Toroidal Mode induced Fano Resonance in Spiral Dielectric Metasurface for Terahertz Sensing

In this paper, Fano resonance generated from the metasurface of all-dielectric particles is numerically studied. It is found that the resonance has a higher Q-factor than the conventional electric and magnetic resonance. Through numerically computing the scattered power of different multipole moments of the structure, it reveals the destructive interference between toroidal dipole mode and magnetic quadrupole dipole mode produces a high Q-factor Fano resonance. Based on the obtained results, the resonance wavelength induced by the toroidal mode depends on the refractive index of the upper layer of the analyte, showing a sensitivity of up to 30 μm/RIU. Our research provides theoretical foundation for the research of singular toroidal dipole and opens a new route based on the application of toroidal dipole resonance.