Ultra-high-Q silicon microring resonator enabled by optimized Bezier curved taper

An ultra-high-Q microring resonator (MRR) based on a spliced waveguide architecture with inverse-designed Bézier curved taper is experimentally demonstrated. This resonant cavity incorporates 0.45- μ m -wide single-mode arc waveguides to ensure fundamental mode purity in the coupling region, alongside 1.6- μ m -wide multi-mode arc waveguides at the maximum proportions to reduce scattering loss from fabrication-induced surface roughness, and Bézier curved tapers to provide a seamless and adiabatic connection between the two segments. Crucially, the taper employs dual 6th-order Bézier curves to construct a 15 ∘ gradually-expanding arc, achieving curvature continuity between the various waveguide sections within the resonant cavity, thereby effectively preventing mode crosstalk from deteriorating the Q-factor of the resonator. Benefiting from this optimized geometric structure, the taper exhibits an extremely low transmission loss of 0.11 dB/cm and a simulated average excitation ratio of higher-order modes of -44.43 dB in the C-band. The spliced MRR features a compact design with a radius of 120 μ m and a corresponding cavity length of only 0.75 m m . The MRR is fabricated using standard etching process provided by a wafer foundry. Experimental results show that the intrinsic Q-factor is 2.76 × 10 6 , with a free spectral range (FSR) of 0.84 n m . This indicates that the optimized Bézier curved taper provides a compact, low loss, and low mode crosstalk strategy for integrated photonic MRRs.