Capacity enhancement of few-mode fiber transmission systems impaired by mode-dependent loss

Space-division multiplexing over few-mode fibers is a promising solution to increase the capacity of the future generation of optical transmission systems. Mode-dependent loss (MDL) is known to have a detrimental impact on the capacity of few-mode fiber systems. In the presence of MDL, spatial modes experience different attenuations which results in capacity reduction. In this work, we propose a digital signal processing solution and an optical solution to mitigate the impact of MDL and improve the channel capacity. First, we show that statistical channel state information can be used for a better power allocation for spatial modes instead of equal launch power to increase the system capacity. Afterwards, we propose a deterministic mode scrambling strategy to efficiently reduces the impact of MDL and improves few-mode fiber systems capacity. This scrambling strategy can be efficiently combined with the optimal power allocation to further enhance the capacity. Through numerical simulations of the average and outage capacities, we show that the proposed techniques bring significant capacity gains.