7-Tb/s $(7\times1.284~{\rm Tb}/{\rm s}/{\rm ch})$ Signal Transmission Over 320 km Using PDM-64QAM Modulation

We have transmitted a 7×1.284 Tb/s/ch signal over 320-km conventional single mode fiber (SMF-28) with hybrid amplifier spans of 80 km. Each terabit superchannel comprises ten Nyquist wavelength division multiplexing polarization division multiplexing 64 quadrature amplitude modulation subchannels occupying 137.5 GHz, which gives a spectral-efficiency of 7.65 b/s/Hz per superchannel. The bit error ratio of all channels after transmission over 320 km is measured smaller than 2×10^-2, the soft-decision forward error correction limit.