Laser Diode Microsystems

348 Pages·2004·8.811 MB·English

by  Professor Dr. Hans Zappe (auth.)

MICROTECHNOLOGY AND MEMS
Springer-Verlag Berlin Heidelberg GmbH
ONLINE LIBRARY
Physics and Astronomy
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MICROTECHNOLOGY AND MEMS
Series Editor: H. Baltes D. Liepmann
The series Microtechnology and MEMS comprises text books, monographs, and
state-of-the-art reports in the very active field of micro systems and microtech
nology. Written by leading physicists and engineers, the books describe the basic
science, device design, and applications. Theywill appeal to researchers, engineers,
and advanced students.
Mechanical Microsensors
By M. Elwenspoek and R. Wiegerink
CMOS Cantilever Sensor Systems
Atomic Force Microscopy and Gas Sensing Applications
By D. Lange, O. Brand, and H. Baltes
Micromachines as Tools for Nanotechnology
Editor: H. Fujita
Modelling of Microfabrication Systems
By R. Nassar and W. Dai
Laser Diode Microsystems
ByH.Zappe
Silicon Microchannel Heat Sinks
Theories and Phenomena
By L. Zhang, K.E. Goodson, and T. W. Kenny
Hans Zappe
laser Diode Microsystems
With 167 Figures
" Springer
Professor Dr. H. Zappe
Laboratory for Micro-optics
Institute of Microsystem Technology
University of Freiburg
79110 Freiburg, Germany
E-mai!: [email protected]
Series Editors:
Professor Dr. H. Baltes
ETH Ziirich, Physical Electronics Laboratory
ETH Hoenggerberg, HPT-H6, 8093 Ziirich, Switzerland
Professor Dr. Hiroyuki Fujita
University of Tokyo, Institute ofIndustrial Science
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
Professor Dr. Dorian Liepmann
University of California, Department of Bioengineering
466 Evans Han, #1762, Berkeley, CA 94720-1762, USA
ISSN 1439-6599
ISBN 978-3-642-07333-5
Library of Congress Cataloging in Publication Data.
Zappe, Hans P.
Laser diode microsystems / Hans Zappe.
p.cm. - (Microtechnology and MEMS)
lncludes bibliographical references and index.
ISBN 978-3-642-07333-5 ISBN 978-3-662-08249-2 (eBook)
DOI 10.1007/978-3-662-08249-2
1. Microelectronics. 2. Solid-state lasers. 3. Diodes, Semiconductor. I. Title. II. Series.
TK7874.Z37 2003 621.36'6-dc21 2003054229
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Preface
The functionality of micro systems is increasing daily. Whereas a decade ago a
purely mechanical silicon micro-machined device was justifiably considered a
technical marvel, microsystems may now include electrical, magnetic, chemical,
optical or biological functions. The increasingly interdisciplinary approach
required for advanced work in this area is one of the reasons that microsystem tech
nology has become one of the most exciting fields in which to work.
Optics in microsystems has seen considerable growth due in part to significant
demand from industry, particularly that involved in telecommunications. Optical
microsystems are in use and under development for transmission, switching and
reception of optical data streams, for complex optical sensor systems, for optical
data storage and a host of medical applications. As many of these applications
mature, light-based microsystems will become increasingly industrially viable and
of widening technological importance.
Optical microsystems require a source of photons. Due to their miniscule size,
high efficiency and broad range of available wavelengths and output powers, semi
conductor laser diodes (as well as, frequently, light-emitting diodes) are most often
the photon source of choice for inclusion in a compact, high-performance optical
microsystem. With an estimated almost $3 billion market share in 2003, the micro
scopic laser diode has eclipsed all macroscopic types of lasers and is by its very
nature ideal for employment in microsystems.
This text covers the physics, technology and application of laser diodes for use
in optical microsystems.1t is intended for students studying and working in micro
system or MEMS engineering as well as engineers and scientists active in any of
the broad spectrum of disciplines in which micro systems are becoming increas
ingly relevant. Our tour through this field will encompass a discussion of basic
laser diode physics as well as the structure, fabrication techniques and operating
characteristics of a variety of diode lasers. An examination of the most important
micro-optical components as well as the assembly techniques required for the con
struction of a complete optical micro system will give the reader a hint of the
breadth of optical technology available at these physical dimensions.
VIII Preface
Acknowledgments
It is with pleasure that I am able to thank many individuals who have contributed
their time and intellectual effort to the successful completion of this book.
A number of people have dedicated significant energy to reading and correcting
large portions of the manuscript. I am very grateful to my colleagues Wolfgang
Monch and Oliver Paul here at the Institute for Microsystem Technology at the
University of Freiburg, Markus Rossi of Heptagon Oy, Zurich, Joachim Wagner of
the Fraunhofer Institute for Applied Solid State Physics, Freiburg, and Olav Sol
gaard of Stanford University, California, for their thorough reading and extensive
review of portions of the text. I am likewise indebted to Henry Baltes of the ETH
Zurich for his reading of and commenting on the text as well as his assistance in
seeing the book to publication. Special thanks are due to my father, Hans H. Zappe,
of San Jose, California, for his thorough analysis of the first chapter and his insight
ful comments into a number of physical phenomena.
I have the truly great pleasure of working with a devoted team in the Micro
optics Laboratory at the Institute for Microsystem Technology and many of my co
workers have contributed in some form to the text. I am indebted to Bernd Aatz and
Carsten Glasenapp for the extensive measurement of laser characteristics which we
use as examples in Chapter 5 and for not being given to exasperation when I
wanted yet something else measured anew; Dennis Hohlfeld for providing the VCL
cavity calculations and the photograph of his thermally-tunable filter shown in
Fig. 6.36; Mario Hug and Florian Krogmann for micro-optical lens and component
data; Alexander Hodapp for the refractive micro-lens of Fig. 6.12; Andreas Mohr
for the Fresnel lens of Fig. 6.15; and David Kallweit for the calculated fiber mode
profile of Fig. 6.29. I am most grateful to Nadja Kattbagen for keeping things in the
lab running when my brain was, as it usually is, elsewhere.
The linewidth and noise characteristics presented in Chapter 5 were done at
CSEM, Zurich, and I am particularly grateful to Fabrice Monti di Sopra and Martin
Hess for enabling or performing these measurements. The VCL wafer map of
Fig. 5.38 was likewise a product of my CSEM days and a warm thanks to all my
colleagues from those times is in order. I extend my gratitude to Rainer Michalzik
of the University of Ulm, and Dieter Wiedenmann of U-L-M photonics GmbH for
taking the photograph presented in Fig. 5.4 especially for this text. Many thanks are
due to Markus Rossi of Heptagon Oy for supplying the photograph of the pattern
generator in Fig. 6.25.
I am indebted to Josef Rosenzweig and Michael Schlechtweg of the Fraunhofer
Institute for Applied Solid State Physics, Freiburg, as well as Konrad Czotscher of
Lucent Technologies, Nuremberg, for the very nice eye diagram of Fig. 5.18.
Grateful thanks to Eiji Higurashi of the NTT Microsystem Laboratories, Kana
gawa, for the diagrams and photo of the integrated optical blood-flow sensor of
Fig. 1.1 and Fig. 1.2. and to Ulrike Wallrabe of the Forschungszentrum Karlsruhe,
for supplying photos and diagrams of the hybrid optical displacement sensor of
Fig. 1.3 and Fig. 1.4. I am likewise grateful to Anton Ambrosy of the Alcatel Cor-
Preface IX
porate Research Center, Stuttgart, for the illustrations of the transceiver structure
shown in Fig. 1.5 and Fig. 1.6.
Many of the topics addressed have been the subject of courses for students in
Microsystem Technology at the University of Freiburg and in short courses orga
nized by the Fondation Suisse pour la Recherche en Microtechnique (FSRM)
throughout Europe. I am grateful to all past students and course participants who
provided suggestions, criticisms, comments and general feedback on the material
in an effort to make the presentation clearer and more concise.
Freiburg, July 2003 Hans Zappe
Contents
1 Introduction •.....................•.•.................•...........•......................•...................... 1
1.1 Laser Diodes: A Very Brief History ..................................................... 1
1.2 Laser Diodes in Microsystems ............................................................. 5
1.2.1 Non-Invasive Blood-Flow Monitoring .................................... 5
1.2.2 Optical Distance Measurement ................................................ 7
1.2.3 Optoelectronic Transceiver ...................................................... 8
1.3 Thematic Outline .................................................................................. 9
2 Basic Laser Physics ...................................................................................... 13
2.1 The Handwaving Laser ....................................................................... 13
2.2 Wave Properties of Light.. .................................................................. 15
2.2.1 The Wave Equation ................................................................ 15
2.2.2 Solutions to the Wave Equation ............................................. 17
2.2.3 Spatial and Temporal Frequencies ......................................... 18
2.2.4 Polarization ............................................................................ 21
2.2.5 Energy .................................................................................... 22
2.2.6 Interference ............................................................................ 25
2.2.7 Coherence .............................................................................. 26
2.2.8 Light-Matter Interaction ........................................................ 28
2.3 Quantum Properties of Light .............................................................. 31
2.3.1 Photon Emission and Absorption ........................................... 32
2.3.2 Thermal Equilibrium .............................................................. 34
2.3.3 Transition Rates ..................................................................... 38
2.3.4 Spectral Shape ........................................................................ 40
2.4 Optical Amplification ......................................................................... 43
2.4.1 Absorption vs. Amplification ................................................. 43
2.4.2 Gain ........................................................................................ 45
2.4.3 Laser Beam Growth ............................................................... 48
2.5 Optical Resonant Cavities .................................................................. 49
2.5.1 Fabry-Perot Etalon ................................................................ 49
2.5.2 Resonator Characteristics ....................................................... 52
2.6 Laser Oscillation ................................................................................. 55
2.6.1 The Etalon with Gain ............................................................. 56
2.6.2 Threshold ............................................................................... 57
2.6.3 Lasing Summary .................................................................... 59
XII Contents
3 Semiconductors for Lasers .......................................................................... 63
3.1 Electrical Properties ........................................................................... 63
3.1.1 The Band Structure ................................................................ 64
3.1.2 The Fermi LeveL .................................................................... 67
3.1.3 Carrier Concentration ............................................................ 70
3.1.4 Doping ................................................................................... 75
3.1.5 Carrier Transport .................................................................... 77
3.1.6 The pn Junction ...................................................................... 79
3.2 Optical Properties ............................................................................... 83
3.2.1 Radiative Transitions ............................................................. 83
3.2.2 Absorption ............................................................................. 84
3.2.3 Emission ................................................................................. 86
3.2.4 Non-Radiative Transitions ..................................................... 88
3.2.5 Gain ........................................................................................ 89
3.3 Semiconductor Laser Materials .......................................................... 92
3.3 .1 III-V Semiconductors ............................................................ 92
3.3.2 Wavelength Ranges ............................................................... 95
3.3.3 Heterostructures ..................................................................... 97
3.3.4 Quantum Wells .................................................................... 100
3.4 Waveguides ...................................................................................... 104
3.4.1 Waveguiding: The Ray Optic ModeL ................................ 105
3.4.2 Electromagnetic Model ........................................................ 108
3.4.3 Confinement. ........................................................................ 111
3.4.4 Stripe Waveguides ............................................................... 112
4 Laser Diode Structures .............................................................................. 115
4 .1 Light-Emitting Diodes ...................................................................... 115
4.1.1 Structure ............................................................................... 116
4.1.2 Operating Principle .............................................................. 120
4.1.3 Fabrication Issues ................................................................ 120
4.1.4 Microsystem Aspects ........................................................... 121
4.2 Broad-Area Lasers ............................................................................ 124
4.2.1 Structure ............................................................................... 124
4.2.2 Fabrication Issues ................................................................ 125
4.2.3 Operating Principle .............................................................. 125
4.2.4 Microsystem Aspects ........................................................... 126
4.3 Fabry-Perot Stripe Lasers ................................................................ 126
4.3.1 Structure ............................................................................... 127
4.3.2 Operating Principle .............................................................. 131
4.3.3 Fabrication Issues ................................................................ 131
4.3.4 Microsystem Aspects ........................................................... 133
4.4 Distributed Feedback Lasers ............................................................ 134
4.4.1 Structure ............................................................................... 134
4.4.2 Operating Principle .............................................................. 137
4.4.3 Fabrication Issues ................................................................ 140