PHOTOREFRACTIVE POLYMERS

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Abstract
▪ Abstract Rapid advances in the field of photorefractive polymers and composites have in the brief time since their inception in 1991 led to the development of high-performance materials with refractive index modulations approaching 0.01, dif-fraction efficiencies close to 100%, and net two-beam coupling gain coefficients exceeding 200 cm−1in samples typically 100 μm thick. This paper reviews the current state of research, from the most successful synthetic strategies to produce polymeric photorefractive materials, to their emerging uses in applications. Two-beam coupling and four-wave mixing measurement techniques are presented and their importance in the characterization of the photorefractive properties of new materials is explained. The physics of the photorefractive effect in polymers is discussed with emphasis placed on the differences compared with the traditional inorganic photorefractive crystals. In particular, the orientational enhancement mechanism, which is believed to be responsible for the high performance of most of the low-glass-transition-temperature systems, is discussed in detail.