This paper reviews and extends a method for the semi-analytical solution of the coupled linear differential equations that describe the linear mode coupling arising in fewmode fibers due to waveguide imperfections. The semi-analytical solutions obtained proved to be accurate when compared to numerical solution methods. These solutions were integrated into a multi-section model with split-steps for mode dispersion and mode coupling. Simulations using this model matched the analytical predictions for the statistics of group-delays in fewmode fiber links, considering different coupling regimes with and without mode delay management.

Linear equalization performance for delay-managed few-mode links in the nonlinear regime with intermediate linear coupling is studied for the first time. Existing fibers can allow similar performance per mode to that of uncoupled single-mode propagation.

this paper reviews and extends the study of nonlinear performance of few-mode fiber links operating in all different linear coupling regimes for different mode delay maps. The single-mode split-step Fourier method is modified to include semi-analytical solutions for linear mode coupling of arbitrary strength. The optimum link configurations minimizing the nonlinear penalty at practical levels of equalization complexity are presented, namely: the coupling strength required to give suppression of nonlinear distortion below the isolated propagation without mode coupling, for different mode delay maps. Finally, the limits of the extension of the single-mode Manakov approximation to the multi-mode case are accurately validated against a fully stochastic model developed considering distribution linear mode coupling.

Single-mode optical fibres now underpin telecommunication systems and have allowed continuous increases in traffic volume and bandwidth demand whilst simultaneously reducing cost- and energy-per-bit over the last 40 years. However, it is now recognised that such systems are rapidly approaching the limits imposed by the nonlinear Kerr effect. To address this, recent research has been carried out into mitigating Kerr nonlinearities to increase the nonlinear threshold and into spatial multiplexing to offer additional spatial pathways. However, given the complexity associated with nonlinear transmission in spatial multiplexed systems subject to random inter-spatial-path nonlinearities it is widely believed that these technologies are mutually exclusive. By investigating the linear and nonlinear crosstalk in few-mode fibres based optical communications, we numerically demonstrate, for the first time, that even in the presence of significant random mixing of signals, substantial performance benefits are possible. To achieve this, the impact of linear mixing on the Kerr nonlinearities should be taken into account using different compensation strategies for different linear mixing regimes. For the optical communication systems studied, we demonstrate that the performance may be more than doubled with the appropriate selection of compensation method for fibre characteristics which match those presented in the literature.

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