Merging of omnidirectional defect modes in one-dimensional photonic crystals with a single-negative material defect

Abstract

Merging omnidirectional defect modes are found in one-dimensional photonic crystals composed of periodic single-negative-permittivity and single-negative-permeability media layers and a single-negative defect. By increasing the defect size or the thickness ratio of the two periodic layers, two defect modes shift to each other from the upper and lower frequency side of the forbidden gap, respectively, then merge at the midfrequency of the gap. Merging conditions for such defect modes are given. These defect modes are insensitive to the incident angle. Moreover, the electric fields at the central frequency of the bandgap could be designed to be strongly localized at just one interface between the defect and the periodic layers in the photonic crystal with low transmission.