Polarization sensitivity engineering in WS2 metasurfaces governed by quasi-bound states in the continuum

Bound states in the continuum (BICs) hold significant potential for enhancing light-matter interactions with high quality (Q) factor resonances. Concurrently, tungsten disulfide (WS₂), a transition metal dichalcogenide (TMDC), provides a pathway to attain the strong-coupling regime, garnering significant interest from researchers. In this study, we engineer polarization sensitivity in metasurfaces constructed from bulk WS₂ slabs, employing two distinct approaches. Firstly, we synthesize a polarization-sensitive metasurface composed of dual slabs with varying dimensions to achieve symmetry-protected BICs. The rotation of the electric field direction of the incident wave leads to a dramatic change in the transmittance response. Conversely, by considering a quad-slab unit cell, we develop a polarization-independent metasurface that exhibits a unique response to any orientation of the electric field of the incident wave. For both types of metasurfaces, we demonstrate the generation and tuning of quasi-BIC resonances by adjusting the degree of asymmetry. Furthermore, we elucidate how to achieve the strong coupling regime characterized by an anticrossing pattern through scaling the in-plane dimensions of the unit cell. In the strong coupling regime, Rabi splitting exhibits two distinct values of 104.2 meV and 116.8 meV for polarization-sensitive and polarization-independent metasurfaces, respectively. The polarization sensitivity engineering presented herein can be applied across various photonic systems, enabling the development of devices that are either highly sensitive or polarization-independent.