Coherent lightwave transmission over 150 km fibre lengths at 400 Mbit/s and 1 Gbit/s data rates using phase modulation

We report coherent lightwave systems experiments over 150 km employing phase modulation at speeds of 400 Mbit/s and 1 Gbit/s. Bit error rates lower than 10−9 were attained with no evidence of an error rate floor. Receiver sensitivities of −53.3 dBm and −44.5 dBm (10−9 BER) achieved at 400 Mbit/s and 1 Gbit/s with a new balanced mixer receiver correspond to improvements of 10.7 dB and 7.5 dB over the best previously published direct detection results.