Analysis of Bandwidth Narrowing in Wavelength Selective Switch Enabled DP-64QAM Systems With Transceiver Noise

The impact of filtering impairments resulting from cascaded, wavelength selective switches is investigated for 32 Gbaud dual-polarization 64-ary quadrature amplitude modulation in the presence of transceiver noise. Training-sequence based adaptive equalization and pilot-aided carrier phase estimation are employed to cope with the combined effects of the transceiver-imposed limitation in achievable signal-to-noise ratio and the filtering-induced signal distortion. For a given level of amplified spontaneous emission noise, transceiver noise reduces the total signal-to-noise ratio resulting in an increased dependence of the bit-wise achievable information rate on filtering-induced bandwidth narrowing. The implications of statistical variations in the overall filter frequency response are also assessed by considering randomly selected responses for each of the individual filters in a cascade. Further, the impact of the frequency response of the demultiplexing filter at the receiver is investigated by considering a 3-channel 32 Gbaud wavelength division multiplexed system with a channel spacing of 37.5 GHz.