Chapter 3 - High-Speed Lasers

Abstract

High-speed semiconductor lasers are an integral part in the implementation of high-bit-rate optical communications systems. They are compact, rugged, reliable, long-lived, and relatively inexpensive sources of coherent light, and due to the very low attenuation window that exists in the silica-based optical fiber they have become the mainstay of optical fiber communication systems. This chapter reviews the present level of understanding of the high-speed properties of semiconductor lasers. High-speed semiconductor lasers in both the GaAs and the InP systems have made great strides over the years. The emphasis here will be on the principles of high-speed operation. Although, InP-based lasers have become technologically important for optical communications system applications, device structures and experimental data will be drawn from both material systems to illustrate the points being discussed. Theoretical treatment and experimental evidence for the carrier transport effects on the high-speed properties of quantum well lasers are presented. A number of issues are discussed with respect to designing and fabricating lasers with large modulation bandwidths. There is an obvious need for good-quality optical material with low internal loss to fabricate lasers with low threshold currents and large output powers. This ensures that the threshold carrier density is low and that the devices can be biased easily at many times the threshold current without the detrimental thermal effects.