Spin-Direction Control of High-Order Plasmonic Vortex With Double-Ring Distributed Nanoslits

A plasmonic vortex lens (PVL) consisting of circularly distributed nanoslits is proposed. It is shown that the tilted angle variance of nanoslits along the azimuthal direction gives an opportunity to add an additional orbital angular momentum (OAM) number to the plasmonic vortex. Using the double-ring nanoslit distribution, homogeneous amplitude of excited surface plasmon along the azimuthal angle is achieved. The proposed structure has advantages compared with conventional PVLs since the spin-assisted OAM number can be an arbitrary integer value, which can enable the spin-direction control of high-order plasmonic vortex.