Impact of quasi-linear pulse evolution on FWM noise in dispersion-managed DPSK DWDM systems

Based on an analytic finite-bandwidth stationary signal noise theory, a semi-analytic model is derived to deterministically calculate the variances of degenerate and non-degenerate four-wave-mixing (FWM) noises including the quasi-linear pulse evolution (QLPE) with distance, walk-off between channels, random bit sequences, random polarization changing along fiber and other important effects for 64 × 40-Gb/s, 50-GHz spaced dispersion-managed (DM) dense wavelength-division multiplexing (DWDM) system with differential phase-shift keying (DPSK) format. Dispersion map assumed here consists of slope-matched inverse dispersion fiber and non-zero dispersion shifted fiber. Example calculations show that the impact of QLPE on FWM noises is very severe and cannot be ignored in most cases. Optimized combination of dispersion map and input optical power per channel is suggested when the impact of QLPE on FWM noise is taken into account. System performance for three types of input pulse shapes are also compared for a given dispersion map and optimal pulse shape is suggested when the FWM noise is included.