Magnetic toroidal dipole resonances with high quality factor in all-dielectric metamaterial

Abstract

Meta-photonics with high quality factor (Q-factor) resonances have been proposed as promising candidates for various practical applications. Recently, the theory of bound states in the continuum (BICs) has drawn great attention as it offers a simple method to pursue high Q-factors by exciting supercavity modes in nanostructures. Here, we report a novel optical metamaterial exhibiting sharp Fano-type resonances driven by quasi-BICs. Unit cell of the proposed metamaterial consists of three bars made of intrinsic silicon. The proposed metamaterial supports strong magnetic toroidal dipole (MTD) resonance, which is verified by both the multipole expansion and localized field distribution. Further analyses show that the Q-factor can be easily modulated by tuning the degree of asymmetry and their relationship follows an inverse quadratic law. Owing to its narrow linewidth, the proposed MTD metamaterial can serve as an optical sensing platform for monitoring surrounding refractive index, whose sensitivity and figure of merit (FOM) can reach to 894 nm/RIU and 3.89×103, respectively.