On-chip ultracompact broadband reflector and high- Q Fabry-Pérot cavity based on inverse design

Photonic integrated circuits require compact broadband passive components. We report an inverse-designed reflector integrated with a high- Q Fabry-Pérot (F-P) cavity on a standard 220-nm silicon-on-insulator (SOI) platform. The 2 µ m × 2 µ m reflector is incorporated into a 400- µ m bus-coupled cavity. The fabricated device exhibits a loaded Q of approximately 1 × 10 5 and a round-trip-loss-limited effective reflectivity of 0.92–0.96 across 1500–1600 nm, providing a lower bound on the mirror reflectivity. The design includes a 250-nm minimum-feature constraint and ±10 nm lithographic-bias tolerance analysis. These results establish a compact, broadband, and fabrication-aware reflector-cavity building block for wavelength-selective silicon photonic circuits.