Robust intrinsic chirality empowered by pair of off-Γ accidental BICs in triangular lattice metasurface

Abstract Optical chiral metasurfaces with high-quality factor enhance light-matter interactions. However, intrinsic chirality based on breaking the symmetry-protected BIC hardly reveals strong circular dichroism (CD) against structural perturbations. Here, we propose a design of the intrinsic chirality empowered by a pair of off-Γ accidental BICs and demonstrate a robust intrinsic chiroptical response continuously exhibiting strong and sign-controllable transmitted CD up to 0.98 and stable high-quality factors under a wide range of perturbations of geometrical parameters. A triangular lattice with slant T-shaped meta-atom is employed to break all mirror symmetries. The at-Γ quality factor of the chiral resonance is enhanced by four C points and maintains in the range of 105 to 106. Our work is beneficial for designing chiral metasurfaces with a strong intrinsic chirality.