Investigation Of Properties Of Symmetry Protected Bound State In The Continuum In Terahertz Metasurface

Terahertz（THz）metasurfaces typically consist of periodic sub-wavelength unit structures that can precisely control and adjust parameters such as amplitude,phase,and polarization of THz waves.Compared to traditional THz devices,THz metasurfaces offer advantages such as low loss,high efficiency,and integration capability.In applications such as nonlinear optics,sensing,and laser technologies,achieving higher quality factor（Q factor）resonances plays a crucial role in improving device performance.Designing high-Q metasurface resonators is a challenging task.Bound states in the continuum（BICs）refer to localized waves that are perfectly confined without any radiation.BICs provide a new avenue for designing high-Q resonators.This article presents THz metasurfaces that can achieve single-band BIC,multi-band BIC,and tunable BIC,exploring their resonance mechanisms and potential applications.The main research content is as follows:1.A THz metasurface capable of high-Q resonances is designed based on a tetramer elliptical silicon.By breaking the mirror symmetry of the unit structure,the ideal BIC to quasi-BIC transition is observed.The relationship between the asymmetric parameters and the Q factor of quasi-BIC is verified to satisfy a negative quadratic inverse proportion.The sensing performance of the device as a refractive index sensor is studied,with a sensitivity of 147.3 GHz/RUI and a maximum FoM of 2319.2.A dielectric metasurface composed of tetramer LiTaO₃ is proposed,with two independent asymmetric parameters that can achieve four quasi-BIC resonances with ultra-high Q factors.The influence of geometric parameters on the transmission spectrum is analyzed,and the sensing performance of the metasurface is studied,with a sensitivity of up to 482 GHz/RIU.Moreover,the sensitivity of the metasurface is proportional to the negative square of the structural gap,and this phenomenon is explained.3.A tunable THz metasurface based on graphene is proposed.Quasi-BIC resonances are achieved through the introduction of perturbations,and Fano fitting is performed on the quasiBIC resonances.The tunable performance of the metasurface is investigated,with the Q factor of the resonance linearly changing when the graphene chemical potential is adjusted in the range of 0.34-1.50 eV.In addition,the influence of incident angle on the transmission spectrum is analyzed.