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

Fiber-Optic

Communication Systems

Third Edition

GOVIND E?AGRAWAL The Institute of Optics University of Rochester Rochester:NY

WILEY-

623 INTERSCIENCE

A JOHN WILEY & SONS, INC., PUBLICATION

For My Parents

Contents

Preface

Since the publication of the first edition of this book in 1992, the state of the art of fiber-optic communication systems has advanced dramatically despite the relatively short period of only 10 years between the first and third editions. For example, the highest capacity of commercial fiber-optic links available in 1992 was only 2.5 Gb/s. A mere 4 years later, the wavelength-division-multiplexed (WDM) systems with the total capacity of 40 Gb/s became available commercially. By 2001, the capacity of commercial WDM systems exceeded 1.6 Tb/s, and the prospect of lightwave systems operating at 3.2 Tb/s or more were in sight. During the last 2 years, the capacity of transoceanic lightwave systems installed worldwide has exploded. Moreover, sev- eral other undersea networks were in the construction phase in December 2001. A global network covering 250,000 km with a capacity of 2.56 Tb/s (64 WDM channels at 10 Gb/s over 4 fiber pairs) is scheduled to be operational in 2002. Several conference papers presented in 2001 have demonstrated that lightwave systems operating at a bit rate of more than 10 Tb/s are within reach. Just a few years ago it was unimaginable that lightwave systems would approach the capacity of even 1 Tb/s by 2001. The second edition of this book appeared in 1997. It has been well received by the scientific community involved with lightwave technology. Because of the rapid ad- vances that have occurred over the last 5 years, the publisher and I deemed it necessary to bring out the third edition if the book were to continue to provide a comprehensive and up-to-date account of fiber-optic communication systems. The result is in your hands. The primary objective of the book remains the same. Specifically, it should be able to serve both as a textbook and a reference monograph. For this reason, the em- phasis is on the physical understanding, but the engineering aspects are also discussed throughout the text. Because of the large amount of material that needed to be added to provide com- prehensive coverage, the book size has increased considerably compared with the first edition. Although all chapters have been updated, the major changes have occurred in Chapters 6–9. I have taken this opportunity to rearrange the material such that it is bet- ter suited for a two-semester course on optical communications. Chapters 1–5 provide the basic foundation while Chapters 6–10 cover the issues related to the design of ad- vanced lightwave systems. More specifically, after the introduction of the elementary concepts in Chapter 1, Chapters 2–4 are devoted to the three primary components of a fiber-optic communications—optical fibers, optical transmitters, and optical receivers. Chapter 5 then focuses on the system design issues. Chapters 6 and 7 are devoted to the advanced techniques used for the management of fiber losses and chromatic dis-

xv

xvi PREFACE

persion, respectively. Chapter 8 focuses on the use of wavelength- and time-division multiplexing techniques for optical networks. Code-division multiplexing is also a part of this chapter. The use of optical solitons for fiber-optic systems is discussed in Chap- ter 9. Coherent lightwave systems are now covered in the last chapter. More than 30% of the material in Chapter 6–9 is new because of the rapid development of the WDM technology over the last 5 years. The contents of the book reflect the state of the art of lightwave transmission systems in 2001. The primary role of this book is as a graduate-level textbook in the field of optical communications. An attempt is made to include as much recent material as possible so that students are exposed to the recent advances in this exciting field. The book can also serve as a reference text for researchers already engaged in or wishing to enter the field of optical fiber communications. The reference list at the end of each chapter is more elaborate than what is common for a typical textbook. The listing of recent research papers should be useful for researchers using this book as a reference. At the same time, students can benefit from it if they are assigned problems requiring reading of the original research papers. A set of problems is included at the end of each chapter to help both the teacher and the student. Although written primarily for graduate students, the book can also be used for an undergraduate course at the senior level with an appropriate selection of topics. Parts of the book can be used for several other related courses. For example, Chapter 2 can be used for a course on optical waveguides, and Chapter 3 can be useful for a course on optoelectronics. Many universities in the United States and elsewhere offer a course on optical com- munications as a part of their curriculum in electrical engineering, physics, or optics. I have taught such a course since 1989 to the graduate students of the Institute of Optics, and this book indeed grew out of my lecture notes. I am aware that it is used as a text- book by many instructors worldwide—a fact that gives me immense satisfaction. I am acutely aware of a problem that is a side effect of an enlarged revised edition. How can a teacher fit all this material in a one-semester course on optical communications? I have to struggle with the same question. In fact, it is impossible to cover the entire book in one semester. The best solution is to offer a two-semester course covering Chapters 1 through 5 during the first semester, leaving the remainder for the second semester. However, not many universities may have the luxury of offering a two-semester course on optical communications. The book can be used for a one-semester course provided that the instructor makes a selection of topics. For example, Chapter 3 can be skipped if the students have taken a laser course previously. If only parts of Chapters 6 through 10 are covered to provide students a glimpse of the recent advances, the material can fit in a single one-semester course offered either at the senior level for undergraduates or to graduate students. This edition of the book features a compact disk (CD) on the back cover provided by the Optiwave Corporation. The CD contains a state-of-the art software package suitable for designing modern lightwave systems. It also contains additional problems for each chapter that can be solved by using the software package. Appendix E provides more details about the software and the problems. It is my hope that the CD will help to train the students and will prepare them better for an industrial job. A large number of persons have contributed to this book either directly or indirectly. It is impossible to mention all of them by name. I thank my graduate students and the

WILEY SERIES IN MICROWAVE AND OPTICAL ENGINEERING

KAI CHANC, Editor Texas A&M University

FIBER-OPTIC COMMUNICATION SYSTEMS, Third Edition l Govind P. Agrawal COHERENT OPTICAL COMMUNICATIONS SYSTEMS l Silvello Betti, Ciancarlo De Marchis and Eugenio lannone HIGH-FREQUENCY ELECTROMAGNETIC TECHNIQUES: RECENT ADVANCES AND APPLICATIONS l Asoke K. Bhattacharyya COMPUTATIONAL METHODS FOR ELECTROMAGNETICS AND MICROWAVES l Richard C. Booton, /r. MICROWAVE RING CIRCUITS AND ANTENNAS l Kai Chang MICROWAVE SOLID-STATE CIRCUITS AND APPLICATIONS l Kai Chang RF AND MICROWAVE WIRELESSSYSTEMS l Kai Chang RF AND MICROWAVE CIRCUIT AND COMPONENT DESIGN FOR WIRELESS SYSTEMS l Kai Chang, lnder Bahl, and Vijay Nair DIODE LASERSAND PHOTONIC INTEGRATED CIRCUITS l Larry Coldren and Scott Corzine RADIO FREQUENCY CIRCUIT DESIGN l W. A/an Davis and Krishna Agarwal MULTICONDUCTOR TRANSMISSION-LINE STRUCTURES: MODAL ANALYSIS TECHNIQUES l

1. A. Brand80 Faria PHASED ARRAY-BASED SYSTEMS AND APPLICATIONS l Nick Fourikis FUNDAMENTALS OF MICROWAVE TRANSMISSION LINES l Ion C. freeman OPTICAL SEMICONDUCTOR DEVICES l Mitsuo Fukuda MICROSTRIP CIRCUITS l Fred Cardiol HIGH-SPEED VLSI INTERCONNECTIONS: MODELING, ANALYSIS, AND SIMULATION l A. K. Coel FUNDAMENTALS OF WAVELETS: THEORY, ALGORITHMS, AND APPLICATIONS l laideva C. Coswami and Andrew K. Chan ANALYSIS AND DESIGN OF INTEGRATED CIRCUIT ANTENNA MODULES l K. C. Cupta and Peter S. Ha// PHASED ARRAY ANTENNAS l R. C. Hansen HIGH-FREQUENCY ANALOG INTEGRATED CIRCUIT DESIGN l Ravender Goyal (ed.) MICROSTRIP FILTERSFOR RF/MICROWAVE APPLICATIONS l jia-Sheng Hong and M. /. Lancaster MICROWAVE APPROACH TO HIGHLY IRREGULAR FIBER OPTICS l Huang Hung-Chia NONLINEAR OPTICAL COMMUNICATION NETWORKS l Eugenio lannone, Francesco Matera, Antonio Mecozzi, and Marina Settembre FINITE ELEMENT SOFTWARE FOR MICROWAVE ENGINEERING l Tatsuo ltoh, Giuseppe Pe/osi and Peter P. Silvester (eds.) INFRARED TECHNOLOGY: APPLICATIONS TO ELECTROOPTICS, PHOTONIC DEVICES, AND SENSORS l A. R. /ha SUPERCONDUCTOR TECHNOLOGY: APPLICATIONS TO MICROWAVE, ELECTRO-OPTICS, ELECTRICAL MACHINES, AND PROPULSION SYSTEMS l A. R. /ha OPTICAL COMPUTING: AN INTRODUCTION l M. A. Karim and A. S. S. Awwal INTRODUCTION TO ELECTROMAGNETIC AND MICROWAVE ENGINEERING l Paul R. Karmel, Gabriel Cl. Colef, and Raymond L. Camisa

MILLIMETER WAVE OPTICAL DIELECTRIC INTEGRATED GUIDES AND CIRCUITS l Shiban K. Koul MICROWAVE DEVICES, CIRCUITS AND THEIR INTERACTION l Char/es A. Lee and C. Conrad Da/man ADVANCES IN MICROSTRIP AND PRINTED ANTENNAS l Kai-Fong Lee and Wei Chen (eds.) SPHEROIDAL WAVE FUNCTIONS IN ELECTROMAGNETIC THEORY l LeWei Li, Xiao-Kang Kang, and Mook-Seng Leong OPTICAL FILTER DESIGN AND ANALYSIS: A SIGNAL PROCESSING APPROACH l Christi K. Madsen and jian H. Zhao THEORY AND PRACTICE OF INFRARED TECHNOLOGY FOR NONDESTRUCTIVE TESTING l Xavier P. V. Maldague OPTOELECTRONIC PACKAGING l A. R. Mickelson, N. R. Basavanhally, and Y. C. Lee (eds.) OPTICAL CHARACTER RECOGNITION l Shunji Mori, Hirobumi Nishida, and Hiromitsu Yamada ANTENNAS FOR RADAR AND COMMUNICATIONS: A POLARIMETRIC APPROACH l Harold Mott INTEGRATED ACTIVE ANTENNAS AND SPATIAL POWER COMBINING l julio A. Navarro and Kai Chang ANALYSIS METHODS FOR RF, MICROWAVE, AND MILLIMETER-WAVE PLANAR TRANSMISSION LINE STRUCTURES l Cam Nguyen FREQUENCY CONTROL OF SEMICONDUCTOR LASERS l Motoichi Ohtsu (ed.) SOLAR CELLS AND THEIR APPLICATIONS l Larry 0. Partain (ed.) ANALYSIS OF MULTICONDUCTOR TRANSMISSION LINES l Clayton R. Paul INTRODUCTION TO ELECTROMAGNETIC COMPATIBILITY l Clayton R. Paul ELECTROMAGNETIC OPTIMIZATION BY GENETIC ALGORITHMS l Yahya Rahmat-Samii and Eric Michielssen (eds.) INTRODUCTION TO HIGH-SPEED ELECTRONICS AND OPTOELECTRONICS. Leonard M. Riaziat NEW FRONTIERS IN MEDICAL DEVICE TECHNOLOGY l Arye Rosen and Hare/ Rosen (eds.) ELECTROMAGNETIC PROPAGATION IN MULTI-MODE RANDOM MEDIA l Harrison E. Rowe ELECTROMAGNETIC PROPAGATION IN ONE-DIMENSIONAL RANDOM MEDIA. Harrison E. Rowe NONLINEAR OPTICS l E. C. Sauter COPLANAR WAVEGUIDE CIRCUITS, COMPONENTS, AND SYSTEMS l Rainee N. Simons ELECTROMAGNETIC FIELDS IN UNCONVENTIONAL MATERIALS AND STRUCTURES l Onkar N. Singh and Akhlesh Lakhtakia (eds.) FUNDAMENTALS OF GLOBAL POSITIONING SYSTEM RECEIVERS:A SOFTWARE APPROACH l lames Bao-yen Tsui InP-BASED MATERIALS AND DEVICES: PHYSICS AND TECHNOLOGY l Osamu Wada and Hideki Hasegawa (eds.) COMPACT AND BROADBAND MICROSTRIP ANTENNAS l Kin-Lu Wong DESIGN OF NONPLANAR MICROSTRIP ANTENNAS AND TRANSMISSION LINES l Kin-Lu Wong FREQUENCY SELECTIVESURFACE AND GRID ARRAY l T. K. Wu (ed.) ACTIVE AND QUASI-OPTICAL ARRAYS FOR SOLID-STATE POWER COMBINING l Robert A. York and Zoya 6. PopoviC (eds.) OPTICAL SIGNAL PROCESSING, COMPUTING AND NEURAL NETWORKS l Francis T. S. Yu and Suganda jutamulia SiGe, GaAs, AND InP HETEROJUNCTION BIPOLAR TRANSISTORS l liann Yuan ELECTRODYNAMICS OF SOLIDS AND MICROWAVE SUPERCONDUCTIVITY l Shu-Ang Zhou

2 CHAPTER 1. INTRODUCTION

Figure 1.1 : Schematic illustration of the optical telegraph and its inventor Claude Chappe. (After Ref. [2]; c©1944 American Association for the Advancement of Science; reprinted with permis- sion.)

coded messages over long distances (∼ 100 km) by the use of intermediate relay sta- tions [2], acting as regenerators or repeaters in the modern-day language. Figure 1. shows the basic idea schematically. The first such “optical telegraph” was put in service between Paris and Lille (two French cities about 200 km apart) in July 1794. By 1830, the network had expanded throughout Europe [1]. The role of light in such systems was simply to make the coded signals visible so that they could be intercepted by the relay stations. The opto-mechanical communication systems of the nineteenth century were inherently slow. In modern-day terminology, the effective bit rate of such systems was less than 1 bit per second ( B < 1 b/s).

1.1.1 Need for Fiber-Optic Communications

The advent of telegraphy in the 1830s replaced the use of light by electricity and began the era of electrical communications [3]. The bit rate B could be increased to ∼ 10 b/s by the use of new coding techniques, such as the Morse code. The use of intermediate relay stations allowed communication over long distances (∼ 1000 km). Indeed, the first successful transatlantic telegraph cable went into operation in 1866. Telegraphy used essentially a digital scheme through two electrical pulses of different durations (dots and dashes of the Morse code). The invention of the telephone in 1876 brought a major change inasmuch as electric signals were transmitted in analog form through a continuously varying electric current [4]. Analog electrical techniques were to domi- nate communication systems for a century or so. The development of worldwide telephone networks during the twentieth century led to many advances in the design of electrical communication systems. The use of coaxial cables in place of wire pairs increased system capacity considerably. The first coaxial-cable system, put into service in 1940, was a 3-MHz system capable of transmitting 300 voice channels or a single television channel. The bandwidth of such systems is limited by the frequency-dependent cable losses, which increase rapidly for frequencies beyond 10 MHz. This limitation led to the development of microwave communication systems in which an electromagnetic carrier wave with frequencies in

Publisher's Note: Permission to reproduce this image online was not granted by the copyright holder. Readers are kindly asked to refer to the printed version of this chapter.

1.1. HISTORICAL PERSPECTIVE 3

Figure 1.2 : Increase in bit rate–distance product BL during the period 1850–2000. The emer- gence of a new technology is marked by a solid circle.

the range of 1–10 GHz is used to transmit the signal by using suitable modulation techniques. The first microwave system operating at the carrier frequency of 4 GHz was put into service in 1948. Since then, both coaxial and microwave systems have evolved considerably and are able to operate at bit rates ∼ 100 Mb/s. The most advanced coax- ial system was put into service in 1975 and operated at a bit rate of 274 Mb/s. A severe drawback of such high-speed coaxial systems is their small repeater spacing (∼ 1 km), which makes the system relatively expensive to operate. Microwave communication systems generally allow for a larger repeater spacing, but their bit rate is also limited by the carrier frequency of such waves. A commonly used figure of merit for commu- nication systems is the bit rate–distance product , BL , where B is the bit rate and L is the repeater spacing. Figure 1.2 shows how the BL product has increased through tech- nological advances during the last century and a half. Communication systems with BL ∼ 100 (Mb/s)-km were available by 1970 and were limited to such values because of fundamental limitations. It was realized during the second half of the twentieth century that an increase of several orders of magnitude in the BL product would be possible if optical waves were used as the carrier. However, neither a coherent optical source nor a suitable transmission medium was available during the 1950s. The invention of the laser and its demonstration in 1960 solved the first problem [5]. Attention was then focused on finding ways for using laser light for optical communications. Many ideas were