Monolithic GaInAs quad-p-i-n photodiodes for polarization-diversity optical receivers

GaInAs quad p-i-n photodiodes which monolithically integrate two sets of twin-p-i-n photodiodes have been fabricated for a polarization-diversity optical receiver designed for practical coherent lightwave transmission systems. Each p-i-n photodiode achieved a very small capacitance of 616-66 fF, a dark current of 6 pA-6 nA, and a high quantum efficiency of 86-88%. The cutoff frequency of the twin-p-i-n photodiodes exceeded 13 GHz. A common-mode rejection ratio (CMRR) of -30 dB was measured for the two sets up to 10 GHz. The optical/electrical crosstalk between the two sets of twin-p-i-n photodiodes was about -40 dB at 14 GHz.<
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