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Unusual mode propagation characteristics of negative index slab waveguides

We study the unusual properties of the guided modes of negative index slab waveguides (NI-SWs). It is shown that for specific frequency bands, the structure can excite guided modes with similar field distributions but different propagation constants, which we refer to as dual-wavenumber modes (DWMs). The characteristics of evanescent fields of DWMs are studied. It is shown that when interfering destructively, the evanescent fields of the DWMs grow temporarily before they decay permanently.