Inverse-Designed Ultrabroadband Low-loss Silicon Nitride Waveguide Crossing for Visible and Short-Wave Infrared Bands

We experimentally demonstrate an inverse-designed ultrabroadband waveguide crossing leveraging a single-hidden layer neural network-based inverse method, achieving record performance on a monolithic silicon nitride platform. This approach integrates analog topology optimizations, thereby enabling robust broadband operation. Fabricated with standard photolithography (200 nm feature size), the telecom-band device spans 365 nm (O-L bands) with an average excess loss of -0.07 dB and crosstalk below -40 dB, while the visible-band counterpart (639–663 nm) maintains exceptional performance with an average excess loss of -0.048 dB and crosstalk under -35 dB. This work provides a universal methodology for realizing high performance waveguide crossings, enabling advanced photonic integrated circuits for applications in visible photonics, quantum computing, and optical interconnects.