Omnidirectional gap and defect mode of one-dimensional photonic crystals with single-negative materials

A new type of omnidirectional gaps is theoretically found in one-dimensional photonic crystals (1DPCs) composed of two kinds of single-negative (SNG) (permittivity- or permeability-negative) materials. In contrast to the Bragg gaps, the properties (the central frequency and width of the gap) of such omnidirectional gaps are insensitive to the incident angles and the light polarizations, and are invariant upon the change of scale length. Such omnidirectional gaps result from the interaction of evanescent waves. When a defect layer is introduced, a defect mode appears inside the omnidirectional gap, and the spectral position of the defect mode is almost independent of incident angles and nearly invariant with the scaling.