One of the most important applications for semiconductor lasers is for use in digital optical transmission systems. Within such an environment, many demands are placed on the laser performance; it must operate over a wide temperature range, have high output power which must couple efficiently into a monomode optical fibre, it must be capable of high modulation rate and its spectral output must be stable. In this chapter we consider many of the design features which are incorporated into practical devices in order to meet these requirements. These include the types of laser cavity which are used to control the spatial and spectral output, and which strongly influence both the laser to fibre coupling efficiency and the overall system dispersion characteristics. The influence of materials parameters on device performance, in particular the transient behaviour and linewidth are considered, and finally some of the possible advantages of quantum well lasers are discussed.
KeywordsActive Layer Carrier Density Semiconductor Laser Longitudinal Mode Active Layer Thickness
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