Modeling of Coherent and Incoherent Rayleigh Crosstalk in Conventional Optical Links

Performance of Rayleigh-dominated transmission is modeled using approximated and exact noise power spectral densities (PSDs) and results are compared to experimental measurements for nonreturn-to-zero, return-to-zero, and duobinary modulation formats. Both models accurately predict penalties associated with coherent Rayleigh crosstalk for all three formats with typical accuracy within 1 dB. For incoherent Rayleigh crosstalk, the numerical model using exact PSDs improves prediction accuracy by as much as 4 dB over the analytic model. The large, previously unexplained disagreement is attributed to the set of analytic approximations. Our results indicate that a rigorous description of the channel spectrum should be used when calculating impairments caused by incoherent Rayleigh crosstalk, particularly in very dense wavelength-division-multiplexed systems requiring a narrow optical filtering.