Multiple toroidal dipole Fano resonances of asymmetric dielectric nanohole arrays

The toroidal dipole is a fundamental electromagnetic excitation independent from the well-known electric and magnetic dipoles, which enables strong resonances in nanostructure systems due to the reduction of radiative loss. In this paper, we demonstrate multiple toroidal dipole resonances in a series of silicon nanohole structures with symmetry breaking in the near-infrared range. Detailed multipole decompositions and field distributions are performed to discuss the excitation of these resonances. The following experimental verifications support the theoretical predictions. Such a two-dimensional nanohole platform could be more technically available compared to other complicated nanostructures. Our results may provide remarkable potentials in facilitating the light-matter interaction at the nanoscale, such as light emission, subtle sensing, and so on.