Nonlinear Signal–Noise Interaction in Optical Links With Nonlinear Equalization

We investigate nonlinear signal-noise interaction (NSNI) in dispersion uncompensated links by means of the enhanced Gaussian noise (EGN) model. We include a first-order perturbative description of digital backpropagation (DBP) in the EGN model, thus accounting for NSNI not just along the optical link but even inside DBP. Thanks to the EGN model, we are able to evaluate the impact of NSNI in a setup with 133 channels, thus filling the entire bandwidth of erbium-doped fiber amplifiers. We discuss the main implications of NSNI showing that it mainly impacts the part of the nonlinear interference variance predicted by the Gaussian noise model. A simple formula to extend noiseless results to the realistic case with NSNI is proposed. Finally, the reduced efficiency of DBP in presence of NSNI is investigated and discussed.