Anomalous group velocity in a 3D photonic nanostructure

Experiments have confirmed the existence of both behaviors in three-dimensional ordered nanostructures, in the spectral range where the wavelength of light is on the order, or smaller, than the lattice constant. Using periodic boundary conditions in a band structure calculation of a perfect 3D photonic crystal one finds that, in such frequency range, only propagating modes with a vanishing slope dispersion relation exist and, hence, a reduced group velocity is predicted. In this paper, we study such group velocity behavior for finite thin artificial opal slabs made of a reduced number of layers. In our model extinction is included. The group velocity and group index of the electromagnetic waves from the linear response of the crystal, is determined in the high energy spectral region.