Unified Framework for Spin Photonics at Structured Interfaces

While many fascinating spin‐dependent optical effects, such as spin‐controlled vortex generation (SCVG), position‐space photonic spin‐Hall effect (PPSHE), and momentum‐space photonic spin‐Hall effect (MPSHE), are investigated as a light beam strikes a structured interface, the intrinsic connections among them are obscure which hinders our manipulation of them. Here, we present a unified framework to understand these effects and reveal their inherent connections. We show, both theoretically and experimentally, that a transition from SCVG to MPSHE can happen as an optical Q‐plate is illuminated by a circularly polarized light beam whose center gradually moves. Such a transition, induced by the competition of two effects — vortex phases leading to SCVG and gradient phases leading to MPSHE, is found to share the same physics with the SCVG‐PPSHE transition at an air/dielectric interface, only with position and momentum indices interchanged. These findings unify our understanding of distinct spin‐dependent optical effects at structured interfaces, which may stimulate many applications in spin photonics.