1 Gsymbol/s, 64 QAM coherent optical transmission over 150 km with a spectral efficiency of 3 bit/s/Hz

A 1 Gsymbol/s, 64 QAM coherent signal was successfully transmitted over 150 k m using heterodyne detection with a frequency-stabilized fiber laser and an optical phase-locked-loop technique. The spectral efficiency reached as high as 3 bit/s/Hz.