Multipole interference and optical sensing based on the bound states in the continuum formed in dimer metasurfaces

Abstract

The all-dielectric metasurface supporting BIC based on dimer structures is proposed with the rectangular holes etched in amorphous silicon thin films. By introducing perturbations of the rotation angle of the rectangular hole as well as the difference in length and width, quasi-BIC modes in the near-infrared band can be created. Meanwhile, the research found that two different perturbations display different tuning abilities on the Fano resonance induced by the quasi-BIC. This paper reveals that the formation of the BIC mode originates from the interference between competing multipole moments, which ultimately leads to the emergence of a pair of reverse parallel electric dipoles. It explains the mismatch between the macroscopic response of the structure under the influence of competing multipole moments and the results of the multipole expansion. From the perspective of the influence of asymmetry on multipole moments, we explain the resulting radiation sources. The study demonstrates that the proposed dimer metasurface can support optical sensing under both x-polarization and circular polarization excitation, and it is observed that different perturbations have different abilities to modulate the sensitivity, which has great potential for device performance optimization and precise modulation.