Coupling-Mediated Selective Spin-to-Plasmonic-Orbital Angular Momentum Conversion

Orbital angular momentum (OAM) has been recently introduced to plasmonics for generating plasmonic vortices with a helical wavefront, opening avenues for exotic on-chip applications such as quantum information processing and communications. In previous demonstrations, carefully designed optical elements are used to convert left- and right-circular polarizations into plasmonic vortices with different topological charges, resulting in conversion from optical spin angular momentum (SAM) to plasmonic OAM. Here, it is demonstrated theoretically and experimentally that by utilizing the near-field coupling between paired resonators in a metasurface, selective conversion from optical SAM to plasmonic OAM is realized, where generation of plasmonic vortices can be achieved for incident light of one circular polarization while significantly suppressed for the other circular polarization. The proposed design scheme may motivate the design and fabrication of future practical plasmonic devices.