Spectrally-Efficient 400-Gb/s Single Carrier Transport Over 7 200 km

Since the advent of wavelength division multiplexed optical systems, increasing the bit rate per optical carrier has proved to be the most effective method to drive the overall cost of optical systems down. However, multicarrier approaches have gained momentum for 400-Gb/s transport to cope with bandwidth limitations of optoelectronic components. In this paper, single carrier modulated 400-Gb/s transport over transatlantic distances is demonstrated for the first time. Using high-speed digital-to-analog converters, we successfully generated a 64 GBaud dual-polarization signal modulated using 16-ary quadrature amplitude modulation. Thanks to Nyquist pulse shaping, our channels are closely packed with 66.7 and 75 GHz channel spacing, resulting on 6 and 5.33-bit/s/Hz of spectral efficiencies, respectively. Transceiver design is based on an optimization procedure of inter-symbol interference mitigation and forward error correction overhead. A spatially-coupled low density parity check code with decoder-aware degree optimization is used to reduce the gap to capacity. We validated our transceiver design by transporting five channels over 6600 and 7200-km with 6 and 5.33-bit/s/Hz of spectral efficiency, respectively. We analyze as well the performance gain provided by non-linear mitigation using filtered digital back-propagation algorithm.