Azimuthally Polarized and Unidirectional Excitonic Emission from Deep Subwavelength Transition Metal Dichalcogenide Annular Heterostructures

Monolayer transition metal dichalcogenides (TMDs) are essential to the scaling down of light-emitting devices to the nanoscale. But the spatial manipulation of their emission at the deep subwavelength scale has remained challenging, limiting their applications in compact directional lighting systems. Here, we present an experimental demonstration of directional and azimuthally polarized excitonic emission from monolayer tungsten diselenide (WSe2) integrated with deep subwavelength tungsten disulfide (WS2) circular gratings. For such nanoscale heterostructures, the high refractive index of WS2 enables the existence of guided mode resonances in annular gratings with thicknesses down to the lambda/50 length scale. As such, the excitonic photoluminescence from WSe2 couples into the guided mode resonances of WS2 nanostructures and radiates as an azimuthally polarized and symmetric beam in the momentum space. Such ring-shaped exciton emission at the deep subwavelength scale provides more possibilities to miniaturize functional light-emitting devices for azimuthally isotropic illumination.