Unlocking Wavefront Manipulation in Exciton-Polaritons by Structuring WS₂ as Phase Gradient Metasurfaces.

Abstract

Exciton-polaritons (EPs), originating from the coherent hybridization of photons and excitons, are half-light and half-matter quasiparticles possessing nanoscale field confinement. Although EPs can push the spatial resolution of light manipulation to the nanoscale, their pixelated phase control remains a challenge. In this work, we demonstrate EP wavefront shaping by using geometrically tailored tungsten disulfide (WS₂) metasurfaces. In these metasurfaces, elliptical WS₂ nanodisks support localized Mie resonances that strongly couple with WS₂ excitons, forming self-hybridized EPs with a Rabi splitting of ∼150 meV. Meanwhile, the anisotropic nanoantenna geometry induces high birefringence, yielding two orthogonally polarized EP resonances for efficient cross-polarization conversion. Leveraging the geometric phase principle, spatially arranged meta-atoms imprint pixelated phase profiles onto the EP output beam. Experimentally, we realize deflection and focusing of the EP beam. This work merges the subwavelength polariton confinement with metasurface wavefront engineering, paving the way toward compact multifunctional polaritonic devices.