- Measurements of transmission and reflection from thick silica opal slabs were performed in the spectral range 0.3–3.5 μm. A wide transmission stop band due to photonic band gap with no signs of reentrance to high-transmission regime down to 0.3 μm was observed. In addition, a new stop band in the range 2.7–3.6 μm was observed, where the transmittance oscillates fringe like about a small level in spite of negligible dispersion and absorption. In the reflection measurements two strong rejection bands were observed around 9.0 μm and 20.9 μm, which are due to anomalous dispersion in SiO 2 . The results obtained were explained using concepts of photonic band structure and photonic transport in disordered medium. An effective-medium theory was used to compute the infrared optical properties. A semi-quantitative agreement between the simulated and measured infrared reflectance was found.