Analysis on dual Fano resonance in a coupled-resonator waveguide

Dual Fano resonance was demonstrated in a compact coupling system without additional large footprint tunable devices consisting of a grating-coupled waveguide and a micro-racetrack resonator on thin film lithium niobate. A multimode interference model was proposed for the dual Fano resonance system. The inverse design method was used to realize model fitting, validate our model, and analyze our model. Based on the parameters obtained by the inverse design, we further analyzed the influence of different parameters. Our research also shows that through the interaction of two Fano resonance modes, tunable line shape and enhanced extinction ratio can be realized in the transmission spectrum, which has potential applications in optical sensing.