Spin‐Locked WS2 Vortex Emission via Photonic Crystal Bound States in the Continuum

Abstract

AbstractOwing to their strong exciton effects and valley polarization properties, monolayer transition‐metal dichalcogenides (1L TMDs) have unfolded the prospects of spin‐polarized light‐emitting devices. However, the wavefront control of exciton emission, which is critical to generate structured optical fields, remains elusive. In this work, the experimental demonstration of spin‐locked vortex emission from monolayer Tungsten Disulfide (1L WS2) integrated with Silicon Nitride (SiNx) PhC slabs is presented. The symmetry‐protected bound states in the continuum (BIC) in the SiNx PhC slabs engender azimuthal polarization field distribution in the momentum space with a topological singularity in the center of the Brillouin zone, which imposes the resonantly enhanced WS2 exciton emission with a spin‐correlated spiral phase front by taking advantage of the winding topologies of resonances with the assistance of geometric phase scheme. As a result, exciton emission from 1L WS2 exhibits helical wavefront and doughnut‐shaped intensity beam profile in the momentum space with topological charges locked to the spins of light. This strategy on spin‐dependent excitonic vortex emission may offer the unparalleled capability of valley‐polarized structured light generation for 1L TMDs.