Localized gap-edge fields of one-dimensional photonic crystals with an epsilon-negative and a mu-negative defect

We study the properties of one-dimensional photonic crystals with an epsilon-negative and a mu-negative defect. With suitable parameters, the pair defect is equivalent to a transparent material with zero effective refractive index. This special pair defect has no influence on the spectral gap formed by the interference of propagating waves in positive-refractive-index materials. However, the field distribution is modified noticeably by the decaying wave in the pair defect. Particularly, the gap-edge field can be a highly localized wave instead of the usual standing wave as the size of the pair defect increases. The localized gap-edge field can reduce the switching thresholds for bistability greatly when Kerr-type nonlinear mu-negative material is involved. A nonideal model when the epsilon-negative and mu-negative materials are dispersive and lossy is used to verify the unusual properties.