Table Of ContentLASER DIODE MODULATION AND NOISE
Advances in Optoelectronics (ADOP)
Editor: T. OKOSHI (Univ. of Tokyo)
Associate Editor: T. KAMIYA (Univ. of Tokyo)
Editorial Board:
G. A. ACKET (Philips Res. Labs., The Netherlands)
J. A. ARNAUD (Univ. Limoges, France)
S. A. BENTON (Mass. Inst. Technol., U.S.A.)
W. A. GAMBLING (Univ. ofS outhampton, England)
T. G. GIALLORENZI (Naval Res. Lab., U.S.A.)
J. W. GOODMAN (Stanford Univ., U.S.A.)
I. HAYASHI (Optoelectr. Joint Res. Lab., Japan)
H. INABA (Tohoku Univ., Japan)
E. A. J. MARCATILI (AT&fBellLabs., U.S.A.)
Y. SUEMATSU (Tokyo Inst. Technol.,Japan)
J. TSUJIUCHI (Tokyo lnst. Technol., Japan)
R. ULRICH (Tech. Univ. Hamburg-Harburg, West Germany)
H.-G. UNGER (Tech. Univ. Braunschweig, West Germany)
Emil WOLF (Univ. ofR ochester, U.S.A.)
H. YANAI (Toshiba Corp. & Shibaura lnst. Technol., Japan)
LASER
DIODE
MODULATION
AND NOISE
K. Petermann
lnstitut fur Hochfrequenztechnik,
Technische Universitiit Berlin
Kluwer Academic Publishers
Dordrecht I Boston I London
==
I.
KTK Scientific Publishers / Tokyo
Library of Congress Cataloging-in-Publication Data
Petermann, K_ (Klaus)
Laser diode modulation and noise.
(Advances in optoelectronics ; 3)
Bibliography: p.
Includes index.
1. Semiconductor lasers. 2. Seviconductor lasers-
Noise. 3. Modulation (Electronics) I. Title.
II. Series.
TA1700.P47 1988 621.3815'22 88-3011
ISBN-l3: 978-0-7923-1204-8 e-ISBN-13: 978-94-009-2907-4
001: 10.1007/978-94-009-2907-4
Published by Kluwer Academic Publishers
P.O. Box 17,3300 AA Dordrecht, The Netherlands.
in co-publication with KTK Scientific Publishers (KTK), Tokyo, Japan
Sold and distributed in the U.S.A. and Canada
by KJuwer Academic Publishers,
101 Philip Drive, Norwell, MA 02061, U.S.A.
in Japan by KTK Scientific Publishers (KTK),
307 Shibuyadai-haim, 4-17 Sakuragaoka-cho, Shibuya-ku, Tokyo 150, Japan
In all other countries, sold and distributed
by KJuwer Academic Publishers,
P.O. Box 322, 3300 AH Dordrecht, Holland
All Rights Reserved
Copyright © 1988 by KJuwer Academic Publishers
Softcover reprint of the hardcover 1s t edition 1988
No part of the material protected by this copyright notice may be reproduced or utilized in
any form or by any means, electronic or mechanical, including photocopying, recording or
by any informational storage and retrieval system, without written permission from the
copyright owner.
CONTENTS
PREFACE ~
Chapter 1
INTRODUCTION 1
Chapter 2
BASIC LASER CHARACTERISTICS 5
2.1 Double heterostructure characteristics 5
2.2 Direct and indirect semiconductors 7
2.2.1 Energy-and momentum conservation 7
2.2.2 Semiconductor materials for direct and indirect semi-
conductors 8
2.3 Emission and absorption 10
2.3.1 Density of photon oscillation states 11
2.3.2 Principal mechanisms of radiative transitions 12
2.3.3 Carrier lifetime and lifetime of spontaneous emission 15
2.3.4 Gain and stimulated emission 18
2.4 Lasing characteristics of Fabry-Perot-type lasers 25
2.4.1 Lasing conditions 25
2.4.2 Dynamic characteristics of laser operation 28
2.4.3 Light current characteristics, threshold current and
quantum efficiency 32
2.4.4 Basic laser structures 36
2.4.5 Modifications for the spontaneous emission term 41
2.5 Dynamic single-mode laser structures 44
2.5.1 DFB laser characteristics 47
References 52
Chapter 3
LONGITUDINAL MODE SPECTRUM OF LASING EMISSION 59
vi Contents
3.1 Multimode rate equations 59
3.2 Spectral envelope for Fabry-Perot-type lasers (linear gain) 61
3.3 Influence of nonlinear gain on the spectral characteristics 65
3.3.1 Symmetric nonlinear gain 65
3.3.2 Asymmetric nonlinear gain 69
3.3.3 Nonlinear gain, conclusions 75
References 76
Chapter 4
INTENSITY-MODULATION CHARACTERISTICS OF
LASER DIODES 78
4.1 Modulation characteristics by studying single-mode rate
equations 78
4.1.1 Tum-on delay 81
4.1.2 Rate equations, small signal analysis 83
4.1.3 Relaxation oscillation damping 86
4.1.4 Upper limits for the modulation bandwidth of laser
diodes 88
4.2 Influence of lateral carrier diffusion on relaxation oscillation
damping 91
4.3 Modulation bandwidth limits due to parasitic elements 93
4.4 Examples for high speed modulation of laser diodes 95
4.5 Modulation and longitudinal mode spectrum 97
4.5.1 Transient spectra of laser diodes 98
4.5.2 Lasing spectra under high speed modulation 100
4.5.3 Dynamic single-mode condition 105
4.6 Modulation with binary signals 106
4.7 Harmonic and intermodulation distortions (without fibre
interaction) 108
4.7.1 Harmonic and intermodulation distortions for low
modulation frequencies 109
4.7.2 Harmonic and intermodulation distortions for high
modulation frequencies 113
References 114
Chapter 5
FREQUENCY-MODULATION CHARACTERISTICS OF
LASER DIODES 119
5.1 Relation between intensity-modulation and frequency modu-
lation 119
5.2 Current/frequency-modulation characteristics 122
5.3 Chirp effects in directly modulated laser diodes 125
Contents vii
5.3.1 Spectral line broadening due to laser chirping 125
5.3.2 Chirp-reduction by proper pulse shaping 127
5.3.3 Time-bandwidth product of chirped pulses 128
5.304 Transmission of chirped pulses over single-mode fibres 131
504 Possibilities of modifying the chirp parameter a 135
504.1 Dispersion ofthe chirp parameter a 135
504.2 Chirp oflaser diodes, coupled to optical cavities 136
References 141
Chapter 6
INSTABILITIES AND BISTABILITY IN LASER DIODES 145
6.1 Repetitive self-pulsations due to lateral instabilities 146
6.2 Instability and bistability in laser diodes with segmented
contacts 147
References 150
Chapter 7
NOISE CHARACTERISTICS OF SOLITARY LASER DIODES 152
7.1 Relative intensity noise (RIN) 152
7.1.1 Basic properties of noise signals 152
7.1.2 Definition and measurement of RIN 154
7.1.3 Requirement of RIN for intensity modulated systems 155
7.2 Introduction of the spontaneous emission noise 157
7.3 Intensity noise of laser diodes 160
7.3.1 Intensity noise of laser diodes by studying single-
mode rate equations 160
7.3.2 Mode partition noise 163
7.3.3 Mode partition noise analysis for nearly single-mode
lasers 166
7.304 Mode-hopping noise 170
7.3.5 1/f -intensity noise 172
7 A Statistics of intensity noise 173
704.1 Statistics of amplified spontaneous emission 176
7.4.2 Probability density distribution for the total laser light
output 180
704.3 Statistics of mode partition noise 181
7.404 Turn-on jitter in laser diodes 184
7.5 Mode partition noise for the transmission of pulse-code
modulated (PCM)-signals 186
7.5.1 Multimode lasers 186
7.5.2 The mode partition coefficient k 192
7.5.3 Nearly single-mode lasers 194
viii Contents
7.6 Phase and frequency noise 196
7.6.1 Phase and frequency noise characterization in general 196
7.6.2 Spectral line shape for white frequency noise 198
7.6.3 Spectral line shape for 1I f-frequency noise 200
7.6.4 Frequency noise and spectral linewidth for single-
mode laser diodes 202
7.6.5 Power-independent contribution to the linewidth of
laser diodes 205
7.6.6 Correlation between FM-noise and AM-noise 207
References 208
-:hapter 8
l~OISE IN INTERFEROMETERS INCLUDING MODAL
NOISE AND DISTORTIONS 214
8.1 Noise in interferometers 215
8.1.1 Complex degree of coherence 215
8.1.2 Interferometric noise analysis for single-mode lasers 216
8.1.3 Interferometric set-ups for measuring the linewidth
and the degree of coherence 224
8.1.4 Interferometric noise analysis for multimode lasers 227
8.2 Modal noise 232
8.2.1 Modal noise for monochromatic light sources 233
8.2.2 Modal noise for single-mode lasers with finite spectral
linewidth 238
8.2.3 Modal noise for multimode laser diodes 242
8.2.4 Modal distortions 243
8.3 Modal noise and distortions in single-mode fibres 243
References 246
Chapter 9
SEMICONDUCTOR LASERS WITH OPTICAL FEEDBACK 250
9.1 Amplitude and phase conditions for laser diodes with
external cavities 251
9.1.1 Short external reflectors for longitudinal mode stabili-
zation 256
9.1.2 Emission frequency shifts due to optical feedback 258
9.1.3 Single external cavity mode condition 259
9.1.4 Spectral linewidth for laser diodes with external
opticaJfeedback 261
9.2 Dynamics of laser diodes with external reflections 267
9.2.1 Derivation ofthe time-dependent electric field 267
9.2.2 Modulation characteristics of external-cavity lasers 269
9.3 Laser diodes with distant reflections 271
Contents ix
9.3.1 Classification of feedback regimes 273
9.3.2 Phase and frequency noise of laser diodes with distant
reflectors 275
9.3.3 Intensity noise in laser diodes with distant reflectors 276
9.3.4 Coherence collapse 279
9.3.5 Tolerable feedback levels 282
References 285
Chapter 10
LASER DIODES WITH NEGATIVE ELECTRONIC
FEEDBACK 291
10.1 Modulation characteristics of laser diodes with negative
electronicfeedback 291
10.2 Linewidth narrowing and phase noise reduction with nega-
tive electronic feedback 294
References 296
Chapter 11
CIRCUITRY FOR DRIVING THE LASER DIODE 298
11.1 Schemes for stabilizing the bias current 298
11.2 Laser drivers with optoelectronic integration 302
References 305
APPENDIX 306
INDEX 308
PREFACE
Laser diodes represent a key element in the emerging field of opto
electronics which includes, for example, optical communication, optical
sensors or optical disc systems. For all these applications, information is
either transmitted, stored or read out. The performance of these systems
depends to a great deal on the performance of the laser diode with regard
to its modulation and noise characteristics.
Since the modulation and noise characteristics of laser diodes are of
vital importance for optoelectronic systems, the need for a book arises
that concentrates on this subject. This book thus closes the gap between
books on the device physics of semiconductor lasers and books on system
design.
Complementary to the specific topics concerning modulation and noise,
the first part of this book reviews the basic laser characteristics, so that
even a reader without detailed knowledge of laser diodes may follow the
text. In order to understand the book, the reader should have a basic
knowledge of electronics, semiconductor physics and optical communica
tions. The work is primarily written for the engineer or scientist working in
the field of optoelectronics; however, since the book is self-contained and
since it contains a lot of numerical examples, it may serve as a textbook
for graduate students.
In the field of laser diode modulation and noise a vast amount has been
published during recent years. Even though the book contains more than
600 references, only a small part of the existing literature is included.
Actually, the book contains only those references which are directly used
in the text.
I am indebted to many colleagues for helpful discussions and advice.
Especially, I wish to express my thanks to my associates N. Schunk and V.
Kriiger for reviewing all parts of the manuscript. I am also indebted to Dr
A. P. Mozer from SEL, Stuttgart, and Dr G. Arnold from AEG, Vim, for
a critical reading of the manuscript with helpful comments. I also thank Dr
