Plasmonic Spiral Nanostructure for Analyzing the Angular Momentum of Light

A compound plasmonic light analyzer with an elliptical Archimedean spiral nanostructure is proposed analytically and analyzed numerically. The elliptical Archimedean spiral is analogous to an ellipse but has varying semimajor axes. When the structure is illuminated by the incident light with different angular momentum, surface plasmon polaritons (SPPs) are excited, and various plasmonic vortexes indicating the angular momentum of the light are generated. Incident light with different spin angular momentum can create plasmonic vortexes centered at different points, and the orbital angular momentum of light determines the size of the vortex, which manifests its topological charge. Thus, both spin and orbital angular momentum states of the incident light can be estimated simultaneously by observing the position and the size of the plasmonic vortex. We provide an analytical description of the structure and it is well consistent with the finite-difference time-domain (FDTD) numerical simulation results. This plasmonic light analyzer may provide various potential applications in nanophotonics device and optical information technology.