Potential of high Q dual band Mid-Infrared metasurfaces with Quasi-BIC for refractive index sensing

Dielectric metasurface supporting quasibound states in the continuum (QBIC) are expected to be applied to high-performance optical devices such as refractive index (RI) sensors, narrow band filters, optical switches, and nonlinear optics due to its ultra-narrow linewidth resonance. Here, we design a metasurface consisting of four parallel-arranged silicon elliptical nanodisks, with a silicon circular nanodisk in its center as a coupler, which can relax the conditions for achieving QBIC. It is found that dual-band mid-infrared high Q resonance is generated when the radius of the circular nanodisk is 370 nm, with Q factors of 12,677 and 4362. Their sensitivities are 604.55 nm/RIU and 2307.57 nm/RIU, with the figure of merit values (FOM) of 1400 RIU−1 and 1792 RIU−1. The electric field analysis shows that the resonant modes of the structure are electric quadrupole and electric dipole. This work provides a new way to realize high-performance mid-infrared refractive index sensors that are easy to process.