Vortex Beam Detection Based on Plasmonic in Plane Zone-Plate

A plasmonic in-plane zone-plate (IPZP) is analytically proposed and numerically analyzed. The proposed scheme consists of several discretely metallic nano-slits, which couple incident vortices into SPP and form focal spots. Wave front information of incident beam is reflected in the field distribution along "focal plane" of IPZP, and therefore, the proposed structure can be used for topological charge detection. Besides, an orthogonal slit array IPZP achieving simultaneous spin and orbital angular momentum detection is elaborated. IPZP structure has relatively high fabrication tolerance and the parameters can be adjusted to fit various operating wavelength. The proposed structure is expected to find potential applications in orbital angular momentum communication and high-dimensional quantum entanglement.