Optical Communication and Networks M.N. Bandyopadhyay Director National Institute of Technology (NIT) Calicut Delhi-110092 2014
OPTICAL COMMUNICATION AND NETWORKS M.N. Bandyopadhyay 2014 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-4854-7 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Mohan Makhijani at Rekha Printers Private Limited, New Delhi-110020.
To Dr. Soumendra Nath Bandyopadhyay (Son) Debendra Nath Bandyopadhyay (Grandson)
Contents Preface xiii 1 OPTICAL COMMUNICATION 1 4 1.1 Introduction 1 2 SEMICONDUCTORS AND OPTICAL FIBER 5 28 2.1 Introduction 5 2.2 Maxwell s Equation 5 2.3 Optoelectronic Interaction 5 2.4 Band Gap Energy and Photon Energy 6 2.5 Absorption Spectrum 6 2.6 Radiative Transition and Non-radiative Transition 8 2.7 Wide Band Gap Semiconductors 8 2.8 Concept of Optical Fiber 9 2.9 Optical Fiber Communication System 9 2.10 Description of Optical Fiber 10 2.11 Principle of Total Internal Reflection 11 2.12 Various Types of Optical Fibers 16 2.12.1 Definition of Modes 16 2.13 Difference between Step Index and Graded Index Fibers 17 2.14 Optical Fiber Categories 18 2.15 Types of Optical Fibers Based on Materials Used 18 2.16 Fabrication Process 19 2.16.1 External CVD Process 20 2.16.2 Vapour Phase Axial Deposition Process 21 2.16.3 Internal CVD Process 21 2.16.4 Plasma CVD Process 22 2.16.5 Multielement Glasses 23 2.16.6 Phasil System 24 v
vi Contents 2.17 Double Crucible Method 24 2.18 Rod-in-tube Procedure 25 2.19 Procedure to Drawn Fiber 26 Summary 27 Review Questions 28 3 CABLES 29 48 3.1 Optical Fiber Cables 29 3.1.1 Slotted Core Cable 30 3.1.2 Loose Fiber Bundle Cable 31 3.1.3 Loose Tube Cable 31 3.1.4 Ribbon Cable 33 3.1.5 Tightly Buffered Cable 33 3.1.6 Tightly Packed Cable 34 3.2 Properties of the Cable 35 3.3 Cable structure 35 3.4 Fiber Splices and Connectors 36 3.4.1 Types of Splices 36 3.5 Requirements of Splicing Techniques 40 3.6 Procedure for good quality splicing 41 3.7 Optical Fiber Connectors 41 3.8 Characteristic of a Good Connector 43 3.9 Splice and Connector Losses 44 3.10 Procedure for Measurement of Losses of Splices and Connectors 46 Summary 47 Review Questions 47 4 OPTICAL FIBER LOSS, SIGNAL DISTORTION AND SPECTRAL DISPERSION 49 81 4.1 Introduction 49 4.1.1 Absorption Loss 49 4.1.2 Scattering Loss 50 4.1.3 Radiative Loss 54 4.2 Distortion of Signal 55 4.3 Fiber Dispersion 56 4.3.1 Material, Chromatic or Spectral Dispersion 57 4.3.2 Waveguide Dispersion 57 4.3.3 Intermodal Dispersion or Group Delay 58 4.4 Mathematical Expression for Dispersion 60 4.4.1 Expression for Material Dispersion 60 4.4.2 Expression for Waveguide Dispersion 61 4.4.3 Polarization Dispersion 65 4.5 Dispersion for Different Light Sources 65 4.6 Fiber Dispersion 66 4.6.1 Multimode Fibers 66 4.6.2 Single Mode Fiber 67
Contents vii 4.7 Design Optimization 67 4.7.1 Refractive Index Profiles 68 4.8 Relation between Dispersion and Bandwidth 72 4.9 Dispersion Limit 73 4.10 Measurement of Information Capacity of An Optical Waveguide 76 4.10.1 Multimode Dispersion Measurement in Multimode Fibers 76 4.10.2 Intermodal or Chromatic Dispersion Measurement in Single Mode Fibers 78 4.11 Mode Coupling 79 Summary 80 Review Questions 81 5 MATHEMATICAL ANALYSIS OF OPTICAL FIBER OPERATION 82 121 5.1 Introduction 82 5.2 Mathematical Expression for Fiber 82 5.3 Mathematical Analysis of Meridional Rays 84 5.4 Mathematical Analysis of Skew Rays 86 5.5 Mathematical Analysis of Total Internal Reflection 87 5.6 Mathematical Analysis of TE and TM Waves 89 5.7 Mathematical Analysis of Propagation Constant in the Fiber 92 5.8 Calculation of V Number of the Fiber 93 5.9 Solved Problems 94 Summary 116 Review Questions 116 6 STUDY OF OPTICAL SOURCES 122 164 6.1 Introduction 122 6.2 Description of LED 123 6.3 Mathematical Analysis of LED 127 6.4 Merits and Demerits of LEDs 131 6.5 Properties and Uses of LED 131 6.6 Description of Laser 132 6.6.1 Structures of Laser Diode 133 6.6.2 Special Types of Structure of Index Guided Laser 137 6.6.3 Operation of Double Heterostructure GaAs Laser Diode and InP Laser Diode 138 6.6.4 Modes of Laser Diode 138 6.6.5 Patterns of Mode 140 6.6.6 Fabry Pérot Resonator 140 6.7 Distributed Feedback Laser 141 6.8 Distributed Bragg Reflector Laser 142 6.9 Coupled Cavity Lasers 143 6.10 Quantum Well Laser 143 6.11 Optical Amplifiers 145 6.11.1 Fiber Amplifiers 145 6.11.2 Stimulated Raman Scattering Fiber Amplifier 148
viii Contents 6.11.3 Stimulated Brillouin Scattering Fiber Amplifier 149 6.11.4 Comparative Analysis between Different Optical Amplifiers 149 6.12 Uses of Optical Amplifier 150 6.12.1 Amplification of Power 151 6.12.2 Use as Preamplifier 151 6.12.3 Application in In-line Amplifier 151 6.12.4 Application of Optical Amplifiers in Optical Switch 151 6.12.5 Application in Nonlinear Processing 152 6.12.6 Application in Soliton Transmission 152 6.13 Mathematical Analysis and Problems Related to Optical Source 152 6.14 Noise in Optical Amplifiers 160 6.15 Noise Source of Laser 161 6.16 Comparative Study between LED and LASER Diode 162 Summary 163 Review Questions 163 7 STUDY OF OPTICAL DETECTORS 165 200 7.1 Introduction 165 7.2 Photodetector Characteristics 165 7.3 Classification of Photodetectors 167 7.3.1 Conventional PN Junction Photodiode 167 7.3.2 PIN Photodetector 168 7.3.3 Avalanche Photodiode 171 7.3.4 Photoconductor 174 7.3.5 Phototransistor 175 7.3.6 Photodarlington Transistor 175 7.4 Noise in Photodetector 176 7.4.1 Dark Current Noise 176 7.4.2 Shot Noise 177 7.4.3 Thermal Noise 177 7.5 Noise in Avalanche Photodetector 177 7.6 Temperature Effect on Avalanche Photodetector 178 7.7 Mathematical Analysis 178 7.8 Applications of Phototransistors 196 7.9 Metal semiconductor metal (MSM) Photodiode 197 7.10 Coherent Technique for Detection 198 7.11 Preamplifier 199 Summary 199 Review Questions 200 8 BASIC PRINCIPLES OF OPTICAL COMMUNICATION SYSTEM 201 218 8.1 Introduction 201 8.2 Point-to-Point Transmission Link 201 8.3 Analog and Digital Communication 203 8.4 Coherent and Incoherent Detection 205 8.5 Photon Counting 205
Contents ix 8.6 Modulation Code 205 8.7 Merits of Optical Communication 206 8.8 Description of Optical Communication 206 8.9 Components of Optical Communication 207 8.9.1 Bidirectional WDM 208 8.9.2 Performance Criteria of WDM Technique 208 8.10 Multiple Access in Optical Communication 209 8.11 Switching in Communication Network 209 8.11.1 Switching Criteria 209 8.12 Architecture of Switching 211 8.12.1 Multiple Stage Switches 212 8.12.2 Two-dimensional Switches 212 8.12.3 Scalable Switches 213 8.13 Switching in Optical Communication 214 8.14 Topology in Optical Communication 214 8.15 Optical Domain Analysis 215 8.16 Major Applications of Light Wave Technology 216 8.17 Sensitivity 217 Summary 217 Review Questions 217 9 TRANSMITTERS AND RECEIVERS 219 234 9.1 Introduction 219 9.2 Transmitter for Optical Communication 219 9.3 LED Transmitter 220 9.3.1 Digital LED Transmitter 222 9.4 Laser Transmitter 223 9.4.1 Analog Laser Transmitter 225 9.4.2 Digital Laser Transmitter 226 9.5 Resemblence and Difference between Analog and Digital Transmitters 226 9.6 Design of Transmitter 227 9.7 Design of Receiver 227 9.8 Equivalent Circuit of Optical Receiver 231 9.9 Equivalent Circuit of Pre-amplifier 232 Summary 234 Review Questions 234 10 OPTICAL FIELD ACCESS 235 274 10.1 Introduction 235 10.2 Field Access Techniques 235 10.2.1 Tapering 236 10.2.2 Polishing 236 10.2.3 Etching 236 10.2.4 Cleaving 236 10.2.5 Bending 237
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