All-dielectric metasurface-based multimode sensing with symmetry-protected and accidental bound states in the continuum

Abstract

Symmetry-protected and accidental bound states in the continuum (BICs) are generated by various triggering mechanisms, and it is challenging to use them together for sensing. This study designed an all-dielectric metasurface that produced BICs in the terahertz band. Moreover, we investigated eight mode distributions by energy band analysis, of which four modes had symmetry-protected BICs at the high-symmetry Γ point, and three had accidental BICs at the non-Γ point, all with quality factors up to 109. Using multipole analysis and parameter adjustment, we investigated the contribution of multipole moments to the far field, the electromagnetically induced transparency caused by the intermodal coupling, and the merging of accidental BICs. Finally, we used six BICs for multimode sensing, where the figure of merit (FOM) of the symmetry-protected BICs reached 108, and the FOM of the accidental BICs reached 105, providing a new perspective on terahertz linear sensor devices. These findings will open a new avenue for the study of terahertz multimode sensors with ultra-high FOM.