Ultra-broadband, high-efficiency, and compact Si crossing.

The explosive growth of global data traffic demands broadband and high-density photonic integration. Silicon photonics, a scalable and CMOS-compatible platform, is a promising solution, but achieving broadband performance in fundamental components such as waveguide crossings remains challenging. Here, we demonstrate the silicon waveguide crossing operating efficiently across the full S + C + L bands (1460-1625 nm), achieving an unprecedented 165-nm bandwidth with insertion loss below -0.12 dB and crosstalk below -35 dB. This marks a substantial 175% improvement over prior designs, which typically achieved only 60 nm bandwidth. Our approach leverages inverse design via particle swarm optimization and FDTD simulations to realize a compact 8 × 8 μm footprint. Importantly, the structure is fully compatible with standard commercial silicon photonics foundry processes. Large-scale experimental validation confirms fabrication robustness, with insertion loss as low as -0.08 dB at 1550 nm. This work represents a key advance in silicon photonic integration, underscoring the transformative potential of inverse design to deliver broadband, low-loss, and fabrication-tolerant devices for next-generation optical interconnects.