On the mode-dependent loss compensation for mode-division multiplexed systems

Mode-division multiplexing has emerged as an imminent step to increase the capacity of long-haul transmission systems and avoid the so-called “capacity crunch”. One way to realize such systems is by means of few-mode fibers (FMFs). One of the challenges that has to be addressed in order to implement FMF-based commercial systems is the mitigation of mode-dependent loss (MDL). All kinds of inline optical devices can attenuate or amplify the modes differently, leading to different performance among the modes. This paper presents simulations, which study the system MDL tolerance under the influence of mode coupling and possible methods to improve the performance of MDL-impaired systems. We find that the combination of strong mode coupling and advanced detection schemes, such as maximum-likelihood (ML) detection can improve the system performance in the presence of MDL. However, the effectiveness of ML detection has to be traded off with its larger computational complexity compared to linear equalization such as minimum mean square error equalization.