High-Q Fano Terahertz resonance based on bound states in the continuum in All-dielectric metasurface

In recent years, the concept of bound states in the continuum (BICs) in metasurfaces has become a research focus, providing an important physical mechanism for engineering high-quality-factor (Q-factor) optical resonances in high-index dielectric nanoparticles and all-dielectric metasurfaces. In this paper, the basic concept of BICs is first introduced, and then, a sampling of relevant literature on the application of BICs in terahertz (THz) metasurfaces is summarized. An approach that allows the effective control of the appearance of sharp resonances in metasurfaces associated with the BICs is discussed. A novel structure is then proposed, and an interesting attribute of BICs with a sharp resonance dip is demonstrated. High Q factors can manifest due to high confinement of light and near-field enhancement of the physical mechanism, where BICs transform into quasi-BICs due to the width adjustment of the crystals. Moreover, the transmission is stable, despite the variations of the structural parameters. When this metasurface is used as a refractive-index sensor, a sensitivity of 465.74 GHz/RIU and a figure of merit of 32,984 are obtained, indicating excellent performance.