Phase delay and group velocity determination at a planar defect state in three dimensional photonic crystals

3 pages, 3 figures.-- PACS: 42.70.Qs; 78.20.Ci; 71.55.-iPhase sensitive optical transmission measurements have been performed on three dimensional opal-based photonic crystals containing a planar defect. From numerical derivation of the measured phase, the group velocity has been retrieved. Strong modulations in the group velocity are seen to correlate with a recovery in the transmission inside the forbidden spectral interval, demonstrating the presence of a localized defect state. Accordingly, the phase change measured across the forbidden interval doubles in the lattice containing a planar defect with respect to the defect-free crystal, as expected when introducing a localized state inside the pseudogap. All results have been modeled with a scalar wave approximation in a two band model including extinction.This work has been partially funded by the CARIPLO Foundation, the Spanish Ministry of Science and Education under Grant No. MAT2005-03028, and by the Ramón Areces Foundation. J.F.G.L. was sponsored by the Postdoctoral Program of the Spanish Ministry of Science and Education.Peer reviewe