Features of Degenerate Defect Modes in One-Dimensional Photonic Crystals with Two Defects

The different cases of degenerate defect modes in one-dimensional photonic crystals with two defect layers are studied. Degenerate defect modes occur when two or more defect modes merge at a given wavelength in the photonic crystal reflection spectrum. Such defect modes have a variety of potential practical applications, including the increase of sensitivity in optical sensors. The appearance of each type of degenerate defect modes is determined by the structural features and parameters of the photonic crystal. For this reason, we have derived analytical equations containing the photonic crystal parameters describing each type of defect modes merging. Analytical expressions for the zero imaginary phase for any type of defect mode merging have been also obtained. These general relationships can be used to simplify the modeling of one-dimensional photonic crystals with two defect layers and for further analysis of degenerate defect modes.