10$\,\times\,$ 224-Gb/s WDM Transmission of 56-Gbaud PDM-QPSK Signals Over 1890 km of Fiber

We demonstrate ten-channel wavelength-division-multiplexed (WDM) transmission of 56-Gbaud polarization-division-multiplexed quadrature phase-shift keying signals (i.e., at a line rate of 224 Gb/s) over 1890 km of fiber on a 100-GHz WDM grid (spectral efficiency of ~2 b/s/Hz). The coherent intradyne receiver digitizes the signal at 80 GSamples/s, and is followed by offline digital signal processing.