Development of Ultra-High-Speed and Ultra-Stable Single-Mode Semiconductor Lasers Based on Gain-Couplek Distributed Optical feedback

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1. Theoretical Study of Gain-Coupled (GC) Distributed-Feedback (DFB) Semiconductor Lasers : Theoretical analyses have been conducted on such issues as polarization dependence of coupling coefficients, linewidth enhancement factor, and enhancement of external efficiency by asymmetric facet coating. A number of important results have been obtained.2. Quantum Well GC DFB Lasers : By using organo-metallic vapor phase epitaxy (OMVPE) of a single quantum well (SQW) on a substrate Having a diffraction grating corrugation, we have obtained an SQW whose thickness changes periodically with the grating pitch. We have confirmed the existence of the gain coupling in this structure, and achieved room-temperature CW oscillation with 30mA threshold, 47dB side-mode suppression ratio (SMSR), and high single-longitudinal-mode (SLM)yield.3. InGaAsP/InP Long-Wavelength GC DFB Lasers : By utilizing OMVPE and reactive (RIE), we have succeeded in fabricating corrugated active layers of inGaAsP quaternary mate … More rials, and made fabrication of long-wavelength GC DFB lansers possible for the first time. The threshold current of room-temperature CW operation in these lasers was as low as 12-16mA, and SMSR was as large as 55dB (which is the largest among ever reported values). Minimum spectral linewidth in a 600um device was 2.35MHz. Gain switching operation of these devices resulted in option short pulses with and 0.15nm (time-averaged) spectral width. The effective linewidth enhancement factor calculated from these data is 0.76, a remarkably low value. The spectral width at -20dB under 2.4GHz direct modulation was also measured, and was as small as 0.2nm.4. Absorptive Grating GC DFB Lasers : We have determined an optimum duty Factor of the periodic absorptive Grating theoretically. We have also proposed use of conduction-type inversion for the adsorptive region in order to suppress nonlinear operation due to the saturable nature of the aborption. These measures have been applied to a multiple quantum well (MQW) GaAs/GaAlAs lasers, and resulted in low threshold current of 8.5mA, high differential efficiency of 0.8mW/mA, and large SMSR of 47dB in the fabricated device. Despite the fact that the lasers had as-cleaved facets, the yield of SLM operation was very high, i.e., 75%-95%. The minimum spectral linewidth of 2.2MHz measured in a 200um device was very narrow. Less