Multinarrowband Perfect Absorption With Bound States in the Continuum for Sensing Application

Accidental and symmetry-protected bound states in the continuums (BICs) generated by different triggering mechanisms have been demonstrated to hold great promise for confining light waves within the nanoscale. These BIC modes offer an elegant solution for manipulating the quality (
${Q}$
) factor, which is a primary performance index for devices relying on dielectric nanostructures. Here, using dielectric metasurfaces above a metal substrate, three eigenmodes are investigated, one of which corresponds to an accidental BIC with in-plane magnetic dipole (MD) characteristics, while the other two correspond to symmetry-protected BICs with out-of-plane electric dipole (ED) characteristics. Through parameter adjustment, the BICs can transition into high-
${Q}$
quasi-BICs that can simultaneously achieve perfect absorption. The metasurface exhibits considerable potential as a sensor, showcasing a maximum sensitivity of 374.7 nm/RIU and a maximum figure of merit of 72 RIU−1 within the sensing refractive index range of 1–1.1. In the context of temperature sensing, the sensitivity can reach up to 0.845 nm/°C within the sensing temperature range of 20 °C–100 °C. Our work will open a new avenue for the study of refractive index and temperature sensors with ultrahigh sensitivity.