Didier Riehl

Second-order optical nonlinearities of azo chromophores covalently attached to a sol-gel matrix

Optically nonlinear disperse red 1 (DR1) was covalently bound into a silica gel network by the coupling of DR1 and 3-isocyanatopropyltriethoxysilane. Organic-inorganic hybrid materials present a large resonant second-order susceptibility (d33 = 55 pm/V for a fundamental wavelength of 1.06 μm) with an excellent room-temperature stability.

Stable photorefractive memory effect in sol-gel materials

We report on the synthesis and the optical characterization of a photorefractive sol-gel material which contains nonlinear azo chromophore and carbazole charge transporting molecules. Both of these functional groups are covalently attached to the silica based backbone. Thin sol-gel films exhibit stable optically nonlinear properties: the electro-optic coefficient r13 measured at 633 nm is found to be 17 pm/V one day after corona poling and 15 pm/V after three weeks and over a period of several months. Photorefractivity is demonstrated by two beam coupling experiments without external applied electric field. Sol-gel films present a stable photorefractive memory effect with a net internal gain of 200 cm−1.

Modified sol-gel films for optical storage

Substituted azobenzene molecules (DR1, DO3, DR17, DY7, Magneson1, DR19C1 and DR19CICI) are grafted onto a silicon alkoxide precursor. Films are prepared by the sol-gel process. We have conducted preliminary optical experiments with DR1 and DO3 functionalized oxide gels. Optical information is written on the sol-gel film via the trans-cis-trans photoisomerization process with a polarized argon laser beam and read with a low power He-Ne laser. A stable signal (up to 60% of the maximum birefringence) is read a long time after the writing beam had been turned off. This shows the ability of the azo oxide gels to store optical information.

Photorefractive Sol-Gel Materials

The authors report the synthesis and characterization of photorefractive sol-gel materials that possess covalently attached push-pull azobenzene and carbazole moieties. Molecular structural characterization of the modified silane monomers was achieved by {sup 1}H NMR and infra red spectroscopy. The second-order nonlinear optical properties of the organic-inorganic hybrid films prepared from modified silane monomers were evaluated by second-harmonic generation. The stabilized value of the second harmonic coefficient, d{sub 33}, of films poled by corona discharge, at 1,064 nm fundamental wavelength was found to be 107 pm/V. Photorefractivity was clearly displayed from a two beam coupling experiment.

Optical properties of push-pull azo groups covalently bonded to a silica-gel matrix

The sol-gel synthesis of organic-inorganic composite materials with push pull azobenzene molecules covalently bonded to the silica matrix is used for fabricating low cost optical channel waveguides for integrated optics applications and optical information storage. The refractive index change is obtained through the orientation of the nonlinear active molecules induced by a trans-cis-trans photoisomerization process. The index change and anisotropy are created by illuminating the thin film at a wavelength located inside the absorption band of the chromophores. At short irradiation times, the induced birefringence and dichroism are the consequence of the usual reorientation phenomenon due to the trans-cis-trans isomerization. At long pumping times, a photobleaching is observed corresponding to an irreversible transformation in the silica matrix. This property is used to write channel waveguides and gratings.