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Spie Press Book

Tunable Laser Diodes and Related Optical Sources, Second Edition
Author(s): Jens Buus; Markus-Christian Amann; Daniel J. Blumenthal
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Book Description

Buus, Amann, and Blumenthal significantly expand the 1998 edition of Tunable Laser Diodes, which reflects the developments in the engineering and applications of the field. The authors cover essential subjects on tunable laser diodes, from theory to applications, as well as those of modern laser diodes in general. They present properties of semiconductor lasers and foundations, and summarize principles of operation for single-mode lasers. The key concepts, design, and practice of tunable laser diodes are described, with emphasis on extremely widely tunable lasers. Practical issues such as control, aging, and dynamics are discussed, and a review of other DWDM sources such as external-cavity lasers, tunable VCSELs, laser arrays, fiber and waveguide lasers, and tunable pulse sources is included. Anyone interested in the new and powerful applications of tunable lasers in optical networks, optical communication, radar, environmental sensing, reflectometry, and circuit analysis will find this book invaluable.

Co-published by SPIE Press and Wiley-IEEE Press.


Book Details

Date Published: 2 February 2005
Pages: 448
ISBN: 9780471208167
Volume: PM144

Table of Contents
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Foreword xi
Preface xiii
1 Introduction 1
2 Fundamental Laser Diode Characteristics 7
2.1 Optical Gain in Semiconductors 7
2.2 Semiconductor Heterostructures 12
2.2.1 Carrier Confinement 13
2.2.2 Optical Confinement 14
2.2.3 Material Systems 15
2.3 Waveguiding and Transverse Laser Modes 16
2.3.1 The Slab Waveguide 16
2.3.2 Lateral Waveguiding 19
2.4 Laser Structures 22
2.5 The Fabry�Perot Laser 23
2.6 The Rate Equations 27
2.6.1 Stationary Solution of the Rate Equations 28
2.6.2 Laser Spectrum and Side-Mode Suppression 30
2.6.3 Small-Signal Modulation Behavior 33
2.7 Quantum Well Laser Diodes 35
3 Single-Mode Laser Diodes 43
3.1 Mode Selectivity Requirements 44
3.2 Wave Propagation in Periodic Structures 44
3.2.1 Alternative Derivation of the Coupled-Mode Equations 47
3.2.2 Solution of the Coupled-Mode Equations 48
3.3 Distributed Bragg-Reflector Lasers 50
3.3.1 Magnitude and Phase of Reflection 50
3.3.2 Grating Shapes 53
3.3.3 DBR Laser Structures 56
3.4 Distributed-Feedback Lasers 59
3.4.1 DFB Laser With Nonreflecting Facets 59
3.4.2 DFB Lasers With Reflecting Facets 63
3.4.3 Phase-Shifted and Gain-Coupled DFB Lasers 66
3.5 Laser Fabrication and Tolerances 68
3.5.1 Wavelength Dependence on Structural Parameters 70
3.5.2 Thermal Properties under CW Operation 71
3.6 Spectral Linewidth 73
4 Basic Concepts of Tunable Laser Diodes 79
4.1 Continuous, Discontinuous, and Quasicontinuous Tuning Schemes 79
4.2 Tuning of Cavity Gain Characteristic 82
4.3 Tuning of Comb-Mode Spectrum 84
4.4 Simultaneous Tuning of Cavity Gain and Comb-Mode Spectrum 86
4.5 Electronic Wavelength Control 89
4.5.1 The Free-Carrier Plasma Effect 91
4.5.2 The Quantum-Confined Stark Effect 95
4.5.3 Thermal Tuning 96
4.6 Integration Techniques 97
4.7 Dynamic Behavior 99
5 Wavelength-Tunable Single-Mode Laser Diodes 107
5.1 Longitudinally Integrated Structures 107
5.1.1 Two-Section DBR Laser 111
5.1.2 Three-Section DBR Laser 114
5.1.3 Multisection DFB Laser 118
5.2 Transversely Integrated Structures 121
5.2.1 Tunable Twin-Guide DFB Laser 125
5.2.2 Striped Heater DFB Laser 131
5.3 Integration Technology 132
5.4 Physical Limitations on the Continuous Tuning Range 136
5.5 Tuning Dynamics and Modulation 141
6 Linewidth Broadening 151
6.1 Injection-Shot Noise in the Tuning Region 152
6.2 Impedance and Thermal Noise of Bias Source 159
6.3 Spatial Correlation 163
6.4 1/f Noise 164
6.5 Fluctuations of Bias Source 166
7 Widely Tunable Monolithic Laser Diodes 169
7.1 The Vernier Effect 169
7.2 DBR-type Laser Structures 173
7.2.1 Sampled-Grating DBR Lasers 174
7.2.2 Superstructure-Grating DBR Lasers 179
7.2.3 Digital Supermode DBR Lasers 184
7.2.4 Superimposed and Binary Gratings 185
7.3 Interferometric Structures 187
7.3.1 Lateral Integration: The Y-Laser 188
7.3.2 Transverse Integration: The VMZ Laser 190
7.4 Codirectionally Coupled Laser Diodes 192
7.4.1 Theory for Codirectional Coupling 193
7.4.2 Tuning and Mode Spacing 198
7.4.3 Longitudinally Integrated Structures 200
7.4.4 Transversely Integrated Structures 202
7.5 Combination of Techniques 206
7.5.1 The Grating-Coupled Sampled-Reflector Laser 206
7.5.2 The Modulated-Grating Y-structure Laser 208
7.6 Comparison of Widely Tunable Monolithic Laser Structures 211
8 Practical Issues Related to Monolithic Tunable Laser Diodes 221
8.1 Characterization and Control 221
8.1.1 DFB and DBR Lasers 221
8.1.2 Widely Tunable Lasers 224
8.2 Wavelength Stability and Aging 228
8.3 Modulation and Wavelength-Switching Dynamics 232
8.3.1 Modulation and Transmission 232
8.3.2 Wavelength Switching 234
8.4 Monolithic Integration 237
9 Related DWDM Sources 247
9.1 External-Cavity Lasers 247
9.1.1 External Grating and External Filter Cavities 247
9.1.2 MEMS External Cavities 250
9.1.3 Hybrid Structures 251
9.2 Vertical-Cavity Lasers 252
9.2.1 VCSEL Basics 252
9.2.2 Tunable VCSELs 254
9.3 Laser Arrays 257
9.3.1 Multistripe Arrays 257
9.3.2 Selectable Arrays 259
9.3.3 DBR Arrays 262
9.3.4 Phased Arrays 263
9.4 Technology Summary 265
9.5 Fiber and Waveguide Lasers 266
9.6 Tunable Pulse Sources and Comb Generators 268
10 Communications Applications and Requirements 285
10.1 Wavelength Tunability 285
10.1.1 Tuning Speed and Latency 286
10.1.2 Tuning Continuity 287
10.1.3 Tuning Uniformity 288
10.1.4 Tuning Stability and Accuracy 288
10.1.5 Other Design Considerations 289
10.2 Functions and Components 289
10.2.1 Tunable Transmitters and Transponders 290
10.2.2 Tunable Wavelength Converters with 194
Regeneration Capability
10.2.3 Optical Wavelength Switches 302
10.3 Communications Applications 306
10.3.1 Point-to-Point Links and Networks 306
10.3.2 Fixed-Wavelength Networks 309
10.3.3 Reconfigurable Networks 310
10.3.4 Optical-Protection Switching 311
10.3.5 Optical-Burst Switching 313
10.3.6 Photonic-Packet Switching 314
11 Other Applications 325
11.1 Optical Frequency-Modulated Continuous-Wave Radar 325
11.2 Optical Components Characterization 330
11.3 Trace-Gas Sensing, Environmental Analysis, and Spectroscopy 331
11.4 Heterodyne Techniques 334
11.5 Optical Spectrum and Network Analysis 334
11.6 Anemometry 335
Appendix A Refractive Index of InGaAsP 339
Appendix B The Slab Waveguide 343
Appendix C Transfer Matrices 351
Appendix D Thermal Response of a Laser Diode 355
D.1 Pulse Response in the Time Domain 355
D.2 Response in the Frequency Domain 358
Appendix E Theory for General Reflectors 361
Appendix F Codirectional Coupling 367
List of Symbols 371
List of Acronyms 377
Index 389

Foreword

A wavelength-tunable laser diode is a wavelength-specific device, characterized by its wavelength tunability, that is expected to be a key device for advanced optical communication, as well as for a variety of optical measurements. The first edition of this book was written by two experts in the field of optoelectronics, Dr. Jens Buus and Professor Markus-Christian Amann, who have been doing pioneering work in the development of advanced laser diodes. They are joined in this new edition by Professor Daniel Blumenthal, who is known for his work on optical networks. This book covers tunable laser diodes from the fundamentals of laser diodes and the basic principles and practice of wavelength-tunable lasers to application areas. Thus, I believe that this book is an excellent textbook for final-year undergraduate students, graduate students, researchers working on semiconductor lasers, and also for system engineers interested in the application of tunable laser diodes.

A semiconductor laser itself is a key device for optoelectronics, owing to its superior performance and small size, low power consumption, high efficiency, longer device life, flexibility for selecting wavelength, and adaptability for photonic integrated circuits, and so on. Efforts have been concentrated on their further development. An integrated laser diode with external waveguide was developed with the intention of exploring the possibility of implementing monolithic integration of optoelectronic devices and components. A wavelength-tunable laser diode was created as an extension of the laser diode monolithically integrated with tuning sections within the laser cavity; see "Wavelength Tunable 1.5 _m Bundle-Integrated- Guide Distributed Bragg Reflector (BIG-DBR) Lasers" by Y. Tohmori, K. Komori, S. Arai, Y. Suematsu, and H. Oohashi, Transactions of the IECE of Japan, E68, 788�790, 1985. After the first trials of the electronically wavelength-tunable laser, efforts have been made to achieve excellent performance with wider wavelengthtuning range. Presently, the wavelength-tunable lasers find many application areas as mentioned in this book.

This book covers almost all of the essential subjects on tunable laser diodes, from theory to applications. It covers fundamentals not only of tunable laser diodes, but of modern laser diodes in general. In Chapter 2, "Fundamental Laser Diode Characteristics," basic properties of semiconductor lasers are presented, and in Chapter 3, "Single-Mode Laser Diodes," essential properties for single-mode lasers are summarized, together with the basic principles of operation. In Chapters 4 to 7, the principles, design, and practice of tunable laser diodes are described with an emphasis on extremely widely tunable lasers. In Chapter 8, practical issues such as control, aging, and dynamics are discussed, and Chapter 9 reviews other DWDM sources such as external cavity lasers, tunable VCSELs, laser arrays, fiber and waveguide lasers, and tunable pulse sources. Chapter 10 deals with the application of tunable lasers in optical networks, and Chapter 11 covers other applications such as optical communication, radar, environmental sensing, reflectometry, and circuit analysis. Finally, in the Appendixes, important factors such as the refractive index of semiconductors, optical waveguiding and transfer matrices, and the thermal response of laser diodes and the general theory for reflection from structures with varying refractive index are treated.

I hope that this book will be read by all people who are interested in the use of these new and powerful devices in the optoelectronics area.

Preface

The objective of this book is to give a complete account, as of early 2004, of the state of the art of monolithic tunable laser diodes and their applications. It is the authors' objective to include all relevant material and to provide a balanced presentation of the underlying theoretical aspects and practical issues of tunable laser diodes. We are combining this account with general background material such as basic laser diode properties (Chapter 2 and the Appendices), the physical principles of tunable laser diodes (Chapter 4), and the theories for propagation in structures with contradirectional or codirectional coupling (Chapters 3 and 7, respectively). Device structures and performance are discussed in detail (Chapters 5 to 7) and material on related topics (Chapter 8) and applications (Chapter 9) is provided as well. By including this material, we hope that the book can be used in different ways by different groups of readers: As a textbook in specialized courses for postgraduate students, as a reference book for scientists working in this or related areas, and as a handbook for engineers using tunable lasers.

Selection of references is always problematic. Rather than trying to include all published papers, we have adopted the following approach: All references to quoted results (theoretical or experimental) are included, using primary references unless a more detailed description has been published later by the same authors. References to conference papers are generally avoided if the material has been published elsewhere. In addition, we include a number of more general references in which the reader can find additional details that have not been possible to include here. Since the publication of the first edition of this book in 1998, tunable lasers have continued to attract a high level of technical attention, although the slowdown in anything related telecom following the euphoria of 1999/2000 has had its impact also in this area. During this period, developments have been related more to engineering and applications than to basic research. This is also reflected in this book; we have expanded the coverage of practical issues and applications significantly. In fact the "old" Chapter 9 dealing with these issues has been split into three new chapters with each of the original sections forming the basis for a whole chapter. Other parts of the book have been corrected, improved, updated, and, in some cases, expanded. We estimate that nearly one-third of the book is either completely new or substantially revised.

We would also like to thank a number of authors who have given permission for use of their artwork. We are grateful for access to original artwork as well as stillunpublished material from a large number of individuals and organizations. In a several cases, this material has been supplied in electronic form, thereby easing our work significantly.


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