Electrical Engineering Research Electrical Engineering
Gary Evans1993, SURFACE EMITTING SEMICONDUCTOR LASERS AND ARRAYS
Practical demonstrations of diode laser emission from the broad surface area rather than from the cleaved facet of the wafer are relatively recent. This is so despite the fact that the concepts are many years old. The vertical-cavity approach was demonstrated by Melngailis in 1964, and the grating surface emitting and folded-cavity approach were reported by many authors in the mid to late 1970s. Many, perhaps most, of the concepts discussed in this book were around for many years before they were actively pursued. The advances over the last ten years, mainly in materials, are largely responsible for the capability to implement the ideas presented into working devices. We can look forward to continued progress in materials, processing, and design during the next decade and can expect to see semiconductor laser performance outstripping even our present dreams. There are now frequent reports on all three principal types of diode laser and diode laser array surface emitters in the literature. Unlike edge-emitting semiconductor lasers, the surface emission approach allows the use of mass production techniques throughout the fabrication process. In addition, the surface emission approach allows testing of the completed devices at the wafer level, before dicing and packaging. These same capabilities yielded tremendous reductions in cost and enormous increases in the performance and reliability of transistors and other solid state electronic devices. Surface-emitting approaches also allow the integration of single or numerous lasers to form photonic integrated circuits or high power, monolithic, two-dimensional arrays. Because of the now extensive literature on surface-emitting diode lasers and arrays and the proposed and emerging applications of these exciting and practical new devices in a variety of systems, we feel that this in-depth book covering the field will be useful to researchers, users, and students interested in the field of lasers, electrooptics, and optical communication. Recent work has been motivated by numerous goals, including low power, integrated sources to replace electrical interconnects with optical interconnects for ultra large-scale integrated circuits; two-dimensional, independently addressable laser arrays for neural networks; steerable output beams for optical computers; high power with large emitting areas for pumping solid-state lasers; and coherent, single frequency, high-power operation with a controlled output beam for space communication and second harmonic generation. The information in this book is intended to provide the reader with both knowledge about fundamental concepts and the present state of the art of surface-emitting lasers. There are definitive chapters on vertical-cavity, etched facet-mirror, and grating surface emitters. Additional chapters treat the operation of Bragg grating couplers; edge-emitting diode laser arrays; the theory of phase locking, modes, and beam steering of surface-emitting arrays; external methods of phase locking arrays; coherence and phase control in laser arrays; and thermal considerations in two-dimensional surface-emitting arrays. We have fortunately been able to enlist some of the leading researchers and developers of surface-emitting diode lasers to contribute to this book. We wish to thank them for many interesting and productive discussions in connection with the preparation of this work. We also wish· to thank RCA Laboratories (now the David Sarnoff Research Center), Princeton, New Jersey, for providing both of us with talented collaborators, up-to-date equipment, and a pleasant environment in which most of our work described herein was carried out.
