Ultra-Large FSR Silicon Adiabatic Microring Resonators Based on Euler Curve and Modified Bezier Curve

A design method for ultra-compact adiabatic microrings is proposed and demonstrated. The microring design features two identical 180-degree bends, with the outer contour traced by double Euler curves. Moreover, we optimized the inner contour of the ultra-compact bends based on inverse-designed high-order Bezier curve. This optimization significantly reduces propagation loss due to sidewall roughness and multimode loss resulting from the excitation of higher-order modes. Additionally, simulation results indicate that the ultra-compact adiabatic microrings have ultra-low mode crosstalk, particularly when the free spectral range (FSR) is approximately 42 nm.