Optical Fiber Communications [3rd ed] 9780072321012, 0-07-232101-6, 0072356804, 0072360763

A revision of the senior/graduate level text for courses dealing with the theory and application of Optical Fiber Commun

271 97 30MB

English Pages 622 Year 2000

Report DMCA / Copyright

DOWNLOAD PDF FILE

Recommend Papers

Optical Fiber Communications

437 75 5KB Read more

Optical Fiber Communications 9780136382485, 0136382487, 0136382223

This book is quite good for the beginners who want to know about fiber optics and its feature. Nevertheless, need to be

414 97 27MB Read more

Ultrahigh-Speed Optical Transmission Technology (Optical and Fiber Communications Reports) [1 ed.] 3540238786, 9783540238782, 9783540680055

This book is a detailed description of all the aspects of ultrahigh speed optical transmission technology. Ultrahigh-spe

380 18 99KB Read more

Optical Communications

449 29 342KB Read more

Polarization Mode Dispersion (Optical and Fiber Communications Reports) [1 ed.] 0387231935, 9780387231938, 9780387263076

This book contains a series of tutorial essays on polarization mode dispersion (PMD) by the leading experts in the field

385 82 4MB Read more

Polarization Mode Dispersion (Optical and Fiber Communications Reports) [1 ed.] 0387231935, 9780387231938, 9780387263076

This book contains a series of tutorial essays on polarization mode dispersion (PMD) by the leading experts in the field

404 78 4MB Read more

Polarization Mode Dispersion (Optical and Fiber Communications Reports) [1 ed.] 0387231935, 9780387231938, 9780387263076

This book contains a series of tutorial essays on polarization mode dispersion (PMD) by the leading experts in the field

356 50 4MB Read more

Plasmonic Optical Fiber Biosensors 9781630819712

147 61 31MB Read more

Free-Space Laser Communications: Principles and Advances (Optical and Fiber Communications Reports) [1 ed.] 0387286527, 9780387286525

480 69 25MB Read more

Fiber Optic Communications 9813346647, 9789813346642

This book highlights the fundamental principles of optical fiber technology required for understanding modern high-capac

100 78 14MB Read more

Optical Fiber Communications [3rd ed]
9780072321012, 0-07-232101-6, 0072356804, 0072360763

Author / Uploaded
Gerd Keiser

0 0 0
Like this paper and download? You can publish your own PDF file online for free in a few minutes! Sign Up

File loading please wait...

Citation preview

6.1

Band gap

PHYSICAL PRINCIPLES OF PHOTODIODES

Ρ

FIGURE 6-2 Conduction band

Simple energy-band diagram for a pin photodiode. Photons with an energy greater than or equal to the band-gap energy Eg can generate free electronhole pairs which act as photocurrent carriers.

Photon hv›Eg

J —Depletion region—^

η

Valence band

flow in an external circuit, with one electron flowing for every carrier pair generated. This current flow is known as the photocurrent. As the charge carriers flow through the material, some electron-hole pairs will recombine and hence disappear. On the average, the charge carriers move a distance L„ or Lp for electrons and holes, respectively. This distance is known as the diffusion length. The time it takes for an electron or hole to recombine is known as the carrier lifetime a n d is represented by τ„ and τ^, respectively. The lifetimes and the diffusiori lengths are related by the expressions Ln = {D„τ„y^

and

Lp = (DpTp)

where D„ and Dp are the electron and hole diffusion coefficients (or constants), respectively, which are expressed in units of centimeters squared per second. Optical radiation is absorbed in the semiconductor material according to the exponential law Pix) = P o ( l - e-

)

(6-1)

Here, α^(λ) is the absorption coefficient at a wavelength λ, PQ is the incident optical power level, and P{x) is the optical power absorbed in a distance x. The dependence of the optical absorption coefficient on wavelength is shown in Fig. 6-3 for several photodiode materials.'^ As the curves clearly show, depends strongly on the wavelength. Thus, a particular semiconductor material can be used only over a limited wavelength range. The upper wavelength cutoff λc is determined by the band-gap energy Eg of the material. If Eg is expressed in units of electron volts (eV), then λ^. is given in units of micrometers (µm) by he _ 1.24 λ ‚( µm) =:-=- = Eg-Eg(cW)

(6-2)

The cutoff wavelength is about 1.06µm for Si and 1.6/xm for G e . F o r longer wavelengths, the p h o t o n energy is not sufficient to excite an electron from the valence to the conduction band.

245