The elastic coupling between the a-SiO2 spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves.
Three-dimensional opal–VO2 photonic crystals were prepared by the chemical bath deposition technique. The x-ray diffraction and Raman spectroscopic data confirm the crystalline perfection of VO2 impregnated into synthetic opal pores. It is shown from the optical reflectivity measurements that the photonic bandgap of the opal–VO2 composite is governed by the phase transition in VO2.
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