High-Sensitivity Optical Sensor Driven by the High-Q Quasi-Bound States in the Continuum of an Asymmetric Bow-Tie Metasurface

All-dielectric metasurfaces based on quasi-bound states in the continuum (quasi-BICs) have emerged as a powerful platform for nanophotonic sensing, as they support high-Q resonances and strong near-field enhancements. Herein, we propose and numerically investigate an asymmetric bow-tie metasurface composed of two silicon semi-cylinders with unequal radii and a central bar to achieve a quasi-BIC resonance with a Q-factor of 11,000. The transition mechanism of the BIC modes in the asymmetric bow-tie metasurface is analyzed. Additionally, the spectral features of the asymmetric bow-tie metasurface as a function of the refractive index and temperature of the local environment are also investigated. The proposed structure exhibits a refractive index sensitivity of 454 nm/RIU and a temperature sensitivity of 134 pm/°C. Furthermore, a high figure of merit (FOM) of 3159 RIU−1 is achieved, and the nearly 100% modulation depth maintained across three distinct resonance dips. Our study suggests that the proposed asymmetric bow-tie metasurface offers a promising approach for the development of high-sensitivity biosensing platforms.