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Development of Highly Photosensitive Low Loss Inorganic Sol‑Gel Films for Direct Ultraviolet‑Imprinting of Planar Waveguides

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Development of Highly Photosensitive Low Loss Inorganic Sol‑Gel Films for Direct Ultraviolet‑Imprinting of Planar Waveguides This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. Development of highly photosensitive low loss inorganic sol‑gel films for direct ultraviolet‑imprinting of planar waveguides Rajni 2008 Rajni. (2008). Development of highly photosensitive low loss inorganic sol‑gel films for direct ultraviolet‑imprinting of planar waveguides. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/4113 https://doi.org/10.32657/10356/4113 Nanyang Technological University Downloaded on 04 Oct 2021 19:26:37 SGT ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Development of Highly Photosensitive Low Loss Inorganic Sol-Gel Films for Direct Ultraviolet- Imprinting of Planar Waveguides Rajni School of Electrical and Electronic Engineering A thesis submitted to the Nanyang Technological University in fulfilment of the requirement for the degree of Doctor of Philosophy 2008 ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library To My Family For affectionate support in all my endeavours........ ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Acknowledgements This is indeed a privilege and a great pleasure to express my gratitude and deep regards to my supervisor Prof. Kantisara Pita for giving me the opportunity to associate myself with the exciting academic atmosphere of photonics research group (School of Electrical and Electronics) of Nanyang Technological University (NTU) as a Doctor of Philosophy student. It will be always less whatever I say, however I express myself to honour his invaluable guidance, keen interest and encouragement throughout my research work. He encouraged me to develop my research skills and introduced me to the scientific community time to time. Despite my intruding at any hour or day into his busy schedule, he took it in a good positive attitude. I am very grateful to him, as my supervisor’s door was always open to discuss the problems. In particular, I wish to thank him from the bottom of my heart as he had shown enough patience to review my written work. I gratefully acknowledge the financial support provided by NTU in the form of research scholarship during my studies. I would also like to express my sincere thanks to Prof. Tjin Swee Chuan and Prof. Yu Siu Fung for the helpful suggestions and their input on the various topics. I thank the support of Prof. Thomas Osipowicz of National University of Singapore (NUS) for the Rutherford backscattering measurements of my samples. i ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library ACKNOWLEDGEMENTS I thank Charles K. F. Ho who introduced me to the sol-gel process and for his useful discussions that saved my many hours of self teaching nightmare. I also thank to Shuh Ying Lee for helping me in BPM simulations. Finally, I would like to mention Lipi Mohanthy, Chong Munkit, Samson Tua Halomoan Silalahi and other friends for making it comfortable to be at NTU. I also appreciate laboratory technicians Low Poh Chee, Yong Kim Lam, Debbie, Desmond and Seet Lye Ping for helping me in the laboratory experiments and Yee Yang Boey for keeping my computer happy. Last but definitely not least, I like to thank my family for their continued love, support and patience through out the years and specially my husband Rajiv Kashyap for his encouragement and support during this PhD program. Many thanks to all of you! Rajni ii ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Contents Acknowledgements ····································································································· i Contents···················································································································· iii Summary ···················································································································ix List of Abbreviations ································································································xiv List of Figures··········································································································xvi List of Tables ·······································································································xxviii Chapter 1 Introduction······································································································· 1 1.1. Motivation·······························································································1 1.2. Objective·································································································4 1.3. Major contributions of the Thesis······························································5 1.4. Organization of the Thesis········································································9 Chapter 2 Literature Review··························································································· 12 2.1. Introduction ···························································································12 2.2. Introduction to integrated photonics devices ············································13 2.3. Technologies for the photonic waveguide device fabrication ····················15 iii ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library CONTENTS 2.3.1. Conventional waveguide fabrication method ································15 2.3.2. Waveguide development by ion-implantation ·······························18 2.3.3. Waveguide development by direct electron-beam writing··············19 2.3.4. Waveguide development by direct proton-beam writing················20 2.3.5. Waveguide development by direct laser writing····························21 2.3.5.1. Self-writing waveguide fabrication technique ··············22 2.3.5.2. Direct UV-writing and UV-imprinting waveguide fabrication technique··················································24 2.4. Inorganic materials for photonic waveguide devices·································27 2.4.1. Silicate material ··········································································27 2.4.2. Doped silicate materials·······························································28 2.4.3. Germanosilicate material system··················································31 2.5. Review of germanosilicate photosensitivity ·············································32 2.5.1. Introduction of the photosensitivity of germanosilicate··················32 2.5.2. Mechanism of photosensitivity in germanosilicate ························34 2.5.2.1. Model-I: Color-Center Model ·····································34 2.5.2.2. Model-II: Stress relaxation model································36 2.5.2.3. Model-III: Densification (compaction) model ··············37 2.5.3. Complex nature of germanosilicate photosensitivity······················37 2.5.4. Enhancement techniques for germanosilicate photosensitivity ·······38 2.5.4.1. Hydrogen loading treatment········································38 2.5.4.2. CO2 laser exposure prior to UV-illumination················41 2.5.4.3. Mechanical treatment ·················································41 2.5.4.4. Annealing in reducing atmosphere·······························42 2.5.4.5. Boron co-doping ························································42 2.6. Silica-on-silicon deposition techniques····················································43 iv ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library CONTENTS 2.6.1. Sputtering process·······································································43 2.6.2. Chemical vapor deposition process ··············································44 2.6.3. Flame hydrolysis deposition process ············································45 2.6.4. Sol-gel process············································································46 2.7. Review of sol-gel process·······································································47 2.7.1. Introduction of sol-gel method·····················································47 2.7.2. Fundamentals of sol-gel process ··················································48 2.7.3. Formation of silica films by sol-gel··············································49 2.7.4. Sol-gel processing steps ······························································51 2.7.5. Various critical parameters of sol-gel reaction mechanism·············54 2.7.6. Formation of germanosilicate films by sol-gel ······························58 2.7.7. Sol-gel process limitations···························································59 2.8. Summary·······························································································59 Chapter 3 Theory of Optical Waveguides ····································································· 61 3.1. Introduction ···························································································61 3.2. Introduction to the planar slab-waveguide ···············································61 3.3. The wave equations for planar slab-waveguide ········································63 3.4. Solution for a planar slab-waveguide·······················································65
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