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.