Ultra-Broadband Dual-Polarization Silicon Waveguide Crossing Architecture for Scalable Multi-Port Operation Across ITU and 2 µm MIR Bands

We present and experimentally demonstrate a compact, ultra-broadband, and scalable multi-port waveguide crossing architecture that supports dual-polarization operation across both the O–L communication bands and the emerging 2 μm mid-infrared (MIR) window. The design is based on a composite subwavelength grating structure and implemented on a standard 220 nm silicon-on-insulator platform using a single-step etching process. A unified multimode interference-based building block enables highly compact 2 × 2, 3 × 3, and 4 × 4 configurations with symmetric layouts, achieving footprints as small as 14 × 14 μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the international telecommunication union (ITU) bands and 16 × 16 μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 2 μm. The 2 × 2 crossing demonstrates record-wide bandwidths of ∼380 nm (1300–1680 nm) with low insertion losses of <0.3 dB/<0.2 dB (TE/TM) and crosstalk below −20 dB/−30 dB across the ITU bands. Even better performance is achieved for the TE mode in the 2 μm MIR range ∼400 nm (1760–2150 nm). To the best of our knowledge, this is the first demonstration of a dual-polarization waveguide crossing with such extensive bandwidth coverage in the ITU bands and the widest reported in the 2 μm MIR regime. The proposed architecture offers a scalable, fabrication-friendly solution for next-generation high-density photonic integrated circuits with polarization- and wavelength-division multiplexing capabilities across multiple spectral domains.