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  • 1.Fiber-Optic Communications Systems, Third Edition. Govind P. AgrawalCopyright 2002 John Wiley & Sons, Inc.ISBNs: 0-471-21571-6 (Hardback); 0-471-22114-7 (Electronic)

2. Fiber-OpticCommunication SystemsThird EditionGOVIND E?AGRAWALThe Institute of OpticsUniversity of RochesterRochester:NY623WILEY- INTERSCIENCEA JOHN WILEY & SONS, INC., PUBLICATION 3. Designations used by companies to distinguish their products are oftenclaimed as trademarks. In all instances where John Wiley & Sons, Inc., isaware of a claim, the product names appear in initial capital or ALLCAPITAL LETTERS. Readers, however, should contact the appropriatecompanies for more complete information regarding trademarks andregistration.Copyright 2002 by John Wiley & Sons, Inc. All rights reserved.No part of this publication may be reproduced, stored in a retrieval systemor transmitted in any form or by any means, electronic or mechanical,including uploading, downloading, printing, decompiling, recording orotherwise, except as permitted under Sections 107 or 108 of the 1976United States Copyright Act, without the prior written permission of thePublisher. Requests to the Publisher for permission should be addressed tothe Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue,New York, NY 10158-0012, (212) 850-6011, fax (212) 850-6008,E-Mail: PERMREQ@WILEY.COM.This publication is designed to provide accurate and authoritativeinformation in regard to the subject matter covered. It is sold with theunderstanding that the publisher is not engaged in rendering professionalservices. If professional advice or other expert assistance is required, theservices of a competent professional person should be sought.ISBN 0-471-22114-7This title is also available in print as ISBN 0-471-21571-6.For more information about Wiley products, visit our web site atwww.Wiley.com. 4. For My Parents 5. ContentsPrefacexv1 Introduction11.1 Historical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . .1 1.1.1 Need for Fiber-Optic Communications . . . . . . . . . . . .2 1.1.2 Evolution of Lightwave Systems . . . . . . .. . . . . . . . .41.2 Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 1.2.1 Analog and Digital Signals . . . . . . . . . .. . . . . . . . .8 1.2.2 Channel Multiplexing . . . . . . . . . . . .. . . . . . . . . 11 1.2.3 Modulation Formats . . . . . . . . . . . . .. . . . . . . . . 131.3 Optical Communication Systems . . . . . . . . . . .. . . . . . . . . 151.4 Lightwave System Components . . . . . . . . . . .. . . . . . . . . 16 1.4.1 Optical Fibers as a Communication Channel . . . . . . . . . . 17 1.4.2 Optical Transmitters . . . . . . . . . . . . .. . . . . . . . . 17 1.4.3 Optical Receivers . . . . . . . . . . . . . . . . . . . . . . . . 18Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Optical Fibers 232.1 Geometrical-Optics Description . . . . . . . . . . . . . . . . . . . . 23 2.1.1 Step-Index Fibers . . . . . . . . . . . . . . . . . . . . . . . . 24 2.1.2 Graded-Index Fibers . . . . . . . . . . . . . . . . . . . . . . 262.2 Wave Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.2.1 Maxwells Equations . . . . . . . . . . . . . . . . . . . . . . 29 2.2.2 Fiber Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.2.3 Single-Mode Fibers . . . . . .. . . . . . . . . . . . . . . . . 342.3 Dispersion in Single-Mode Fibers . . . . . . . . . . . . . . . . . . . 37 2.3.1 Group-Velocity Dispersion . . . . . . . . . . . . . . . . . . . 38 2.3.2 Material Dispersion . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.3 Waveguide Dispersion . . . .. . . . . . . . . . . . . . . . . 41 2.3.4 Higher-Order Dispersion . . . . . . . . . . . . . . . . . . . . 42 2.3.5 Polarization-Mode Dispersion. . . . . . . . . . . . . . . . . 432.4 Dispersion-Induced Limitations . . . . . . . . . . . . . . . . . . . . 45 2.4.1 Basic Propagation Equation .. . . . . . . . . . . . . . . . . 46vii 6. viiiCONTENTS2.4.2 Chirped Gaussian Pulses . . . . . . . . . . . . . . . . . . . . 472.4.3 Limitations on the Bit Rate . . . . . . . . . . . . . . . . . . . 502.4.4 Fiber Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 53 2.5 Fiber Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552.5.1 Attenuation Coefcient . . .. . . . . . . . . . . . . . . . . . 552.5.2 Material Absorption . . . . . . . . . . . . . . . . . . . . . . 562.5.3 Rayleigh Scattering . . . . . . . . . . . . . . . . . . . . . . . 572.5.4 Waveguide Imperfections . . . . . . . . . . . . . . . . . . . . 58 2.6 Nonlinear Optical Effects . . . . . .. . . . . . . . . . . . . . . . . . 592.6.1 Stimulated Light Scattering . . . . . . . . . . . . . . . . . . 592.6.2 Nonlinear Phase Modulation. . . . . . . . . . . . . . . . . . 642.6.3 Four-Wave Mixing . . . . .. . . . . . . . . . . . . . . . . . 66 2.7 Fiber Manufacturing . . . . . . . .. . . . . . . . . . . . . . . . . . 672.7.1 Design Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 672.7.2 Fabrication Methods . . . . . . . . . . . . . . . . . . . . . . 682.7.3 Cables and Connectors . . . . . . . . . . . . . . . . . . . . . 70 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743 Optical Transmitters 773.1 Basic Concepts . . . . . . . . . . . . . . . . .. . . . . . . . . . . .77 3.1.1 Emission and Absorption Rates . . . .. . . . . . . . . . . .78 3.1.2 pn Junctions . . . . . . . . . . . . . .. . . . . . . . . . . .81 3.1.3 Nonradiative Recombination . . . . . . . . . . . . . . . . . .83 3.1.4 Semiconductor Materials . . . . . . . .. . . . . . . . . . . .843.2 Light-Emitting Diodes . . . . . . . . . . . . . . . . . . . . . . . . .87 3.2.1 PowerCurrent Characteristics . . . . .. . . . . . . . . . . .87 3.2.2 LED Spectrum . . . . . . . . . . . . . . . . . . . . . . . . .89 3.2.3 Modulation Response . . . . . . . . .. . . . . . . . . . . .90 3.2.4 LED Structures . . . . . . . . . . . . . . . . . . . . . . . . .913.3 Semiconductor Lasers . . . . . . . . . . . . . .. . . . . . . . . . . .92 3.3.1 Optical Gain . . . . . . . . . . . . . . . . . . . . . . . . . .93 3.3.2 Feedback and Laser Threshold . . . . . . . . . . . . . . . . .94 3.3.3 Laser Structures . . . . . . . . . . . . . . . . . . . . . . . .963.4 Control of Longitudinal Modes . . . . . . . . . . . . . . . . . . . . .99 3.4.1 Distributed Feedback Lasers . . . . . .. . . . . . . . . . . . 100 3.4.2 Coupled-Cavity Semiconductor Lasers. . . . . . . . . . . . 102 3.4.3 Tunable Semiconductor Lasers . . . . . . . . . . . . . . . . . 103 3.4.4 Vertical-Cavity Surface-Emitting Lasers. . . . . . . . . . . . 1053.5 Laser Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 106 3.5.1 CW Characteristics . . . . . . . . . . . . . . . . . . . . . . . 107 3.5.2 Small-Signal Modulation . . . . . . . .. . . . . . . . . . . . 110 3.5.3 Large-Signal Modulation . . . . . . . .. . . . . . . . . . . . 112 3.5.4 Relative Intensity Noise . . . . . . . . . . . . . . . . . . . . 114 3.5.5 Spectral Linewidth . . . . . . . . . . . . . . . . . . . . . . . 1163.6 Transmitter Design . . . . . . . . . . . . . . .. . . . . . . . . . . . 118 7. CONTENTS ix3.6.1 SourceFiber Coupling . . . . . . . . . . . . . . . . . . . . . 1183.6.2 Driving Circuitry . . . . . . . . . . . . . . . . . . . . . . . . 1213.6.3 Optical Modulators . . . .. . . . . . . . . . . . . . . . . . . 1223.6.4 Optoelectronic Integration. . . . . . . . . . . . . . . . . . . 1233.6.5 Reliability and Packaging . . . . . . . . . . . . . . . . . . . 124 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1274 Optical Receivers 1334.1 Basic Concepts . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 133 4.1.1 Detector Responsivity . . . . . .. . . . . . . . . . . . . . . 133 4.1.2 Rise Time and Bandwidth . . . .. . . . . . . . . . . . . . . 1354.2 Common Photodetectors . . . . . . . . . . . . . . . . . . . . . . . . 136 4.2.1 pn Photodiodes . . . . . . . . .. . . . . . . . . . . . . . . 137 4.2.2 pin Photodiodes . . . . . . . .. . . . . . . . . . . . . . . 138 4.2.3 Avalanche Photodiodes . . . . . .. . . . . . . . . . . . . . . 142 4.2.4 MSM Photodetectors . . . . . . . . . . . . . . . . . . . . . . 1484.3 Receiver Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 4.3.1 Front End . . . . . . . . . . . . .. . . . . . . . . . . . . . . 149 4.3.2 Linear Channel . . . . . . . . . . . . . . . . . . . . . . . . . 150 4.3.3 Decision Circuit . . . . . . . . . . . . . . . . . . . . . . . . 152 4.3.4 Integrated Receivers . . . . . . . . . . . . . . . . . . . . . . 1534.4 Receiver Noise . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 155 4.4.1 Noise Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 156 4.4.2 pin Receivers . . . . . . . . . .. . . . . . . . . . . . . . . 158 4.4.3 APD Receivers . . . . . . . . . .. . . . . . . . . . . . . . . 1594.5 Receiver Sensitivity . . . . . . . . . . . .. . . . . . . . . . . . . . . 162 4.5.1 Bit-Error Rate . . . . . . . . . . . . . . . . . . . . . . . . . . 162 4.5.2 Minimum Received Power . . . . . . . . . . . . . . . . . . . 164 4.5.3 Quantum Limit of Photodetection. . . . . . . . . . . . . . . 1674.6 Sensitivity Degradation . . . . . . . . . . . . . . . . . . . . . . . . . 168 4.6.1 Extinction Ratio . . . . . . . . . . . . . . . . . . . . . . . . 168 4.6.2 Intensity Noise . . . . . . . . . .. . . . . . . . . . . . . . . 169 4.6.3 Timing Jitter . . . . . . . . . . .. . . . . . . . . . . . . . . 1714.7 Receiver Performance . . . . . . . . . . .. . . . . . . . . . . . . . . 174Problems . . . . . . . . . . . . . . . . . . . .. . . . . .