Broadband four-mode (de)multiplexer based on MMI using subwavelength grating structure.

Mode (de)multiplexer is one of the key components of mode-division multiplexing (MDM) system, which is regarded as an effective approach to further enhance the transmission capacity of optical interconnects. However, it's working bandwidth is intrinsically limited by the waveguide's dispersion. To address this challenge, we present what we believe to be a novel broadband four-mode (de)multiplexer for on-chip MDM that combines subwavelength grating (SWG) with beam shaping techniques. The proposed device utilizes SWG-based multimode interference couplers (2 × 2 MMI and 4 × 4 MMI) and passive phase shifters to achieve simultaneous TE∼TE mode multiplexing. By implementing beam shaping through Y-junctions rather than conventional mode coupling, our design alleviates the wavelength sensitivity associated with intrinsic material group-velocity dispersion (GVD). Comprehensive simulations demonstrate exceptional performance across a 200 nm bandwidth (1450∼1650 nm), with insertion loss (IL) < 1.2 dB and crosstalk (CT) < -19 dB for all modes. This design provides a scalable solution of broadband (de)multiplexer for next-generation MDM systems, enabling significant capacity enhancement in photonic integrated circuits.