Choice of MUX/DEMUX filter characteristics for NRZ, RZ, and CSRZ DWDM systems

We investigate the influence of filter bandwidth and flank steepness of both multiplexing (MUX) and demultiplexing (DEMUX) filters in dense wavelength-division multiplexed (DWDM) systems (spectral efficiency 0.8 b/s/Hz) in the presence of coherent WDM crosstalk. Using a recently introduced technique for the statistically reliable performance prediction of systems impaired by coherent WDM crosstalk, we present numerical results for non return-to-zero (NRZ), 33% duty cycle return-to-zero (RZ), and 67% duty cycle carrier-suppressed return-to-zero (CSRZ) signals. We confirm that steep filter flanks are generally preferable, both in terms of OSNR penalty and in terms of filter bandwidth tolerance.