The Impact of Kerr Nonlinearity on the SNR Variability Induced by Polarization-Dependent Loss

We provide through numerical simulations new insights on the polarization-dependent loss (PDL)-induced variability of the signal-to-noise ratio (SNR) in dual-polarization coherent systems when Kerr nonlinearity is significant. We show that the interplay between PDL and nonlinearities provides an SNR distribution broader than the one induced by PDL in the only presence of amplified spontaneous emission noise. Such a broadening is missed by handy state-of-art models as the reverse channel method (RCM) that do not account for fiber nonlinearity, thus resulting inaccurate to estimate the SNR variability at practical launch powers. We show that such an inaccuracy persists even by considering in the RCM the nonlinear noise contribution. We show that the SNR distribution broadening in the presence of fiber nonlinearity is the result of a change in dynamics between the performance of those that can be identified for each PDL draw as best- and worst-performing polarization tributaries. By numerically decoupling the main contributions to fiber nonlinearity we also identify the nonlinear effects responsible for such a change of dynamics. Finally, we qualitatively validate our findings by mean of an experimental result.