Development of DFB Lasers with New Structures for Complete Single-Longitudinal-Mode Oscillation

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As a primary step to develop 0.8 <mu> m range distributed feedback (DFB) lasers with modulated stripe width structure, the head investigator and coworkers fabricated and studied GaAlAs/GaAs ridge waveguide DFB lasers in 1985 academic year and achieved the lowest threshold current and high differential quantum efficiency at that time. Possibility of obtaining feasible DFB lasers in the short wavelength regime was thereby shown, yet it was found from a precise lateral mode analysis that this waveguide structure is not necessarily favorable to liquid phase epitaxy (LPE). In 1986 academic year, double channel planar buried heterostructure was instead employed in fabricating GaAlAs/GaAs DFB lasers for the first time, as a more appropriate waveguide structure for LPE. Significant improvements in characteristics were attained in the resulting devices, such as threshold current of 12mA which was the lowerst ever reported. Various stripe width modulation schemes were then applied to the develop … More ed devices, where complete single-longitudinal= mode (SLM) oscillation was in practice accomplished, being consistent with theoretical predictions.Investigator Kamiya studied material physics of semiconductor lasers toward another evolution of their functions. He determined carrier lifetime and recombination coefficients in semiconductors making use of a phase shift method. The effects of Auger recombination on temperature dependence of bistable characteristics in semiconducor lasers were also discussed. These studies contributed to obtaining detailed rate equations describing semiconductor lasers, and acquiring increased accuracy in material parameters.Investigator Nagai examined SLM operation of DFB lasers by means of both facets cleaved structure. He discussed theoretically and experimentally SLM probability and temperature range of SLM operation in 1.3 and 1.5 <mu> m devices with cleaved facets, thus contributing to clarification of the effectiveness of the cleaved facet structure.Investigator Akiba studied SLM oscillation by quarter-wave-shifted structure. Through detailed theoretical examination and experimental observation of 1.5 <mu> m range quarter-wave-shifted devices, he established design principles and fabrication techniques, thereby contributed toward practical applications of such lasers. Less