Scalable low-modal-crosstalk mode-group demultiplexer for MDM transmission over MMF

Weakly-coupled mode-division multiplexing (MDM) transmission technique over widely-deployed multimode fiber (MMF) is considered a promising approach to enhance the capacity of optical fiber communication systems. In order to be compatible with cost-efficient intensity-modulation/direct-detection (IM/DD) systems, effective mode-group demultiplexing approaches to simultaneously receive each mode group of MMF are highly desired. In this paper, we propose a scalable low-modal-crosstalk mode-group demultiplexer over MMF using multi-plane light conversion (MPLC), in which input Hermite-Gaussian (HG) modes of MMF are first converted to bridging modes that composed of HG₀₀ modes distributed as a right-angled triangle in Cartesian coordinates, and then each HG₀₀ mode belonging to the same mode group are respectively converted to different HG_n0 modes at the same output for simultaneous detection. With the help of bridging modes, the MPLC-based mode-group demultiplexer can scale to demultiplex more mode groups with relatively few phase masks. A 5 mode-group demultiplexer is also design for demonstration, and simulation results show that the modal-crosstalk are lower than -22.26 dB for all mode groups.