Anomalous transmission through near unit index contrast dielectric photonic crystals

We present calculations that reveal a limitation for devices that demand photonic crystals with very narrow band gaps. The opaque regions of the transmission spectra through finite length crystals may be substantially broader than the band gap of the corresponding infinite crystals. This is a consequence of the crystals’ near unit dielectric index contrast. The opaque spectral width decreases gradually with increasing thickness. Many hundreds of layers may be needed to obtain a transmission null which approaches the width of the band gap for the infinite crystal. The analysis is done for two configurations of interest for optical applications due to their relative ease of manufacturer. The first is a two-dimensional triangular array of dielectric rods for which finite difference time domain simulations are done to determine the transmission spectra. The second is a one-dimensional dielectric stack for which transmission is analytically calculated.