This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. Investigation of low coherence interferometry techniques for biomedical applications Chow, Tzu Hao 2014 Chow, T. H. (2014). Investigation of low coherence interferometry techniques for biomedical applications. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/59219 https://doi.org/10.32657/10356/59219 Downloaded on 06 Oct 2021 11:02:09 SGT INVESTIGATION OF LOW COHERENCE INTERFEROMETRY TECHNIQUES FOR BIOMEDICAL APPLICATIONS CHOW TZU HAO CHOW TZU HAO n School of Electrical and Electronic Engineering A thesis submitted to the Nanyang Technological University in partial fulfillment of the requirement for the degree of Doctor of Philosophy 2014 To my lovely wife, Ng Hwan Teng and my dear sons, Qi Xuan and Xuan Dong. ACKNOWLEDGEMENTS The journey to complete the thesis is a long and challenging one. Without the guidance and support from many people, I would not be able to see the finish line. First and foremost, I would like to thank my supervisor, Assoc Prof Ng Beng Koon for his guidance and patience. I am very grateful for his valuable feedback and comments for the entire period. I would also like to thank Dr Sirajudeen s/o Gulam Razul for his advice on signal processing algorithms. For the area optical engineering, I wish to express my sincere thanks to Prof Colin Sheppard and Dr George Chen. They offered valuable guidance to the optical designs and imaging theories. I am appreciative of Dr Chia Tet Fatt being always available to fill in my vast gaps in botany. The advice provided by Assoc Prof Goh Wang Ling kick-started my fruitful journey. I am very fortunate to have wonderful and caring friends to support me. I would like to express my thanks to Dr Benjamin Tay Chia Meng, Dr Eddie Tan Khay Ming, Dr Lee Woei Ming, Dr Fu Chit Yaw, Dr James Kah Chen Yong, Mr Song Kin San and Dr Landobasa Tosef Mario A L Tobing. Being fellow PhD students at various time-points, they have taught me in various ways how to soldier-on during tough times and how to enjoy the fruits of labor. I am grateful for the help and guidance from the staff and friends from Photonics Research Centre. I would also like to extend my thanks to my collaborators at Changi General Hospital for their patience and time. They are Dr Eng Soh Ping, Dr Poh Wee Ting, Dr David Chin and the wonderful staff at the Histopathological department. At A*Star, Dr Allen Yeo and Dr Gideon Ho provided the vision to define the general i scope for the program. I would also like to thank my current employer, Avago Technologies and my colleagues for being supportive during the final stretch of this journey. Finally, I would like to reserve my deepest heartfelt thanks to my family members. Their unwavering support and patience have always given me hope throughout this period. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS .......................................................................................... i TABLE OF CONTENTS ............................................................................................ iii ABSTRACT ................................................................................................................ ix LIST OF FIGURES .................................................................................................... xii LIST OF TABLES ..................................................................................................... xxi ABBREVIATION ..................................................................................................... xxii Chapter 1 INTRODUCTION ................................................................................. 1 1-1 Motivation ............................................................................................... 1 1-2 Objectives ................................................................................................ 6 1-3 Originality of Thesis ................................................................................ 8 1-4 Organization of Thesis .......................................................................... 10 Chapter 2 BACKGROUND .................................................................................. 12 2-1 Fundamentals of Interferometry ............................................................ 12 2-1-1 Amplitude-splitting interferometer ....................................................... 14 2-1-2 Low coherence interferometry .............................................................. 17 2-2 Optical Coherence Tomography ........................................................... 21 2-2-1 Time-Domain OCT ............................................................................... 26 2-2-2 Fourier Domain OCT ............................................................................ 29 iii 2-3 OCT Key Parameters ............................................................................ 37 2-3-1 Axial resolution ..................................................................................... 37 2-3-1-1 Effects of dispersion mismatches .................................................... 38 2-3-1-2 Effects of polarization mismatches .................................................. 40 2-3-2 Lateral resolution ................................................................................... 44 2-3-3 Sensitivity .............................................................................................. 46 2-3-4 Dynamic range ...................................................................................... 51 2-4 Optical Techniques for Tissue Imaging ................................................ 51 2-4-1 Tissue Imaging with OCT ..................................................................... 53 2-5 Summary ............................................................................................... 57 Chapter 3 INVESTIGATION OF LCI FOR LOCALIZING THE POSITION OF OPTICALLY TRAPPED OBJECTS ................................................................. 58 3-1 Introduction ........................................................................................... 58 3-2 Principles of Optical Tweezers ............................................................. 61 3-2-1 Momentum Transfer .............................................................................. 61 3-2-2 Ray Optics ............................................................................................. 62 3-2-3 Restoration to Equilibrium Position ...................................................... 66 3-2-4 Damped Harmonic Oscillator ................................................................ 67 3-2-5 Determination of Optical Trap Stiffness ............................................... 69 3-3 Position Detection Mechanisms ............................................................ 71 3-4 LCI-Trapping Experimental Setup ........................................................ 77 iv 3-5 Results ................................................................................................... 79 3-5-1 Long Range Tracking ............................................................................ 79 3-5-2 Tracking Multiple Microspheres ........................................................... 81 3-5-3 Axial Resolution Measurement ............................................................. 83 3-5-4 Microsphere Dynamics ......................................................................... 85 3-5-5 Dual Counter-Propagating Beam Trap .................................................. 87 3-6 Discussion ............................................................................................. 90 3-7 Summary ............................................................................................... 92 Chapter 4 DETECTION OF VIRUS INFECTED ORCHIDS USING OCT .. 94 4-1 Introduction ........................................................................................... 94 4-1-1 Virus Infection in Orchids ..................................................................... 94 4-1-2 Motivation ............................................................................................. 96 4-2 Background ........................................................................................... 98 4-2-1 Structure of Orchid Leaves.................................................................... 98 4-2-2 Plant Viruses ....................................................................................... 100 4-3 Materials and Methods ........................................................................ 102 4-3-1 Optical Coherence Tomography ......................................................... 102 4-3-2 Plant Materials ..................................................................................... 105 4-4 Results ................................................................................................. 106 4-4-1 OCT Analysis ...................................................................................... 106 v 4-4-2 Histological Analysis .......................................................................... 111 4-5 Discussion ........................................................................................... 114 4-6 Summary ............................................................................................. 116 Chapter 5 DESIGN OF AN OCT PROBE AND SYSTEM FOR IN VIVO NASOPHARYNX IMAGING .................................................................................