Ultra-broadband polarization-insensitive dual-mode silicon waveguide crossing enabled by subwavelength grating-array-assisted multimode engineering

We demonstrate an ultra-broadband polarization-insensitive dual-mode silicon waveguide crossing enabled by subwavelength grating (SWG) array-assisted multimode engineering. The device incorporates multi-row nano-hole SWG arrays within the multimode interference region and fan-shaped bent SWGs between crossings to align modal phases and suppress crosstalk (CT). At 1550 nm, the crossing exhibits simulated insertion losses (ILs) of 0.09–0.46 dB and CT below –24 dB for the TE₀, TM₀, TE₁, and TM₁ modes. Over the 1260–1675 nm range, all modes maintain ILs below 1 dB and CT below –22 dB. Fabricated on a 220 nm SOI platform, the devices show consistent performance experimentally, with ILs below 1 dB and CT below –20 dB from 1300 to 1650 nm. The proposed structure offers record bandwidth and full dual-polarization support for high-capacity multimode photonic integration.