Impact of splices on the nonlinear impairments in mode-division mul-tiplexed few mode fibers

It is shown that mode coupling due to splices highly degrades the performance in nonlinear mode-division multiplexed transmission systems that employ few-mode fibers. Current long-haul transmission systems are composed by fiber segments that are spliced together about every 2 km. In few-mode fiber systems, splices introduce coupling between guided modes as well as mode-dependent loss. Therefore, we simulated transmission systems with spliced graded index few-mode fibers that guide three spatial modes in one polarization, while we varied the splice tolerances in a statistical way. We analyzed the Error Vector Magnitude (EVM) of the received constellation diagram of a QPSK signal after ideally compensating all linear effects, including loss, dispersion and linear coupling. It turns out that the received constellation diagrams are highly distorted, while the strength of the nonlinear impact depends on the position of the splices in the link as well as the loss that is connected to each splice.