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.