Toroidal dipolar response by a dielectric microtube metamaterial in the terahertz regime.

Due to metal losses in plasmonic metamaterials, high-refractive-index dielectrics are promising to improve optical performances of their metallic counterparts. In this paper, a LiTaO(3) microtube metamaterial is numerically investigated to explore the toroidal dipolar resonance based on the multipole expansion theory. The local field strength probed on the central axis of the microtube is greatly enhanced for the toroidal dipolar mode, forming a strong hot spot concentrated in the deep-subwavelength scale. Furthermore, we also show the influences of geometrical parameter on the quality (Q) factor of the toroidal mode. The high Q factor and strongly concentrated field strength in the toroidal microtube metamaterial offer application potentials such as sensing, energy havesting, particle trapping, and nonlinear optical effects.