Quasi-BIC mode and refractive index sensing by asymmetric silicon nanodisk arrays

Abstract

This study proposes a metasurface consisting of silicon nanodisk arrays periodically arranged on a silica substrate to excite quasi-bound states in the continuum(Q-BIC) modes. Through introducing symmetry breaking, the metasurface successfully excites Q-BIC modes with an exceptionally high quality factor(Q-factor). To further elucidate the generation mechanisms and the key factors contributing to the high Q-factor, the multipolar radiation characteristics, optical field distributions, and sensing performance are systematically investigated under three distinct symmetry-breaking configurations. The transmission spectra and electric field distributions, calculated using the finite-difference time-domain method, are complemented by the multipolar radiation theory, which provides profound insights into the underlying physical mechanisms and optical responses of structural symmetry breaking. The resonant peaks that emerge in the transmission spectra exhibit pronounced Fano line shapes that are characteristic of Q-BIC modes. Based on the advantage of optical field modulation enabled by the asymmetric silicon nanodisk array, we apply it to refractive index sensing. The metasurface delivers outstanding performance, exhibiting a maximum Q-factor of 81696 and a maximum sensitivity of 541 nm/RIU⁻¹ in the gas environment. These results confirm that the proposed metasurface sustains ultra-high-Q resonances with exceptional sensitivity, highlighting its significant potential for next-generation optical sensing and modulation technologies.