Design of optical components and optical data storage in photochromic sol-gel films containing dithienylethene or azobenzene derivatives.

We present results on photochromic properties of hybrid organic-inorganic host matrices in which dithienylethene or azobenzene derivatives are trapped. Materials were prepared by the sol-gel process in the form of thin films. To increase the photochrome content inside the silica-based gel, modified alkoxysilanes were synthetized. The photochromic funtionalized monomers were copolymerized with methyltriethoxysilane or tetraethoxysilane. The study of sol-gel films containing dithienylethene both in the colored and discolored state shows that a large refractive index change, as high as 4.10(-2) can be reached. Design of optical components was performed. Furthermore from the colored state high remanent optical anisotropy can be photoinduced by discoloration with linearly polarized visible light. This anisotropy induces a linear dichroism in the visible absorption band and an important birefringence in the near-infrared transparency region. Optical data storage is one of the most fascinating potential applications of this effect. Concerning azobenzene containing materials, we took advantage of material deformation, subsequent to the photoisomerization of the photochromes, to design optical components. Thus, stable surface relief gratings having high modulation depth and high diffraction efficiencies (>30%) were inscribed on hybrid films. Experiments using near-field optical techniques were performed on the two systems in order to improve density data storage.