Tunable multi-channel sensing and bidirectional optical switching enabled by all-dielectric metasurfaces with Quasi-BIC Fano resonances

Abstract In this article, a novel all-dielectric metasurface consisting of a parallel-arranged Si tetramer and SiO 2 substrate is proposed. Fano resonances for quasi-bound states in the continuum (BIC) with narrow linewidths are excited by breaking the symmetry of the structure. These Fano resonances can concentrate the energy of the electromagnetic field, achieving a high-quality (Q) factor up to 3.09 × 10 4 . Using the finite-difference time-domain (FDTD) method, we analyze the electromagnetic field distributions of the three Fano resonances. The results reveal that each mode is primarily influenced by a different dipole: the toroidal dipole (TD), the electric dipole (ED), and the magnetic dipole (MD), respectively. The designed structure can be used as a bidirectional optical switch, as three Fano resonance peaks are turned off and two Fano resonance peaks are turned on when the angle of polarized light is changed. Additionally, the sensing ability of the structure is investigated under different environmental conditions by altering the refractive index of the surrounding medium. The findings indicate that the highest sensitivity achieved is 496 nm RIU −1 , and the remarkable figure of merit (FOM) reaches 1.24 × 10 4 RIU −1 , demonstrating excellent sensing properties. The innovative design of the proposed metastructure could enhance functionality and performance in advanced photonic devices, refractive index sensors, and multi-wavelength communications, contributing to the development of sustainable optical technologies.