Compensation of Nonlinear Fibre Impairments in Coherent Systems Employing Spectrally Efficient Modulation Formats

We investigate electronic mitigation of linear and nonlinear fibre impairments and compare various digital signal processing techniques, including electronic dispersion compensation (EDC), single-channel back-propagation (SC-BP) and backpropagation with multiple channel processing (MC-BP) in a ninechannel 112 Gb/s PM-mQAM (m=4,16) WDM system, for reaches up to 6,320 km. We show that, for a sufficiently high local dispersion, SCBP is sufficient to provide a significant performance enhancement when compared to EDC, and is adequate to achieve BER below FEC threshold. For these conditions we report that a sampling rate of two samples per symbol is sufficient for practical SC-BP, without significant penalties. key words: Optical fibre communication, Nonlinear optics, Digital signal processing, coherent communication.