High-Q toroidal resonances enabled by tailoring field spatial localization in all-dielectric metasurfaces

Abstract

High-Q toroidal dipole resonances in all-dielectric metasurfaces have attracted intense attention due to their exceptional light-matter interaction capability. Here, we present and experimentally demonstrate an all-dielectric metasurface supporting polarization-insensitive high-quality (Q) factor toroidal resonances. By breaking in-plane structural symmetry via unequal circular air holes within a silicon-on-insulator unit cell, we transform symmetry-protected bound states in the continuum into high-Q quasi-toroidal dipole resonances. Because the intrinsic field perturbation occurs primarily within the weak field region, toroidal resonances maintains an ultra-narrow linewidth. Crucially, the macroscopic C 4 rotational symmetry guarantees a completely polarization-independent spectral response. Experimental measurements show excellent agreement with finite-difference time-domain simulations, capturing a sharp resonance with a measured Q-factor reaching ∼1931. Our high-Q toroidal-resonance metasurfaces offer great promise for polarization-insensitive filters, high-sensitivity biosensors, and nonlinear nanophotonic devices.