Monolithic Diode-Laser Arrays

404 Pages·1994·9.04 MB·English

by  Dr. Nils W. Carlson (auth.)

Springer Series in
Electronics and Photonics 33
Edited by A.L. Schawlow
Springer Series in Electronics and Photonics
Editors: I. P. Kaminov W. Engl T. Sugano
Managing Editor: H. K. V. Lotsch
Volume 22 High-Speed Electronics
Basic Physical Phenomena and Device Principles
Editors: B. Kiillbiick and H. Beneking
Volume 23 Guided-Wave Acousto-Optics
Interactions, Devices, and Applications
Editors: C. S. Tsai
Volume 24 Picosecond Electronics and Optoelectronics II
Editors: F. J. Leonberger, C. H. Lee, F. Capasso, and H. Morkoc
Volume 25 Photonic Switching
Editors: T. K. Gustafson and P. W. Smith
Volume 26 Guided-Wave Optoelectronics
Editor: T. Tamir
Volume 27 Ultra-Fast Silicon Bipolar Technology
Editors: L. Treitinger and M. Miura-Mattausch
Volume 28 Physics of Quantum Electron Devices
Editor: F. Capasso
Volume 29 Photonic Switching II
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Volume 30 Nonlinear Photonics
Editors: H. M. Gibbs, G. Khitrova, and N. Peyghambarian
Volume 31 Single-Electron Tunneling and Mesoscopic Devices
Editors: H. Koch and H. Liibbig
Volume 32 Silicon-Based Millimeter-Wave Devices
Editors: J. F. Luy and P. Russer
Volume 33 Monolithic Diode-Laser Arrays
By N. W. Carlson
This series was originally published under the title
Springer Series in Electrophysics
and has been renamed starting with Volume 22.
Volumes 1-21 are listed at the end of the book
Nils W. Carlson
Monolithic
Diode-Laser Arrays
With 178 Figures
Springer-Verlag
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Dr. Nils W. Carlson
Lawrence Livermore National Laboratories, P. O. Box 808,
Livermore, CA 94551, USA
Guest Editor:
Professor A.L. Schawlow
Department of Physics, Stanford University,
Stanford, CA 94305-4060, USA
Series Editors:
Dr. Ivan P. Kaminow
AT&T Bell Laboratories, P. O. Box 400, Holmdel, NJ 07733, USA
Professor Walter Engl
Institut ftir Theoretische Elektrotechnik, Rhein.-Westf. Technische Hochschule,
Kopernikusstrasse 16,0-52074 Aachen, Germany
Professor Takuo Sugano
Department of Electrical and Electronic Engineering, Toyo University,
2100 Kujirai Kawagoe Saitama 350, Japan
Managing Editor: Dr.-Ing. Helmut K. V. Lotsch
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0-69121 Heidelberg, Germany
ISBN -13: 978-3-642-78944-1 e-ISBN-13 :978-3-642-78942-7
DOl: 10.1007/978-3-642-78942-7
Library of Congress Cataloging-in-Publication Data. Carlson, Nils William. Monolithic diode-laser arrays: Nils W.
Carlson. p. cm. - (Springer series in electronics and photonics; vol. 33) Includes bibliographical references and
index. ISBN-13:978-3-642-78944-1
I.Semiconductor lasers. 1. Title. II. Series: Springer series in electronics and photonics: v. 33.
TA1700.C36 1994 621.36'61-dc20 94-11598
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Preface
The last ten years have witnessed an explosive development in the field of
semiconductor-diode lasers. Diode lasers have spread rapidly into the com
mercial applications areas of telecommunications, optical recording, laser au
dio/video, laser printing, and pump sources for solid-state lasers. Because
of its compact size and high efficiency, the semiconductor-diode laser can
offer unparalleled advantages in these and many other optical systems appli
cations. A widespread vision has persisted over the last decade, that more
reliable monolithic semiconductor laser sources could eventually be made to
replace gas, dye, and solid-state lasers in many applications that would de
rive great benefit from compact lasers sources with high average power and
high-brightness output capabilities. The initial driving force behind this vi
sion has been the notion that both high-power output and high brightness
could be increased by coherently coupling an array of single-element diode
lasers. With the combined projected advantages of better reliability and high
power output from a very compact device, it is easy to see the attraction of
the monolithic semiconductor diode laser array as a particularly user-friendly
laser source.
Over the last twenty years, many approaches and concepts for monolithic
diode laser arrays have evolved in the quest for a high-power, single-frequency
source. But even today, the ultimate monolithic diode laser array has not yet
been achieved. Whereas ten years ago or so, there was a diversity of mono
lithic diode laser designs being actively persued, today the field of concepts
and design approaches has narrowed and converged to just a few promising
designs. Some approaches such as the unstable-resonator semiconductor laser
and the master oscillator power amplifier are well-known from other areas of
laser science. But other approaches such as the antiguided-diode laser ar
ray and the active-grating surface emitting amplifier are, so far, unique to
semiconductor diode lasers.
The goal of this book is to give a unified presention of the physical prin
ciples, optical design, operating characteristics, and ultimate performance
projections of monolithic diode-laser arrays for single-mode, high-power op
eration. Emphasis is placed on developing an understanding. of the mode
discrimination properties of the diode-laser array structures. The book is in
tended for scientists, engineers, and advanced graduate students working in
VI Preface
the field of semiconductor lasers and optoelectronics, as well as those working
in other fields of laser science. Phenomenological descriptions have been the
preferred mode of presentation. Some detailed mathematical derivations are
included to validate certain of the models that are used, and in a few in
stances, to explain those subjects which cannot be adequately dealt with us
ing the canonical models. The significant developments that have contributed
to, and shaped, the present state of the field are reviewed. Numerous refer
ences, from the early to the most recent literature, are provided as research
in monolithic high-brightness semiconductor laser sources is still an active
and expanding field. The book should provide the reader with a perspec
tive on the development of high-power semiconductor lasers and the issues
important for mode discrimination. Hopefully, the reader will be left with
an appreciation of the potential that semiconductor lasers offer as compact,
efficient high-brightness sources of light, as well as the challenging scientific
problems that still need to be solved in order for the potential to be realized.
The focus of this book will be limited to the physical principles, design,
and performance projections of monolithic diode lasers and diode-laser ar
rays for high-power single-frequency operation with diffraction-limited qual
ity output beams. In Chaps. 1-4, basic concepts are reviewed that are im
portant for understanding the mode discrimination properties and operating
principles of high-power diode-laser devices. Chapter 1 presents a brief history
of the diode-laser arrays, as well as some background on the factors that have
motivated the development of diode-lasers arrays, and a review of diode-laser
array design concepts. In Chap. 2, the physics and design issues related to
high-power operation of semiconductor diode lasers and diode-laser arrays are
presented. Issues related to mode discrimination (both spectral and spatial)
in semiconductor lasers and laser arrays are reviewed in Chap. 3. Theoretical
models for diode-laser arrays are the subject of Chap. 4. The remaining four
chapters (Chaps. 5-8) discuss the experimental and theoretical analyses of
specific types of diode-laser arrays and other novel semiconductor laser de
signs, where the potential for single-mode, beam-quality operation at high
power outputs has been investigated. Basic edge-emitting gain-guided diode
laser arrays are covered in Chap. 5, while Chap. 6 deals with edge-emitting,
index-guided diode-laser structures. Surface-emitting diode-laser arrays are
presented in Chap. 7, and Chap. 8 covers master-oscillator power amplifier
semiconductor lasers (both surface and edge emitting).
I am grateful to Prof. Arthur Schawlow for encouraging me to write this
book. Also, I wish to thank Dr Helmut Lotsch of Springer-Verlag for his assis
tance and encouragement throughout the writing of the book. I am grateful
to Prof. Jerome Butler for his encouragement and crtical reviews of parts of
the manuscript, as well as for introducing me to TEX. When I began writing
this book, I was at the David Sarnoff Research Center; and about halfway
through the project, I moved to my present position at the Lawrence Liv
ermore National Laboratory. Hence, I have enjoyed the benefit of technical
Preface VII
interactions with colleagues at both laboratories, as well as the use of the fine
libraries at each of these institutions.
It is with pleasure that I acknowledge the many scientists whose work has
been cited, as their contributions are the fabric of this book. I am especially
grateful to Prof. Dan Botez, Prof. Gary Evans, Dr. Robert Amantea, Dr.
Ray Beach, Dr. Mark Emanuel, and Dr. Richard Solarz for their critical
reviews of parts of the manuscript. I am thankful to Guinevere for her quiet
companionship, during many hours spent typing at the computer. Finally,
I would like to express my gratitude to my wife, Diane, for her patience,
understanding, and encouragement, and I dedicate this book to her.
Danville, California Nils W. Carlson
April 1994
Table of Contents
1. Introduction and Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 History of Diode-Laser Array Development. . . . . . . . . . . . . . . . 1
1.2 Nonsemiconductor Laser Arrays. . . . . . . . . . . . . . . . . . . . . . . . .. 11
1.3 Contributing Factors to Developing
Monolithic Diode-Laser Arrays. . . . . . . . . . . . . . . . . . . . . . . . . .. 12
1.3.1 Key Technological Advances. . . . . . . . . . . . . . . . . . . . . .. 13
1.3.2 Performance Limitations of Single-Element
Diode Lasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14
1.3.3 Distinction Between Coherent
and Incoherent Diode-Laser Arrays. . . . . . . . . . . . . . . .. 15
1.3.4 Applications for Diode-Laser Arrays. . . . . . . . . . . . . . .. 18
1.4 Design Concepts for Coherent Diode-Laser Arrays. . . . . . . . .. 19
1.4.1 Laterally Coupled Diode-Laser Array Concepts. . . . . .. 21
1.4.2 Longitudinally Coupled Diode-Laser Array Concepts.. 26
1.4.3 Output Coupling Mechanisms. . . . . . . . . . . . . . . . . . . . .. 29
2. Fundamentals of High-Power Operation. . .. . . .. .. . .. . .. .. 31
2.1 Threshold Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31
2.2 Current-Gain Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37
2.3 Optimizing Operation Above-Threshold. . . . . . . . . . . . . . . . . .. 41
2.3.1 Differential Quantum Efficiency. . . . . . . . . . . . . . . . . . .. 41
2.3.2 Conversion Efficiency .. . . . . . . . . . . . . . . . . . . . . . . . . . .. 44
2.3.3 Maximizing Conversion Efficiency .................. 46
2.3.4 Nonlinear Gain Saturation and Conversion Efficiency. 49
2.3.5 Maximizing Power-Extraction Efficiency. . . . . . . . . . . .. 53
2.3.6 Efficiency and Power-Current Characteristics:
Nonlinear Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55
2.4 Scaling Properties of Semiconductor
and Non-Semiconductor Lasers. . . . . . . . . . . . . . . . . . . . . . . . . .. 58
2.5 Scaling Limitations on Power Performance of Diode Lasers .. 63
2.6 Effect of Carriers on Optical Properties ................... 66
2.7 Linewidth Broadening Factor. . . . . . . . . . . . . . . . . . . . . . . . . . .. 70
2.8 Thermal Effects in High-Power Arrays. . . . . . . . . . . . . . . . . . .. 72
2.8.1 Effect of Heating on Diode-Laser Characteristics. . . .. 72
X Table of Contents
2.8.2 Heat Dissipation in Diode-Laser Arrays. . . . . .. . . . . .. 74
2.8.3 Thermal Management and Performance Limitations.. 79
3. Spatial and Spectral Mode Discrimination. . . . . . . . . . . . . . .. 83
3.1 Spatial Modes of Planar Semiconductor Waveguides. . . . . . .. 83
3.1.1 Index Guiding. . . . . . . . .. . . . .. . . .. . . . . . . . . . . .. . . .. 88
3.1.2 Gain Guiding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 89
3.1.3 Mixed Guiding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 90
3.1.4 Parabolic Dielectic-Profile Waveguide Model. . . . . . . .. 91
3.2 Lateral-Mode Discrimination and Modal Gain.. . . .. . . . . . . .. 94
3.3 Single-Frequency Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 99
3.3.1 Number of Modes in Diode-Laser Arrays ............ 100
3.3.2 Spontaneous-Emission Factor ...................... 103
3.3.3 Longitudinal Mode Structure ...................... 108
3.3.4 Spectral Linewidth ............................... 111
3.4 Frequency-Locking of Diode-Laser Oscillators .............. 114
3.4.1 Frequency Locking of Independent Laser Oscillators .. 115
3.4.2 Influence of Nonuniformities on Frequency Locking ... 121
4. Theoretical Models for Monolithic Diode-Laser Arrays ... 125
4.1 Multi-Layer Waveguide Structures ........................ 125
4.2 Analysis of Diode-Laser Waveguide Structures ............. 127
4.2.1 Effective-Index Method ........................... 128
4.2.2 Coupled-Mode Approximation ..................... 131
4.2.3 Bloch-Function Analysis of Laser Arrays ............ 138
4.2.4 Two-Dimensional Waveguide Model of Laser Arrays .. 146
4.3 Self-Consistent Models .................................. 150
4.3.1 Electric-Field Propagation Model ................... 151
4.3.2 Carrier-Transport Model .......................... 152
4.3.3 Thermal Model .................................. 154
4.3.4 Outline of Self-Consistent Numerical Procedure ...... 156
4.3.5 Instability of Spatial Modes ........................ 157
4.4 Optical Coherence Theory ............................... 164
4.4.1 Mutual Coherence ................................ 164
4.4.2 Cross-Power Spectrum ............................ 165
4.4.3 Propagation of the Cross-Power Spectrum ........... 166
4.4.4 Far-Field Mutual Coherence ....................... 168
4.4.5 Cross-Spectral Purity ............................. 169
5. Gain-Guided Diode-Laser Oscillators ..................... 171
5.1 Multiple-Stripe Gain-Guided Laser Array Structures ........ 172
5.2 Gain-Tailored Structures ................................ 178
5.3 Unstable-Resonator Diode Lasers ......................... 183
5.3.1 Geometric Optics Analysis of Unstable Resonators .... 185
Table of Contents XI
5.3.2 Unstable-Resonator Diode Lasers with Self-Collimated
Output Beams ................................... 186
5.3.3 Half-Symmetric Unstable-Resonator Diode Lasers .... 187
5.3.4 Tapered-Cavity Diode Lasers ...................... 192
6. Index-Guided Diode-Laser Array Oscillators .............. 197
6.1 Channeled-Substrate Planar Laser Arrays ................. 197
6.2 Ridge-Guided Laser Arrays .............................. 203
6.3 Leaky-Wave-Coupled Arrays ............................. 208
6.3.1 Resonant Optical-Wave Coupling Model. ............ 209
6.3.2 Transverse and Lateral Structures
of Antiguided Arrays ............................. 216
6.3.3 Basic Modal Characteristics
of Antiguided Laser Arrays ........................ 216
6.3.4 Rigorous Modeling of Structural Tolerances
for Antiguided Laser Arrays ....................... 222
6.3.5 Above-Threshold Mode Stability
of an Antiguided Array ........................... 224
7. Surface-Emitting Diode-Laser Arrays ..................... 233
7.1 Fundamentals of GSE Diode-Laser Arrays ................. 233
7.1.1 Grating Feedback and Output-Coupling Elements .... 234
7.1.2 Principles of GSE Laser Array Design and Operation. 239
7.2 Mode Discrimination Properties of GSE Laser Arrays ....... 250
7.2.1 Boundary-Element Model
of Grating-Coupled Waveguides .................... 250
7.2.2 Coupled-Wave Model of GSE Laser Arrays .......... 254
7.2.3 Network Models of GSE Laser Arrays ............... 266
7.2.4 Network Analysis of Ring-Configured
GSE Laser Array. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
7.3 Vertical-Cavity Surface-Emitting Laser Arrays ............. 276
7.3.1 Scaling of Two-Dimensional VCSEL Arrays .......... 277
7.3.2 Modal Properties of Two-Dimensional
VCSEL Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
8. Master-Oscillator Power-Amplifier Diode Lasers .......... 285
8.1 Edge-Emitting MOPAs .................................. 286
8.1.1 Semiconductor-Diode Amplifier Arrays .............. 288
8-.1.2 Discrete Broad-Area MOPAs ...................... 289
8.1.3 Monolithic Edge-Emitting MOPAs ................. 293
8.1.4 Tapered MOPAs ................................. 299
8.2 Grating-Coupled Surface-Emitting MOPAs ................ 310
8.2.1 Cascaded Grating-Coupled Surface-Emitting MOPAs . 311
8.2.2 Active Grating-Coupled MOPAs:
Operating Principles .............................. 317