A low noise balanced receiver for coherent transmission systems

The authors describe a receiver which is tailored in particular for coherent systems. A pair of low capacitance, high quantum efficiency InGaAs PIN detectors are incorporated to obtain performance near to the quantum limit. Inductive peaking is used to reduce high frequency noise. The circuit was simulated using both SPICE and COMPACT. Inclusion of a prototype front end into a 160 Mbit/s FSK Heterodyne system has resulted in a sensitivity within 3.6 dB to the quantum limit. It is concluded that discrete circuit techniques are capable of delivering high bandwidth, low noise balanced optical receivers. These make possible the implementation of coherent systems operating near the quantum limit with existing local oscillator power levels and linewidths. The use of high quantum efficiency, low capacitance detectors in the front end is fundamental to such systems