Electromagnetic multipolar quasi-bound states in the continuum for optical sensing

Optical sensing is of vital importance in many applications, which has received extensive attention in recent years. The pursuit of optical sensing mechanism with higher figure of merit (FOM) is very important for various sensing applications. Bound states in the continuum (BIC) with theoretical infinite Q factor is an ideal candidate to effectively improve the FOM of optical sensor. Herein, we propose and numerically demonstrate an optical refractive index sensor based on the electromagnetic multipolar quasi-BICs of all-dielectric metasurfaces. Based on the eigen-solution and excitation simulation, we find that magnetic dipole (MD) quasi-BIC is the best candidate for optical refractive index sensing among the electromagnetic multipolar quasi-BICs in the proposed all dielectric metasurface. The sensitivity (S) and the value of FOM for the optical refractive index sensor are 225.27 nm/RIU and 441762.93, respectively. It is anticipated that our results might shed new light on the optical refractive index sensing of high sensitivity and ultra-high FOM.