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Results of a development program for light-emitting-diode (LED)-pumped neodymium-doped yttrium aluminum garnet (Nd: YAG) lasers highlight a significant design feature: an index-matching method to increase the coupling efficiency of the laser. A solid-glass half-cylinder measuring 5.0×5.6 cm was used for index matching and also as a pumping cavity reflector. An array of twenty 0.034×0.254-cm GaAlAs diodes, connected in series, aligned such that the emission area formed a straight line, was used to excite a 1.5×56-mm laser rod. The interfaces between the diode array, glass half-cylinder, and laser rod were filled with viscous fluid of refractive index n = 1.55. Experiments performed with both the glass half-cylinder and a gold-coated stainless steel reflector under the same operating conditions indicated that the index-matching half-cylinder gave 160–200% improvement of coupling efficiency over the metal reflector at various operating temperatures. For a 207-A/cm2 driving current density the laser produced cw output power of 27 mW.

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We report the pump-probe study results of the nonlinear switching behaviors in an all-activesemiconductor-optical-amplifier loop device as depicted in Fig. 1. The ridge-loading waveguide loop has a radius 300 pm with a ridge width 4 pm. The loop is connected to a multi-mode interference (MMI) waveguide with a length 500 pm and a ridge width 8 pm which serves as the nonlinear element. Then, the input and output ports are also 4 pm waveguides with both lengths about 100 p n . For injecting different currents in different