Toroidal dipole bound states in the continuum in all-dielectric metasurface for high-performance refractive index and temperature sensing

In this numerical study, an all-dielectric metasurface consisting of silicon disks with tilted split gap, which can measure the refractive index and temperature is proposed. It is demonstrated that the double resonances in the near-infrared wavelength are excited by toroidal dipole (TD) resonance in different directions. Further analysis proves that the resonance at the short wavelength corresponds to the TD resonance governed by the symmetry-protected bound state in the continuum (BIC), and it can be transformed to the TD quasi-BIC resonance with a high quality-factor (Q-factor) by breaking symmetry. The spectral responses to different incidence angles are evaluated. The high Q-factor of the TD quasi-BIC makes the designed metasurface a promising sensing candidate; the results show that the sensitivity and figure of merit for refractive index sensing are 746 nm/RIU and 18650 RIU−1, respectively. For temperature sensing, the sensitivity can be as high as 54 pm/°C. This study provides a new approach for the excitation of strong TD resonance quasi-BIC, which facilitates the design of high-performance sensing applications.