Photonic bands and group-velocity dispersion in Si/SiO2 photonic crystals from white-light interferometry

The phase delay of a light beam transmitted through (Si/SiO2)m multilayers with m52,4,6,8 is measured by white-light interferometry based on a fixed Mach-Zehnder interferometer coupled to a scanning Michelson interferometer. Results for photonic band and group velocity dispersion are obtained in a wide frequency spectrum and compare successfully with the predictions of electromagnetic theory. In particular, a strong slowing down of the group velocity at the band edges and superluminal propagation within the gap are demonstrated.