Physical layer modeling for high capacity optical communication systems

Nowadays, ultra-wideband (UWB) and space-division multiplexing (SDM) transmissions are emerging as the best candidates to further push the capacity offered by optical communication systems. The former strategy aims at increasing the capacity by enlarging the transmission bandwidth. For these systems, a fully numerical approach for the performance estimation has a prohibitive computational time, due to the wide bandwidth. On the other hand, an SDM system exploits spatial diversity to increase the amount of transmitted data. However, the random nature of the interaction among spatial paths requires several numerical simulations to collect enough results to build the system performance statistics. In such complex scenarios, analytical modeling stands out as a fast yet accurate tool for system performance estimation, well-suited to assist in the network design and in traffic routing. In this thesis, we propose extensions of analytical models for the estimation of the system performance for UWB and SDM systems, with a particular focus on the modeling of the optical fiber nonlinearities. In the context of UWB transmissions, we first focused on modeling the interaction between the optical fiber Kerr effect and stimulated Raman scattering (SRS). We proposed a model for the nonlinear interference (NLI) variance which takes into account the positioning of the equalizers for the SRS compensation. The model is validated against UWB numerical simulations, showing a very good agreement along with the importance of addressing the equalizer positioning along the link. Then, we moved the focus on the modeling of semiconductor optical amplifiers (SOAs). As a trade-off between simplicity and complexity, we proposed a parametric model for describing the SOA dynamics. Regarding SDM transmissions, we first addressed the inclusion of polarization-dependent loss (PDL) in the NLI modeling. The proposed model accounting for PDL in single-mode transmissions opens the door to the more general case of mode-dependent loss in SDM systems. Then, we derived a theoretical model of the NLI in the presence of arbitrary mode dispersion among strongly coupled modes. Both models are validated against numerical simulations, repeated for several random realizations, showing excellent agreement.