56-Gbaud PDM-QPSK: coherent detection and 2,500-km transmission

A 56-Gbaud (224-Gb/s line rate) polarization-division multiplexed quadrature phase shift keyed (PDM-QPSK) signal is transmitted over 2,500 km (32 × 80 km) of fiber and is coherently detected using two 80-GSamples/s oscilloscopes with off-line signal processing.