We present novel substrates for the elaboration of organic active devices for use in integrated optics. The selected materials are based on photopolymerizable matrices doped with optically active molecules. In such organic complexes, photoinduced chemical reactions initiate the polymerization of small monomers inducing an increase in density as well as in viscosity. Since these reactions are limited to the illuminated regions, the properties of these materials are easily patterned. Indeed, a refractive index increase occurs with the densification. Thus, it is possible to create a spatial modulation of the refractive index which can be used to make optical waveguides or phase holograms. Moreover, we induce quadratic non linear optical (NLO) properties by doping the photopolymers with push-pull chromophores. For this purpose, we need a non centro-symmetric alignment of the quadratic optical chromophores. This is obtained by orienting these polar entities with an external static electric field followed by the freeze of their orientation through the viscosity increase associated with the polymerization process. The non linear properties can then be patterned by irradiating the samples through appropriate masks. Long life-time periodically poled structures obtained with NLO chromophores doped photopolymers will be presented.
Polymers doped with nonlinear optical (NLO) chromophores are attractive candidates for manufacturing optical integrated devices, especially for applications based on second order non-linearities. Such optical devices require to select accurately the areas where the NLO push-pull molecules embedded in the matrix are oriented. This is usually achieved using patterned electrodes deposited onto the samples or microlithography techniques. We suggest a novel approach to control the spatial distribution of the oriented chromophores, based on the use of photopolymerizable mixtures. The formulation developed, which consists of a triacrylate monomer and a photoinitiator, is polymerized upon a visible light irradiation. It is doped with chromophores specially synthesized for this purpose, transparent at the actinic wavelength and highly soluble in the acrylate monomer. The doped photopolymerizable films are poled with a static electric field before irradiation and the orientation of the chromophores is then frozen in the desired areas by irradiating the samples with an appropriate pattern of light. We observed the ability of the polymerized medium to slow down the chromophore relaxation compared to the unexposed solutions. The influence of the formulation composition and irradiation parameters on the temporal stability of the chromophore orientation was studied through second harmonic generation measurements. Infrared spectroscopy measurements enabled to draw a correlation with the monomer conversion degree of the polymer host.
Organic materials are of increasing interest for optical devices, especially in applications based on quadratic optical non linearities. In this context, we have studied photopolymerizable mixtures doped with non linear optical push-pull chromophores. The doped photopolymerizable films are poled with a static electric field and polymerized with a spatially controled irradiation in order to freeze the orientation of the chromophores in the desired areas only. The temporal stability of the chromophore orientation is checked by second harmonic measurements. The photopolymerizable system was chosen by taking into account the possibilities of microstructuration under visible illumination. This property was demonstrated by recording permanent thick phase gratings. Simultaneously, optimization of the polymer matrix from the viewpoint of chemical composition, conditioning and functionalization of the chromophore was performed in order to improve the stability of the chromophore orientation. Formulating of the material requires a fair knowledge of the coupling between photochemical conversion, mass transport, stiffening of the polymer matrix. Photostructuration together with stable non linear optical properties allows now to consider realistic applications.
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