Integrated Optics

Springer-Verlag Berlin Heidelberg GmbH

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Advanced Texts in Physics

This pro gram of advanced texts covers a broad spectrum of topics which are of current and emerging interest in physics. Each book provides a comprehensive and yet accessible introduction to a field at the forefront of modern research. As such, these texts are intended for senior undergraduate and graduate students at the MS and PhD level; however, research scientists seeking an introduction to particular areas of physics will also benefit from the titles in this collection.

Robert G. Hunsperger

Integrated Optics Theory and Technology

Fifth Edition

With 260 Figures and 26 rabIes

Solutions Manual for Instructors on Request Direct1y from Springer-Verlag

i Springer

Prof. Robert G. Hunsperger University of Delaware Dept. of Electrical Engineering 140 Evans Hall Newark, DE19716, USA

Library of Congress Cataloging-in-Publication Data

Hunsperger, Robert G. Integrated optics : theory and technology 1 Robert G. Hunsperger.-- 5th ed.

p. cm. -- (Advanced texts in physics, ISSN 1439-2674) Includes bibliographical references and index. ISBN 978-3-662-12096-5 ISBN 978-3-540-38843-2 (eBook) DOI 10.1007/978-3-540-38843-2

1. Integrated optics. r. Title. Ir. Series.

TA1660 .H86 2002 621.36'93--dc21 2002020921

The first three editions appeared as Vol. 33 of Springer Series in Optical Sciences

ISSN 1439-2674

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To our grandchildren,

Cameron Hunsperger Wilson

and Caitlin Margaret Wilson

Preface to the Fourth Edition

Once again it has become necessary to produce a new edition in order to update material provided in earlier editions and to add new descriptions of recently emerging technology. All of the chapters have been revised to inc1ude new developments, and to incorporate additionalliterature references.

In the past few years there has been a vast expansion of worldwide telecom­munications and data transmission networks. In many localities fiber-to-the-home and integrated services digital networks (ISDN) have become a reality .. Many people are now logging-on to the Internet and the World Wide Web. The growth of these networks has created a strong demand for inexpensive, yet efficient and reliable, integrated optic components such as signal splitters, couplers and multiplexers. Be­cause of this demand, there has been a great deal of work recently on devices made using polymers and glas ses. Descriptions of these components have been added to the book in the appropriate chapters.

A number of new practice problems have been added, and an updated booklet of problem solutions is available. The supplementary series of videotaped lectures de­scribed in the preface to earlier editions continues to be available. Inquires regarding these materials should be sent directly to the author.

The author wishes to thank Mrs. Barbara Westog, who helped with the organi­zation of new material and typed the revisions.

Newark, July 1995 R.G. Hunsperger

Preface to the Third Edition

The field of integrated optics is continuing to develop at a rapid pace, necessitating the writing of this third edition in order to update the material contained in earlier editions. All of the chapters have been revised to reflect the latest developments in the field and a new chapter has been added to explain the important topic of newly invented quantum well devices. These promise to significantly improve the operating characteristics of lasers, modulators and detectors.

The trend of telecommunications toward the use of single mode systems operat -ing at the longer wavelengths of 1.3 and 1.55 I-lm has been explained and documented with illustrations of recently developed devices and systems. In this regard, broader coverage of GalnAsP devices and optical integrated circuits has been provided, and the new growth techniques of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) have been described. The extensive develop­ment of hybrid optical integrated circuits in lithium niobate has also been described. Notably, this progress has led to the production of the first commercially available optical integrated circuits.

A number of new practice problems have been added. An updated booklet of problem solutions is available, and the supplementary series of videotaped lectures described in the preface to the first edition has been expanded and updated. Inquiries regarding these materials should be sent directly to the author.

The author wishes to thank Mr. Garfield Simms, who has generated the artwork for a number of the new illustrations which appear in this edition, and Mrs. Barbara Westog, who typed the revisions.

Newark, January 1991 R.G. HUNSPERGER

Preface to the Second Edition

Our intent in producing this book was to provide a text that would be comprehensive enough far an introductory course in integrated optics, yet concise enough in its mathematical derivations to be easily readable by a practicing engineer who desires an overview of the field. The response to the first edition has indeed been gratifying; unusually strong demand has caused it to be sold out during the initial year of publication, thus providing us with an early opportunity to produce this updated and improved second edition.

This development is fortunate, because integrated optics is a very rapidly pro­gressing field, with significant new research being regularly reported. Hence, a new chapter (Chap. 17) has been added to review recent progress and to provide numer­ous additional references to the relevant technical literature. Also, thirty-five new problems for practice have been included to supplement those at the ends of chapters in the first edition. Chapters 1 through 16 are essentially unchanged, except for brief updating revisions and corrections of typographical errors.

Because of the time !imitations imposed by the need to provide an uninterrupted supply of this book to those using it as a course text, it has been possible to include new references and to briefty describe recent developments only in Chapter 17. However, we hope to provide details of this continuing progress in a future edition.

The authar wishes to thank Mr. Mark Bendett, Mr. Jung-Ho Park, and Dr. John Zavada far their valuable help in locating typographical errars and in developing new problems for this edition.

Newark, December 1983 R.G. HUNSPERGER

Preface to the First Edition

This book is an introduction to the theory and technology of integrated optics for graduate students in electrical engineering, and for practicing engineers and scientists who wish to improve their understanding of the principles and applications of this relatively new, and rapidly growing field.

Integrated Optics is the name given to a new generation of opto-electronic systems in which the familiar wires and cables are replaced by light-waveguiding optical fibers, and conventional integrated circuits are replaced by optical integrated circuits (OIC's). In an OIC, the signal is carried by means of a beam of light rather than by an electrical current, and the various circuit elements are interconnected on the substrate wafer by optical waveguides. Some advantages of an integrated­optic system are reduced weight, increased bandwidth (or multiplexing capability), resistance to electromagnetic interference, and low loss signal transmission.

Because of the voluminous work that has been done in the field of integrated optics since its inception in the late 1960's, the areas of fiber optics and optical inte­grated circuits have usually been treated separately at conferences and in textbooks. In the author's opinion, this separation is unfortunate because the two areas are closely related. Nevertheless, it cannot be denied that it may be a practical necessity. Hence, this book includes an overview of the entire field of integrated optics in the first chapter, which relates the work on optical integrated circuits to progress in fiber-optics development. Specific examples of applications of both fibers and the OIC's are given in the final chapter. The remaining chapters of the book are devoted to the detailed study of the phenomena, devices and technology of optical integrated circuits.

This book is an outgrowth of a graduate level, single-semester course in integrated optics taught first at the University of Southem Califomia in 1975 and later at the University of Delaware. The course has also been produced as aseries of 20 color videotaped lectures, which can be used along with this book for self-study of the subject. A booklet of solutions to the problems given at the end of the chapters is also available. Inquiries regarding these supplementary materials should be sent directly to the author.

The author wishes to thank those persons who have contributed to making this book a reality. In particular, the critical comments and constructive suggestions provided by Dr. T. Tamir throughout the preparation of the manuscript have been most

XIV

helpful. The continuing support and encouragement ofDr. H. Lotsch are also greatly appreciated. The competent and efficient typing of the manuscript by Mrs. Anne Seibel and Miss Jacqueline Gregg has greatly facilitated timely publication.

Newark, April 1982 R.G. HUNSPERGER

Contents

1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Advantages ofIntegrated Optics. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.1.1 Comparison of Optical Fibers with Other Interconnectors . 3 1.1.2 Comparison of Optical Integrated Circuits

with Electrical Integrated Circuits. . . . . . . . . . . . . . . . . . . . 7 1.2 Substrate Materials for Optical Integrated Circuits . . . . . . . . . . . . . . 9

1.2.1 Hybrid Versus Monolithic Approach. . . . . . . . . . . . . . . . . . 9 1.2.2 III-V and II-VI Ternary Systems. . . . . . . . . . . . . . . . . . . .. 10 1.2.3 Hybrid OIC's in LiNb03 . . . . . . . . . . . . . . . . . . . . . . . . . .. 12 1.2.4 Organization ofthis Book . . . . . . . . . . . . . . . . . . . . . . . . .. 12

2. Optical Waveguide Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17 2.1 Modes in a Planar Waveguide Structure . . . . . . . . . . . . . . . . . . . . .. 17

2.1.1 Theoretical Description of the Modes of a Three-Layer Planar Waveguide . . . . . . . . . . . . . . . . .. 17

2.1.2 Cutoff Conditions ......... . . . . . . . . . . . . . . . . . . . . . .. 19 2.1.3 Experimental Observation ofWaveguide Modes ........ 20

2.2 The Ray-Optic Approach to Optical Mode Theory. . . . . . . . . . . . .. 24 2.2.1 Ray Patterns in the Three-Layer Planar Waveguide . . . . .. 25 2.2.2 The Discrete Nature ofthe Propagation Constant ß . . . . .. 28

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29

3. Theory of Optical Waveguides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31 3.1 Planar Waveguides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31

3.1.1 The Basic Three-Layer Planar Waveguide . . . . . . . . . . . .. 31 3.1.2 The Symmetrie Waveguide . . . . . . . . . . . . . . . . . . . . . . . .. 34 3.1.3 The Asymmetrie Waveguide . . . . . . . . . . . . . . . . . . . . . . .. 35

3.2 Rectangular Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37 3.2.1 Channel Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37 3.2.2 Strip-Loaded Waveguides . . . . . . . . . . . . . . . . . . . . . . . . .. 42

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 45

XVI Contents

4. Waveguide Fabrication Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 47 4.1 Deposited Thin Films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 47

4.1.1 Sputtered Dielectric Films. . . . . . . . . . . . . . . . . . . . . . . . .. 47 4.1.2 Deposition from Solutions. . . . . . . . . . . . . . . . . . . . . . . . .. 50 4.1.3 Organosilicon Films. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50

4.2 Substitutional Dopant Atoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51 4.2.1 Diffused Dopants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51 4.2.2 Ion Exchange and Migration. . . . . . . . . . . . . . . . . . . . . . .. 52 4.2.3 Ion Implantation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53

4.3 Carrier-Concentration-Reduction Waveguides .. . . . . . . . . . . . . . .. 56 4.3.1 Basic Properties

of Carrier-Concentration-Reduction Waveguides . . . . . . .. 56 4.3.2 Carrier Removal by Proton Bombardment . . . . . . . . . . . .. 57

4.4 Epitaxial Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 58 4.4.1 Basic Properties ofEpitaxially Grown Waveguides . . . . .. 59 4.4.2 Gal-xAlxAs Epitaxially Grown Waveguides . . . . . . . . . .. 59 4.4.3 Epitaxial Waveguides

in Other III-V and lI-VI and IV Materials. . . . . . . . . . . . .. 63 4.4.4 Molecular Beam Epitaxy . . . . . . . . . . . . . . . . . . . . . . . . . .. 64 4.4.5 Metal-Organic Chernical Vapor Deposition . . . . . . . . . . .. 65

4.5 Electro-Optic Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 65 4.6 Oxidation.............................................. 67 4.7 Methods for Fabricating Channel Waveguides . . . . . . . . . . . . . . . .. 68

4.7.1 Ridged Waveguides Formed by Etching . . . . . . . . . . . . . .. 68 4.7.2 Strip-Loaded Waveguides . . . . . . . . . . . . . . . . . . . . . . . . .. 69 4.7.3 Masked Ion Implantation or Diffusion. . . . . . . . . . . . . . .. 70

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71

5. Polymer and Fiber Integrated Optics . . . . . . . . . . . . . . . . . . . . . . . . . .. 73 5.1 Types ofPolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 73 5.2 Polymer Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75

5.2.1 Processing ofPolystyrene . . . . . . . . . . . . . . . . . . . . . . . . .. 75 5.2.2 Processing of Polyimide . . . . . . . . . . . . . . . . . . . . . . . . . .. 77 5.2.3 Post-Deposition Processing. . . . . . . . . . . . . . . . . . . . . . . .. 77

5.3 Applications of Polymer Waveguide Interconnections . . . . . . . . . .. 78 5.4 Polymer Waveguide Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 80

5.4.1 Passive Polymer Devices. . . . . . . . . . . . . . . . . . . . . . . . . .. 81 5.4.2 Active Polymer Devices ........................... 84

5.5 Optical Fiber Waveguide Devices . . . . . . . . . . . . . . . . . . . . . . . . . .. 86 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 90

Contents XVII

6. Losses in Optical Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93 6.1 Scattering Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93

6.1.1 Surface Scattering Loss . . . . . . . . . . . . . . . . . . . . . . . . . . .. 94 6.2 Absorption Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96

6.2.1 Interband Absorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96 6.2.2 Free Carrier Absorption. . . . . . . . . . . . . . . . . . . . . . . . . . .. 98

6.3 Radiation Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 102 6.3.1 Radiation Loss from Planar

and Straight Charmel Waveguides . . . . . . . . . . . . . . . . . . .. 102 6.3.2 Radiation Loss from Curved Channel Waveguides . . . . . .. 102

6.4 Measurement of Waveguide Losses . . . . . . . . . . . . . . . . . . . . . . . . .. 106 6.4.1 End-Fire Coupling to Waveguides of Different Length. . .. 106 6.4.2 Prism-Coupled Loss Measurements . . . . . . . . . . . . . . . . .. 107 6.4.3 Scattering Loss Measurements . . . . . . . . . . . . . . . . . . . . .. 108

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 110

7. Waveguide Input and Output Couplers ......................... 113 7.1 Fundamentals of Optical Coupling . . . . . . . . . . . . . . . . . . . . . . . . .. 113 7.2 Transverse Couplers ...................................... 114

7.2.1 Direct Focusing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 114 7.2.2 End-Butt Coupling ................................ 115

7.3 Prism Couplers .......................................... 119 7.4 Grating Couplers ........................................ 122

7.4.1 Basic Theory ofthe Grating Coupler. ................. 123 7.4.2 Grating Fabrication ............................... 124

7.5 Tapered Couplers ........................................ 126 7.6 Tapered Mode Size Converters ............................. 127 7.7 Fiber to Waveguide Couplers ............................... 128

7.7.1 Butt Coupling .................................... 128 7.7.2 High Density Multifiber Connectors .................. 131

Problems ................................................... 132

8. Coupling Between Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 135 8.1 Multilayer Planar Waveguide Couplers . . . . . . . . . . . . . . . . . . . . . .. 135 8.2 Dual-Channel Directional Couplers .......................... 136

8.2.1 Operating Characteristics of the Dual-Channel Coupler. .. 136 8.2.2 Coupled-Mode Theory of Synchronous Coupling ....... 138 8.2.3 Methods of Fabricating

Dual-Channel Directional Couplers .................. 142 8.2.4 Applications Involving Directional Couplers ........... 145

8.3 Butt-Coupled Ridge Waveguides ............................ 146 8.4 Branching Waveguide Couplers ............................. 146 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 148

XVIII Contents

9. Electro-Optic Modulators . ................................... 149 9.1 Basic Operating Characteristics of Switches and Modulators ...... 149

9.1.1 Modulation Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 149 9.1.2 Bandwidth ...................................... 150 9.1.3 Insertion Loss .................................... 150 9.1.4 Power Consumption ............................... 151 9.1.5 Isolation ........................................ 151

9.2 The Electro-Optic Effect .................................. 152 9.3 Single-Waveguide Electro-Optic Modulators .................. 152

9.3.1 Phase Modulation ................................ 153 9.3.2 Polarization Modulation ........................... 154 9.3.3 Intensity Modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 155 9.3.4 Electro-Absorption Modulation. . . . . . . . . . . . . . . . . . . . .. 155

9.4 Dual-Channel Waveguide Electro-Optic Modulators ............ 158 9.4.1 Theory of Operation .............................. 159 9.4.2 Operating Characteristics of Dual-Channel Modulators. .. 160

9.5 Mach-Zehnder Type Electro-Optic Modulators ................. 164 9.6 Electro-Optic Modulators Employing Reflection or Diffraction .... 165

9.6.1 Bragg-Effect Electro-Optic Modulators ............... 165 9.6.2 Electro-Optic Reflection Modulators .................. 166

9.7 Comparison ofWaveguide Modulators to Bulk Electro-Optic Modulators ........................... 168

9.8 Traveling Wave Electrode Configurations ..................... 170 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 172

10. Acousto-Optic Modulators . ................................... 175 10.1 Fundamental Principles of the Acousto-Optic Effect . . . . . . . . . . .. 175 10.2 Raman-Nath-Type Modulators ............................. 177 10.3 Bragg-Type Modulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 178 10.4 Bragg-Type Beam Deflectors and Switches ................... 181 10.5 Performance Characteristics

of Acoustic-Optic Modulators and Beam Deflectors. . . . . . . . . . . .. 184 10.6 Accusto-Optic Frequency Shifters. . . . . . . . . . . . . . . . . . . . . . . . . .. 187 Problems ................................................... 190

11. Basic Principles of Light Emission in Semiconductors . . . . . . . . . . . .. 193 11.1 A Microscopic Model for Light Generation and Absorption

in a Crystalline Solid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 193 11.1.1 Basic Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 193 11.1.2 Conservation of Energy and Momentum. . . . . . . . . . . . . .. 195

11.2 Light Emission in Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . .. 198 11.2.1 Spontaneous Emission. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 198 11.2.2 Stimulated Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 203

11.3 Lasing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 206 11.3.1 Semiconductor Laser Structures . . . . . . . . . . . . . . . . . . . .. 206

Contents XIX

11.3.2 Lasing Threshold ................................. 207 11.3.3 Efficiency of Light Emission ....................... , 209

Problems ................................................... 209

12. Semiconductor Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 211 12.1 The Laser Diode ......................................... 211

12.1.1 Basic Structure ................................... 211 12.1.2 Optical Modes ................................... 212 12.1.3 Lasing Threshold Conditions ....................... , 213 12.1.4 Output Power and Efficiency ........................ 217

12.2 The Tunnel-Injection Laser ................................ 219 12.2.1 Basic Structure ................................... 219 12.2.2 Lasing Threshold Conditions ........................ 221

12.3 Polymer Lasers ......................................... , 222 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 223

13. Optical Amplifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 225 13.1 Optical Fiber Amplifiers .................................. 225

13.1.1 Erbium Doped Fiber Amplifiers ..................... 225 13 .1.2 Raman Optical Fiber Amplifiers . . . . . . . . . . . . . . . . . . . .. 228 13.1.3 Other Optical Fiber Amplifiers ...................... 230

13.2 Non-Fiber Ion-Doped Optical Amplifiers ..................... 231 13.3 Semiconductor Optical Amplifiers .......................... 231

13.3.1 Integrated Semiconductor Optical Amplifiers ........... 233 13.4 Comparison of Ion-Doped Fiber Amplifiers with SOAs . . . . . . . . .. 235

13.4.1 Wavelength Range. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 235 13.4.2 Performance Characteristics ........................ 235

13.5 Gain Equalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 236 13.6 Fiber Lasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 237 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 239

14. Heterostructure, Confined-Field Lasers . ........................ 241 14.1 Basic Heterojunction Laser Structures ....................... , 242

14.1.1 Single Heterojunction (SH) Lasers ................... 242 14.1.2 Double Heterostructure (DH) Lasers. . . . . . . . . . . . . . . . .. 243

14.2 Performance Characteristics ofthe Heterojunction Laser ......... 244 14.2.1 Optical Field Confinement .......................... 244 14.2.2 Carrier Confinement .............................. 247 14.2.3 Comparison of Laser Emission Characteristics. . . . . . . . .. 248

14.3 Control of Emitted Wavelength . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 249 14.3.1 Ga(1_x)AlxAs Lasers for Fiber-Optic Applications ...... , 249 14.3.2 Lasers Made of Quatemary Materials ................. 251 14.3.3 Long-Wavelength Lasers ........................... 251

14.4 Advanced Heterojunction Laser Structures .................... 251 14.4.1 Stripe Geometry Lasers. . . . . . . . . . . . . . . . . . . . . . . . . . .. 251

XX Contents

14.4.2 Single-Mode Lasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 253 14.4.3 Integrated Laser Structures ......................... 254

14.5 Reliability .............................................. 258 14.5.1 Catastrophic Failure ............................... 259 14.5.2 Gradual Degradation .............................. 259

14.6 VerticaI Cavity Lasers .................................... 259 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 261

15. Distributed-Feedback Lasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 263 15.1 TheoreticaI Considerations ................................ 263

15.1.1 Wavelength Dependence ofBragg Reflections .......... 263 15.1.2 Coupling Efficiency ............................... 265 15.1.3 Lasing with Distributed Feedback .................... 268

15.2 Fabrication Techniques ................................... 269 15.2.1 Effects ofLattice Damage .......................... 269 15.2.2 Grating Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 270 15.2.3 DBR Lasers ..................................... 272

15.3 Performance Characteristics ............................... 275 15.3.1 Wavelength Selectability ........................... 275 15.3.2 Optical Emission Linewidth ........................ 276 15.3.3 Stability ........................................ 277 15.3.4 Threshold Current Density and Output Power .......... 278

15.4 Semiconductor Air Bragg Reflector Lasers .................... 279 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 280

16. Direct Modulation of Semiconductor Lasers. . . . . . . . . . . . . . . . . . . .. 281 16.1 Basic Principles of Direct Modulation ........................ 281

16.1.1 Amplitude Modulation ............................. 281 16.1.2 Pulse Modulation ................................. 284 16.1.3 Frequency Modulation ............................. 286

16.2 Microwave Frequency Modulation of Laser Diodes . . . . . . . . . . . .. 287 16.2.1 Summary ofEar1y Experimental Results .............. 287 16.2.2 Factors Limiting Modulation Frequency . . . . . . . . . . . . . .. 288 16.2.3 Design ofLaser Diode Packages

for Microwave Modulation . . . . . . . . . . . . . . . . . . . . . . . .. 292 16.3 Monolithically Integrated Direct Modulators .................. 293 16.4 Amplified Laser Modulation ............................... 295 16.5 Future Prospects for Microwave Modulation of Laser Diodes ..... 296 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 296

17. Integrated Optical Detectors .................................. 299 17.1 Depletion Layer Photodiodes ............................... 299

17.1.1 Conventional Discrete Photodiodes ................. " 299 17.1.2 Waveguide Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . .. 302 17.1.3 Effects of Scattering and Free-Carrier Absorption . . . . . .. 303

Contents XXI

17.2 Specialized Photodiode Structures ........................... 304 17.2.1 Schottky-Barrier Photodiode. . . . . . . . . . . . . . . . . . . . . . .. 304 17.2.2 Avalanche Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . .. 305 17.2.3 p-i-n Photodiodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 307 17.2.4 Metal-Semiconductor-Metal Photodiodes .............. 307

17.3 Techniques for Modifying Spectral Response. . . . . . . . . . . . . . . . .. 308 17.3.1 Hybrid Structures ................................. 309 17.3.2 Heteroepitaxial Growth ............................ 310 17.3.3 Proton Bombardment. ............................. 313 17.3.4 Electro-Absorption ............................... 316

17.4 Factors Limiting Performance ofIntegrated Detectors ........... 319 17.4.1 High Frequency Cutoff ............................ 319 17.4.2 Linearity ........................................ 320 17.4.3 Noise .......................................... 320

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 320

18. Quantum-WeIl Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 325 18.1 Quantum WeHs and Superlattices ........................... 325 18.2 Quantum-WeH Lasers .................................... 327

18.2.1 Single-Quantum-WeH Lasers ........................ 327 18.2.2 Multiple Quantum WeH Lasers ...................... 330

18.3 Quantum-WeH Modulators and Switches ..................... 334 18.3.1 Electro-Absorption Modulators ...................... 334 18.3.2 Electro-Optic Effect in Quantum WeHs ................ 338 18.3.3 Multiple Quantum WeH Switches .................... 339

18.4 Quantum-WeIl Detectors .................................. 341 18.4.1 Photoconductive Detectors ......................... 341 18.4.2 MQW Avalanche Photodiodes ....................... 342

18.5 Self-Electro-Optic Effect Devices ........................... 343 18.6 Quantum-WeH Devices in OEIC's ........................... 344

18.6.1 Integrated Laser/Modulators ........................ 344 18.6.2 A Four-Channel Transmitter Array with MQW Lasers .... 346

Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 347

19. Micro-Optical-Electro-Mechanical Devices ...................... 349 19.1 Basic Equations of Mechanics. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 349

19.1.1 Axial Stress and Strain ............................. 350 19.1.2 Thin Membranes ................................. 351 19.1.3 Cantilever Beams ................................. 352 19.1.4 Torsion Plates .................................... 353

19.2 Thin Membrane Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 354 19.3 Cantilever Beam Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 356 19.4 Torsional Devices ........................................ 359 19.5 Optical Elements ........................................ 362 19.6 Future Directions in MOEMS Development ................... 364

XXII Contents

19.7 Mechanica1 Properties of Silicon. . . . . ...................... , 365 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 365

20. Applications of Integrated Optics and Current Trends . . . . . . . . . . .. 367 20.1 Applications of Optical Integrated Circuits . . . . . . . . . . . . . . . . . . .. 367

20.1.1 RF Spectrum Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . .. 367 20.1.2 Monolithic Wavelength-Multiplexed Optical Source ..... 370 20.l.3 Analog-to-Digital Converter (ADC) .................. 371 20.1.4 Integrated-Optic Doppler Velocimeter . . . . . . . . . . . . . . .. 372 20.1.5 An 10 Optical Disk Readhead ....................... 374 20.1.6 OIC Temperature Sensor. . . . . . . . . . . . . . . . . . . . . . . . . .. 376 20.1.7 10 High Voltage Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . .. 377 20.1.8 10 Wave1ength Meters and Spectrum Analyzers ......... 378 20.1.9 10 Chemical Sensors .............................. 379

20.2 Opto-Electronic Integrated Circuits. . . . . . . . . . . . . . . . . . . . . . . . .. 379 20.2.1 An OEIC Transmitter. ............................. 381 20.2.2 An OEIC Receiver ................................ 381 20.2.3 An OEIC Phased-Array Antenna Driver. . . . . . . . . . . . . .. 382

20.3 Devices and Systems for Telecommunications . . . . . . . . . . . . . . . .. 383 20.3.1 Trends in Optical Telecommunications ................ 383 20.3.2 New Devices for Telecommunications ................ 387

Problems ................................................... 391

21. Photonic and Microwave Wireless Systems . . . . . . . . . . . . . . . . . . . . .. 393 21.1 Merging of Photonics and Microwave Technology . . . . . . . . . . . . .. 393 21.2 Fiber-Optic Transmission of RF and Microwave Signals. . . . . . . .. 395

21.2.1 Basic Principles .................................. 396 21.2.2 Device Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 398 21.2.3 System Performance .............................. 399

21.3 Microwave Carrier Generation by Optical Techniques ........... 401 21.4 Future Projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 405 Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 406

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 407

Subject Index ................................................. " 441