60 Gbit/s, 64 QAM LD-based injection-locked coherent heterodyne transmission over 160 km with a spectral efficiency of 9 bit/s/Hz

Abstract

We report an injection-locked 60 Gbit/s 64 QAM coherent transmission employing a laser diode (LD) based heterodyne demodulation circuit. The LDs for the transmitter and receiver were InP-based external cavity laser diodes (ECLDs) emitting at 1538.8 nm. By using an injection locking technique with locking range of 100 MHz, we achieved low phase noise carrier synchronization between the data and the local oscillator with a phase noise of 0.3 deg. As a result, a polarization-multiplexed 64 QAM data signal was successfully transmitted over 160 km with a spectral efficiency of 9 bit/s/Hz.