Plasmonic space folding: focusing surface plasmons via negative refraction in complementary media.

We extend designs of perfect lenses to the focusing of surface plasmon polaritons (SPPs) propagating at the interface between two anisotropic media of opposite permittivity sign. We identify the role played by the components of anisotropic and heterogeneous tensors of permittivity and permeability, deduced from a coordinate transformation, in the dispersion relation governing propagation of SPPs. We illustrate our theory with three-dimensional finite element computations for focusing of SPPs by perfect flat and cylindrical lenses. Finally, we propose a design of a flat SPP lens consisting of dielectric cylinders arranged in a periodic fashion (along a hexagonal array) on a metal plate.