Waveguide-integrated graphene spatial mode filters for on-chip mode-division multiplexing.

On-chip mode-division multiplexing (MDM), as a promising method of scaling communication bandwidth, has attracted tremendous attention due to potential applications in optical interconnects ranging from intra-chip to board-to-board communications. However, the MDM technique usually suffers from signal degradation due to crosstalk between spatial modes in multimode waveguide devices. Here we design waveguide-integrated graphene spatial mode filters for on-chip MDM to overcome this limitation. Specifically, TE-mode-pass and TE-mode-pass filters are designed based on different waveguide architectures. For the TE-mode-pass filters, we have obtained a maximum TE-to-TE modal extinction ratio (ER) of 9.19 dB in a 200-μm-long waveguide. While, for the TE-mode-pass filters, we have achieved a maximum TE-to-TE modal ER of 5.37 dB and TE-to-TE modal ER of 6.44 dB in a 200-μm-long waveguide. Our study could help improve the signal-to-noise ratio for on-chip MDM optical interconnects.