Abstract
We report a polarization-multiplexed 10Gsymbol/s, 64QAM (120Gbit/s) coherent transmission over 150km by using an optical phase-locked loop (OPLL) circuit employing narrow linewidth LDs. The OPLL realized low phase noise demodulation of 64QAM signal. As a result, 120Gbit/s data signal were transmitted with a bit error rate (BER) performance below a forward error correction (FEC) threshold of 2×10-3.