Properties of defect modes and band gaps of mirror symmetric metal-dielectric 1D photonic crystals

Inserting of any sort of irregularity in a photonic crystal (PC) with a perfect periodicity can produce defect modes. Great interest has been directed towards defect modes due to many potential applications. In this work, a binary PC consisting of silica (SiO2) and silver (Ag) is assumed. The PC is supposed to have a mirror symmetry with the structure (SiO2/Ag)(N)(Ag/SiO2)(N), where 2 N is the number of periods of the PC. The transmission spectra of the PC are investigated in the visible and IR wavelengths. It is found that when the thickness of Ag layer increases, band gaps are broadened, more band gaps appear starting at low wavelengths and all these band gaps are shifted toward loner wavelengths. Defect modes appear at certain thicknesses of Ag, diminish gradually and then entirely disappear. When the incidence angle increases, band gaps are blue shifted in contrary to their behavior with the increase of the thickness of the metal and SiO2 layers.