Progress in Optomechatronics: Proceedings of the 20th International Symposium on Optomechatronic Technology (ISOT 2019), India [1st ed.] 9789811564666, 9789811564673

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Springer Proceedings in Physics 249

Indrani Bhattacharya Yukitoshi Otani Philippe Lutz Sudhir Cherukulappurath   Editors

Progress in Optomechatronics Proceedings of the 20th International Symposium on Optomechatronic Technology (ISOT 2019), India

Springer Proceedings in Physics Volume 249

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Indrani Bhattacharya Yukitoshi Otani Philippe Lutz Sudhir Cherukulappurath •

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Editors

Progress in Optomechatronics Proceedings of the 20th International Symposium on Optomechatronic Technology (ISOT 2019), India

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Editors Indrani Bhattacharya University of Calcutta Kolkata, West Bengal, India University of Eastern Finland Joensuu, Finland Philippe Lutz FEMTO-ST The Université de Franche-Comté Besancon, France

Yukitoshi Otani Center for Optical Research and Education Utsunomiya University Utsunomiya, Tochigi, Japan Sudhir Cherukulappurath Goa University Goa, India

ISSN 0930-8989 ISSN 1867-4941 (electronic) Springer Proceedings in Physics ISBN 978-981-15-6466-6 ISBN 978-981-15-6467-3 (eBook) https://doi.org/10.1007/978-981-15-6467-3 © Springer Nature Singapore Pte Ltd. 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

This volume contains a series of technical papers presented in 20th International Symposium on Optomechatronic Technology, ISOT 2019, held in Resort Marinha Dourada, Goa, India from November 11–13, 2019. ISOT 2019 was organized jointly by University of Calcutta, Kolkata, India, and Goa University, Goa, India, in technical support and collaboration with International Society of Optomechatronics, ISOM, and financially assisted by Science and Engineering Research Board, SERB, of Department of Science and Technology, DST, Government of India. ISOT 2019 was a three-day conference consisted of plenary, invited, and contributory oral and poster sessions. All contributory submissions are peer reviewed. Interactive sessions were conducted to foster networking and formation of well-focused collaborations among research groups and industry sessions. In the symposium, discussion and dissemination had taken place on research topics related to adaptive optics, optomechanics, machine vision, tracking and control, image-based micro-/nano-manipulation, control engineering for optomechatronics, optical metrology, optical sensors and light-based actuators, optomechatronics for astronomy and space applications, optical-based inspection and fault diagnosis, polarization sensing and imaging, micro-/nano-optomechanical systems (MOEMS), optofluidics, optical assembly and packaging optical and vision-based manufacturing, processes, monitoring, and control optomechatronics systems in bio- and medical technologies (such as optical coherence tomography, OCT based systems, endoscopes and optical-based medical instruments). The editors express their sincere thanks and gratitude to Prof. Dr. Kallol Bhattacharya, Professor, Department of Applied Optics and Photonics (AOP), University of Calcutta, the convener and technical chair of ISOT 2019, for his sincere effort to make this meeting possible in India for the first time as well as to make it successful along with Dr. Sudhir Cherakulappurath., Assistant Professor, of Department of Physics, University of Goa, India, who acted as joint convener of the conference.

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The editors also wish to acknowledge Prof. Dr. Rajib Chakraborty Professor, Department of AOP, University of Calcutta for his active support and Dr. Kanik Palodhi, to render his valuable service as the treasurer and a contributor of this book. Sincere thanks and gratitude to very active and enthusiast students of Department of Applied Optics and Photonics, University of Calcutta, along with the students of the Department of Physics, Goa University for their excellent support and cooperation to make the conference successful. The editors wish to acknowledge and convey sincere thanks to all authors who have contributed to this volume along with the presenters, reviewers, and session chairs for their participation, support, and valuable contribution to make the symposium successful. Joensuu, Finland

Indrani Bhattacharya Editor

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Astronomical Adaptive Optics at the Indian Institute of Astrophysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sridharan Rengaswamy, Ravinder Banyal, Sreekanth Vallapureddy, and Hemanth Pruthvi Local Temperature Monitoring Method of a Rotor Using Near-Infrared Fiber Bragg Grating . . . . . . . . . . . . . . . . . . . . . . . . Rita Abboud, Hani Al Hajjar, Alejandro Ospina, Jad Abou Chaaya, Youssef Zaatar, and Frédéric Lamarque

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Blood Oxygenation Monitoring from Human Lips by Using Diffuse Reflectance Spectroscopy . . . . . . . . . . . . . . . . . . . Ajay Kumar and Rajesh Kanawade

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A Photonic Crystal Ring Resonator with Circular Air Slot to Achieve High Quality Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . Akash Kumar Pradhan, Anis Kumar Kabiraj, and Mrinal Sen

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III–V Nitrides and Graphene SPR Biosensor for Hemoglobin Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Mohanty and B. K. Sahoo

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Theoretical Implications for Surface Plasmon Resonance Based on Microstructured Optical Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . D. K. Sharma and S. M. Tripathi

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Analyzing Thermal Stress Distribution in Metallic Components Using Digital Holography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gaurav Dwivedi and Raj Kumar

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Development of Chipping Inspection System of Cutting Knife Edge Using Spatial Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hibiki Shiga, Takanori Yazawa, Tatsuki Otsubo, and Megumu Kuroiwa

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Fiber Optic Sensor for Acid Detection: An Efficient and Fast Approach for Concentrated Sulphuric Acid Detection . . . . . . . . . . Karvan Kaushal, Ajay Kumar, Dnyandeo Pawar, Kamlesh Kumar, and Rajesh Kanawade

10 Optically Induced Transparency in Two Cavity System . . . . . . . . . Kousik Mukherjee and Paresh Chandra Jana

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11 Exhaled Breath CH4 and H2S Sensing Using Mid-IR Quantum Cascade Laser (QCL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mithun Pal and Manik Pradhan

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12 Fourier Optics Analysis of Phase and Amplitude Grating with Uniform Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prashant Povel Dwivedi

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13 A Low-Cost Pathological Gait Detection System in Multi-Kinect Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saikat Chakraborty, Rishabh Mishra, Anurag Dwivedi, Tania Das, and Anup Nandy

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14 Generation of Triangular Pulse by a Highly Nonlinear Normally Dispersive Chalcogenide Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Somen Adhikary, Binoy Krishna Ghosh, and Mousumi Basu 15 Optical Design for Directed Infrared Counter Measure with Spiral Scanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Vishal Bhushan, P. K. Sharma, and Amitava Ghosh 16 Study of Increase in Temperature of Solar Modules Using Hot Mirror . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Arnab Panda, Joydeep Chatterjee, Tathagata Sarkar, Anirban Jyoti Ray, and Kanik Palodhi 17 Digital Holo-Microscopy of Reflecting Surface Using In-Line Laser Interferometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Chandan Sengupta, Sanjukta Sarkar, and K. Bhattacharya 18 Theoretical Insight of Plasmonic Resonance in WS2–Graphene Based Hetrostructure with Ag–Au Bimetal for Optical Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Jayeta Banerjee and Mina Ray 19 Quantitative Estimation of Spatially Varying Refractive Index in Optical Fibre Preform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Tania Das and Kallol Bhattacharya 20 Selective Edge Enhancement Using Walsh Filters . . . . . . . . . . . . . . 143 Joydeep Chatterjee, Semanti Chakraborty, and Kanik Palodhi

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21 Measurement of Load on a Mobile LCD Screen Using Moiré Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Rajarshee Roy, Joydeep Chatterjee, Semanti Chakraborty, and Kanik Palodhi 22 Refractive Index Measurements of Liquids Using Moiré Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Shruti De, Joydeep Chatterjee, Semanti Chakraborty, and Kanik Palodhi 23 Supercontinuum Laser Based Photoacoustic Spectroscopic Sensor for Acetylene Gas Detection . . . . . . . . . . . . . . . . . . . . . . . . 165 Bintomol Baby, Ramya Selvaraj, Nilesh J. Vasa, and Jobin K. Antony

Editors and Contributors

About the Editors Indrani Bhattacharya is presently working as a Post-doctoral researcher in Institute of Photonics, University of Eastern Finland, Joensuu. She was previously associated with Prof. Ayan Banerjee of Light Matter Interaction Lab, Indian Institute of Science Education and Research, IISER, Kolkata and Prof. Vasudevan Lakshminarayanan of School of Optometry and Vision Science, University of Waterloo, Canada as a freelance postdoctoral researcher. She has completed her B.Sc. with Hons. in Physics and M.Sc.(Tech.) in Applied Physics with specialization in Optics and Opto-electronics from University of Calcutta, India. She came back to academia to do her Ph.D. in Technology from Department of Applied Optics and Photonics, University of Calcutta after a long period of almost 20 years serving in industry working in fibre optics. Her research areas include Diffractive Optics, Biomimetics, Optical Tweezers, Point Spread Function Engineering, In-Vivo and In-Vitro Biomedical Applications, Optical Fibre Sensors. She is the current Chair of Steering Committee members of International Society of Optomechatronic Technology, ISOT, a member of Optical Society of India and serving as the Scholarship Committee Member of SPIE. She is the Convener and Organizer of several International Conferences in Optics and Photonics and Editor of Springer Proceedings in Physics of Volumes 166, 194, 233 and another in progress and has published several research articles.

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Yukitoshi Otani is a professor at Department of Optical Engineering and a vice director of Center for Optical Research and Education (CORE), Utsunomiya University, Japan. He received his master’s degree from Tokyo University of Agriculture and Technology in 1990 and his doctor’s degree from the University of Tokyo in 1995. After working for a brief period at HOYA Corp., he was an associate professor at Tokyo University of Agriculture and Technology until 2010. He was a visiting professor at College of Optical Sciences, the University of Arizona from 2004 to 2005. He joined the CORE from April 2010. His current interests include polarization engineering and optomechatoronics. He is a fellow of SPIE from 2010, an associate editor of OSA continuum. Philippe Lutz is Professor at the University of Franche-Comté, Besancon, France. He is the Director of the Control science and Micromechatronic Systems Research department of the Research Institute FEMTO-ST (www.femto-st.fr). He was the Director of the Ph.D. graduate school of Engineering science and Microsystems (400 Ph.D. students) from 2011 to 2017, and he is currently the head of the Doctoral College of University of Bourgogne Franche-Comté. His research activities are focused on the design and control of micro-nanosystems, micro-nanogrippers and micro-nanorobots. His main contributions for optomechatronics is the use of micro robotic means for realizing nanophotonic devices. Member of the Steering Committee of ISOT, he chaired it during 2 years. He authored over 100 refereed publications (55 in high standard journals), received awards, served as Associate/Technical Editor for the IEEE T-ASE and IEEE/ASME TMECH, is senior editor for IEEE CASE and IROS, and is member of the IEEE RAS Committee on Micro-Nano Robotics.

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Dr. Sudhir Cherukulappurath is a UGC-Assistant Professor in the Physics Department of Goa University, India. He completed his M.Sc. in Physics and M.Tech., in Optoelectronics and Laser Technology from Cochin University of Science and Technology. After a brief tenure as Optical engineer in Deposition Sciences Inc., USA, he pursued research in the field of nonlinear optics at the Laboratoire POMA, University of Angers, France. He obtained Ph.D. from University of Angers, France. He was postdoctoral fellow at the University of Bourgogne, France and ICFO, Barcelona. He was postdoctoral associate in the Department of Electrical and Computer Engineering of the University of Minnesota. He has more than 15 years of research experience in the field of photonics, nano optics and plasmonics. He has published more than 25 research articles and is currently a member of the American Chemical Society. His main research areas include plasmonics, surface-enhanced Raman spectroscopy and optical tweezers.

Contributors Rita Abboud CNRS, FRE 2012 Laboratoire Roberval, Sorbonne Universités, Université de Technologie de Compiègne (UTC), Compiègne, France; Applied Physics Laboratory, Faculty of Science, Lebanese University, Jdeidet, Lebanon Somen Adhikary Department of Physics, IIEST Shibpur, Howrah, West Bengal, India Hani Al Hajjar CNRS, FRE 2012 Laboratoire Roberval, Sorbonne Universités, Université de Technologie de Compiègne (UTC), Compiègne, France Jobin K. Antony Rajagiri School of Engineering and Technology, Rajagiri Valley, Kakkanad, Kochi, India Bintomol Baby Rajagiri School of Engineering and Technology, Kakkanad, Kochi, India Jayeta Banerjee Department of Applied Optics and Photonics, Acharya Prafulla Chandra Roy Siksha Prangan, University of Calcutta (Technology Campus), Salt Lake, Kolkata, India Ravinder Banyal Indian Institute of Astrophysics, Bangalore, Karnataka, India

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Editors and Contributors

Mousumi Basu Department of Physics, IIEST Shibpur, Howrah, West Bengal, India K. Bhattacharya Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India Kallol Bhattacharya Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India Vishal Bhushan Instruments Dehradun, Uttarakhnad, India

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Development

Establishment,

Jad Abou Chaaya Applied Physics Laboratory, Faculty of Science, Lebanese University, Jdeidet, Lebanon Saikat Chakraborty Machine Intelligence and Bio-motion Research Lab, Department of Computer Science and Engineering, National Institute of Technology Rourkela, Rourkela, Odisha, India Semanti Chakraborty Department of Electronics and Engineering, Amity University, New Town, Kolkata, India

Communication

Joydeep Chatterjee Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India Tania Das Department of Electronics and Communication Engineering, Heritage Institute of Technology, Kolkata, West Bengal, India Shruti De Department of Applied Optics and Photonics, University of Calcutta, Kolkata, India Anurag Dwivedi Department of Computer Science and Engineering, National Institute of Technology Sikkim, Sikkim, India Gaurav Dwivedi CSIR-Central Scientific Instruments Organisation, Chandigarh, India; Academy of Scientific & Innovative Research (AcSIR), CSIR-CSIO, Chandigarh, India Prashant Povel Dwivedi Department of Electronics and Communication Engineering, Manipal University Jaipur, Jaipur, Rajasthan, India Amitava Ghosh Instruments Dehradun, Uttarakhnad, India

Research

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Development

Establishment,

Binoy Krishna Ghosh Department of Physics, IIEST Shibpur, Howrah, West Bengal, India Paresh Chandra Jana Department of Physics and Technophysics, Vidyasagar University, Midnapore, India Anirban Jyoti Ray Greenovera India Private Limited, Taltala, Kolkata, West Bengal, India

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Anis Kumar Kabiraj Department of Electronics Engineering, IIT(ISM) Dhanbad, Dhanbad, India Rajesh Kanawade CSIR-Central Scientific Instruments Organisation, Sector 30-C, Chandigarh, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India Karvan Kaushal CSIR-Central Scientific Instruments Organisation, Sector 30-C, Chandigarh, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India Ajay Kumar CSIR-Central Scientific Instruments Organisation, Sector 30-C, Chandigarh, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India Raj Kumar CSIR-Central Scientific Instruments Organisation, Chandigarh, India; Academy of Scientific & Innovative Research (AcSIR), CSIR-CSIO, Chandigarh, India Kamlesh Kumar CSIR-Central Scientific Instruments Organisation, Sector 30-C, Chandigarh, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India Megumu Kuroiwa Graduate School of Engineering, Nagasaki University, Nagasaki, Japan Frédéric Lamarque CNRS, FRE 2012 Laboratoire Roberval, Sorbonne Universités, Université de Technologie de Compiègne (UTC), Compiègne, France Rishabh Mishra Department of Computer Science and Engineering, National Institute of Technology Sikkim, Sikkim, India G. Mohanty Department of Physics, Lovely Professional University, Phagwara, Punjab, India Kousik Mukherjee Department of Physics and Technophysics, Vidyasagar University, Midnapore, India Anup Nandy Machine Intelligence and Bio-motion Research Lab, Department of Computer Science and Engineering, National Institute of Technology Rourkela, Rourkela, Odisha, India Alejandro Ospina CNRS, FRE 2012 Laboratoire Roberval, Sorbonne Universités, Université de Technologie de Compiègne (UTC), Compiègne, France Tatsuki Otsubo Graduate School of Engineering, Nagasaki University, Nagasaki, Japan Mithun Pal Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata, India

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Kanik Palodhi Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India Arnab Panda Department of Applied Optics and Photonics, University of Calcutta, JD-2, Sector III, Salt Lake, Kolkata, India Dnyandeo Pawar College of Materials Science and Engineering, Shenzhen University, Shenzhen, China Akash Kumar Pradhan Department of Electronics Engineering, IIT(ISM) Dhanbad, Dhanbad, India Manik Pradhan Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Salt Lake, JD Block, Sector III, Kolkata, India; Technical Research Centre, S. N. Bose National Centre for Basic Sciences, Salt Lake, JD Block, Sector III, Kolkata, India Hemanth Pruthvi Leibniz-Institut für Sonnenphysik, Freiburg, Germany Mina Ray Department of Applied Optics and Photonics, Acharya Prafulla Chandra Roy Siksha Prangan, University of Calcutta (Technology Campus), Salt Lake, Kolkata, India Sridharan Rengaswamy Indian Institute of Astrophysics, Bangalore, Karnataka, India Rajarshee Roy Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India B. K. Sahoo Department of Physics, National Institute of Technology, Raipur, India Sanjukta Sarkar Department of Electronics and Communication, TechnoIndia, Saltlake City, Kolkata, India Tathagata Sarkar Macquarie-Conergy Solar Platform, Singapore, Singapore Ramya Selvaraj Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India Mrinal Sen Department of Electronics Engineering, IIT(ISM) Dhanbad, Dhanbad, India Chandan Sengupta Department of Applied Optics and Photonics, University of Calcutta, Salt Lake, Kolkata, India D. K. Sharma Center for Lasers and Photonics, Indian Institute of Technology Kanpur, Kanpur, India P. K. Sharma Instruments Research and Development Establishment, Dehradun, Uttarakhnad, India

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Hibiki Shiga Graduate School of Engineering, Nagasaki University, Nagasaki, Japan S. M. Tripathi Center for Lasers and Photonics, Indian Institute of Technology Kanpur, Kanpur, India; Department of Physics, Indian Institute of Technology Kanpur, Kanpur, India Sreekanth Vallapureddy Indian Institute of Astrophysics, Bangalore, Karnataka, India Nilesh J. Vasa Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India Takanori Yazawa Graduate School of Engineering, Nagasaki University, Nagasaki, Japan Youssef Zaatar Applied Physics Laboratory, Faculty of Science, Lebanese University, Jdeidet, Lebanon

Chapter 1

Astronomical Adaptive Optics at the Indian Institute of Astrophysics Sridharan Rengaswamy, Ravinder Banyal, Sreekanth Vallapureddy, and Hemanth Pruthvi

Abstract Astronomical Adaptive Optics (AO) technology enables real time diffraction-limited imaging and spectroscopy with high sensitivity from groundbased telescopes. It is achieved by using corrective optical elements in the path of the light beam before the final image is formed. The Indian Institute of Astrophysics is deliberating on building new large solar and stellar telescopes, namely the National Large Solar Telescope (NLST) and the National Large Optical Telescope (NLOT) equipped with AO. In view of this, an AO program has been initiated at IIA, with the primary objective of generating expertise in the field of astronomical adaptive optics by developing and demonstrating AO systems in existing small telescopes. In this paper, we start with an overview of astronomical adaptive optics and elaborate on the AO related activities carried out at IIA.

1.1 Introduction Ever since the invention of the telescopes, humanity has been striving to have a clear view of the heavens by building large ground-based telescopes. It was not up until the mid twentieth century astronomers realized that the Earth’s atmospheric turbulence distorts the light, making the image formed by a large telescope to wander randomly, and therefore appear enlarged, at the focal plane. The resultant angular resolution—typically a second of arc in diameter irrespective of the diameter of the telescope—is poorer than the theoretical resolution due to diffraction alone. Mr. Hemanth Pruthvi was affiliated with IIA till April 2019. S. Rengaswamy (B) · R. Banyal · S. Vallapureddy Indian Institute of Astrophysics, Koramangala II Block,Bangalore, Karnataka 560034, India e-mail: [email protected] R. Banyal e-mail: [email protected] H. Pruthvi Leibniz-Institut für Sonnenphysik, Schöneckstraße 6, Freiburg 79104, Germany © Springer Nature Singapore Pte Ltd. 2020 I. Bhattacharya et al. (eds.), Progress in Optomechatronics, Springer Proceedings in Physics 249, https://doi.org/10.1007/978-981-15-6467-3_1

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The image formed by a telescope is sharp when its diameter is comparable to the typical size of the atmospheric turbulent eddies. It gets blurred when the size of the atmospheric turbulent eddies is much smaller than the diameter of the telescope. The phenomenon is widely known as the atmospheric seeing. In the year 1953, the American astronomer Babcock [1] came up with a revolutionary idea of compensating for the atmospheric seeing in real time, thereby giving birth to what has now grown as the adaptive optics technology. He showed, experimentally, albeit with certain limitations, that the schlieren pattern observed at the objective of the telescope due to atmospheric turbulent eddies could be electrically transferred to alter the surface tension of the oil covering a mirror so that the light reflected by this oil covered mirror mimics the shape of the original distortion. When this operation is done at a sufficiently fast rate substantial improvement in the image quality could be achieved. The technology was immediately adopted by the US military forces leading to the first demonstration of the adaptive optics technology on a 1.6 m telescope at Halaekala in Hawaii in 1982. It was soon realized that the technique will be restricted only to bright objects and an artificial star would have to be created to measure the distortions, giving rise the birth of Laser Guide Star (LGS) adaptive optics in 1989 with a 1.5 m telescope at Starfire Optical Range [2]. Astronomers started developing adaptive optics systems in the early 90s. The technology has been further advanced and refined to such an extent that the modern adaptive optics corrected images from ground-based adaptive optics systems are comparable to those with the space-based telescopes. Figure 1.1 shows the images of the planet Neptune taken with the VLT’s state of the art ground-based adaptive optics system and that with the Hubble Space Telescope. Although these image are not simultaneous and thus contain different surface features, they exhibit similar resolutions.

Fig. 1.1 Images of the planet Neptune taken with the Very Large Telescope and the Hubble Space telescope. Credit ESO/P. Weilbacher (AIP)/NASA, ESA, and M. H. Wong and J. Tollefson (UC Berkeley)

1 Astronomical Adaptive Optics at the Indian Institute of Astrophysics

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In the recent years, adaptive optics technology has been applied to diverse fields such as vision science and cellular-biology. The major breakthrough in vision science is the 3-D imaging of the human retina. It is also used in surgery. It has also been demonstrated in confocal laser scanning microscopes. New image-based aberration sensing schemes (as against Shack-Hartmann wave-front sensors used in astronomy) have been developed [3]. In what follows, we restrict ourselves to the astronomical adaptive optics. In Sect. 1.2 we briefly describe the various components of astronomical adaptive optics. In Sect. 1.3 we describe the adaptive optics program carried out at IIA and highlight a few milestones.

1.2 Adaptive Optics Components Any adaptive optics system would generally consist of a wave-front sensor—device which measures the wave-front distortion caused by the Earth’s atmospheric turbulence, a wave-front corrector—a mirror (mounted on an optomechanical system) whose surface can be changed dynamically to mimic the distorted wave-front at high speed and a control computer which basically acts an interface unit between the wave-front sensor and the corrector, converting the wave-front sensor data to a format suitable for the corrector. A fraction of the light from the star is used by the wave-front sensor to measure the distortions when the starlight is bright. A nearby bright star is used when the starlight is faint. This nearby bright star is commonly known as the natural guide star. An intrinsic limitation in using the natural guide stars is the lack of availability of such stars in all parts of the sky. This limitation is overcome by generating artificial stars known as laser guide stars—which are basically laser beam focused at certain heights of the atmosphere acting as beacon to aid the wave-front sensing. There are two types of laser guide stars, one is the Raleigh beacon which is due to the scattering of air molecules at a height of about 10 km and the other is the sodium beacon which is due to excitation of sodium atoms at a height of ∼ 95 km. The latter estimates the wave-front distortions better than the former as it samples wave-fronts from a larger atmospheric volume than that of the former. Nevertheless, both these systems do not exactly reproduce the distortions that would have been measured with a natural guide star because they are located at a finite height in the atmosphere (as against the plane wave-front from natural guide stars). Laser guide stars often lead to incorrect estimation of the global tilt of the wave-front. In the case of solar adaptive optics [4], solar surface features such as the solar granulation, sunspots, pores are used as reference to measure the wave-front distortions.

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1.2.1 Wave-Front Sensing The most commonly used wave-front sensor is the Shack-Hartmann wave-front sensor (SHWFS). It consists of an array of micro-lenses of identical focal length. The lenses form an array of spots at their focal plane when the plane wave-front incident on them has no distortions. The spots are displaced from their original position when the incident plane wave-front has atmospherically-induced distortions. The magnitude of the displacement of the spots is proportional to the local slope of distorted wave-front over the lenses. The global wave-front shape is determined from these local slopes. Another variety of wave-front sensor is the curvature sensor [5]. It is based the principle that the difference of extra-focal intensities is proportional to the local curvature of the wave-front. Such wave-front senors are easy to calibrate as the wave-front sensor data directly gives the curvature without any need for conversion. In the recent years, pyramid wave-front sensors [6] are also used. They consist of a relay lens and an oscillating pyramidal shaped prism, capable of forming four pupil images on a single detector containing the wave-front slope information. Unlike the SHWFS, the wave-front distortions are measured at the pupil plane in a pyramid sensor. In a closed-loop operation, wave-front sensors measure the residual wave-front distortions.

1.2.2 Wave-Front Correction Wave-front correctors are generally mirrors whose surface shape can be deformed to match the distorted wave-fronts. There are two types, one with thin continuous face sheet whose shape can be altered by actuators attached to their back surface and the other with segmented mirrors with actuators on their back. Typically, the number of actuators are of the order of (D/r0 )2 where D is the telescope diameter and r0 is the atmospheric coherence diameter. They are manufactured with different technologies, viz; stacked array deformable mirrors, bimorph deformable mirrors, voice-coil actuator deformable mirrors and membrane deformable mirrors [7].

1.2.3 Real-Time Computation The real-time computation is usually done in a computer. The basic tasks involve acquiring images from the sensing camera at a fast rate, estimating the local wavefront slopes or local curvatures and transforming that information to a set of voltages to be applied to the actuators of the wave-front corrector. The voltages are applied following suitable controllers (Proportional, Integrator and Differential) that try to minimize the difference between actual and the currently estimated wave-fronts.

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When applied to large telescopes (or when the ratio of the telescope diameter to the atmospheric coherence diameter is more than 10), the computational time can be minimized by using dedicated hardware (Field Programmable Gate Arrays).

1.3 Adaptive Optics Program at the Indian Institute of Astrophysics The Indian Institute of Astrophysics (IIA) is deliberating on building a large solar telescope—The National Large Solar Telescope [8], and a large stellar telescope— The National Large Optical Telescope [9, 10]. These large telescopes will certainly be equipped with the adaptive optics technology. As none of the currently operating telescopes have adaptive optics technology with them, it is imperative that necessary expertise in astronomical adaptive optics is generated in-house before embarking on such large projects. Consequently, an adaptive optics program has been initiated at IIA [11] with the aim of developing and demonstrating adaptive optics systems on existing small telescopes. While earlier attempts [12, 13] have been restricted mostly to the laboratory experiments on various aspects of adaptive optics, current efforts are focused at on-sky demonstrations of adaptive optics systems. As mentioned earlier, the effect of the atmospheric seeing is manifested at the image plane by the random wandering of the image (image motion) and the image blurring [14]. The image motion is a result of the global tilt of the distorted wavefront. The global wave-front tilt—the linear term in the polynomial decomposition of the distorted wave-front—forms the major component of the wave-front distortion due to the atmospheric turbulence [15]. Thus, the wave-front tilt correction becomes the first step in an adaptive optics system. It is achieved by measuring the relative shift between consecutive images at the focal plane and converting this information into appropriate voltage signals that could drive piezo-actuator controlled fast steering mirrors (FSM) positioned either at the re-imaged pupil plane or in the converging beam before the focus, in two orthogonal directions with a typical speed of 0.1– 1 kHz. Such a correction minimizes the stroke required for the deformable mirror which is used at the re-imaged pupil plane to correct for the higher (than tilt) order wave-front distortions. In general, the corrections by the FSM and the deformable mirrors are simultaneous but independent of each other.

1.3.1 Solar Adaptive Optics It has been planned to demonstrate solar adaptive optics system on the existing solar tower telescope at Kodaikanal Observatory [16]. It is primarily meant for high angular resolution imaging and high resolution sepctroscopy of solar features. It has a twomirror(fused quartz of 60 cm diameter) coelostat system which directs the sunlight

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vertically down to the one end of a 60 m long underground tunnel. Another 60 cm diameter quartz mirror redirects the sunlight horizontally inside the tunnel onto a 38 cm diameter achromatic doublet objective lens placed near the entrance of the tunnel. This doublet forms a 34 cm diameter image of the sun at the entrance of high resolution spectrograph located at distance of 36 m from the objective.

1.3.1.1

Image Stabilization System Setup

Figure 1.2 shows the schematic of the optical setup used to demonstrate the wavefront tilt correction. The f/95 beam from the objective is reflected off by the tip/tilt mirror. It is an 1-in. flat glued onto a piezo-electric actuator based tip/tilt stage by Piezosystemjena. The stage has an associated 2-channel controller that takes analog input voltage in the range of 0 to 10 V, amplifies by a factor of 15 and applies to the actuators with a bias of −20 V. It can induce tilts of up to ±4 milli-radians. The dichroic beam splitter passes the long wavelength light to the back-end instrument and reflects the short wavelength light to the re-imaging system consisting of a relay lens, neutral density filters and a 100Å broadband filter centered at 540 nm. The detector is an sCMOS camera from ANDOR, capable of recording a 128 × 128 pixels image at 563 frames per second. The computer has an Intel i5 3470 3.2 GHz processor, operating in 64 bit, Windows 7 operating system. It acts as an interface between the tip/tilt sensor (detector) and the piezo-electric actuator.

sunlight

cMOS detector

computer

Imaging objective

re−imaging optics

f/95 beam

tip/tilt mirror

Dichroic beam−splitter

backend Instrument

folding mirror

Fig. 1.2 The Schematic of the optical/mechanical/electronic setup used in the solar tip/tilt correction system. Tip/tilt mirror is an 1-in. flat glued to piezo-electric actuator. The image motion deduced from the detector frames is used to feed back that information to the tip/tilt mirror to stabilize the image

1 Astronomical Adaptive Optics at the Indian Institute of Astrophysics

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Calibration and Data Processing

At the beginning of each observing run, the system is calibrated. It involves estimation incremental voltages that need to be applied to the piezoelectric actuators for an observed image shift in x and y directions. This is easily achieved as follows: A f/95 beam from the Sun is used to cast the shadow of an aperture onto the detector. A series of voltages is applied to the actuators sequentially, one actuator at a time, and the corresponding position of the spot on the detector is noted. Plots of applied voltages vs the centroid positions (x and y positions on the detector) of the spot are obtained for each actuator. The slopes obtained these plots (two actuators, two positions, so totally four slopes) map the incremental voltages applied to the actuators to the image shifts observed at the detector plane. Inversion of the 2 × 2 matrix containing the slopes (known as calibration matrix) generates a another 2×2 matrix known as the control matrix. The elements of this control matrix are multiplied with observed x and y shifts to estimate the incremental voltages to be applied to the actuators. After the calibrations, image stabilization observations are started. A portion of the solar image of size ∼ 14 arc-sec2 corresponding to 128 × 128 pixels on the detector is recorded sequentially at 563 frames per second. The first image is considered as a reference image and the consecutive images (also known as current images) are cross-correlated with the first image to obtain the relative shifts between them. The shift vectors are converted into incremental voltage vectors using the control matrix estimated previously through the calibration. The voltage vectors are applied to the piezo-electric actuators using a digital PID controller. The reference image itself is changed once in a few seconds to account for the intrinsic changes in the solar features with time. Prior to the cross-correlation, both the reference and current images are dark subtracted, gain calibrated and multiplied by a 2-d Hanning window to prevent the spectral leakage error in the Fourier domain. The images are also subjected to an optional bi-linear surface fit subtraction before correlation when they exhibit large intensity gradients (typical of a large sunspot). We have developed a FFTW based cross-correlation algorithm and optimized it well for the speed.

1.3.1.3

Results

The left and the right panels of the Fig. 1.3 show the image motion without and with tip/tilt correction, and the corresponding Fourier power spectra, respectively. The image motion without tip/tilt correction is cotemporaneous with that of image motion with tip/tilt correction, as it was estimated from the knowledge of voltage applied to the actuators and the calibration matrix. We find that the image motion has been reduced to a large extent, leading to an decrease in the residual rms image motion by a factor of ≈25. This is also reflected in in the Fourier power spectra as a reduction in the power at low frequencies. The two power spectra merge at 110 Hz, which is the system bandwidth.

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Fig. 1.3 Left: The image motion along two orthogonal axes without (dark line) and with (grey line) tilt correction. The rms image motion has been reduced by a factor of 25. Right: Corresponding power spectra of image motion. Power at low frequencies has considerably reduced. The two power spectra merge at 110 Hz, which corresponds to the system bandwidth

1.3.2 Stellar Adaptive Optics It has been planned to demonstrate the stellar adaptive system on the new 1.3 m Bhattacharya Telescope [17] of the Vainu Bappu Observatory located at Kavalur near Jawadhi Hills at an altitude of 700 m [78◦ 49 14 E,12◦ 34 29 N]. It is a RitcheyChrétien telescope with a f/8 beam. It has three instrument ports. It is equipped with a 2k×2k camera for direct imaging and a 1k×1k camera that allows fast readouts with short exposures. The atmospheric turbulence parameters for this site have been established from short exposure images obtained over a period of two years [17].

1.3.2.1

Image Stabilization System Setup

Figure 1.4 shows the tip/tilt correction system attached to one of the side ports of the telescope. The image formed by the f/8 beam of the telescope is re-imaged on to the sensing and the imaging cameras using two achromatic lenses with field-of-views of 40 ×40 and 1 ×1 respectively. The tip/tilt mirror– a 1-inch flat glued onto a piezo actuator stage from the Physik Instrumente (PI)—is placed at the re-imaged pupil plane. The sensing camera is used to capture the images at fast rates up to 290 frames per second. The imaging camera is capable of recording images with long exposures taking advantage of the fact that image motion as a blurring mechanism has been minimized by the system through appropriate feedback mechanism. 1.3.2.2

Data Processing

The image motion is measured as the shift in the centroid positions of the consecutive images recorded by the sensing camera. Unlike the solar case, the tip/tilt stage used for stellar images has an in-built strain gauge that helps to achieve closed-loop operations

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Fig. 1.4 The Schematic of tip/tilt correction system at one of the side ports of the telescope. The image formed by the telescope is re-imaged onto a sensing camera, and, on to an imaging camera simultaneously with the help of two achromatic doublets.The tip/tilt mirror is a 1-inch flat glued onto a piezo actuator stage from the Physik Instrumente (PI). It is placed at the re-imaged pupil plane

although with a reduced bandwidth [18]. In our case, this is further increased with the addition of a software based PID controller. The software for running the system has been developed suing National Instruments’ LabView platform. The software has a master and slave loops which work independently [19].

1.3.2.3

Results

The left panel of Fig. 1.5 shows the image motion with tip/tilt correction (closedloop) and without tip/tilt correction (open-loop). Clearly, the rms image motion has reduced considerably. The power spectra of these image motions, shown on the right panel, exhibit considerable reduction of the power at low frequencies. The effective bandwidth of the system is found to be about 26 Hz. These motions were recorded at the sensing camera. The effect of tip/tilt correction is also seen clearly on the imaging detector, where relatively long exposure images have been recorded. A comparison of the images with and without tip/tilt correction is shown on the bottom left panel of Fig. 1.6. The right panel of Fig. 1.6 shows the observed increase in the angular resolution (ratio of the equivalent widths) is comparable to what is to be expected theoretically.

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Fig. 1.5 Left: The plot of closed-loop (blue) and open-loop image motions (orange) along the horizontal and the vertical axes of the imaging sensor recorded successively after a negligible time interval. The rms image motion has reduced by a factor of 14 in the closed-loop. Right: The corresponding power spectra merge at about 26 Hz which defines the bandwidth of the system

Fig. 1.6 Left: Increase in the peak brightness of components of a binary star system with and without tip/tilt correction (surface plots (top) and scaled intensity images (bottom) clearly indicates good performance of the tip/tilt system. A factor of 2.8 increase in the brightness has been observed. Right: A theoretical plot of the ratio of equivalent widths of the images without and with tip/tilt correction; The measured ratio of six of the observed targets have been over-plotted (in orange). It indicates that observed ratios are comparable to what is to be expected theoretically

1.4 Summary After a brief introduction to the astronomical adaptive optics, we have described the goals of IIA’s adaptive optics program. So far, we have successfully demonstrated and completed the tip/tilt correction both on a solar telescope and on a stellar telescope. The residual image motions have been reduced to about a tenth of the diffraction limited point spread function in the case of solar tip/tilt correction system. In the case of the stellar tip/tilt correction system, we have reduced the rms image motion by a factor of 14, increased the peak brightness by a factor of 2.8 and improved the resolution by 57%.

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References 1. H.W. Babcock, The possibility of compensating astronomical seeing. Publ. Astron. Soc. Pac. 65, 229 (1953) 2. R.Q. Fugate, D.L. Fried, G.A. Ameer, B.R. Boeke, S.L. Browne, P.H. Roberts, R.E. Ruane, G.A. Tyler, L.M. Wopat, Measurement of atmospheric wavefront distortion using scattered light from a laser guide-star. Nature 353(6340), 144–146 (1991) 3. N. Stockton, From cosmology to biology, SPIE Professional, 20–24 (April–June 2019) 4. T. Rimmele, J. Marino, D. Schmidt, G.Taylor, F. Wöger, Solar adaptive optics: challenges and new developments, in Imaging and Applied Optics (Optical Society of America, 2013), p. OM1A.1 5. F. Roddier, Curvature sensing and compensation: a new concept in adaptive optics. Appl. Opt. 27, 1223–1225 (1988) 6. R. Ragazzoni, Pupil plane wavefront sensing with an oscillating prism. J. Mod. Opt. 43(2), 289–293 (1996) 7. P. Madec, Overview of deformable mirror technologies for adaptive optics, in Imaging and Applied Optics 2015 (Optical Society of America, 2015), AOTh2C.1 8. https://www.iiap.res.in/nlst/ 9. P. Parihar, T.K. Sharma, A. Surendran, P.M.M. Kemkar, Dadul, U. Stanzin, G.C. Anupama, Characterization of sites for Indian large optical telescope project. J. Phys. Conf. Ser. 595, 012025 (2015) 10. https://astron-soc.in/asi2019/workshop2 11. R. Sridharan, R. Banyal, Roadmap for adaptive optics program at Indian institute of astrophysics. Internal document, March 2016, IIA, Bengaluru 12. V. Chinnappan, A New Approach to Stellar Image Correction for Atmospherically Degraded Images. Ph.D. Thesis (Bangalore University, Bangalore, 2006) 13. J.P. Lancelot Chellaraj Thangadurai, Wavefront Sensing for Adaptive Optics. Ph.D. Thesis (Bangalore University, Bangalore, 2007) 14. F. Roddier, The effects of atmospheric turbulence in optical astronomy, Progress in Optics, vol. 19, pp. 281–376 (Elsevier, 1981) 15. D.L. Fried, Statistics of a geometric representation of wavefront distortion. J. Opt. Soc. Am. 55, 1427–1435 (1965) 16. M.K.V. Bappu, Solar physics at Kodaikanal. Sol. Phys. 1, 151–156 (1967) 17. R.V. Sreekanth, R.K. Banyal, R. Sridharan, A. Selvaraj, Measurements of atmospheric turbulence parameters at vainu bappu observatory using short-exposure CCD images. Res. Astron. Astrophys. 19, 074 (2019) 18. G. Schitter, R.W. Stark, A. Stemmer, Sensors for closed-loop piezo control: strain gauges versus optical sensors. Meas. Sci. Technol. 13, N47 (2002) 19. R.V. Sreekanth, R.K. Banyal, R.S.P.U. Kamath, A. Selvaraj, Development of image motion compensation system for 1.3 m telescope at vainu bappu observatory. Res. Astron. Astrophys. 20(1), 12 (2019)

Chapter 2

Local Temperature Monitoring Method of a Rotor Using Near-Infrared Fiber Bragg Grating Rita Abboud, Hani Al Hajjar, Alejandro Ospina, Jad Abou Chaaya, Youssef Zaatar, and Frédéric Lamarque Abstract This article proposes a temperature monitoring method that is able to get the local variation of temperature in several positions of the rotor of an electrical machine during its rotation. The measurement principle uses a structured Polymer Optical Fiber Bragg Grating (POFBG) sensor. The existing methods estimates the temperature based on the external casing or hot spots. The aim of the proposed method is to monitor the temperature of the rotor during its operation in order to detect early thermal aging of electrical machines. The proposed contactless measurement concept and implementation into an academic rotating machine are described. Then, optical modeling of the POFBG is realized and the optical heating system is calibrated. Finally, experimental setup is carried out to make possible the temperature measurements.

2.1 Introduction The global warming is due to the high consumption of primary sources of energy. In fact, one of the primary sources of energy is the petroleum source. In the next decades, the primary sources of energy will be replaced progressively by secondary renewable sources of energy produced by solar cells, wind or marine turbines. This is called the energy transition. The consumption of petroleum energy is very high in many fields especially in the transportation systems. Therefore, in automotive industry, energy transition from petrol powered engines to performing electrical machines is required. In fact, the energy transition involves a very strong use of electrical machines. According to the IEA source [1], electrical motors represent R. Abboud (B) · H. Al Hajjar · A. Ospina · F. Lamarque CNRS, FRE 2012 Laboratoire Roberval, Sorbonne Universités, Université de Technologie de Compiègne (UTC), 60203 Compiègne, France e-mail: [email protected] R. Abboud · J. A. Chaaya · Y. Zaatar Applied Physics Laboratory, Faculty of Science, Lebanese University, PoBox 90656, Jdeidet, Lebanon © Springer Nature Singapore Pte Ltd. 2020 I. Bhattacharya et al. (eds.), Progress in Optomechatronics, Springer Proceedings in Physics 249, https://doi.org/10.1007/978-981-15-6467-3_2

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between 43 and 46% of all global electricity consumption. In this new era, electrical machines occupy a main position. This change in primary source of energy (oil to electric) will be accompanied by the integration of new smart electrical systems that are efficient and compact. Better performance of electrical components is required since the electrification will widely attack a lot of systems inside the vehicle such as on board computers. Therefore, the temperature of these components should be monitored due to the heating problems.

2.1.1 Importance of Motor Temperature Monitoring in Electrical Machine In this new era, the integration of rotating electrical machines and compact electrical systems (computer, phone) into mechanical systems leads to the problems of hot temperature spots and thermal evacuation. In the transportation system domain, the loss of magnetization appears in the permanent magnet machines and the electrical insulators and the magnetic materials heating problems appear with the temperature increase in the other types of machines. Nowadays, in the classical design of electrical machines, thermal analysis should be considered in the initial design, control and monitoring of electrical machines. The measurement of local temperature especially in the rotor is important for several reasons: – It helps access the predictive temperature information, which have a direct influence on the lifetime of the electrical machine components (insulators of conductors, magnets, etc.). – It also protects the machine by stopping its operation due to a heat peak. Besides, localizing the hot spots inside the machine will allow the development of appropriate cooling systems. – It helps developing the machine performance: the knowledge of the overheating problems in these points, can give information on heat losses in different location such as the rotor and stator, which helps improve the energy efficiency of electrical motors and generators. – In addition, it helps optimizing the control of the machine such as the identification of the variation of the parameters as a function of temperature. Therefore, the localization of the hot spots can allow rapid monitoring and diagnosis technique.

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2.1.2 Approaches for Measuring Temperature in the Literature Numerous approaches for temperature measurement are described in the literature. The measurement of local temperature of any motor drive system, especially inside the rotor, offers several benefits including diagnostics, protection and extending lifetime of the electrical machine components. For a long time ago, the electrical industry has relied on the use of thermocouples, thermistors, infrared sensors (point measurement), infra-red cameras (temperature field) and the use of a model with localized semi-empirical constants for measuring the temperature in the rotor. However, these approaches suffer from huge limitations such as susceptibility to electromagnetic interference when used in harsh environment [2]. They are complex and expensive systems because of the installation of the recovery system, either by slip rings connected by brushes to the temperature reading system, or via a wireless radio link. The determination of the emissivity of the different surfaces composing the rotor is also a problem for non-contact temperature measurement systems [3]. Moreover, certain models have the problem of the determination of the heat exchange coefficients (mainly conduction and convection) [4].

2.1.3 Advantages of Using Fiber Bragg Gratings (FBGs) The material properties of glass and plastic are function of temperature, pressure, vibration and strain. Thereby, it is not surprising to find that an optical waveguide itself is sensitive to its environment and its cladding’s refractive index as well. Over the past 20 years, FBGs were researched principally for sensor applications as the refractive index of a waveguide is function of temperature, humidity and strain. FBG is gaining a strong interest among researchers due to their applications in numerous highly active fields such as biomedical sensing, respiration monitoring, structural health monitoring, civil engineering, aeronautics, railways systems and nuclear environments [5–8]. Temperature sensing using FBG is gaining wide application in electrical machine due to its advantages over other temperature sensors. It has the following properties: – Immunity to electromagnetic interference (EMI) (no electrical current flowing at the sensing point), – Small size and low weight for easy integration, – Safe (no explosion when used in harsh environment), – Distributed sensing capabilities and ability to resist in harsh environments [9], – A single fibre is used to measure several temperature positions using wavelength division multiplexing (WDM).

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Therefore, using FBG sensors is a good solution to monitor rotors during their operation in order to detect early thermal aging of electrical machines. It has the advantage of decreasing the installation cost and the number of copper wires. This paper describes a new approach that uses a specific optical temperature sensor (FBG) for measuring temperature in different points of a rotor of an electric machine during its operation, unlike what currently exists by measuring the average value of the temperature using a thermal camera, thermocouples, thermistors or platinum probes. This sensor allows local and/or distributed measurements on the area. Fiber Bragg Gratings (FBGs) were mainly used for sensor applications. The sensing principle is based on the change of the refractive index of the grating as a function of temperature, humidity or strain [10]. Among the existing works, few of them deal with the FBG sensors taking into account temperature monitoring into the rotor of the electrical machines. The integration of FBG in high power (MW) and large scales (meters) electrical machines (p.e. hydro-generators) is much easier than small ones (low power, small sizes). Many works address the FBG temperature sensors in high power electrical machines. Hudon et al. have measured rotor temperature of field windings of hydro-generators using FBG sensors [11, 12]. Werneck et al. monitored temperature variations, with FBGs, of the 216 MW UHE-Samuel Hydro-electric power generator which operates at 95 °C at full load [13]. Hind et al. were limited in temperature range (