Propagating Modes Generated by the Coupling of Evanescent Surface Modes in Metamaterial Slab Waveguides

Here, we report that evanescent surface modes at the interfaces between ε-negative and μ-negative metamaterials can be made into a propagating one via the introduction of symmetric slab structures. The slab induces strong coupling between double interfaces comprising the slab and also between two evanescent surface modes localized at each interface. The novel propagating mode has its origin in this strong coupling so that it becomes cut off when the core size (i.e., distance between double interfaces) becomes large enough to make the coupling effects negligible.