High-Q all-dielectric metasurface refractive index sensor based on quasi-BICs

Bound states in the continuum (BICs) are ideal for realizing optical resonances with ultra-high quality factors (Q) because of their extreme ability to facilitate light-matter interactions and strong field confinement. In this work, an all-dielectric metasurface whose unit cell consists of a silicon disc is designed, on which a symmetry-protected BIC (SP-BIC) is observed, and the breaking of the in-plane symmetry can be made to transform it into a quasi-BIC (QBIC) with a high-quality factor. A refractive index sensor is realized based on the principle that the resonance peak's position changes with the background refractive index change. Using the quadratic inverse relationship between the quality factor and the asymmetry parameter, the quality factor is changed by adjusting the asymmetry parameter to optimize the sensing performance. After tuning, the refractive index sensing sensitivity and figure of merit of this metasurface reached 265.58 nm/RIU and 2178.31 RIU-1, respectively, a parameter that exceeds many existing research results. This all-dielectric metasurface design with a high Q-factor pushes the BIC-based refractive index sensing to higher sensitivity and higher accuracy.