High-performance nonlocal metasurface optical sensor with toroidal dipole bound states in the continuum

All-dielectric metasurfaces have been extensively investigated for their support of both local and nonlocal resonances in optical sensing applications. Typically, traditional sensors based on local resonance suffer from a trade-off between the sensitivity ( S ) and quality ( Q ) factor, whereas nonlocal resonance leverages strong interactions between adjacent unit cells to reduce sensing detection limits while enhancing the figure of merit (FOM). Here, we propose and experimentally demonstrate a high-performance optical polarization-independent sensor based on a hexagonal lattice all-dielectric metasurface, which could excite two toroidal dipole (TD) resonances in the near-infrared wavelength range. The nonlocal tuning of TD resonance through parameter space enables the excitation of bound states in the continuum (BICs) at a short wavelength (theoretical Q -factor of 4.18×10 7 ). Parameter optimization achieves quasi-BIC with strong nonlocal characteristics and a Q -factor of 4373, which is more than 20-fold higher than that of other localized TD resonances experimentally. Simulations and experiments have consistently demonstrated that nonlocal resonance significantly outperforms local resonance in refractive index (RI) sensing, owing to its superior lateral control of the electric field via nonlocal leakage modes. This work proposes an effective method to address the trade-off between the S and Q -factor in traditional sensors by utilizing nonlocal leakage modes, while also demonstrating a positive correlation between sensor performance and nonlocality. To our knowledge, this work represents the highest experimental S (1480 nm/RIU) and FOM (4228 RIU −1 ) values reported for RI sensing by utilizing leaky modes in nonlocal metasurfaces. The sensor provides theoretical and experimental support for integrated highly sensitive optical sensors.