DMD-Unmanaged Long-Haul SDM Transmission Over 2500-km 12-Core × 3-Mode MC-FMF and 6300-km 3-Mode FMF Employing Intermodal Interference Canceling Technique

Abstract

We demonstrate differential mode delay (DMD) unmanaged 2500-km 12-core × 3-mode multicore few-mode fiber (MC-FMF) and 6300-km 3-mode FMF transmission. Mode-division multiplexed signals exhibit different transmission behavior depending on excited spatial modes in the presence of mode-relevant physical phenomena including DMD and mode-dependent loss (MDL). In weakly coupled FMF transmission over long distance where overall DMD and MDL grow almost linearly with fiber length, these phenomena restrict achievable information capacity and/or transmission reach. This paper presents a newly developed transmission scheme and a multiple-input multiple-output (MIMO) signal processing technique that are designed for achieving long-haul FMF transmission. Permutating spatial channels cyclically at each span induced quasi-strongly coupled transmission regime and hence significantly suppressed DMD-induced pulse broadening. Layered MIMO signal processing comprising multiple stages performing successive signal detection and intermodal interference canceling mitigated MDL impact with more than 2-dB Q-factor improvement. The combined use of these techniques enabled us to achieve the first-ever transoceanic-class long-haul FMF transmission.