Ultra-Low Loss and Ultra-Compact Polarization-Insensitive SOI Multimode Waveguide Crossing Based on an Inverse Design Method

Polarization-insensitive waveguide crossings are indispensable components of photonic integrated circuits (PICs), enabling the concurrent computing of optical signals from diverse waveguides inside the limits of a restricted spatial footprint. Leveraging mirror symmetry direct binary search, we successfully demonstrate an ultra-compact and ultra-low loss polarization-insensitive waveguide crossing that achieves insertion losses below −0.11 dB and crosstalk levels beneath −22.6 dB for transverse electric (TE) mode, as well as insertion losses below 0.05 dB and crosstalk levels beneath −24.5 dB for transverse magnetic (TM) mode across the C-band with a footprint of 3 × 4 μm2. The results confirm that this mirror symmetry optimization method yields high-efficiency devices while reducing computational time. We believe this high-efficiency polarization-insensitive waveguide crossing can have potential applications in dense PIC systems.