Achieving a high- Q response in metamaterials by manipulating the toroidal excitations

Abstract

The excitation of toroidal multipoles in metamaterials is investigated for a high-$Q$ response at a subwavelength scale. In this paper, we explore the optimization of toroidal excitations in a planar metamaterial comprised of asymmetric split ring resonators (ASRRs). It is found that the scattering power of a toroidal dipole can be remarkably strengthened by adjusting the characteristic parameter of ASRRs: an asymmetric factor. Interestingly, the improvement in toroidal excitation accompanies an increment of the $Q$ factor of the toroidal metamaterial; it is shown that both the scattering power of the toroidal dipole and the $Q$ factor increase more than one order by changing the asymmetric factor of ASRRs. The optimization in the excitation of a toroidal multipole provides an opportunity to further increase the $Q$ factor of the metamaterial and boost light-matter interactions at the subwavelength scale for potential applications in low-power nonlinear processing and sensitive photonic applications.