Symmetric metasurface with dual band polarization-independent high-Q resonances governed by symmetry-protected BIC.

Abstract

In this Letter, we propose a symmetric metasurface composed of single-sized amorphous-silicon (a-Si) cuboids tetramer clusters that support two resonances with opposite symmetry, i.e., in-plane magnetic dipole (MD) resonance and in-plane toroidal dipole (TD) resonance governed by symmetry-protected bound states in the continuum (SP-BIC) in the near-infrared region. Since the cuboids tetramer of the metasurface retains C4v symmetry and mirror symmetry, both resonances are polarization independent. Multipolar decomposition of scattering power and electromagnetic distribution are performed to clarify the physical mechanism of dual quasi-BIC resonances. The effects of geometric parameters on both high-quality (Q) resonances are also studied. Additionally, the sensing performance of the designed metasurface is evaluated. The effects of the material's loss on both resonances are also studied. Our work provides a new route to designing dual mode polarization- independent resonators without multi-sized complex structures that may facilitate designing high-performance sensing applications.