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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. [ABSTRACT FROM AUTHOR]

Optical microcavity has proven its potential for unlabeled sensing. Here, we propose and demonstrate in a lithium niobate on insulator microcavity an enhanced sensing approach enabled by the nonlinear mode oscillation generated by the competition between thermal-optic and photorefractive effect, which breaks the intrinsic limitation in wavelength resolution set by the cavity's optical quality factor. It allows us to perform precise measurements of the mode shifting introduced by a nanoscale scatterer with a signal to noise ratio of 13.1 dB and paves a distinctive way to improve resonance shift resolution in widely studied microcavity sensors with a platform of great integration capability. [ABSTRACT FROM AUTHOR]