Toroidal Dipole All-Dielectric Metasurfaces with High Sensitivity, High Figure of Merit, and Robustness for Refractive Index Sensing

Refractive index sensing is of great significance in biological detection. Especially, all-dielectric metasurfaces can greatly improve the sensitivity of biological detection. However, the Q factor and electric field enhancement of most metasurfaces are generally low, resulting in low sensitivity and figure of merit (FOM). Meanwhile, fabrication tolerances may result in inability to achieve high-performance refractive index sensing. Here, we use finite element method (FEM) simulation to design a conical hole structure on an all-dielectric metasurface. The toroidal dipole resonance based on a conical hole structure can achieve a large-area electric field enhancement and a high Q factor, thereby achieving a sensitivity of 540 nm/RIU and FOM of 154.3. Meanwhile, considering the real fabrication tolerance, the proposed structure can still achieve high-sensitivity sensing when the conical hole structure changes the ellipsoidal structure. Therefore, the high sensitivity, high FOM, and robustness of the proposed structure make it highly significant for practical applications.