Fig. 2
a–c Left: schematic of a homogeneous nanograting, a double grating, and a spin-Hall meta-slit integrated double grating for the up, middle, and down parts, respectively; right: FDTD simulation results for |Ez| generated in the left structure under illumination of an LCP OAM beam with topological charge l = 1. d–f Schematic of the k-vector coupling in the left three grating structures with an l = 1 LCP OAM incident beam. The dashed black/red circles represent the possible directions of \({\mathop{K}\limits^{\rightharpoonup}\!}_{{{SPP}}}\) and \({\mathop{K}\limits^{\rightharpoonup}\!}_{{{OAM}}}\), respectively; the radius of the circle represents the values of \(\left| {{\mathop{K}\limits^{\rightharpoonup}\!}_{{{SPP}}}} \right|\) and \(\left| {{\mathop{K}\limits^{\rightharpoonup}\!}_{{{OAM}}}} \right|\); the black/red arrows represent \({\mathop{K}\limits^{\rightharpoonup}\!}_{{{SPP}}}\) and \({\mathop{K}\limits^{\rightharpoonup}\!}_{{{OAM}}}\), respectively; the grey arrow represents \({\mathop{G}\limits^{\rightharpoonup}\!}_0\) introduced by the homogenous grating, as shown in (a), and the blue/green arrows represent \({\mathop{G}\limits^{\rightharpoonup}\!}_{1}\) and \({\mathop{G}\limits^{\rightharpoonup}\!}_{2}\) introduced by the upper and lower parts of the asymmetric grating, respectively, as shown in (b). For the upper/lower part of the composite grating, only \({\mathop{G}\limits^{\rightharpoonup}\!}_{1}/{\mathop{G}\limits^{\rightharpoonup}\!}_{2}\) is involved in the k-vector coupling process. The violet cross illustrates that the SPP is inhibited
