We demonstrate ultrafast shifting of a photonic stop band driven by a photoinduced phase transition in vanadium dioxide (VO2) forming a three-dimensional photonic crystal. An ultrashort 120-fs laser pulse induces a phase transition in VO2 filling the pores of an artificial silica opal, thus changing the effective dielectric constant of the opal. Consequently, the spectral position of the photonic stop band blue-shifts producing large changes in the reflectivity. The observed switching of the photonic crystal is faster that 350 fs. The demonstrated properties of opal-VO2 composite are relevant for potential applications in all-optical switches, optical memories, low-threshold lasers, and optical computers.
In this paper we analyze linear and ultrafast non-linear properties of a three-dimensional photonic crystal composed of close-packed SiO2/Au/SiO2 core-shell colloidal particles. Strong coupling between incident light and surface plasmon of spherical gold microcavities appears as sharp features in observed reflectivity spectra in the visible. In a single layer of gold-shell particles, a highly directional diffraction pattern was observed with hexagonal symmetry. The non-linear dynamics of the reflectivity has been studied by femtosecond white-light pump-probe experiments. Abrupt changes limited by the instrumental time resolution, were observed in time-resolved reflection spectra while the signal recovers in about 10 ps. Ultrafast changes in reflectivity reach values as high as 20%. The results are compared with theory.