Phase-detection-based high-sensitivity refractive index sensing via chiral BIC metasurfaces

Chiral structures have wide applications in sensing, communication, and spectral analysis. Among them, chiral refractive index sensors have attracted significant attention due to their excellent biocompatibility. However, their relatively low sensitivity limits further development, especially in the terahertz regime. In this study, we designed a chiral metasurface based on single-crystal silicon (Si) that supports bound states in the continuum (BIC). This metasurface not only achieves nearly unit intrinsic and extrinsic chirality but also exhibits a high Q-factor and excellent robustness. When used for refractive index sensing, it achieves a sensitivity of up to 1220 THz/RIU by detecting phase variations, significantly surpassing existing terahertz refractive index sensors. This study provides a novel approach for the design of terahertz refractive index sensors.