Strong coupling between excitons and chiral quasibound states in the continuum of the bulk WS₂ metasurface

In the fields of optics and photonics, the topic of light-matter interactions, particularly strong coupling effects, is a developing area of research. Exciton polariton, a hybridized state brought about by strong coupling, is a hot topic, especially from the standpoint of chiral optics. Under the incidence of right circularly polarized light and left circularly polarized (RCP and LCP) light, we investigate the strong coupling between excitons and quasibound states in the continuum (Q-BICs) resonance in a bulk WS₂ metasurface. It is discovered that the Q-BICs are affected obviously on center frequencies and linewidth by structure parameters; while the exciton peaks are impacted insignificantly. Furtherly Q-BIC shows chiral enhancing features. When we take into account both Q-BIC and excitons of the metasurface simultaneously, there is a strong coupling as evidenced by the Rabi splitting up to 182 meV and the clear anti-crossing behavior in the transmittance and reflectance spectra of left and right circularly polarized light, respectively. Notably, a quasi-induced transparency window forms in the circular dichroism (CD) spectrum around the exciton band due to the non-chirality of exciton peaks. This enables the removal of excitons that are not involved in the strong coupling. The bulk WS₂ chiral metasurface as a strong coupling system not only provides a way to understand the strong Light-matter interaction, but also generate a potential possibility for realizing the application of chiral optics. Additionally, it can realize the strong chiral coupling with a single self-hybridized element in the structure. Our results have potential implications in the chiral optical field and provide a chiral perspective on the study of strong photon-exciton coupling.