Theoretical investigation of space division multiplexing capacity of unaltered and D-shaped multimode step-index POF

The influence of mode coupling on two and three spatially multiplexed optical channels in unaltered and D-shaped multimode step-index plastic optical fibers (SI POFs) is analyzed by solving the power flow equation (PFE). The D-shaped technique applies controlled perturbations to suppress high-order modes, thereby improving the fiber's bandwidth. Our numerical results show that mode coupling significantly limits the fiber length over which space division multiplexing (SDM) can be implemented with minimal crosstalk between adjacent channels. This limitation is especially pronounced when external perturbations, such as D-shaping of the fiber, increase mode coupling, further reducing the fiber's capacity for SDM. In particular, two and three spatially multiplexed channels exhibit lower crosstalk over longer distances in unaltered SI POFs compared to their D-shaped counterparts. These findings highlight the importance of fiber characterization when designing SDM-based optical transmission systems.