Fig. 1.

Schematic of SLPC. (A) (Left) The polarization on the Poincaré sphere, where the three Stokes parameters are S₁=|E_y|²-|E_x|², S₂ = 2|E_x||E_y|sinδ, and S₃ = 2|E_x||E_y|cosδ, and δ is the phase difference between the x and y axis field components. (Right) LCP and RCP photonic states (helicity−orbital coupling). (B) A 2D square lattice SLPC consisting of stacked PE and PM superlattice constituents in vacuum background. The positive domain and stacking direction of PE (red arrows) and PM (black arrows) media are along the z axis. Lattice constants of photonic crystal and PE/PM superlattice are $a$ and $2d$, respectively. The radius of cylinder is $r=0.11a$. LCP and RCP edge states propagate in x−y plane at the boundary (with a separation distance of $0.5a$) between SLPC and cladding layer.