Tailoring intrinsic chirality in a two-dimensional planar waveguide grating via quasibound states in the continuum
Dandan Zhang, Tingting Liu, Linlin Lei, Wei‐Min Deng, Tongbiao Wang, Qinghua Liao, Wenxing Liu, Shuyuan Xiao, Tianbao Yu
Abstract
The strong chiral light-matter interaction is crucial for various important fields such as chiral optics, quantum optics, and biomedical optics, driving a quest for the extreme intrinsic chirality assisted by ultra-high-quality ($Q$-) factor resonances. In this quest we propose a straightforward method to achieve extreme intrinsic chirality in lossless planar structures by manipulating the quasi-BIC through in-plane perturbation. The temporal coupled-mode theory is employed to derive the conditions necessary for achieving maximal intrinsic chirality. The quasi-BIC should be excited within the transparent spectral range of the structure and couple with $x$- and $y$-polarized waves with the same intensity but a phase difference of $\ensuremath{\pi}/2$. For an illustration, a planar chiral dielectric dimeric waveguide grating is designed that strongly interacts with left circularly polarized light while decoupling from right circularly polarized light through in-plane symmetry engineering. Furthermore, by adjusting the magnitude of the in-plane asymmetry, we can independently manipulate the $Q$ factors of the chiral quasi-BIC while maintaining near unity circular dichroism. Our results provide a simple yet powerful paradigm for achieving extreme intrinsic chirality on an easily manufacturable platform, which may have potential applications in chiral emission, chiral sensing, and enantiomer separation.