Ultra-Wideband Modeling of Optical Fibre Nonlinearity in Hybrid-Amplified Links

Ultra-wideband (UWB) transmission using hybrid Raman amplifier technologies is an attractive option to increase the total throughput of a transmission link satisfying the demands for data traffic in optical fibre systems. This amplification technology achieves improved system performance when compared to that obtained with the utilisation of lumped amplifiers only. However, accurate and real-time system performance estimation is required. This paper presents the characteristics of the first analytical model to estimate the performance of the optical system in the presence of hybrid Raman amplifiers and inter-channel stimulated Raman scattering (ISRS). The model accounts for the fibre nonlinear interference (NLI), amplified spontaneous emission (ASE) generated by Raman amplification (RA) and lumped amplification (LA), and transceiver ($\text{TRX}$) noise. It also allows for any RA setup, such as an arbitrary number of forward (FW) and/or backward (BW) pumps, wavelength-dependent fibre parameters, variable modulation formats, per-channel launch powers and channel bandwidths. The model is used to evaluate the performance of a multi-span 18.4 THz transmission system (with 80-km spans) and capacity-maximising hybrid Raman amplifiers are designed based on a particle swarm optimisation (PSO) algorithm, where the semi-analytical nonlinear model was used to achieve real-time optimisation. An extensive theoretical investigation for different systems configurations ranging from short to metro, long-haul and trans-Atlantic links is described, demonstrating the trade-off between the various sources of noise and amplifier technologies.