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.