MPLC-based low-modal-crosstalk nine-mode-group demultiplexer for DSP-free IM/DD MDM transmission over MMF

Abstract

Weakly coupled mode-division multiplexing (MDM) transmission over legacy laid multimode fiber (MMF) has great economic efficiency and can enormously enhance the capacity of short-reach optical interconnections. In order to be compatible with cost-efficient intensity-modulation/direct-detection (IM/DD) transceivers, weakly coupled mode-group demultiplexers that can simultaneously receive each mode group of MMFs are highly desired. In this paper, we propose a scalable low-modal-crosstalk mode-group demultiplexer over MMF based on multiplane light conversion (MPLC). Multiple input Hermite–Gaussian (HG) modes of MMF are first converted to bridging modes that are composed of HG00 modes distributed as a right-angle triangle in Cartesian coordinates, and then each HG00 mode belonging to a degenerate mode group is mapped to different overlapped HGn0 modes with vertical orientation for simultaneous detection. With the help of bridging modes, the MPLC-based mode-group demultiplexer can efficiently demultiplex all mode groups in standard MMFs with less than 20 phase masks. A nine-mode-group demultiplexer is further designed for demonstration, and simulation results show that the MPLC-based demultiplexer achieves low modal crosstalk of lower than −22.3dB at 1550 nm and lower than −17.9dB over the C-band for all the nine mode groups with only 16 phase masks.