directional excitation of surface plasmon polaritons by circularly polarized vortex beams

We investigate the excitation of surface plasmon polaritons (spps) using a metallic nanoaperture array illuminated by circularly polarized laguerre-gaussian (lg) vortex beams. the direction of spp excitation is tunable by changing the circular polarization and topological charge of lg beams. the left- or right-handed circular polarization determines spp propagation on either side of the nanoaperture array. furthermore, varying the topological charge of lg beam will result in beam splitting of spps. we also utilize a composite nanoaperture array with different periods to achieve unidirectional excitation of spps. the study provides an interesting approach to control the excitation direction of spps and find great applications in spp generators and optical switches.