Optical diffraction and high-energy features in three-dimensional photonic crystals

We provide a band-structure-based interpretation of the diffraction phenomena observed in three-dimensional photonic crystals. Qualitative and quantitative information about these patterns is obtained in a simple manner from the band structure. Our conclusions and experimental results explain phenomena occurring at frequencies above the first stop band that were not previously understood. Optical features observed in transmission spectra from opaline photonic crystals are now clarified by relating them to diffraction phenomena. We also observe an intriguing change in the diffraction pattern symmetry when the photonic-crystal refractive-index contrast is modified.