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Chiral metasurfaces have attracted considerable attention because of their immense potential for diverse applications requiring chiral light-matter interactions. Recently, boosted by a mechanism based on the concept of bound states in the continuum (BICs), high Q factor chiroptical resonances have been exhibited by breaking the inversion symmetries of planar metasurfaces. However, the optical chirality of these chiral metasurfaces is generally intolerable with respect to the structural geometries, especially the geometric asymmetry. Here, we present a novel chiral quasi-BIC with strong optical chirality in an all-dielectric metasurface. By simultaneously breaking the in-plane C 2 rotational and mirror symmetries, the chiral metasurface shows enhanced chiroptical resonances with near-unity CD (∼0.996) and high Q factors (∼2274) at terahertz frequencies. Further analyses based on numerical simulations reveal that the CD of the chiroptical resonance depicts exceptional remarkable tolerableness to the geometry asymmetry δ when δ are present in a broad range, while the corresponding Q factor is modulated accordingly. The results may develop a novel approach to manipulating the advanced optical chirality for potential applications requiring strong CD with enhanced light-matter interactions. [ABSTRACT FROM AUTHOR]

Optical devices based on bound states in the continuum (BIC) have attracted significant attention owing to their various potential applications. However, when changing their structural parameters, most of these devices exhibit a BIC resonance, limiting their utilization in practical applications requiring dynamic modulation. This paper proposes two modulators based on VO 2 –metal hybridized metamaterials for a dynamic modulation in the terahertz regime. By replacing a part of the metallic structure with structured vanadium dioxide (VO 2), we could enable switching between the BIC and quasi-BIC states via a temperature-dependent insulator-to-metal transition in VO 2. The Q factor and the asymmetry parameters of the modulators were found to be consistent with the inverse quadratic law, demonstrating the existence of a BIC state. • A VO 2 -metal hybridized metamaterial is proposed for the free switching between BIC and quasi-Bic states by temperature control. • The vanadium dioxide metal-mixed metamaterial proposed in this paper has a high modulation depth of 0.86. • In this paper, the modulation depth of vanadium dioxide metal mixed metamaterials changes with temperature. • The multipole expansion of the metamaterial is calculated, and it is confirmed that the excitation of the quasi-BIC state. [ABSTRACT FROM AUTHOR]

High quality factor resonances with enhanced light-mater interactions are of great importance for diverse applications such as nano-lasering and biosensing. Recently, Fano-sharp resonances with ultrahigh Q factor up to hundreds of thousands have been realized in all-dielectric metasurfaces based on the concept of bound states in the continuum (BIC). However, once being fabricated, these metasurfaces only offer unique characteristics and cannot be modulated. Here, we numerically demonstrate a tunable electromagnetic induced transparency (EIT) analogous resonances based on the interaction between two accidental quasi-BICs in an Se 2 Sb 3 -silicon hybridized metasurface. The silicon metasurface consists of a silicon square with two rectangular slots in the unit cell. Two accidental quasi-BICs (A-qBICs) are excited by changing the spacing between slots, and further results in EIT-analogous resonances when the spacing between slots and the polarization angle of incident light are varied simultaneously. Owing to the tunable characteristic of Sb 2 Se 3 , we demonstrate the active control of EIT effects by integrating the Sb 2 Se 3 film with the silicon metasurface supporting A-qBICs, which yields excellent tunable performances in terms of both the transmission amplitude and group delay of EIT analogous resonances. These results provide a new pathway to dynamically tunable and reconfigurable metadevices with high performances. • Accidental quasi-BIC resonances are excited in a silicon metasurface by tuning the structural parameter without breaking the symmetry. • EIT analogous resonances are excited due to the interaction between accidental quasi-BICs by varying the structural parameter and the polarization angle of incident light. • Active modulations of the transmission and group delay of EIT analogous resonances are achieved in the Se 2 Sb 3 -silicon metasurface due to the phase transition of Se 2 Sb 3. [ABSTRACT FROM AUTHOR]