Observing and modeling wideband generation of non-linear interference

Optical line systems are going beyond the C-band by exploiting multi-band transmission to expand the fiber capacity without installing new fiber cables. Moreover, operators are progressively pushing towards the implementation of the open optical network paradigm. This requires the capability to quickly estimate the lightpath Quality-of-Transmission (QoT) given by the generalized signal-to-noise ratio (GSNR), including both the effects of ASE noise and non-linear interference (NLI) accumulation. In order to predict the effect of NLI on GSNR degradation of multi-band OLS, we first observe that the NLI generation can be spectrally disaggregated, by separating the single-channel - self-phase modulation (SPM) - from the multi-channel effects - cross-phase modulation (XPM). Then, relying on the Gaussian-Noise model hypotheses, we derive a mathematical model to assess the multichannel impairments, validated by accurate split-step simulations. We show that the model conservatively predicts the disaggregated multi-channel NLI intensity with excellent accuracy.