Plasmonic spin-multiplexing metasurface for controlling the generation and in-plane propagation of surface plasmon polaritons

Abstract

Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric interface and are finding an ever-increasing number of applications in newly emerging nano-photonic and optoelectronic technologies. Different from the traditional approach to excite SPPs using prism or grating, metallic metasurfaces incorporating nano-slots with different orientations enable the photonic spin-dependent directional coupling of SPPs, which shows the unique spin tunability. However, the propagations of these generated SPPs are still correlative due to the conjugated phase profiles of metasurfaces for two incident orthogonal spin states. Here, we propose a plasmonic spin-multiplexing metasurface composed of nano-slots with different geometric dimensions and orientations to efficiently control the near-field generation and in-plane propagation of SPPs. By taking into account both the geometric phase and resonant phase of the nano-slots, the metasurface can generate two independent and fully decoupled SPP fields for a pair of orthogonal spin states. As proof-of-concept, we design a series of spin-multiplexing metasurfaces to numerically demonstrate different near-field optical functionalities, including spin-controlled plasmonic bi-focusing, self-accelerating beams, and vortices. We envision this approach may have potential applications in designing polarization-dependent tunable plasmonic nano-devices.