Graphene-loaded wire medium for tunable broadband subwavelength imaging

In this paper, we demonstrate that a wire medium (WM) slab loaded with graphene sheets enables the enhancement of the near field for subwavelength imaging at terahertz frequencies. The analysis is based on the nonlocal homogenization model for WM with the additional boundary condition at the connection of wires to graphene. The principle of the operation of the proposed lens depends on the enhancement of evanescent waves, wherein the excited surface plasmons at the lower and upper graphene interfaces are coupled by an array of metallic wires. The resolution and the operating frequency of the subwavelength imaging device are mainly determined by the tunability of graphene and the structural parameters of the WM slab. The proposed structure has a resolution better than lambda/10 with the advantages of broad bandwidth, low sensitivity to losses, and tunability with respect to the chemical potential even if the distance between two graphene sheets is a significant fraction of wavelength. Severe challenges in the fabrication of the lens have been studied in-depth, and a promising approach for a practical realization has been proposed.