Multiple Toroidal Dipole Resonances in All-dielectric Dimer Metasurfaces

Abstract

Bound states in the continuum (BICs) have been studied in a wide range of electromagnetic systems. In this letter, we present an all-dielectric metasurface consisting of an array of crosses. By introducing the in-plane perturbation, our proposed metasurface supports sharp Fano resonances in the near-infrared range, which are governed by symmetry-protected BICs. Toroidal dipole moments are demonstrated to be the dominant roles that excite these two Fano resonances by performing the multipole decomposition method and near-field analysis. In addition, the designed metasurface shows good sensing performance as a refractive index sensor. Our work may provide new reference for the design of other optical devices supporting strong resonances.