Nonlinear optical materials are essential for photonics. One basic approach is the use of photorefractive materials, which show a light induced refractive index change. Even though being an optical nonlinear effect ,this effect occurs at relative low light intensities of a few µW. This quality makes this class of material highly interesting for photonic applications.

In general there are two classes of photorefractive materials. One the one hand inorganic crystals, such as LiNbO3, LiTaO3, BaTiO3, SBN, sillenites and Bismuttellurite. In these crystals the photorefractive effect was observed first and is very well understood. On the other hand photorefractive polymers which where synthesized for the first time at the beginning of the 1990th. The polymers can be realized by two different approaches. The first one are photopolymers, which can polymerize under light illumination resulting in a change of density. This density change acts as a change of refractive index. Very well known photopolymers are based on polymethyl methacrylate (PMMA) and polyvinyl alcohole (PVA). The other approach for light induced refractve index changes in polymers can be realized with electrooptic composites on PVK (polyvinyl carbazole) and PMMA basis. The refractive index change in these composites is build up by an space charge field like in inorganic photorefractive crystals. This effect is reversible, so that electrooptic photorefractive materials can be used for dynamic applications.

For selection and optimization of such a material always the wanted application determines the needed properties. The possible fields of operation are always dependend on properties such as optical quality, optical nonlinearity, reaction time and mechanical stability of the material. This ends in the necessity of the combination of all processes beginning with the synthesis going over to the optimization and ending with the use of these highly specialized materials. These qualities must be suited to the respective requirements.