Unveiling Spin‐Orbital Angular Momentum Locking in Photonic Dirac Vortex Cavities

ABSTRACT Dirac vortices, originally studied in quantum field theories to predict localized zero‐energy modes, were recently realized in photonics, leading to Dirac vortex cavities. With topological protection, Dirac vortex cavities offer robust single‐mode large‐area localized modes appealing for high‐performance micro‐lasers and other applications. As a spectrally‐isolated single mode, the radiation of a Dirac vortex cavity mode was believed as having vanishing orbital angular momentum due to time‐reversal symmetry. Here, we report the direct observation of orbital angular momentum radiation of a Dirac vortex cavity through spin‐resolved measurements. Remarkably, we confirm the spin‐orbital angular momentum locking in such radiation due to the spin‐valley locking and inter‐valley couplings. We demonstrate that the spin‐orbital angular momentum locking is controlled by the chirality of the Kekulé modulation and propose design schemes for arbitrary‐order single‐mode OAM radiation.