High sensitivity 636 Mb/s polarization diversity SF-FSK system for field use

A 636 Mb/s coherent polarization diversity SF-FSK (frequency shift keying) system for field use is presented. The system features a high performance AMI (alternate mark inversion) coder in the transmitter, a polarization-diversity optical unit for balanced detection with less than 1.0 dB loss and 17 dB extinction ratio, a phase noise robust receiver front-end designed in microstrip technology with 2.4 GHz bandwidth and a record low noise spectral density of below 4 pA/ square root Hz, as well as a nearly ideal square law detector (based on a monolithic integrated mixer) which has 35 dB dynamic range. The system has a sensitivity of -44.7 dBm, (2/sup 23/-1 PRBS) and a maximum penalty due to polarization fluctuations of 1.0 dB. The system is now ready for a field trial. >