Pulse-shaping versus digital backpropagation in 224Gbit/s PDM-16QAM transmission.

We investigate the transmission performance of 224Gbit/s polarization-division-multiplexed 16-state quadrature amplitude modulation (PDM-16QAM) for systems employing standard single mode fiber (SSMF) and erbium doped fiber amplifiers (EDFAs). We consider the effectiveness of return-to-zero (RZ) data pulses with varying duty cycles and digital backpropagation (DBP) in reducing nonlinear distortion in wavelength-division- multiplexed (WDM) links with 3, 5, 7 and 9 channels. Similar improvement in transmission reach of 18-25% was achieved either by pulse-carving at the transmitter or by DBP, yielding maximum transmission distances of up to 1760km for RZ-pulse-shapes and 1280km for NRZ.