Controlling the plasmonic orbital angular momentum by combining the geometric and dynamic phases.

The tunable orbit angular momentum (OAM) of surface plasmon polaritons (SPPs) is theoretically studied with appropriately designed metasurfaces. By controlling both the orientation angle and the spatial position of a nano aperture array on an ultrathin gold film, the field distributions of the surface waves can be engineered to contain both spin dependent and independent OAM components. Simultaneous control over the geometric phase and the optical path difference induced phase (dynamic phase) provides extra degrees of freedom for manipulating the OAM of SPPs. We show that an arbitrary combination of OAM numbers can be realized for the SPPs excited by incident light of different circular polarizations. Our results provide powerful control over the OAM of SPPs, which will have potential applications in optical trapping, imaging, communications and even quantum information processing.