Surface waves along a boundary of single-negative and double-positive materials

Existence of a surface wave along the boundary between the semi-infinite materials, one of which is a free-space and the other is a material with either negative permeability or negative permittivity, is presented theoretically in this paper. Surface waves exist in only limited combination of negative and positive sign of the material parameters. In addition, by analyzing the surface wave in a finite-thickness slab with negative permeability, the even- and odd-symmetry modal profiles have been obtained. From these results, the present paper predicts the possibility of a surface wave directional coupler based on a single slab transmission along its top and bottom surfaces.