Multiple quasi‑BIC excitations and refractive index sensing in dielectric metasurfaces enabled by symmetry breaking

Abstract

In this work, an all-dielectric metasurface employing symmetry-breaking engineering is designed to support multiple quasi-BIC (quasi-BICs) for refractive index sensing applications. The unit cell is composed of two silicon elliptical nanopillars, a centrally positioned rectangular nanobar, and a symmetrically etched slot region. Lateral displacement of the etched slot breaks the in-plane symmetry, thereby transforming symmetry-protected BICs into radiatively accessible quasi-BIC modes. Numerical simulations demonstrate that three high-Q Fano resonances can be simultaneously excited in the near-infrared range, achieving a maximum quality factor of 1.75 × 104. The physical origins of these resonances are further elucidated through near-field distribution analysis and multipole decomposition. In addition, a systematic study of the geometric parameters is conducted to evaluate and optimize the sensing performance. The designed metasurface exhibits a maximum sensitivity of 360.2 nm/RIU and a figure of merit (FOM) of 3.86 × 104 RIU-1, confirming its strong potential for high-Q multimode refractive index sensing applications.