Chiroptical resonances with high Q factors driven by quasi bound states in the continuum in all-dielectric metasurface at terahertz frequencies

Optical chirality pursues active manuscription of the light polarization state which is vital for practical applications related to chiroptical properties of matter. Recently, based on the concept of bound states in continuum (BIC), several metamaterials with out-of-plane perturbations have been proposed for strong optical chirality, which require complicated fabrication processes. Here, we present a novel all-dielectric metasurface which excites chiroptical resonances without breaking the out-of-plane symmetry. By simultaneously breaking the in-plane and mirror symmetries, the proposed metasurface exhibit quasi-BICs with high Q factors and strong circular dichroisms (CDs) for both transmitted and reflected waves. Moreover, the linewidths and chirality of the proposed metasurface can be flexibly tuned via modulating the in-plane asymmetry. Chiroptical resonances with high Q factors and strong CDs in the proposed chiral metasurface pave a new way for practical applications such as chiral sensing, chiral lasering, and chiral nonlinear optics.