Geometrical-optics resonator photonics.

Conventional waveguide optical resonators face inherent limitations of low damage thresholds, limited coupling tunability, and stochastic resonance. To overcome these, we introduce a geometrical-optics resonator (GOR) framework, emulating free-space reflection and thin-film coupling on-chip. Using ultra-wide waveguides with total internal reflection (TIR) mirrors and frustrated-TIR couplers, GORs eliminate conventional constraints. Fabricated devices achieve intrinsic Q-factors >1 million and enable tunable microwave photonic filters operating distortion-free at about 10× higher optical power. Design flexibility allows precisely tuned coupled resonators, facilitating cascaded networks for spectral engineering. Demonstrated GOR photonic molecules exhibit dynamically adjustable mode splitting (0.49 free spectral range), nearing theoretical limits. The platform also realizes record-large-scale Floquet topological photonic insulators with 1281 GOR lattices, supporting robust edge modes against defects and a broadband continuum. The GOR sets new performance benchmarks, enabling scalable platforms for quantum simulation and topological networks while driving integrated photonics toward higher density and system-level integration.