Strong coupling between high-Q guided mode resonance and excitons in a mirror-coupled WS₂ grating structure

High-quality resonant metasurfaces that utilize guided mode resonance (GMR) or bound states in the continuum (BICs), in conjunction with the strong coupling potential of transition metal dichalcogenides (TMDs), present new opportunities for achieving significant Rabi splitting and nonlinear optical phenomena. In this study, we present a mirror-coupled WS₂ grating structure specifically designed to enhance GMR-exciton coupling. By integrating a WS₂ grating with a Si₃N₄ dielectric spacer and an Ag reflective mirror, the structure enables the generation of BIC modes within a narrow spectral range. Additionally, strong GMR-exciton coupling is demonstrated, resulting in a Rabi splitting of 220 meV, as supported by the coupled-mode theory (CMT). This work advances the understanding of optical mode dynamics and coupling mechanisms in hybrid grating systems, offering a versatile platform for next-generation photonic and optoelectronic technologies.