Photonic Spin-Locking via Momentum-Biased Higher-Order Topological Orbital Hybridization

The advanced manipulation of topological photonic states with expanded degrees of freedom offers innovative ways of achieving robust light modulation and control. Here, by harnessing the orbital degree of freedom, strong spin-orbit coupling (SOC) and associated photonic spin-locking of Type-II higher-order topological states (HOTSs) are theoretically and experimentally demonstrated via momentum-biased orbital hybridization at the apex of a Kagome triangle lattice. The momentum bias, induced by the tilted incident light, not only produces symmetry breaking of the Kagome triangle lattice, but also introduces orbital momentum to Type-II HOTS. By attaining strong spin-locked SOC through momentum-biased topological orbital hybridization of Type-II HOTSs, the way is paved for the spin-based interplay and control between near-field and far-field in higher-order topological photonic crystals, with potential applications in polarization manipulation, spatial light modulation, quantum emitter control, and beyond.