INP-BASED 10-GHZ BANDWIDTH POLARIZATION DIVERSITY HETERODYNE PHOTORECEIVER WITH ELECTROOPTICAL ADJUSTABILITY

A polarization diversity optical receiver, integrated with two pairs of balanced photodiodes in the InP/InGaAsP material system, is described. This circuit includes two polarization splitters based on modal birefringence and, for the first time, adjustable 3-dB TE and TM directional couplers (relaxing fabrication tolerances). On-chip losses are below 2.5 dB (TE) and 5.5dB (TM). Waveguide to PIN coupling efficiency is > 95%. Polarization crosstalk is in the 9-10-dB range, 3-dB couplers balance can be recovered, and common mode rejection ratio (CMRR) lower than -30dB is obtained and remains below -20dB over 6GHz. Balanced receiver circuit 3-dB bandwidth is in excess of 10GHz.