Ultrathin WS₂ Polariton Waveguide for Efficient Light Guiding

Abstract Light confinement to sub‐wavelength scales is actively studied for nanophotonic applications because it gives rise to intriguing optical properties with enhanced light‐matter interaction. Herein, an ultrathin exciton–polariton waveguide based on a WS₂ multilayer is proposed for sub‐wavelength light guiding. A WS₂ waveguide supports guided exciton–polariton modes even with a few tens of nanometers of thickness. It is theoretically confirmed that the WS₂ waveguide has significantly lower propagation loss than a plasmonic mode, although its thickness may be similar to that of a plasmonic waveguide. By injecting white light into a fabricated WS₂ waveguide, light guiding is experimentally demonstrated through a 20 nm thick WS₂ waveguide. Notably, this study integrated the WS₂ waveguide with a WSe₂ monolayer to demonstrate the coupling of monolayer emission to the polariton waveguide. The results suggest that WS₂ multilayers provide a novel material platform with potential for nanophotonic applications, including ultrathin optical integrated circuits.