Fabrication and photo-response of monolithic 90° hybrid-photodetector array chip for QPSK detection

A quadrature phase-shift keying[QPSK]coherent photodetector chip consisting of a 4×4 multimode interference 90° optical hybrid and a four-channel evanescent photodetector array is designed and fabricated with its photo-response in the L-band characterized.The metal organic chemical vapor deposition regrowth method is adopted to realize active-passive monolithic integration.The chip exhibits a low dark current below 100 nA for each photodetector in the array,a low excess loss of 0.85 dB,a common mode ratio rejection better than 13.6 dB,and a phase deviation within±10° over the 40 nm wavelength span.