Single-channel 768 Tbit/s, 64 QAM coherent Nyquist pulse transmission over 150 km with a spectral efficiency of 97 bit/s/Hz

We achieved a record capacity of 7.68 Tbit/s in a single-channel OTDM transmission with a 9.7 bit/s/Hz spectral efficiency, where a polarization-multiplexed 640 Gbaud, 64 QAM coherent Nyquist pulse has been transmitted over 150 km. In this scheme, a 1.39 ps optical Nyquist pulse with an OSNR of 53 dB at a 0.1 nm resolution was generated by combining a mode-locked laser and a highly nonlinear fiber and used at both the transmitter and receiver. Phase synchronization was achieved between these pulse sources with an advanced optical phase-locked loop based on the higher harmonics of the mode-locked laser mode. In addition, we suppressed a nonlinear phase rotation at an EDFA in the transmitter by broadening the pulse width with second-order dispersion and recompressed it to the original pulse width before a 150 km transmission link. We succeeded in a bit error rate below 2 x 10 -2 for all tributaries.