Attenuation in Two-Dimensional Photonic Crystals Containing Defects

We have investigated the optical-path-length dependence of visible-region attenuations which occur at gaps in the band structure of two-dimensional photonic crystals. We attribute the observed variation in the attenuation strengths to the presence of structural defects in our photonic crystals. These crystals are fabricated from Rnanochannel glassS materials, consisting of triangular arrays of glass or air cylinders within a matrix of a different glass. The samples we have studied to date have had periodicities as low as 190 nm and have typically contained more than 10^7 elements (cylinders). Although the nanochannel glass arrays are nearly perfect, occasional structural defects do occur, usually along lattice planes. These defects have been characterized by scanning-electron microscopy. The concentration and configuration of such defects appear to have a measurable effect on the strengths of the attenuations, especially in the case of relatively narrow attenuations (photonic band gaps). Our preliminary finite-difference time-domain transmission computations have attempted to reproduce the experimental results and to clarify the relative contributions of various defect configurations.