Compact inverse-designed tilted waveguide crossing.

Waveguide crossings are key components for increasing integration density and routing flexibility. We propose a novel, to the best of our knowledge, compact, tilted silicon waveguide crossing designed using inverse design methods, specifically optimized to minimize both insertion loss and crosstalk. Through adjoint optimization algorithms and finite-difference time-domain simulations, we achieve a significant reduction in crosstalk from -46 dB at 90° to -54 dB at 86°, with a remarkably low insertion loss of -0.14 dB at 1310 nm. The footprint is further minimized to only 8 × 8 μm, setting what we believe to be a new benchmark in terms of both size and performance compared to existing silicon waveguide crossings. The impact of the tilt angle on performance is thoroughly analyzed through both simulations and experimental validation. This device highlights the potential of inverse design to deliver optimized overall performance while maintaining an ultra-compact footprint. Fabricated on a commercial foundry, with its low loss, low crosstalk, and small size, our waveguide crossing is ideally suited for high-density photonic integrated circuits, offering promising applications in data centers and quantum photonics.