Bilayer holey plasmonic vortex lenses for the far field transmission of pure orbital angular momentum light states.

We report the design of a holey plasmonic vortex lens (PVL) structure able to couple circularly polarized impinging light to a plasmonic vortex in the form of the fundamental TM mode of a metal-insulator-metal plasmonic waveguide. The field transmitted through the hole milled at the center of the second metal layer of the structure is characterized by a well-defined spiral harmonic, entirely determined by the spin of impinging light and by the chirality of the PVL structure. Scattering finite elements simulations are presented for single layer standard PVLs and for bilayer ones, comparing the spiral spectra of the transmitted field and the efficiencies of the architectures.