Semiconductor Optical Switches Utilizing Thickness Modulation in Depletion Layer

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This research project was to fabricate semiconductor optical switches/modulators for further development of optical communication system and optical information processing. The operating mechanism of our switches is based on the absorption change by depleting around the p-n junction, which is newly proposed by the authors. Two different types of the switch were fabricated. One is the wave-guide type and another is the panel type. Both types were made of AlGaAs/GaAs alloy system grown with the liquid phase epitaxy.As the progress of the wave-guide type switches, 3% change of the transmission was obtained with 8V variation of the applied voltage in 1989, and reached to 99.97% (35dB) of the change in 1990, which may be the top record in world among all optical switches operating with any electronic mechanism. The reason of our progress comes from honest investigation on the diffusion effect of the impurity atom caused under the crystal growth and improvement of the designing method of the … More device. We confirmed the operation of the fabricated device based on the above mentioned mechanism through several measurements. The modulation band width of the device was several 10MHz, which was well characterized with the electric capacitance. By reducing of the capacitance by makiing multi-layer structure as well as narrow stripe structure, the modulation band width may be more widened in future.We also fabricated the panel type structure in succeeding to the wave-guide type. We fabricated preliminary structure consisting with two sets of the p-n junctions because of technical difficulty on crystal growth with liquid phase epitaxy, although the final structure of the panel should consist with large number of the p-n junctions. Connecting three pieces of the device, that is, consisting of 6 sets of the junctions, 10% change of the incident light was observed with 18V variation of the applied voltage. We will improve the device by changing the voltage applying method and making the multi-layer structure in future.We named our device as EDAC (Electron Depleting Absorption Control) Optical Switch/Modulator. Less