Effect of absorption on photonic band gap

In order to investigate numerically the effect of absorption on the photonic band gap, we consider a one-dimensional (1D) composite photonic crystal composed of alternating layers having complex dielectric constants. We perform calculations on the reflective spectra using the transfer matrix technique for the composite photonic crystal and find that the reflectance depends on material loss tangent Im(epsilon)/Re(epsilon) and the scaled frequency omega/omega0. It is shown that the absorption in composite photonic crystal breaks the periodic band structure produced by Bragg reflection in perfect photonic crystal. It pushes stop band-edges down, and raises the bottom of the pass band. The absorption makes the discrete stop bands become gradually a continuous stop band in larger-frequency range as material loss tangent Im(epsilon)/Re(epsilon) increases.