Manipulation for Superposition of Orbital Angular Momentum States in Surface Plasmon Polaritons

摘要

Superposition of orbital angular momentum (OAM) states and the structured intensity are providing new approaches for manipulating optical information and light-matter interactions. While superposition of OAMs in free space has been well studied, further extensions to surface plasmon polariton (SPP) confined in near-field would be crucial for miniaturing and integrating platforms. Here, the plasmonic metasurfaces consisting of rotated nanoslits arranged in a segmented spiral are proposed to realize the superposition of two SPP OAM states. The nanoslit rotation and the azimuthally variant radius of segmented spiral introduce the spin-dependent geometric phase and position-dependent dynamic phase, respectively, and combination of two phases generates two incorporating OAM states. By designing metasurfaces with different parameters, the superposition of two different OAM states and complex structured pattern can be achieved. The four degrees of freedom including rotation order q, spiral order m, initial orientation angle alpha(0), and incident circular polarization sigma, enable the superposition of SPP OAM states in a straightforward and flexible manner. This work would be of significance for applications of OAMs such as micro-manipulations, optical trapping, and sensitive angular metrology.