Low-loss monolithic integration of balanced twin-photodetectors with a 3 dB waveguide coupler for coherent lightwave receivers

Low-loss monolithic integration of a 3-dB waveguide coupler with twin photodetectors using large-mode size guides, mirror coupling, and low-capacitance lateral detectors is demonstrated. Waveguide-mirror integration introduces only approximately=1 dB optical insertion loss at 1.54 mu m wavelength, compared to top-illuminated detectors. Full balanced operation of the monolithic circuit with 33-dB local oscillator intensity noise suppression is demonstrated.>