On the Interplay of Nonlinear Interference Generation With Stimulated Raman Scattering for QoT Estimation

To effectively operate multivendor disaggregated networks, the performance of the physical layer needs to be assessed by a quality-of transmission estimator (QoT-E) delivering quick results with a given reliability range. Current state-of-the-art wavelength-division-multiplexing channels are based on multilevel modulation formats relying on DSP-operated coherent receivers, propagating on uncompensated and amplified optical links. In this transmission scenario, beside amplified spontaneous emission noise accumulation, nonlinear propagation impairments are well summarized by the accumulation of a Gaussian-distributed disturbance: the nonlinear interference (NLI). When exploiting a transmission bandwidth exceeding the C-band, the interaction of NLI generation with the stimulated Raman scattering (SRS) must be properly considered. We present the derivation of the generalized Gaussian noise (GGN) model for NLI generation, including the SRS and, in general, a spectral and spatial variation of gain/loss. We validate its accuracy by comparing performances predicted by a QoT-E based on the GGN model with measurements on a testbed exploiting commercial equipment, including 100 Gb/s transponders. Considering that operational parameters of the commercial equipment are known with a large range of uncertainty, an excellent agreement with errors within 0.5 dB on the generalized Signal-to-noise ratio ( $\text{SNR}$ ) is shown, demonstrating that the GGN-model can be used for the QoT-E in multivendor network scenarios. Moreover, the GGN model has shown the capability to predict the spectral tilting due to SRS in $\text{SNR}$ performances, enabling its application to evaluate the impact of linear pretilting for SRS precompensation and NLI generation.