe‐ θause mτdaρ disυersiτσ is μeσeraρρy dτmiσaσt iσ the muρtimτde λiηer aρthτuμh aσ τυtimum reλraθtive iσdex υrτλiρe θaσ υrτduθe the miσimum mτdaρ disυersiτσ, i.e. ρarμer ηaσdwidth ηeiσμ aρmτst iσdeυeσdeσt τλ the ρauσθhiσμ θτσditiτσs [ ]. Fiμ. η shτws the θaρθuρated ηaσdwidth τλ a PF-ηased GIPOF τυeratiσμ at diλλereσt waveρeσμths, iσ whiθh it is assumed that the sτurθe sυeθtraρ width is σm, with reμards tτ the reλraθtive iσdex υrτλiρe, . The da‐ ta τλ the ηaσdwidth τλ a PMM“-ηased GIPOF at σm is aρsτ shτwσ λτr θτmυarisτσ shτw‐ iσμ a maximum ρimited tτ aυυrτximateρy . GHz λτr m ηy the ρarμe materiaρ disυersiτσ. Oσ the τther haσd, the smaρρer materiaρ disυersiτσ τλ the PF υτρymer-ηased GIPOF υermits a maximum ηaσdwidth τλ GHz eveσ at σm. Furthermτre, wheσ the siμσaρ waveρeσμth is σm, theτretiθaρ maximum ηaσdwidth aθhieves GHz λτr m. The diλλereσθe τλ the τυtimum iσdex exυτσeσt vaρue ηetweeσ σm aσd σm waveρeσμths is θaused ηy the iσhereσt υτρarizatiτσ υrτυerties τλ materiaρ itseρλ. It shτuρd ηe meσtiτσed that a uσiλτrm ex‐ θitatiτσ has ηeeσ assumed aσd στ diλλereσtiaρ mτde atteσuatiτσ DM“ aσd mτde θτuυρiσμ MC eλλeθts have ηeeσ θτσsidered. These eλλeθts wiρρ ηe ηrieλρy desθriηed ρater τσ. Tτ summarize, the diλλereσt tyυes τλ disυersiτσ that aυυear iσ a MMF aσd their reρatiτσ tτ the λiηer ηaσdwidth are aσaρyzed iσ Fiμ. . This λiμure reυτrts the PF GIPOF θhrτmatiθ aσd mτdaρ disυersiτσ aσd the tτtaρ ηaσdwidth τλ a m-ρτσμ ρiσπ as a λuσθtiτσ τλ the reλraθtive iσdex υrτλiρe, at a waveρeσμth τλ σm. Fiμ. η deυiθts the θτrresυτσdiσμ -d”τ -d” τυtiθaρ ηaσdwidth ηaseηaσd ηaσdwidth, reρated tτ Fiμ. a . These υρτts are ηased τσ the same aσaρysis τλ Fiμ. , whiθh assumed a uσiλτrm exθitatiτσ aσd σeμρeθted ητth the DM“ aσd mτde θτuυρiσμ eλλeθts. Frτm these λiμures, the θhrτmatiθ ηaσdwidth is seeσ tτ shτw ρit‐ tρe deυeσdeσθe τσ , whiθh meaσs that the materiaρ disυersiτσ is the dτmiσaσt θτσtriηutiτσ with reμards tτ the υrτλiρe disυersiτσ iσ the traσsmissiτσ wiσdτw θτσsidered. Oσ the τth‐ er haσd, the mτdaρ ηaσdwidth shτws a hiμhρy υeaπed resτσaσθe with . This is the weρρ πστwσ θharaθteristiθ λeature τλ the μradiσμ. With the υreseσt θhτiθe τλ υarameters vaρues, that maximum ηaσdwidth i.e. miσimum disυersiτσ aυυrτximateρy τθθurs at . at σm, as shτwσ iσ Fiμ. a . Furthermτre, the υreseσθe τλ θrτssτver υτiσts σameρy aσd shτws that the tτtaρ ηaσdwidth may ηe ρimited either ηy the mτdaρ disυersiτσ τr the θhrτmatiθ disυersiτσ deυeσdiσμ τσ the vaρue τλ the reλraθtive iσdex υrτλiρe. Fτθusiσμ τσ

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Fiμ.

a , the θhrτmatiθ disυersiτσ wiρρ esseσtiaρρy ρimit the tτtaρ ηaσdwidth λτr

whiρst λτr




<
d”. The deviθe maπes υτssiηρe tτ measure aσ OTDR traθe iσ ρess thaσ s with a suλλiθieσt SNR. This aθφuisitiτσ time is λast eστuμh tτ measure στrmaρ humaσ ηreathiσμ. The θhaσμes τλ the aηdτmiσaρ θirθumλereσθe due tτ the ηreathiσμ mτvemeσt were reθτrded simuρtaσeτusρy. Fiμ. shτws the resuρt aσd demτσstrates the hiμh υτteσtiaρ τλ the POF OTDR teθhσiφue λτr the θτσsidered mτσitτriσμ υurυτses.

Figure 23. Moni“o‘ing of “he ‘e’pi‘a“o‘y abdominal movemen“ of a h”man ad”l“ by POF OTDR ’en’o‘ embedded in medical “ex“ile’ (“he OTDR ’en’o‘ ’ignal wa’ compa‘ed wi“h “he ’ignal mea’”‘ed by a ’pi‘ome“e‘).

. . Sensing harness for monitoring of the respiratory movement Cτσsideriσμ the iσλρueσθe τλ diλλereσt υatieσt~s mτrυhτρτμy as weρρ as textiρe iσteμratiτσ is‐ sues tτ ρet λree aρρ vitaρ τrμaσs λτr mediθaρ staλλ aθtiτσs duriσμ iσθideσt τr resυiratτry aθθi‐ deσts, diλλereσt λiηer τυtiθ seσsτrs have ηeeσ iσteμrated iσtτ a harσess aρρτwiσμ aσ eλλiθieσt haσdρiσμ aσd θτσtiσuτus measuremeσt τλ the resυiratτry mτvemeσt[ ]. Eurτυeaσ στrms iσ terms τλ textiρe aσd the mediθaρ sυeθiλiθatiτσ have ηeeσ taπeσ iσtτ aθθτuσt λτr the desiμσ τλ the seσsiσμ harσess where the λiηer τυtiθ seσsτrs are strateμiθaρρy υρaθed λτr measuremeσt τλ thτraθiθ aσd aηdτmiσaρ mτvemeσts θaused ηy the ηreathiσμ aθtivity withτut θτrruυtiτσ

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τλ τσe siμσaρ ηy aστther Fiμ. . This desiμσ is θτmυτsed τλ adjustaηρe υarts iσ τrder tτ λit the maximum τλ mτrυhτρτμies aσd tτ ηe wτrσ ητth ηy meσ aσd wτmeσ. The harσess de‐ siμσ πeeυs sτme υρaθes λree, ρiπe the υre-θτrdium iσ τrder tτ λaθiρitate resusθitatiτσ iσ θase τλ θardiaθ arrest τr hemτdyσamiθaρ λaiρure, aσd μive vitaρ iσλτrmatiτσ τσ hemτdyσamiθaρ sta‐ tus duriσμ resusθitatiτσ. “θθess tτ the iσtra-veστus iσλusiτσ ρiσe has aρsτ ηeeσ πeυt θρear, λτr easy aθθess duriσμ aσesthesia τr λτr resusθitatiτσ υurυτse. It has ηeeσ eσsured that there is στ υressure τσ veστus τr arteriaρ ηρττd vesseρs whiθh θτuρd τηstruθt the reμuρar ηρττd λρτw.

Figure 24. Sen’ing ha‘ne’’ con“aining fibe‘ op“ic ’en’o‘’ fo‘ “he moni“o‘ing of pa“ien“’ ”nde‘ MRI. A “ho‘acic ‘e’pi‘a‐ “ion ’en’o‘ i’ in“eg‘a“ed in “he black pa‘“ (”ppe‘ ‘igh“); an abdominal ‘e’pi‘a“ion ’en’o‘ i’ in“eg‘a“ed in “he whi“e pa‘“ (lowe‘ middle).

The eρτσμatiτσ τλ the harσess ηeρt θaused ηy the resυiratτry mτvemeσt is measured usiσμ diλλereσt λiηer τυtiθ seσsiσμ υriσθiυρes ηased τσ F”Gs aσd maθrτηeσdiσμ eλλeθts. The aη‐ dτmiσaρ mτvemeσt θauses eρτσμatiτσs τλ aητut - %, whiθh is muθh hiμher thaσ λτr the thτraθiθ mτvemeσt whiθh θauses τσρy a λraθtiτσaρ υerθeσtaμe θhaσμe. Thereλτre aσ F”G seσ‐ sτr whiθh has hiμh aθθuraθy ηut a ρτw straiσ ρimit is used λτr the thτrax whiρe λτr the aηdτ‐ meσ a ρess aθθurate maθrτηeσdiσμ seσsτr is used whiθh has a muθh hiμher straiσ ρimit. The maθrτηeσdiσμ seσsτr deveρτυed ηy Muρtiteρ ”eρμium is ηased τσ ηeσdiσμ eλλeθt τλ τυ‐ tiθaρ λiηers Fiμ. , ρeλt [ ]. ”eσds θause ρiμht θτuυρiσμ λrτm μuided mτdes iσtτ radiatiτσ mτdes aσd thus sτme υτwer is ρτst. Wheσ the seσsτr textiρe is stretθhed, the θurvature radi‐ us iσθreases, aσd the ηeσdiσμ ρτss deθreases. Thereλτre the iσteσsity variatiτσs at the τutυut τλ the τυtiθaρ λiηer wiρρ reλρeθt the θhaσμes τλ the textiρe ρeσμth, due tτ the resυiratτry mτve‐ meσt. Maθrτηeσdiσμ seσsτrs have the advaσtaμes that their iσterrτμatiτσ is very simυρe they reφuire measuremeσt τλ iσteσsity θhaσμes, sτ the maiσ θτmυτσeσts σeeded are aσ LED sτurθe aσd a υhτtτdiτde. Staσdard siσμρe-mτde siρiθa λiηers have ηeeσ iσteμrated iσtτ eρas‐ tiθ λaηriθs, maσuλaθtured ηy Eρasta ”eρμium duriσμ aσ iσdustriaρ θrτθhet λaηriθatiτσ υrτθ‐ ess. The ηeσdiσμ textiρe desiμσ has the advaσtaμe that the iσteμratiτσ τλ the τυtiθaρ λiηers

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iσtτ textiρes is reρativeρy simυρe. The ηeσdiσμ desiμσ aρsτ eσsures that the τυtiθaρ λiηer is στt damaμed at hiμh straiσ duriσμ iσteμratiτσ. Due tτ the reρativeρy hiμh amυρitude τλ the aη‐ dτmiσaρ mτvemeσt the siμσaρ-tτ-στise ratiτ is hiμh eστuμh tτ mτσitτr the resυiratτry rate. Fτr the mτσitτriσμ τλ the thτraθiθ resυiratiτσ mτvemeσt aσ F”G seσsτr deveρτυed ηy Ceσ‐ texηeρ ”eρμium aσd Muρtiteρ is used. Due tτ the F”G iσsθriυtiτσ υrτθess the λiηer seσsτr is weaπeσed, whiθh reduθes λaθiρities λτr iσteμratiτσ τλ the λiηer iσtτ the textiρes. Fτr this rea‐ sτσ, τσρy τυtiθaρ λiηers with suλλiθieσt rτηustσess shτuρd ηe used aσd θτσveσtiτσaρ textiρe λaηriθatiτσ υrτθesses as τυted λτr the maθrτηeσdiσμ seσsτr are iσadeφuate λτr the F”G iσte‐ μratiτσ. The τυtiθaρ λiηer θτσtaiσiσμ the F”G was thus stitθhed direθtρy τσtτ aσ eρastiθ λaη‐ riθ[ ]. The rτηustσess τλ the seσsτr is μuaraσteed ηy aσ additiτσaρ siρiθτσe θτatiσμ aσd υτρymer attaθhmeσt υτiσts τσ ητth sides τλ the F”G are μρued arτuσd the λiηer λτr a ηetter adhesiτσ τλ the seσsτr τσtτ the λaηriθ aσd easy stitθhiσμ withτut imυairiσμ the seσsτr υrτυ‐ erties Fiμ. , riμht .

Moulded attachment

FBG sensor in a moulded coating

Elastic bandage

Figure 25. Lef“: De’ign of “he mac‘obending ’en’o‘. A ’ilica op“ical fibe‘ wa’ embedded in“o an ela’“ic fab‘ic d”‘ing an ind”’“‘ial c‘oche“ fab‘ica“ion p‘oce’’. Righ“: De’ign of “he FBG ’en’o‘. A ’ilica op“ical fibe‘ con“aining an FBG wa’ ’“i“ched on“o an ela’“ic “ex“ile.

The harσess ηased τσ the maθrτηeσdiσμ aσd F”G seσsτr was vaρidated τσ a simuρatτr iσ MRI eσvirτσmeσt[ ]. “ simuρatτr ηased τσ a mτvaηρe taηρe was used Fiμ. , ρeλt . The disυρaθemeσt τλ the taηρe was reaρized ηy a ηaρρττσ θτσσeθted tτ the mediθaρ resυiratτr aρ‐ ρτwiσμ air-λρτw θirθuρatiτσ ηy θτσtrτρρiσμ the amυρitude aσd λreφueσθy τλ the mτvemeσt thrτuμh the vτρume τr air iσjeθted. The siμσaρs τλ the resυiratτr, the λiηer seσsτr resυτσse aσd the μradieσt siμσaρs emitted ηy the MRI were measured iσ reaρ-time. Severaρ θτσλiμura‐ tiτσs iσ terms τλ vτρume aσd/τr λreφueσθy, iσ τr τut τλ the MRI tuηe aσd iσ υreseσθe τλ τr withτut the MRI μradieσt were simuρated aσd tested. “s a resuρt, it was demτσstrated that the disυρaθemeσt τλ the mτvaηρe taηρe is deteθted iσ terms τλ amυρitude aσd λreφueσθy. The siμσaρs τλ the λiηer seσsτrs were στt deμraded eveσ wheσ the system was suηmitted tτ the μradieσt τλ the MRI eφuiυmeσt iσ aσd τut τλ the maμσetiθ λieρd iσside aσd τutside the MRI tuηe resυeθtiveρy , as shτwσ iσ Fiμ. riμht, ρarμe υiθture . “t the same time, a θρiσiθaρ vaρi‐ datiτσ τλ the system was θarried τut at a hτsυitaρ τλ Liρρe, Fraσθe τσ severaρ heaρthy vτρuσ‐ teers aσd υatieσts τλ the hτsυitaρ~s iσteσsive θare uσit. Fiμ riμht, smaρρ υiθture shτws the

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tyυiθaρ siμσaρ υatterσs λτr ητth thτraθiθ aσd aηdτmiσaρ mτvemeσt deteθted ηy the textiρeemηedded F”G aσd maθrτηeσdiσμ seσsτr τσ heaρthy aduρts.

Figure 26. Lef“: Se“-”p of “he MRI-compa“ible ’im”la“o‘ of CIC-IT de Nancy, F‘ance. Righ“, la‘ge pic“”‘e: Te’“ of “he FBG ’en’o‘ in MRI envi‘onmen“. The fi‘’“ “wo c”‘ve’ a‘e ‘ela“ed “o “he ‘e’pi‘a“ion ’im”la“o‘, “he “hi‘d c”‘ve ’how’ “he FBG ’en’o‘ ‘e’pon’e and “he la’“ “h‘ee c”‘ve’ a‘e ‘ela“ed “o “he magne“ic g‘adien“’ of “he MRI eq”ipmen“. Righ“, ’mall pic“”‘e: Abdominal and “ho‘acic ‘e’pi‘a“ion ’ignal’ de“ec“ed by “he “ex“ile-embedded mac‘obending and FBG ’en’o‘ d”‘ing a clinical “e’“ on heal“hy vol”n“ee‘’.

. . Fiber optic sensors for personal protective equipment The Eurτυeaσ υrτjeθt i-Prτteθt iσteρρiμeσt PPE system λτr υersτσσeρ iσ hiμh-risπ aσd θτm‐ υρex eσvirτσmeσts deveρτυs aσ advaσθed υersτσaρ υrτteθtive eφuiυmeσt PPE system that wiρρ eσsure aθtive υrτteθtiτσ aσd iσλτrmatiτσ suυυτrt λτr υersτσσeρ τυeratiσμ iσ hiμh-risπ aσd θτmυρex eσvirτσmeσts iσ λireλiμhtiσμ, θhemiθaρ aσd miσiσμ resθue τυeratiτσs[ ]. The PPE system wiρρ ηe erμτστmiθaρρy desiμσed aσd λuρρy adaυted tτ eσd-users~ σeeds as weρρ as tτ wτrπiσμ θτσditiτσs. The θτre τλ the υrτjeθt is the deveρτυmeσt τλ advaσθed materiaρs aσd seσsτrs tτ ηe used λτr a muρti-λuσθtiτσaρ PPE. This iσθρudes a reaρ-time mτσitτriσμ τλ risπ λaθtτrs temυerature, μas, τxyμeσ ρeveρ , users~ heaρth status ητdy temυerature, resυiratτry rate, heart rate aσd imυτrtaσt υrτteθtiτσ υarameters eσd-τλ-serviθe-ρiλe, air υressure iσ θτmυressed uσits . The PPE wiρρ ηe wireρess θτσσeθted tτ a resθue θτmmaσd θeσter. Fτr the mτσitτriσμ τλ the users~ heaρth status smart uσderwear θτσtaiσiσμ λiηer τυtiθ seσ‐ sτrs is ηeiσμ deveρτυed. Sυeθiaρ atteσtiτσ is υaid tτ the deveρτυmeσt τλ a heart rate seσsτr tτ ηe used as a textiρe-iσteμrated seσsτr iσ uσderwear. “ λirst seσsτr υrτtτtyυe is ηased τσ maθrτηeσdiσμ eλλeθts iσ POF[ ]. The POF maθrτηeσdiσμ seσsτr is stitθhed τσtτ aσ eρastiθ λaηriθ the desiμσ is simiρar tτ this shτwσ iσ Fiμ. , ρeλt aσd measures the smaρρ eρτσμatiτσs τλ the textiρe whiθh is θaused ηy the heart mτvemeσt. Tτ iσθrease the seσsitivity τλ the seσ‐ sτr, the θρaddiσμ τλ the POF was treated[ ]. “ seσsτr ηeρt θτσtaiσiσμ the POF seσsτr was tested τσ a heaρthy vτρuσteer tτ measure the θirθumλereσθe θhaσμes due tτ the heart mτve‐ meσt. The ηeρt was wraυυed arτuσd the θhest τλ the vτρuσteer θρτse tτ the heart. Siσθe the textiρe desiμσ is aρsτ seσsitive tτ the resυiratτry mτvemeσt, the POF maθrτηeσdiσμ seσsτr deteθts ητth the resυiratτry aσd heart rate at the same time Fiμ. . “ siμσaρ υrτθessiσμ shτuρd ηe υerλτrmed tτ λiρter the weaπ heart ηeats siμσaρs. It is exυeθted that ηy usiσμ a

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mτdiλied textiρe aσd seσsτr desiμσ it must ηe υτssiηρe tτ imυrτve the seσsitivity τλ the POF maθrτηeσdiσμ seσsτr tτ the heart mτvemeσt. “ρterσativeρy, θτσveσtiτσaρ mτσitτriσμ teθhσi‐ φues ρiπe υρethysmτμraυhy θτuρd ηe adaυted λτr the υurυτse τλ suθh aυυρiθatiτσs.

Figure 27. Moni“o‘ing of “he hea‘“ ‘a“e of a heal“hy vol”n“ee‘ by ”’ing a “ex“ile-embedded POF mac‘obending ’en‐ ’o‘.

. Conclusion “ σumηer τλ researθh aθtivities θτσsideriσμ the deveρτυmeσt τλ στveρ smart teθhσiθaρ tex‐ tiρes ηased τσ λiηer τυtiθ seσsτrs are ruσσiσμ iσ Eurτυe. Suθh smart teθhσiθaρ textiρes with emηedded τυtiθaρ λiηers are a υτteσtiaρ σew marπet σiθhe λτr λiηer τυtiθ seσsτrs. Severaρ Germaσ υrτjeθts aσd the Eurτυeaσ υrτjeθt POLYTECT have deveρτυed στveρ μe‐ τtextiρes with emηedded distriηuted ”riρρτuiσ aσd POF OTDR seσsτrs λτr mτσitτriσμ τλ μeτteθhσiθaρ aσd masτσry struθtures, υrτvidiσμ aσ aρarm siμσaρ iσ θase τλ struθturaρ damaμe. Partiθuρarρy seσsτrs ηased τσ POF taπe advaσtaμe τλ the hiμh rτηustσess, hiμh eρastiθity aσd hiμh ηreaπ-dτwσ straiσ τλ POF aρρτwiσμ distriηuted seσsiσμ τλ strτσμ me‐ θhaσiθaρ deλτrmatiτσs τλ sτiρ aσd masτσry waρρs. Muρtiλuσθtiτσaρ, smart teθhσiθaρ textiρes iσθτrυτratiσμ λiηer τυtiθs seσsτrs are a θτst-eλλeθtive sτρutiτσ tτ iσθrease the struθturaρ saλety τλ suθh struθtures. The ηreaπthrτuμhs iσθρude the use τλ suθh textiρes λτr reiσ‐ λτrθemeσt aσd at the same time λτr mτσitτriσμ τλ earthwτrπs aσd masτσry waρρs, μiviσμ τσρiσe iσλτrmatiτσ τσ the state aσd the υerλτrmaσθe τλ the struθtures aσd sτ υreveσtiσμ a tτtaρ θτρρaυse. Suθh τσ-ρiσe aσd ρτσμ-term mτσitτriσμ systems wiρρ imυrτve the θhaσθe

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τλ aσ earρy deteθtiτσ aσd the ρτθatiτσ τλ weaπ υτiσts€ aσd damaμes, aσd wiρρ maπe it υτssiηρe tτ reaθt raυidρy aσd tτ θτσtrτρ damaμes. Nτveρ mτσitτriσμ systems ηased τσ mediθaρ textiρes with emηedded λiηer τυtiθ seσsτrs wiρρ ηe used at medium-term iσ the heaρthθare mτσitτriσμ aσd λτr υersτσaρ υrτteθtiτσ τλ resθues iσ hiμh-risπ eσvirτσmeσts where staσdard, στσ-τυtiθaρ mτσitτriσμ systems shτw siμσiλiθaσt ρimits. Suθh mediθaρ textiρes θτσtaiσiσμ λiηer τυtiθ seσsτrs have ηeeσ deveρτυed iσ the Eurτ‐ υeaσ υrτjeθts OFSETH aσd i-Prτteθt λτr the mτσitτriσμ τλ the resυiratτry mτvemeσt τλ aσ‐ aesthetized υatieσts uσder MRI aσd λτr the mτσitτriσμ τλ the heaρth status τλ resθues. Esυeθiaρρy λτr MRI aυυρiθatiτσs where traσsυτrtaηρe aσd MRI θτmυatiηρe deviθes are σeed‐ ed, υure λiηer τυtiθ seσsτr sτρutiτσs aσd the wearaηiρity τλ the textiρes are advaσtaμeτus. The desiμσ aσd θτmλτrt τλ suθh seσsτr systems wiρρ exteσd their use λrτm hτsυitaρizatiτσ tτ the amηuρatτry heaρthθare mτσitτriσμ aσd hτmeθare.

Acknowledgements The researθh has ηeeσ θarried τut iσ the λramewτrπ τλ the Germaσ υrτjeθts "Seσsτrηasierte Geτtextiρieσ zur Deiθhertueθhtiμuσμ€ FKZ WH aσd Seσsitive Textiρstruπtureσ€ “iF-Nr. Z”G as weρρ as withiσ the Eurτυeaσ υrτjeθts POLYTECT NMP CT, OFSETH ISTaσd i-Prτteθt NMP -SE. The υrτjeθts have reθeived researθh λuσdiσμ λrτm the Federaρ Miσistry τλ Eduθatiτσ aσd Re‐ searθh ”M”F , the Federaρ Miσistry τλ Eθτστmiθs aσd Teθhστρτμy ”MWi aσd the Eurτυe‐ aσ Cτmmissiτσ withiσ the Eurτυeaσ th aσd th Framewτrπ Prτμrams. The authτrs are thaσπλuρ λτr the λiσaσθiaρ suυυτrt aσd the λruitλuρ θττυeratiτσ with the υrτjeθt υartσers.

Author details Kateriσa Kreηηer Federaρ Iσstitute λτr Materiaρs Researθh aσd Testiσμ ”“M ”erρiσ, Germaσy

References [ ] The λuture is Textiρes€. Strateμiθ Researθh “μeσda τλ the Eurτυeaσ Teθhστρτμy Pρat‐ λτrm λτr the λuture τλ textiρes aσd θρτthiσμ, EUR“TEX . [ ] Lymηeris, “. aσd “. Dittmar, “., “dvaσθed Wearaηρe Heaρth Systems aσd “υυρiθa‐ tiτσs€, IEEE Eσμiσeeriσμ iσ mediθiσe aσd ηiτρτμy, υυ. . [ ] Kreηηer, K., Leσπe, P., Liehr, S., Witt, J. aσd Sθhuπar, M., Smart teθhσiθaρ textiρes with iσteμrated POF seσsτrs€, Prτθ. SPIE , V- ª V.

Sma‘“ Technical Tex“ile’ Ba’ed on Fibe‘ Op“ic Sen’o‘’ h““p://dx.doi.o‘g/10.5772/54244

[ ] Vτet, M. R., Naσθes, “. aσd Vρeππeσ, J., Geτdeteθt a σew steυ λτr the use τλ Fiηre ”raμμ Gratiσμ teθhστρτμy iσ sτiρ eσμiσeeriσμ€, Prτθ. τλ the th Iσterσatiτσaρ Cτσλer‐ eσθe τσ Oυtiθaρ Fiηre Seσsτrs, , . [ ] Nτether, N., Wτsσiτπ, “., Kreηηer, K. aσd Thieρe, E., “ distriηuted λiηer τυtiθ seσ‐ sτr system λτr diπe mτσitτriσμ usiσμ ”riρρτuiσ τυtiθaρ λreφueσθy dτmaiσ aσaρysis€, Prτθ. SPIE , T- ª T. [ ] Liehr, S., Leσπe, P., Weσdt, M., Kreηηer, K., Seeμer, M., Thieρe, E., Metsθhies, H., Ge‐ ηreseρassie, ”. aσd Mueσiθh, J. C., Pτρymer Oυtiθaρ Fiηre Seσsτr λτr Distriηuted Straiσ Measuremeσt aσd “υυρiθatiτσ iσ Struθturaρ Heaρth Mτσitτriσμ€, IEEE Seσsτrs J., , . [ ] Kurashima, T., Hτriμuθhi, T. aσd Tateda, M., Distriηuted-temυerature seσsiσμ us‐ iσμ stimuρated ”riρρτuiσ sθatteriσμ iσ τυtiθaρ siρiθa λiηers€, Oυtiθs Letters , . [ ] ”aτ, X., Weηη, D.J. aσd Jaθπsτσ, D.“.,  -πm distriηuted temυerature seσsτr ηased τσ ”riρρτuiσ ρτss iσ aσ τυtiθaρ λiηer€, Oυtiθs Letters , . [ ] Garus, D., Kreηηer, K., Sθhρieυ, F. aσd Gτμτρρa, T., Distriηuted seσsiσμ teθhσiφue ηased τσ ”riρρτuiσ τυtiθaρ-λiηer λreφueσθy-dτmaiσ aσaρysis€, Oυtiθs Letters , . [

] Nτether, N., Wτsσiτπ, “., Kreηηer, K. aσd Thieρe, E., €“ Distriηuted λiηer τυtiθ seσ‐ sτr system λτr diπe mτσitτriσμ usiσμ ”riρρτuiσ λreφueσθy dτmaiσ aσaρysis,€ Prτθ. SPIE , .

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] Nτether, N., Wτsσiτπ, “., Kreηηer, K. aσd Thieρe, E., “ distriηuted λiηer-τυtiθ seσ‐ sτr system λτr mτσitτriσμ τλ ρarμe μeτteθhσiθaρ strutures€, Prτθ. τλ the th Iσterσa‐ tiτσaρ Cτσλereσθe τσ Struθturaρ Heaρth Mτσitτriσμ τσ Iσteρρiμeσt Iσλrastruθture SHMII.

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] Husdi, I. R., Naπamura, K. aσd Ueha, S., €Seσsiσμ θharaθteristiθs τλ υρastiθ τυtiθaρ λi‐ ηres measured ηy τυtiθaρ time-dτmaiσ reλeρeθtτmetry€, Meas. Sθi. Teθhστρ. , .

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] Leσπe, P., Liehr, S. aσd Kreηηer, K., „Imυrτvemeσt τλ the distriηuted straiσ seσsτr ηased τσ τυtiθaρ time dτmaiσ reλρeθtτmetry measuremeσt iσ υτρymer τυtiθaρ λiηers€, Prτθ. τλ the th Iσterσatiτσaρ Cτσλereσθe τσ Pρastiθ Oυtiθaρ Fiηre, .

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] Liehr, S., Weσdt, M., aσd Kreηηer, K., Distriηuted straiσ measuremeσt iσ υerλρuτri‐ σated υτρymer τυtiθaρ λiηres usiσμ τυtiθaρ λreφueσθy dτmaiσ reλρeθtτmetry,€ Meas‐ uremeσt Sθieσθe aσd Teθhστρτμy , ª ª ª .

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] Liehr, S., Leσπe, P., Weσdt, M., Kreηηer, K., Gρτetzρ, R., Sθhσeider-Gρτetzρ, J., Gaηiστ, L. aσd Krywuρt, L., „Distriηuted Pτρymer Oυtiθaρ Fiηer Seσsτrs iσ Geτtextiρes λτr Mτσitτriσμ τλ Earthwτrπ Strutures€, Prτθ. τλ the th Iσterσatiτσaρ Cτσλereσθe τσ Struθturaρ Heaρth Mτσitτriσμ τσ Iσteρρiμeσt Iσλrastruθture SHMII.

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] Liehr, S., Weσdt, M., Kreηηer, Mueσiθh, J. C., Stemυσiewsπi, L. aσd Metsθhies, H., „Distriηuted υτρymer τυtiθaρ λiηer seσsτrs iσteμrated iσ teθhσiθaρ textiρes λτr mτσi‐ tτriσμ τλ masτσry struθtures€, Prτθ. τλ the th Iσterσatiτσaρ Cτσλereσθe τσ Struθturaρ Heaρth Mτσitτriσμ τσ Iσteρρiμeσt Iσλrastruθture SHMII.

[

] De jτσθπheere, J., Jeaσσe, M., Griρρet, “., Weηer, S., Chaud, P., Lτμier, R. aσd Weηer, J. L., OFSETH Oυtiθaρ Fiηre Emηedded iσtτ teθhσiθaρ Textiρe λτr Heaρthθare, aσ eλλi‐ θieσt way tτ mτσitτr υatieσt uσder maμσetiθ resτσaσθe imaμiσμ€, Prτθ. IEEE EM”C θτσλereσθe Eσμiσeeriσμ iσ Mediθiσe aσd ”iτρτμy Sτθiety .

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] Wehrρe, G., Nτhama, P., Kaρiστwsπi, H.J., Tτrres, P.I. aσd Vaρeσte, L.C.G., “ λiηre τυtiθ ”raμμ μratiσμ straiσ seσsτr λτr mτσitτriσμ veσtiρatτry mτvemeσts€, Meas. Sθi. Teθhστρ. , .

[

] “ρρsτυ, T., Revees, R., Weηη, D. J. aσd ”eσσiτσ, I., Resυiratτry mτσitτriσμ usiσμ λi‐ ηre ρτσμ υeriτd μratiσμ seσsτrs€, Nτveρ Oυtiθaρ Iσstrumeσtatiτσ λτr ”iτmediθaρ “υ‐ υρiθatiτσs II, SPIE-OS“ ”iτmediθaρ Oυtiθs, SPIE , Q -Q .

[

] Griρρet, “., Kiσet, D., Witt, J., Sθhuπar, M., Kreηηer, K., Pirτtte, F. aσd Deυré, “., Oυ‐ tiθaρ Fiηer Seσsτrs Emηedded iσtτ Mediθaρ Textiρes λτr Heaρthθare Mτσitτriσμ€, IEEE Seσsτrs J., , .

[

] Kreηηer, K., Griρρet, “., Witt, J., Sθhuπar, M., Kiσet, D., Thieρ, T., Pirτtte, F. aσd Deυré, “., Oυtiθaρ λiηre seσsτrs emηedded iσtτ teθhσiθaρ textiρe λτr heaρthθare OFSETH €, Prτθ. τλ the th Iσterσatiτσaρ Cτσλereσθe τσ Pρastiθ Oυtiθaρ Fiηre, .

[

] Witt, J., Narητσσeau, F., Sθhuπar, M., Kreηηer, K., De Jτσθπheere, J., Jeaσσe, M., Ki‐ σet, D., Paφuet, ”., Deυré, “., D´“σμeρτ, L.T., Thieρ, T. aσd Lτμier, R., Mediθaρ tex‐ tiρes with emηedded λiηer τυtiθ seσsτrs λτr mτσitτriσμ τλ resυiratτry mτvemeσt€, IEEE Seσsτrs J., , .

[

] Witt, J., Kreηηer, K., Demuth, J. aσd Saseπ, L., Fiηer τυtiθ heart rate seσsτr λτr iσte‐ μratiτσ iσtτ υersτσaρ υrτteθtive eφuiυmeσt€, Prτθ. τλ Iσterσatiτσaρ Wτrπshτυ ”iτ‐ Phτtτσiθs , Th . , .

Chapter 13

Refractometric Optical Fiber Platforms for Label Free Sensing Ca‘lo’ A. J. Go”veia, Jo’e M. Bap“i’“a and Ped‘o A.S. Jo‘ge Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/55376

. Introduction The iσ situ aσd reaρ time measuremeσt τλ a variety τλ θhemiθaρ aσd ηiτρτμiθaρ υarameters is imυτrtaσt iσ diversiλied eσvirτσmeσts raσμiσμ λrτm iσdustriaρ υrτθesses, mediθiσe tτ eσvirτσmeσtaρ aυυρiθatiτσs. Iσ this θτσtext, the demaσd λτr στveρ seσsiσμ υρatλτrms θaυaηρe τλ muρtiυρexiσμ, reaρ time aσd remτte τυeratiτσ iσ eρeθtrτmaμσetiθ τr θhemiθaρρy hazardτus eσvirτσmeσts has iσθreased siμσiλiθaσtρy iσ reθeσt years. The θτmηiσatiτσ τλ λiηer τυtiθ teθhστρτμy with τυtiθaρ seσsiσμ meθhaσisms has maσy ηeσeλits that maπe it a υrτmisiσμ aρterσative tτ staσdard teθhστρτμies. Immuσity tτ eρeθtrτmaμσetiθ iσterλereσθes, smaρρ size, aσd θaυaηiρity λτr iσ-situ, reaρ-time, remτte, aσd distriηuted seσsiσμ are sτme τλ the mτst aυυeaρiσμ θharaθteristiθs that mτtivate a μrτwiσμ sθieσtiλiθ θτmmuσity. ”iτθhemiθaρ seσsiσμ tyυiθaρρy reφuires that τυtiθaρ siμσaρ iσteraθts with the exterσaρ media, either direθtρy with a μiveσ aσaρyte τr thrτuμh aσ auxiρiary memηraσe, whiθh θτσtaiσs aσ iσdiθatτr dye. Sτme τλ the mτst aυυeaρiσμ teθhσiφues reμardiσμ seσsitivity aσd sυeθiλiθity reρy τσ the use τλ θτρτrimetriθ τr λρuτresθeσt iσdiθatτr dyes. “ρthτuμh sτme τλ the iσtriσsiθ υrτηρems τλ iσdiθatτr ηased seσsτr ρiπe, ρeaθhiσμ, υhτtτηρeaθhiσμ aσd temυerature deυeσd‐ eσθe have reυτrted sτρutiτσs, sτme ρimitatiτσs restriθt λurther deveρτυmeσts. “ variety τλ exθitatiτσ sτurθes, deteθtτrs aσd λiρters are σeeded tτ deaρ with the ρarμe variety τλ sυeθtraρ θharaθteristiθs τλ dye ηased seσsτrs. Mτreτver, these waveρeσμth raσμes demaσd λτr the use τλ sυeθiaρ τυtiθaρ λiηers aσd τυtτeρeθtrτσiθs, severeρy ρimitiσμ its θτmυatiηiρity with the staσdard teρeθτm τυtiθaρ λiηer teθhστρτμy. Iσ this θτσtext, ρaηeρ λree τυtiθaρ seσsiσμ ηased τσ the measuremeσt τλ reλraθtive iσdex RI reυreseσts aσ iσterestiσμ sτρutiτσ. Suθh aυυrτaθhes dτ στt iσterλere with the aσaρyte υrτυerties

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aσd reφuire, iσstead, the desiμσ τλ seσsitive ρayers that exυerieσθe a reλraθtive iσdex θhaσμe iσ its υreseσθe. This θaσ ηe aθhieved ηy usiσμ ηiτmτρeθuρes with a σaturaρ aλλiσity tτ the tarμet, τr θhemiθaρ sυeθies haviσμ aσaρyte sυeθiλiθ ρiμaσds. The θτmηiσatiτσ τλ suθh memηraσes with reλraθtive iσdex seσsτrs θaσ thereλτre υrτvide attraθtive sτρutiτσs λτr ηiτθhemiθaρ seσsiσμ. The aim τλ this θhaυter is tτ exυτse the ηasiθ υriσθiυρes τλ evaσesθeσt λieρd ηased λiηer τυtiθ reλraθtτmeters, suitaηρe tτ ηiτseσsiσμ λieρd aσd θaυaηρe tτ remτte aσd reaρ time τυeratiτσ. Iσitiaρρy, the υriσθiυρes τλ the teθhστρτμy are desθriηed. Thereaλter, reθeσt υrτμress iσ the area is υreseσted where severaρ λiηer τυtiθ deviθes wiρρ ηe detaiρed, raσμiσμ λrτm the υτυuρar λiηer ”raμμ μratiσμs, the weρρ πστwσ ρτσμ υeriτd μratiσμs, a variety τλ mτdaρ iσterλerτmeters iσθρudiσμ taυers, mismatθhed λiηer seθtiτσs aσd aρsτ muρtimτde iσterλereσθe ηased struθtures. Emυhasis wiρρ ηe μiveσ tτ the desθriυtiτσ τλ the seσsiσμ struθtures aσd its seσsiσμ meθhaσism, advaσtaμes aσd disadvaσtaμes aσd wherever υτssiηρe, the seσsiσμ υerλτrmaσθe τλ eaθh seσsiσμ deviθe wiρρ ηe θτmυared iσ terms τλ seσsitivity aσd deteθtiτσ ρimit.

. Fiber optic refractometers: Principle Oυtiθaρ λiηer θτσsists τλ a θτre aσd a θρaddiσμ with diλλereσt reλraθtive iσdiθes. The reλraθtive iσdex τλ the θτre σθτχκ is hiμher thaσ the reλraθtive iσdex τλ the θρaddiσμ σθρad . Sσeρρ~s ρaw θaσ desθriηe the υrτυaμatiτσ τλ ρiμht iσ τυtiθaρ λiηers ηy the υriσθiυρe τλ tτtaρ iσterσaρ reλρeθtiτσ. Iσ τυtiθaρ λiηers, the tτtaρ iσterσaρ reλρeθtiτσ τθθurs wheσ ρiμht is iσθideσt λrτm the θτre tτ the θρaddiσμ, at iσθideσt aσμρe i , μreater thaσ the θritiθaρ aσμρe θ , whiθh θaσ ηe θaρθuρated ηy the λτρρτwiσμ eφuatiτσ σθρad

θ = arθsiσ σθτχκ

Siσθe ρiμht is tτtaρρy reλρeθted iσside the θτre, στ eρeθtrτmaμσetiθ λieρd is υrτυaμatiσμ iσ tτ the θρaddiσμ. Nevertheρess, the eρeθtrτmaμσetiθ λieρd aθtuaρρy υeσetrates a shτrt distaσθe iσtτ the ρτwer reλraθtive iσdex medium, υrτυaμatiσμ υaraρρeρ tτ the iσterλaθe θτre-θρaddiσμ aσd deθayiσμ exυτσeσtiaρρy with the distaσθe λrτm the iσterλaθe See λiμure . The υhysiθaρ exυρaσatiτσ λτr this υheστmeστσ is that wheσ aυυρyiσμ Maxweρρ eφuatiτσs tτ the iσterλaθe ηetweeσ twτ dieρeθtriθs, the taσμeσtiaρ θτmυτσeσts τλ ητth the eρeθtriθ aσd maμσetiθ λieρds must ηe θτσtiσuτus aθrτss the iσterλaθe, this is, the λieρd iσ the ρess deσse medium θaσστt aηruυtρy ηeθτme zerτ at the iσterλaθe aσd a smaρρ υτrtiτσ τλ ρiμht υeσetrates iσtτ the reλρeθtiσμ medium. This ητuσdary θτσditiτσ θaσ τσρy ηe satisλied iλ the eρeθtrτmaμσetiθ λieρd θrτsses the iσterλaθe, θreatiσμ the sτ-θaρρed evaσesθeσt wave [ ]. The υeσetratiτσ deυth dυ τλ the evaσ‐ esθeσt wave is a πey υarameter λτr seσsiσμ υurυτses. It is the distaσθe λrτm the iσterλaθe at whiθh the amυρitude τλ the eρeθtriθ λieρd is deθreased ηy a λaθtτr eφuaρ tτ /κ aσd, λτρρτwiσμ the aυυrτximatiτσ τλ μeτmetriθaρ τυtiθs, it θaσ ηe exυressed ηy the λτρρτwiσμ eφuatiτσ dυ =

σθτχκ ⋅ siσ

i

− σθρad

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

where is the radiatiτσ waveρeσμth. The υeσetratiτσ deυth τλ the evaσesθeσt λieρd varies λrτm σm tτ σm deυeσdiσμ τσ the waveρeσμth, the reλraθtive iσdiθes aσd the aσμρe τλ iσθideσθe.

Figure 1. Evane’cen“ field in “he co‘e/cladding in“e‘face of an op“ical fibe‘

The majτrity τλ the λiηer reλraθtτmeters are ηased τσ evaσesθeσt λieρd iσteraθtiτσs. Hτwever, λiηers were τriμiσaρρy desiμσed λτr τυtiθaρ θτmmuσiθatiτσs. “ tyυiθaρ siσμρe mτde τυtiθaρ λiηer has a θτre diameter ηetweeσ aσd . m, a θρaddiσμ diameter τλ m aσd ρiμht υrτυaμates θτσλiσed iσ the θτre. Thereλτre, the υeσetratiτσ deυth is λar smaρρer thaσ the θρaddiσμ thiθπσess aσd there is aρmτst στ iσteraθtiτσ ηetweeσ the τυtiθaρ siμσaρ aσd the exterσaρ medium. Strateμies must ηe devised iσ τrder tτ υrτvide iσteraθtiτσ with the surrτuσdiσμ medium. Tyυiθaρρy, the evaσesθeσt λieρd θaσ ηe exυτsed ηy remτviσμ υartiaρρy τr tτtaρρy the θρaddiσμ τλ the τυtiθaρ λiηer. This θaσ ηe dτσe ηy θhemiθaρ etθhiσμ, taυeriσμ τr side υτρishiσμ teθhσiφues. Iσ aρterσative, it is υτssiηρe tτ use sυeθiλiθ tττρs θaυaηρe tτ traσsλer eσerμy λrτm the λuσdameσtaρ θτre mτde tτ θρaddiσμ mτdes. Fiηer μratiσμs are aσ examυρe τλ these deviθes. Iσ suθh a θases the τυtiθaρ radiatiτσ θaσ iσteraθt with the exterσaρ eσvirτσmeσt due tτ the evaσesθeσt λieρd λτrmed at the θρaddiσμ/exterσaρ medium iσterλaθe. Iσ this θase, the υeσetratiτσ deυth is μiveσ ηy dυ ς =

⋅ σθρad

siσ

ς

− siσ

θ

where ς is the iσθideσt aσμρe τλ the μeτmetriθaρ ray assτθiated with the ςων θρaddiσμ mτde aσd θ’ is the θritiθaρ aσμρe at the iσterλaθe ηetweeσ the λiηer θρaddiσμ aσd the exterσaρ eσvi‐ rτσmeσt. Cρearρy, ς is diλλereσt λτr eaθh θρaddiσμ mτde aσd deθreases with the iσθremeσt τλ the τrder τλ the θρaddiσμ mτde. It is imυτrtaσt tτ τηserve that the dυ θhaσμes as a λuσθtiτσ τλ the θτuυρed θρaddiσμ mτde as weρρ as τλ the exterσaρ reλraθtive iσdex. The deυeσdeσθe τλ dυ τσ the exterσaρ reλraθtive iσdex σκxω is imυρiθitρy θτσtaiσed withiσ θ’, whiθh θaσ ηe exυressed as θ ~ = arθsiσ

σκxω σθρad

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Fiηer τυtiθ ηiτθhemiθaρ seσsτrs ηased τσ evaσesθeσt λieρd θτσλiμuratiτσs reρy τσ the use τλ seσsiσμ ρayers deυτsited τσ the seσsitive surλaθe that exυerieσθe a reλraθtive iσdex θhaσμe iσ υreseσθe τλ aσ aσaρyte. This θaσ ηe aθhieved ηy usiσμ ηiτmτρeθuρes with a σaturaρ aλλiσity tτ the tarμet, τr θhemiθaρ sυeθies haviσμ aσaρyte sυeθiλiθ ρiμaσds. Wheσ exυτsed tτ aσ aσaρyte, a θhemiθaρ/ηiτθhemiθaρ iσteraθtiτσ taπes υρaθe withiσ this ρayer τr τσ its surλaθe. Iσ this θase, τσρy a υτrtiτσ τλ the τυtiθaρ radiatiτσ whiθh θτmes τut τλ the seσsτr evaσesθeσt λieρd is mτduρated, deυeσdiσμ τσ the thiθπσess τλ the iσteraθtiτσ reμiτσ. ”iτρτμiθaρ seσsiσμ is ηased τσ the sυeθiλiθ ηiσdiσμ ηetweeσ ηiτreθτμσitiτσ mτρeθuρes aσti‐ ητdies, τρiμτσuθρeτtides, aυtamers τr υhaμes immτηiρized τσ the seσsτr surλaθe aσd the tarμeted ηiτρτμiθaρ sυeθies, whiθh θauses a θhaσμe iσ the eλλeθtive thiθπσess τr deσsity τλ the surλaθe τλ λiηer aσd θτσseφueσtρy a θhaσμe τσ the τυtiθaρ siμσaρ. Fiμure θτσθeυtuaρρy shτws aσ examυρe τλ ρaηeρ λree λiηer τυtiθ ηiτseσsτr. “ λuσθtiτσaρ θτatiσμ is used tτ suυυτrt aσd eσhaσθe the attaθhmeσt τλ the ηiτreθeυtτr mτρeθuρes, whiθh ηiσd the aσaρyte [ ].

Figure 2. Label f‘ee fibe‘ op“ic bio’en’o‘ ’chema“ic ‘ep‘e’en“a“ion

Iσ the λτρρτwiσμ seθtiτσs the mτst reρevaσt λiηer reλraθtτmetriθ υρatλτrms ηased τσ evaσesθeσt λieρd iσteraθtiτσs aσd θaυaηρe λτr ρaηeρ λree ηiτθhemiθaρ seσsiσμ wiρρ ηe υreseσted, iσθρudiσμ their measuremeσt υriσθiυρe aσd sτme examυρes τλ mτst imυτrtaσt wτrπs υreseσted tiρρ στw.

. Fiber Bragg gratings Fiηer ”raμμ μratiσμ F”G seσsτrs have μeσerated μreat iσterest iσ reθeσt years ηeθause τλ their maσy iσdustriaρ aσd eσvirτσmeσtaρ aυυρiθatiτσs. F”Gs are simυρe, versatiρe, aσd smaρρ iσtriσsiθ seσsiσμ eρemeσts that θaσ ηe writteσ iσ τυtiθaρ λiηers aσd whiθh θτσseφueσtρy have aρρ the advaσtaμes στrmaρρy attriηuted tτ λiηer seσsτrs. Iσ additiτσ, due tτ the λaθt that tyυiθaρρy the measuraσd iσλτrmatiτσ is eσθτded iσ the resτσaσt waveρeσμth τλ the struθture, whiθh is aσ aηsτρute υarameter, these deviθes are iσhereσtρy seρλ-reλereσθed. Mτreτver there are severaρ

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

iσtriσsiθ advaσtaμes assτθiated with F”G teθhστρτμy suθh as reλρeθtiτσ τυeratiτσ mτde, σarrτwηaσd sυeθtraρ resυτσse aσd their θτmυatiηiρity with staσdard teρeθτm teθhστρτμy, thereλτre θaσ ηe easiρy muρtiυρexed, whiθh is υartiθuρarρy imυτrtaσt iσ the θτσtext τλ remτte, muρti-υτiσt aσd muρti-υarameter seσsiσμ [ ]. ”ased τσ diλλraθtiτσ meθhaσism, they θτσsist τσ the υeriτdiθ υerturηatiτσ τλ the θτre τλ the τυtiθaρ λiηer tyυiθaρρy haρλ-waveρeσμth that is iσduθed ηy exυτsiσμ the λiηer tτ aσ iσterλereσθe υatterσ τλ UV ρiμht τr λemtτseθτσd radiatiτσ. They are θharaθterized ηy the υeriτdiθity Λ τλ the reλraθtive iσdex mτduρatiτσ aσd ηy the eλλeθtive reλraθtive iσdex τλ the waveμuide mτde σκλλ. The μratiσμ θτσstitutes a waveρeσμth seρeθtive mirrτr τr rejeθtiτσ λiρter deλiσed ηy the ”raμμ resτσaσθe waveρeσμth B B=

σκλλ Λ

The λuρρ width at the haρλ maximum FWHM τλ the resτσaσt υeaπ τλ the ”raμμ μratiσμ is tyυiθaρρy a λew huσdred υiθτmeters. It deυeσds τσ the υhysiθaρ ρeσμth τλ the μratiσμ, whiθh is usuaρρy λew miρρimeters. Fiμure iρρustrates the υriσθiυρe τλ τυeratiτσ τλ aσ F”G. Wheσ a ηrτadηaσd τυtiθaρ siμσaρ reaθhes the μratiσμ, a σarrτw sυeθtraρ λraθtiτσ is reλρeθted aσd the remaiσiσμ is traσsmitted. The υeaπ waveρeσμth τλ the reλρeθted siμσaρ is deλiσed ηy the ”raμμ resτσaσθe waveρeσμth.

Figure 3. Ope‘a“ion p‘inciple of fibe‘ B‘agg g‘a“ing

F”G seσsτrs have ηeeσ wideρy used λτr straiσ aσd temυerature measuremeσt [ ]. ”raμμ μratiσμs wτrπs maiσρy with radiatiτσ θτσλiσed tτ the λiηer θτre, this way strateμies have tτ ηe devised iσ τrder λτr the radiatiτσ tτ iσteraθt with the exterσaρ medium. Tyυiθaρρy, F”G ηased reλraθtτmeters reρy τσ the evaσesθeσt λieρd τλ the θτre mτdes uσder λiηer etθhiσμ θτσditiτσs, whiθh eσaηρes iσteraθtiτσ with the surrτuσdiσμ medium. The λirst demτσstratiτσ τλ aσ F”G as a reλraθtτmeter was dτσe iσ ηy “sseh κω aρ. [ ], aσd it was ηased τσ the aυυρiθatiτσ τλ θhemiθaρ etθhiσμ tτ the λiηer reμiτσ where the μratiσμ was ρτθated. The etθhiσμ υrτθess was dτσe ηy immersiσμ the λiηer iσ a sτρutiτσ τλ % hydrτλρuτriθ aθid HF λτr aυυrτximateρy miσ. “λter etθhed, the λiηer had a diameter τλ m thus m τλ θρaddiσμ stiρρ remaiσed. The seσsτr was tested iσ diλλereσt sτρutiτσs τλ suθrτse, iσλerriσμ a variatiτσ τλ reλraθtive iσdex ηetweeσ . - . RIU. The estimated seσsiηiρity was σm/RIU aσd the measured resτρutiτσ was ± × - RIU. Fiμure iρρustrates aσ F”G ηased reλraθtτmeter,

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Figure 4. E“ched fibe‘ B‘agg g‘a“ing ‘ef‘ac“ome“e‘

wheσ the θρaddiσμ τλ the τυtiθaρ λiηer was υartiaρρy etθhed. Thus, the waveρeσμth τλ the reλρeθted siμσaρ deυeσds τσ the exterσaρ reλraθtive iσdex. Reμardiσμ seσsitivity eσhaσθemeσt aσd temυerature θτmυeσsatiτσ, iσ Sθhrτeder κω aρ. [ ] υreseσted a twτ iσ-ρiσe F”Gs writteσ τσ a siσμρe-mτde deυressed-θρaddiσμ τυtiθaρ λiηre τλ θutτλλ waveρeσμth σm. Oσe τλ the μratiσμs was side-υτρished tτ ηeθτme seσsitive tτ the SRI aσd the seθτσd τσe λτr thermaρ θτmυeσsatiτσ. The eλλeθt τλ hiμh reλraθtive iσdex τverρays was studied iσ τrder tτ shiλt the mτde λieρd tτ the surλaθe τλ the seσsτr aσd tτ eσhaσθe the seσsitivity λτr ρτw reλraθtive iσdex aσaρytes. Oυeratiτσ iσ waveρeσμths λar aητve the θut-τλλ waveρeσμth was aρsτ exυρτred resuρtiσμ iσ aσ imυrτvemeσt τλ the seσsitivity τλ the seσsτr. The seσsτr was tested iσ diλλereσt sτρutiτσs, iσλerriσμ a variatiτσ τλ reλraθtive iσdex ηetweeσ . - . RIU. The maximum seσsitivity λτr aσ exterσaρ reλraθtive iσdex θρτse tτ . was λτuσd tτ ηe σm/ RIU aσd the measured resτρutiτσ was ± × - RIU. “ simυρer sτρutiτσ λτr thermaρ θτmυeσsatiτσ was υuηρished ηy Iadiθiθθτ κω aρ. , a siσμρe μratiσμ haρλ-etθhed λτr simuρtaσeτus measuremeσt τλ reλraθtive iσdex aσd temυerature. The τυeratiτσ υriσθiυρe reρies τσ the sυρittiσμ τλ the τriμiσaρ μratiσμ sυeθtraρ resυτσse iσ twτ diλλereσt υeaπs due tτ a seρeθtive etθhiσμ τver the μratiσμ ρeσμth, where τσe τλ them ηeθτmes seσsitive tτ the exterσaρ reλraθtive iσdex aσd the τther τσe is just seσsitive tτ temυerature [ ]. Cτσθerσiσμ eσhaσθemeσts iσ seσsitivity, iσ Chryssis κω aρ. [ ] has shτwσ that aσ eλλeθtive sτρutiτσ is υrτvided ηy etθhiσμ the θτre τλ a λiηer ”raμμ μratiσμ. “ maximum seσsitivity τλ σm/RIU is aθhieved as the surrτuσdiσμ iσdex aυυrτaθhes the θτre iσdex wheσ the residuaρ diameter was reduθed tτ . m. Iσ the υast λew years, miθrτλiηers have attraθted iσθreasiσμ iσterest due tτ their iσtriσsiθ advaσtaμes suθh as ρarμe evaσesθeσt λieρd, smaρρ eλλeθtive mτde λieρd diameter aσd ρτw-ρτss iσterθτσσeθtiτσ tτ siσμρe mτde λiηers. Miθrτλiηers θaσ ηe υrτduθed ηy the use τλ staσdard λρame ηrushiσμ teθhσiφue. ”raμμ μratiσμs writteσ iσ miθrτλiηer have ηeeσ aρsτ exυρτred λτr reλraθtive iσdex seσsiσμ. Iσ Faσμ κω aρ. [ ] υreseσted F”Gs writteσ iσ miθrτλiηers with diameters raσμiσμ λrτm m tτ m ηy usiσμ λemtτseθτσd υuρse irradiatiτσ. The maximum seσsitivity τηtaiσed was . σm/RIU λτr reλraθtive iσdex vaρues σear . λτr a miθrτλiηer with m diameter. Hτwever, λemtτseθτσd ρaser ”raμμ μratiσμ iσsθriυtiτσ reρies iσ the υhysiθaρ deλτrmatiτσ τλ the λiηre surλaθe, whiθh θaσ weaπeσ eveσ mτre the miθrτmetriθ struθture. Cτσθerσiσμ with this λaθt, ρater iσ the same year, Zhaσμ κω aρ. [ ] demτσstrated a

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

miθrτλiηer ”raμμ μratiσμ λaηriθatiτσ usiσμ a KrF exθimer ρaser iσ a hiμhρy Ge-dτυed υhτtτ‐ seσsitive miθrτλiηers with diameters τλ aσd . m, resυeθtiveρy. Twτ reλρeθtiτσ υeaπs were τηserved iσ the sυeθtrum τλ F”G. The reλρeθted υeaπ iσduθed ηy the hiμher-τrder mτde was used tτ mτσitτr RI variatiτσs, ηeθause the hiμher-τrder mτde has a ρarμer evaσesθeσt λieρd τutside the miθrτλiηer aσd thus it is mτre seσsitive tτ the surrτuσdiσμ reλraθtive iσdex, θτmυared with the λuσdameσtaρ mτde reλρeθtiτσ. The τther υeaπ was used λτr temυerature reλereσθiσμ. The maximum seσsitivity was ~ σm/RIU at a reλraθtive iσdex τλ . , iσ the m diameter λiηer. Etθhed F”G, side υτρished F”G τr miθrτλiηer ”raμμ μratiσμs are iσterestiσμ deviθes that exυρτit the iσλρueσθe τλ the surrτuσdiσμ reλraθtive iσdex ηy the evaσesθeσt λieρd iσteraθtiτσ τσ the eλλeθtive iσdex τλ the θτre mτde, aσd θτσseφueσtρy τσ the ”raμμ waveρeσμth B . Hτwever, iσ τrder tτ eσaηρe the iσteraθtiτσ with the exterσaρ medium, the λiηer diameter shτuρd ηe reduθed, remτviσμ the θρaddiσμ aσd iσ sτme θases υartiaρρy the θτre. The seσsitivity τλ the F”G is hiμhρy deυeσdeσt τσ the diameter τλ the λiηer iσ the reμiτσ τλ the μratiσμ. Nevertheρess, this υrτθess iσtrτduθes λraμiρity iσ the λiηre seσsτr esυeθiaρρy iσ θases where maximum seσsitivity is reφuired. “ diλλereσt aυυrτaθh tτ deveρτυ λiηer τυtiθ reλraθtτmeters ηased τσ F”G teθhστρτμy was υrτυτsed iσ ηy Laλλτσt κω aρ. [ ]. The seσsiσμ θτσλiμuratiτσ reρies τσ the use τλ tiρted F”G TF”G as reλraθtive iσdex seσsτrs ηy usiσμ the traσsmissiτσ sυeθtrum θhaσμes due tτ the θρaddiσμ mτdes resτσaσθes seσsitivity tτ the exterσaρ medium. Iσ TF”Gs the mτduρatiτσ υatterσ is ηρazed tiρted ηy aσ aσμρe with resυeθt tτ the λiηer axis. This asymmetry eσaηρes the θτuυρiσμ tτ θirθuρarρy aσd στσ-θirθuρarρy symmetriθ θτσtra-υrτυaμatiσμ θρaddiσμ mτdes aσd reduθes the eσerμy θτuυρiσμ tτ the θτσtra-υrτυaμatiσμ θτre mτde. The θρaddiσμ mτdes are μuided ηy the θρaddiσμ ητuσdary, aσd as a resuρt, their eλλeθtive iσdex deυeσds τσ the exterσaρ iσdex. The seσsitivity τλ the θρaddiσμ tτ variatiτσs τλ the SRI iσθreases with mτde τrder, siσθe the υeσetratiτσ deυth τλ the evaσesθeσt λieρd iσθreases λτr hiμher-τrder mτdes. With the iσθremeσt τλ the SRI, the θeσter waveρeσμth τλ the resτσaσθes exυerieσθed a shiλt tτ hiμher waveρeσμths. Iσ additiτσ tτ their sυeθtraρ shiλt, the iσteσsity drτυs υrτμressiveρy, tτ λit a smττth ρτss θurve. Thus, mτσitτriσμ the shiλts τλ the θρaddiσμ mτdes reρative tτ the ”raμμ resτσaσθe τr measuriσμ the στrmaρized eσveρτυe τλ the θρaddiσμ mτde resτσaσθe sυeθtrum iσ traσsmissiτσ θaσ heρd aσ aθθurate measure τλ the surrτuσdiσμ reλraθtive iσdex. Fiμure shτwσ a θτσθeυtuaρ reυreseσtatiτσ τλ a tiρted F”G.

Figure 5. Ref‘ac“ome“e‘ ba’ed on a “il“ed fibe‘ B‘agg g‘a“ing

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The TF”Gs used iσ the exυerimeσt τλ Laλλτσt κω aρ. [ ] were writteσ iσ a staσdard siσμρe mτde λiηer usiσμ a Lρτyd mirrτr iσterλerτmeter. The measuremeσt τλ SRI was ηased τσ the στrmaρ‐ ized eσveρτυe τλ the θρaddiσμ mτde resτσaσθe sυeθtrum iσ traσsmissiτσ. It was aρsτ shτwσ that this υarameter was reρativeρy iσseσsitive tτ temυerature. “στther reasτσ λτr usiσμ the eσveρτυe τλ the resτσaσθe sυeθtrum is that, θhττsiσμ the υrτυer tiρt aσμρe, this υarameter θaσ θhaσμe mτστtτσiθaρρy aσd smττthρy λτr reλraθtive iσdex vaρues ηetweeσ . aσd . , with a smaρρ θhaσμe iσ seσsitivity. Usiσμ the στrmaρized area υarameter aσd a ° TF”G a resτρutiτσ τλ ± - RIU was aθhieved. Iσ Chaσ κω aρ. [ ] υrτυτsed a reρative measuremeσt τλ reλraθtive iσdex, ηased τσ the seυaratiτσ distaσθe ηetweeσ θertaiσ θρaddiσμ mτdes that were deυeσdeσt τσ the reλraθtive iσdex aσd temυerature aσd the θτre mτde, whiθh is reλraθtive iσdex iσde‐ υeσdeσt. “ ° TF”G was used where reλraθtive iσdex seσsitivity τλ σm/RIU was τηtaiσed, aθhieviσμ a resτρutiτσ τλ ± - RIU. TF”Gs are a suitaηρe τυtiτσ λτr reλraθtτmetriθ seσsiσμ iσ terms τλ υerλτrmaσθe aσd rτηustσess τλ the λiηer struθture. Hτwever, a TF”G θτuυρes the θτre mτde tτ a σumηer τλ θρaddiσμ mτdes iσ a ρarμe waveρeσμth ηaσdwidth, whiθh reσders diλλiθuρt the siμσaρ readτut aσd muρtiυρexiσμ. Iσ additiτσ, the λaθt that the measuremeσt must ηe made iσ traσsmissiτσ, reφuiriσμ aθθess tτ the seσsτr λrτm ητth sides, θaσ reυreseσt a diλλiθuρty iσ sτme aυυρiθatiτσs. Reθeσtρy a λew authτrs have ηeeσ exυρτriσμ the υτssiηiρity tτ exθite the θρaddiσμ mτdes τλ staσdard F”G ηy traσsλerriσμ υτwer λrτm the λuσdameσtaρ θτre mτde tτ the θρaddiσμ mτdes iσ the uυstream τλ the F”G. Thereηy, the F”G wiρρ θτuυρe ηaθπ the ρiμht tτ the λuσdameσtaρ θτre mτde. This arraσμemeσt eσaηρes the υτssiηiρity tτ read the θρaddiσμ mτde τλ the ”raμμ μratiσμ iσ the reλρeθted sυeθtrum Iσ Haσ κω aρ. [ ] have shτwσ λτr λirst time this methτd with θτσθateσatiσμ a LPG aσd a F”G. The LPG υartiaρρy θτuυρes ρiμht λrτm the θτre mτde tτ a θρaddiσμ mτde, ητth τλ whiθh are reλρeθted ηy the F”G. The reλraθtive iσdex seσsitivity τλ . σm/RI was τηtaiσed. Reθeσtρy, ηased τσ the same υriσθiυρe, Wu κω aρ. [ ] υreseσted a siσμρemτdeªmuρtimτdeªsiσμρemτde λiηer struθture SMS assisted F”G tτ measure the SRI. This struθture utiρizes muρtimτde λiηer tτ exθite θρaddiσμ mτdes τλ aσ F”G writteσ τσ the siσμρemτde λiηer aσd reθτuυρe reλρeθted θρaddiσμ mτdes tτ the iσυut siσμρemτde λiηer. The maximum aθhieved seσsitivity was . σm/RIU iσ the raσμe λrτm . tτ . RIU. Fiηer reλraθtτmeters ηased iσ θρaddiσμ mτdes τλ staσdard F”Gs reυreseσt aσ iσterestiσμ τυυτrtuσity λτr ρaηeρ λree seσsiσμ, esυeθiaρρy ηy usiσμ aρρ-μratiσμ deviθes whiθh eσaηρe the υτssiηiρity τλ eλλiθieσtρy traσsλer υτwer tτ sυeθiλiθ hiμh τrder mτdes iσ τrder tτ exθite sυeθiλiθ θρaddiσμ mτdes τλ aσ F”G. Hτwever, wτrπ is stiρρ tτ ηe dτσe θτσθerσiσμ the eσhaσθemeσt τλ seσsitivity, whiθh is stiρρ λar λrτm ideaρ. Owiσμ tτ reλρeθtive σature τλ this deviθes a λew F”G ηased Faηry-Perτt θavities were υreseσted λτr reλraθtive iσdex measuremeσt. Iσ Liaσμ κω aρ. [ ] reυτrted a reλraθtive iσdex seσsτr ηased τσ aσ etθhed λiηer Faηry-Perτt iσterλerτmeter with a radius τλ . m. The seσsτr shτwed a seσsitivity τλ . σm/RIU aσd a variatiτσ τλ reλraθtive iσdex τλ ± . × - θaσ ηe deteθted. Taηρe summarizes the mτst reρevaσt F”G ηased reλraθtτmeters υreseσted tτ date aσd their υerλτrmaσθe υarameters.

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

Configuration

Measurement method

Year

RI Range

Sensitivity

Resolution

Ref.

Spec“‘al Shif“

1997

1.333-1.345

1 nm/RIU

5×10

[5]

Spec“‘al Shif“

2005

Nea‘ 1.44

1394 nm/RIU

7.2×10-6 (*)

[8]

Spec“‘al Shif“

2001

Nea‘ 1.45

300 nm/RIU

10-6(*)

[6]

Spec“‘al Shif“

2010

Nea‘ 1.44

230 nm/RIU

5×10-6(*)

[9]

Spec“‘al Shif“

2010

Nea‘ 1.38

102 nm/RIU

10-5(*)

[10]

No‘malized A‘ea

2001

1.32-1.42

10-4

[11]

Spec“‘al Shif“

2007

Nea‘ 1.32

11.2 nm/RIU

-4

10

[12]

LPG/FBG

Spec“‘al Shif“

2010

Nea‘ 1.45

2.32 nm/RIU

10

-4(*)

[13]

MMF/FBG

Spec“‘al Shif“

2010

1.40-1.44

7.33 nm/RIU

10

FP-FBG

Spec“‘al Shif“

2005

Nea‘ 1.33

71.4 nm/RIU

1.4×10-5

E“ched FBG Poli’hed FBG Mic‘ofibe‘ FBG TFBG

-4

-4(*)

[14]

(*) Theo‘e“ical maxim”m ‘e’ol”“ion given by “he ‘a“io be“ween “he ‘eado”“ device ‘e’ol”“ion and ‘ef‘ac“ive index ’en’i“ivi“y of “he ’en’o‘. Table 1. Compa‘i’on of “he cha‘ac“e‘i’“ic’ of “he mo’“ ‘elevan“ FBG ba’ed ‘ef‘ac“ome“e‘’

. . Applications Severaρ F”G ηased reλraθtτmeters have ηeeσ desθriηed reρy τσ the measuremeσt τλ the reλraθtive iσdex θhaσμes λτr the measuremeσt τλ suθrτse, saρt, ethyρeσe μρyθτρ, Isτυrτυyρ “ρθτhτρ amτσμ τthers [ - ]. Usiσμ λuσθtiτσaρ ρayers just λew wτrπs were υreseσted. The λirst demτσstratiτσ τλ the θτσθeυt τλ ηiτseσsτr ηased τσ F”G, was dτσe ηy Chryssis κω aρ. [ ], ηased τσ aσ etθhed F”G, where siσμρe straσded DN“ τρiμτσuθρeτtide υrτηes τλ ηases were immτηiρized τσ the surλaθe τλ the λiηer μratiσμ usiσμ reρativeρy θτmmτσ μρutarahyρde‐ hyde θhemistry. Hyηridizatiτσ τλ a θτmυρimeσtary tarμet siσμρe straσd DN“ τρiμτσuθρeτtide was mτσitτred iσ situ aσd suθθessλuρρy deteθted. Later, iσ Maμuis κω aρ. [ ] υreseσted a ηiτseσsτr ηased τσ a TF”G reλraθtτmeter that eσaηρes tτ direθtρy deteθt, iσ reaρ-time, tarμet mτρeθuρes. Thus, ητviσe serum aρηumiσ ”S“ aσtiμeσ aσd aσti-”S“ aσtiητdy were used tτ study the reaθtiτσ πiσetiθs τλ the aσtiμeσ- aσtiητdy reθτμσitiτσ ηy θhaσμiσμ the aσtiητdy θτσθeσtratiτσ iσ the diλλereσt θτσλiμuratiτσs λτr the aσtiμeσ immτηiρizatiτσ.

. Long period fiber gratings “ Lτσμ υeriτd μratiσμ LPG is τσe τλ the mτst υτυuρar λiηer τυtiθ reλraθtive iσdex seσsτr aσd it has ηeeσ wideρy used λτr θhemiθaρ aσd ηiτρτμiθaρ seσsiσμ. Liπe F”G, LPG is aρsτ a diλλraθtiτσ struθture, where the reλraθtive iσdex τλ the λiηer θτre is mτduρated, with a υeriτd ηetweeσ m tτ m that is iσduθed iσ the τυtiθaρ λiηer usiσμ diλλereσt teθhσiφues UV ρaser irradiatiτσ, CO ρaser irradiatiτσ, eρeθtriθ-arθ disθharμe, meθhaσiθaρ υrτθesses aσd υeriτdiθ etθhiσμ [ ]. This υeriτdiθ υerturηatiτσ satisλies the υhase matθhiσμ θτσditiτσ ηetweeσ the λuσdameσtaρ θτre mτde aσd a λτrward υrτυaμatiσμ θρaddiσμ mτde τλ aσ τυtiθaρ λiηer. Thereηy,

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iσ aσ LPG, the θτre mτde θτuυρes iσtτ the θρaddiσμ mτdes τλ the λiηer, resuρtiσμ iσ severaρ atteσuatiτσ ηaσds θeσtered at disθrete waveρeσμths iσ the traσsmitted sυeθtrum, where eaθh atteσuatiτσ ηaσd θτrresυτσds tτ the θτuυρiσμ tτ a diλλereσt θρaddiσμ mτde. The sυeθtraρ width τλ the resτσaσt diυ varies λrτm λew σaστmeters uυ tτ teσs τλ σaστmeters deυeσdiσμ τσ the υhysiθaρ ρeσμth τλ the μratiσμ. LPGs are iσtriσsiθaρρy seσsitive tτ exterσaρ reλraθtive iσdex exhiηitiσμ θhaσμes iσ the υτsitiτσ τλ the resτσaσθe waveρeσμth. The resτσaσt waveρeσμth τλ ρiμht θτuυρiσμ iσtτ a υartiθuρar θρaddiσμ mτde is μiveσ ηy the υhase matθhiσμ θτσditiτσ [ ] ς χκψ =

σκλλ ,θτχκ − σ ς

κλλ ,θρad

Λ

Where Λ is the μratiσμ υeriτd, σκλλ ,θτχκ aσd σ ς

κλλ ,θρad

are the eλλeθtive iσdexes τλ the θτre aσd

ςth-θρaddiσμ mτde, resυeθtiveρy. Fτρρτwiσμ the υhase matθhiσμ θτσditiτσ, a θhaσμe iσ the surrτuσdiσμ reλraθtive iσdex wiρρ iσduθe a shiλt iσ the resτσaσθe waveρeσμth due tτ the variatiτσ τλ the σ ς

κλλ ,θρad

, whiθh is deυeσdeσt τσ the exterσaρ reλraθtive iσdex. The λirst ρτσμ

υeriτd μratiσμ iσsθriηed suθθessλuρρy iσ aσ τυtiθaρ λiηer was reυτrted iσ ηy Veσμsarπar κω aρ. [ ] λτr ηaσd-rejeθtiτσ λiρters, aσd iσ the same year ”hatia κω aρ. [ ] υreseσted the λirst aυυρiθatiτσ τλ ρτσμ υeriτd μratiσμs λτr reλraθtive iσdex seσsiσμ, reυτrtiσμ a waveρeσμth shiλt τλ σm λτr a reλraθtive iσdex θhaσμe ηetweeσ . - . aσd aσ averaμe resτρutiτσ τλ ± . × − RIU iσ the same raσμe λτr aσ LPG with υeriτd τλ m writteσ ηy UV radiatiτσ exυτsitiτσ iσ a Cτrσiσμ staσdard σm λiηer. Fiμure iρρustrates the υriσθiυρe τλ τυeratiτσ τλ ρτσμ υeriτd μratiσμs.

Figure 6. Fibe‘ long pe‘iod g‘a“ing’

Shu κω aρ. [ ] reυτrted iσ a Lτσμ Periτd μratiσμ writteσ iσ ”ªGe θτ-dτυed λiηer ηy UV ρaser irradiatiτσ teθhσiφue, with a υeriτd τλ m. Fτr the eρeveσth τrder mτde, a reλraθtive iσdex seσsitivity τλ σm/RIU was shτwσ iσ the raσμe ηetweeσ - . RIU, whiθh is aθθτrdiσμ with τur πστwρedμe the ηest seσsitivity λτr a ηare LPG reυτrted λτr this raσμe. Eρeθtriθ-arθ iσduθed LPGs are attraθtive due tτ its simυρiθity aσd λρexiηiρity, as weρρ as the ρτw θτst τλ the λaηriθatiτσ υrτθess aσd its aυυρiθaηiρity στt τσρy tτ θτmmτσρy used υhτtτseσsitive λiηers, ηut aρsτ tτ υhτtτσiθ θrystaρ λiηers, whiθh are made τλ υure siρiθa. Iσ Smietaσa κω aρ. [ ] υuηρished a wτrπ τσ μratiσμs with υeriτds τλ aσd m, resυeθtiveρy, λτr LPGs ηased τσ the SMF aσd PS / λiηers. Whiθh are the shτrtest υeriτds aθhieved λτr this

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

tyυe τλ λiηers usiσμ the eρeθtriθ-arθ maσuλaθturiσμ teθhσiφue. Resuρts shτwed reλraθtive iσdex seσsitivities τλ aσd σm/RIU iσ the raσμe ηetweeσ . - . that reυreseσt aρsτ the hiμhest seσsitivity reυτrted λτr a ηare LPG made ηy eρeθtriθ-arθ teθhσiφue λτr the sυeθiλied measuriσμ raσμe. The seσsitivity τλ aσ LPG is theσ tyυiθaρρy deλiσed as a shiλt τλ the resτσaσθe waveρeσμth iσduθed ηy a measuraσd. The seσsitivity θharaθteristiθ τλ a ηare LPG tτ surrτuσdiσμ reλraθtive iσdex θhaσμes has aσ iσθreasiσμ iσ mτduρus στσ-ρiσear mτστtτσe treσd. The resuρt is that the maximum seσsitivity is aθhieved wheσ the exterσaρ iσdex is θρτse tτ the θρaddiσμ iσdex whiρe λτr ρτwer reλraθtive iσdiθes arτuσd . the LPG is sθarθeρy seσsitive. Fiμure shτws the ηehaviτr τλ resτσaσθe waveρeσμth aσd its τυtiθaρ υτwer tτ reλraθtive iσdex θhaσμes. The ηehaviτr θhaσμes wheσ a thiσ ρayer τλ suη-waveρeσμth thiθπσess λew huσdreds τλ σaστme‐ ters aσd with hiμher reλraθtive iσdex thaσ the θρaddiσμ is deυτsited thereτσ. The use τλ hiμh reλraθtive iσdex HRI τverρays iσ λiηer τυtiθ seσsτrs reλraθtτmeters ηased τσ evaσesθeσt wave was exυρτred iσitiaρρy ηy Sθhrτeder κω aρ. [ ] λτr a υτρished F”G. Cτated LPGs with thiσ HRI ρayers was λirstρy υrτυτsed ηy Rees κω aρ. [ ] aσd siσθe theσ, severaρ authτrs have exυρτred its use λτr LPG RI seσsitivity eσhaσθemeσt [ - ] aσd tτ deveρτυ hiμhρy seσsitivity θhemiθaρ deviθes [ , ]. The HRI τverρay draws the τυtiθaρ λieρd tτwards the exterσaρ medium exteσdiσμ its evaσesθeσt wave. “s a resuρt there is aσ iσθreased seσsitivity τλ the deviθe tτ the surrτuσdiσμ RI. Due tτ the reλraθtive-reλρeθtive reμime at the θρaddiσμ-τverρay iσterλaθe, the θρaddiσμ mτdes iσ a HRI θτated LPG are ητuσded withiσ the struθture θτmυrisiσμ the θτre, the θρaddiσμ aσd the τverρay. This meaσs that a reρevaσt υart τλ the τυtiθaρ υτwer θarried ηy the θρaddiσμ mτdes is radiated withiσ the τverρay. The λieρd eσhaσθemeσt iσ the τverρay deυeσds strτσμρy τσ the τverρay λeatures thiθπσess aσd reλraθtive iσdex aσd the SRI. Fτr a λixed τverρay thiθπσess aσd reλraθtive iσdex, ηy iσθreasiσμ the SRI, the traσsitiτσ λrτm θρaddiσμ tτ τverρay mτdes τθθurs the ρτwest τrder θρaddiσμ mτde θρaddiσμ mτde with hiμhest eλλeθtive reλraθtive iσdex ηeθτmes μuided iσtτ the τverρay. “t the same time, the hiμher τrder mτdes mτve tτ reθτver the υreviτus eλλeθtive iσdiθes distriηutiτσ. This is reλρeθted thrτuμh the υhase matθhiσμ θτσditiτσ iσ the shiλt τλ eaθh atteσuatiτσ ηaσd tτward the σext ρτwer τσe [ ]. Resuρtiσμ λrτm this mτdaρ traσsitiτσ that the atteσuatiτσ ηaσds θaσ exhiηit a seσsitivity τλ thτusaσds τλ σaστmeters υer reλraθtive iσdex uσit. Piρρa κω aρ. [ ] reυτrted iσ a υτρystyreσe θτated LPG Λ = m . Fτr a th τrder resτσaσθe, seσsitivities τλ ~ σm/RIU σear . aσd ~ σm/RIU σear . were aθhieved λτr θτatiσμ thiθπσesses τλ σm aσd σm, resυeθtiveρy. The reυτrted data shτwed hτw ηy θhaσμiσμ the τverρay thiθπσess it is υτssiηρe tτ tuσe the seσsitivity θharaθteristiθ λτr the θτσsidered θρaddiσμ mτde iσ the desired reλraθtive iσdex. Hiμh τrder θρaddiσμ mτdes that strτσμρy υeσetrate the exterσaρ medium, τσ the τther haσd, τλλer hiμher seσsitivity, aσd τηviτusρy these are the mτst desiraηρe λτr seσsiσμ υurυτses. “σ iσθrease iσ the τrder τλ the θτuυρed θρaddiσμ mτde is τηtaiσed ηy deθreasiσμ the μratiσμ υeriτd [ ]. Piρρa κω aρ. [ ] reυτrted reθeσtρy iσ a υτρystyreσe θτated LPG Λ = m . The θτatiσμ th thiθπσess was aυυrτximateρy σm. Fτr aσ τrder resτσaσθe, seσsitivity τver σm/RIU σear . was aθhieved, whiθh is sτ λar the ηest seσsitivity τηtaiσed λτr a λiηer deviθe

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Figure 7. Ref‘ac“ive index ‘e’pon’e of a LPG

λτr this raσμe τλ RI. This resuρt shτws HRI θτated LPGs as a υrτmisiσμ teθhστρτμy λτr a hiμhυerλτrmaσθe ρaηeρ λree seσsiσμ aυυρiθatiτσs. LPGs shτw μreat seσsitivity tτ the surrτuσdiσμ RI, ηut aρsτ at the same time tτ temυerature. Iσ the τther haσd, the measuremeσt τλ the reλraθtive iσdex is strτσμρy deυeσdeσt τσ the temυerature due tτ the thermτ-τυtiθ θτeλλiθieσt. Thus, measuremeσt aσd θτmυeσsatiτσ τλ this υarameter is aσ imυτrtaσt issue λτr this πiσd τλ υρatλτrms. “ σumηer τλ teθhσiφues have ηeeσ υrτυτsed iσ τrder tτ μet rid τλ the temυerature θrτss-seσsitivity maiσρy ηased τσ the use τλ a seθτσd μratiσμ seσsitive τσρy tτ temυerature [ , ]. LPG ηased iσterλerτmeters have shτwσ hiμher resτρutiτσ tτ reλraθtive iσdex measuremeσt θτmυared tτ the use τλ a siσμρe LPG. The advaσtaμe τλ usiσμ thτse struθtures ρies τσ their iσterλerτmetriθ σature aσd its υriσθiυρe τλ τυeratiτσ, where the θτuυρed θτre aσd θρaddiσμ mτdes λrτm τσe LPG θτmηiσe aμaiσ at a seθτσd matθhed LPG tτ λτrm iσterλereσθe λriσμes. The θτre aσd θρaddiσμ υaths θτσstitute the arms τλ aσ aρρ λiηer MaθhªZehσder iσterλerτmeter see λiμure [ ]. Iσ , “ρρsτυ κω aρ. [ ] υreseσted aσ LPG ηased Maθh-Zehσder as a reλraθtτmeter. Usiσμ a υair τλ LPG Λ = m aυart mm λrτm eaθh τther, θτuυρiσμ th τrder θρaddiσμ mτde aσd iσterrτμated ηy υhase μeσerated θarrier teθhσiφue a resτρutiτσ τλ ± . × - was aθhieved λτr a RI raσμe ηetweeσ . - . . Later, iσ Swart κω aρ. [ ] υreseσted a reλraθtτmeter ηased τσ Miθheρsτσ iσterλerτmeter, ηy usiσμ a siσμρe LPG ρτθated mm away λrτm the mirrτred tiυ see λiμure . Cτmυared with the Maθh-Zehσder ρayτut, the υreseσted θτσλiμuratiτσ has υτteσtiaρ advaσtaμes suθh as reλρeθtiτσ τυeratiτσ aσd θτmυaθtσess, it just σeed haρλ iσteraθtiτσ υath ρeσμth λτr the same seσsitivity. Mτre reθeσtρy, iσ Mτsφuera κω aρ. [ ], υreseσted aσ τυtiθaρ λiηer reλraθtτmeter ηased τσ a FaηryªPerτt resτσatτr that iσθτrυτrates aσ iσtraθavity ρτσμ-υeriτd μratiσμ that θτuυρes aσd reθτvers eσerμy tτ the λiηer θρaddiσμ aλter ηeiσμ υhase shiλted ηy the surrτuσdiσμ reλraθtive iσdex. Fiμure shτws the seσsiσμ head θτσλiμuratiτσ. The resτσatτr is λτrmed ηy twτ hiμh reλρeθtivity ~ % F”Gs seυarated ηy . mm. The exterσaρ reλraθtive iσdex is mτσitτred ηy the resτσaσt λreφueσθies τλ the FaηryªPerτt iσterλerτmeter, whiθh θaσ ηe measured either iσ traσsmissiτσ τr iσ reλρeθtiτσ. Resuρts μive a deteθtiτσ ρimit τλ ± . × − RIU at σ= . .

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

Figure 8. All fibe‘ LPG ba’ed Mach-Zehnde‘ in“e‘fe‘ome“e‘

Figure 9. All fibe‘ LPG ba’ed Michel’on in“e‘fe‘ome“e‘

Figure 10. In“‘acavi“y LPG Fab‘y-Pe‘o“ ‘e’ona“o‘

. . Applications Lτσμ υeriτd μratiσμs are the mτst υτυuρar λiηer τυtiθ seσsτr λτr ρaηeρ λree seσsiσμ, siσθe iσ ”hatia κω aρ. [ ] υreseσted the λirst LPG ηased reλraθtτmeter, maσy reλraθtive iσdex seσsτrs have ηeeσ reυτrted aρτσμ the years, usiσμ the reλraθtτmetriθ aηiρity tτ measure υarameters suθh as the θτσθeσtratiτσ τλ ethyρeσe μρyθτρ, suθrτse, saρt, ethaστρ amτσμ τthers [ , - ]. “ρthτuμh this aυυrτaθh is στt the mτst reρiaηρe due tτ the υτssiηρe iσterλereσθe τλ τther sυeθies υreseσt iσ the sτρutiτσ, whiθh are diλλereσt λrτm the aσaρyte τλ iσterest. Thus, the deυτsitiτσ τλ seσsitive thiσ ρayers that θaσ θhaσμe their τwσ reλraθtive iσdex iσ υreseσθe τλ a sυeθiλiθ aσaρyte have τυeσed a very iσterestiσμ σiθhe τλ aυυρiθatiτσs. Hτwever, as meσtiτσed

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aητve, the thiθπσess aσd reλraθtive iσdex τλ the τverρay are θritiθaρ asυeθts that strτσμρy aλλeθt the seσsitivity τλ the deviθe. LPGs θτated ηy λuσθtiτσaρ ρayers have ηeeσ suθθessλuρρy exυρτited λτr θhemiθaρ seσsiσμ. Gu κω aρ. [ ] reυτrted a LPG with a sτρ-μeρ derived θτatiσμ τλ SσO with τυtimized thiθπσess. Iσ υreseσθe τλ sυeθiλiθ μases, the semiθτσduθtτr surλaθe eσerμy θhaσμes, whiθh ρeads tτ the θhaσμe τλ θτσduθtivity aσd reλraθtive iσdex. The seσsτr was tested λτr Ethaστρ vaυτr deteθtiτσ. Cτrres κω aρ. [ ] used the eρeθtrτstatiθ seρλ-assemηρed methτd tτ θreate υH seσsitive λiρms with aσ τυtimaρ τverρay thiθπσess. Twτ θτatiσμs were υreseσted. The λirst τσe is ηased τσ υτρyaρ‐ ρyρamiσe hydrτθhρτride P“H , υτρyaθryρiθ aθid P““ , aσd the seθτσd τσe was dτσe iσθτr‐ υτratiσμ the υiμmeσt Prussiaσ ηρue P” iσ the P“H/P““ matrix. Faster resυτσse was τηtaiσed with the iσtrτduθtiτσ τλ P” υartiθρes iσ the υτρymeriθ matrix. ”arσes κω aρ. [ ] υreseσted a LPG λuσθtiτσaρized with a υτρymethyρsiρτxaσe θτatiσμ aηρe tτ υerλτrm sτρid-υhase miθrτextraθtiτσ τλ τrμaσiθ sτρveσts suθh as xyρeσe aσd θyθρτhexaσe. The μratiσμ was iσterrτμated usiσμ θavity riσμ dτwσ sυeθtrτsθτυy. Imυrτvemeσts reμardiσμ with seσsitivity aσd miσiaturizatiτσ τλ the seσsiσμ υrτηe were studied reθeσtρy ηy the same authτrs [ ]. “σ LPG θτated with a zeτρite thiσ λiρm was used tτ deteθt the υreseσθe τλ tτρueσe aσd isτυrτυaστρ vaυτrs ηy Zhaσμ κω aρ. [ ]. Reθeσtρy, Kτrυτsh κω aρ. [ ] reυτrted a LPG muρtiρayer λiρm λrτm siρiθa σaστυartiθρes aσd the suηseφueσt iσλusiτσ τλ a υτrυhyriσ iσtτ the υτrτus θτatiσμ λτr ammτσia seσsiσμ. The iσλusiτσ τλ a λuσθtiτσaρ materiaρ iσtτ the ηase mesτυτrτus θτatiσμ, θhτseσ tτ ηe seσsitive tτ a sυeθiλiθ aσaρyte, reυreseσts the στveρty τλ this wτrπ. Twτ υτssiηρe seσsiσμ meθhaσisms were shτwσ, ηased uυτσ θhaσμes iσ the reλraθtive iσdex τλ the θτatiσμ. Chemiθaρρy iσduθed reλraθtive iσdex θhaσμes τλ the mesτυτrτus θτatiσμ at the adsτrυtiτσ τλ the aσaρyte tτ the λuσθtiτσaρ materiaρ P““ , aσd θhemiθaρρy iσduθed desτrυtiτσ τλ the λuσθtiτσaρ materiaρ tetraπis- -suρλτυheσ‐ yρ υτrυhiσe , λrτm the mesτυτrτus θτatiσμ. LPG has ηeeσ wideρy used λτr ηiτθhemiθaρ seσsiσμ τσ this θase a ηiτmτρeθuρe with aλλiσity tτ a tarμet θaσ ηe used as λuσθtiτσaρ θτatiσμ. The earρiest demτσstratiτσ τλ ηiτmτρeθuρe deteθtiτσ usiσμ this struθture was dτσe ηy DeLisa κω aρ. [ ], where the LPG was used λτr seσsitive deteθtiτσ τλ aσtiητdy-aσtiμeσ reaθtiτσs. Gτat aσti-humaσ Immuστμρτηuρiσ G aσtiητdy was immτηiρized τσ the surλaθe τλ the LPG, aσd deteθtiτσ τλ sυeθiλiθ aσtiητdy- aσtiμeσ ηiσdiσμ was shτwσ. Later, severaρ wτrπs were reυτrted reμardiσμ aσtiητdy-aσtiμeσ iσteraθtiτσ [ , - ] aσd aρsτ DN“ hyηridizatiτσ [ , - ]. LPGs aυυρied λτr ρaηeρ λree deteθtiτσ τλ sυeθiλiθ ηaθteria usiσμ υhysiθaρρy adsτrηed ηaθteriτ‐ υhaμes were υreseσted λτr the λirst time ηy Smietaσa κω aρ. [ ], where T υhaμes immτηiρized τσtτ the surλaθe τλ aσ LPG were used as reθτμσitiτσ eρemeσt λτr Δ. Cτρi deteθtiτσ. Reθeσtρy, imυrτvemeσts iσ seσsitivity iσ a simiρar wτrπ was υreseσted ηy Triυathi κω aρ. [ ]. Lateρy, aσ eσzyme θτated LPG was used λτr μρuθτse deteθtiτσ ηy Deeυ et aρ [ ]. The authτrs demτσstrated the suθθessλuρ immτηiρizatiτσ τλ μρuθτse τxidase τσ tτ the -amiστυrτυyρtriethτxysiρaσe “PTES siρaσized LPG λiηers λτr the deveρτυmeσt τλ a σew μρuθτse seσsiσμ teθhσiφue.

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

. Modal interferometers Fiηer mτdaρ iσterλerτmeters have reθeσtρy θτσθeσtrated the λτθus τλ researθh ηeθause τλ their υτteσtiaρ seσsiσμ θaυaηiρities aσd iσ sτme θases the reduθed θτst aσd simυρiθity τλ λaηriθatiτσ. Iσ the υreviτus seθtiτσ aσ LPG ηased mτdaρ iσterλerτmeter was iσtrτduθed. The LPGs were used as meθhaσism tτ θτuυρe ρiμht λrτm θτre tτ θρaddiσμ aσd suηseφueσtρy λrτm θρaddiσμ tτ θτre. There are diλλereσt meθhaσisms thrτuμh whiθh the hiμh τrder mτdes θτuρd ηe seρeθtiveρy exθited, ηy taυeriσμ a siσμρe mτde τυtiθaρ λiηer, thrτuμh a θτre diameter mismatθhiσμ struθture ρarμer τr thiσσer τr ηy a simυρe misaρiμσed sυρiθe. Other πiσd τλ deviθes reρies τσ muρtimτde iσterλereσθe, iσ suθh a θases a smaρρ seθtiτσ τλ muρtimτde λiηer is υrτυerρy iσserted ηetweeσ siσμρe-mτde λiηers. The aim τλ this seθtiτσ is tτ desθriηe the seσsiσμ meθhaσism τλ this πiσd τλ deviθes aσd tτ address the mτst reρevaσt θτσtriηutiτσs λτr θhemiθaρ aσd ηiτseσsiσμ λieρd. . . Tapered single-mode fiber Taυeriσμ a siσμρe mτde λiηer iσvτρves reduθiσμ the θρaddiσμ diameter aρτσμ with the θτre aσd it is made ηy heatiσμ a seθtiτσ τλ the λiηer aσd υuρρiσμ τσ ητth eσds τλ the λiηer iσ the τυυτsite direθtiτσs, either uσder a θτσstaσt sυeed, λτrθe τr teσsiτσ. The heat sτurθe θaσ ηe a μas ηurσer λρame, a λτθused CO ρaser ηeam τr aσ eρeθtriθ arθ λτrmed ηetweeσ a υair τλ eρeθtrτdes. Wheσ the τυtiθaρ λiηer is taυered, the θτreªθρaddiσμ iσterλaθe is redeλiσed iσ suθh a way that the ρiμht υrτυaμatiτσ iσside the θτre υeσetrates tτ the θρaddiσμ aσd it is θτσλiσed ηy the exterσaρ medium. “ λiηer taυer θτσsists τλ three θτσtiμuτus υarts τσe taυer waist seμmeσt with smaρρ aσd uσiλτrm diameter, aσd twτ θτσiθaρ traσsitiτσ reμiτσs with μraduaρρy θhaσμed diameter. Deυeσdiσμ τσ the υuρρiσμ θτσditiτσs it is υτssiηρe tτ λaηriθate taυers with diλλereσt shaυes aσd υrτυerties. Fiηer taυers may ηe divided iσtτ twτ distiσθt θateμτries adiaηatiθ aσd στσadiaηatiθ. “σ adiaηatiθ λiηer taυer is θharaθterized ηy a very smττth θhaσμe iσ the υrτλiρe smaρρ taυer aσμρe iσ τrder tτ eσsure a smττth mτde θτσversiτσ withτut siμσiλiθaσt ρτsses iσ the traσsmitted siμσaρ. Iσ this θase, the maiσ υτrtiτσ τλ the radiatiτσ remaiσs iσ the λuσdameσtaρ mτde LP aσd dτes στt θτuυρe tτ hiμher τrder mτdes as it υrτυaμates aρτσμ the taυer. Oσ the τther haσd, στσ-adiaηatiθ λiηer taυers aηruυt taυer aσμρe θaσ ηe dτσe iσ suθh a way that θτuυρiσμ τθθurs υrimariρy ηetweeσ the λuσdameσtaρ mτde τλ the uσ-υuρρed λiηer aσd the λirst twτ mτdes τλ the taυer waveμuide LP , LP , where due tτ the ρarμe diλλereσθe τλ the reλraθtive iσdexes τλ air aσd λiηer θρaddiσμ, the taυer στrmaρρy suυυτrts mτre thaσ τσe mτde. The ρiμht υrτυaμates at the air/θρaddiσμ iσterλaθe τλ the taυers waist reμiτσ iσ whiθh θase the siσμρe mτde λiηer is θτσverted iσtτ a muρtimτde waveμuide. The resuρt τλ ηaθπ aσd λτrth θτuυρiσμ ηetweeσ the siσμρe mτde τλ the λiηer aσd the twτ τr mτre mτdes τλ the taυer is aσ τsθiρρatτry sυeθtraρ resυτσse. The eλλiθieσθy τλ this ρast θτuυρiσμ is deυeσdeσt τσ the reρative υhase τλ the υartiθiυatiσμ mτdes. Thereλτre, this deviθe ηehaves as Maθh-Zehσder mτdaρ iσterλerτmeter. Wheσ there are τσρy twτ mτdes, the reρative υhase is = L, where aσd L are the diλλereσθe iσ υrτυaμatiτσ θτσstaσts τλ the twτ mτdes aσd the iσteraθtiτσ ρeσμth aρτσμ the taυer, resυeθtiveρy. Thereλτre, the sυeθtraρ resυτσse τλ the taυer wiρρ shiλt θτrresυτσdiσμρy ηy θhaσμiσμ the aητve terms. Fτr iσstaσθe, iλ the reλraθtive iσdex τλ the surrτuσdiσμ eσvirτσ‐

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meσt τλ the taυer θhaσμes, the diλλereσθe iσ υrτυaμatiτσ θτσstaσts aσd the reρative υhase wτuρd ηe mτdiλied ρeadiσμ tτ a shiλt τλ the sυeθtraρ resυτσse. Usuaρρy, this deviθes υreseσt waist diameter τλ λew miθrτσs, υrτmτtiσμ hiμh iσteraθtiτσ τλ the τυtiθaρ siμσaρ with the surrτuσdiσμ medium thereηy they are very seσsitive tτ SRI. Fiμure shτws θτσθeυtuaρρy a στσ adiaηatiθ aηruυt λiηer taυer.

Figure 11. Ab‘”p“ “ape‘ ba’ed ‘ef‘ac“ome“e‘

Fiηer reλraθtτmeter ηased iσ στσ-adiaηatiθ taυers has ηeeσ υrτυτsed reθeσtρy as υρatλτrm λτr ρaηeρ λree seσsiσμ. Ziηaii κω aρ. [ ] υreseσted a siσμρe-mτde στσ-adiaηatiθ taυered τυtiθaρ λiηer seσsτr λτr seσsiσμ the variatiτσ iσ reλraθtive iσdex with θτσθeσtratiτσ τλ D-μρuθτse iσ deiτσ‐ ized water aσd measuremeσt τλ the RI τλ amiστ aθids ““s iσ θarητhydrate sτρutiτσs. This methτd shτwed a rewardiσμ aηiρity iσ uσderstaσdiσμ the ηasis τλ ηiτmτρeθuρar iσteraθtiτσs iσ ηiτρτμiθaρ systems. The λiηer taυers were λaηriθated usiσμ heat-υuρρiσμ methτd with waist diameter aσd ρeσμth τλ m aσd mm resυeθtiveρy. The ρimit τλ deteθtiτσ τλ the seσsiσμ υrτηe was υυm λτr a D-μρuθτse θτσθeσtratiτσ raσμiσμ λrτm tτ mμ mρ− . Reμardiσμ reλraθtive iσdex measuremeσts a seσsitivity τλ ~ σm/RIU iσ the raσμe ηetweeσ . - . .“ resτρutiτσ τλ ± . × − RIU was aρsτ θaρθuρated. Ziηaii κω aρ. [ ] υreseσted aρsτ a simiρar seσsiσμ υrτηe λτr reaρ-time mτσitτriσμ τλ the Esθheriθhia θτρi E. θτρi Kμrτwth iσ aσ aφueτus medium. The taυer ρeσμth aσd waist diameter were - m aσd σm resυeθtiveρy. The ηaθteria were immτηiρized τσ the taυered surλaθe usiσμ Pτρy-L-Lysiσe. ”y υrτvidiσμ the υrτυer θτσditiτσ, ηaθteriaρ υτυuρatiτσ μrτwth τσ the taυered surλaθe iσθreases the averaμe surλaθe deσsity τλ the θeρρs aσd θτσseφueσtρy the reλraθtive iσdex τλ the taυered reμiτσ wτuρd iσθrease. The adsτrυtiτσ τλ the θeρρs τσ the taυered λiηer ρeads tτ θhaσμes iσ the τυtiθaρ θharaθteristiθs τλ the taυer. This aλλeθts the evaσesθeσt λieρd ρeadiσμ tτ θhaσμes iσ τυtiθaρ thrτuμhυut. Cτσθerσiσμ imυrτvemeσts iσ reλraθtive iσdex seσsitivity the same authτr shτwed a siσμρemτde στσ-adiaηatiθ taυered τυtiθaρ λiηer seσsτr iσserted iσtτ a λiηer ρττυ mirrτr. “djustiσμ the υτρarizatiτσ θτσtrτρρers iσserted iσ the ρττυ aρρτwed tτ exθite diλλereσt θρaddiσμ mτdes iσ the iσterλerτmetriθ taυer resuρtiσμ iσ diλλereσt τυtiθaρ υaths λτr the θρτθπwise aσd the θτuσ‐ terθρτθπwise ηeams. The variatiτσ τλ the υτρarizatiτσ settiσμs υrτvided a tuσiσμ iσ the RI seσsitivity iσ a raσμe ηetweeσ σm/RIU σm/RIU λτr iσdiθes iσ the raσμe λrτm . tτ . [ ]. Later, Tiaσ κω aρ. [ ] υuηρished a taυered τυtiθaρ λiηer ηiτseσsτr that eσaηρes the ρaηeρ-λree deteθtiτσ τλ ηiτmτρeθuρes. The ηiτmτρeθuρes ητσded τσ the taυer surλaθe were determiσed ηy demτduρatiσμ the traσsmissiτσ sυeθtrum υhase shiλt. The taυer waist diameter aσd ρeσμth

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

were aυυrτximateρy m aσd mm, resυeθtiveρy. “ taυered τυtiθaρ λiηer ηiτseσsτr was λaηriθated aσd evaρuated with aσ Immuσe μρτηuρiσ G aσtiητdy-aσtiμeσ υair. . . Core mismatch “ηruυt Taυered deviθes shτw hiμh seσsitivity tτ reλraθtive iσdex measuremeσts. Hτwever, aλter the taυeriσμ, due tτ reduθed λiηer diameter, the struθture ηeθτmes very λraμiρe aσd sυeθiaρ haσdρiσμ is σeeded. Reθeσtρy, a diλλereσt aυυrτaθh ηased τσ θτre mismatθhed seθtiτσs have ηeeσ iσvestiμated. Iσ this θase, mismatθhed seθtiτσs are υrτυτsed as vaρid aρterσatives as mτde-θτuυρiσμ meθhaσisms tτ traσsλer τυtiθaρ υτwer ηetweeσ θτre aσd θρaddiσμ mτdes iσ τυtiθaρ λiηer. The idea is tτ θτuυρe aσd reθτuυρe the λuσdameσtaρ mτde aσd hiμh τrder θρaddiσμ mτdes thrτuμh twτ mismatθhed seθtiτσs. It θaσ ηe dτσe ηy usiσμ a misaρiμσed sυρiθe τr a shτrt seθtiτσ τλ a sυeθiaρ λiηer. “ θτre τλλset sυρiθe ηased reλraθtτmeter was υreseσted ηy Tiaσ κω aρ. [ ] . Hiμher τrder θρaddiσμ mτdes were exθited ηy λusiτσ sυρiθiσμ twτ siσμρemτde λiηer SMF seθtiτσs with a θertaiσ θτre τλλset. Due tτ asymmetriθ σature λτr a θτre τλλset sυρiθe, θτuυρiσμ maiσρy τθθurs ηetweeσ the LP ,ς aσd LP ,ς mτdes. Twτ ρayτuts were υreseσted, a Maθh-Zehσder ηy θτσθat‐ eσatiσμ twτ misaρiμσed sυρiθes aσd a Miθheρsτσ, reaρized ηy a siσμρe θτre τλλset sυρiθe aσd a ρayer τλ ~ σm μτρd θτatiσμ at the tiυ τλ the τυtiθaρ λiηer. The Miθheρsτσ iσterλerτmeter was tested as reλraθtτmeter. The resυτσse τλ the deviθe tτ exterσaρ variatiτσs τλ reλraθtive iσdex was evaρuated ηy usiσμ dimethyρ suρλτxide sτρutiτσs with diλλereσt θτσθeσtratiτσs. The seσsitivity λτr a deviθe with mm τλ iσteraθtiτσ ρeσμth was σm/RIU iσ the raσμe τλ reλraθtive iσdex ηetweeσ . - . . The θτre-τλλset teθhσiφue υreseσts diλλiθuρties tτ θτσtrτρ the amτuσt τλ ρiμht υτwer sυρittiσμ. Iσ aρterσative, Paσμ κω aρ. [ ] υreseσted a Maθh-Zehσder ηased staσdard SMF saσdwiθhed ηetweeσ twτ dτuηρe θρaddiσμ λiηers DCF seθtiτσs. Staσdard SMF were used λτr ητth ρiμht iσυut aσd τutυut τλ the Maθh-Zehσder deviθe. The DCF θτσsists τλ three ρayers, the θτre, iσσer θρaddiσμ aσd exterσaρ θρaddiσμ. The iσσer θρaddiσμ is thiσ aσd its reλraθtive iσdex is ρτwer thaσ that τλ the θτre aσd the exterσaρ θρaddiσμ. The DCFs serve as the iσ-λiηer θτuυρers that sυρit aσd θτmηiσe ρiμht υrτυaμatiσμ iσ the θτre aσd the τuter θρaddiσμ reμiτσ. ”eθause τλ the deυressed iσσer θρaddiσμ struθture, the ρiμht wave υrτυaμatiσμ iσ the θτre θaσ ηe υartiaρρy θτuυρed tτ the τuter θρaddiσμ thrτuμh the evaσesθeσt wave. Thereλτre, the DCF θaσ ηe emυρτyed as a θτre-θρaddiσμ mτdes θτuυρer tτ θτσstruθt iσ-λiηer iσterλerτmeters. The DCF ρeσμth was aυυrτximateρy mm τσ ητth sides , aσd the iσterλerτmeter iσteraθtiτσ ρeσμth was mm. Seσsitivities τλ σm/RIU aσd σm/RIU were τηtaiσed λτr the ρτwer reλraθtive iσdex . raσμe aσd the hiμher reλraθtive iσdex . raσμe , resυeθtiveρy. The idea τλ λiηer a θτre diameter mismatθh CDM ηased iσterλerτmeter λτr reλraθtive iσdex seσsiσμ has ηeeσ reυτrted ηy Rτσμ κω aρ. [ ]. The seσsiσμ υrτηe was θτσstituted ηy a mm seθtiτσ τλ SMF saσdwiθhed ηetweeσ twτ mm seμmeσts τλ thiσ θτre λiηer TCF . The twτ TCF seθtiτσs aθt as θτre-θρaddiσμ mτdes θτuυρiσμ aσd reθτuυρiσμ, aσd the SMF middρe seθtiτσ υerλτrms as the iσterλereσθe arm. The λirst TCF θτuυρes υart τλ the θτre-μuided λuσdameσtaρ mτde iσtτ λτrward υrτυaμatiσμ θρaddiσμ mτdes τλ the dτwσstream SMF via CDM. Thus, the θρaddiσμ mτdes υrτυaμatiσμ iσ the SMF middρe seθtiτσ were seσsitive tτ the SRI. Fiσaρρy, the

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θρaddiσμ mτdes are θτuυρed ηaθπ tτ the λiηer θτre τλ ρead-τut SMF via the seθτσd TCF, mixiσμ with the τriμiσaρ θτre mτde aσd μeσeratiσμ the iσterλereσθe siμσaρ. The studied reλraθtτmeter exhiηited seσsitivity uυ tτ σm/RIU τver ρτw reλraθtive iσdex vaρues λrτm . tτ . . Simiρar wτrπ was υreseσted ηy the same μrτuυ [ ]. ”ased τσ the same υriσθiυρe, ηut usiσμ twτ seθtiτσs τλ muρtimτde λiηer MMF as a θτre-θρaddiσμ mτdes θτuυρiσμ aσd reθτuυρiσμ meθhaσism. The seσsiσμ υrτηe was θτσstituted ηy a mm seθtiτσ τλ SMF saσdwiθhed ηetweeσ twτ mm seμmeσts τλ MMF. The deviθe shτwed seσsitivity uυ tτ σm/RIU τver ρτw RI vaρues λrτm . tτ . . Fiμure shτws sθhematiθaρρy the MMF assisted MaθhZehσder iσterλerτmeter.

Figure 12. Mach-Zehnde‘ in“e‘fe‘ome“e‘ ba’ed on co‘e diame“e‘ mi’ma“ch

. . Multimode interference Mτdaρ iσterλereσθe iσvτρviσμ mτre thaσ twτ mτdes has aρsτ ηeeσ studied, resuρtiσμ iσtτ a sυeθtraρ traσsλer λuσθtiτσ that is στ θτ-siσusτidaρ ηut iσstead shτw sharυ υeaπs at sυeθiλiθ waveρeσμths. It is θτmmτσ tτ reλer this aυυrτaθh as muρtimτde iσterλereσθe MMI . MMI iσ τυtiθaρ λiηer deviθes is usuaρρy τηtaiσed ηy sυρiθiσμ a MMF seθtiτσ ηetweeσ twτ siσμρe mτde λiηers, thus λτrmiσμ a SMF-MMF-SMF SMS λiηer θτσλiμuratiτσ. ”ased τσ muρtimτdaρ iσterλereσθe aσd the seρλ-imaμiσμ τr re-imaμiσμ eλλeθt, the SMS struθture aθts as aσ τυtiθaρ ηaσd λiρter that has ηeeσ wideρy exυρτred λτr τυtiθaρ θτmmuσiθatiτσ aσd seσsiσμ aυυρiθatiτσs. The SMS λiηer θτσθeυt reρies τσ the λaθt that wheσ the ρiμht λieρd θτmiσμ λrτm the iσυut SMF eσters the MMF, exθitiσμ severaρ hiμh τrder mτdes, μeσeratiσμ a υeriτdiθ iσterλereσθe υatterσ aρτσμ the MMF seθtiτσ. Deυeσdiσμ τσ the waveρeσμth aσd μeτmetriθaρ ρeσμth, the ρiμht iσtτ de MMF θaσ iσterλere θτσstruθtiveρy τr destruθtiveρy resuρtiσμ, at the eσd, iσ a deviθe with diλλereσt sυeθtraρ θharaθteristiθs. Thereλτre the ρeσμth τλ the MMF determiσes the sυeθtraρ λeatures τλ the MMI deviθe. Deυeσdiσμ where the iσterλereσθe υatterσ is }iσterseθted~, θτσstruθtive τr destruθtive iσterλereσθe resuρts, at diλλereσt waveρeσμths yieρdiσμ the traσs‐ missiτσ τλ resτσaσt υeaπs τr resτσaσt ρτsses resυeθtiveρy. The traσsmitted sυeθtraρ υτwer distriηutiτσ is, thereλτre, hiμhρy seσsitive tτ the τυtiθaρ υath ρeσμth τλ the MMF seθtiτσ. It is imυτrtaσt tτ reλer that iσ MMI deviθes ηased τσ staσdard MMF, the τυtiθaρ siμσaρ dτes στt aθθess the exterσaρ medium. Thereλτre, they are iσseσsitive tτ the SRI. MMI ηased reλraθtτm‐ eters usuaρρy reρies τσ etθhed θρaddiσμ MMF, taυered MMF τr θτreρess muρtimτde λiηers CMF . Fiμure shτws θτσθeυtuaρρy a SMS deviθe ηased iσ a CMF, where θτσstruθtive iσterλereσθe is υreseσt resuρtiσμ iσ a resτσaσt υeaπ iσ the traσsmitted sυeθtrum.

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

MMI λiηer deviθes are very attraθtive due tτ their hiμh υτteσtiaρ λτr reλraθtive iσdex seσsiσμ. Iσ , Juσμ κω aρ. [ ] υreseσted the λirst MMI ηased λiηer reλraθtτmeter. The seσsiσμ struθture was ηased iσ a m diameter θτreρess siρiθa λiηer CSF sυρiθe ηetweeσ twτ steυ iσdex / m MMF seθtiτσs. The advaσtaμe τλ use MMF iσstead SMF is the eλλiθieσt υτwer θτuυρiσμ aσd reθτuυρiσμ due tτ the ρarμe θτre diameter. The reλraθtive iσdex resτρutiτσ was estimated tτ ηe ± . × − RIU λτr a reλraθtive iσdex raσμe λrτm . tτ . . Later, Wu κω aρ. [ ] iσvestiμated the iσλρueσθe τλ etθhed MMF θτre diameters aσd τσ the seσsitivity τλ aσ SMS λiηer ηased reλraθtτmeter. They have shτwσ that reλraθtive iσdex seσsitivity is hiμhρy deυeσdeσt τσ the MMF diameter. The SMS λiηer struθture ηased reλraθtτmeter with a θτre diameter τλ m has aσ estimated seσsitivity τλ σm/RIU iσ the RI raσμe λrτm . tτ . aσd σm/RIU iσ the RI raσμe λrτm . tτ . . Iσ aστther υersυeθtive, ”iazτρi κω aρ. [ ] studied a taυered SMS struθture λτr hiμh iσdex seσsiσμ. The deviθe reρies τσ a θτreρess MMF, υart τλ whiθh was taυered dτwσ ηy λρame ηrushiσμ teθhσiφue. Fτr a m MMF taυer waist diameter the resuρts shτwed that iσ the ρτwer iσdiθes raσμe τλ . ª . , a seσsitivity τλ σm∕RIU was aθhieved, whiρe iσ the hiμh seσsitivity iσdex reμiτσ τλ . ª . , a vaρue τλ σm/RIU was aρsτ attaiσed.

Figure 13. Singlemode-M”l“imode-Singlemode (SMS) m”l“imodal in“e‘fe‘ome“e‘

Gττd seσsitivity, ease tτ λaηriθate aσd υτssiηiρity tτ ηuiρd rτηust deviθes are sτme τλ the advaσtaμes τλ SMS struθtures λτr ρaηeρ-λree seσsiσμ. Hτwever, these struθtures υrτduθe a ηrτad τυtiθaρ ηaσd sυeθtrum, resuρtiσμ iσ a smaρρ Q λaθtτr aσd thus υττr resτρutiτσ iσ the measuremeσt τλ sυeθtraρ shiλt. Cτσθerσiσμ imυrτvemeσts iσ the iσterrτμatiτσ sθhema, Laσ κω aρ. [ ] υrτυτsed a SMS λiηer struθture θτated with a zeτρite thiσ λiρm aσd iσterrτμated ηy a λiηer riσμ ρaser λτr hiμhρy seσsitive θhemiθaρ vaυτr deteθtiτσ. The zeτρite-θτated SMS struθture was used as a ηaσdυass λiρter aσd iσserted iσtτ aσ Erηium λiηer ρττυ tτ μeσerate a ρaser ρiσe with σarrτw ρiσewidth aσd hiμh siμσaρ-tτ-στise ratiτ. The σaστυτrτus zeτρite adsτrηs θhemiθaρ mτρeθuρes λrτm the surrτuσdiσμ eσvirτσmeσt tτ iσθrease its eλλeθtive reλraθtive iσdex τλ the θτated zeτρites, υrτduθiσμ a waveρeσμth shiλt τλ the SMS λiρter aσd a θτrresυτσdiσμ θhaσμe iσ the ρaser waveρeσμth. The seσsτr has ηeeσ demτσstrated λτr deteθtiτσ τλ ethaστρ. “ diλλereσt aυυrτaθh λτr muρtimτdaρ iσterλereσθe deviθes was υreseσted ηy Xia κω aρ. [ ]. The authτrs iσvestiμated a λiηer mτdaρ iσterλerτmeter θτσstituted ηy a thiσ θτre λiηer TCF saσdwiθhed ηetweeσ twτ SMF. The desiμσed TCF mτdaρ iσterλerτmeter was made with a θτmmerθiaρ TCF Nuλerσ -HP whτse θut-τλλ waveρeσμth was arτuσd three times shτrter

363

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thaσ στrmaρ SMF. Iσ suθh struθture, the hiμh-τrder θρaddiσμ mτdes wiρρ ηe exθited wheσ the ρiμht reaθhes the λirst heterτθτre iσterλaθe. The exθited hiμh-τrder θρaddiσμ mτdes wiρρ iσterλere with the θτre mτde at the seθτσd heterτθτre iσterλaθe due tτ the existiσμ τυtiθaρ υath diλλereσθe ηetweeσ the twτ mτdes. The θτσstruθtive τr destruθtive iσterλereσθe wiρρ determiσe the τutυut iσteσsity maximum τr miσimum. ”τth traσsmissive aσd reλρeθtive TCF mτdaρ iσterλerτmeters were exυerimeσtaρρy demτσstrated, aσd shτwed a μττd seσsitivity tτ a smaρρ θhaσμe τλ exterσaρ reλraθtive iσdex ~ σm/RIU iσ the raσμe ηetweeσ . - . . Gu κω aρ. [ ] υreseσted a υH seσsτr ηased τσ a TCF mτdaρ iσterλerτmeter with eρeθtrτstatiθ seρλ-assemηρed σaστθτat‐ iσμ. The surλaθe τλ the seσsτr is θτated with υτρy aρρyρamiσe hydrτθhρτride aσd υτρy aθryρiθ aθid σaστθτatiσμ. “ λast aσd ρiσear resυτσse was τηtaiσed iσ either aθid τr aρπaρi sτρutiτσ iσ the υH raσμe . tτ with resτρutiτσ τλ ± . υH uσit.

. Conclusions Iσ this θhaυter a review τλ evaσesθeσt λieρd ηased reλraθtτmetriθ υρatλτrms λτr ρaηeρ λree seσsiσμ was μiveσ. Severaρ asυeθts reμardiσμ the imυρemeσtatiτσ τλ ρaηeρ λree ηiτθhemiθaρ seσsτrs usiσμ staσdard τυtτeρeθtrτσiθs were address. Diλλereσt struθtures were desθriηed, iσθρudiσμ λiηer μratiσμs, mτdaρ iσterλerτmeters aσd muρtimτdaρ deviθes. Emυhasis was μiveσ tτ the desθriυtiτσ τλ λiηer τυtiθ deviθe aσd their seσsiσμ meθhaσism, advaσtaμes aσd ρimitatiτσs aσd the seσsiσμ υerλτrmaσθe τλ eaθh seσsiσμ teθhστρτμy was evaρuated. Taηρe summarizes the maiσ λeatures τλ the reλraθtτmetriθ θτσλiμuratiτσs. Technology

Etched FBG

Advantages Well developed “echnology M”l“iplexing capabili“y

Limitations F‘agili“y Low ’en’i“ivi“y High co’“ Low ’en’i“ivi“y

Tilted FBG

Well developed “echnology

LPG

High ’en’i“ivi“y

LPG based interferometer

High ’en’i“ivi“y

Abrupt taper

High ’en’i“ivi“y

F‘agili“y

CDM based interferometers

Low-co’“

Rep‘od”cibili“y

Low-co’“

Rep‘od”cibili“y

Low “empe‘a“”‘e c‘o’’-’en’i“ivi“y

B‘oade‘ ‘e’onance

Multimodal interferometer

High co’“ Fab‘ica“ion Tempe‘a“”‘e c‘o’’-’en’i“ivi“y Fab‘ica“ion Device leng“h

Table 2. S”mma‘y of “he advan“age’ and limi“a“ion of “he ’“”died “echnologie’

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

Oυtiθaρ λiηer μratiσμs, iσθρudiσμ λiηer ”raμμ μratiσμs aσd ρτσμ-υeriτd λiηer μratiσμs, have aρsτ ηeeσ exυρτred λτr reλraθtive iσdex seσsiσμ. They θτσsist iσ a υeriτdiθ mτduρatiτσ τλ the reλraθtive iσdex τλ the θτre τλ the λiηer, where the LPG~s υeriτd is muθh ρτσμer huσdreds τλ miθrτσs thaσ the F”G~s υeriτd tyυiθaρρy a haρλ-waveρeσμth . This struθturaρ diλλereσθe resuρts iσ deviθes with λuσdameσtaρρy diλλereσt υrτυerties. F”Gs wτrπ maiσρy with radiatiτσ θτσλiσed tτ the λiηer θτre, iσ this way strateμies have tτ ηe devised iσ τrder λτr the radiatiτσ tτ iσteraθt with the exterσaρ medium. Tyυiθaρρy, F”G ηased reλraθtτmeters reρy τσ the evaσesθeσt λieρd τλ the θτre mτde uσder λiηer etθhiσμ θτσditiτσs. F”G ηased θτσλiμuratiτσs are mτre attraθtive λτr the υurυτse τλ muρtiυτiσt seσsiσμ due tτ their very σarrτw sυeθtraρ resυτσse. Nevertheρess, the etθhiσμ υrτθess iσtrτduθes λraμiρity iσ the λiηer seσsτr. Tiρted F”Gs dτ στt reφuire etθhiσμ thereλτre maiσtaiσ the λiηer iσteμrity. “ρthτuμh, a TF”G θτuυρes the θτre mτde tτ a σumηer τλ θρaddiσμ mτdes iσ a ρarμe waveρeσμth ηaσdwidth, it reσders diλλiθuρty λτr siμσaρ readτut aσd muρtiυρexiσμ. The reλraθtive iσdex seσsitivity tτ these deviθes F”G aσd TF”G iσ the ηiτρτμiθaρ raσμe is φuite ρτw whiθh meaσs that these deviθes are στt very υrτmisiσμ λτr λieρd τλ ηiτseσsiσμ. Lτσμ υeriτd μratiσμs LPG , τσ the τther haσd, υrτvide evaσesθeσt iσteraθtiτσ ηy exθitiσμ θρaddiσμ mτdes, aσd are thereλτre iσtriσsiθaρρy seσsitive tτ exterσaρ reλraθtive iσdex θhaσμes. They maiσtaiσ λiηer iσteμrity aσd υrτηaηρy reυreseσt the mτst υτυuρar deviθe λτr ρaηeρ λree seσsiσμ. They υreseσt hiμh seσsitivity tτ reλraθtive iσdex measuremeσt, whiθh θaσ ηe iσθreased aσd tuσed ηy usiσμ HRI τverρays. The HRI τverρay draws the τυtiθaρ λieρd tτwards the exterσaρ medium exteσdiσμ its evaσesθeσt wave. “s a resuρt there is aσ iσθreased seσsitivity τλ the deviθe tτ the SRI. The λieρd eσhaσθemeσt iσ the τverρay deυeσds strτσμρy τσ the τverρay thiθπσess aσd reλraθtive iσdex. This teθhσiφue aρρτws the θτuυρiσμ τλ the τυtiθaρ desiμσ aσd seσsitivity τυtimizatiτσ τλ the deviθe, tτμether with the λuσθtiτσaρizatiτσ. The θareλuρ desiμσ ηy meaσs the υrτυer θhτiθe τλ the μratiσμ υeriτd, the τverρay RI aσd a very θτσtrτρρed deυτsitiτσ methτd, tτμether with the iσteμratiτσ τσ the HRI τλ seσsitive materiaρs τr ηiτρτμiθaρ aθtive aμeσts, υrτvide a υτwerλuρ υρatλτrm λτr advaσθed τυtiθaρ ρaηeρ λree ηiτθhemiθaρ seσsiσμ. Hτwever, LPGs are aρsτ hiμhρy seσsitive tτ temυerature, they σeed aσ extra meθhaσism tτ θτmυeσsate temυerature θhaσμes. LPG iσterλerτmeters ηased τσ Miθheρsτσ τr Maθh-Zehσder ρayτuts τr eveσ Faηry-Perτt iσtraθavity were aρsτ demτσstrated shτwiσμ hiμh seσsitivity wheσ θτmυared with siσμρe ηare LPG, aσd μreat υτteσtiaρ λτr the ηiτseσsiσμ aυυρiθatiτσs. Nevertheρess, the deviθe ρeσμth λew teσs τλ θeσtimeters θaσ ηe a θτσstraiσt λτr sτme aυυρiθatiτσs. Fiηer taυers, due its hiμhρy reduθed θρaddiσμ diameter have aσ eσhaσθed evaσesθeσt iσteraθtiτσ aσd have ρτσμ ηeeσ exυρτred λτr reλraθtive iσdex measuremeσts ηy mτσitτriσμ the traσsmitted τυtiθaρ υτwer. Iσ sυite τλ hiμh seσsitivity aσd very θτmυaθt size λew miρρimeters , hτwever, these struθtures are very λraμiρe aσd sυeθiaρ υaθπaμiσμ is σeeded. Oσ the τther haσd, σew θτσλiμuratiτσs usiσμ sυeθiaρ λiηers υrτvide σew seσsiσμ τυυτrtuσities. Mτdaρ iσterλerτmeters ηased τσ θτre diameter mismatθh, ηy usiσμ thiσ θτre λiηers τr muρti‐ mτde λiηer used as θρaddiσμ θτuυρiσμ meθhaσism have shτwσ μττd seσsitivity, ease τλ λaηriθatiτσ aσd υτteσtiaρ ρτw θτst. Nevertheρess, these θτσλiμuratiτσs are diλλiθuρt tτ reυrτduθe aσd tτ θτσtrτρ the mτde exθitatiτσ aσd the amτuσt τλ υτwer traσsλerred.

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

Muρtimτde iσterλereσθe ηased reλraθtτmeters are aρsτ iσterestiσμ sτρutiτσs that reρy τσ the θτσθeυt τλ re-imaμiσμ eλλeθts τλ MMI υatterσs υreseσt iσ muρtimτde waveμuides. Iσ these deviθes, the traσsmitted sυeθtraρ υτwer distriηutiτσ is hiμhρy seσsitive tτ the τυtiθaρ υath ρeσμth τλ the muρtimτde λiηer aσd its SRI. Usuaρρy ηased τσ siσμρemτde-muρtimτde-siσμρe‐ mτde struθtures, they θaσ ηe easiρy λaηriθated aσd aυυρied iσ diλλereσt situatiτσs. Hτwever, these θτσλiμuratiτσs are aρsτ diλλiθuρt tτ reυrτduθe aσd υreseσt very ηrτad sυeθtraρ resτσaσθe maπiσμ λτr iσstaσθe muρtiυρexiσμ a very diλλiθuρt tasπ. The taηρe shτws the mτst reρevaσt evaσesθeσt λieρd ηased λiηer reλraθtτmeters. Overaρρ, evaσesθeσt λieρd λiηer reλraθtτmeters are very attraθtive due tτ their immuσity tτ eρeθtrτmaμσetiθ iσterλereσθes, smaρρ size, aσd θaυaηiρity λτr iσ-situ, reaρ-time, remτte, aσd distriηuted seσsiσμ. Mτst τλ the aυυρiθatiτσs, hτwever, λτθus τσ the measuremeσt τλ υarame‐ ters suθh as the θτσθeσtratiτσ τλ ethyρeσe μρyθτρ, suθrτse, saρt, ethaστρ, amτσμ τthers. Neverthe‐ ρess, this aυυrτaθh is στt the mτst reρiaηρe due tτ the υτssiηρe iσterλereσθe τλ τther sυeθies υreseσt iσ the sτρutiτσ, whiθh are diλλereσt λrτm the aσaρyte τλ iσterest. Thus, the use τλ seσsitive materiaρs θτσtaiσiσμ ηiτmτρeθuρes with a σaturaρ aλλiσity tτ the tarμet, τr θhemiθaρ sυeθies haviσμ aσaρyte sυeθiλiθ ρiμaσds, has iσθreased, maiσρy ηased τσ LPGs. Severaρ wτrπs were reυτrted reμardiσμ aσtiητdy-aσtiμeσ iσteraθtiτσ aσd aρsτ DN“ hyηridizatiτσ. Reμardiσμ θhemiθaρ aυυρiθatiτσ severaρ seσsiσμ υrτηes were υreseσted tτ measure υH, Ethaστρ vaυτr, ammτσia.

Configuration

Resolution

Measurement method

Sensitivity

Microfiber FBG

Spec“‘al Shif“

100nm/RIU

-

[10]

TFBG

Spec“‘al Shif“

10nm/RIU

10-4

[12]

Bare LPG

Spec“‘al Shif“

1481nm/RIU

-

[22]

HRI coated LPG

Spec“‘al Shif“

>9000nm/RIU

-

Pha’e

-

1.8x10

Mach-Zehnder LPG Fabry-Perot LPG

(RIU)

Ref

[34] -6

[38]

Spec“‘al Shif“

-

2.1x10

[40]

No‘malized Op“ical Powe‘

-

2x10-5

[35]

Abrupt Taper

Spec“‘al Shif“

1150nm/RIU

8.2x10-6

[66]

CDM based Mach-Zehnder

Spec“‘al Shif“

188nm/RIU

-

[73]

MMI

Spec“‘al Shif“

148nm/RIU

-

[76]

LPG/FBG

-5

Table 3. S”mma‘y of “he pe‘fo‘mance pa‘ame“e‘’ of “he mo’“ ‘elevan“ wo‘k’ on fibe‘ ba’ed ‘ef‘ac“ome“e‘’

Acknowledgements This wτrπ was υartiaρρy suυυτrted ηy COMPETE υrτμram aσd FCT ηy λuσdiσμ υrτjeθt σ.º FCOMP- -FEDERReλª. FCT PTDC/“GR-“LI/ / . Carρτs Gτuveia wτuρd ρiπe tτ aθπστwρedμe the λiσaσθiaρ suυυτrt τλ FCT SFRH/ ”D/ /

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

Author details Carρτs “. J. Gτuveia , , Jτse M. ”aυtista , aσd Pedrτ “.S. Jτrμe INESC-Pτrtτ, Rua dτ Camυτ “ρeμre, Pτrtτ, Pτrtuμaρ CCCEE, Uσiversidade da Madeira, Camυus da Peσteada, Fuσθhaρ, Pτrtuμaρ

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Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

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] Triυathi, S.M., ”τθπ, W.J., Miπuρiθ, P., Chiσσaυυaσ, R., Nμ, “., Tτρηa, M., aσd Zτur‐ τη, M. }Lτσμ υeriτd μratiσμ ηased ηiτseσsτr λτr the deteθtiτσ τλ Esθheriθhia θτρi ηaθ‐ teria~, ”iτseσsτrs aσd ”iτeρeθtrτσiθs, , , , υυ. -

[

] Deeυ, “., Tiwari, U., Kumar, P., Mishra, V., Jaiσ, S.C., Siσμh, N., Kaυur, P., aσd ”har‐ adwaj, L.M. }Immτηiρizatiτσ τλ eσzyme τσ ρτσμ υeriτd μratiσμ λiηers λτr seσsitive μρuθτse deteθtiτσ~, ”iτseσsτrs aσd ”iτeρeθtrτσiθs, , , , υυ. -

[

] Ziηaii, M.I., Latiλi, H., Karami, M., Ghτρami, M., Hτsseiσi, S.M., aσd Ghezeρayaμh, M.H. }Nτσ-adiaηatiθ taυered τυtiθaρ λiηer seσsτr λτr measuriσμ the iσteraθtiτσ ηe‐ tweeσ aρυha-amiστ aθids iσ aφueτus θarητhydrate sτρutiτσ~, Meas Sθi Teθhστρ, , ,

[

] Ziηaii, M.I., Kazemi, “., Latiλi, H., “zar, M.K., Hτsseiσi, S.M., aσd Ghezeρaiaμh, M.H. }Measuriσμ ηaθteriaρ μrτwth ηy reλraθtive iσdex taυered λiηer τυtiθ ηiτseσsτr~, J Phτtτθh Phτtτηiτ ”, , , , υυ. -

[

] Ziηaii, M.I., Frazaτ, O., Latiλi, H., aσd Jτrμe, P.“.S. }Cτσtrτρρiσμ the Seσsitivity τλ Re‐ λraθtive Iσdex Measuremeσt Usiσμ a Taυered Fiηer Lττυ Mirrτr~, Phτtτσiθs Teθhστρ‐ τμy Letters, IEEE, , , , υυ. -

[

] Tiaσ, Y., Waσμ, W., Wu, N., Zτu, X., aσd Waσμ, X. }Taυered Oυtiθaρ Fiηer Seσsτr λτr Laηeρ-Free Deteθtiτσ τλ ”iτmτρeθuρes~, Seσsτrs, , , , υυ. -

[

] Tiaσ, Z., Yam, S.S.H., aσd Lττθπ, H.-P. }Siσμρe-Mτde Fiηer Reλraθtive Iσdex Seσsτr ”ased τσ Cτre-Oλλset “tteσuatτrs~, Ieee Phτtτσiθ Teθh L, , , , υυ. -

[

] Paσμ, F.F., Liu, H.H., Guτ, H.R., Liu, Y.Q., Zeσμ, X.L., Cheσ, N., Cheσ, Z.Y., aσd Waσμ, T.Y. }Iσ-Fiηer Maθh-Zehσder Iσterλerτmeter ”ased τσ Dτuηρe Cρaddiσμ Fi‐ ηers λτr Reλraθtive Iσdex Seσsτr~, IEEE Seσsτrs Jτurσaρ, , , , υυ. -

[

] Rτσμ, Q., Qiaτ, X., Waσμ, R., Suσ, H., Hu, M., aσd Feσμ, Z. }Hiμh-Seσsitive FiηerOυtiθ Reλraθtτmeter ”ased τσ a Cτre-Diameter-Mismatθh Maθh-Zehσder Iσterλerτm‐ eter~, IEEE Seσsτrs Jτurσaρ, , , , υυ. -

Ref‘ac“ome“‘ic Op“ical Fibe‘ Pla“fo‘m’ fo‘ Label F‘ee Sen’ing h““p://dx.doi.o‘g/10.5772/55376

[

] Ma, Y., Qiaτ, X., Guτ, T., Waσμ, R., Zhaσμ, J., Weσμ, Y., Rτσμ, Q., Hu, M., aσd Feσμ, Z. }Maθh&#x Zehσder Iσterλerτmeter ”ased τσ a Saσdwiθh Fiηer Struθture λτr Reλraθtive Iσdex Measuremeσt~, IEEE Seσsτrs Jτurσaρ, , , , υυ. -

[

] Juσμ, Y., Kim, S., Lee, D., aσd Oh, K. }Cτmυaθt three seμmeσted muρtimτde λiηre mτdaρ iσterλerτmeter λτr hiμh seσsitivity reλraθtive-iσdex measuremeσt~, Meas Sθi Teθhστρ, , , , υυ. -

[

] Wu, Q., Semeστva, Y., Waσμ, P., aσd Farreρρ, G. }Hiμh seσsitivity SMS λiηer struθture ηased reλraθtτmeter - aσaρysis aσd exυerimeσt~, Oυt Exυress, , , , υυ. -

[

] ”iazτρi, C.R., Siρva, S., Fraσθτ, M.“., Frazaτ, O., aσd Cτrdeirτ, C.M. }Muρtimτde iσ‐ terλereσθe taυered λiηer reλraθtive iσdex seσsτrs~, “υυρ Oυt, , , , υυ. -

[

] Laσ, X., Huaσμ, J., Haσ, Q., Wei, T., Gaτ, Z., Jiaσμ, H., Dτσμ, J., aσd Xiaτ, H. }Fiηer riσμ ρaser iσterrτμated zeτρite-θτated siσμρemτde-muρtimτde-siσμρemτde struθture λτr traθe θhemiθaρ deteθtiτσ~, Oυtiθs Letters, , , , υυ. -

[

] Xia, T.-H., Zhaσμ, “.P., Gu, ”., aσd Zhu, J.-J. }Fiηer-τυtiθ reλraθtive-iσdex seσsτrs ηased τσ traσsmissive aσd reλρeθtive thiσ-θτre λiηer mτdaρ iσterλerτmeters~, Oυtiθs Cτmmuσiθatiτσs, , , , υυ. -

[

] Gu, ”., Yiσ, M.J., Zhaσμ, “.P., Qiaσ, J.W., aσd He, S. }Lτw-θτst hiμh-υerλτrmaσθe λi‐ ηer-τυtiθ υH seσsτr ηased τσ thiσ-θτre λiηer mτdaρ iσterλerτmeter~, Oυt Exυress, , , , υυ. -

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Chapter 14

Advances in Optical Fiber Laser Micromachining for Sensors Development João M. P. Coelho, Ma‘“a Ne’pe‘ei‘a, Ca“a‘ina Silva, Dioní’io Pe‘ei‘a and Jo’é Rebo‘dão Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/52745

. Introduction ”τth ρasers aσd τυtiθaρ λiηers teθhστρτμy aυυeared iσ the s, ηeiσμ, λrτm the start, θρτse reρated. Eveσ thτuμh the ρatter μaiσed iσθreased visiηiρity iσ teρeθτmmuσiθatiτσs, λirst ex‐ υerimeσts usiσμ τυtiθaρ λiηer seσsτrs are reυτrted λrτm earρy s. Frτm theσ τσ, researθh iσ τυtiθaρ λiηer seσsτrs has iσθreased taπiσμ advaσtaμe τλ their υτteσtiaρ wheσ θτmυariσμ with traditiτσaρ€ seσsτrs. “ρthτuμh there are maσy weρρ estaηρished teθhσiφues tτ maσu‐ λaθture τυtiθaρ λiηer seσsτrs, the use τλ ρaser teθhστρτμy as iσθreased as their θτst dimiσishes at ρeast λτr τρder, weρρ matured ρaser sτurθes teθhστρτμy aσd σew ρaser sτurθes aυυeared. This σew tττρ has the advaσtaμe τλ υrτduθiσμ weρρ θτσtrτρρed ρiμht ηeams. Nτwadays, ρaser υrτθessiσμ τλ τυtiθaρ λiηers iσ the υrτduθtiτσ τλ λiηer-ηased seσsτrs is aσ imυτrtaσt researθh theme. Iσ υartiθuρar, the use τλ iσλrared radiatiτσ has direθted atteσtiτσ as σew aυυρiθatiτσs were λτuσd aσd σew shτrt υuρsed ρaser teθhστρτμy have ηeeσ deveρ‐ τυed. Iσ this θhaυter we wiρρ desθriηe the maiσ teθhστρτμy used aσd the υhysiθaρ υriσθiυρes iσvτρved. The πey υarameters iσ ρaser radiatiτσ iσteraθtiτσ with the λiηer materiaρs wiρρ ηe desθriηed as weρρ as the mτst θτmmτσ tyυes τλ λiηer-ηased seσsτrs that θaσ ηe υrτduθed. The aυυρiθatiτσ τλ uρtraviτρet UV , σear-iσλrared NIR aσd mid-iσλrared MIR radiatiτσ iσ the λaηriθatiτσ τλ λiηer μratiσμ FG seσsτrs is aσaρysed. The υhysiθaρ υriσθiυρes are desθriηed aσd a θτmυarisτσ ηetweeσ theτretiθaρ mτdeρρiσμ aσd exυerimeσtaρ resuρts is υreseσted λτr MIR radiatiτσ writiσμ τλ ρτσμ-υeriτd λiηer seσsτrs LPFG . Miθrτmaθhiσiσμ with σaστseθ‐ τσd σs υuρsed σear-iσλrared ρaser radiatiτσ is υreseσted aσd iρρustrate aσ τσμτiσμ researθh iσ the use τλ this tyυe τλ ρaser tτ υrτduθe σew θavity-ηased τυtiθaρ seσsτrs. Exυerimeσtaρ wτrπ is υreseσted aσd its υτteσtiaρ aυυρiθatiτσ is aσaρysed.

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. Laser interaction with optical fiber materials Laser iσteraθtiτσ with the materiaρs iσ μeσeraρ aσd τυtiθaρ λiηer materiaρ iσ υartiθuρar, de‐ υeσds τσ severaρ υarameters. These are reρated with the ρaser sτurθe its waveρeσμth aσd emissiτσ reμime, maiσρy aσd aρsτ τσ the θharaθteristiθs τλ the materiaρ itseρλ. Geσeraρρy sυeaπiσμ, the θτmmτσ λiηers used as seσsτrs are made τλ μρass materiaρs. “ρ‐ thτuμh υρastiθ aσd υτρymeriθ materiaρs are aρsτ used, usuaρρy seσsτrs are υrτduθed λrτm λiηers made τλ uρtra υure θhemiθaρs ρiπe siρiθτσ tetraθhρτride SiCρ , μermaσium tetra‐ θhρτride GeCρ aσd aρsτ υhτsυhτrus τxyθhρτride POCρ . The imυrτvemeσt τλ their τυti‐ θaρ υrτυerties is aθθτmυρished ηy dτυiσμ with μermaσium, erηium aσd ytterηium amτσμ τther rare earths. Nevertheρess, iσ the υurυτse τλ this θhaυter, λused siρiθa υure τr dτυ‐ ed wiρρ ηe θτσsidered as the tyυiθaρ ηuρπ materiaρ λτr ρaser iσteraθtiτσ reμardiσμ λiηerηased τυtiθaρ seσsτrs. The mτst θτmmτσ ρasers emit either iσ the UV, visiηρe τr iσλrared IR . Hτwever, UV aσd IR ρasers have ηeeσ the majτr υρayers iσ the λieρd τλ υrτθessiσμ τυtiθaρ λiηers μiveσ that the re‐ suρtiσμ iσteraθtiτσ meθhaσisms are mτre eλλiθieσt λτr these waveρeσμths taπiσμ advaσtaμe τλ hiμher aηsτrυtiτσ iσ thτse reμimes. The twτ maiσ reμimes as ρaser sτurθes θτσθerσs are θτσtiσuτus wave CW aσd υuρsed emissiτσ. Reθeσt year~s ρaser deveρτυmeσts aρρτwed ρaser sτurθes tτ υreseσt a ηrτad raσμe τλ avaiρaηρe υuρsed reμimes, λrτm miρρiseθτσds ms tτ λemtτseθτσds λs υuρse widths. This avaiρaηiρity has υτteσtiated σew ways τλ usiσμ the ρaser as a tττρ λτr τυtiθaρ λiηer υrτθessiσμ. Uσder ρaser irradiatiτσ, aσd deυeσdiσμ τσ the meσtiτσed sτurθe υarameters, the maiσ υhys‐ iθaρ meθhaσisms θaσ ηe divided iσ thermaρ aσd υhτtτσiθ στσ-thermaρ eλλeθts. These υhysi‐ θaρ υrτθesses are used tτ θreate diλλereσt λiηer-ηased seσsτrs, as it wiρρ ηe desθriηed iσ the λτρρτwiσμ seθtiτσs. . . Thermal effects Thermaρ υrτθesses arise λrτm aηsτrυtiτσ τλ the ρaser eσerμy iσ the materiaρ, aσd iσ μeσeraρ aυυρy λτr θτσtiσuτus wave CW τυeratiτσ, ρτσμ υuρse ρeσμths aσd hiμh-υuρse-reυetitiτσλreφueσθy υuρse traiσs. Iσ this θase, the aηsτrηed radiatiτσ θreates aσ exθess τλ eσerμy due tτ the exθitatiτσ τλ the ρattiθe whiθh is traσsλτrmed iσtτ heat, iσθreasiσμ the materiaρ~s temυer‐ ature λrτm its surλaθe tτ its ηuρπ ηy heat θτσduθtiτσ, sτ the mτst ηasiθ thermaρ eλλeθt is heat‐ iσμ, that deυeσds τσ irradiatiτσ time aσd thermaρ diλλusivity τλ the materiaρ. Heatiσμ is the eλλeθt ηehiσd LPFG λaηriθatiτσ usiσμ CO ρaser, where the reλraθtiτσ iσdex θhaσμe is aθhieved ηy heatiσμ a λiηer suηmitted tτ a teσsiρe stress. Iλ the irradiaσθe is hiμh eστuμh, υhase traσsλτrmatiτσs are υrτduθed. Fτr siρiθa-ηase materiaρs, meρtiσμ is υrτduθed wheσ the irradiaσθe has a maμσitude τλ ~ W/θm aσd deυeσdiσμ τσ the irradiatiτσ time, the meρted materiaρ iσθreases its deυth iσtτ the ηuρπ. Oσθe the ητiρiσμ υτiσt is aθhieved, iλ the irradiaσθe reaθhes vaρues τλ >> W/θm [ ] vaυτrizatiτσ is iσitiated. This ρast steυ is the ηasis τλ the thermaρ υhτtτaηρatiτσ, whiθh θτσsists iσ the υreθise remτvaρ τλ materiaρ, ηy surλaθe vaυτrizatiτσ τr sυaρρatiτσ due tτ thermaρ stresses [ ].

Advance’ in Op“ical Fibe‘ La’e‘ Mic‘omachining fo‘ Sen’o‘’ Developmen“ h““p://dx.doi.o‘g/10.5772/52745

. . Photonic effects Phτtτiτσizatiτσ is a tyυe τλ ρaser matter iσteraθtiτσ ηy whiθh a ρaser υuρse mτdiλies the λuσ‐ dameσtaρ struθture τλ a materiaρ thrτuμh υhysiθaρ υrτθesses ρiπe στσ- thermaρ exθitatiτσ, iτσizatiτσ aσd dissτθiatiτσ τλ atτms aσd mτρeθuρes, deυeσdiσμ τσ the ρiμht aσd materiaρ υrτυerties. The simυρest υrτθess is the siσμρe υhτtτσ iτσizatiτσ SPI θτσsistiσμ iσ the aη‐ sτrυtiτσ τλ a siσμρe υhτtτσ with resuρtiσμ remτvaρ τλ τσe eρeθtrτσ. This υrτθess is strτσμρy deυeσdeσt τσ the waveρeσμth, ρayiσμ iσ the UV λτr the iσteraθtiτσ with μρass materiaρs, aσd reφuires ρτw irradiaσθe ρeveρs < Wθm- [ ]. This eλλeθt is the ηasis τλ the ρaser iσduθed reλraθtiτσ iσdex θhaσμes iσ FG λaηriθatiτσ where this πiσd τλ υhτtτθhemiθaρ reaθtiτσ is υrτ‐ duθed τσ UV υhτtτseσsitive Ge-dτυed λiηers. The meθhaσisms τλ υhτtτseσsitivity θaσ ηe exυρaiσed ηy the iσteraθtiτσ τλ UV radiatiτσ iσ a sυeθiaρ struθture iσ the λiηer~s ηuρπ σamed Germaσium τxyμeσ deλiθieσt θeσter GODC , whiθh is aηρe tτ aηsτrη τσe τr twτ υhτtτσ. The υhτtτseσsitivity meθhaσism is iσtriσsiθaρρy assτθiated with the dτυaσts iσθτrυτrated duriσμ the siρiθa-ηased τυtiθaρ λiηer λaηriθatiτσ. Thereλτre, it is υρausiηρe that the τriμiσs τλ this υrτθess are reρated with the μermaστsiρiθate μρass syσthesis, iσ whiθh a θτσtrτρρed seφueσθe τλ θhemiθaρ reaθtiτσs that iσvτρves a mixture τλ severaρ μases at hiμh temυerature τθθurs aθθτrdiσμρy with the reaθtiτσs [ ] T ì ïSiCρ + O ® SiO + Cρ ï T ï íGκCρ + O ® GκO + Cρ ï T ïGκO ® GκO + O ïî

These reaθtiτσs shτw that the υreseσθe τλ μermaσium υrτmτtes GeO λτrmatiτσ. Truρy, the λτrmatiτσ τλ GeO deλeθts is υrτmτted due tτ the thermτdyσamiθs τλ the μaseτus μermaσi‐ um redτx reaθtiτσ at the hiμh syσthesis temυerature aσd is dτmiσaσt, siσθe the Ge-O ητσd is weaπer thaσ the Si-O ητσd. Desυite the υτssiηiρity τλ τther suητxides ηeiσμ λτrmed, GeOx {x= tτ } , the GeO is the mτst θτmmτσ suη-υrτduθt iσside the μermaστsiρiθate μρass amτr‐ υhτus struθture, GeO -SiO , as a sτurθe τλ μρass deλeθts [ ]. The GODC, τθθurs wheσ a Ge atτm is ητσded tτ a Si τr Ge atτm, iσ the aηseσθe τλ aσ τxyμeσ atτm, μiviσμ rise tτ a strτσμ aηsτrυtiτσ at σm ηaσd [ ]. The mτdeρ τλ aσ τxyμeσ vaθaσθy σeiμhητuriσμ a Ge atτm was suμμested, ηased τσ the aσaρτμy τλ the sυeθtrτsθτυiθ υrτυerties τλ this Ge-reρated deλeθt with thτse mτσitτred τσ aσ τxyμeσ vaθaσθy iσ υure v-SiO . This is θτσsisteσt with the τσe υhτtτσ σature υathway, θτrresυτσdiσμ tτ the GODC~s triυρet state aσdits iσteσsity iσθreases ρiσearρy with the θτσθeσtratiτσ τλ GeO [ ]. The υhτtτseσsitivity meθhaσism θaσ aρsτ ηe triμμered thrτuμh a twτ υhτtτσ aηsτrυtiτσ meθhaσism, aσd its eλλiθieσθy is aλλeθted ηy severaρ υarameters ρiπe ρiμht~s υτwer deσsity, atteσuatiτσ aσd ρiμht [ ]. Desυite the λaθt that υure siρiθa μρasses exhiηits υττr υhτtτseσsitiv‐ ity tτ UV-ρaser ρiμht eveσ iλ exυτsed tτ ρarμe aθθumuρated λρueσθe vaρues θρτse tτ πJ/θm ,

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this θaσ ηe reversed wheσ a λs-ρaser ηeam at ≈ strτσμ υermaσeσt θhaσμes iσ the reλraθtive iσdex

σm waveρeσμth is used [ ]. Iσ this θase, - × - are attaiσaηρe.

The twτ υhτtτσ aηsτrυtiτσ υheστmeστσ is θτσsidered τσe τλ the muρti-υhτtτσ iτσizatiτσ MPI υrτθesses whiθh θτσsist iσ the aηsτrυtiτσ τλ twτ, three τr eveσ λive υhτtτσs exθitiσμ the eρeθtrτσs tτ the θτσduθtiτσ ηaσd. The diλλereσθe ηetweeσ the twτ υrτθesses θaσ ηe ex‐ υρaiσed θτmυariσμ the σumηer τλ υhτtτυrτduθts versus the irradiatiτσ iσteσsity [ ]. Tyυi‐ θaρρy, this is a hiμh-iσteσsity I~ Wθm- [ ] aσd very λast υrτθess, ρyiσμ iσ the λsraσμe. Twτ reμimes are distiσμuished, λs-UV aσd λs-IR, aθθτrdiσμ with the waveρeσμth emυρτyed. Iσ the UV reμime, the maiσ meθhaσism is the υreviτusρy twτ υhτtτσ aηsτrυtiτσ whiρe iσ the IR meθhaσism the three aσd λive υhτtτσ aηsτrυtiτσ are υredτmiσaσt. Laser-iσduθed τυtiθaρ ηreaπdτwσ is a υrτθess τλ υhτtτiτσizatiτσ whiθh has the resuρt τλ υρasma λτrmatiτσ aσd υhτtτaηρatiτσ. The maiσ υhτtτiτσizatiτσ meθhaσisms are the aρready meσtiτσed SPI aσd MPI. Fτr υs- aσd σs-υuρses the τυtiθaρ ηreaπdτwσ is exυρaiσed ηy the avaρaσθhe mτdeρ. It~s a damaμe meθhaσism that starts with τσe τr mτre eρeθtrτσs iσ the θτσ‐ duθtiτσ ηaσd, heated ηy the ρaser λieρd. The eρeθtrτσ θτρρides with the matrix, μaiσiσμ eστuμh πiσetiθ eσerμy ηy iσverse Bχκςψωχaνρuσμ tτ λree a seθτσd eρeθtrτσ. The same υrτθess reυeats uσtiρ the eρeθtrτσ deσsity aυυrτaθhes the θritiθaρ υρasma deσsity ~ e-/ m , resuρt‐ iσμ iσ υhτtτaηρatiτσ. “σ iσθτσveσieσt is that iσ the σs-time sθaρe, mτst τλ the υρasma eσerμy is traσsλerred tτ the matrix ηeiσμ aηρe tτ υrτduθe θτρρateraρ thermaρ damaμe aσd λraθtures, wτrseσiσμ the φuaρity τλ aηρatiτσ [ ]. This eλλeθt θaσ ηe avτided iσ the λs-sθaρe, siσθe there~s στ time λτr aσ avaρaσθhe λuρρy deveρτυ, aσd MPI assumes eφuaρ imυτrtaσθe tτ eρeθtrτσ ava‐ ρaσθhe. Thus, the heat diλλusiτσ is λrτzeσ aσd thermaρ damaμes are eρimiσated. This υrτθess is πστwσ as θτρd aηρatiτσ€ [ ]. Theτretiθaρρy, aθθτrdiσμ tτ the eρeθtrτσ avaρaσθhe mτdeρ, the ρaser λρueσθe threshτρd λτr aηρatiτσ is strτσμρy deυeσdeσt tτ the ρaser waveρeσμth, imυρyiσμ that this threshτρd shτuρd iσθrease sρiμhtρy as the waveρeσμth deθreases ηut reυτrted exυerimeσtaρ data shτws the τυ‐ υτsite. This θτuρd meaσ that τther υhτtτiτσizatiτσ υrτθesses θτuρd ηe imυρied iσ τυtiθaρ ηreaπdτwσ τλ siρiθa aσd haviσμ iσ miσd that ρattiθe deλeθts are mτre aηsτrυtive iσ the UV thaσ iσ MIR [ ].

. Fundamentals of optical fiber sensors The uσderstaσdiσμ τλ the υτteσtiaρ τλ usiσμ ρaser teθhστρτμy tτ θreate λiηer-ηased seσsτrs deυeσds aρsτ τσ the uσderstaσdiσμ τλ the reφuiremeσts thτse seσsτrs have. The υrτθess τλ iσteraθtiτσ must ρead tτ a θertaiσ θhaσμe iσ the λiηer υrτυerties that must υrτduθe the re‐ φuired seσsitivity tτ aσ exterσaρ θhaσμe. Iσ this seθtiτσ, the λuσdameσtaρs τλ the mτst θτm‐ mτσ λiηer-ηased seσsτrs is υreseσted with λτθus τσ thτse ηeiσμ tarμeted as aηρe tτ ηe υrτduθed ηy ρaser irradiatiτσ. Cavity-ηased seσsτrs aσd reλraθtive-iσdex mτduρated seσsτrs υriσθiυρes wiρρ ηe desθriηed.

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. . Optical fiber grating sensors FGs are τυtiθaρ deviθes ηased iσ the υriσθiυρe τλ υhτtτ-reλraθtive eλλeθt λirst disθτvered ηy Hiρρ κω aρ. [ ]. Siσθe theσ, their deveρτυmeσt had a siμσiλiθaσt imυaθt τσ researθh aσd deveρ‐ τυmeσt τλ teρeθτmmuσiθatiτσs systems aσd λiηer τυtiθ seσsτrs. It use as seσsiσμ eρemeσt is advaσtaμeτus due tτ the iσtriσsiθ θharaθteristiθs τλ the λiηer seσsτrs, suθh as muρtiυρexiσμ, remτte seσsiσμ, hiμh λρexiηiρity, ρτw υrτυaμatiσμ ρτss, hiμh seσsitivity, ρτw λaηriθatiτσ θτst, weiμht aσd θτmυaθtσess, hiμh aθθuraθy, simuρtaσeτus seσsiσμ aηiρity, aσd immuσity tτ eρeθ‐ trτmaμσetiθ iσterλereσθe. FGs are τλteσ θρassiλied iσtτ twτ tyυes ”raμμ μratiσμs aρsτ θaρρed reλρeθtiτσ τr shτrt-υeriτd μratiσμs , iσ whiθh θτuυρiσμ τθθurs ηetweeσ mτdes traveρρiσμ iσ τυυτsite direθtiτσs aσd traσsmissiτσ μratiσμs τr LPFGs , iσ whiθh the θτuυρiσμ is ηetweeσ mτdes traveρρiσμ iσ the same direθtiτσ. These τυtiθaρ deviθes are θτmυarativeρy simυρe aσd iσ its mτst ηasiθ λτrm, it θτσsists τσ a υeriτdiθ mτduρatiτσ τλ the υrτυerties τλ aσ τυtiθaρ λiηer usuaρρy the reλraθtiτσ iσdex τλ the θτre . This θaσ ηe made ηy υermaσeσt mτdiλiθatiτσ τλ the reλraθtive iσdex τλ the τυtiθaρ λiηer θτre τr ηy the υhysiθaρ deλτrmatiτσ τλ the λiηre. Iσ this seθtiτσ, it is υreseσted the λuσdameσtaρ asυeθts τλ ητth tyυes τλ μratiσμs, aσd their seσsiσμ aυυρiθatiτσ. . . . Fiηκχ Bχaμμ μχaωiσμ F”Gs are sυeθtraρ λiρters ηased τσ the υriσθiυρe τλ ”raμμ reλρeθtiτσ. These υeriτdiθ struθtures τυerate iσ reλρeθtiτσ mτde aσd are maσuλaθtured with a υeriτd τλ ρess thaσ m. Their suηmiθrτσ υeriτd υrτvide θτuυρiσμ ηetweeσ the mτdes that υrτυaμate iσ τυυτsite direθtiτσs. The υriσθiυρe τλ τυeratiτσ τλ these τυtiθaρ deviθes is sθhematized iσ Fiμure . “ staσdard F”G θτσsists τλ a reλraθtive iσdex mτduρatiτσ iσ the θτre τλ aσ τυtiθaρ λiηre that aθts tτ θτu‐ υρe the λuσdameσtaρ λτrward υrτυaμatiσμ mτde tτ the θτσtra-υrτυaμatiσμ θτre mτde. Wheσ a ηrτad-sυeθtrum ρiμht ηeam iσside iσ the λiηer μratiσμ, a σarrτw waveρeσμth raσμe is re‐ λρeθted aσd aρρ τther waveρeσμths are traσsmitted. The reλρeθted ρiμht siμσaρ wiρρ ηe θeσtered at the ”raμμ waveρeσμth. The sυeθtraρ resυτσse τλ the F”G is μτverσed ηy the υhase matθh‐ iσμ θτσditiτσ, B = σκλλ.Λ, where B is the ”raμμ waveρeσμth, σκλλ the eλλeθtive reλraθtive iσdex τλ the λiηer θτre aσd Λ the ”raμμ μratiσμ υeriτd [ ]. “σy θhaσμe iσ the mτdaρ iσdex τr μra‐ tiσμ υitθh τλ the λiηer θaused ηy straiσ τr temυerature resuρts iσ a shiλt τλ the ”raμμ wave‐ ρeσμth.

Figure 1. Schema“ic ‘ep‘e’en“a“ion of Fibe‘ B‘agg g‘a“ing p‘inciple of ope‘a“ion.

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Cτσsider a uσiλτrm ”raμμ μratiσμ λτrmed withiσ the θτre τλ aσ τυtiθaρ ηer. The reλraθtiτσ iσdex υrτ ρe θaσ ηe exυressed as σ x = σ.θτs /Λ , where σ is the amυρitude τλ the iσ‐ duθed reλraθtive-iσdex υerturηatiτσ tyυiθaρρy, - ª - aσd x is the distaσθe aρτσμ the ηer~s ρτσμitudiσaρ axis. The θτuυρed-mτde theτry aσaρytiθaρ eσaηρes the desθriυtiτσ τλ the re eθtiτσ υrτυerties τλ ”raμμ μratiσμs. The re eθtivity τλ a μratiσμ with ρeσμth L aσd θτσ‐ staσt mτduρatiτσ amυρitude aσd υeriτd is μiveσ ηy R L, = taσh .L [ ] were the θτu‐ υρiσμ θτeλλiθieσt λτr a siσμρe mτde λiηer is = . σ/ . F”Gs have ηeeσ aυυρied iσ teρeθτmmuσiθatiτσs[ ] aσd aρsτ λτr a wide variety τλ seσsiσμ aυυρiθatiτσs iσ severaρ λieρds [ ]. Hτwever, F”Gs has υraθtiθaρ imυρemeσtatiτσ ρimitatiτσs, iσθρudiσμ the σeeds τλ sυeθiaρ υτst-υrτθessiσμ λτr seσsiσμ τλ exterσaρ reλraθtive iσdex aσd reduθtiτσ τλ the seσsτr~s meθhaσiθaρ streσμth [ ]. . . . Lτσμ υκχiτd λiηκχ μχaωiσμψ LPFGs are υrτduθed ηy iσduθiσμ a υeriτdiθ reλraθtive iσdex mτduρatiτσ tiυiθaρρy - iσ the λiηer θτre with υeriτds tyυiθaρρy iσ the raσμe λrτm m tτ m [ ]. These τυtiθaρ deviθes τυerate iσ traσsmissiτσ mτde aσd their ρarμe mτduρatiτσ υeriτd υrτmτtes the ρiμht θτuυρiσμ ηetweeσ θτ-υrτυaμatiσμ mτdes τλ the τυtiθaρ λiηre. Iσ the θase τλ siσμρe mτde λi‐ ηers, this taπes υρaθe ηetweeσ the λuσdameσtaρ aσd θρaddiσμ mτdes, iσ the same direθtiτσ. This υriσθiυρe is iρρustrated iσ Fiμure . The θρaddiσμ mτdes are φuiθπρy atteσuated resuρtiσμ iσ a series τλ atteσuatiτσ ηaσds iσ the traσsmissiτσ sυeθtrum. Eaθh atteσuatiτσ ηaσd θτrre‐ sυτσds tτ θτuυρiσμ tτ a diλλereσt θρaddiσμ mτde. The υhase matθhiσμ waveρeσμths are μτv‐ erσed ηy the exυressiτσ χκψς = σκλλ,θτª σκλλ,θρς .Λ [ , ], where Λ is the μratiσμ υeriτd, σκλλ,θτ aσdσκλλ,θρ are the eλλeθtive reλraθtive iσdexes τλ the θτre aσd ςth-θρaddiσμ mτdes, resυeθtive‐ ρy. The reλraθtive iσdex seσsitivity τλ LPFGs arises λrτm the deυeσdeσθe τλ the θτuυρiσμ waveρeσμth uυτσ the eλλeθtive iσdex τλ the θρaddiσμ mτde.

Figure 2. Schema“ic diag‘am of long pe‘iod fibe‘ g‘a“ing.

Liμht traσsmissiτσ thrτuμh the θτre λτρρτws a siσusτidaρ λuσθtiτσ τλ the θτre reλraθtive iσ‐ dex mτduρatiτσ λτr the waveρeσμths iσ the resτσaσθe [ ] is μiveσ ηy T = θτs Γ.L/ , where L is the μratiσμ ρeσμth aσd Γ is a θτuυρiσμ θτeλλiθieσt υrτυτrtiτσaρ tτ the θτre iσdex mτduρa‐ tiτσ. The ηaσdwidth τλ the resτσaσθe diυs deυeσds τσ ητth the θτuυρiσμ θτeλλiθieσt aσd the diλλereσθe ηetweeσ the θτre aσd θρaddiσμ iσdexes

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DlFWHM =

(

lς

ς σκλλ ,θτ - σκλλ ,θρ

)

Γ pL

Exterσaρ θhaσμes iσ υarameters ρiπe reλraθtive iσdex, temυerature τr straiσ θaσ aλλeθt the terms iσ the ruρiσμ eφuatiτσs aσd θτσseφueσtρy shiλt the atteσuatiτσ diυs aσd aρter their ηaσdwidths [ ] . These τυtiθaρ deviθes are very seσsitive tτ θhaσμes iσ υhysiθaρ υarameters, suθh as, temυera‐ ture, straiσ, ηeσdiσμ, tτrsiτσ, aσd reλraθtive iσdex τλ the surrτuσdiσμ medium [ ]. This maπes υτssiηρe the use τλ the LPFGs as a muρti-υarameter seσsτr [ ]. Their seσsiηiρity τλ tτ exterσaρ eσvirτσmeσt υarameters is determiσed ηy the maμσitude τλ the υerturηatiτσ iσ the reλraθtive iσdex, the υeriτd τλ the μratiσμ, aσd its ρeσμth. Cτmυared tτ τther τυtiθaρ deviθes, LPFGs have a σumηer τλ uσiφue advaσtaμes suθh as ρτw iσsertiτσ ρτsses υτρarizatiτσ iσdeυeσdeσθe, hiμh temυerature seσsitivity, aσd reρativeρy sim‐ υρe λaηriθatiτσ. “ λurther advaσtaμe τλ these deviθes is their hiμher seσsitivity tτ the eσvi‐ rτσmeσtaρ reλraθtive iσdex θhaσμe withτut the σeed λτr aθθess tτ the evaσesθeσt λieρd, as iσ the θase τλ the F”Gs. The extreme seσsitivity τλ the LPFGs tτ eσvirτσmeσtaρ θhaσμes θτuρd ηe a disadvaσtaμe iσ teρeθτmmuσiθatiτσs deviθes θrτss seσsitive υrτηρems . . . Cavity based optical fiber sensor Oυtiθaρ λiηer FaηryªPerτt FP iσterλerτmetriθ seσsτrs are the maiσ θavity-ηased tyυe τλ λi‐ ηer-seσsτrs aσd demτσstrate a μreat versatiρity iσ diλλereσt aυυρiθatiτσs [ , ]. The θavityηased seσsτrs are υartiθuρarρy attraθtive due tτ its iσhereσt advaσtaμes, iσθρudiσμ smaρρ size, reρativeρy ρτw temυerature θrτss-seσsitivity aσd θτrrτsiτσ resistaσθe, hiμh seσsitivity, hiμh λreφueσθy resυτσse aσd immuσity tτ eρeθtrτmaμσetiθ iσterλereσθe. Iσ its simυρest λτrm, the FP θavity θτσsists iσ twτ reλρeθtive surλaθes arraσμed iσ υaraρρeρ λτrmiσμ a resτσaσt θavity. The reλρeθtiτσs at the twτ eσd surλaθes τλ the θavity θreate aσ iσ‐ terλereσθe siμσaρ whiθh is a λuσθtiτσ τλ the ρeσμth aσd reλraθtive iσdex τλ the θavity. Chaσμes iσ eσvirτσmeσt θauses a υhase shiλt iσ the iσterλereσθe υatterσ aσd, as a resuρt, a λiηer FP seσsτr is θaυaηρe τλ measuriσμ variτus υarameters iσθρudiσμ temυerature, υressure, straiσ [ ]. Cτσsideriσμ a μeσeraρ aσaρysis, the traσsmissiτσ λuσθtiτσ is [ ] T=

(

-R

)

- R - R θτs (f )

ηeiσμ R the reλρeθtivity τλ the surλaθes, assumiσμ that ητth are eφuaρ, aσd that the υhase diλ‐ λereσθe ηetweeσ eaθh suθθeediσμ reλρeθtiτσs is = .σ.L.θτs / . The υriσθiυρe τλ a seσsτr ηased iσ deviθes ρiπe these is ηased iσ the λaθt that θhaσμes τσ the θavity distaσθe τr aσμρe τr iσ the reλraθtive iσdex τλ the diλλereσt media υrτduθes a θhaσμe

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iσ the traσsmitted siμσaρ τr reλρeθted, siσθe, the reλρeθted siμσaρ is eφuaρ tτ -T, στt θτσsider‐ iσμ aηsτrυtiτσ . The resτρutiτσ τλ the seσsτr θaσ ηe evaρuated thrτuμh a υarameter σamed λiσesse, F, reρatiσμ the distaσθe ηetweeσ υeaπs, , aσd the λuρρ-width haρλ-maximum τλ the υeaπs, F= / . Naturaρρy, reaρ λiηer seσsτrs are mτre θτmυρex aσd the aυυρied theτry diλλers λrτm θase tτ θase. Traditiτσaρρy, FP θavities have ηeeσ divided iσ iσtriσsiθ where the seσsiσμ eρemeσt is the λiηer itseρλ , extriσsiθ twτ λiηer υieθes υhysiθaρρy seυarated λτrmiσμ a θavity ητuσded tyυi‐ θaρρy with a θaυiρρary μρass tuηe τr hyηrid sυρiθiσμ seθtiτσs τλ diλλereσt tyυes τλ λiηers, λτr examυρe [ , - ]. Hτwever, τther methτds τλ θreatiσμ these θavities have ηeeσ researθhed ρiπe θhemiθaρ etθhiσμ aσd ρaser υrτθessiσμ. Chemiθaρ etθhiσμ is aσ eλλiθieσt aσd ρτw θτst way τλ υrτduθiσμ FP θavities iσ τυtiθaρ λiηers, ηut the θτσtrτρ τλ the θavity ρeσμth is ρess aθθurate aσd deυeσds τσ the υreθise θτσtrτρ τλ the υrτθess, maiσρy the duratiτσ τλ the etθhiσμ[ ]. Reθeσt methτds use ρaser ηeams tτ υrτduθe the θavities, either ηy remτviσμ materiaρ ρateraρ‐ ρy iσ the λiηer [ ] τr τυeσiσμ hτρes τσ the λiηer~s eσd [ ] as sθhematized iσ Fiμure . Raσ κω aρ. υreseσt aσ iσterestiσμ examυρe [ ] τλ a reλraθtive iσdex seσsτr ηased τσ a θavity θreated ηy a σm waveρeσμth ρaser ηeam τσ the eσd τλ aσ τυtiθaρ λiηer. The miθrτυatterσed λiηer is theσ sυρiθed tτ aστther λiηerθreatiσμ aσ air θavity. With this μeτmetry Fiμure a , the reλraθtive iσdex measures θaσ ηe aθθτmυρished withτut the σeed τλ λiρρiσμ the miθrτmetriθ θavity. Iσ this θase, reλρeθtiτσ iσ a third iσterλaθe must ηe θτσsidered aσd eφuatiτσ re‐ υρaθed aθθτrdiσμρy [ , ], aσd the aσaρyzed siμσaρ is the reλρeθted iσstead τλ the traσsmit‐ ted. This tyυe τλ seσsτr, with a θavity λτrmed λrτm a hτρe with a deυth τλ arτuσd m aσd m diameter aσd mm distaσθe tτ the tiυ , aρρτwed tτ measure reλraθtive iσdexes τλ ρiφ‐ uids with a resτρutiτσ τλ ~ x - , aσd is θτσsidered as the μuideρiσe λτr the researθh υreseσt‐ ed iσ seθtiτσ .

Figure 3. Schema“ic of “wo po’’ible config”‘a“ion’ fo‘ cavi“y-ba’ed op“ical ’en’o‘’.

. FGs sensors fabrication using laser radiation FGs are imυτrtaσt λiηer-ηased seσsτrs. Traditiτσaρρy they are υrτduθed ηy arθ-disθharμes τr UV-exυτsure. Hτwever, iσ the ρast years the use τλ CO ρasers, emittiσμ iσ the MIR, aσd λs ρasers, emittiσμ iσ the NIR, tτ write FGs has emerμed as aσ imυτrtaσt aρterσative. Iσ this seθ‐ tiτσ, the maiσ ρaser maσuλaθturiσμ teθhσiφues τλ λiηer μratiσμ seσsτrs are υreseσted, θτσsid‐

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eriσμ UV, MIR aσd NIR radiatiτσs. Iσ this sθτυe, aσ aσaρytiθaρ theτretiθaρ mτdeρ λτr the writiσμ τλ LPFG ηy MIR radiatiτσ is υreseσted aσd θτmυared with exυerimeσtaρ data. . . FG writing using UV lasers The use τλ UV ρaser radiatiτσ was iσ the ηase τλ ητth F”G aσd LPFG deveρτυmeσt. The λτr‐ matiτσ τλ μratiσμs iσ aσ τυtiθaρ λiηer was λirst reυτrted iσ ηy Kawasaπi κω aρ. [ ] usiσμ aσ arμτσ-iτσ ρaser at σm UV waveρeσμth. “ λew years ρatter, the λirst LPFG was iσtrτ‐ duθed iσ ηy Veσμsarπar whτ exυτsed υhτtτseσsitive τυtiθaρ λiηers tτ σm waveρeσμth UV πryυtτσ λρuτride, KrF, ρaser ρiμht [ ]. “ρthτuμh the λirst F”Gs have ηeeσ maσuλaθtured ηy iσterσaρ writiσμ [ ] usiσμ the iσterλer‐ eσθe ηetweeσ the traσsmitted ηeam aσd reλρeθted ηeams aσd hτρτμraυhy twτ τverρaυυiσμ UV ρiμht ηeams iσterλere υrτduθiσμ a υeriτdiθ iσterλereσθe υatterσ [ ], the υhase-masπ teθhσiφue has φuiθπρy ηeθτme usuaρ, aσd eveσ used iσ a simiρar way λrτm the start λτr LPFG writiσμ. Usuaρρy, the υhase-masπ is made λrτm a λρat υieθe τλ siρiθa μρass traσsυareσt tτ UV radia‐ tiτσ where a τσe dimeσsiτσaρ υeriτdiθ surλaθe reρieλ is etθhed usiσμ υhτtτρithτμraυhiθ teθhσiφues iσ τσe τλ the surλaθes. Thus, the υhase-masπ ηeθτmes aσ τυtiθaρ eρemeσt with the θaυaηiρity tτ diλλraθt the UV ηeam iσ traσsmissiτσ. The iσterλereσθe τλ the traσsmitted ηeams θτrresυτσds tτ diλλereσt diλλraθtiτσ τrders iσ the υrτximity τλ the surλaθe, τriμiσatiσμ a λriσμe υatterσ, aσd ρeadiσμ tτ ”raμμ μratiσμs λaηriθatiτσ ηy mτduρatiτσ τλ the reλraθtive iσdex iσ the θτre τλ the τυtiθaρ λiηre. The υrτλiρe τλ the υhase μratiσμ is θhτseσ suθh that the zerτ-τrder diλλraθted ηeam is suυυressed tτ ρess thaσ % τλ the traσsmitted υτwer. Iσ addi‐ tiτσ, the υriσθiυaρ ηeams diλλraθted ηy the υhase-masπ θτrresυτσd tτ υρus aσd miσus λirst τrders, θτσtaiσiσμ eaθh τσe, tyυiθaρρy, mτre thaσ % τλ the traσsmitted υτwer. Theσ the υrτduθed iσterλereσθe υatterσ υhτtτ-imυriσts a reλraθtive iσdex mτduρatiτσ iσ the θτre τλ the υhτtτseσsitive τυtiθaρ λiηre υρaθed iσ θτσtaθt, τr iσ θρτse υrτximity, immediateρy ηehiσd the υhase masπ. Tyυiθaρρy, the λriσμe υatterσ is λτθused aρτσμ the λiηer~s θτre with the heρυ τλ a θyρiσdriθaρ ρeσs. The υhase-masπ teθhσiφue has the advaσtaμe τλ μreatρy simυρiλyiσμ the maσuλaθturiσμ υrτθess λτr ”raμμ μratiσμs, yet yieρdiσμ hiμh υerλτrmaσθe μratiσμs. Iσ θτm‐ υarisτσ with the hτρτμraυhiθ teθhσiφue, the υhase-masπ teθhσiφue τλλers easier λiηer/ρaser aρiμσmeσt, reduθed staηiρity reφuiremeσts τσ the writiσμ aυυaratus aσd ρτwer θτhereσθe re‐ φuiremeσts τσ the UV ρaser ηeam. “στther writiσμ methτd uses the υτiσt-ηy-υτiσt teθhσiφue. Iσ this θase, siσμρe UV ρaser ηeam is used tτ imυriσt the μratiσμ iσtτ the λiηers eφueσtiaρρy aρτσμ the λiηer~s ρeσμth. The iσθideσt ρaser ηeam is λτθused τσ the τυtiθaρ λiηer θτre τr θρaddiσμ λτr either F”G τr LPFG, resυeθtiveρy usiσμ a ρeσs. The υeriτdiθ irradiatiτσ is aθθτmυρished ηy θτmυuter θτσtrτρ τλ the ρaser ηeam aσd the mτvemeσt τλ the λiηer, sτ the υeriτds are iσsθriηed. “στther way tτ υrτduθe the υeriτdiθ iσsθriυtiτσ is ηy sθaσσiσμ the ρaser ηeam λτθus τver the τυtiθaρ λiηer, στt τσρy tτ υrτduθe the ρτσμitudiσaρ mτduρatiτσ ηut aρsτ tτ υrτduθe eaθh traσsversaρ reλraθ‐ tive iσdex θhaσμe zτσe. This υrτθess is iρρustrated iσ seθtiτσ . . reμardiσμ MIR irradiatiτσ teθhσiφues. Fiμure iρρustrate ητth writiσμ teθhσiφues.

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The meσtiτσed methτds aυυρy iσdeυeσdeσtρy τλ the UV ρaser used, aσd thus λrτm the υhysiθaρ meθhaσisms iσvτρved see seθtiτσ . Hτwever, ρaser teθhστρτμy siμσiλiθaσtρy diλλers, a θharaθ‐ teristiθ τλ υrτduθiσμ FG usiσμ UV ρaser radiatiτσ. Usuaρρy, exθimer ρasers are used tτ write FGs thrτuμh the siσμρe- τr dτuηρe-υhτtτσ ρτw eσerμy υhysiθaρ υriσθiυρes desθriηed iσ seθtiτσ . Waveρeσμths τλ σm, aσd iσ the raσμes σm tτ σm τr σm tτ σm are tyυiθaρ ei‐ ther λτr F”Gs τr LPFGs. ”esides aυυρied waveρeσμth, the reφuired irradiaσθes deυeσd strτσμρy iσ the τυtiθaρ λiηer ηeiσμ θτσsidered maiσρy its υhτtτseσsitivity θharaθteristiθs ηut θaσ rτuμh‐ ρy ηeiσμ θτσsidered iσ the raσμe λrτm a λew W/θm tτ teσths τλ MW/θm [ ].

Figure 4. Ill”’“‘a“ion of (a) pha’e-ma’k and (b) poin“-by-poin“ w‘i“ing “echniq”e’.

Reμardiσμ muρtiυhτtτσiθ hiμh-exθitatiτσ eσerμy UV irradiatiτσ, this is aθθτmυρished usiσμ the reρativeρy σew λs-υuρsed ρaser teθhστρτμy, tyυiθaρρy emittiσμ with waveρeσμths ρτwer thaσ σm. Iσ these θases, irradiaσθes are iσ the τrder τλ GW/θm τr hiμher [ ]. This teθh‐ στρτμy ηased iσ λs-υuρses aρρτws τηtaiσiσμ exθeρρeσt φuaρity FGs maiσρy tτ the ρaser hiμh sυatiaρ uσiλτrmity [ ]. Hτwever, this teθhστρτμy is stiρρ very exυeσsive whiθh ρimits its ηrτader use wheσ θτmυariσμ with τther teθhστρτμies either iσ UV τr IR . . . LPFG writing using CO lasers The use τλ CO ρasers tτ υrτduθe LPFGs was λirst reυτrted ηy Davis κω aρ. [ ] aσd “πiyama κω aρ. [ ] iσ . Frτm theσ τσ, the aυυρiθatiτσ τλ this teθhστρτμy has ρead tτ aσ iσθreasiσμ researθh τσ its aυυρiθatiτσ λτr the deveρτυmeσt τλ σew τυtiθaρ λiηer seσsτrs [ ]. Usiσμ this tyυe τλ MIR emissiτσ ρaser has severaρ advaσtaμes reμardiσμ the τther twτ weρρ estaηρished methτds UV ρasers aσd arθ disθharμes . The μratiσμs θaσ ηe iσsθriηed direθtρy iσ mτst teρeθτmmuσiθatiτσ λiηers, suυυτrt hiμh temυeratures withτut vaσishiσμ iσ τυυτsitiτσ tτ thτse υrτduθed ηy UV the υrτθess has hiμh reυeataηiρity aσd υrediθtaηiρity iσ τυυτsi‐ tiτσ tτ the arθ-disθharμe methτd . “ρsτ, siσθe CO ρaser systems are θτmmτσρy used tτ υrτθ‐ ess severaρ materiaρs aσd have a ρτσμ estaηρished iσdustriaρ aυυρiθatiτσ, avaiρaηρe systems are rτηust aσd ρτw-υriθe. The aυυρiθatiτσ τλ MIR ρaser radiatiτσ tτ υrτduθe a LPFG has υhysiθaρ υriσθiυρes simiρar tτ the τσes θτσsidered λτr arθ-iσduθed LPFGs [ ]. ”τth reρy iσ thermaρ eλλeθts aθtiσμ iσ the λi‐ ηer ηuρπ materiaρs. Hτwever, whiρe the ρatter θaσ ηe θτσsidered as a vτρume eλλeθt, ηeiσμ aυ‐ υρied aρτσμ the traσsversaρ seθtiτσ τλ the λiηer, ηetweeσ the twτ eρeθtrτdes, the materiaρ~s

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hiμh suυerλiθiaρ aηsτrυtiτσ θτσsidered iσ MIR irradiatiτσ υrτmτtes heat θτσduθtiτσ as a majτr υρayer iσ the υhysiθaρ meθhaσisms iσvτρved. . . . Pνyψiθaρ ςκθνaσiψςψ Cτσsideriσμ a staσdard siρiθa-ηased τυtiθaρ λiηer uσder teσsiτσ aσd irradiated ηy a Gaussi‐ aσ . m waveρeσμth ηeam emitted λrτm a CO ρaser, twτ maiσ υheστmeσa must ηe θτσ‐ sidered the thermaρ heatiσμ due tτ the iσteraθtiτσ ηetweeσ the υhτtτσs aσd the μρass mτρeθuρar struθture aσd the stress due tτ the diλλereσθes ηetweeσ a reρativeρy ρτw-visθτsity dτυed siρiθa θτre aσd a reρativeρy hiμh-visθτsity υure siρiθa θρaddiσμ [ ]. Diλλereσθes ηe‐ tweeσ θτre aσd θρaddiσμ thermaρ exυaσsiτσ θτeλλiθieσts aσd visθτsity ρead tτ residuaρ ther‐ maρ stresses aσd draw-iσduθed residuaρ stresses. These eλλeθts are ρτθaρized aσd, wheσ υeriτdiθaρρy iσduθed iσ the λiηer~s ρeσμth, θaσ ηe resυτσsiηρe λτr the θreatiτσ τλ the μratiσμs. This eλλeθt is due tτ the reλraθtive iσdex θhaσμe resuρtiσμ λrτm λrτzeσ-iσ visθτeρastiθity [ ]. The temυerature distriηutiτσ T χ,z,ω , with χ = x + y λτr ρaser heatiσμ τλ a hτmτμeσeτus me‐ dium θaσ ηe τηtaiσed ηy sτρviσμ the D heat λρτw eφuatiτσ. Cτσsideriσμ K = K T , deλiσiσμ the thermaρ diλλusivity π [m s- ] as π = K/ Cυ , where is the deσsity, Cυ the sυeθiλiθ heat, K the thermaρ θτσduθtivity aσd assumiσμ them θτσstaσts, the resuρtiσμ temυerature θaσ ηe aυ‐ υrτximated λτr Gaussiaσ eρρiυtiθaρ ρaser ηeams thrτuμh [ - ] T ( x, y, z,ω ) =

(

- R) P

é æa ψ Y ( x , y , ψ ) × êexυ ( aT z ) κχλθ ç T + êë è æ aT ψ z ö ù + exυ ( - aT z ) × a + η × κχλθ ç - ÷ ú dψ ψ ø ûú è

ò

p πwx w y

Kω

zö ÷+ ψø

with Y ( x, y, ψ) =

(

aT ψ ψ wx w y

)

é ( a ψ) y x × exυ ê + T êw + ψ wy + ψ + ë x

ù ú ú û

ηeiσμ R the reλρeθtivity at the air/λiηer iσterλaθe λτr the assumed waveρeσμth, P the ρaser υτwer, aT the aηsτrυtiτσ θτeλλiθieσt assumed θτσstaσt aσd wx aσd wy the ηeam's radii at λτθus λτr eaθh axis . With the temυerature, T, the resuρtiσμ residuaρ thermaρ stresses θaσ ηe θaρθuρated usiσμ [ ]

sx =

Δ -n

é n ê êë χθ

ù

ò χ = aTχdχ -aT úú χθ

û

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ηeiσμχθ is the radius θρaddiσμ τr θτre , Δ is the Yτuσμ~s mτduρus aσd

the Pτissτσ~s ratiτ.

Iλ the θτre is the ρτwer visθτsity μρass e.μ. Ge-dτυed siρiθa θτre with υure siρiθa θρaddiσμ , the residuaρ axiaρ eρastiθ stresses iσ the θρaddiσμ aσd θτre, θρ aσd θτ, resυeθtiveρy, resuρtiσμ λrτm a draw teσsiτσ F, τver the eφuivaρeσt θrτss-seθtiτσaρ areas Aθρ aσd Aθτ θaσ ηe τηtaiσed λrτm [ ]

s x ,θρ =

ö Aθτ Δθτ F æ çç ÷ Aθρ è Aθτ Δθτ + Aθρ Δθρ ÷ø

æ ö Δθτ aσd s x ,θτ = F çç ÷÷ è Aθτ Δθτ + Aθρ Δθρ ø

Taπiσμ iσ θτσsideratiτσ the meσtiτσed stresses, the reλraθtive iσdex θhaσμe iσ a siρiθa-ηased τυtiθaρ λiηer θaσ ηe aυυrτximated ηy the reρatiτσ [ ] ∆σ ≈ - . × - , where reυreseσts the τveraρρ ητth thermaρ aσd drawσ-iσduθed residuaρ stresses iσ MPa iσ the λiηer~s axiaρ direθtiτσ. “θθτrdiσμρy with Yaηρτσ [ ], stresses iσ the τther direθtiτσs θaσ ηe σeμρeθted. ”esides stress-reρated reλraθtive iσdex θhaσμe, ρτθaρized heatiσμ θaσ iσduθe miθrτdeλτrma‐ tiτσ τλ the λiηer aσd aρsτ θhaσμes iσ its μρass struθture. The ρater is ρiπeρy tτ τθθur iσ the θτre λτr whiθh the λiθtive temυerature ηeρτw the λiθtive temυerature the μρass struθture dτesσ~t θhaσμe is ρτwer [ , ]. “s aσ examυρe, it θaσ ηe λτuσd that, λτr a Ge-dτυed θτre, the λiθtive temυerature raσμes λrτm K aσd K [ ]. These aσaρytiθaρ eφuatiτσs dτσ~t θτσsider aρρ the υhysiθaρ υheστmeσa e.μ. θτσveθtiτσ aσd radiatiτσ ρτsses aσd were deveρτυed assumiσμ severaρ simυρiλiθatiτσs maiσρy, σeμρeθtiσμ the temυerature deυeσdeσθe τλ the μρass υarameters . Hτwever, their θaυaηiρity τλ ηeiσμ used as aσ eσμiσeeriσμ tττρ tτ deveρτυ λiηer τυtiθ seσsτrs has ηeeσ demτσstrated [ ]. “ de‐ taiρed aσaρysis θaσ ηe made usiσμ σumeriθaρ methτds aσd θτσsideriσμ that the aηsτrυtiτσ θτeλλiθieσt is temυerature deυeσdeσt, e.μ. aθθτrdiσμρy with MaθLaθhaσ aσd Meyer [ ]. . . . Iχχadiaωiτσ ςκωντdτρτμiκψ Siσθe there is stiρρ στ υhase masπ avaiρaηρe λτr CO ρaser radiatiτσ, methτdτρτμies reρy ηasi‐ θaρρy iσ the υτiσt-ηy-υτiσt teθhσiφue. Nevertheρess, severaρ methτdτρτμies have ηeeσ tested siσθe the λirst exυerieσθes iσ aσd are resumed iσ the sθhematiθ τλ Fiμure . “s aσ exam‐ υρe, Davis [ ] aσd “πiyama [ ] ητth have writteσ eaθh siσμρe υeriτd τλ a μratiσμ ηy λτθu‐ siσμthe ρaser ηeam ηy meaσs τλ sυheriθaρ ρeσses. Sυτts had dimeσsiτσs τλ aητut maσd traσsρatiτσ staμes mτved the λiηer uσder the ρaser sυτt. They used a CW ρaser, aσd the siσμρe υuρse duratiτσ was deλiσed thrτuμh a θτmυuter-θτσtrτρρed shutter. Usuaρρy, CW CO ρaser teθhστρτμy is θhτseσ due tτ its avaiρaηiρity aσd θτst. Lτw υτwer ρa‐ sers aσd meθhaσiθaρ shutters aρρτwiσμ huσdreds τλ ms υuρses υerλτrm weρρ aσd aθθτmυρish the reφuired υerλτrmaσθes. Q-switθh CO ρasers [ ] have aρsτ ηeeσ reυτrted ηy Raτκω aρ. [ ]. Iσ this θase, shτrter υuρses are avaiρaηρe at hiμh λreφueσθy rate iσ the τrder τλ πW . Nevertheρess, siσθe λρueσθe is the maiσ υarameter iσvτρved iσ the iσteraθtiτσ υrτθess, settiσμ ρaser υτwer, υuρse duratiτσ aσd sυτt radius shτuρd ρead tτ simiρar resuρts [ ].

Advance’ in Op“ical Fibe‘ La’e‘ Mic‘omachining fo‘ Sen’o‘’ Developmen“ h““p://dx.doi.o‘g/10.5772/52745

Figure 5. Schema“ic ill”’“‘a“ing “he diffe‘en“ i‘‘adia“ion me“hodologie’ “ha“ can be applied fo‘ each available ope‘a‐ “ional pa‘ame“e‘.

Reμardiσμ the way eaθh reλraθtive iσdex mτduρatiτσ is θreated, there are maiσρy twτ τυ‐ tiτσs a statiθ irradiatiτσ, λτr whiθh the ρaser is aυυρied λτr a determiσed amτuσt τλ time, aσd a dyσamiθ irradiatiτσ where the ρaser ηeam is sθaσσed τver the reμiτσ where the reλraθtive iσdex θhaσμe is tτ ηe θreated. Iσ the λirst θase, ηasiθaρρy, τσe must eσsure that the reμiτσ is λuρρy irradiated i.e. the λτθused sυτt is ρarμer that λiηer~s diameter whiρe iσ the sθaσσiσμ υrτθedure reφuires the τυυτsite sυτt size smaρρer that the λiηer~s diameter . Fiμure sθhematizes the twτ situatiτσs θτσsidered λτr the statiθ υrτθedures aσd the τσe λτr sθaσσiσμ. Fτr the ρatter Fiμure a , the usuaρ υrτθedure is tτ have the ρaser ηeam λτθused iσ a smaρρ sυτt aσd sθaσσed it τver the λiηer usiσμ a μaρvaστmetriθ mirrτr. Iλ twτ τλ suθh mirrτrs are used, τσe τλ them θaσ ηe used tτ mτve the ηeam ρτσμitudiσaρρy aσd thus write the λuρρ LPFG withτut mτviσμ the λiηer. Hτwever, these sθaσσers aσd assτθiated τυtiθs are exυeσsive, aσd aθθτmυρishiσμ smaρρ sυτts is diλλiθuρt λτr the θτσsidered waveρeσμth. The diλ‐ λraθtiτσ ρimited sυτt radius, wd, resuρtiσμ λrτm λτθusiσμ aσ iσitiaρ ηeam τλ waveρeσμth aσd radius w usiσμ a ρeσs τλ λτθaρ distaσθe λ is wd = . .λ/w .

Figure 6. Ill”’“‘a“ion of (a) dynamic ’canning and ’“a“ic (b) ci‘c”la‘ and (c) ellip“ical ’po“’ p‘oced”‘e’ in c‘ea“ing LPFG in an op“ical fibe‘.

Fiμure shτws the diλλraθtiτσ ρimited sυτt radius vaρues λτr a . m waveρeσμth ηeam λτ‐ θused ηy diλλereσt ρeσses. Twτ situatiτσs are υρτtted τσe θτσsiders that the ρaser has aσ iσi‐ tiaρ . mm radius a usuaρ vaρue aσd the τther that this vaρue dτuηρes e.μ. usiσμ a x ηeam exυaσder . “ρsτ υρτtted is the dimeσsiτσ θρaddiσμ radius τλ a θτmmτσ τυtiθaρ λiηer λτr the θase, the SMF- , aρready θτσsidered υreviτusρy . The υρτt iσdiθates that τσρy λτr the ρτwest λτθaρ ρeσμths < mm, averaμiσμ λτr the twτ situatiτσs τσe θaσ τηtaiσ sυτt sizes smaρρer

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thaσ the τυtiθaρ λiηer radius. The θτmmτσ situatiτσ is tτ use λτθaρ ρeσμths iσ the τrder τλ mm, aσd tyυiθaρρy sυτt sizes are iσ the τrder τλ huσdreds τλ miθrτσs. This ρeads tτ the λaθt that usuaρρy a statiθ aυυrτaθh is used. Siσθe a θirθuρar sυτt θreates υτteσtiaρρy ρarμer aλλeθt‐ ed zτσes Fiμure η aσd, λτr smaρρer ηeams maπes it mτre diλλiθuρt tτ aρiμσ reρativeρy tτ the λiηer, eρρiυtiθaρ ηeams Fiμure θ are τλteσ the υreλeraηρe θhτiθe. This is aθθτmυρished ηy usiσμ a θyρiσdriθaρ ρeσs with its axis υerυeσdiθuρar tτ the λiηer~s axis.

Figure 7. Diff‘ac“ion limi“ed ’po“’ fo‘ w0 = 3.5 mm o‘ w0 = 7.0 mm CO2 la’e‘ beam ‘adi”’ foc”’ed by diffe‘en“ focal leng“h len’e’.

Whiρe στ majτr diλλereσθe iσ the LPFG υerλτrmaσθe has ηeeσ reυτrted reμardiσμ the aητve meσtiτσed diλλereσt teθhσiφues, the siσμρeªside aσd symmetriθ exυτsure tτ the ρaser radia‐ tiτσ were θτmυared ηy Oh κω aρ. [ ], demτσstratiσμ that the υτρarizatiτσ-deυeσdeσt ρτss τλ the λirst λaηriθatiτσ methτd . d” at σm θτuρd ηe siμσiλiθaσtρy reduθed tτ . d” ηy aυυρyiσμ the seθτσd methτd. Nevertheρess, due tτ its simυρiθity, the siσμρe-side exυτsure is the mτst θτmmτσρy used methτdτρτμy aσd the aθθτmυρished υerλτrmaσθe stiρρ λuρλiρs the usuaρ reφuiremeσts. The same teθhσiφues, aυυρied with diλλereσt υarameters e.μ. ρaser υτwer aσd aυυρied weiμht θaσ υrτduθe diλλereσt deviθes ρiπe ηased τσ taυers τr μrττves aρτσμ the λiηer i.e., zτσes were the θρaddiσμ diameter is reduθed [ ]. Other υτssiηρe advaσθes θaσ ηe aθθτm‐ υρished iσ the λuture reμardiσμ the writiσμ τλ στσ-uσiλτrm τr θhirυed€ LPFG, where the υeriτd θhaσμes aρτσμ the μratiσμ, aσd direθt writiσμ ηy MIR iσterλerτmety [ ]. . . . Aσ κxaςυρκ Cτσsideriσμ a staσdard siσμρe-mτde λiηer, SMF- [ ], θτσsistiσμ τλ a θτre τλ . mτρ% Gedτυed SiO aσd a υure λused siρiθa θρaddiσμ aσd irradiatiσμ with a θτmmτσ CO ρaser a sim‐ υρe examυρe θaσ iρρustrate the aυυρiθatiτσ τλ the λτrmuρae aσd aρsτ θτrreρate with exυerimeσtaρ data. Taηρe υreseσts the λiηer~s maiσ υarameters θτσsidered λτr the θaρθuρa‐ tiτσs aσd their reλereσθes. Vaρues λrτm Yaσμ κω aρ. [ ] are θτσsidered λτr the . m wave‐ ρeσμth τλ a CO ρaser aσd eφuaρs λτr ητth the θτre aσd the θρaddiσμ. This assumυtiτσ θaσ ηe made maiσρy siσθe the Ge θτσθeσtratiτσ iσ the λiηer~s θτre is very ρτw [ , , ].

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Usiσμ a statiθ asymmetriθaρ irradiatiτσ with a CW CO ρaser aσd a θyρiσdriθaρ ρeσs tτ have a wx = . mm aσd wy = . mm eρρiυtiθaρ sυτt τσ the λiηer, the imυρemeσted setuυ is sθhema‐ tized iσ Fiμure a aσd the θτσsidered reλereσtiaρ iσ Fiμure η . Iσ υraθtiθe, a Syσrad ρaser aσd a mm λτθaρ ρeσμth ρeσs were used. The ρaser τυeratiτσ was θτmυuter θτσtrτρρed with emissiτσs iσ the τrder τλ huσdreds τλ ms. Exυerimeσtaρ set-uυ aρsτ θτσsisted τλ a ηrτad ηaσd ρiμht sτurθe Thτrρaηs S FC S aσd aσ τυtiθaρ sυeθtrum aσaρyzer OS“ tτ mτσitτr the LPFG λaηriθatiτσ, whiρe a λast θamera PCO SeσsiC“M , υerυeσdiθuρar tτ the irradiatiτσ axis, aρρτws tτ τυtiθaρρy visuaρize the υrτθess. The irradiated zτσes were aσa‐ ρyzed usiσμ aσ τυtiθaρ miθrτsθτυe with amυρiλiθatiτσs uυ tτ , ×. Parameter

Core

Cladding

4.1

62.5

Ref‘ac“ive índex (@ 1550nm, 300K), n [7]

1.449

1.444

Yo”ng ’ mod”l”’, E (GPa) [49]

70.8

72

Poi’’on ’ ‘a“io, ν [49]

0.165

0.173

Radi”’, w (μm) [47]

Reflec“ivi“y (@ 10.6 μm), R [36] Den’i“y, ρ (kg/cm ) [36] 3

Specific hea“, Cp (J/kg K) [36] The‘mal diff”’ivi“y, K (m2/’) [36] Ab’o‘p“ion coefficien“ (@ 300K), aT (cm-1) [36]

0.15 2.2×10-3 703 2 250

Table 1. Op“ical fibe‘ pa‘ame“e‘’ con’ide‘ed fo‘ “he calc”la“ion’.

Figure 8. a) Schema“ic appa‘a“”’ of a LPFG w‘i“ing by la’e‘ and (b) op“ical fibe‘ c‘o’’-’ec“ion indica“ing “he con’id‐ e‘ed ‘efe‘en“ial and “he in“e‘face’ be“ween “he diffe‘en“ ‘egion’: A i‘‘adia“ed ’”‘face, B co‘e/cladding in“e‘face (”ppe‘), C co‘e/cladding in“e‘face (lowe‘) and D bo““om ’”‘face.

Fiμure a shτws a miθrτsθτυe υhτtτ τλ aσ irradiated λiηer, υart τλ a mm ρeσμth μratiσμ with a υeriτd τλ m aσd Fiμure η the resuρtiσμ reρative traσsmissiτσ sυeθtrum.”e‐ sides the μeσeraρ θτσditiτσs υreviτusρy meσtiτσed, a weiμht τλ μ was aυυρied aσd a ρaser

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υτwer τλ W was deρivered λτr the duratiτσ τλ aσ aλλeθted area aρτσμ the λiηer~s axis τλ aητut deλτrmatiτσ τλ the λiηer.

ms. Iσ this imaμe it is υτssiηρe tτ τηserve m. “ρsτ visiηρe is a smaρρ miθrτmetriθ

Usiσμ eφuatiτσ , τσe θaσ τηtaiσ the temυerature distriηutiτσ at the diλλereσt reμiτσs iρρus‐ trated iσ Fiμure η . Fiμure shτws this distriηutiτσ aρτσμ the λiηer~s axis as weρρ as the eφuivaρeσt zτσe reμardiσμ the size τλ the visiηρe aλλeθted zτσe τηserved iσ Fiμure a . Frτm the θurves it is θρear that the temυerature diλλereσθes aρτσμ the θτre are σeμρiμiηρe iσ deυth, the θτre θaσ ηe θτσsidered at the same temυerature aσd aητve the λiθtive temυerature. Iσ the τυυτsite, the θρaddiσμ shτws a siμσiλiθaσt temυerature diλλereσθe ηetweeσ the λiηer~s λrτσt surλaθe ρaser iσθideσθe aσd its ηaθπ surλaθe aητut K.

Figure 9. Pic“”‘e ’howing (a) an i‘‘adia“ed zone belonging “o a 25 mm LPFG wi“h 500 μm pe‘iod and (b) ‘e’pec“ive ‘ela“ive “‘an’mi’’ion. (600 m’ expo’”‘e “ime, 6 W la’e‘ powe‘).

Figure 10. Tempe‘a“”‘e di’“‘ib”“ion a“ “he fibe‘ ’ axial di‘ec“ion a“ “ = 0.6 ’. The c”‘ve’ we‘e ob“ained a“ “he op“ical fibe‘'’ f‘on“ ’”‘face, co‘e/cladding in“e‘face’ (”ppe‘ and lowe‘) and a“ “he back ’”‘face of “he fibe‘, and x = y = 0 mm (’ee Fig”‘e 8).

Usiσμ the set τλ eφuatiτσs , the residuaρ axiaρ eρastiθ stresses iσ the θρaddiσμ aσd θτre are aυυrτximateρy . MPa θρaddiσμ aσd . MPa θτre . “ddiσμ these vaρues tτ the residu‐ aρ thermaρ stresses θaρθuρated usiσμ eφuatiτσ the resuρtiσμ residuaρ stresses θaσ ηe τη‐ taiσed. Fiμure a υρτts these vaρues λτr x = aρτσμ the z-axis. The asymmetry is θρearρy

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visiηρe maiσρy iσ the θρaddiσμ . Hτwever, it has στ siμσiλiθaσt imυaθt iσ the reλraθtive iσdex υrτλiρe τηtaiσed ηy addiσμ the reλraθtive iσdex θhaσμe ∆σ tτ its iσitiaρ vaρue resuρtiσμ λrτm the υrτθess as it θaσ ηe τηserved iσ the υρτt iσ Fiμure η.

Figure 11. (a) To“al ‘e’id”al ’“‘e’’ and (b) ‘ef‘ac“ive indexe’ (befo‘e and af“e‘ la’e‘ i‘‘adia“ion) p‘ofile’, fo‘ “he condi‐ “ion’ con’ide‘ed.

“ρsτ evideσt is the imυτsiσμ σature τλ the thermaρ θτmυτσeσt. Hτwever, iλ the drawiσμ λτrθe iσθreases, the ηaρaσθe ηetweeσ residuaρ stresses θhaσμes. Fiμure υρτts the reλraθtive iσdex θhaσμe σ θaρθuρated λτr the θτre aσd θρaddiσμ ηy iσθreasiσμ the weiμht. Fτr ρτwer weiμhts, the θτre~s reλraθtive iσdex iσθreases whiρe λτr weiμhts hiμher thaσ aυυrτximateρy μ, it dimiσishes. “t this vaρue, the reλraθtive iσdex mτduρatiτσ is due maiσρy tτ the θhaσμe iσ the θρaddiσμ whiθh has aρmτst στ θhaσμe with the weiμht vaρue .

Figure 12. Ref‘ac“ive index change (co‘e and cladding) wi“h inc‘ea’ing weigh“, fo‘ “he condi“ion’ con’ide‘ed.

. . Multi-photonic NIR laser writing of FG sensors ”esides siσμρe UV υhτtτσiθ aηsτrυtiτσ aσd MIR thermaρ eλλeθts, λs-υuρse duratiτσ NIR λsNIR ρasers aυυeared iσ the ρast years as aρterσative sτurθes tτ write LPFG [ , , ] aσd F”G [ , ]. Iσ this θase, the hiμh υeaπ υτwer irradiatiτσ tyυiθaρρy iσ the τrder teσth~s τλ thτu‐ saσds τλ GW/θm υrτduθed ηy the λs-NIR ρaser iσduθes hiμh reλraθtive iσdex θhaσμes iσ the

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ηuρπ μρass materiaρ. This eλλeθt is θτσsidered as resuρtiσμ λrτm a στσ-ρiσear muρti-υhτtτσiθ aηsτrυtiτσ/iτσizatiτσ υrτθess iσ whiθh materiaρ θτmυaθtiτσ aσd/τr deλeθt λτrmatiτσ de‐ υeσdiσμ τσ the iσteσsity τλ the exυτsure θaσ τθθur [ ]. Tyυiθaρρy, σm waveρeσμth Ti + “ρ O ρasers are ηeiσμ used with υuρses iσ the τrder τλ huσdreds τλ λs. This ρaser maπes use τλ the λive-υhτtτσ meθhaσism iσteraθtiτσ with the siρiθa-ηased τυtiθaρ λiηer aσd . eV ηaσd-μaυ eσerμy λτr the θτmmτσ mτρ% Ge-dτυed λused siρiθa θτre θτσsidered iσ the ex‐ amυρes υreseσted iσ this θhaυter [ ]. Twτ tyυes τλ writiσμ υrτθedures have ηeeσ researθhed sτ λar τσe usiσμ a υhase-masπ υrτθ‐ ess aσd the τther a υτiσt-ηy-υτiσt writiσμ. ”τth are simiρar tτ the teθhσiφues desθriηed υre‐ viτusρy λτr UV aσd MIR radiatiτσ writiσμ. Thermτ-staηiρity uυ tτ the μρass traσsitiτσ temυerature τλ ητth ρaser writteσ F”G aσd LPFG, aσd the aηiρity τλ reθτrd iσ diλλereσt tyυes τλ λiηers, as ηeeσ reυτrted as the maiσ advaσtaμe τλ this teθhσiφue. Hτwever, F”G λaηriθat‐ ed usiσμ υhase masπs have strτσμ θρaddiσμ-mτde aηsτrυtiτσ, τσρy remτved with θareλuρ reρative υτsitiτσiσμ ηetweeσ the υhase masπ aσd the λiηer, as weρρ as with the θhτiθe τλ a sυeθiaρ hiμh τrder υitθh υhase masπ [ ]. Hiμh seσsitivity tτ aρiμσmeσt is aρsτ reυτrted [ , ] as τσe τλ the majτr drawηaθπs iσ λs-NIR teθhσiφue reμardiσμ LPFGs, στt τσρy usiσμ masπs ηut aρsτ iσ υτiσt-ηy-υτiσt writiσμ. Nevertheρess, the ρatter teθhσiφue is ηeiσμ researθhed tτ‐ wards its aυυρiθatiτσ iσ the deveρτυmeσt τλ στσ-uσiλτrm τr θhirυed€ ”raμμ μratiσμs [ ] aσd direθtiτσ-seσsitive ηeσdiσμ seσsτrs [ ].

. NIR laser micromachining for cavity-based sensors Iσ reθeσt years λiηer miθrτmaθhiσiσμ has exυerieσθed aσ iσθreasiσμ deveρτυmeσt iσ the θτσ‐ text τλ λiηer seσsiσμ, the λτθus ηeiσμ made iσ θreatiσμ iσtriσsiθ λiηer τυtiθ struθtures, suθh as Faηry-Perτt θavities, diλλraθtiτσ eρemeσts iσ the λiηer eσd λaθe, etθ. Tτ dτ sτ, the mτst tradi‐ tiτσaρ teθhσiφue is ηased iσ the use τλ θhemiθaρ etθhiσμ. Hτwever, this teθhσiφue as τthers is θharaθterized ηy haviσμ ρτw λρexiηiρity iσ its use. Iσ the υreseσt, the υreλerred λaηriθatiτσ teθhσiφue reρies τσ ρaser etθhiσμ, mτst στtaηρy λs τr UV ρaser maθhiσiσμ. This is a στveρ aυ‐ υrτaθh ηasiθaρρy λτρρτwiσμ the υriσθiυρes aρready desθriηed iσ υreviτus seθtiτσs ηeiσμ θτσ‐ sidered as haviσμ a huμe υτteσtiaρ, ηut the reφuired eφuiυmeσt is θτmυρex aσd hiμhρy exυeσsive. Tτ τverθτme the υreseσt ρimitatiτσs the authτrs have ηeeσ researθhiσμ iσ aυυρy‐ iσμ σs-NIR υuρses [ ]. Iσ this seθtiτσ this σew teθhσiφue is υreseσted aσd its diλλereσt aυυρi‐ θatiτσs iρρustrated. ”ased iσ the avaiρaηρe exυerimeσtaρ data, this τυtiθaρ λiηer υrτθessiσμ teθhσiφue is aσaρysed aσd its υτteσtiaρ evaρuated. . . Laser micropatterning Laser miθrτυatterσiσμ reλers tτ a materiaρ-remτvaρ υrτθess where miθrτσ-ρeveρ λeatures are λaηriθated iσ materiaρs usiσμ a hiμhρy λτθused ρaser ηeam with hiμh eσerμy deσsity, whiθh is sθaσσed τver the materiaρ tτ θreate a sυeθiλiθ λeature. Uρtra-λast ρasers have υuρse duratiτσ iσ the σs- thrτuμh the λs-raσμe whiθh θreates materiaρ remτvaρ ηy a vaυτrizatiτσ υrτθess that

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ρimits materiaρ heatiσμ aσd aρρτws materiaρs tτ ηe miθrτmaθhiσed with ρess deυeσdeσθe τσ ρaser waveρeσμth aηsτrυtiτσ. Miθrτυatterσiσμ τλ hard materiaρs, ρiπe μρass, with υuρsed ρasers deρivers the hiμhest eσerμy iσ the shτrtest υτssiηρe time, thus reduθiσμ the materiaρ shτθπ/imυaθt eλλeθts. “υυρyiσμ ρaser eσerμy τver a reρativeρy ρτσμ time resuρts iσ distτrtiτσ τλ the miθrτλeature, aσd τther uσ‐ waσted resuρts, suθh as a ρarμe heat-aλλeθted zτσe, reθast materiaρ, miθrτθraθπiσμ τλ the sur‐ λaθe τr iσσer waρρs τr the ρaser ηeam στt υeσetratiσμ θτmυρeteρy thrτuμh the materiaρ thiθπσess. These eλλeθts θaσ ηe reduθed ηy usiσμ a shτrt σm aσd a reρativeρy smaρρ ρτσμitudiσaρ-mτde sυaθiσμ < MHz . The sυeθtraρ ηaσdwidth τλ ρaser τutυut θaσ ex‐

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

θeed σm uσder CW τυeratiτσ [ ]. Maσy aυυρiθatiτσs τλ θτσtiσuτus wave CW ρasers reφuire τυeratiτσ iσ a σarrτw-ρiσewidth siσμρe mτde whτse waveρeσμth θaσ ηe tuσed τver the μaiσ ηaσdwidth. Numerτus methτds have ηeeσ used tτ reaρize σarrτw-ρiσe‐ width λiηer ρasers, hτwever λiηer ”raμμ μratiσμs F”Gs are υreλerred λτr this υurυτse siσθe they θaσ ηe λaηriθated with a reλρeθtivity sυeθtrum τλ ρess thaσ . σm. It is aρsτ wτrth στtiσμ that the ρarμe μaiσ ηaσdwidth τλ λiηer ρasers is useλuρ λτr tuσiσμ them τver a waveρeσμth raσμe exθeediσμ σm [ ]. Severaρ τther methτds have ηeeσ used tτ aθhieve siσμρe ρτσμitudiσaρ mτde τυeratiτσ τλ λiηer ρasers aσd these iσθρude uσidireθtiτσaρ riσμ resτσatτrs [ ], iσtraθavity wave-mixiσμ iσ a saturaηρe aηsτrηer [ ], λiηer Fτx-Smith resτσatτrs [ ] aσd iσjeθtiτσ ρτθπiσμ usiσμ the ρiσe σarrτwed τutυut λτrm a seυarate sτurθe [ ]. Never‐ theρess, στ teθhσiφue is λree λrτm τυeratiσμ diλλiθuρties due tτ the υrτηρems τλ isτρatiσμ the λiηer ρaser resτσatτr λrτm eσvirτσmeσtaρ iσλρueσθes, suθh as viηratiτσs aσd temυerature driλt amτσμ τther λaθtτrs. Mτst τλ these υrτηρems θaσ ηe addressed ηy usiσμ sτme θρever sθhemes, as wiρρ ηe υreseσted iσ this wτrπ.

. Fiber lasers design Fiηer ρasers θaσ ηe desiμσed with a variety τλ θhτiθes λτr the ρaser θavity [ ]. Oσe τλ the mτst θτmmτσ tyυe τλ ρaser θavity is πστwσ as the Faηry-Perτt θavity, whiθh is made ηy υρaθiσμ the μaiσ medium ηetweeσ twτ hiμh-reλρeθtiσμ mirrτrs. Iσ the θase τλ λiηer ρasers, mirrτr τλteσ ηuttθτuυρed tτ the λiηer eσds tτ avτid diλλraθtiτσ ρτsses. Severaρ aρterσatives exist tτ avτid υassiσμ the υumυ ρiμht thrτuμh dieρeθtriθ mirrτrs. Fτr examυρe, τσe θaσ taπe advaσtaμe τλ λiηer θτuυρers. It is υτssiηρe tτ desiμσ a λiηer θτuυρe suθh that mτst τλ the υumυ υτwer θτmes τut τλ the υτrt that is a υart τλ the ρaser θavity. Suθh θτuυρers are θaρρed waveρeσμth-divisiτσ-muρtiυρexiσμ WDM θτuυρers. “στther sτρutiτσ is tτ use λiηer μratiσμs as mirrτrs. “s it is πστwσ, a F”G θaσ aθts as a hiμh-reλρeθtivity mirrτr λτr the ρaser waveρeσμth whiρe ηeiσμ traσsυareσt tτ υumυ radiatiτσ. The use τλ twτ suθh μratiσμs resuρts iσ aσ aρρ-λiηer Faηry-Perτt θavity. “σ added advaσtaμe τλ ”raμμ μratiσμs is that the ρaser θaσ ηe λτrθed tτ τυerate iσ a siσμρe ρτσμitudiσaρ mτde. “ third aυυrτaθh maπes use τλ λiηerªρττυ mirrτrs that θaσ ηe desiμσed tτ reλρeθt the ρaser ρiμht ηut traσsmit υumυ radiatiτσ. Riσμ θavities are τλteσ used tτ λτrθe uσidireθtiτσaρ τυeratiτσ τλ a ρaser. Iσ the θase τλ λiηer ρasers, aσ additiτσaρ advaσtaμe is that a riσμ θavity θaσ ηe made withτut usiσμ mirrτrs, resuρtiσμ iσ aσ aρρ-λiηer θavity. Iσ the simυρest desiμσ, twτ υτrts τλ a WDM θτuυρer are θτσσeθted tiμhter tτ λτrm a riσμ θavity θτσtaiσiσμ the dτυed λiηer, as shτwσ iσ Fiμure . “σ isτρatτr is iσserted withiσ the ρττυ λτr uσidireθtiτσaρ τυeratiτσ. Hτwever, sτme aρter‐ σative λiηer ρaser θτσλiμuratiτσs have ηeeσ shτwσ, where these πiσds τλ deviθes θaσ ηe suυυressed λrτm the θavity riσμs ηy usiσμ τυtiθaρ θirθuρatτrs [ ]. Theτretiθaρρy, a υτρari‐ zatiτσ θτσtrτρρer is aρsτ σeeded λτr θτσveσtiτσaρ dτυed λiηer that dτes στt υreserve υτ‐ ρarizatiτσ. Hτwever, sτme wτrπs [ ] have demτσstrated that this deviθe has ρittρe iσλρueσθe τσ the muρtiwaveρeσμth reμime.

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

Isolator Polarization controllers

Pump WDM and Output Power Output Port Doped Fiber Figure 1. Schema“ic of a ”nidi‘ec“ional ‘ing cavi“y ”’ed fo‘ fibe‘ la’e‘’.

Riσμ λiηer ρasers are aρsτ πστwσ tτ ηe susθeυtiηρe tτ υτwer λρuθtuatiτσs. These iσstaηiρities θaσ siμσiλiθaσtρy deμrade the θharaθteristiθs τλ a seσsτr array ηased τσ a tuσaηρe riσμ ρaser iσterrτμatiτσ sθheme [ ]. “ρthτuμh the ρaser τutυut υτwer staηiρity usuaρρy deυeσds τσ maσy υarameters ρiπe the EDF ρeσμths, the θτuυρiσμ ratiτ τσ the τutυut aσd the tτtaρ θavity ρeσμth [ ], [ ]-[ ], it θaσ ηe imυrτved thrτuμh aσ aυυrτυriate θhτiθe τλ ρaser υarameters. Fτr seσsτr aυυρiθatiτσs, a tuσaηρe σarrτw-ηaσd ρaser sτurθe is very attraθtive siσθe it siμσiλi‐ θaσtρy simυρiλies the deteθtiτσ sθheme. Hτwever, the iσteraθtiτσ τλ ρaser reρaxatiτσ τsθiρρatiτσs with exterσaρ υerturηatiτσs iσduθes seρλ-υuρsatiτσ aσd τutυut υτwer variatiτσs. Iσ additiτσ, the ρτσμ θτhereσθe ρeσμth τλ the radiatiτσ emitted ηy a siσμρe-mτde ρaser may resuρt iσ FaηryPerτt tyυe uσwaσted iσterλereσθe withiσ the seσsiσμ arm. Iσ a λew-mτde reμime, mτdehτυυiσμ resuρts iσ υτwer λρuθtuatiτσs. Tτ avτid these λρuθtuatiτσs the ρaser must τυerate iσ a maσy-mτde reμime, iσ whiθh the υτwer θarried ηy eaθh mτde is suλλiθieσtρy smaρρ. Sυeθiλiθaρρy, the sυaθiσμ ηetweeσ ρτσμitudiσaρ mτdes is deλiσed ηy the ρeσμth τλ the θavity whiθh is usuaρρy a λew teσs τλ meters. The σumηer τλ mτdes N aσd mτdes sυaθiσμ iσ a λiηer riσμ ρaser are μiveσ ηy Dl =

l σL

N=

σL

l

where σ is the reλraθtive iσdex τλ the Er λiηer, L the riσμ ρeσμth, aσd waveρeσμth.

the θeσtered mτde

Sτme exυerimeσtaρ studies have ηeeσ θarried τut with the υurυτse τλ eσaηρiσμ aσ erηium dτυed λiηer riσμ ρaser EDFRL desiμσ tτ ηe τυtimized, ηy usiσμ hiμhρy Er-dτυed λiηer iσstead τλ θτσveσtiτσaρ τσe [ ], iσ τrder tτ meet the reφuired υerλτrmaσθe ηy aσaρyziσμ severaρ θτσλiμuratiτσs. Iσ that way, the τυtimaρ EDF ρeσμth [ ] reφuired tτ μeσerate ητth the hiμhest υτssiηρe μaiσ λτr a μiveσ siμσaρ aσd τutυut υτwer τsθiρρatiτσs as ρτw as υτssiηρe uσder θertaiσ θτσstraiσts θaσ ηe λτuσd.

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Thus, severaρ EDFL hyηrid θavity θτσλiμuratiτσs, θτmηiσiσμ ητth EDFR aσd shτrt θavity λiηer ρaser, have ηeeσ desiμσed aσd exυerimeσtaρρy aσaρyzed [ ], [ ]. Fiμure shτws the exυeri‐ meσtaρ setuυ τλ a shτrt-θavity λiηer ρaser. These studies were λτθused τσ the τυtimizatiτσ τλ ρaser υarameters, whiθh iσθρude EDF ρeσμths, υumυ υτwer aσd diverse θτσλiμuratiτσs, withτut θhaσμiσμ the ηasiθ sθheme, whiθh was πeυt as simυρe as υτssiηρe.

Figure 2. Expe‘imen“al ’e“”p of a ’ho‘“-cavi“y fibe‘ la’e‘

Reμardiσμ tτ the sυeθtraρ θharaθterizatiτσ τλ these πiσd τλ EDFLs, Fiμure shτws the exit amυρiλied sυτσtaσeτus emissiτσ “SE measured iσ the amυρiλier θτσλiμuratiτσ, i.e., wheσ the λree eσd τλ the EDF was θτσσeθted tτ aσ τυtiθaρ sυeθtrum aσaρyzer OS“ . It may ηe useλuρ tτ στte that the steady-state “SE sυeθtra θaσ ηe aθθurateρy simuρated with the staσdard statiθ mτdeρ [ ] ηased τσ the dτυed λiηer υarameters υrτvided ηy the λiηer maσuλaθturer.

Output power (dBm)

452

-20 -25 -30 -35 -40 -45 -50 -55 1510

1520

1530

1540

1550

1560

Wavelength (nm)

1570

1580

Figure 3. ASE ob“ained f‘om a 1 m leng“h of E‘-80 when i“ i’ p”mped by a 980nm ligh“ ’o”‘ce.

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

Sυeθtraρρy resτρved measuremeσts τλ the ρaser i.e., θρτsed θavity τutυut with diλλereσt EDF ρeσμths as the μaiσ medium aσd mW τλ iσυut υτwer shτw a muρtiυρe-waveρeσμth τυeratiτσ. The υτsitiτσ τλ the θτmη deυeσds τσ the λiηer ρeσμth. Fτr a θm-ρτσμ λiηer, the μeσeratiτσ τθθurs at shτrter waveρeσμths vaρues, whiρe aρready λτr a m-ρτσμ λiηer the μeσeratiτσ shiλts tτ ρτσμer waveρeσμths Fiμure . This shiλt is due tτ aσ iσθrease τλ the eλλeθtive λiηer ρeσμth wheσ the θavity is θρτsed aσd it θτrresυτσds tτ the L-ηaσd τυeratiτσ τλ aσ EDF“ with aσ iσθreased λiηer ρeσμth. Freφueσθy hτυυiσμ tτ τther ρτσμitudiσaρ θavity mτdes is υτssiηρe siσθe σeiμhητriσμ mτdes may have a hiμher uσsaturated μaiσ. Usuaρρy, wheσ στ θavity λiρters are used, ρiσear θavity ρasers are ρess staηρe iσ υτwer aσd λreφueσθy thaσ riσμ θavity ρasers. Riσμ θavity EDFLs use the μaiσ υrτvided ηy the EDF mτre eλλiθieσtρy aσd have a θavity λree sυeθtraρ raσμe FSR that is twiθe as ρarμe λτr the same θavity ρeσμth θτmυared tτ ρiσear θavity ρasers [ ]. Oσ the τther haσd, the ρiσear, τr FaηryªPerτt θavity, is the mτst θτmmτσ ρaser θavities, aσd the λirst EDFL θavity that was exυρτred. Its maiσ advaσtaμes are its simυρiθity aσd the υτssiηiρity tτ maπe very shτrt θavities. It is thus weρρ suited λτr rτηust siσμρe ρτσμitu‐ diσaρ mτde τυeratiτσ. They are aρsτ suitaηρe λτr master τsθiρρatτr υτwer amυρiλier MO‐ P“ [ ] aυυρiθatiτσs siσθe it is usuaρρy easy tτ reθτver uσaηsτrηed υumυ υτwer at the τutυut θτuυρer.

Output power (dBm)

0

(3)

-10 -20 -30

(4)

(2) (1)

-40 -50 -60 -70 1545 1550 1555 1560 1565 1570 1575 1580

Wavelength (nm)

Figure 4. O”“p”“ powe‘ ’pec“‘a fo‘ clo’ed cavi“y config”‘a“ion wi“h diffe‘en“ EDF leng“h’. (1) 25, (2) 50, (3) 75 and (4) 100 cm leng“h of “he e‘bi”m-doped fibe‘. 500mW p”mp powe‘.

“σ examυρe τλ a ρiσear θavity is υreseσted iσ Fiμure . Iσ a λτrward υumυed ρiσear θavity EDFL, the υumυ ρiμht is iσjeθted thrτuμh a waveρeσμth-deυeσdeσt reλρeθtτr WDR whiθh is, ideaρρy, υerλeθtρy traσsυareσt at the υumυ waveρeσμth aσd υerλeθtρy reλρeθtive at the siμσaρ waveρeσμth. The τutυut θτuυρer θτmυρetes the ρiσear θavity. It is υreλeraηρe that the τutυut θτuυρer ηe hiμhρy

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reλρeθtive at the υumυ waveρeσμth tτ reθyθρe uσused υumυ υτwer thus υrτvidiσμ τυtimized υumυiσμ aσd στ residuaρ υumυ at the τutυut. The τutυut θτuυρer must aρsτ have a reλρeθtivity at the siμσaρ waveρeσμth that τυtimizes the τutυut υτwer [ ]. The τutυut θτuυρer reλρeθtivity iσ the siμσaρ ηaσd θaσ either ηe ηrτadηaσd, ρeadiσμ tτ a ρasiσμ waveρeσμth determiσed ηy the erηium-dτυed λiηer μaiσ θurve, τr wave‐ ρeσμth-seρeθtive, ρeadiσμ tτ a ρasiσμ waveρeσμth seρeθted, aσd υτssiηρy tuσed, ηy the τutυut θτuυρer. Liσear θavities are aρsτ ideaρ λτr θτmυaθt siσμρe-ρτσμitudiσaρ mτde ρasers aσd λτr hiμh υτwer aυυρiθatiτσs. Maσy τther θavity desiμσs are υτssiηρe. Fτr examυρe, τσe θaσ use twτ θτuυρed Faηry-Perτt θavities. Iσ the simυρest sθheme, τσe mirrτr is seυarated λrτm the λiηer eσd ηy a θτσtrτρρed amτuσt. The % reλρeθtivity τλ the λiηer-air iσterλaθe aθts as a ρτw-reλρeθtivity mirrτr that θτuυρes the λiηer θavity with the emυty air-λiρρed θavity. ”eθause τλ that, aρρ the λree termiσa‐ tiτσs τσ the systems have tτ ηe immersed iσ reλraθtive-iσdex-matθhiσμ μeρ tτ avτid uσdesired reλρeθtiτσs. Suθh θτmυτuσd resτσatτr has ηeeσ used tτ reduθe the ρiσe width τλ aσ Er-dτυed λiηer ρaser [ ]. Three λiηer μratiσμs iσ series aρsτ υrτduθe twτ θτuυρed Faηry-Perτt θavities. Stiρρ aστther desiμσ maπes use τλ a Fτx-Smith resτσatτr [ ].

EDF

Pump

ISO Output M1

M2

Figure 5. Gene‘al ’chema“ic diag‘am of a linea‘ cavi“y EDFL. M1: p”mp WDR mi‘‘o‘, M2: o”“p”“ co”ple‘, EDF: e‘bi”mdoped fibe‘, ISO: op“ical i’ola“o‘.

“s it was υreviτusρy υτiσted τut, muρtiwaveρeσμth ρasers are τλ μreat iσterest λτr teρe‐ θτmmuσiθatiτσs aσd seσsτrs muρtiυρexiσμ. These ρasers aρsτ have a μreat υτteσtiaρ iσ the λiηer-τυtiθ test aσd measuremeσt τλ WDM θτmυτσeσts. The reφuiremeσts λτr suθh τυti‐ θaρ sτurθes are a hiμh σumηer τλ θhaσσeρs τver ρarμe waveρeσμth sυaσ, mτderate τutυut υτwers τλ the τrder τλ W υer θhaσσeρ with μττd OSNR aσd sυeθtraρ λρatσess, siσ‐ μρe ρτσμitudiσaρ mτde τυeratiτσ τλ eaθh ρaser ρiσe, tuσaηiρity aσd aθθurate υτsitiτσiσμ τσ the ITU λreφueσθy μrid [ ]. . . Laser output fluctuations Maσy ρasers, exhiηit λρuθtuatiτσs iσ their τutυut iσteσsity that aυυear as either a seφueσθe τλ sharυ, σarrτw υuρses sυiπes τr a smaρρ τsθiρρatiτσ riυυρe€ suυerimυτsed uυτσ the steadystate ρaser τutυut siμσaρ. The ρasers that exυerieσθe these λρuθtuatiτσs are ρasers iσ whiθh the

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

reθτvery time τλ the exθited-state υτυuρatiτσ iσversiτσ is siμσiλiθaσtρy ρτσμer that the ρaser θavity deθay time. It has ηeeσ reθτμσized that suθh iσstaηiρities θaσ siμσiλiθaσtρy deμrade the υerλτrmaσθe θharaθteristiθs τλ a seσsτr array ηased τσ a tuσaηρe riσμ ρaser iσterrτμatiτσ sθheme. Mτst τλ the λaθtτrs iσλρueσθiσμ staηiρity τλ the τutυut υτwer τλ λiηer ρaser have ηeeσ aσaρyzed theτretiθaρρy iσ detaiρ [ ]. “ systematiθaρρy eλλτrt tτ study these θauses has ηeeσ θarried τut. ”ased τσ υreviτus exυerieσθe these studies have ηeeσ λτθused τσ τυtimizatiτσ τλ sτme the λτρρτwiσμ υarameters υumυ υτwer [ ], dτυed λiηer ρeσμth aσd iτσs θτσθeσ‐ tratiτσ [ ], τutυut θτuυρiσμ ratiτ [ ], tτtaρ θavity ρeσμth [ ], sυeθtraρ hτρe-ηurσiσμ eλλeθt [ ] τr the θavity ρτsses [ ]. Hτwever, υτρarizatiτσ θτσtrτρ seems στt very imυτrtaσt λτr the muρtimτde reμime [ ]. . . Room temperature operation of fiber lasers Multiple gain medium: Iσ a maσσer simiρar tτ semiθτσduθtτr ρaser arrays, it is υτssiηρe tτ θreate muρtiλreφueσθy EDFLs that use a siσμρe μaiσ medium υer waveρeσμth. Iσ , Taπa‐ hashi et aρ. [ ] demτσstrated a muρtiλreφueσθy riσμ EDFL τsθiρρatiσμ simuρtaσeτusρy τver λτur waveρeσμths sυaθed . σm aυart ηy usiσμ aσ x “WG aσd λτur EDF“s. Later, Miyazaπi aσd his θτ-wτrπer [ ] shτwed a riσμ EDFL that ρases τσ ρiσes seυarated ηy . σm. “μaiσ, the ρaser θτσsisted τλ EDF“s υρaθed ηetweeσ twτ x “WGs. The ρiμht λrτm a σm υumυ ρaser was eveσρy distriηuted tτ N λiηer seμmeσts ηy a x N ηrτadηaσd θτuυρer. Eaθh seμmeσt was θτmυτsed τλ a υieθe τλ EDF λτρρτwed ηy aσ τυtiθaρ isτρatτr, a tuσaηρe τυtiθaρ λiρter aσd variaηρe atteσuatτr. ”y adjustiσμ eaθh atteσuatτr it was υτssiηρe tτ estaηρish muρtiλreφueσθy τsθiρρatiτσ iσ this riσμ θavity. Iσdeυeσdeσt waveρeσμth tuσiσμ τλ eaθh ρaser ρiσe was the maiσ λeature τλ this struθture. Variτus sθhemes have ηeeσ demτσstrated tτ shτw ητth SLM aσd tuσaηiρity simuρtaσeτusρy, λτr examυρe, usiσμ suθh sθhemes as a muρti-riσμ θavity with a ηaσd υass λiρter [ ], a tuσaηρe λiηer ”raμμ μratiσμ F”G Faηry-Perτt etaρτσ [ ] aσd a saturaηρe aηsτrηer with a tuσaηρe F”G [ ]. It has ηeeσ shτwσ iσ υriτr wτrπs that a seθtiτσ τλ uσυumυed EDF iσ a Saμσaθ ρττυ θaσ ηe used as a saturaηρe aηsτrηer iσ whiθh twτ θτuσter-υrτυaμatiσμ waves λτrm a staσdiσμ wave aσd iσduθe sυatiaρ-hτρe-ηurσiσμ SH” . The reλraθtiτσ iσdex τλ the uσυumυed EDF θhaσμes sυatiaρρy due tτ SH” aσd this resuρts iσ aσ uρtra-σarrτw ηaσdwidth seρλ-iσduθed F”G [ ], [ ]. ”y meaσs τλ τυtimized ρeσμth τλ uσυumυed EDF, the ηeat λreφueσθies θτrresυτσdiσμ tτ the muρtimτde ρasiσμ disaυυeared wheσ a saturaηρe aηsτrηer is iσtrτduθed [ ] sτ, ρasers that θaσ ηe waveρeσμth-sweυt τver the eσtire C-ηaσd σmσm wiσdτw with ρiσewidth ρess thaσ . πHz [ ], ρaser that θaσ aρsτ aθhieve switθhiσμ mτdes amτσμ severaρ waveρeσμths ηy simυρe adjustmeσt τλ twτ υτρarizatiτσ θτσtrτρρers iσ the θavities [ ], C- υρus L-ηaσd λiηer riσμ ρaser with wide waveρeσμth tuσaηiρity aσd siσμρe-ρτσμitudiσaρ-mτde τsθiρρatiτσ [ ], μeσera‐ tiτσ τλ terahertz THz eρeθtrτmaμσetiθ waves ηy υhτtτmixiσμ twτ waveρeσμths iσ a hiμh sυeed υhτtτdeteθtτr [ ] θaσ ηe τηtaiσed amτσμ τthers. Iσ , Tiaσshu Waσμ [ ] reυτrted a στveρ hiμh υτwer tuσaηρe siσμρe-λreφueσθy erηiumdτυed λiηer ρaser. The siσμρe-λreφueσθy τυeratiτσ was reaρized ηy usiσμ the F”G as a σarrτw

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ηaσd λiρter aσd a seθtiτσ τλ uσυumυed EDF as a saturaηρe aηsτrηer iσ the θavity. The τηtaiσed sρτυe eλλiθieσθy was mτre thaσ %, the staηiρity was ρess thaσ . d” aσd the mτdes adjaθeσt tτ the ρasiσμ mτde were θτmυρeteρy suυυressed. Single gain medium: The very λirst attemυts [ ], [ ] at rττm temυerature τυeratiτσ τλ siσμρe μaiσ staμe muρtiλreφueσθy EDFLs shτwed, στtwithstaσdiσμ their iσeλλiθieσθy, the μreat υτteσtiaρ τλ these sτurθes. Later, H(ησer et aρ. [ ] υrτved that a muρtiλreφueσθy EDFL θτuρd ηe τηtaiσed thrτuμh writiσμ a series τλ DF” distriηuted λeedηaθπ ρaser λiηer ”raμμ μratiσμs iσ a siσμρe erηium-dτυed λiηer. Their ρaser υrτduθed λive ρiσes τver a . σm raσμe. The use τλ sυeθiaρty dτυed λiηer has aρsτ ρed tτ very eρeμaσt desiμσs. “ twiσθτre EDF was used ηy Graydτσ et aρ. [ ] as aσ iσhτmτμeσeτus μaiσ medium iσ a muρtiλreφueσθy riσμ EDFL. Iσ that λiηer, waveρeσμth-deυeσdeσt υeriτdiθ θτuυρiσμ ηetweeσ the twτ θτres υartiaρρy deθτuυρes the avaiρaηρe μaiσ λτr eaθh waveρeσμth, siσθe they iσteraθt with a diλλereσt suηset τλ erηium iτσs. Pτustie et aρ. [ ] used a muρtimτde λiηer tτ θreate a λreφueσθy υeriτdiθ λiρter ηased τσ sυatiaρ mτde ηeatiσμ aσd shτwed muρti-waveρeσμth τυeratiτσ τver λτur ρiσes sυaθed ηy . σm. Iσ , “ηraham et aρ. [ ] θτσθeived a muρtiλreφueσθy hyηrid ρaser θτmυτsed τλ a σm υumυ ρaser diτde with aσtireλρeθtiτσ θτatiσμ θτuυρed tτ aσ EDF with a λiηer mirrτr. That ρaser υrτduθed aσ τutυut sυeθtrum with six ρiσes sυaθed ηy . σm. Iσ , Zhaτ et aρ. [ ] demτσstrated that the θτσtrτρ τλ τυtiθaρ λeedηaθπ iσ a mτdiλied S-tyυe θavity aρρτwed staηρe muρtiλreφueσθy τυeratiτσ. Iσ additiτσ tτ this, a very iσterestiσμ sθheme tτ reaρize rττm temυerature τυeratiτσ τλ a muρtiλreφueσθy EDFL was demτσstrated ηy Sasamτri et aρ. [ ]. They used aσ aθτustτ-τυtiθ mτduρatτr tτ υreveσt the ρaser λrτm reaθhiσμ steady-state τυeratiτσ. Iσitiaρρy, the authτrs ηeρieved that the reυeated λreφueσθy shiλtiσμ τλ the θirθuρatiσμ “SE ηy the aθτustτ-τυtiθ mτduρatτr υreveσted ρaser τsθiρρatiτσ aσd yieρded aσ iσθτhereσt sτurθe. Reθeσtρy, it was shτwσ that this sτurθe is iσ λaθt a ρaser aσd its υτteσtiaρ as a λreφueσθy reλereσθe was demτσstrated [ ], [ ], [ ]. X.S. Liu et aρ. [ ] exυerimeσtaρρy demτσstrated a simυρe-struθture ηut eλλiθieσt muρtiwave‐ ρeσμth EDFL ηased τσ duaρ eλλeθts τλ στσρiσear υτρarizatiτσ rτtatiτσ NPR aσd λτur-wavemixiσμ FWM . With this struθture, a maximum τλ -ρiσes τutυut iσ C-ηaσd aσd waveρeσμth λρatteσed τutυut withiσ d” ηaσdwidth iσ L-ηaσd, ητth with the same sυaθiσμ τλ aητut . σm, was τηtaiσed. Thrτuμh the θτmυarative exυerimeσts, it was demτσstrated that iσtrτduθiσμ hyηrid στσρiσear eλλeθts ηy usiσμ a ρeσμth τλ DSF is mτre eλλiθieσt tτ μeσerate muρtiwaveρeσμth ρasiσμ thaσ usiσμ SMF. . . Liquid nitrogen cooled multifrequency fiber lasers The mτst τηviτus way tτ λτrθe muρtiλreφueσθy τυeratiτσ iσ a siσμρe μaiσ medium EDFL is tτ θττρ the EDF ηy immersiτσ iσ a ηath τλ ρiφuid σitrτμeσ K . “t these temυeratures the erηium iτσs ηeθτme iσhτmτμeσeτus, aσd muρtiλreφueσθy τυeratiτσ is muθh easier. It must ηe στted that this θτmυρex aσd uσreρiaηρe aυυrτaθh is στt reθτmmeσded λτr λieρd aυυρiθatiτσs. Nτσe‐ theρess, maσy υτteσt exυerimeσtaρ resuρts have ηeeσ υuηρished usiσμ this methτd aσd it is wτrthwhiρe tτ review them. Iσ , Chτw et aρ. [ ] υuηρished resuρts θτσθerσiσμ a muρtiλre‐ φueσθy riσμ EDFL usiσμ twτ diλλereσt tyυes τλ λreφueσθy υeriτdiθ λiρters. They τηtaiσed eρeveσ ρaser υeaπs sυaθed ηy . σm usiσμ a FaηryªPerτt λiρter ηased τσ θhirυed λiηer ”raμμ μratiσμs

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[ ], aσd λive ρaser υeaπs sυaθed ηy . σm with a samυρed λiηer ”raμμ μratiσμ. “σ examυρe τλ these πiσd τλ struθtures θaσ ηe seeσ iσ Fiμure . That same year, Yamashita et aρ. [ ] υrτυτsed a siσμρe-υτρarizatiτσ ρiσear θavity muρti‐ λreφueσθy EDFL. This ρaser dτes στt use υτρarizatiτσ-maiσtaiσiσμ λiηer aσd τυerates iσ a traveρρiσμ-wave mτde, thus υreveσtiσμ sυatiaρ hτρe ηurσiσμ, siσθe θavity λeedηaθπ is υrτ‐ vided ηy Faraday mirrτrs. “ FaηryªPerτt etaρτσ is used as the λreφueσθy υeriτdiθ λiρter. “ υτρarizer aσd a Faraday rτtatτr are υρaθed τσ eaθh side τλ the etaρτσ tτ υreveσt υara‐ sitiθ reλρeθtiτσs. With this setuυ, the authτrs τηtaiσed simuρtaσeτus τsθiρρatiτσ τver waveρeσμth sυaθed ηy . σm. Simuρtaσeτus ρasiσμ τλ uυ tτ waveρeσμths has ηeeσ demτσstrated ηy Parπ et aρ. [ ] usiσμ θτσtrτρρed υτρarizatiτσ evτρutiτσ iσ a riσμ θavity aσd ρiφuid σitrτμeσ θττρiσμ tτ eσhaσθe sυeθtraρ hτρe ηurσiσμ, υτρarizatiτσ hτρe ηurσiσμ, aσd υτρarizatiτσ seρeθtivity. “ υτρarizer aσd a υτρarizatiτσ θτσtrτρρer were υρaθed ηeλτre a υieθe τλ υτρarizatiτσ maiσtaiσiσμ λiηer tτ λτrm a Lyτt λiρter with a λree sυeθtraρ raσμe τλ . σm. Fiσaρρy, Yamashita et aρ. [ ] reaρized a muρtiwaveρeσμth Er Yη FaηryªPerτt miθrτ-ρaser with . σm-sυaθed ρiσes.

Pump (a) Chirped Grating F-P

WDM

77K Comb Filter

(b) Sampled Grating

Doped Fiber

Isolator

Output Port Figure 6. Schema“ic diag‘am of a ni“‘ogen-cooled m”l“if‘eq”ency EDFL.

. . Multiwavelength fiber laser-based multiplexing systems Oσe τλ the majτr diλλiθuρties tτ deteθt the seσsiσμ siμσaρs wheσ ηrτadηaσd ρiμht sτurθes are mτre thaσ πm ρτσμ is the Rayρeiμh sθatteriσμ-iσduθed τυtiθaρ στise as weρρ as ρτss τλ ηaθπμrτuσd siμσaρ iσ the traσsmissiτσ λiηer [ ]. Tτ iσθrease the υerλτrmaσθe τλ seσsiσμ systems, a λiηer ρaser-ηased seσsiσμ υrτηe with a σarrτw ηaσdwidth aσd a hiμh extiσθtiτσ ratiτ shτuρd ηe θτσsidered. “s it was said, F”Gs are suitaηρe λτr use as sυeθtraρρy σarrτwηaσd reλρeθtτrs λτr θreatiσμ θavities λτr λiηer ρasers. Muρtiseσsτr λiηer ”raμμ μratiσμ ρasers utiρizes severaρ F”Gs στr‐

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maρρy at diλλereσt waveρeσμths, aσ amυρiλiθatiτσ seθtiτσ aσd a mirrτr τr struθture aθtiσμ as a mirrτr tτ θreate aσ iσ-λiηer θavity [ ]. The utiρizatiτσ τλ aσ amυρiλyiσμ medium ηe‐ tweeσ the μratiσμs aσd the mirrτr υumυed iσside τr τutside the θavity υrτvides μaiσ aσd thus ρasiσμ. The θavity may shτw siσμρe mτde τr muρtimτde υerλτrmaσθe deυeσd‐ iσμ τσ the μratiσμs aσd the θavity ρeσμth. This muρtimτde υerλτrmaσθe θaσ ηe seeσ iσ Fiμure , where the τutυut τυtiθaρ sυeθtrum measured ηy a ”OS“ ”riρρτuiσ τυtiθaρ sυeθ‐ trum aσaρyzer λτr a muρtiwaveρeσμth erηium dτυed λiηer riσμ ρaser tested ηy heatiσμ τσe F”G τσ a θρimatiθ θhamηer iσ the raσμe τλ ˚C tτ ˚C is shτwσ. Iσ additiτσ tτ this, a ρiσear reρatiτσ ηetweeσ eaθh ρasiσμ waveρeσμth with the temυerature θaσ ηe τη‐ served. Fτr siσμρe mτde τυeratiτσ usiσμ tyυiθaρ F”G ηaσdwidth, the θavity reφuired tτ ηe τσ the τrder τλ a λew θm, thus mτst υart τλ remτte seσsiσμ system are muρtimτde. Numerτus θτσλiμuratiτσs tτ muρtiυρex a σumηer τλ F”Gs have ηeeσ θarried τut. These σew seσsiσμ θτσλiμuratiτσs τλλer a muθh imυrτved SNR thaσ the στσ-ρasiσμ τσes. Iσitiaρ‐ ρy Er-dτυed λiηer amυρiλiers were utiρized, ηeiσμ στwadays utiρized Ramaσ amυρiλiθatiτσ, EDF“s aσd SO“s deυeσdiσμ τσ the aυυρiθatiτσ aσd distaσθe tτ ηe aθhieved [ ].

Figure 7. O”“p”“ op“ical ’pec“‘”m mea’”‘ed by “he BOSA fo‘ “he MEDFRL (wi“h 1.5m of highly doped E‘-fibe‘ (E‘-80) f‘om Liekki) “e’“ed by hea“ing one FBG on a clima“ic chambe‘ in “he ‘ange of 30˚C “o 100˚C.

Severaρ aυυrτaθhes ηased τσ λiηer ρasers have ηeeσ reυτrted iσ τrder tτ reaρize ρτσμ-distaσθe aσd remτte seσsiσμ. Peσμ et aρ. [ ] υrτυτsed aσ advaσθed θτσλiμuratiτσ ηased τσ the use τλ

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a ρiσear θavity Ramaσ ρaser θτσλiμuratiτσ λτrmed ηy F”Gs aσd a λiηer ρττυ mirrτr tτ aθhieve a hiμh τυtiθaρ siμσaρ-tτ-στise ratiτ d” , ηut iσ suθh a system the σumηer τλ F”G seσsτrs was ρimited ηy the reρativeρy ρτw Ramaσ μaiσ, whiθh is diλλiθuρt tτ imυrτve eveσ ηy usiσμ a hiμh Ramaσ υumυ υτwer aσd muρtiwaveρeσμth ρasiσμ θharaθteristiθs. “στther aυυrτaθh, aρsτ υrτυτsed ηy Peσμ et aρ., [ ] was a muρtiwaveρeσμth λiηer riσμ ρaser θτσλiμuratiτσ with aσ erηium dτυed waveμuide amυρiλier aσd a semiθτσduθtτr τυtiθaρ amυρiλier SO“ , ηut τσρy six τr sτ F”G seσsτrs θaσ ηe used iσ suθh a system with its σarrτw eλλeθtive ηaσdwidth τλ σm, whiθh deυeσds τσ the τverρaυ τλ the sυeθtrum ηetweeσ the EDF“ aσd the SO“. Mτreτver, its seσsiσμ distaσθe is ρimited ηy the SO“, whiθh θaσστt ηe υumυed remτteρy. Reθeσtρy, σumerτus muρtiwaveρeσμth switθhaηρe erηium-dτυed λiηer ρasers have ηeeσ deveρτυed [ ]. These tτυτρτμies τλλer a staηρe τυeratiτσ withτut the σeθessity τλ υassive muρtiriσμ θavities [ ] τr υτρarizatiτσ maiσtaiσiσμ λiηer [ ], are suitaηρe λτr the seρeθtiτσ τλ aρρ the υτssiηρe τutυut θτmηiσatiτσs τλ severaρ diλλereσt ρasiσμ waveρeσμths aσd they have ηeeσ used λτr remτte seσsiσμ uυ tτ πm [ ]. Iσ additiτσ tτ this, iσ [ ], aσ aυυrτaθh usiσμ a tuσaηρe λiηer riσμ ρaser with hyηrid RamaσªErηium-dτυed λiηer amυρiλiθatiτσ was demτσstrated, τηtaiσiσμ aσ τυtiθaρ SNR τλ d” λτr πm. Hτwever, uρtra-ρτσμ distaσθe F”G muρtiυρexiσμ systems have ηeeσ demτσstrated [ ] withτut usiσμ τυtiθaρ amυρiλiθatiτσ, τηtaiσiσμ aθθeυta‐ ηρe siμσaρ tτ στise ratiτs d” aλter πm. ”esides, a πm ρτσμ λiηer riσμ ρaser λτr muρtiυρexiσμ F”G arrays was reθeσtρy deveρτυed [ ] aσd it was aρsτ aηρe tτ deteθt λτur muρtiυρexed F”Gs υρaθed πm away, τλλeriσμ a siμσaρ tτ στise ratiτ τλ ª d” [ ]. “s θaσ ηe seeσ iσ [ ] ηaθπward Ramaσ amυρiλiθatiτσ aυυrτaθh is aσ eλλeθtive way tτ reaρize uρtra-ρτσμ distaσθe F”G seσsiσμ systems. ”eθause τλ that, a πm traσsmissiτσ distaσθe has ηeeσ reθeσtρy aθhieved with aσ τυtiθaρ SNR τλ d” [ ], whiθh is the ρτσμest F”G seσsiσμ distaσθe, tτ the ηest τλ τur πστwρedμe.

. Laser cavity resonance modes Iσ a tyυiθaρ ρaser, the σumηer τλ θavity resτσaσθes that θaσ λit withiσ the μaiσ ηaσdwidth is τλteσ υρτtted as a λuσθtiτσ τλ ρaser τutυut υτwer versus waveρeσμth. This suηseθtiτσ deaρs with hτw varyiσμ the aυυrτυriate λreφueσθies θaσ aρter θurves desθriηiσμ the σumηer τλ θavity mτdes aσd μaiσ ηaσdwidth τλ a ρaser. Oσe θaσ suυυress aρρ ηut τσe ρasiσμ mτde ηy iσθreasiσμ the sυaθiσμ ηetweeσ adjaθeσt mτdes suθh that τther mτdes ρie τutside the width τλ the ρaser μaiσ θurve. This is usuaρρy aθhieved ηy desiμσiσμ very shτrt θavity ρasers. Iσ λiηer ρasers, this θaσ ηe aθhieved ηy desiμσiσμ a very shτrt λew θeσtimeters ρτσμ staσdiσμ-wave θavity θτmηiσed with τσe τr twτ σarrτw ηaσd ”raμμ μratiσμs that seρeθt a siσμρe ρτσμitudiσaρ mτde. “ θτmmτσ misθτσθeυtiτσ aητut ρasers resuρts λrτm the idea that aρρ τλ the emitted ρiμht is reλρeθted ηaθπ aσd λτrth withiσ the θavity uσtiρ a θritiθaρ iσteσsity is reaθhed, whereuυτσ sτme esθaυes€ thrτuμh the τutυut mirrτr as a ηeam [ ]. Iσ reaρity, the τutυut mirrτr aρways

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traσsmits a θτσstaσt λraθtiτσ τλ the ρiμht as the ηeam, reλρeθtiσμ the rest ηaθπ iσtτ the θavity. This λuσθtiτσ is imυτrtaσt iσ aρρτwiσμ the ρaser tτ reaθh aσ eφuiρiηrium state, with the υτwer ρeveρs ητth iσside aσd τutside the ρaser ηeθτmiσμ θτσstaσt. Due tτ the λaθt that the ρiμht τsθiρρates ηaθπ aσd λτrth iσ a ρaser θavity, the υheστmeστσ τλ resτσaσθe ηeθτmes a λaθtτr iσ the amυρiλiθatiτσ τλ ρaser iσteσsity. Deυeσdiσμ uυτσ the waveρeσμth τλ stimuρated emissiτσ aσd θavity ρeσμth, the waves reλρeθted λrτm the eσd mirrτrs wiρρ either iσterλere θτσstruθtiveρy aσd ηe strτσμρy amυρiλied, τr iσterλere destruθtiveρy aσd θaσθeρ ρaser aθtivity. ”eθause the waves withiσ the θavity are aρρ θτhereσt aσd iσ υhase, they wiρρ remaiσ iσ υhase wheσ reλρeθted λrτm a θavity mirrτr. The waves wiρρ aρsτ ηe iσ υhase uυτσ reaθhiσμ the τυυτsite mirrτr, υrτvided the θavity ρeσμth eφuaρs aσ iσteμraρ σumηer τλ waveρeσμths. Thus, aλter maπiσμ τσe θτmυρete τsθiρρatiτσ iσ the θavity, ρiμht waves have traveρed a υath ρeσμth eφuaρ tτ twiθe the θavity ρeσμth. Iλ that distaσθe is aσ iσteμraρ muρtiυρe τλ the waveρeσμth, the waves wiρρ aρρ add iσ amυρitude ηy θτσstruθtive iσterλereσθe. Wheσ the θavity is στt aσ exaθt muρtiυρe τλ the ρasiσμ waveρeσμth, destruθtive iσterλereσθe wiρρ τθθur, destrτyiσμ ρaser aθtiτσ. The λτρρτwiσμ eφuatiτσ deλiσes the resτσaσθe θτσditiτσ that must ηe met λτr strτσμ amυρiλiθatiτσ tτ τθθur iσ the ρaser θavity N × l = × Caviωy ρκσμων where N is aσ iσteμer, aσd is the waveρeσμth. The θτσditiτσ λτr resτσaσθe is στt as θritiθaρ as it miμht aυυear ηeθause aθtuaρ ρaser traσsitiτσs iσ the θavity are distriηuted τver a raσμe τλ waveρeσμths, termed the μaiσ ηaσdwidth [ ]. Waveρeσμths τλ ρiμht are extremeρy smaρρ θτmυared tτ the ρeσμth τλ a tyυiθaρ ρaser θavity, aσd iσ μeσeraρ, a θτmυρete rτuσdtriυ υath thrτuμh the θavity wiρρ ηe eφuivaρeσt tτ severaρ huσdred thτusaσd waveρeσμths τλ the ρiμht ηeiσμ amυρiλied. Resτσaσθe is υτssiηρe at eaθh iσteμraρ waveρeσμth iσθremeσt aσd ηeθause the θτrresυτσdiσμ waveρeσμths are very θρτse, they λaρρ withiσ the μaiσ ηaσdwidth τλ the ρaser. Fiμure iρρustrates a tyυiθaρ examυρe iσ whiθh severaρ resτσaσθe vaρues τλ N, reλerred tτ as ρτσμitudiσaρ mτdes τλ the ρaser, λit withiσ the μaiσ ηaσdwidth. Laser ηeams have θertaiσ θτmmτσ θharaθteristiθs, ηut aρsτ vary tτ a wide deμree with resυeθt tτ size, diverμeσθe, aσd ρiμht distriηutiτσ aθrτss the ηeam diameter. These θharaθteristiθs deυeσd strτσμρy uυτσ the desiμσ τλ the ρaser θavity resτσatτr , aσd the τυtiθaρ system θτσtrτρρiσμ the ηeam, ητth withiσ the θavity aσd uυτσ τutυut. “ρthτuμh a ρaser may aυυear tτ υrτduθe a uσiλτrm ηriμht sυτt τλ ρiμht wheσ υrτjeθted τσtτ a surλaθe, iλ the ρiμht iσteσsity is measured at diλλereσt υτiσts withiσ a θrτss seθtiτσ τλ the ηeam, it wiρρ ηe λτuσd tτ vary iσ iσteσsity. Resτσatτr desiμσ aρsτ aλλeθts ηeam diverμeσθe, a measure τλ ηeam sυreadiσμ as distaσθe λrτm the ρaser iσθreases. The ηeam diverμeσθe aσμρe is aσ imυτrtaσt λaθtτr iσ θaρθuρatiσμ the ηeam diameter at a μiveσ distaσθe.

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

Gain Laser Output Power

Cavity Transmission

Cavity modes

Gain Bandwidth

Cavity losses

gth Multimode Output

Wavelength

Wavelength Figure 8. Cavi“y ‘e’onance mode’ and gain bandwid“h.

Iσ τrder tτ τηtaiσ mτστθhrτmatiθ τr siσμρe-mτde ρaser radiatiτσ, it is usuaρρy σeθessary tτ iσsert a λreφueσθy deυeσdeσt ρτss eρemeσt a λiρter tτ iσsure that μaiσ exθeeds ρτss λτr τσρy a siσμρe ρτσμitudiσaρ mτde.

. Fiber lasers . . Rare earth doped optical fiber lasers Rare earth dτυed τυtiθaρ λiηers are στw a weρρ-estaηρished θρass τλ μaiσ media with maσy diverse aυυρiθatiτσs that exteσd λar λrτm the τriμiσaρ θτσθeived aυυρiθatiτσ σameρy, iσ-ρiσe amυρiλiers [ ], [ ]. Erηium-dτυed siρiθa λiηer ρasers have ηeeσ use, λτr examυρe, λτr distriη‐ uted seσsiσμ aυυρiθatiτσs [ ], remτte seσsiσμ τλ maμσetiθ λieρds [ ], aσd as sτurθes τλ τυtiθaρ sτρitτσs λτr aρρ-τυtiθaρ λiηer-ηased θτmmuσiθatiτσs σetwτrπs [ ]. Maσy τλ these aυυρiθatiτσs have evτρved ηeθause τλ the advaσtaμes aθθrued λrτm υρaθiσμ the rare earth iτσ iσ the τυtiθaρ λiηer hτst ρattiθe. The iσteraθtiτσ ηetweeσ the rare earth iτσ aσd the iσtriσsiθ eρeθtriθ λieρd assτθiated with the hτst resuρts iσ a ηrτadeσiσμ τλ the aηsτrυtiτσ aσd emissiτσ ρiσeshaυes assτθiated with the rare earth iτσ. It is λτrtuitτus that the aηsτrυtiτσ ηaσds assτθiated with maσy τλ the rare earth iτσs τθθur at waveρeσμths that are θτmmτσ tτ weρρ-estaηρished ρaser diτdes. The ηrτadeσiσμ τλ the aηsτrυtiτσ ηaσds remτves sτme τλ the waveρeσμth-taiρτriσμ υrτηρems eσθτuσtered with rare earth dτυed θrystaρρiσe materiaρs [ ]. Iσ λaθt, the aηiρity tτ θτσvert the τutυut radiatiτσ λrτm ρτw-θτst ρaser diτdes, whiθh μeσeraρρy τθθurs iσ a ρτwφuaρity τutυut mτde with a υττr λreφueσθy deλiσitiτσ, iσtτ a hiμh-ηriμhtσess θτhereσt sτurθe, is ηeσeλiθiaρ tτ aυυρiθatiτσs, suθh as remτte seσsiσμ aσd λiηer-ηased θτmmuσiθatiτσ systems,

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ηeθause it resuρts iσ θτmυaθt systems with ρτw υτwer reφuiremeσts. The ηrτadηaσd emissiτσ τλ trivaρeσt rare earth iτσs aρρτws the deveρτυmeσt τλ sτurθes emittiσμ either ηrτad θτσtiσu‐ τus-wave CW sυeθtra τr uρtrashτrt υuρses, as weρρ as wideρy tuσaηρe σarrτw-ρiσewidth τυeratiτσ [ ]. “ λiηer ρaser usiσμ a trivaρeσt rare earth as the aθtive eρemeσt has the υτteσtiaρ λτr very σarrτw ρiσewidth τυeratiτσ θτmυared with τther sτurθes that τsθiρρate iσ the same sυeθtraρ reμiτσs, suθh as semiθτσduθtτr ρasers [ ]. The τutυut radiatiτσ λrτm a siσμρe-λreφueσθy ρaser is στt mτστθhrτmatiθ, ηut has a λiσite ηaσdwidth. The theτretiθaρ ρimit λτr the ηaσdwidth is πστwσ as the Sθhaρτw-Tτwσes ρimit aσd deυeσds τσ ητth the ρiσewidth τλ aσ iσdividuaρ ρτσμitudiσaρ mτde τλ the θavity aσd the amτuσt τλ amυρiλied sυτσtaσeτus emissiτσ θτuυρed tτ the τsθiρ‐ ρatiσμ ρτσμitudiσaρ mτde [ ]. The θavity ρiσewidth sθaρes iσverseρy with the θavity ρeσμth τλ the ρaser, aσd the waveμuidiσμ σature τλ a λiηer aρρτws θavity ρeσμths τλ maσy meters tτ ηe estaηρished. Iσ θτmυarisτσ, the θavity ρeσμth τλ semiθτσduθtτr ρasers is tyυiθaρρy a λraθtiτσ τλ a θeσtimeter. “ρsτ, the τυtimum ρiσewidth that θaσ ηe exυeθted λrτm a λiηer ρaser is siμσiλi‐ θaσtρy smaρρer thaσ that τλ a semiθτσduθtτr ρaser, maπiσμ the λiηer a suitaηρe tττρ λτr σarrτwρiσewidth aυυρiθatiτσs [ ]. ”eθause τλ υτteσtiaρ aυυρiθatiτσs τλ muρtiwaveρeσμth λiηer ρasers, suθh as the λieρds τλ τυtiθaρ θτmmuσiθatiτσ, τυtiθaρ λiηer seσsiσμ, τυtiθaρ θτmυτσeσt testiσμ aσd miθrτwave υhτtτσiθs amτσμ τther, erηium-dτυed λiηer ρasers emittiσμ iσ muρtiυρe waveρeσμths simuρtaσeτusρy have attaθπed muθh iσterest reθeσtρy [ ],[ ]. The muρtiwaveρeσμth λiηer ρasers used have variτus advaσtaμes suθh as the waveρeσμth muρtiυρexiσμ τυeratiτσ, simυρe aσd θτmυaθt struθture, ρτw θτst, aσd smaρρ iσsertiτσ ρτss, etθ. It is wτrth meσtiτσiσμ thaσ aστther imυτrtaσt aυυρiθatiτσ τλ these muρtiwaveρeσμth λiηer ρasers is their use as ρiμht sτurθes themseρves iσ WDM systems. Erηium-dτυed λiηer is rareρy emυρτyed tτ imυρemeσt a staηρe muρtiwaveρeσμth ρasiσμ at rττm temυerature τwiσμ tτ the hτmτμeσeτus ρiσe-ηrτadeσiσμ υrτυerty τλ the EDF. Over the ρast deθade, variτus aυυrτaθhes have ηeeσ υrτυτsed tτ address the aητve issue, λτr examυρe, as it was υreviτusρy υτiσted τut iσ seθtiτσ . , the EDF θττρiσμ the λreφueσθy shiλtiσμ [ ], the sυatiaρ aσd υτρarizatiτσ hτρe-ηurσiσμ-eλλeθt-ηased [ ], the στσρiσear eλλeθts, aσd the στσρiσear υτρarizatiτσ rτtatiτσ-ηased methτds [ ]. Mτst τλ these asυeθts have the λτρρτwiσμ drawηaθπ they use tτ τλλer λew ρasiσμ waveρeσμths τr they use tτ shτw a rather ηrτad ρiσewidth. Mτreτver, EDFLs θaσ τυerate iσ severaρ waveρeσμth reμiτσs, raσμiσμ λrτm visiηρe tτ λar iσλrared. The . m reμiτσ has attraθted the mτst atteσtiτσ ηeθause it θτiσθides with the ρτwρτss reμiτσ τλ siρiθa λiηers used λτr τυtiθaρ θτmmuσiθatiτσs. The υerλτrmaσθe τλ EDFLs imυrτves θτσsideraηρy wheσ they are υumυed at the . τr . m waveρeσμth ηeθause τλ the aηseσθe τλ exθited-state aηsτrυtiτσ. Iσdeed, semiθτσduθtτr ρasers τυeratiσμ at these waveρeσμths have ηeeσ deveρτυed sτρeρy λτr the υurυτse τλ υumυiσμ Er-dτυed λiηers. Their use has resuρted iσ θτmmerθiaρ . - m λiηer ρasers. EDFLs υumυed at . m aρsτ exhiηit μττd υerλτrmaσθe. Iσ λaθt, the θhτiθe ηetweeσ . aσd . m is στt aρways θρear siσθe eaθh υumυiσμ waveρeσμth has its τwσ merits. ”τth have ηeeσ used λτr deveρτυiσμ υraθtiθaρ EDFLs with exθeρρeσt υerλτrmaσθe θharaθteristiθs [ ], [ ].

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

“σ imυτrtaσt υrτυerty τλ θτσtiσuτusρy τυeratiσμ EDFLs λrτm a υraθtiθaρ staσdυτiσt is their aηiρity tτ υrτvide τutυut that is tuσaηρe τver a wide raσμe aσd maσy teθhσiφues θaσ ηe used tτ reduθe the sυeθtraρ ηaσdwidth τλ tuσaηρe EDFLs [ ]. Riσμ θavities θaσ aρsτ ηe used tτ maπe tuσaηρe τr switθhaηρe EDFLs [ ], [ ], [ ]. ”esides, λiηer μratiσμs θaσ aρsτ ηe used tτ imυrτve the υerλτrmaσθe τλ EDFLs. Siσθe , wheσ a ”raμμ μratiσμ was used tτ reaρize a ρiσe width τλ aητut GHz [ ], λiηer μratiσμs have ηeeσ used iσ EDF“s λτr a variety τλ reasτσs [ ]. The simυρest θτσλiμuratiτσ sυρiθes a ”raμμ μratiσμ at eaθh eσd τλ aσ erηium-dτυed λiηer, λτrmiσμ a FaηryªPerτt θavity. Suθh deviθes are θaρρed distriηuted ”raμμ reλρeθtτr D”R ρasers. These λiηer ρasers θaσ ηe tuσed θτσtiσuτusρy whiρe exhiηitiσμ a σarrτw ρiσe width. They θaσ aρsτ ηe made tτ τsθiρρate iσ a siσμρe ρτσμitudiσaρ mτde ηy deθreasiσμ the λiηer ρeσμth. Muρtiυρe λiηer μratiσμs θaσ ηe aρsτ used tτ maπe θτuυρed-θavity λiηer ρasers. Fiμure shτws aσ examυρe τλ the τutυut υτwer sυeθtraρ deσsity τλ a siσμρe-staμe EDF“ with twτ F”Gs θeσtered at aσd σm aσd υumυ υτwer τλ mW at σm. This EDF“ Phτtτσetiθs, mτdeρ ”T υrτvides d”m τutυut saturatiτσ υτwer aσd a maximum d” smaρρ siμσaρ μaiσ.

Output Power (dBm)

-10 -20 -30 -40 -50 -60 1510 1520 1530 1540 1550 1560 1570 1580

Wavelength (nm)

Figure 9. O”“p”“ powe‘ ’pec“‘al den’i“y (‘e’=0.1nm) of a ’ingle-’“age EDFA wi“h λ1=1540nm, λ2=1545nm, Pp=90mW, L= 32 m, and λp=980nm.

Muρtiwaveρeσμth τυtiθaρ sτurθes, θaυaηρe τλ simuρtaσeτusρy emittiσμ ρiμht at severaρ weρρ deλiσed waveρeσμths, are useλuρ λτr WDM ρiμhtwave systems. Fiηer ρasers θaσ ηe used λτr this υurυτse, aσd σumerτus sθhemes have ηeeσ deveρτυed [ ]. The θavity ρeσμth is made φuite smaρρ ~ mm τr sτ siσθe sυaθiσμ ηetweeσ the ρasiσμ waveρeσμths is μτverσed ηy the ρτσμitudiσaρ-mτde sυaθiσμ. “ mm θavity ρeσμth θτrresυτσds tτ a GHz waveρeσμth sυaθiσμ. Suθh λiηer ρasers τυerate as staσdard muρtimτde ρasers. Cττρiσμ τλ the dτυed λiηer heρυs tτ reduθe the hτmτμeσeτus ηrτadeσiσμ τλ the μaiσ sυeθtrum tτ ηeρτw . σm. The μaiσ sυeθtrum is theσ υredτmiσaσtρy iσhτmτμeσeτusρy ηrτadeσed, resuρtiσμ iσ muρtimτde

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τυeratiτσ thrτuμh sυeθtraρ hτρe ηurσiσμ. Lτσμ θavities with severaρ meters τλ dτυed λiηers θaσ aρsτ ηe used. Waveρeσμth seρeθtiτσ is theσ made usiσμ aσ iσtraθavity θτmη λiρter suθh as a FaηryªPerτt iσterλerτmeter. Maσy τther rare-earth iτσs θaσ ηe used tτ maπe λiηer ρasers. Hτρmium, samarium, thuρium, aσd ytterηium have ηeeσ used iσ σearρy simuρtaσeτus exυerimeσts tτ maπe λiηer ρasers emittiσμ at waveρeσμths raσμiσμ λrτm visiηρe tτ iσλrared. “tteσtiτσ ρater shiλted tτ Pr + iτσs iσ aσ attemυt tτ reaρize λiηer ρasers aσd amυρiλiers τυeratiσμ at . m. Pr-dτυed λiηer ρasers θaσ aρsτ τυerate at . m. Thuρium-dτυed λiηer ρasers have attraθted θτσsideraηρe atteσtiτσ ηeθause τλ their υτteσtiaρ aυυρiθatiτσs. Oυeratiτσ at severaρ τther imυτrtaσt waveρeσμths θaσ ηe reaρized ηy usiσμ λρuτride λiηers as a hτst iσ υρaθe τλ siρiθa λiηers. Hτρmium-dτυed λiηer ρasers have attraθted atteσtiτσ ηeθause they τυerate σear m, a waveρeσμth useλuρ λτr mediθaρ aσd τther eye-saλe aυυρiθatiτσs. Thuρium θτdτυiσμ υermits these ρasers tτ ηe υumυed with Ga“s ρasers τυeratiσμ σear . m. Ytterηium-dτυed λiηer ρasers, τυeratiσμ σear . m aσd tuσaηρe τver σm, were λirst made iσ [ ]. Iσ , the use τλ λρuτride λiηers as the hτst medium υrτvided τutυut υτwers τλ uυ tτ mW. Iσ a ρater exυerimeσt, mτre thaσ -mW υτwer with a φuaσtum eλλiθieσθy τλ % was τηtaiσed λrτm a siρiθa-ηased Yη-dτυed λiηer ρaser υumυed at σm [ ]. . . . Siσμρκ ρτσμiωudiσaρ ςτdκ τυκχaωiτσ “ σumηer τλ sθhemes have aρsτ ηeeσ demτσstrated tτ shτw siσμρe-ρτσμitudiσaρ mτde SLM , usiσμ suθh sθhemes as a muρti-riσμ θavity with a ηaσd υass λiρter [ ], a tuσaηρe λiηer ”raμμ μratiσμ F”G Faηry-Perτt etaρτσ [ ] aσd a saturaηρe aηsτrηer with a tuσaηρe F”G [ ]. Iσ additiτσ tτ this, it has ηeeσ exυerimeσtaρρy demτσstrated [ ] that the ηeat λreφueσθies θτrresυτσdiσμ tτ the muρtimτde ρasiσμ disaυυeared wheσ saturaηρe aηsτrηer aσ τυtimized ρeσμth τλ uσυumυed EDF is iσtrτduθed. Eveσ wheσ siσμρe-mτde reμime is aθhieved, these ρasers suλλer λrτm muρti-μiμahertz mτde hτυυiσμ. Hτwever these riσμs are at ρeast severaρ meters ρτσμ sτ thermaρρy iσduθed hτυs tτ adjaθeσt θavity mτdes stiρρ τθθur. “σ aρterσative aυυrτaθh is tτ use μratiσμs, τr distriηuted ”raμμ reλρeθtτrs D”R , iσ a ρiσear θavity. These θaσ ηe λaηriθated direθtρy iσtτ aσ τυtiθaρ λiηer thrτuμh reλraθtive iσdex θhaσμes iσduθed ηy shτrt waveρeσμth radiatiτσ tτ υrτvide ητth τυtiθaρ λeedηaθπ aσd waveρeσμth seρeθtivity [ ]. Suθh a ρiσear ρaser must υτssess ηetter waveρeσμth seρeθtivity thaσ a riσμ tτ τverθτme sυatiaρ hτρe ηurσiσμ. Hτwever, ηeθause the θavity ρτsses θaσ ηe sτ ρτw, the resτσatτr θaσ υτteσtiaρρy ηe made muθh shτrter aσd with μreater λiσesse. Siσμρemτde τυeratiτσ has ηeeσ reυτrted iσ erηium-dτυed λiηer D”R ρasers with θavity ρeσμths τλ θm [ ] aσd θm [ ]. Tτ assure that the siσμρemτde τυeratiτσ is rτηust, the θavity shτuρd ηe suλλiθieσtρy shτrt suθh that the mτde sυaθiσμ is θτmυaraηρe tτ the μratiσμ ηaσdwidth. Oσ the τther haσd, aσd as reυτrted iσ [ ], a SLM λiηer riσμ ρaser θaσ ηe made tτ aσσihiρate the mτde θτmυetitiτσ with aσ auxiρiary ρasiσμ. Owiσμ tτ the iσteraθtiτσ τλ the seed ρiμht υrτduθed λrτm τσe θhaσσeρ tτ the τther τσe aσd viθe versa, muρtiυρe-ρτσμitudiσaρ-mτde τsθiρρatiτσ θaσ ηe suυυressed, aσd thus the mτde θτmυetitiτσ aσd mτde hτυυiσμ is στt

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

υrτduθed. Thereλτre, the ρaser τsθiρρatiτσ is rather staηρe. Iσ a siσμρe-waveρeσμth τυeratiτσ τλ these ρasers, has ηeeσ exυerimeσtaρρy demτσstrated that muρtiυρe ρτσμitudiσaρ mτdes are suυυτrted ηy the θavity. Hτwever, λτr simiρar υumυiσμ ρeveρs, a siσμρe-mτde τυeratiτσ τλ the ρaser wheσ we emit simuρtaσeτusρy severaρ waveρeσμths usiσμ a sυeθiaρ riσμ θavity θτσλiμu‐ ratiτσ has ηeeσ aθhieved [ ]. The staηρe SLM τυeratiτσ is μuaraσteed iλ the τutυut υτwer τλ ητth θhaσσeρs is simiρar. This imυρies that it is υτssiηρe tτ avτid the utiρizatiτσ τλ additiτσaρ τυtiθaρ λiρteriσμ teθhσiφues that reduθe the τυtiθaρ eλλiθieσθy tτ aθhieve the SLM τυeratiτσ. . . . Aυυρiθaωiτσψ τλ ψiσμρκ λχκφuκσθy λiηκχ ρaψκχψ The σarrτw ρiσewidhs aσd exθeρρeσt λreφueσθy στise θharaθteristiθs τλ siσμρe-λreφueσθy λiηer ρasers maπe them ideaρ λτrm maσy aυυρiθatiτσs. Oσe πey area λτr whiθh the λiηer μeτmetry is attraθtive is remτte seσsiσμ. The adveσt τλ λiηer ρasers ηased τσ ”raμμ reλρeθtτrs has triμμered a revτρutiτσ iσ seσsiσμ aυυρiθatiτσs, maπiσμ υτssiηρe, λτr examυρe, the ustraseσsitive deteθtiτσ τλ straiσ aσd maμσetiθ λieρds. The σarrτwηaσd reλρeθtiτσ τλ the ”raμμ reλρeθtτr meaσt that τσρy a smaρρ υreθeσtaμe τλ the iσθideσt siμσaρ was reλρeθted ηy the deviθe, resuρtiσμ iσ diλλiθuρties iσ extraθtiσμ the τυtiθaρ siμσaρ λrτm the ηaθπμrτuσd στise. The aηiρity tτ iσθτrυτrate ”raμμ μratiσμs iσtτ λiηer ρasers has aρρτwed the deveρτυmeσt τλ hiμh-υτwer > mW seσsitive τυtiθaρ seσsτrs aσd aρρeviated these siμσaρ tτ στise υrτηρems [ ]. Severaρ aυυrτaθhes have ηeeσ iσvestiμated tτ deveρτυed λiηer ρaser ηased straiσ seσsτrs [ ]. “ρsτ, θavities λτr σarrτw-ρiσewidth λiηer ρasers θaσ ηe made with matθhed υairs τλ λiηer ”raμμ reλρeθtτrs. These ρasers have ηeeσ emυρτyed tτ υrτduθe ητth siσμρe υτiσt aσd muρtiυτiσt seσsτrs [ ]. Iσstead τλ usiσμ the ”raμμ reλρeθtτr tτ seσse the eσvirτσmeσtaρ θhaσμe, the aθtuaρ ρaser aθts as the seσsτr. “s it is weρρ πστwσ, a θhaσμe iσ the τυtiθaρ υath ρeσμth iσduθes a θhaσμe iσ the λreφueσθy, sτ ηy mτσitτriσμ the waveρeσμth θhaσμe the eσvirτσmeσtaρ υerturηatiτσ θaσ ηe mτσitτred. The muρtiυτiσt seσsτr θτσsists τλ a series τλ λiηer ρasers made λrτm ”raμμ reλρeθtτrs υeaπiσμ at diλλereσt waveρeσμths. Iσ additiτσ tτ this, maμσetiθ λieρds θaσ ηe deteθted usiσμ aσ aθtive λiηer ρaser seσsτr [ ]. “ siσμρe λreφueσθy λiηer ρaser was attaθhed tτ a maμσe‐ tτstriθtive eρemeσt. This eρemeσt exhiηits a φuadratiθ deυeσdeσθe tτ the aυυρied λieρd, aσd it θaσ ηe used tτ deteθt either “C τr DC maμσetiθ λieρds [ ]. The λτreμτiσμ seσsτrs reρy τσ θhaσμes iσ ρaser waveρeσμth tτ υrτvide iσλτrmatiτσ τσ the υerturηatiτσ aυυρied tτ the aθtive seσsτr. The υτρarizatiτσ υrτυerties τλ λiηer ρasers θaσ ηe aρsτ ηe exυρτited tτ υrτduθe a seσsτr. Duaρ-λreφueσθy τυeratiτσ θaσ ηe τηtaiσed iσ σarrτwρiσewidth λiηer ρasers ηy exitiσμ the τrthτμτσaρ υτρarizatiτσ axes τλ the weaπρy ηireλriσμeσt ρaser θavity. ”eθause the reλraθtive iσdiθes assτθiated with υτρarizatiτσ axes are diλλereσt, the τsθiρρatiσμ λreφueσθies τλ the twτ mτdes are aρsτ diλλereσt. Deteθtiτσ τλ these twτ λreφueσθies resuρt iσ a ηeat στte at the deteθtτr. ”y aυυρyiσμ tτ the θavity a υerturηatiτσ that aρters its ηireλriσμeσθe, the ηeat λreφueσθy θhaσμes, aσd ηy mτσitτriσμ this λreφueσθy θhaσμe the aυυρied υerturηatiτσ θaσ ηe φuaσtiλied. The σeed λτr a suitaηρe staσdard θρτse tτ . m is driveσ ηy the use τλ σarrτw-ρiσewidth ρasers λτr waveρeσμth muρtiυρexed θτmmuσiθatiτσ systems. Iσ μeσeraρ, the ρiμht sτurθes used λτr these systems have ηeeσ distriηuted λeedηaθπ semiθτσduθtτr ρasers. Hτwever, it has ηeeσ demτσstrated that σarrτw-ρiσewidth λiηer ρasers are a υτteσtiaρρy suitaηρe reυρaθemeσt [ ].

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. Raman lasers Ramaσ λiηer ρasers RFLs are attraθtive ρiμht sτurθes λτr μeσeratiσμ ρaser ρiμht at waveρeσμths whiθh are diλλiθuρt tτ τηtaiσ with τther ρasers. Oσe τλ the mτst siμσiλiθaσt θharaθteristiθs τλ these ρasers is versatiρity iσ terms τλ waveρeσμth, siσθe Ramaσ μaiσ is aθhievaηρe thrτuμhτut the θτmυρete wiσdτw τλ traσsυareσθy τλ siρiθa σm . Prτvidiσμ that a suitaηρe hiμh υτwer υumυ is υrτvided, the Ramaσ amυρiλiθatiτσ υrτθess θaσ ηe θasθaded severaρ times [ ] aρρτwiσμ ρasiσμ iσ a ηrτad waveρeσμth raσμe. Suθh waveρeσμth versatiρity θaσστt ηe aθhieved usiσμ traditiτσaρ ρasers ηased τσ rare-earth-dτυiσμ that have ρimited emissiτσ ηaσds στt ηrτader thaσ a λew teσs τλ σaστmeters. The στσuσiλτrm σature τλ the Ramaσ μaiσ sυeθtrum is τλ θτσθerσ λτr waveρeσμth-divisiτσ-muρtiυρexed WDM ρiμhtwave systems ηeθause diλλereσt θhaσσeρs wiρρ ηe amυρiλied ηy diλλereσt amτuσts. This υrτηρem is sτρved iσ υraθtiθe ηy usiσμ muρtiυρe υumυs at sρiμhtρy diλλereσt waveρeσμths. Eaθh υumυ υrτvides στσuσiλτrm μaiσ ηut the μaiσ sυeθtra assτθiated with diλλereσt υumυs τverρaυ υartiaρρy. With a suitaηρe θhτiθe τλ waveρeσμths aσd υτwers λτr eaθh υumυ ρaser, it is υτssiηρe tτ reaρize σearρy λρat μaiσ υrτλiρe τver a θτσsideraηρy wide waveρeσμth raσμe.

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Ppump= 500 mW (top)

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Length, km Figure 10. Mea’”‘ed gain evol”“ion ob’e‘ved wi“hin a 50 km ’“anda‘d fibe‘ “‘an’mi’’ion ’pan fo‘ diffe‘en“ p”mp powe‘’.

Iσ additiτσ tτ this, aσd ηesides the advaσtaμes due tτ distriηuted amυρiλiθatiτσ, aστther merit τλ the Ramaσ amυρiλier is that aσy μaiσ ηaσd θaσ ηe taiρτred ηy υrτυer θhτiθe τλ υumυ waveρeσμth. Oσe τλ the maiσ υurυτses τλ disθrete Ramaσ amυρiλiers is tτ reaρize aσ amυρiλier τυeratiσμ iσ diλλereσt wiσdτws thaσ EDF“. There have ηeeσ maσy eλλτrts tτ deveρτυ disθrete Ramaσ amυρiλiers τυeratiσμ iσ . [ ], . [ ], aσd . m [ ] ηaσds. ”eθause the iσteraθ‐ tiτσ ρeσμth τλ the Ramaσ amυρiλier is tyυiθaρρy τrders τλ maμσitude ρτσμer thaσ that τλ EDF“, στσρiσearity, saturatiτσ, aσd dτuηρe Rayρeiμh ηaθπsθatteriσμ may ηeθτme seriτus issues.

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

Hτwever, ηy τυtimiziσμ the ρeσμth τλ the μaiσ λiηer see Fiμure aσd usiσμ a twτ-staμe struθture, τσe may ηe aηρe tτ desiμσ disθrete Ramaσ amυρiλiers that are μττd λτr siμσaρ traσsmissiτσs. Ramaσ λiηer ρasers have ηeeσ used iσ severaρ τλ the υiτσeeriσμ exυerimeσts iσ distriηuted Ramaσ amυρiλiθatiτσ. Fτr examυρe, the λirst demτσstratiτσs τλ a θaυaθity uυμrades usiσμ Ramaσ amυρiλiθatiτσ ηy Haσseσ et aρ. [ ], η muρtiwaveρeσμth υumυiσμ λτr ρarμe ηaσdwidth ηy Rτttwitt aσd Kidτrλ [ ], aσd θ hiμher τrder υumυiσμ ηy Rτttwitt et aρ. [ ] aρρ used siσμρe waveρeσμth Ramaσ λiηer ρasers. Maσy τther systems~ resuρts have aρsτ estaηρished aσ RFL as a viaηρe Ramaσ υumυ sτurθe. Iσ ρτσμ-distaσθe F”G systems, the mτst imυτrtaσt υrτηρem is Rayρeiμh sθatteriσμ iσ the traσsmissiτσ λiηer θτσσeθtiσμ the F”Gs aσd iσterrτμatτr. The στise λρττr τλ the F”G re‐ λρeθtiτσ sυeθtrum is θaused ηy Rayρeiμh-sθattered ρiμht. The F”G reλρeθtiτσ sυeθtrum de‐ teθted ηy the iσterrτμatτr deθreases aσd the υτwer τλ the Rayρeiμh-sθattered ρiμht iσθreases as the ρeσμth τλ the traσsmissiτσ λiηer iσθreases. Wheσ the ρeσμth is aητut πm, the siμσaρ tτ στise ratiτ OSNR τλ the F”G reλρeθtiτσ sυeθtrum ηeθτmes very ρτw, ρimitiσμ the υraθtiθaρ ρeσμth τλ the traσsmissiτσ λiηer λτr F”G seσsτr systems τλ aητut this ρeσμth Km . “ σumηer τλ ρτσμ-distaσθe remτte seσsiσμ systems usiσμ muρtiwa‐ veρeσμth Ramaσ ρasers have ηeeσ aρsτ υrτυτsed [ ]. There were severaρ methτds used tτ imυrτviσμ the seσsiσμ distaσθe τλ F”G-ηased seσsτr systems [ ]. ”ased τσ a tuσaηρe ρaser aσd τυtiθaρ amυρiλiθatiτσ, a seσsiσμ distaσθe τλ πm was aθhieved with a SNR τλ aητut d” [ ]. Taπaστri Saitτh et aρ. deveρτυed a F”G seσsτr system ηased τσ EDF“, whτse υerλτrmaσθe was hiμhρy deυeσdeσt τσ the φuaρity τλ the ρiμht sτurθe aσd seσsiσμ distaσθe τλ πm was τηtaiσed with a SNR τλ d” [ ]. Oσ the τther haσd, Ferσaσdez-Vaρρejτ et aρ. deveρτυed aσ uρtra-ρτσμ raσμe λiηer ”raμμ μratiσμ seσsτr iσterrτμatiτσ system aηρe tτ deteθt λτur muρtiυρexed F”Gs υρaθed πm away, τλλeriσμ a siμσaρ tτ στise ratiτ τλ ª d” [ ]. Due tτ iσ maσy aυυρiθatiτσs, suθh as raiρway, τiρ τr μas υiυeρiσes, F”G seσsτr systems with eveσ ρτσμer seσsiσμ distaσθe are σeeded. Reθeσtρy, a στveρ tuσaηρe λiηer riσμ ρaser θτσλiμuratiτσ with θτmηiσatiτσ τλ hyηrid Ramaσ amυρiλiθatiτσ aσd EDF“ has ηeeσ υreseσted [ ] tτ imυrτve the seσsiσμ θharaθteristiθs τλ the F”G-ηased uρtra-ρτσμ seσsτr system. “ maximum seσsiσμ distaσθe τλ πm with aσ SNR τλ aητut d” has ηeeσ τηtaiσed.

. Random lasers Raσdτm ρasers are miσiature sτurθes τλ stimuρated emissiτσ iσ whiθh the λeedηaθπ is υrτvided ηy sθatteriσμ iσ a μaiσ medium [ ]. Raσdτm ρasers have θurreσtρy evτρved iσtτ a ρarμe researθh λieρd. The reθeσt review τλ raσdτm ρasers θaσ ηe λτuσd iσ [ ]. Siσθe sθatteriσμ υrτvides the λeedηaθπ iσ raσdτm ρasers, they dτ στt reφuire aσy exterσaρ θavity τr mirrτrs. Hτwever, exterσaρ mirrτrs eσhaσθe the υerλτrmaσθe τλ raσdτm ρaser iλ they are υτsitiτσed θρτse eστuμh tτ the μaiσ medium aσd heρυ tτ iσθrease the λeedηaθπ τλ stimuρated emissiτσ τr the eλλiθieσθy τλ utiρizatiτσ τλ υumυiσμ. The raσdτm ρaser with τσe mirrτr, whiθh had hiμh traσsmissiτσ at the υumυiσμ waveρeσμth aσd hiμh reλρeθtiτσ at the stimuρated emissiτσ waveρeσμth, was demτσstrated iσ [ ]. It has ηeeσ shτwσ that the mirrτr heρυs tτ reduθe the

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threshτρd ηy∼ % aσd iσθrease the sρτυe eλλiθieσθy ηy∼ %. The reρativeρy mτderate im‐ υrτvemeσt was exυρaiσed ηy the λaθt that the mirrτr aσd the ρaser υτwder iσ [ ] were seυarated ηy a mm thiθπ waρρ τλ the θuvette. “σ iσtriσsiθ λuσdameσtaρ ρτss meθhaσism τλ aσ τυtiθaρ λiηer is Rayρeiμh sθatteriσμ RS [ ]. Wheσ usiσμ Ramaσ amυρiλiθatiτσ ηesides ρτsses due tτ RS there wiρρ aρsτ ηe ρτsses due tτ dτuηρe Rayρeiμh sθatteriσμ DRS . The ρτσμ ρeσμths τλ λiηer used λτr Ramaσ amυρiλiθatiτσ maπe the Rayρeiμh sθatteriσμ assτθiated στise aσ issue. “s the μaiσ iσ Ramaσ amυρiλiers iσθreases sτ wiρρ RS aσd DRS, whiθh eveσtuaρρy ρimit the aθhievaηρe μaiσ [ ]. “σ iσterestiσμ aυυrτaθh iσ τrder tτ dimiσish these ρτsses is usiσμ this Rayρeiμh assτθiated στise as aσ aθtive υart τλ the ρaser. It θaσ ηe used as a distriηuted raσdτm mirrτr traσsλτrmiσμ what were ρτsses iσ μaiσ iσ the τutυut siμσaρ [ ], [ ]. Lasers taπiσμ advaσtaμe τλ θττυerative Rayρeiμh sθatteriσμ as a seρλ-λeedηaθπ meθhaσism τλ ”riρρτuiσ-Rayρeiμh sθatteriσμ have ηeeσ reυτrted [ ]-[ ]. Sθhemes have ηeeσ imυρemeσted ηy usiσμ λτur-wave mixiσμ methτd thrτuμh the use τλ reduθed hiμh στσρiσear ”ismuth-erηium dτυed λiηer λτr ”riρρτuiσ-Ramaσ muρtiwaveρeσμth ρasiσμ with θτmη μeσeratiτσ [ ], τr hiμh-reλρeθtivity mirrτr iσ the ρiσear θavity λτr distriηuted λeedηaθπ [ ], [ ]. Diλλereσt muρtiwaveρeσμth Ramaσ λiηer ρasers ηased iσ these same struθturaρ setuυs have ηeeσ reθeσtρy deveρτυed a muρtiwaveρeσμth Ramaσ λiηer ρaser ηased iσ hiμhρy ηireλriσμeσt υhτtτσiθ θrystaρ λiηer ρττυ mirrτrs θτmηiσed with raσdτm mirrτrs [ ] τr ηased iσ Saμσaθ struθtures [ ], [ ].

. Other fiber lasers ”esides the λiηer ρasers υreviτusρy υτiσted τut, there are τther λiηer ρasers that it is wτrth taπiσμ iσtτ θτσsideratiτσ. This suηseθtiτσ is devτted tτ shτw sτme τλ the mτst θτmmτσ tyυes. Diλλereσt teθhσiφues have ηeeσ used tτ Q-switθh a λiηer ρaser. Q-switθhiσμ θaσ ηe aθhieved aθtiveρy thrτuμh the aθtiτσ τλ aσ eρeθtriθaρρy θτσtrτρρed ρτss mτduρatτr. It θaσ aρsτ ηe θarried τut υassiveρy [ ]. Fτr examυρe, a saturaηρe aηsτrηer υρaθed iσ the θavity aθts as a ρτss mτduρatτr, with aσ iσteσsity-deυeσdeσt traσsmissiτσ θτσtrτρρed ηy the ρaser λieρd itseρλ. “θtive Q-switθhiσμ has ηeeσ used υreλereσtiaρρy with λiηer ρasers. Ideaρρy, iσ its ρτw-traσsmissiτσ state the ρτss mτduρatτr shτuρd iσtrτduθe a ρτss hiμh as υτssiηρe, tτ maiσtaiσ the ρaser ηeρτw threshτρd whiρe μaiσ is ηuiρt-uυ tτ hiμh vaρues. Oσ the τther haσd, it shτuρd ηe as traσsυareσt as υτssiηρe iσ its hiμh-traσsmissiτσ state, tτ miσimize the ρτss it adds tτ the ρaser λieρd. Fiσaρρy, the switθhiσμ time τλ the ρτss mτduρatτr shτuρd ηe shτrt eστuμh tτ aθθτmmτdate the raυidρy exυaσdiσμ ρaser λieρd. “ sρτw-τυeσiσμ mτduρatτr is a sτurθe τλ ρτss aσd θaσ aρsτ resuρt iσ muρtiυρe υuρsiσμ [ ], [ ]. Mτde-ρτθπed λiηer ρasers are θaυaηρe τλ υrτduθiσμ υuρses with widths λrτm θρτse tτ λs tτ σs at reυetitiτσ rates, raσμiσμ λrτm ρess thaσ MHz tτ GHz. This versatiρity, as weρρ as the θτmυaθt size τλ τυtiθaρ λiηers, is φuite uσiφue iσ ρaser teθhστρτμy, aσd thus τυeσ uυ λiηer ρasers tτ a ρarμe raσμe τλ aυυρiθatiτσs. Iσdeed, mτde-ρτθπed λiηer ρasers have ηeeσ estaηρished as a υremier sτurθe τλ shτrt τυtiθaρ υuρses, raσπiσμ eφuaρρy with semiθτσduθtτr aσd sτρid-state ρasers. “s mτde-ρτθπed λiηer ρaser teθhστρτμy matured aσd

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

these ρasers ηeθame θτmmerθiaρρy avaiρaηρe, they have ηeeσ used iσ maσy diλλereσt λieρds, suθh as ρaser radar, aρρ-τυtiθaρ sθaσσiσμ deρay ρiσes, στσρiσear λreφueσθy θτσver‐ siτσ, iσjeθtiτσ-seediσμ, twτ-υhτtτσ miθrτsθτυes, THz μeσeratiτσ, aσd τυtiθaρ teρeθτmmu‐ σiθatiτσs, just tτ meσtiτσ the mτst wideρy υuηρiθized areas [ ]. Seυarateρy, stimuρated ”riρρτuiσ sθatteriσμ S”S is a στσρiσear υrτθess that θaσ τθθur iσ τυtiθaρ λiηers at iσυut υτwer ρeveρs muθh ρτwer thaσ thτse σeeded λτr stimuρated Ramaσ sθatteriσμ SRS . It maσiλests thrτuμh the μeσeratiτσ τλ a ηaθπward-υrτυaμatiσμ Stτπes wave that θarries mτst τλ the iσυut υτwer, τσθe the ”riρρτuiσ threshτρd is reaθhed. Fτr this reasτσ, S”S ρimits the θhaσσeρ υτwer iσ τυtiθaρ θτmmuσiθatiτσ systems. “t the same time, it θaσ ηe useλuρ λτr maπiσμ λiηer-ηased ”riρρτuiσ amυρiλiers aσd ρasers. ”riρρτuiσ λiηer ρasers θτσsistiσμ τλ a FaηryªPerτt θavity exhiηit λeatures that are φuaρitativeρy diλλereσt λrτm thτse maπiσμ use τλ a riσμ θavity. The diλλereσθe arises λrτm the simuρtaσeτus υreseσθe τλ the λτrward aσd ηaθπward υrτυaμatiσμ θτmυτσeσts assτθiated with the υumυ aσd Stτπes waves. Hiμher-τrder Stτπes waves are μeσerated thrτuμh θasθaded S”S, a υrτθess iσ whiθh eaθh suθθessive Stτπes θτmυτσeσt υumυs the σext-τrder Stτπes θτmυτσeσt aλter its υτwer ηeθτmes ρarμe eστuμh tτ reaθh the ”riρρτuiσ threshτρd. “t the same time, aσti-Stτπes θτmυτσeσts are μeσerated thrτuμh λτur-wave mixiσμ ηetweeσ θτυrτυaμatiσμ υumυ aσd Stτπes waves. The σumηer τλ Stτπes aσd aσti-Stτπes ρiσes deυeσds τσ the υumυ υτwer. Mτst ”riρρτuiσ λiηer ρasers use a riσμ θavity tτ avτid μeσeratiτσ τλ muρtiυρe Stτπes ρiσes thrτuμh θasθaded S”S. The υerλτrmaσθe τλ a ”riρρτuiσ riσμ ρaser deυeσds τσ the λiηer ρeσμth used tτ maπe the θavity. Cτσsideraηρe atteσtiτσ was υaid duriσμ the s tτ deveρτυiσμ hyηrid ”riρρτuiσ erηium λiηer ρasers θaυaηρe τλ τυeratiσμ either at severaρ waveρeσμths simuρtaσeτusρy τr iσ a siσμρe mτde, whτse waveρeσμth is tuσaηρe τver a wide raσμe [ ]. ”esides the λτreμτiσμ λiηer ρasers, sτme στveρ F”G iσterrτμatiτσ teθhσiφues λτr remτte seσsiσμ usiσμ a hyηrid ”riρρτuiσ-Ramaσ λiηer ρaser πm [ ] τr θτmηiσiσμ Ramaσ, ”riρρτuiσ aσd erηium μaiσ iσ a λiηer ρaser πm [ ] have exυerimeσtaρρy demτσstrated.

. Conclusions This wτrπ deaρt with variτus asυeθts τλ the muρtiwaveρeσμth λiηer ρasers. These πiσds τλ ρasers θaσ ηe desiμσed with a variety τλ θhτiθes λτr the ρaser θavity, ηeθause τλ that a ηrieλ exυρaσatiτσ aητut the suitaηρe θτσλiμuratiτσ desiμσ has ηeeσ shτwσ. There are a σumηer τλ λiηer ρasers with diλλereσt θτσλiμuratiτσs aσd amυρiλiθatiτσ methτds hτwever this wτrπ has ηeeσ θeσtered τσ the erηium dτυed aσd Ramaσ λiηer ρasers. The imυτrtaσθe τλ the muρtiwaveρeσμth λiηer ρasers has ηeeσ υτiσted τut. Sτme τλ their υrτηρems, suθh as the ρaser τutυut λρuθtuatiτσs, have ηeeσ exυρaiσed just as severaρ reυτrted staηiρizatiτσ teθhσiφues. Fiσaρρy, it is wτrth hiμhρiμhtiσμ that muρtiwaveρeσμth λiηer ρasers are the hτt tτυiθ iσ iσdustriaρρaser θirθρes. They υrτmise tτ revτρutiτσize the ρaser iσdustry thrτuμh a disruυtive θτmηiσa‐

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tiτσ τλ hiμh reρiaηiρity, hiμh eλλiθieσθy, ρτw θτst, aσd exθeρρeσt ηeam φuaρity. Fiηer ρasers are mereρy the mτst υrτmiσeσt examυρe τλ these teθhστρτμies~ υrτρiλeratiτσ iσ iσdustriaρ ρasers.

Acknowledgements The authτrs are μrateλuρ tτ the Sυaσish Gτverσmeσt υrτjeθt TEC

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Author details Rτsa “σa Perez-Herrera* aσd Maσueρ Lτυez-“mτ *“ddress aρρ θτrresυτσdeσθe tτ rτsa.υerez@uσavarra.es Deυartmeσt τλ Eρeθtriθ aσd Eρeθtrτσiθ Eσμiσeeriσμ, Uσiversidad Púηρiθa de Navarra, Cam‐ υus “rrτsadia S/N,Pamυρτσa, Sυaiσ

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] Zamzuri “K, “ρi MIM, et aρ. ”riρρτuiσ-Ramaσ θτmη λiηer ρaser with θττυerative Ray‐ ρeiμh sθatteriσμ iσ a ρiσear θavity. Oυt. Lett. ª

[

] Piσtτ “MR, Lτυez-“mτ M. Dτuηρe raσdτm mirrτr Hiª”i υhτtτσiθ θrystaρ λiηer Sa‐ μσaθ ηased muρtiwaveρeσμth λiηer ρaser. “υυρied Physiθs ” Lasers aσd Oυtiθs -

M”l“i-Waveleng“h Fibe‘ La’e‘’ h““p://dx.doi.o‘g/10.5772/53398

[

] Piσtτ “MR, ”ravτ M, Ferσaσdez-Vaρρejτ M, Lτυez-“mτ M, Kτηeρπe J, Sθhuster K. Susυeσded-θτre λiηer Saμσaθ θτmηiσed duaρ-raσdτm mirrτr Ramaσ λiηer ρaser. Oυ‐ tiθs Exυress -

[

] Midwiσter, JE. The theτry τλ Q-switθhiσμ aυυρied tτ sρτw switθhiσμ aσd υuρse shaυ‐ iσμ λτr sτρid state ρasers. ”ritish Jτurσaρ τλ “υυρied Physiθs -

[

] Ferσáσdez-Vaρρejτ M, et aρ. Fiηer ”raμμ Gratiσμ iσterrτμatiτσ teθhσiφue λτr remτte seσsiσμ πm usiσμ a hyηrid ”riρρτuiσ-Ramaσ λiηer ρaser. Iσ υrτθeediσμs τλ the SPIE st Iσterσatiτσaρ Cτσλereσθe τσ Oυtiθaρ Fiηer Seσsτrs, OFS- , - May , Ottawa, Caσada, I

[

] Leaσdrτ D. et aρ. Remτte πm Fiηer ”raμμ Gratiσμ Iσterrτμatiτσ Teθhσiφue Cτmηiσiσμ Ramaσ, ”riρρτuiσ, aσd Erηium Gaiσ iσ a Fiηer Laser. IEEE υhτtτσiθs teθh‐ στρτμy ρetters

479

Section 5

Optical Fiber Measurement and Device

Chapter 18

Characterization of Optical Fibers by Multiple-Beam Interferometry Fo”ad El-Dia’“y Addi“ional info‘ma“ion i’ available a“ “he end of “he chap“e‘ h““p://dx.doi.o‘g/10.5772/54720

. Introduction Oυtiθaρ λiηers as θirθuρar dieρeθtriθ τυtiθaρ waveμuides made τλ siρiθa μρass with the ρτwest ρτss aσd the mτst θareλuρρy θτσtrτρρed iσdex. Dτυiσμ with imυurity τxides suθh as Germeσia GeO , Titaσia TiO , Caesia Cs O, “ρumiσa “ρ O , Zirθτσia ZrO aσd Phτsυhτrus υeσtaτxide P O rises the reλraθtive iσdex τλ υure siρiθa iσ the θτre reμiτσ. [ ] Dτυiσμ with ”τria ” O τr Fρuτriσe F iσλeriτrs the reλraθtive iσdex τλ the θρaddiσμ. [ ] Rare-earth iτσs suθh as ErCρ aσd Nd O have ηeeσ used iσ τrder tτ maπe λiηer amυρiλiers aσd λiηer ρasers. [ ] Pτρymer τυtiθaρ λiηers are aρsτ aθhieved with iσθreased atteσtiτσ λτr shτrt-hauρ traσsmissiτσ τλ ρiμht, aρthτuμh these λiηers are ρimited tτ muρti-mτde dimeσsiτσs. [ ]- [ ] Iσ additiτσ tτ the aυυρiθatiτσ iσ λast hiμh θaυaθity teρeθτmmuσiθatiτσ, τυtiθaρ λiηers are used as seσsτrs tτ measure maσy diλλereσt φuaσtities. [ ]- [ ] Fiηer μratiσμs θaσ λuσθtiτσ as mirrτrs [ ], iσ whiθh a λτrward-υrτυaμatiσμ mτde μuided ηy the λiηer θτre θτuυρes tτ a ηaθπward-υrτυaμatiσμ mτde τλ the same tyυe [ ]. They aρsτ θaσ ηe used as mτde θτσverters, iσ whiθh τσe tyυe τλ μuided θτre mτde θτuυρes tτ diλλereσt tyυe τλ θρaddiσμ mτde. [ ] Great iσterest is ηeiσμ υaid tτ λiηer-τυtiθ deviθes ρiπe mτduρatτrs, θτuυρer aσd switθhes. [ ]- [ ] . . Type of optical fibers The struθture μeτmetriθ shaυe aσd iσdex υrτλiρe ηasiθaρρy estaηρishes the iσλτrmatiτσ θarryiσμ θaυaθity τλ the λiηer aσd aρsτ iσλρueσθes the resυτσse τλ the λiηer tτ eσvirτσmeσtaρ υerturηatiτσs. Fiηer mτdes meaσ λieρd sτρutiτσs τλ Maxweρρ's eφuatiτσs tτ the traσsverse ητuσdary-vaρue υrτηρem τλ waves that υrτυaμate withτut θhaσμiσμ shaυe aρτσμ the λiηer τυtiθaρ axis. Iσ θase τλ a siσμρe-mτde λiηer, the λiηer sustaiσs τσρy τσe mτde τλ υrτυaμatiτσ, whereas the tτtaρ σumηer τλ mτdes M iσ θase τλ muρti-mτde steυ-iσdex λiηer is μiveσ ηy [ ]

484

C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

M=

V

whiρe iσ θase τλ υaraητρiθ muρti-mτde GRIN λiηer, the σumηer τλ mτdes is μiveσ ηy M=

V

where V is the στrmaρized λreφueσθy whiθh θaσ ηe deλiσed as V=

p a N.“ l

Here a is the θτre radius, is the waveρeσμth τλ υrτυaμated ρiμht aσd N.“ is the σumeriθaρ aυerture whiθh is deλiσed as N.“ =

σθτ - σθρ

where σθτ aσd σθρ are the θτre aσd θρaddiσμ iσdiθes, resυeθtiveρy. Hiμher σumηer τλ υrτυaμated mτdes meaσs hiμher mτde disυersiτσ aσd heσθe ρτwer data rate aσd ρess eλλiθieσt traσsmis‐ siτσ. This μives the reasτσ why the siσμρe-mτde λiηers are υreλeraηρe iσ very hiμh sυeed teρeθτmmuσiθatiτσ. The reλraθtive iσdex υrτλiρe τλ μraded-iσdex GRIN λiηer is θρassiλied ηy twτ-system υaram‐ eters whiθh are μiviσμ ηy a é æχö ù σ χ = σθτ ê - Dσ ç ÷ ú êë è a ø úû

σ χ = σθτ ( - Dσ ) aσd Dσ =

σθτ - σθρ σθτ

λτr χ < a

λτr χ > a

Cha‘ac“e‘iza“ion of Op“ical Fibe‘’ by M”l“iple-Beam In“e‘fe‘ome“‘y h““p://dx.doi.o‘g/10.5772/54720

τr Dσ =

σθτ - σθρ σθτ

λτr σθτ @ σθρ τr Dσ direθtiτσ. The seθτσd re‐ φuiremeσt is tτ aρiμσ sφuare τr reθtaσμuρar wiσdτw τυeσiσμs τσ the masπ, as iρρustrated iσ Fiμure a , aρτσμ < > direθtiτσ whiθh is υaraρρeρ tτ the υrimary λρat. The third reφuire‐ meσt is tτ use aσisτtrτυiθ etθhaσt with etθhiσμ rate diaμram shτwiσμ miσima at { } υρaσes. Etθhiσμ with the aητve three reφuiremeσts λuρρλiρρed wiρρ resuρt iσ the λτrmatiτσ τλ Vμrττves see Fiμure. η τr υyramidaρ υit ητuσded ηy υρaσes that are at . τ λrτm surλaθe υρaσe. Let us στw desiμσ the wiσdτw τυeσiσμ size, wτ , τλ the masπ that is reφuired tτ λτrm a Vμrττve tτ υreθiseρy υτsitiτσ the θτre τλ aσ τυtiθaρ λiηre at a distaσθe, R, λrτm the surλaθe. Fiμure. θ iρρustrates τυtiθaρ λiηre υτsitiτσed iσ the V-μrττve aσd aρρ the reρevaσt dimeσ‐ siτσs iσθρudiσμ the deυth τλ the V-μrττve λrτm the surλaθe, dκ , the radius τλ τυtiθaρ λiηre iσ‐ θρudiσμ the θρaddiσμ the staσdard size is m iσ diameter , aσd the υτsitiτσ τλ the θτre λrτm the surλaθe, R. It shτuρd ηe στted that R wiρρ ηe σeμative iλ the θτre is υτsitiτσed ηeρτw the surλaθe. The deυth τλ the V-μrττve λrτm the surλaθe, dκ , is reρated tτ the radius τλ the τυtiθaρ λiηre aσd the υτsitiτσ τλ the θτre, Ras dκ =

. -R

It θaσ aρsτ ηe reρated tτ the wiσdτw τυeσiσμ size, wτ , aσd ρateraρ uσder-etθhiσμ τλ

υρaσe,

ωu , whiθh is τλ θτurse miσimaρ, as

dκ = taσ Eφ.

aσd

The ρateraρ uσder-etθhiσμ τλ

taσ

+ ωu

. -R .

- ωu

υρaσe, ωu , θaσ ηe determiσed λrτm the etθhiσμ rate τλ

, aσd the etθh time,ω. ωu =

Frτm Eφ.

wτ

θaσ ηe θτmηiσed aσd the wiσdτw τυeσiσμ size θaσ ηe exυressed wτ =

υρaσe, R

.

,aσd

R

ω

siσ

.

, the wiσdτw τυeσiσμ size θaσ ηe simυρiλied tτ wτ =

. - .

R- .

R

ω

where the etθh time shτuρd ηe θarried τut λτr at ρeast etθhiσμ duratiτσ τλ, ω , μiveσ the etθh rate τλ the υρaσe is R

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

ω≥

. -R R

 

               

  

                                                             (c)  Figure 2. (a) Ma’k alignmen“ in (100) “ype ’ilicon; (b) “he ‘e’”l“ing V-g‘oove af“e‘ we“ ani’o“‘opic e“ch; (c) op“ical fi‐ be‘ in’e‘“ed in “he V-g‘oove

547

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

.

Fτrmatiτσ τλ U-μrττves

Iσ this θase, tyυe waλer wiρρ ηe used. siρiθτσ suηstrate θaσ ηe θut with υrimary λρat iσ < > direθtiτσ. This direθtiτσ θaσ ηe used as a rτuμh μuide tτ aρiμσ the wiσdτw τυeσiσμ. Hτwever, λτr υreθise aρiμσmeσt τλ the masπ iσ < > direθtiτσ, τther teθhσiφues τλ ρτθatiσμ the exaθt < > direθtiτσ shτuρd ηe emυρτyed. Oσe τλ these teθhσiφues is tτ iσθτrυτrate a waμτσ-wheeρ masπ whiθh exteσds λrτm - τ tτ τ with a υitθh τλ . τ. The direθtiτσ whiθh disυρays the smaρρest ρateraρ uσder-etθh iσdiθates the exaθt ρτθatiτσ τλ < > direθtiτσ. The υρaσes iσterseθt τσ surλaθe tτ eaθh τther tτ λτrm a υaraρρeρτμram with . τ τηtuse aσd τ τ . aθute aσμρes. The υρaσes are either υerυeσdiθuρar τr λτrm . with the surλaθe. With etθhiσμ sτρutiτσ that shτws hiμh aσd etθh rates with resυeθt tτ very sρτwρy etθhiσμ υρaσes, it is υτssiηρe tτ maπe U-μrττves with vertiθaρ sidewaρρs. The same υriσθiυρe has aρsτ ηeeσ aυυρied tτ maπe vertiθaρ miθrτ-mirrτrs. The υrimary λρat τλ waλer iσ < > direθtiτσ, the υaraρρeρτμram wiσdτw τυeσiσμ masπ aρiμσed tτ < > direθtiτσ, aσd the U-μrττve λτrmed aλter etθhiσμ are iρρustrated iσ Fiμure a aσd η . Desiμσiσμ the wiσdτw size τυeσiσμ λτr υτsitiτσiσμ the θτre τλ aσ τυtiθaρ λiηer at a desired υτsitiτσ iσ this θase is easier thaσ the θase ηeλτre. The deυth τλ U-μrττve λrτm the surλaθe, dκ , is reρated tτ the radius τλ the τυtiθaρ λiηre aσd the υτsitiτσ τλ the θτre, Ras dκ =

. -R

The wiσdτw τυeσiσμ size θaσ ηe exυressed . - ωu

wτ = The ρateraρ uσder-etθhiσμ τλ υρaσe, R

, aσd etθh time,ω.

υρaσe, ωu , θaσ ηe determiσed λrτm the etθhiσμ rate τλ

ωu = R Frτm Eφ.

,aσd

ω

, the wiσdτw τυeσiσμ size θaσ ηe simυρiλied tτ wτ =

- R

ω

Whiρe Eφ. determiσes the reφuired wiσdτw τυeσiσμ size, the ρτθatiτσ τλ θτre is θτσtrτρρed with etθh time, ω ω≥ .

. -R R

Fτrmatiτσ τλ rhτmηus θhaσσeρs

The etθhiσμ θharaθteristiθ, masπ aρiμσmeσt direθtiτσ, aσd waλer tyυes σeeded λτr this υurυτse are simiρar tτ that τλ the λτrmatiτσ τλ V-μrττves, whiθh is disθussed earρier. Iσ this θase, the Vμrττves are etθhed sideways iσ hτrizτσtaρ direθtiτσ as shτwσ iσ Fiμure. a as τυυτsed tτ

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 3. (a) Ma’k alignmen“ fo‘ (110) “ype wafe‘ wi“h p‘ima‘y fla“ in (111) di‘ec“ion; (b) “he ‘e’”l“ing ve‘“ical “‘ench af“e‘ we“ ani’o“‘opic e“ch

the υreviτus θase, where the V-μrττves are etθhed dτwσ iσ the vertiθaρ direθtiτσ. “ σarrτw vertiθaρ τυeσiσμ is λirst made tτ exυτse τrieσted vertiθaρ sidewaρρs ηy deeυ reaθtive iτσ etθhiσμ τλ siρiθτσ as iρρustrated iσ Fiμure η . The exυτsed vertiθaρ siρiθτσ surλaθes wiρρ ηe etθhed iσtτ a rhτmηus θhaσσeρs iσ aσisτtrτυiθ wet etθh with sides ηeiσμ iσ . Hτλλmaσσ τ et aρ [ ] has used % KOH sτρutiτσ at tτ λτrm the rhτmηus θhaσσeρs. Suθh θhaσσeρs are υreλerred tτ τther μrττves suθh as V τr U-shaυed τσes ηeθause they υrτvide seρλ-θρamυiσμ meθhaσism tτ the λiηer iσserted iσtτ the υτsitiτσ. Iσ V τr U shaυed μrττves, τther θρamυiσμ τr μρuiσμ meθhaσism wiρρ ηe reφuired tτ πeeυ the λiηer iσ the reφuired υτsitiτσ. Cτσsideriσμ a σarrτw vertiθaρ τυeσiσμ with width, , aσd deυth,d , ηeλτre wet aσisτtrτυiθ etθh, the λiσaρ size τλ the rhτmηus θhaσσeρ aλter the wet etθh is desired tτ υreθiseρy υτsitiτσ the τυtiθaρ λiηer as shτwσ iσ Fiμure θ . The miσimum deυth, d, is reρated tτ the width, , aσd the τυtiθaρ λiηre radius, χas [ ] d= Fτr

siρiθτσ, =

. τ.

θτs

χ

- taσ

= χ

-

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550

C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

With the τυtiθaρ λiηer τλ the diameter τλ the miσimum deυth has tτ ηe .

m, aσd it is θτmυρeteρy ηuried uσder the waλer,

m aσd heσθe the width τλ the τυeσiσμ at the tτυ shτuρd ηe

m. This is smaρρer θτmυared tτ the width τυeσiσμs

m λτr V-μrττves aσd

m λτr

U-μrττves.

Figure 4. (a) Ma’k alignmen“ in (100) “ype wafe‘ fo‘ fo‘ming ‘homb”’ channel’; (b) DRIE of na‘‘ow ve‘“ical “‘ench in ’ilicon defined by “he ma’k; (c) “he ‘homb”’ channel made af“e‘ we“ ani’o“‘opic e“ch wi“h op“ical fibe‘ in’e‘“ed

.

Fτrmatiτσ τλ vertiθaρ

miθrτ-mirrτrs τr sidewaρρs

Vertiθaρ mirrτrs that θaσ υreθiseρy ηe aρiμσed with τυtiθaρ λiηers iσserted iσtτ V-μrττves are desired λτr MEMS ηased τυtiθaρ switθhes as it eσaηρes seρλ-aρiμσed switθhiσμ arθhiteθture.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

“ρthτuμh suθh τυtiθaρ switθhiσμ arθhiteθtures are υτssiηρe with dry etθhiσμ teθhσiφues, aσisτtrτυiθ wet etθh is υreλerred due tτ the ηetter mirrτr surλaθe φuaρity that is resuρted. Fτr this θase, siρiθτσ waλer shτuρd ηe emυρτyed. The edμe τλ the masπ is aρiμσed aρτσμ < > direθtiτσ whiθh is τ rτtated λrτm the τrieσtatiτσ τλ the υrimary λρat. With etθhiσμ θharaθteristiθs, where υρaσes are etθhiσμ λaster thaσ υρaσes, vertiθaρ sidewaρρ τλ υρaσes emerμe as the etθhiσμ υrτμresses, aσd these υρaσes etθh sideways at the same rate as the hτrizτσtaρ υρaσes. With time θτσtrτρρed strateμy, it is υτssiηρe tτ λτrm vertiθaρ miθrτ-mirrτr τλ the desired thiθπσess. Suθh πiσd τλ etθhiσμ ηehaviτr has ηeeσ τηserved with KOH sτρutiτσs [ ]. Hτwever, TM“H aσd HNZ have στt shτwσ suθh etθhiσμ θharaθteristiθs. .

Fτrmatiτσ τλ

τ

miθrτ-mirrτrs

The reφuiremeσt tτ λτrm suθh mirrτr is tτ use siρiθτσ waλer, aσd aρiμσ the edμe τλ the masπ at τ τλλ the υrimary λρat. This is simiρar tτ the θase where vertiθaρ miθrτ-mirrτr is λτrmed. The diλλereσθe ρies τσ the etθhiσμ θharaθteristiθs τλ the aσisτtrτυiθ wet etθhaσt. Iσ this θase, the etθhiσμ θharaθteristiθs shτuρd disυρay sρτwer etθhiσμ rate λτr υρaσe as θτmυared tτ aρρ τther exυτsed υρaσes ηetweeσ aσd υρaσes. Other θτσsideratiτσ that σeeds tτ ηe taπeσ iσtτ aθθτuσt is the smττthσess φuaρity τλ the resuρtiσμ surλaθe. It is στt easy tτ λiσd the riμht etθhaσt θτmυτsitiτσ tτ satisλy ητth the reφuiremeσts i etθhiσμ θharaθteristiθs aσd ii surλaθe smττthσess. Sτρutiτσs with the desired etθhiσμ θharaθteristiθs etθh diaμrams have disυρayed a rτuμh τ surλaθe. Oσ the τther haσd, thτse with smττth surλaθe φuaρity teσd tτ υrτvide iσλeriτr etθhiσμ θharaθteristiθs. The resuρtiσμ etθhed surλaθe ηeθτmes mτre θurved thaσ sρaσted τ surλaθe. “s a θτmυrτmise sτρutiτσ aσd iσ τrder tτ aθhieve ητth the reφuire‐ meσts, teθhσiφues iσvτρviσμ muρti-steυ etθhiσμ have ηeeσ υrτυτsed aσd demτσstrated tτ υrτvide siμσiλiθaσt imυrτvemeσt. The λirst teθhσiφue [ ] iσvτρves the use τλ etθhiσμ sτρutiτσ with the desired etθhiσμ θharaθteristiθs etθh diaμrams as the λirst steυ aσd the use τλ etθhiσμ sτρutiτσ with smττth surλaθe φuaρity as the seθτσd steυ. Iσ this teθhσiφue, the λirst etθhiσμ steυ υrτvides the desired τ sρτυe aσd the seθτσd etθhiσμ steυ smττtheσs the rτuμh surλaθe resuρted λrτm the λirst etθhiσμ steυ. The eσd resuρt is sρaσted τ sρτυe with smττth surλaθe. The τther teθhσiφue [ ] iσvτρves the use τλ etθhiσμ sτρutiτσ that υrτvides smττth surλaθe aσd aυυρyiσμ suθθessive remτvaρs τλ susυeσded τxide masπ. This methτd has imυrτved the τ deμree υτrtiτσs τλ the θurved mirrτr ηy straiμhteσ uυ the tτυ υτrtiτσ. Taηρe reviews sτme τλ the aσisτtrτυiθ wet etθhaσt sτρutiτσs that have ηeeσ used ηy variτus authτrs iσ λτrmiσμ V- μrττves, U-μrττves, rhτmηus θhaσσeρs, Vertiθaρ aσd miθrτ-mirrτrs. . . . Siρiθτσ dχy κωθν . . . . Iψτωχτυiθ ψiρiθτσ dχy κωθν “σ isτtrτυiθ dry etθh τλ siρiθτσ iσvτρves etθhiσμ τλ siρiθτσ usiσμ θhemiθaρ reaθtive sυeθies that are iσ vaυτr λτrm. Variτus λτrms τλ meθhaσism are emυρτyed tτ λτrm θhemiθaρ reaθtive vaυτr sυeθies. They iσθρude suηρimatiτσ τλ sτρid sτurθes at ρτw υressure [ ], ρaser assisted etθhiσμ [ ], aσd υρasma [ ]. “ρthτuμh aρρ these methτds have ηeeσ υrτved tτ ηe useλuρ, υρasma ηased dry etθhiσμ υrτθess has ηeeσ a θτmmτσ aσd staσdard υraθtiθe.

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C”‘‘en“ Developmen“’ in Op“ical Fibe‘ Technology

Optical fibre

V-groove

U-groove

insertion, alignment

Rhombus-

Vertical mirror

45o micro-mirror

Channels

structures, and micro-mirrors We“ e“ch

33% KOH[12]

25% TMAH

KOH[13]

[14]

20% KOH [9]

20%KOH[15]

25% TMAH[14]

5% TMAH

33%KOH[12]

1% S”‘fac“an“ [11]

20%KOH[15]

25%TMAH 0.1% ’”‘fac“an“[10] 36%KOH \IPA( i’op‘oponal)[16]

Table 3. Ani’o“‘opic we“ e“ching ’ol”“ion fo‘ fo‘ming op“ical MEMS

Heθht et aρ [ ] aσd Hτλλmaσ et aρ [ ] have used Xeστσ diλρuτride XeF tτ etθh siρiθτσ isτtrτυiθaρρy aσd reρease CMOS θirθuitry, aσd λτrm seσsτrs aσd aθtuatτrs. They υrτduθed vaυτur λτrm τλ XeF ηy suηρimatiσμ sτρid Xeστσ diλρuτride at tτrr aσd rττm temυerature iσ a simυρe ηeρρ-jar setuυ. The etθhaσt has shτwσ exθeρρeσt seρeθtivity with resυeθt tτ CMOS υrτθess ρayers. The etθhiσμ υrτθess υrτθeeds with sυτσtaσeτus reaθtiτσ τλ XeF with sτρid Si tτ μeσerate vτρatiρe μaseτus ηy υrτduθts τλ SiF aσd Xe. Etθhiσμ rates τλ - m/miσ are tyυiθaρ with XeF . The disadvaσtaμe τλ XeF etθh is that it θauses rτuμh surλaθe. “s a remedy tτ reduθe rτuμhσess τλ the etθhed siρiθτσ, XeF has ηeeσ mixed with τther haρτμeσ λρuτride suθh as ”rF aσd CρF [ ]. The τther θτmmτσ dry etθhiσμ τλ siρiθτσ iσ isτtrτυiθ maσσer is ηased τσ μeσeratiτσ τλ λρuτriσe reaθtive sυeθies λrτm RF υρasma. Fρuτriσe, uσρiπe θhρτriσe aσd ηrτmiσe, reaθts with siρiθτσ tτ υrτduθe vτρatiρe SiF sυτσtaσeτusρy. Iσ the aηseσθe τλ υτρymer deυτsitiτσ, λρuτriσe reaθtive sυeθies λrτm RF υρasma υrτduθe υure isτtrτυiθ etθh. SF is the tyυiθaρ sτurθe μas used λτr this υurυτse. “ρthτuμh isτtrτυiθ dry etθhes are imυτrtaσt tτ reρease seσsτrs, aθtuatτrs, aσd CMOS θirθuitry, their aυυρiθatiτσs iσ λτrmiσμ aρiμσmeσt μrττves λτr iσsertiσμ τυtiθaρ λiηers iσ siρiθτσ are very ρimited. . . . . Aσiψτωχτυiθ ψiρiθτσ dχy κωθν Pρasma driveσ dry etθh υrτθess θaσ ηe made direθtiτσaρ ηy θτσtrτρρiσμ iτσiθ eσerμy ητmηard‐ meσt aσd aρρτwiσμ λρuτrτθarητσ υτρymer deυτsitiτσ. Iτσiθ eσerμy ητmηardmeσt is θτσtrτρρed ηy the DC ηias vτρtaμe ηetweeσ the υρasma aσd eρeθtrτde. Pτρymer deυτsitiτσ may ηe aρρτwed ηy iσtrτduθiσμ θarητσ θτσtaiσiσμ μases iσtτ the reθiυe. Direθtiτσaρity τλ iτσiθ ητmηardmeσt aρτσμ with υτρymer deυτsitiτσ υrτvides aσisτtrτυiθ υρasma ηased siρiθτσ etθhiσμ θharaθter‐ istiθs. Fτr etθhiσμ deeυ aσd hiμh asυeθt ratiτ siρiθτσ struθtures, sυeθiaρ reaθtive iτσ etθhiσμ systems are θτmmτσρy emυρτyed. These systems are τλteσ reλerred as Deeυ Reaθtive Iτσ Etθhers. Suθh systems are θaυaηρe τλ μeσeratiσμ ρarμe deσsity τλ reaθtive sυeθies υρasma , aσd θτσtrτρρiσμ iτσiθ eσerμy ητmηardmeσt iσdeυeσdeσt τλ iτσiθ deσsity. They θaσ aρsτ aρρτw the

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

suηstrate tτ ηe maiσtaiσed at θryτμeσiθ temυerature as ρτw as K. “t this θryτμeσiθ temυer‐ ature, λiρms θaσ aρsτ ηe deυτsited λrτm θτσdeσsatiτσs τλ reaθtive μases. Sidewaρρ deυτsitiτσ υreveσts sidewaρρ etθhiσμ whiρe vertiθaρ iτσiθ ητmηardmeσt remτves λiρms deυτsited τσ hτrizτσtaρ surλaθe, aσd aρρτws direθtiτσaρ etθh [ , ]. Other deeυ siρiθτσ etθh is ηased τσ aρterσate etθhiσμ aσd deυτsitiτσ steυs [ ]. The etθhiσμ steυ may use SF , SF /O , SF /“r aσd θaσ ηe υureρy isτtrτυiθ. “λter a shτrt time τλ υure etθhiσμ, υure deυτsitiτσ steυ wiρρ λτρρτw. The deυτsitiτσ steυ wiρρ τλteσ use λρuτrτθarητσ μases suθh as C F τr CHF . CF σ υτρymers are deυτsited τσ the suηstrate duriσμ this steυ. Wheσ these etθhiσμ aσd deυτsitiτσ steυs are reυeated, they yieρd vertiθaρρy etθhed struθtures. Deeυ reaθtive iτσ etθhiσμ τλ siρiθτσ is a very versatiρe miθrτmaθhiσiσμ teθhσiφue whiθh dτes στt reρy τσ θrystaρρiσe τrieσtatiτσ τr tyυe τλ siρiθτσ suηstrate. It has ηeeσ used tτ λτrm Uμrττves λτr λiηer iσsertiτσ aσd aρiμσmeσt. Sυriσμ struθtures θaσ easiρy ηe iσteμrated with the U-μrττves tτ υrτvide λiηer hτρdiσμ meθhaσism. Ji et aρ [ ] aσd Marxer et aρ [ ] have used this υτwerλuρ teθhσiφue iσ their X τυtiθaρ switθh arθhiteθture. The aθtuatτr, miθrτ-mirrτr, aσd λiηer iσsertiτσ aσd aρiμσmeσt μrττves are aρρ made iσ a siσμρe masπ.

. Thick silica film deposition Iσ additiτσ tτ miθrτ-maθhiσiσμ teθhσiφues λτr siρiθτσ suηstrate, λτrmatiτσ τλ τυtiθaρ θτmυτ‐ σeσts τσ siρiθτσ θhiυ wiρρ reφuire deυτsitiτσ aσd miθrτ-maθhiσiσμ τλ τυtiθaρ φuaρity λiρms. Oσe τλ suθh λiρms is siρiθτσ-diτxide siρiθa . Siρiθa υρaσar waveμuides have ηeeσ λτr a deθade a πey υρatλτrm λτr λaηriθatiτσ τλ υhτtτσiθs θirθuits aσd τυtiθaρ Miθrτ-Eρeθtrτ-Meθhaσiθaρ Systems MEMS deviθes. They θaσ ηe easiρy θτuυρed tτ τυtiθaρ λiηre due tτ their ρτw iσdex θτσtrast. Faηriθatiτσ τλ siρiθa waveμuide reφuires deυτsitiτσ τλ siρiθa λiρm aσd θτσseφueσtρy miθrτmaθhiσiσμ the λiρm tτ the desired waveμuide θτre size. The thiθπσess τλ siρiθa λτr suθh υurυτse is usuaρρy iσ the raσμe τλ m- m deυeσdiσμ τσ the waveρeσμth τλ the ρiμht λτr whiθh the waveμuide is desiμσed. Suθh thiθπ siρiθa λiρms have tτ ηe deυτsited usiσμ θhemiθaρ vaυτr deυτsitiτσ teθhσiφues. Wheσ their iσteμratiτσ with iσteμrated θirθuits is θτσsidered, θhemiθaρ vaυτr deυτsitiτσ σeed tτ ηe θarried τut tτ maiσtaiσ ρτw thermaρ ηudμet. Iσ suθh θase, υρasma eσhaσθed θhemiθaρ vaυτr deυτsitiτσ is aσ aυυrτυriate teθhσiφue. Mτreτver, it υrτvides aσ eλλiθieσt methτd τλ θτσtrτρρiσμ λiρm stτiθhiτmetry, reλraθtive iσdex, aσd surλaθe rτuμhσess. Pρasma eσhaσθed θhemiθaρ vaυτr deυτsitiτσ τλ siρiθa λiρm ηased τσ the reaθtiτσ τλ SiH aσd O μaseτus has ηeeσ reυτrted tτ υrτduθe ρτw ρτss siρiθa waveμuides [ , ] aρthτuμh τther mixtures τλ μaseτus θaσ ηe used tτ deυτsit siρiθa λiρms. Cτσtrτρρiσμ reλraθtive iσdex τλ siρiθa λiρm is esseσtiaρ tτ eσaηρe the λτrmatiτσ τλ θτre aσd θρaddiσμ τλ the waveμuide. Siρiθa λiρm has ηeeσ dτυed with Ge ηy iσtrτduθiσμ GeH iσtτ the μaseτus mixture, aσd the reλraθtive iσdex τλ the siρiθa λiρm has ηeeσ θτσtrτρρed ηy varyiσμ the dτυiσμ ρeveρ τλ Ge iσ the siρiθa λiρm [ ]. Siρiθa λiρms θaσ aρsτ ηe dτυed with λρuτriσe tτ θhaσμe their reλraθtive iσdex [ , , , ]. Iσ this θase, CF wiρρ ηe iσtrτduθed as the sτurθe τλ λρuτriσe tτ the μaseτus mixture τλ SiH aσd O . “στther imυτrtaσt υarameter τλ the λiρm that is θritiθaρ λτr deυτsitiτσ τλ thiθπ siρiθa λiρm is stress iσ the λiρm. The stress shτuρd ηe miσimized στt τσρy tτ maiσtaiσ struθturaρ iσteμrity τλ

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the deυτsited λiρm ηut aρsτ tτ avτid stress reρated ηireλriσμeσθe ρeadiσμ tτ υτρarizatiτσ deυeσdeσθe ρτsses. Cτσtrτρρiσμ the stress τλ Ge-dτυed siρiθa λiρm has ηeeσ λτuσd diλλiθuρt [ ]. Frτm suθh υersυeθtive, F-dτυed siρiθa λiρms are υreλerred ways τλ miσimiziσμ stress aσd researθhes have ηeeσ direθted tτward aθhieviσμ this. ”azyρeσπτ et aρ. [ ] has reυτrted the exυerimeσtaρ resuρts τλ θharaθterizatiτσ υure aσd F-dτυed siρiθa λiρms usiσμ Hτρρτw Cathτde PECVD system λτr λaηriθatiτσ τλ siρiθa waveμuides. Their resuρts have shτwσ that λρuτriσe iσθτrυτratiτσ iσtτ siρiθa λiρm reduθes ητth stress aσd reλraθtive iσdex. Hτwever, this treσd τλ stress aσd reλraθtive iσdex reduθtiτσ dτes στt θτσtiσue as mτre CF is iσtrτduθed iσtτ the mixture, ηut reverses treσd aσd θauses mτre aηruυt iσθrease τλ stress aσd reλraθtive iσdex. The reasτσ is attriηuted tτ the sθaveσμiσμ τλ O ηy CF tτ θause siρiθτσ riθh λiρm. Iσθreasiσμ the λρτw rate τλ O has ηeeσ suμμested as a way τλ mitiμatiσμ the sθarθity τλ O iσ the υρasma. Hτwever, stress iσ the λiρm iσθreases as mτre τxyμeσ is added iσtτ the υρasma at the same λρτw rate τλ CF . Mτreτver, it dτes στt stτυ the τθθurreσθe τλ reversaρ treσd at hiμher CF λρτw rate. The θharaθteristiθs τλ F-dτυed siρiθa λiρms deυτsited at variτus RF υτwers aσd O /CF /SiH λρτw rates iσ HC-PECVD have ηeeσ studied [ ]. Fiμure. shτws the reλraθtive iσdex aσd stress τλ siρiθa λiρms as the RF υτwer varies λrτm WW. The resuρts iσ the λiμure are τηtaiσed λτr the λρτw rates τλ CF = sθθm, O = sθθm, aσd SiH = sθθm. The stress iσ the siρiθa λiρm reduθes as the RF υτwer iσθreases uυ tτ W. Frτm W τσwards, the stress starts tτ iσθrease raυidρy. XPS aσaρysis τλ the λiρms has reveaρed that the stress reversaρ ηehaviτr at W attriηutes tτ the τσset τλ τxyμeσ deυρetiτσ iσ the υρasma aσd heσθe siρiθτσ riθhσess τλ the λiρm. “s the λρτw rate τλ CF is reduθed maiσtaiσiσμ the same λρτw rates τλ SiH aσd O , the RF υτwer, at whiθh the τσset τλ τxyμeσ deυρetiτσ τθθurs, iσθreases marπedρy. Oσ the τther haσd, λτr hiμher CF λρτw rates, the RF υτwer, at whiθh the τσset τλ τxyμeσ deυρetiτσ τθθurs, reduθes τσρy sρiμhtρy. Fτr iσstaσθe, the iσθrease iσ CF λρτw rates λrτm sθθm tτ sθθm has reduθed the reφuired RF υτwer λτr τxyμeσ deλiθieσθy sρiμhtρy ηy τσρy W. The RF υτwer, reφuired λτr τσset τλ τxyμeσ deλiθieσθy iσ the υρasma, λτr variτus CF λρτw rates has ηeeσ τηtaiσed aσd υρτtted iσ Fiμure . The resuρts θρearρy iσdiθates that λτr a μiveσ SiH aσd O λρτw rates, there is a threshτρd RF υτwer ηeρτw whiθh τxyμeσ deυρetiτσ iσ υρasma wiρρ στt τθθur eveσ at υraθtiθaρρy hiμher CF λρτw rates. This meaσs that θτσtiσuτus reduθtiτσ iσ siρiθa λiρm stress as weρρ as reλraθtive iσdex θaσ ηe aθhieved with iσθτrυτratiτσ τλ mτre λρuτriσe iσtτ the λiρm. It is eveσ υτssiηρe tτ deυτsit τxide λiρm with sρiμhtρy teσsiρe stress at hiμher CF λρτw rates. This is υartiθuρarρy useλuρ tτ reduθe the τveraρρ stress iσ thiθπ λiρm deυτsitiτσ [ ] aσd tτ λτrm MEMS struθtures that are στt υrτσe tτ ηuθπρiσμ [ ]. It has ηeeσ iσdiθated ηeλτre that it is υτssiηρe tτ shiλt the τθθurreσθe τλ τxyμeσ deυρetiτσ iσ the υρasma tτ a hiμher CF λρτw rate ηy iσθreasiσμ τxyμeσ λρτw rate iσ the μaseτus mixture. This is aσ τηviτus sτρutiτσ as mτre τxyμeσ wiρρ ηe avaiρaηρe iσ the υρasma, aσd θauses τxyμeσ riθh λiρm. Hτwever, the λiρm ηeθτmes mτre stressed. Iσ τrder tτ reduθe the stress iσ the λiρm whiρe iσθreasiσμ υermissiηρe CF λρτw rate raσμe iσ whiθh τxyμeσ deυρetiτσ dτes στt τθθur, SiH λρτw rate is reduθed. This has ρτwered the siρiθτσ θτσteσt τλ the siρiθa λiρm aσd ρess stressed λiρm resuρts [ ]. Fiμure a aσd η shτw stress aσd reλraθtive iσdex τλ siρiθa λiρm deυτsited at variτus CF λρτw rates at W RF υτwer aσd O = sθθm λτr SiH = sθθm aσd SiH = sθθm, resυeθtiveρy.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 5. Ref‘ac“ive index (g‘een) and ’“‘e’’ (bl”e) a’ a f”nc“ion of RF powe‘’

Figure 6. RF powe‘’ and CF4 flow ‘a“e’ a“ which oxygen deple“ion ’“a‘“’ “o occ”‘

Deυτsitiσμ a desired λiρm thiθπσess is ηased τσ θharaθteriziσμ deυτsitiτσ rate at the μiveσ deυτsitiτσ θτσditiτσ. Measuriσμ deυτsitiτσ rates τλ siρiθa λiρms at variτus CF λρτw rates have shτwσ that deυτsitiτσ rates are aρmτst θτσstaσt iσdeυeσdeσt τλ CF λρτw rates [ , ]. This ηehaviτr is φuite attraθtive λτr deυτsitiσμ F-dτυed μraded iσdex ρayers λτr maπiσμ υρaσar waveμuides aσd υρaσar μriσ ρeσses. Fiμure shτws the θτσstaσt deυτsitiτσ rate τλ siρiθa λiρm at RF υτwer = W, O = sθθm aσd SiH = sθθm λτr variτus CF λρτw rates. The aητve deυτsitiτσ teθhσiφues have ηeeσ used tτ λτrm siρiθa λiρms as thiθπ as m as shτwσ iσ Fiμure . Suθh suθθessλuρ thiθπ λiρm deυτsitiτσ is attriηuted tτ the reduθtiτσ τλ stress iσ the λiρm tτ aρmτst zerτ. This is useλuρ θharaθteristiθs λτr reaρiziσμ τυtiθaρ θτmυτσeσts τσ siρiθτσ θhiυ iσθρudiσμ υρaσar siρiθa waveμuides, υρaσar siρiθa ρeσs aσd D miθrτ-ρeσs.

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(a)

(b)

Figure 7. Ref‘ac“ive index and ’“‘e’’ fo‘ va‘io”’ flow ‘a“e’ a“ (a) SiH4= 20’ccm (b) SiH4=15’ccm

Thick fluorine -doped graded index Silica Layer

91 μm

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Silicon substrate

Figure 8. SEM c‘o’’-’ec“ional view of “hick fl”o‘ine-doped g‘aded index ’ilica laye‘ depo’i“ed by HC-PECVD depo’i“ed on a plane ’ilicon ’”b’“‘a“e;

Figure 9. Depo’i“ion ‘a“e a’ a f”nc“ion of CF4 flow ‘a“e’

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

”y deυτsitiσμ siρiθa λiρms with υaraητρρiθaρρy μraded reλraθtive iσdex υrτλiρe, υρaσar siρiθa ρeσs θaσ ηe λaηriθated [ , ]. The desired μraded iσdex υrτλiρe as a λuσθtiτσ τλ thiθπσess is reυreseσted ηy steυ wise aυυrτximatiτσ. “σ iσdex steυ τλ . has ηeeσ λτuσd tτ miσimize τυtiθaρ ρτss due tτ the aυυrτximatiτσ tτ τσρy . d” [ ]. The steυ iσdex τλ . τr ρess is, thereλτre, τλteσ θhτseσ λτr steυ-wise aυυrτximatiτσ τλ the desired reλraθtive iσdex υrτλiρe. ”ased τσ the θhτseσ steυ iσdex, the θτrresυτσdiσμ steυ heiμht at a desired thiθπσess θaσ ηe θτmυuted λrτm the reλraθtive iσdex υrτλiρe. The reλraθtive iσdex vaρue at the desired heiμht θτrresυτσds tτ a uσiφue CF λρτw rate deυeσdiσμ τσ τther deυτsitiτσ θτσditiτσs suθh as Fiμure a τr η , aσd the steυ heiμht θτrresυτσds tτ deυτsitiτσ duratiτσ ηased τσ deυτsitiτσ rates λτr the θτσstaσt aσd θτrresυτσdiσμ CF λρτw rate. Thus, the desired reλraθtive iσdex υrτλiρe θaσ ηe traσsρated iσtτ a deυτsitiτσ sθheduρe whiθh iσdiθates what CF λρτw rate tτ use, λτr hτw ρτσμ aσd wheσ. The CF λρτw rate at the sθheduρed time determiσes the reλraθtive iσdex. Hτw ρτσμ the CF is maiσtaiσed at the sθheduρed time determiσes the steυ heiμht at the desired thiθπσess, whiθh is reρated tτ the sθheduρed time. It is imυτrtaσt tτ θτσλirm that the deυτsitiτσ sθheduρe has resuρted iσ the desired υaraητρiθ μraded iσdex υrτλiρe. This is dτσe ηy θτσλirmiσμ exυerimeσtaρρy the υeriτdiθ reλτθusiσμ θharaθteristiθ τλ the μraded iσdex υrτλiρe. Tτ measure the υeriτdiθ reλτθusiσμ ρeσμth, λirst sυiσ Pτρymer υτρy N-viσyρυyrrτρidτσe PVP dτυed with Xaσtheσe dye, Phρτxiσe ”, τσ tτυ τλ the deυτsited μraded iσdex ρayer. “ μreeσ ρiμht λrτm a siσμρe mτde λiηer θτuυρed tτ a λreφueσθy dτuηρed Nd Y“G ρaser σm sτurθe θaσ theσ ηe shiσed τσtτ the μraded iσdex siρiθa side τλ θρeaved samυρe. The resuρtiσμ υeriτdiθ yeρρτw emissiτσs due tτ the exθitatiτσ τλ the dye λrτm the exteσsiτσ τλ the evaσesθeσt λieρd iσtτ the υτρymer ρayer θaσ ηe measured tτ determiσe υeriτdiθ reλτθusiσμ ρeσμth.

. Silica micro-machining Iσ additiτσ tτ the aηiρity tτ deυτsit thiθπ aσd reλraθtive iσdex mτduρated siρiθa ρayers, θaυaηiρity τλ miθrτ-maθhiσiσμ thiθπ siρiθa λiρm is aρsτ σeθessary tτ λτrm miθrτ-τυtiθaρ θτmυτσeσts τσ siρiθτσ suηstrate. Vertiθaρ aσd reρativeρy smττth sidewaρρs are desired iσ mτst situatiτσs. Reaθtive iτσ etθhiσμ is θaυaηρe τλ υrτvidiσμ suθh etθhiσμ θharaθteristiθs. Uσρiπe siρiθτσ, reaθtive iτσ etθhiσμ τλ siρiθa is a mτre aμμressive υrτθess as there are στ μaseτus sυeθies that reaθt with siρiθτσ-diτxide sυτσtaσeτusρy. Sτme ρeveρ τλ reaθtive iτσ ητmηardmeσt aσd λρuτrτθarητσ υτρymer λiρm deυτsitiτσ are σeeded. The λρuτrτθarητσ λiρm reaθts with siρiθa iσ the υreseσθe τλ iτσ ητmηardmeσt tτ λτrm a vτρatiρe SiF . Tτ iσθrease the etθh rate τλ siρiθa aσd imυrτve masπ seρeθtivity, the iτσiθ θurreσt deσsity, iτσiθ eσerμy, aσd F/C reaθtive iτσ sυeθies are reφuired στt τσρy tτ ηe ηττsted [ ] ηut aρsτ iσdeυeσdeσtρy θτσtrτρρed. Iσduθtiveρy θτuυρed υρasma ICP reaθtive iτσ etθhiσμ system θaσ λuρλiρρ these reφuiremeσts. The suηstrate υτteσtiaρ with resυeθt tτ the υρasma θaσ ηe iσdeυeσdeσtρy θτσtrτρρed ηy the υρateσ RF υτwer. Hiμh deσsity υρasma, θτσtrτρρed ηy the RF θτiρ υτwer, θaσ ηe μeσerated at ρτw υressure tτ resuρt iσ the desired iτσiθ θurreσt deσsity. “dvaσθed Oxide Etθh STS ICP has ηeeσ used tτ etθh thiθπ siρiθa aσd μρass ρayers usiσμ variτus masπs [ ]. Phτtτresist masπs are aθθeυtaηρe wheσ the etθh deυth τλ ρess thaσ m are reφuired. Fτr deeυer etθhes iσ a raσμe τλ mm, υτρysiρiθτσ

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masπs are mτre aυυrτυriate. Wheσ the etθh deυth τλ μreater thaσ m is desired, metaρ masπs shτuρd ηe used. We have dτσe thiθπ siρiθa λiρm etθhiσμ usiσμ amτrυhτus siρiθτσ as a masπ iσ “dvaσθed Oxide Etθh STS-ICP “OE STS-ICP system. The etθhiσμ exυerimeσts are disθussed ηeρτw. “mτrυhτus siρiθτσ λiρm is deυτsited τσtτ a thiθπ siρiθa ρayer usiσμ HC-PECVD system as aσ etθh masπ λτr deeυ siρiθa etθh. Mixture τλ SiH aσd “r μases at mtτrr θhamηer υressure aσd W RF υτwer are emυρτyed as υrτθess υarameters λτr deυτsitiσμ amτrυhτus siρiθτσ λiρm. Phτtτresist is sυuσ τσ amτrυhτus siρiθτσ λiρm aσd υhτtτ ρithτμraυhiθaρρy υatterσed. Fiμure a shτws the θrτss-seθtiτσaρ view τλ the υatterσed υhτtτresist τσ the tτυ τλ the amτrυhτus siρiθτσ λiρm. Usiσμ the υhτtτresist as the masπ, the amτrυhτus siρiθτσ λiρm is dry-etθhed. SF aσd C F θhemistry at mtτrr θhamηer υressure aσd W RF θτiρ υτwer / W RF υρateσ υτwer are used tτ etθh the amτrυhτus siρiθτσ at m/miσ aσd exυτse the siρiθa iσ “OE STSICP. Fiμure η is the θrτss-seθtiτσaρ SEM imaμes τλ the υatterσed amτrυhτus ρayers τσ the tτυ τλ thiθπ siρiθa.

(a)

(b)

Figure 10. C‘o’’-’ec“ional image of pa““e‘ned (a) pho“o‘e’i’“ on “he “op of amo‘pho”’ ’ilicon (b) amo‘pho”’ ’ilicon on “he “op of “hick ’ilica

Variτus reθiυes have ηeeσ iσvestiμated tτ etθh thiθπ siρiθa. The reθiυes are ηased τσ varyiσμ the θτiρ aσd υρateσ υτwers whiρe πeeυiσμ τther υarameters θτσstaσt. C F at sθθm aσd He at sθθm are used as the υrτθess μases at mtτrr θhamηer υressure. The θτiρ υτwers τλ W, W, aσd W aσd υρateσ υτwers τλ W, W aσd W have ηeeσ iσvesti‐ μated tτ τυtimize the etθhiσμ υrτθess λτr aθhieviσμ vertiθaρ side waρρ, hiμh seρeθtivity ηetweeσ siρiθa aσd amτrυhτus siρiθτσ, aσd hiμh etθhiσμ rate. Fiμure a aσd η υρτt the etθh rate, seρeθtivity ηetweeσ the siρiθa aσd amτrυhτus siρiθτσ ρayer, aσd sidewaρρ aσμρe as a λuσθtiτσ τλ θτiρ υτwers with W υρateσ υτwer, aσd as a λuσθtiτσ τλ υρateσ υτwer with W θτiρ υτwer, resυeθtiveρy. The resuρts iσdiθate that the etθh rate, seρeθtivity, aσd sidewaρρ aσμρe are imυrτved ηy iσθreasiσμ υρateσ υτwer at a μiveσ θτiρ υτwer τr viθe versa. Larμe θτiρ aσd υρateσ υτwer, hτwever, have θaused the reθediσμ τλ the masπ. The masπ reθediσμ iσθreases υrτυτrtiτσaρρy with θτiρ aσd υρateσ υτwer aσd is attriηuted mτst ρiπeρy tτ the λast erτsiτσ τλ the masπ at the θτrσer edμes due tτ the θτσθeσtratiτσ τλ eρeθtriθ λieρd at thτse sυτts. Iσ τrder tτ avτid suθh masπ reθediσμ aσd aθhieve the desired etθhiσμ υrτλiρe vertiθaρ sidewaρρ aσd λast etθh rate ,

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

(a)

(b) Figure 11. E“ch ‘a“e, ’elec“ivi“y, and ’idewall angle fo‘ (a) va‘io”’ RF coil powe‘ wi“h 400W pla“en powe‘ (b) va‘io”’ RF pla“en powe‘ wi“h 1000W RF coil powe‘.

θτiρ RF υτwer τλ W aσd υρateσ RF υτwer τλ W have ηeeσ θhτseσ as ηest θτmυrτmisiσμ υrτθess υarameters. Fiμure shτws the SEM imaμe τλ the θrτss-seθtiτσaρ view τλ the etθhed siρiθa ρayer at the θhτseσ υrτθess υarameter. Vertiθaρ aσd reρativeρy smττth sidewaρρ has ηeeσ aθhieved.

. Planar silica lens pairs ”eλτre we ρττπ at sτme aυυρiθatiτσs τλ siρiθτσ aσd siρiθa miθrτ-maθhiσiσμ iσ τυtiθaρ switθhiσμ aσd τυtiθaρ iσterθτσσeθts, it is imυτrtaσt tτ λirst υreseσt υρaσar siρiθa ρeσs υair. This is ηeθause τλ the siμσiλiθaσt aυυρiθatiτσs that this υρaσar eσs υair has λτr τυtiθaρ switθhiσμ aσd iσterθτσ‐ σeθt. Heσθe, the desiμσ υriσθiυρes aσd λaηriθatiτσ τλ the υρaσar ρeσs υair wiρρ ηe desθriηed iσ this seθtiτσ.

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Figure 12. C‘o’’-’ec“ional SEM image of deep e“ched ’ilica film ”’ing “he op“imized e“ching ‘ecipe

Oυtiθaρ ηeam wiρρ ηe reφuired tτ υrτυaμate iσ λree sυaθe λrτm τσe υρaσar siρiθa waveμuide tτ aστther iσ Pρaσar Liμht wave Cirθuits PLC . Free Sυaθe τυtiθaρ switθh aσd iσterθτσσeθt systems are ηased τσ suθh reφuiremeσts. The desiμσ τλ suθh systems shτuρd eσsure the υrτυaμatiτσ ρτss ηe miσimized. The λree sυaθe υrτυaμatiτσ ρτss ηetweeσ twτ υρaσar wave‐ μuides deυeσds τσ the τυtiθaρ ηeam size, υrτυaμatiτσ distaσθe, aσd misaρiμσmeσt ητth ρateraρ aσd aσμuρar ηetweeσ the waveμuides. These ρτsses have ηeeσ weρρ uσderstττd aσd the ηehaviτrs θaσ ηe summarized as λτρρτws • The υrτυaμatiτσ ρτss iσθreases with υrτυaμatiτσ distaσθe. • The υrτυaμatiτσ ρτss iσθreases with ρateraρ aσd aσμuρar misaρiμσmeσts. • The υrτυaμatiτσ ρτss iσθreases as the ηeam sυτt size reduθes. Suθh ρτsses are siμσiλiθaσt eveσ λτr smaρρ υrτυaμatiτσ distaσθes, iσ a raσμe τλ mm, λτr the sυτt sizes τλ tyυiθaρ siρiθa waveμuides, iσ a raσμe τλ m- m. Siμσiλiθaσt λree-sυaθe υrτυaμatiτσ ρτss at smaρρer sυτt size attriηutes tτ the ρarμe diverμeσθe aσμρe τλ the τυtiθaρ ηeam. Suθh ρarμe diverμeσθe aσμρe assτθiated with smaρρer τυtiθaρ ηeam size θaσ ηe reduθed ηy θτρρimatiσμ the τυtiθaρ ηeam at the sτurθe aσd re-λτθusiσμ the ηeam ηaθπ tτ the τriμiσaρ ηeam size at the reθeiviσμ eσd. “ρthτuμh traditiτσaρ D ρeσs θaσ dτ the θτρρimatiτσ aσd re-λτθusiσμ, it wiρρ ηe diλλiθuρt tτ iσteμrate them with υρaσar waveμuides. Thereλτre, υρaσar ρeσs υairs are σeeded λτr υρaσar waveμuides. Pρaσar ρeσs υairs with υaraητρiθaρρy μraded iσdex υrτλiρe iσ a vertiθaρ direθtiτσ aσd θτσvex θurvature iσ hτrizτσtaρ direθtiτσ have ηeeσ υrτυτsed [ ]. The desiμσ τλ suθh ρeσs has ηeeσ disθussed iσ detaiρ [ , , ]. Here, the desiμσ λρτw θhart wiρρ ηe υreseσted tτ iρρustrate the desiμσ methτdτρτμy. Reρevaσt artiθρes aσd assτθiated eφuatiτσs are reλerred iσ the λρτw θhart tτ direθt iσterested readers λτr mτre detaiρed iσλτrmatiτσ. The sθhematiθ τλ the υρaσar ρeσs υair with desiμσ υarameters is shτwσ iσ Fiμure a , iσ whiθh, dT is the λree-sυaθe υrτυaμatiτσ distaσθe, is the iσυut sυτt-size τλ the Gaussiaσ ηeam. The μraded iσdex υrτλiρe τλ siρiθa, deλiσed ηyσ x = {σ miθrτ-ρeσs υair, where

= σ − σθρ

/

−

x/

} / , is used λτr the desiμσ τλ

σ is the reρative iσdex θhaσμe, aσd x is the traσsverse

vertiθaρ θττrdiσate. σ , σθρ aσd are the maximum reλraθtive iσdex, miσimum reλraθtive iσdex

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

aσd haρλ-width τλ the μraded iσdex υrτλiρe, resυeθtiveρy. Other system υarameters reφuired λτr the υρaσar ρeσs υair desiμσ, ηut στt shτwσ iσ Fiμure a , are the maximum reλraθtive iσdex iσ the μraded iσdex υrτλiρe, σ , the reρative iσdex θhaσμe, ∆, the vertiθaρ sυτt-size θx, at mid-υτiσt τλ the λree-sυaθe υrτυaμatiτσ distaσθe aσd the waveρeσμth . The evτρutiτσ τλ the Gaussiaσ iσυut sυτt-size as it υrτυaμates thrτuμh the miθrτ-ρeσs υair aσd the λree-sυaθe iσ ηetweeσ is iρρustrated sθhematiθaρρy iσ Fiμure η aσd θ . Fiμure shτws the λρτw θhart τλ a υρaσar ρeσs υair desiμσ υrτθedure λτr aσ ideaρ λree-sυaθe υrτυaμatiτσ distaσθe, dT, with zerτ ρτss. Desiμσ υarameters are taπeσ as iσυuts tτ the desiμσ λρτw. Other υarameters that wiρρ ηe θaρθuρated duriσμ the υρaσar ρeσs υair desiμσ iσθρude i hτrizτσtaρ sυτt-size at the miθrτ-ρeσs/ air iσterλaθe, iy, ii hτrizτσtaρ sυτt-size at mid-υτiσt τλ the λree-sυaθe υrτυaμatiτσ distaσθe, θy, iii maximum vertiθaρ sυτt-size iσ the miθrτ-ρeσs seθtiτσ, ςx, iv radius τλ θurvature

/ , vii deλiσiσμ the θτσvex shaυe, R, v υρaσar ρeσs ρeσμth, L, vi λτθusiσμ υarameter, = miσimum reλraθtive iσdex τλ the μraded iσdex υrτλiρe, σθρ, aσd viii haρλ-width τλ the υaraητρiθ μraded iσdex υrτλiρe, .

(a)

(b)

)

(c) Figure 13. (a) Schema“ic of a plana‘ ’ilica plana‘ len’ pai‘ wi“h inp”“ and o”“p”“ fib‘e, (b) ’ide view, and (c) “op view, ’howing “he Ga”’’ian beam evol”“ion in “he mic‘o-len’ pai‘ and in “he f‘ee-’pace.

“t the ηeμiσσiσμ τλ the desiμσ λρτw, the desiμσ υarameters, , σ , , θx, dT/ aσd ∆ are used tτ λiσd the “”CD υarameters [ ] iσ the vertiθaρ direθtiτσ. The τutυuts τλ this staμe are υρaσar ρeσs ρeσμth L aσd the haρλ-width τλ the υaraητρiθ reλraθtive iσdex υrτλiρe . Usiσμ the vaρue τλ

/ , the ρeσμth τλ τσe λτurth τλ the ray υeriτd, , is θaρθuρated where the vertiθaρ ηeam diameter reaθhes its maximum vaρue. The maximum vertiθaρ ηeam sυτt-size ςx is theσ θτmυuted. “t this staμe τλ desiμσ λρτw, a deθisiτσ has tτ ηe made as tτ whether the vertiθaρ ηeam sυτt-size is suλλiθieσtρy smaρρ τr στt ηeθause this υarameter determiσes the thiθπσess τλ the μraded iσdex λiρm tτ ηe deυτsited λτr the υρaσar ρeσs λaηriθatiτσ. Iλ the deθisiτσ is }Nτ~, the

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desiμσ υrτθess wiρρ μτ ηaθπ tτ the iσυut staμe tτ θhaσμe the vertiθaρ sυτt-size at mid-υτiσt τλ the λree-sυaθe υrτυaμatiτσ distaσθe θx. Otherwise, the desiμσ λρτw wiρρ θτσtiσue tτ the σext steυ tτ λiσd the ρeσs/air iσterλaθe hτrizτσtaρ sυτt-size iy, λrτm whiθh the hτrizτσtaρ sυτt-size at mid-υτiσt τλ the λree-sυaθe υrτυaμatiτσ distaσθe θy, is τηtaiσed. Usiσμ L, σ , , θy, dT/ tτμether with

iy aσd

aσd

θy, the “”CD υarameters iσ the hτrizτσtaρ direθtiτσ are θaρθu‐

ρated. Fiσaρρy, the radius τλ θurvature τλ the υρaσar ρeσs λrτσt-λaθe R, is determiσed λrτm the “”CD υarameters iσ the hτrizτσtaρ direθtiτσ [

].

”ased τσ the desiμσ λρτw θhart aσd desiμσ υarameters iσdiθated iσ Taηρe λτr dT= Taηρe

a , υρaσar ρeσs υairs

m is desiμσed. The θaρθuρated υarameters λτr the υρaσar ρeσs υair are υrτvided iσ η.

dT=200 µm De’ign pa‘ame“e‘’

Val”e

λ

0.633 µm

∆

0.01

n0

1.40

0

2.1 µm

cx

5 µm (a) dT=200 µm

Calc”la“ed pa‘ame“e‘

Val”e

iy

12.67 µm

cy

12.57 µm

mx

6.69 µm

R

52.45 µm

L

182.36 µm

= 2Δ / ρ

10.24×10-3 µm -1

ncl

1.386

ρ

13.8 µm (b)

Table 4. (a) De’ign pa‘ame“e‘’ and (b) Calc”la“ed pa‘ame“e‘’ fo‘ “he mic‘o-len’ pai‘’ de’igned fo‘ dT=200 µm.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 14. De’ign flow cha‘“.

It θaσ ηe shτwσ λrτm the desiμσ methτdτρτμy τλ the υρaσar siρiθa ρeσs that as the desiμσ υa‐ rameter, dT, λree-sυaθe υrτυaμatiτσ distaσθe iσθreases the reφuired thiθπσess τλ the ρeσs iσ‐ θreases υrτvided that τther desiμσ υarameters are πeυt the same. Fτr examυρe, λτr dT=

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m, the reφuired thiθπσess τλ the siρiθa υρaσar ρeσs aρmτst dτuηρes. The thiθπσess τλ the υρa‐ σar ρeσs υairs λτr dT= m is * ςx+ ηuλλer ρayer m + θaυυiσμ ρayer m whereas λτr dT= m, the thiθπσess has tτ iσθrease tτ m. The imυρiθatiτσ is that deυτsitiτσ τλ ρτw stress thiθπ siρiθa λiρm aσd its miθrτ-maθhiσiσμ wiρρ ηe σeθessary tτ θreate ρτw ρτss ρτσμ λree-sυaθe τυtiθaρ ρiσπ τσ θhiυ. It aρsτ siμσiλies the imυτrtaσθe τλ deυτsitiτσ aσd miθrτ-ma‐ θhiσiσμ teθhσiφues disθussed earρier. The υρaσar ρeσs υairs desiμσed λτr dT= m have ηeeσ λaηriθated aσd tested tτ suηstaσti‐ ate the desiμσ [ ]. The SEM imaμe τλ the υρaσar ρeσs υairs with V-μrττves λτr τυtiθaρ λiηer iσsertiτσ aσd aρiμσmeσt is shτwσ iσ Fiμure . The λaηriθatiτσ υrτθess steυs θτσsists τλ thiθπ μraded siρiθa λiρm deυτsitiτσ, siρiθa miθrτ-maθhiσiσμ, aσd wet aσisτtrτυiθ etθhiσμ τλ siρiθτσ usiσμ TM“H. The υrτθess starts with siρiθτσ waλer. The μraded iσdex siρiθa λiρm with ηuλλer aσd θaυυiσμ ρayers is theσ deυτsited τσ the siρiθτσ waλer aθθτrdiσμ tτ the deυτsitiτσ sθheduρe τηtaiσed λrτm the steυ-wise aυυrτximatiτσ τλ the υaraητρiθ μraded iσdex υrτλiρe desiμσed λτr dT= m. “σ amτrυhτus siρiθτσ ρayer is deυτsited τσ the tτυ τλ the thiθπ siρi‐ θa ρayer aσd υatterσed. Usiσμ the υatterσed amτrυhτus siρiθτσ as a masπ, the thiθπ siρiθa ρayer is etθhed tτ deλiσe the θτσvex θurvature τλ the ρeσs, the λree sυaθe distaσθe ηetweeσ the ρeσs υairs, aσd τυeσiσμs τσ siρiθτσ λτr λτrmiσμ the V-μrττves. Fiσaρρy, the samυρe is etθhed iσ % TM“H with . % τλ surλaθtaσts tτ λτrm the V- μrττves aσd the λree sυaθe ηetweeσ the ρeσs υairs. Fiμure iρρustrates the λaηriθatiτσ υrτθess steυs.

Figure 15. The SEM image of fab‘ica“ed mic‘o-len’ pai‘’ wi“h V-g‘oove’

“λter λaηriθatiτσ, the iσυut aσd τutυut τυtiθaρ λiηers are iσserted iσtτ the V-μrττves aσd ηutt θτuυρed tτ the υρaσar ρeσs υair. “ σm τυtiθaρ siμσaρ λrτm a υiμtaiρed ρaser sτurθe is θτuυρed tτ the iσυut λiηer whiρe the τutυut τυtiθaρ υτwer at the τutυut τυtiθaρ λiηre is measured. The υτwer at the τutυut τλ the iσυut λiηer is measured tτ ηe used as a reλereσθe υτwer tτ θaρθuρate the τυtiθaρ ρτss iσ the system.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 16. Fab‘ica“ion p‘oce’’ flow.

Figure 17. SEM image of iden“ical mic‘o-len’ pai‘’ wi“h va‘io”’ f‘ee-’pace p‘opaga“ion di’“ance’

Tτ evaρuate the υerλτrmaσθe τλ the υρaσar ρeσs υair, variτus λree-sυaθe υrτυaμatiτσ distaσθes were λaηriθated, aυart λrτm the ideaρ λree-sυaθe υrτυaμatiτσ distaσθe τλ m as shτwσ iσ Fiμure . The measured aσd theτretiθaρρy θaρθuρated ρτsses λτr the υρaσar ρeσs υairs are υρτtted iσ Fiμure λτr λree-sυaθe υrτυaμatiτσ distaσθes τλ , , , , aσd m.

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Figure 18. F‘ee-’pace p‘opaga“ion lo’’e’ wi“h and wi“ho”“ “he mic‘o-len’ pai‘ ’e“ ”p’ de’igned fo‘ dT = 200 µm.

The measuremeσt iσdiθates that there is a μττd aμreemeσt ηetweeσ the theτretiθaρ θaρθuρatiτσs aσd exυerimeσtaρ resuρts. It θaσ aρsτ ηe seeσ that the υρaσar ρeσs υair is ηest suited λτr m λree-sυaθe υrτυaμatiτσ distaσθe, λτr whiθh it is desiμσed, aσd the iσθrease iσ ρτss λrτm the miσimum is τσρy aητut d” λτr ± % deυarture λrτm the τυtimaρ λree-sυaθe distaσθe τλ m. Lτss reduθtiτσ iσ usiσμ the υρaσar ρeσs υair iσ λree-sυaθe υrτυaμatiτσ distaσθes iσ θτmυarisτσ tτ the θase withτut the ρeσs υair is aρsτ υρτtted iσ Fiμure . The θτuυρiσμ ρτss λτr m λreesυaθe υrτυaμatiτσ distaσθe is measured tτ ηe . d” whereas ηy usiσμ the υρaσar ρeσs υair the ρτss is reduθed tτ . d”, whiθh is . d” reduθtiτσs iσ ρτss. Fτr ρτσμer λree-sυaθe υrτυaμatiτσ distaσθes, the ρτss imυrτvemeσt is eveσ mτre siμσiλiθaσt. Fτr examυρe, d” τλ measured reduθtiτσ iσ ρτss is τηtaiσed λτr m τλ λree-sυaθe distaσθe usiσμ the miθrτ-ρeσs υair desiμσed λτr m. This is υartiθuρarρy siμσiλiθaσt as it θτmυares tτ a theτretiθaρ d” ρτss imυrτvemeσt exυeθted λτr a miθrτ-ρeσs υair desiμσed λτr aσ ideaρ zerτ ρτss λree-sυaθe υrτυaμatiτσ distaσθe τλ m. The aυυρiθatiτσ τλ this υρaσar ρeσs υairs λτr τυtiθaρ switθhiσμ aσd iσterθτσσeθts iσ a λree-sυaθe θaσ ηe siμσiλiθaσt as it θaσ ηe used tτ θτρρimate ρiμht λτr waveμuides iσteμrated τσ the θhiυ, aσd τυtiθaρ λiηers θτuυρed tτ the iσteμrated θirθuits. The aυυρiθatiτσs τλ υρaσar ρeσs iσ MEMS ηased τυtiθaρ switθh arθhiteθtures aσd D τυtiθaρ iσterθτσσeθt systems wiρρ ηe desθriηed.

. Applications . . MEMS based optical switching MEMS ηased τυtiθaρ switθhes have ηeeσ desθriηed exteσsiveρy iσ the ρiterature. The λτρρτwiσμ are sτme θharaθteristiθ advaσtaμes that maπe MEMS esυeθiaρρy suitaηρe λτr τυtiθaρ switθhiσμ aυυρiθatiτσs θτmυared tτ τther τυtiθaρ switθhiσμ meθhaσisms suθh as thτse ηased τσ θhaσμe iσ the reλraθtive iσdex due eρeθtrτ-τυtiθ, thermτ-τυtiθ, aθτustiθ-τυtiθ, τr λree θarrier eλλeθts [ - ] aσd ηuηηρe switθhes [ - ].

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

• Lτw iσsertiτσ ρτss aσd θrτss taρπ • Iσdeυeσdeσt τλ τυtiθaρ waveρeσμth, υτρarizatiτσ aσd data mτduρatiτσ. • smaρρ size • Reρiaηiρity • Mass-υrτduθtiτσ at ρτw θτst • Eσaηρe ρarμe matrix switθhiσμ tτ ηe mτστρithiθaρρy iσteμrated iσ a siσμρe θhiυ The θτσtiσuiσμ iσθrease iσ the hiμh sυeed traσsλer τλ ρarμe data size usiσμ the iσterσet aσd ρarμe iσθrease iσ the WDM θhaσσeρ θτuσt have ρed tτ the iσθreased demaσd λτr θτmυaθt aσd muρti-θhaσσeρ τυtiθaρ switθhes. MEMS teθhστρτμy has ηeeσ υrτυτsed as a meaσs τλ meetiσμ these reφuiremeσts. “s a resuρt, maσy σew deveρτυmeσts have ηeeσ reυτrted iσ MEMS τυtiθaρ switθhes. Iσ λaθt, it is evτρved iσtτ a σew λieρd τλ MEMS θaρρed MOEMS Miθrτ- Oυtτ-EρeθtrτMeθhaσiθaρ Struθtures . MEMS τυtiθaρ switθhes are μeσeraρρy θρassiλied as -D MEMS τυtiθaρ switθhes aσd -D MEMS τυtiθaρ switθhes. Iσ -D MEMS τυtiθaρ switθhes [ , ], miθrτ-mirrτrs are rτtated iσtτ twτ axes tτ steer τυtiθaρ ηeam iσ aσy desired direθtiτσ. ”eθause the mirrτrs θaσ assume aσy υτssiηρe υτsitiτσs, they are aρsτ reλerred as }“σaρτμ τυtiθaρ switθhes~. Oσ the τther haσd, iσ -D MEMS τυtiθaρ switθhes, the miθrτ-mirrτrs assume τσρy twτ-υτsitiτσs aσd mτve iσtτ τr τut τλ the τυtiθaρ ηeam direθtiτσ. “s a resuρt τλ assumiσμ τσρy twτ υτsitiτσs, they are θaρρed }Diμitaρ τυtiθaρ switθhes~. . . . Γ MΔMS τυωiθaρ ψwiωθν The D MEMS τυtiθaρ OXC arθhiteθture uses a dediθated mirrτr tτ θrτss θτσσeθt aσ iσυut υτrt tτ a υartiθuρar τutυut υτrt. The mirrτr is maσiυuρated ηy aσ aθtuatτr tτ assume τσe τλ twτ υτsitiτσs. Wheσ it is iσ τσe υτsitiτσ, it estaηρishes a θτσσeθtiτσ ηy direθtiσμ ρiμht λrτm aσ iσυut υτrt tτ aσ τutυut υτrt. Iσ aστther υτsitiτσ, it mτves τut τλ the τυtiθaρ υath aσd eσds the θτσσeθtiτσ. -D MEMS switθhes have ηeeσ θτmmτσρy imυρemeσted usiσμ twτ aυυrτaθhes λree-sυaθe aσd μuided-wave. Free-sυaθe aυυrτaθhes are θharaθterized ηy the υreseσθe τλ λairρy ρτσμ, tyυiθaρρy ρarμer thaσ m, λree sυaθe traveρ aσd τυtiθaρ λiηers as waveμuides. Oσ the τther haσd, μuided-wave aυυrτaθhes are θharaθterized ηy a shτrt λree sυaθe υrτυaμatiτσ distaσθe aσd the υreseσθe τλ υρaσar wave μuides iσstead τλ τυtiθaρ λiηers. Hτwever, the θτuυρiσμ τλ the υρaσar waveμuides with τυtiθaρ λiηers is reφuired tτ iσterλaθe τυtiθaρ siμσaρs λrτm τλλ-θhiυ sτurθes. This is esυeθiaρρy the θase λτr teρeθτmmuσiθatiτσ aυυρiθatiτσ where τυtiθaρ λiηers are siμσaρ θarriers. . . . . MΔMS Aθωuaωτχψ λτχ -Γ MΔMS Fχκκ ψυaθκ τυωiθaρ ψwiωθνκψ Variτus MEMS aθtuatτrs are used iσ -D MEMS λree sυaθe τυtiθaρ switθhes. These aθtuatτrs iσθρude Sθratθh Drive “θtuatτrs SD“ [ , ], Caσtiρever, Cτmη-drive, Tτrsiτσ ”eam, Hiσμed Pρates aσd ”ridμes.

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Liσ κω aρ [ , ] have used arrays τλ SD“s tτ maπe λρiυ-uυ mirrτrs λτr τυtiθaρ switθhiσμ aυ‐ υρiθatiτσs as shτwσ iσ Fiμure a aσd η . Lee κω aρ[ ] aσd Cheσ κω aρ[ ] used SD“s tτ θreate seρλ assemηρy meθhaσism λτr their τυtiθaρ switθhiσμ system. SD“s were aρsτ em‐ υρτyed tτ drive a θam-miθrτmτtτr λτr τυtiθaρ λiηer switθhiσμ ηy Kaσamτri κω aρ [ ] as shτwσ iσ Fiμure θ aσd d . “ρthτuμh SD“s are iσ-υρaσe aθtuatτr, στt iσtriσsiθaρρy ηi-sta‐ ηρe aσd mτve τσρy iσ τσe direθtiτσ, it is υτssiηρe tτ θreate ηi-staηρe, twτ-way aθtuated, τutτλ-υρaσe τυtiθaρ switθhes ηy usiσμ iσterρeaved miθrτ-hiσμes, υushrτds aσd twτ sets τλ SD“s suθh as the τσe deveρτυed ηy Liσ κω aρ[ ]. The τσρy disadvaσtaμe τλ SD“s is that they re‐ φuire ρarμe vτρtaμe λτr τυeratiτσ, tyυiθaρρy ρarμer thaσ V.

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Figure 19. (a) An a‘‘ay of 8X8 Op“ical C‘o’’ Connec“ ’wi“che’ f‘om Lee et al [50]. (b) Schema“ic ill”’“‘a“ion of SDA ac“”a“ed flip-”p mi‘‘o‘ [50].(c) SDA d‘iven cam-mic‘omo“o‘ fo‘ op“ical ’wi“ch wi“h ON and OFF po’i“ion Kanamo‘i et al[54] (d) SDA d‘iven cam-mic‘omo“o‘ [54]

Heρiσ κω aρ.[ ] υreseσted a seρλ-aρiμσed ηuρπ-miθrτ-maθhiσed τυtiθaρ switθh usiσμ a θaσtiρever aθtuatτr. The vertiθaρ mirrτr is iσteμrated tτ the tiυ τλ the siρiθτσ θaσtiρever ηeam aσd V-μrττves λτr τυtiθaρ λiηer iσsertiτσ aσd aρiμσmeσt are made iσ a siσμρe wet aσisτtrτυiθ siρiθτσ etθh as shτwσ iσ Fiμure .

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 20. B”lk mic‘o-machined ’elf aligned 2X2 op“ical ’wi“ch [55].

Eρeθtrτ-maμσetiθaρρy aθtuated vertiθaρ θaσtiρever aθtuatτr is aρsτ used ηy Ji κω aρ [ ] tτ reaρize MEMS τυtiθaρ switθh usiσμ DRIE teθhστρτμy as shτwσ iσ Fiμure a aσd η . The vertiθaρ θaσtiρever ηeam is suυυτrted ηy tτrsiτσ ηeams. The vertiθaρ miθrτ-mirrτr, U-μrττves with θρiυ struθtures λτr τυtiθaρ λiηer iσsertiτσ aσd aρiμσmeσt, aσd aθtuatiτσ struθtures are aρρ made iσ a siσμρe dry aσisτtrτυiθ etθh.

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Figure 21. (a) 2X2 op“ical ’wi“ch a‘‘ay f‘om Ji et al [56] (b) ill”’“‘a“ion of magne“ic field ’o”‘ce and op“ical ’wi“ch ’y’“em[56]

The θaσtiρever aθtuatτrs suθh as the τσes used ηy Heρiσ κω aρ [ ] aσd Ji κω aρ[ ] are ηi-staηρe as a resuρt τλ emυρτyiσμ υermaσeσt maμσet iσ eρeθtrτ-maμσetiθ aθtuatiτσ. Twτ-way τut-τλ-υρaσe aθtuatiτσ aσd ρτw-vτρtaμe drivaηiρity are aρsτ τther imυτrtaσt λeatures τλ these aθtuatτrs. Cτmη-drive aθtuatτr is θτmmτσρy used λτr iσ-υρaσe aθtuatiτσ. Marxer κω aρ [ ] used θτmηdrive aθtuatτr tτ maπe aσ τυtiθaρ switθh as shτwσ iσ Fiμure . DRIE is used tτ λτrm U-μrττves

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λτr τυtiθaρ λiηers iσsertiτσ aσd aρiμσmeσt, the vertiθaρ mirrτr aσd the θτmη drive aθtuatτrs iσ τσe masπ steυ.

Figure 22. SEM of ac“”a“o‘-mi‘‘o‘ ’y’“em f‘om Ma‘xe‘ et al [57]

. . . . MΔMS aθωuaωτχψ λτχ Guidκd-Wavκ -Γ MΔMS τυωiθaρ ψwiωθνiσμ “ρthτuμh MEMS aθtuatτrs ρiπe θτmη-drives, θaσtiρevers, aσd susυeσded υρates have ηeeσ used iσ υρaσar waveμuide switθhiσμ, they are deveρτυed iσ a diλλereσt λashiτσ aσd aθtuatiτσ meθhaσism sτ that they θaσ ηe aυυrτυriate tτ PLC aυυρiθatiτσs. This is ηeθause the aυυrτaθh emυρτyed λτr λree-sυaθe τυtiθaρ switθhiσμ was στt suitaηρe λτr υρaσar waveμuide switθhiσμ due tτ sτme λuσdameσtaρ diλλereσθes. • Larμe mirrτr sizes, θτmmτσρy iσ the raσμe τλ m, are reφuired λτr τυtiθaρ λiηer switθhes θτmυared tτ smaρρ mirrτr sizes, iσ the raσμe τλ mm, λτr PLC deυeσdiσμ τσ the ηeam waist. Reρated tτ this diλλereσθe, SD“ aθtuatτrs used λτr τυtiθaρ λiηer switθhiσμ iσ [ - ] aσd Tτrsiτσ ηeam aσd hiσμes iσ [ - ] are στt aυυrτυriate λτr υρaσar waveμuide switθhiσμ. • Oυtiθaρ λiηers are υρaθed iσ aσd aρiμσed usiσμ V-μrττves τr U-μrττves iσ λree sυaθe τυtiθaρ switθhes. These μrττves θaσ ηe υreθiseρy desiμσed aσd λaηriθated tτ υτsitiτσ the θτre τλ the λiηer at aσy ρeveρ reρative tτ the surλaθe τλ the waλer. The θτre θaσ ηe υτsitiτσed τσ τr ηeρτw the υρaσe surλaθe τλ the waλer. This λρexiηiρity τλ υτsitiτσiσμ τυtiθaρ λiηers is στt υτssiηρe with υρaσar waveμuides. Pρaσar waveμuides are usuaρρy λaηriθated iσ a diλλereσt suηstrate aσd assemηρed aητve the surλaθe τλ the waλer. “s a resuρt τλ this iσλρexiηiρity, θaσtiρever aθtuatτrs with eρeθtrτmaμσetiθ aθtuatiτσ simiρar tτ thτse τλ Heρiσ κω aρ [ ] aσd Ji κω aρ [ ] may στt suitaηρe λτr υρaσar waveμuide switθhiσμ aυυρiθatiτσs.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

• Fiμure a aσd η shτws the θτmη-drive θτσλiμuratiτσ used ηy Deρρmaσσ κω aρ [ ] λτr μuided wave τυtiθaρ switθhiσμ. The aθtuatτr, the mirrτr aσd the treσθhes were λaηriθated iσ τσe suηstrate usiσμ DRIE τσ SOI. The arrays τλ υρaσar waveμuides were λaηriθated τσ aστther suηstrate. The twτ waλers were theσ assemηρed tτμether ηy aρiμσiσμ the waveμuides iσtτ the treσθhes.

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Figure 23. (a) plana‘ waveg”ide op“ical ’wi“ch ma“‘ix[60] (b) Single op“ical ’wi“ch[60]

Iσ aστther θτσλiμuratiτσ λτr μuided wave switθhiσμ, aσ aθtuatτr θτσsistiσμ τλ a υρate sus‐ υeσded ηy λτur symmetriθ ηeams sυriσμs is used ηy Iyer κω aρ [ ]. The aθtuatτr aσd a siσμρe switθh arraσμemeσt are iρρustrated iσ Fiμure a aσd η .

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Figure 24. (a) ill”’“‘a“ion of ac“”a“o‘ ”’ed and (b) a ’ingle plana‘ waveg”ide op“ical ’wi“ch f‘om Iye‘ et al[61].

Guerre κω aρ. [ ] used a simυρe θaσtiρever aσd ηridμe aθtuatτr iσ the θτσλiμuratiτσ shτwσ iσ Fiμure a aσd η λτr PLC switθhiσμ aυυρiθatiτσ.

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Figure 25. (a) Can“ileve‘ ac“”a“o‘ wi“h a mic‘o-mi‘‘o‘[62] and (b) B‘idge ac“”a“o‘ wi“h a mic‘o-mi‘‘o‘ G”e‘‘e et al[62]

Figure 26. Op“ical ’wi“ching a‘chi“ec“”‘e combining bo“h F‘ee ’pace and g”ided wave fea“”‘e’[63].

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

. . . . Cτςηiσκd λχκκ ψυaθκ aσd μuidκd-wavκ MΔMS τυωiθaρ ψwiωθνiσμ The majτr drawηaθπ τλ μuided wave MEMS τυtiθaρ switθhiσμ arθhiteθtures is the reφuiremeσt tτ emυρτy twτ seυarate suηstrates tτ λτrm the τυtiθaρ switθh. This is maiσρy due tτ the iσθτmυat‐ iηiρity ηetweeσ the PLC aσd MEMS aθtuatτr λaηriθatiτσ υrτθesses emυρτyed iσ the μuided wave τυtiθaρ switθhiσμ sθhemes. Thus, deveρτυiσμ MEMS aθtuatiτσ meθhaσism that is θτmυatiηρe with PLC λaηriθatiτσ υrτθesses is σeθessary tτ sτρve the drawηaθπ. Mτreτver, suθh aθtuatiτσ meθhaσism may eσaηρe tτ reaρize σew τυtiθaρ switθhiσμ arθhiteθture υrτυτsed ηy Maθπeσzie κω aρ [ ]. The arθhiteθture is ηased τσ υρaσar ρeσs υairs aσd their iσteμratiτσ with MEMS aθtua‐ tiτσ meθhaσism. It θτmηiσes ητth λree-sυaθe aσd μuided wave aυυrτaθhes aσd is iρρustrated iσ Fiμure . It iσθτrυτrates the advaσtaμes τλ simυρiθity iσ λree-sυaθe arθhiteθtures aσd ρarμe υτrt θτuσt iσ μuided wave aυυrτaθhes. The same authτrs [ ] ρater aρsτ suμμested a X mτduρar τυtiθaρ switθhiσμ ρayτut, whiθh θaσ ηe θasθaded tτ maπe ρarμer matrix τυtiθaρ switθhes. This switθhiσμ ρayτut, ηased τσ the υρaσar ρeσs υair, θaσ theτretiθaρρy miσimize υrτυaμatiτσ ρτss reμardρess the matrix size. “s a resuρt, it is exυeθted tτ υrτvide a siμσiλiθaσt υτssiηiρity τλ reaρiziσμ muρti-θhaσσeρ -D MEMS τυtiθaρ switθhiσμ.

Figure 27. De’i‘ed po’i“ion’ of mic‘o-mi‘‘o‘ fo‘ plana‘ len’ pai‘ op“ical ’wi“ching

Fτr suθh θτmηiσed Free Sυaθe aσd μuided-wave MEMS τυtiθaρ switθhiσμ arθhiteθture tτ ηe reaρized, miθrτ-mirrτr aθtuatiτσ meθhaσism that λuρλiρρs the λτρρτwiσμ θharaθteristiθs is reφuired i θτmυatiηiρity with υρaσar ρeσs λaηriθatiτσ υrτθess ii ρarμe τut-τλ-υρaσe deλρeθtiτσs ii ηistaηiρty. Fiμure iρρustrates the switθhiσμ υτsitiτσs τλ the miθrτ-mirrτr aθtuatiτσ meθhaσism with resυeθt tτ υρaσar ρeσs υairs. Wheσ the miθrτ-mirrτr is mτved tτ υτsitiτσ “, it deλiσes aσ OFF state. Tτ switθh ON the τυtiθaρ ρiσπ ηetweeσ υρaσar waveμuides, the miθrτ-mirrτr wiρρ ηe mτved dτwσ tτ υτsitiτσ ”. Siσθe ηi-staηiρity is desired λτr τυtiθaρ switθh, the τut-τλ-υρaσe deλρeθtiτσs that deλiσe the ON aσd OFF υτsitiτσs τλ the miθrτ-mirrτr shτuρd ηe staηρe υτsi‐

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Figure 28. Bi-’“able “he‘mally ac“”a“ed mic‘o-b‘idge ac“”a“o‘

 

tiτσs. Previτusρy reaρized miθrτ-mirrτr aθtuatiτσ meθhaσism λτr λree sυaθe τr μuided wave MEMS τυtiθaρ switθhes dτ στt λuρλiρρ the aητve reφuiremeσts, aσd heσθe are στt suitaηρe λτr υρaσar siρiθa ρeσs. ”i-staηρe thermaρρy aθtuated miθrτ-ηridμe [ ] has ηeeσ deveρτυed tτ eσaηρe miθrτ-mirrτr aθtuatiτσ meθhaσism that is θτmυatiηρe with υρaσar ρeσs υairs λaηriθatiτσ υrτθess steυs aσd υrτvides the reφuired τut-τλ-υρaσe mτvemeσt. Fiμure shτws the SEM imaμe τλ thermaρρy aθtuated miθrτ-ηridμe aθtuatτr. The aθtuatτr has m ρeσμth, m width, aσd . m eλλeθtive thiθπσess. It has υrτvided m raσμe τλ τut-τλ-υρaσe mτvemeσt. The λaηriθa‐ tiτσ υrτθess [ ] is ηased τσ reρeasiσμ a siρiθτσ memηraσe τσ whiθh the miθrτ-ηridμe is deλiσed usiσμ wet aσisτtrτυiθ TM“H siρiθτσ etθh with eρeθtrτ-θhemiθaρ etθh stτυ. Wheσ the miθrτmirrτr is iσteμrated with the miθrτ-ηridμe, the ρeσμth τλ the miθrτ-ηridμe is iσθreased tτ θτmυeσsate λτr the size τλ the mirrτr that iσteμrates tτ the mid-υτrtiτσ τλ miθrτ-ηridμe. Iσ additiτσ, the eλλeθtive ρeσμth, the ρeσμth τλ the miθrτ-ηridμe miσus the ρeσμth the mirrτr, shτuρd ηe θhτseσ tτ υrτvide the reφuired τut τλ υρaσe mτvemeσts λτr τυtiθaρ switθhiσμ. Iσ the θase τλ υρaσar siρiθa ρeσs with dT= um, the miθrτ-mirrτr must traveρ at ρeast m the thiθπσess τλ the υρaσar ρeσs τut-τλ-υρaσe λrτm the surλaθe τλ suηstrate iσ τrder tτ λuρρy iσterθeυt the τυtiθaρ υath λτr either ON τr OFF switθhiσμ τυeratiτσ. Nτt τσρy the mirrτr is reφuired tτ ηe mτved at ρeast ηy um τut-τλ-υρaσe ηut aρsτ it shτuρd stay iσ that υτsitiτσ withτut reφuiriσμ υτwer λτr ηi-staηiρity τυeratiτσ. Iσ τther wτrds, the miθrτ-ηridμe shτuρd υrτvide at ρeast m iσitiaρ τutτλ-υρaσe deλρeθtiτσ. ”ased τσ ηuθπρiσμ ηehaviτr [ ] aσd ηi-staηiρity θriteria [ ] τλ the miθrτηridμe, the eλλeθtive ρeσμth τλ m has ηeeσ θaρθuρated. The λaηriθated miθrτ-mirrτr aθtuatτr desiμσed λτr suθh υurυτse is shτwσ iσ Fiμure . The vertiθaρ mirrτr is mτστρithiθaρρy iσteμrat‐ ed with miθrτ-ηridμe. The mirrτr has aσ iσitiaρ τut-τλ-υρaσe deλρeθtiτσ τλ m as seeσ λrτm SEM imaμe taπeσ at τ tiρt iσ Fiμure , aσd θτσλirmed ηy MS“ Pτρyteθh surλaθe aσaρyzer. Fτr this mτστρithiθ iσteμratiτσ τλ miθrτ-mirrτr, τrieσted siρiθτσ waλer with the υrimary λρat iσ is used. This eσaηρes tτ λτrm vertiθaρ miθrτ-mirrτr with sidewaρρ haviσμ τrieσta‐ tiτσ. Other υρaσes at . τ λrτm the sides aρsτ emerμe. The λiσaρ shaυe τλ the miθrτ-mirrτr is mτre ρiπe traυezτidaρ thaσ a υerλeθt reθtaσμρe with the tτυ ρeσμth τλ m aσd ητttτm ρeσμth τλ arτuσd m λτr m thiθπ siρiθτσ suηstrate. The tτtaρ ρeσμth τλ the miθrτ-mirrτr aθtuatτr

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

is, thereλτre, aητut m as θaσ ηe measured λrτm Fiμure . The τυtiθaρ θharaθterizatiτσ τλ the miθrτ-mirrτr aθtuatτr [ ] has demτσstrated ρess thaσ . d” τυtiθaρ iσsertiτσ ρτss duriσμ ON state aσd mτre thaσ d” isτρatiτσ ρτss duriσμ OFF state at . m waveρeσμth. Cτmηiσ‐ iσμ this miθrτ-mirrτr aθtuatτr with υρaσar ρeσs υairs iσ X mτduρar τυtiθaρ switθh arθhiteθ‐ tures θaσ υrτvide τυtiθaρ switθh with the maximum τυtiθaρ ρτss τλ τσρy . d”. The τυtiθaρ switθh θaσ ηe exteσded tτ X matrix with the maximum ρτss τλ . d”. The maximum ρτss λτr aσy NX matrix ηased τσ X mτduρar uσit is . + N- * . . Fτr aσ aρρτwaηρe τυtiθaρ ρτss τλ d”, λτr examυρe, the τυtiθaρ switθh matrix θaσ ηe exteσded tτ X .

Figure 29. The mic‘o-mi‘‘o‘ ac“”a“o‘ wi“h monoli“hically in“eg‘a“ed ve‘“ical mic‘o-mi‘‘o‘.

Figure 30. Ini“ial o”“-of-plane deflec“ion of mic‘o-mi‘‘o‘ a’ viewed a“ 80o “il“

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. . MEMS based D optical interconnect Oυtiθaρ ρiσπ has υrτvided a sτρutiτσ tτ ηaσdwidth ρimitatiτσ exhiηited ηy wire ρiσπ. It has ηeeσ λτuσd tτ ηe eλλeθtive wheσ the ρeσμth τλ the ρiσπ is suηstaσtiaρ deυeσdiσμ τσ the data sυeed. Oυtiθaρ ρiσπ is στw uηiφuitτus λτrm τλ iσterθτσσeθt λτr switθhiσμ στdes iσ teρeθτm‐ muσiθatiτσ σetwτrπ, aσd λτr raθπ tτ raθπ θτmmuσiθatiτσ. “s the θτmmuσiθatiτσ sυeed μτes ηeyτσd GHz, τυtiθaρ ρiσπs λτr ητard-tτ-ητard θτmmuσiθatiτσ τσ the PC” aσd θτre-tτ-θτre θτmmuσiθatiτσ τσ muρti-θτre υrτθess τσ a siσμρe θhiυ ηeθτme viaηρe sτρutiτσs στt τσρy tτ resτρve the ηaσdwidth ρimitatiτσ τλ wire iσterθτσσeθts ηut aρsτ tτ reduθe θτst aσd save υτw‐ er θτσsumυtiτσ. “s the σumηer τλ θτres iσ muρti-θτre arθhiteθture iσθreases, it is eσvisaμed that θτmmuσiθatiτσ sυeed iσ τrder τλ THz wiρρ ηe reaθhed. “ρthτuμh TSV Thrτuμh Siρiθτσ Via teθhστρτμy is used tτ reduθe the wire iσterθτσσeθt distaσθe ηetweeσ iσteμrated θirθuits iσ D staθπ tτ iσθrease ηaσdwidth, it is iσevitaηρe that τυtiθaρ ρiσπ iσ D staθπ wiρρ ηe θτst driveσ sτρutiτσ. “ σumηer τλ sτρutiτσs have ηeeσ υrτυτsed tτ θreate suθh τυtiθaρ ρiσπ. Oσe τλ these sτρutiτσs iσvτρves τυtiθaρ υrτυaμatiτσ iσ λree-sυaθe. Fτθusiσμ eρemeσts are reφuired λτr ρτw-ρτss λree sυaθe τυtiθaρ ρiσπ. Fτθusiσμ teθhσiφues ηased τσ Miθrτ-ηaρρ ρeσs [ ], λρuidiθ memηraσe ρeσs [ ], a υρaσar PDMS ρeσs [ ] aσd a υτρymer ρeσs [ ] are στt θτmυatiηρe with υρaσar waveμuides aσd reφuires seυarate assemηρy υrτθesses. Pρaσar siρiθa ρeσs υair disθussed earρier iσ this θhaυter is weρρ suited λτr suθh υurυτse. The iσteμratiτσ τλ this υρa‐ σar ρeσs iσ the D τυtiθaρ iσterθτσσeθt system has ηeeσ demτσstrated [ ]. The D τυtiθaρ iσterθτσσeθt system emυρτys a υair τλ τ miθrτ-mirrτrs iσ τrder tτ estaηρish aσ τυtiθaρ υath ηetweeσ staθπed siρiθτσ dies, as iρρustrated sθhematiθaρρy iσ Fiμure . The λaηriθatiτσ υrτθesses have ηeeσ deveρτυed tτ λτrm ητth λaθiσμ-dτwσ aσd λaθiσμ-uυ τ mi‐ θrτ-mirrτrs. The λτrmatiτσ τλ uρtra-smττth λaθiσμ-uυ τ miθrτ-mirrτrs usiσμ surλaθtaσt added ρτw θτσθeσtratiτσ TM“H has ηeeσ estaηρished [ ]. The υrτθess starts with υ-tyυe siρiθτσ waλer with υrimary λρat iσ direθtiτσ. The siρiθτσ waλer is theσ thermaρρy τxidized tτ μrτw siρiθτσ diτxide. The μrτwσ τxide is υatterσed tτ exυτse siρiθτσ surλaθe us‐ iσμ a reθtaσμuρar masπ rτtated ηy τ λrτm the υrimary λρat sτ that its edμe θaσ τrieσt iσ direθtiτσ. Perλτrmiσμ wet siρiθτσ etθh iσ surλaθtaσt added % ρτw TM“H θτσθeσtra‐ tiτσ % with suθθessive remτvaρ τλ τver-haσμiσμ τxide masπ υrτduθes uρtra-smττth τ miθrτ-mirrτr whτse surλaθe is iσ υρaσe. Fiμure a shτws the SEM θrτss-seθtiτσaρ view λτr the λaηriθated τ λaθiσμ-uυ miθrτ-mirrτr.

Figure 31. Op“ical in“e‘connec“ ’y’“em wi“h plana‘ ’ilica len’ pai‘’

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Figure 32. (a) Facing-”p 45o mic‘o-mi‘‘o‘; (b) Facing-down 45o mic‘o-mi‘‘o‘

”ased τσ the λτrmatiτσ τλ λaθiσμ-uυ τ miθrτ-mirrτrs, υhτsυhτrus diλλusiτσ τσ υ-tyυe suηstrate τσ the side where the λaθiσμ-uυ τ miθrτ-mirrτr is λτrmed, aσd eρeθtrτ-θhemiθaρ etθh stτυ teθhσiφue at υ-σ juσθtiτσ, λaθiσμ-dτwσ τ has ηeeσ reρeased[ ]. The θrτss-seθtiτσaρ view τλ the reρeased λaθiσμ-dτwσ τ miθrτ-mirrτr is shτwσ iσ Fiμure η. The λaηriθatiτσ teθhσiφues tτ λτrm λaθiσμ-uυ aσd dτwσ τ miθrτ-mirrτrs have ηeeσ mτdiλied tτ iσteμrate υρaσar siρiθa ρeσs υairs aσd U-μrττves λτr siσμρe-mτde τυtiθaρ λiηer iσsertiτσs [ , ]. Fiμure aσd shτw the mτdiλied λaηriθatiτσ υrτθess steυs λτr iσteμratiσμ υρaσar ρeσs υairs with λaθiσμ-uυ aσd λaθiσμ-dτwσ τ miθrτ-mirrτr, resυeθtiveρy.

Figure 33. Fab‘ica“ion p‘oce’’ flow fo‘ ’ilica len’ in“eg‘a“ed facing-down 45º mic‘omi‘‘o‘.

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It shτuρd ηe στted that iσ ητth λaηriθatiτσ υrτθess steυs, the thiθπ siρiθa λiρm deυτsitiτσ aσd miθrτ-maθhiσiσμ teθhσiφues are ηased τσ the disθussiτσ we had earρier iσ seθtiτσ . Iσ this θase, hτwever, the υρaσar ρeσs υair desiμσed λτr a λree-sυaθe υrτυaμatiτσ distaσθe τλ m is emυρτyed. The SEM imaμes τλ the λaηriθated tτυ die θτσsistiσμ τλ the λaθiσμ-dτwσ miθrτmirrτr aσd τσe τλ the υρaσar ρeσs υair aσd ητttτm die haviσμ λaθiσμ-uυ miθrτ-mirrτr aσd the τther υρaσar ρeσs υair are μiveσ iσ Fiμure aσd , resυeθtiveρy. Step 1: form 45° micromirror on (100) silicon surface 45° micromirrror Si substrate Step 2: metal layer deposition – Ti/Au/Cr Ti/Au/Cr layer

Step 3: graded index silica deposition by PECVD

fluorine doped thick silica (Si xO yFz) film

Step 4: amorphous silicon depostion amorphous silicon

Step 5: photolithography – pattern photoresist as a masking layer for amorphous silicon etch

photoresist Step 6: amorphous silicon etch by STS -ICP AOE system

Step 7: remove photoresist by wet or dry clean processes

Step 8: deep silica etch using STS-ICP AOE system microlens

Step 9: fiber groove etch by STS-ICP bosch process fiber groove

Step 10: expose Au reflective layer by removing Cr layer Au/Cr layer

Figure 34. Fab‘ica“ion p‘oce’’ flow fo‘ ’ilica len’ in“eg‘a“ed facing-”p 45º mic‘omi‘‘o‘.

Op“ical Fib‘e on a Silicon Chip h““p://dx.doi.o‘g/10.5772/54246

Silica planar GRIN Lens

Front 45° micromirror

Fiber groove

Figure 35. F‘on“ facing mic‘omi‘‘o‘ wi“h plana‘ ’ilica g‘aded index len’.

(a)

(b)

Figure 36. (a) SEM image of ’ilica plana‘ GRIN len’ in“eg‘a“ed wi“h facing-down 45º mic‘o-mi‘‘o‘.Fle‘ioof ’ilica pla‐ na‘; (b) back’ide view of facing-down 45º mic‘o-mi‘‘o‘

“λter λaηriθatiσμ the tτυ aσd ητttτm dies seυarateρy, they are assemηρed aσd aρiμσed τσe τσ the tτυ τλ the τther usiσμ miθrτ-υτsitiτσiσμ system. Iσυut aσd τutυut siσμρe mτde τυtiθaρ λiηers are iσserted iσtτ the U-μrττves λτrmed τσ the dies aσd ηutt-θτuυρed tτ the resυeθtive υρaσar ρeσses. The iσυut τυtiθaρ λiηer is θτuυρed tτ the υiμ-taiρed ρaser diτde sτurθe at σm waveρeσμth. The τutυut λiηer is θτuυρed tτ τυtiθaρ υτwer tτ measure the reθeived υτwer. The tτtaρ τυtiθaρ υτwer ρτss iσ the system is measured tτ ηe . d”. This is aσ imυrτvemeσt τλ mτre thaσ d” aσd demτσstrates the eλλeθtiveσess τλ the υρaσar siρiθa GRIN ρeσs iσ reduθiσμ τυtiθaρ ρτss iσ D τυtiθaρ iσterθτσσeθt systems.

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Author details “. Miθhaeρ, C.Y. Kwτπ, Md. “ρ Haλiz aσd Y.W. Xu Sθhττρ τλ Eρeθtriθaρ Eσμiσeeriσμ aσd Teρeθτmmuσiθatiτσ, UNSW, “ustraρia

References [ ] H.Rτηηiσs aσd ”.Sθhwartz, Chemiθaρ Etθhiσμ τλ Siρiθτσ-II The system HF,HNO , HC C O ,€ J. Eρeθtrτθhem. Sτθ.,vτρ. , υυ. - , . [ ] H.Muraτπa, T.Ohahi, aσd T.Sumitτmτ, Cτσtrτρρed Preλereσtiaρ Etθhiσμ Teθhστρτ‐ μy,€ iσ semiθτσduθtτr siρiθτσ , Chiθaμτ, υυ. [ ] Marθ J. Madτu, Fuσdameσtaρs τλ Miθrτλaηriθatiτσ, seθτσd editiτσ [ ] G.T.Kτvaθs, N.I.Maρuλ, aσd K.E. Petersτσ, ”uρπ Miθrτmaθhiσiσμ τλ Siρiθτσ,€ iσ υrτ‐ θeediσμs τλ the IEEE, Vτρ. , IEEE, , υυ. - . [ ] ”.Sθhwartz, aσd H.Rτηηiσs, Chemiθaρ etθhiσμ τλ Siρiθτσ-IV Etθhiσμ Teθhστρτμy,€ J.Eρeθtrτθhem. Sτθ.,Vτρ. , υυ. - , . [ ] H. Seideρ, L.Cseυreμi,“.Heuηerμer, H. ”aumμarteρ, “σisτtrτυiθ etθhiσμ τλ θrystaρ‐ ρiσe siρiθτσ iσ aρiπaρiσe sτρutiτσs. Part I. Orieσtatiτσ deυeσdeσθe aσd ηehaviτur τλ υassivatiτσ ρayers. Jτurσaρ τλ the Eρeθtrτθhamiθaρ Sτθiety , υυ. . [ ] M. Eρweσυτeπ, H.V. Jaσseσ, Siρiθτσ Miθrτmaθhiσiσμ, Camηridμe uσiversity υress. [ ] R.J.Jaθθτdiσe, Use τλ mτdiλied λree eσerμy theτrems tτ υrediθt eφuiρiηrium μrτwiσμ aσd etθhiσμ shaυes,€ Jτurσaρ τλ “υυρied Physiθs, , υυ. . [ ] Martiσ Hτλλmaσ, Saηiσe Diθπhut, aσd Edμar vτμes, Fiηer Riηητσ “ρiμσmeσt Struθ‐ tures ”ased τσ Rhτmηus Shaυed Chaσσeρs iσ Siρiθτσ,€ IEEE Phτtτσiθs Teθhστρτμy Letters, Vτρ. , Nτ. , , υυ. . [

] D.Cheσμ, M.“.Gτsaρvez,T.Hτri, K.Satτ, M.Shiπida, Imυrτvemeσt iσ smττthσess τλ aσisτtrτυiθaρρy etθhed siρiθτσ surλaθes eλλeθts τλ surλaθtaσt aσd TM“H θτσθeσtra‐ tiτσs,€ Seσsτrs aσd “θtuatτrs “ Physiθaρ, Vτρ. , , υυ. .

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] Y.W.Xu, “.Miθhaeρ, C.Y.Kwτπ, Fτrmatiτσ τλ uρtra-smττth τ miθrτmirrτr τσ siρiθτσ with ρτw θτσθeσtratiτσ TM“H aσd surλaθtaσt Teθhσiφue λτr eσρarμiσμ the truρy τ υτrtiτσ,€ Seσsτrs aσd “θtuatτrs “ Physiθaρ, Vτρ. ,υυ. .

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] Phiρiυυe Heρiσ, Maπτtτ Mita, Tariπ ”τurτuiσa, Giρηert Reyσe, aσd Hirτyuπi Fujita, Seρλ-“ρiμσed Miθrτmaθhiσiσμ Prτθess λτr Larμe-Sθaρe, Free-Sυaθe Oυtiθaρ CrτssCτσσeθts,€ Jτurσaρ τλ Liμht wave Teθhστρτμy, Vτρ. , Nτ. , , υυ. .

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[

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