Deterministic Synthesis of Optical Vortices in Tailored Plasmonic Archimedes Spiral

We demonstrate that the shape and the orientation of a surface plasmon (SP) vortex can be deterministically tailored through the geometrical design of a plasmonic Archimedes spiral (PAS). Noncircular SP vortices exhibiting “c,” triangular, and square patterns are successfully synthesized under circular polarized plane-wave excitations. We provide clear evidence that the topological charges of the shaped SP vortices are dominated by the PAS under all geometrical settings. Our analytical description for the vortices shows excellent agreement with numerical simulations. Our design principle provides unique opportunity to manipulate nanoscale intensity and phase distribution of optical field on a flat area and may find interesting applications in plasmonic optical trapping and subwavelength patterning.