The photorefractive effect is a phenomenon whereby the local index of refraction is modified by spatial variations of the light intensity. It is strongly observed when coherent rays interfere with each other in a photorefractive material which forms a spatially varying pattern of illumination. As a result, charge carriers are produced in the material which migrate owing to drift or diffusion and space charge separation effects. The resulting electric field that is produced induces a refractive index change via the electro-optic effect. Some of applications are: spatial light modulators, 4 wave mixing, phase conjugation, optical memory and computing.
     Sillenite single crystals Bi12SiO20 (BSO) and Bi12GeO20 (BGO) show unique combination of different physical properties. BSO and BGO crystals are very efficient photoconductors with low dark conductivity that allow to build up large photo-induced space-charges. Also strong spectral dependence of the photoconductivity and their electrooptic properties allow to develop and produce a wide range of optical device and systems. BSO and BGO crystals are used in spatial light modulators, dynamic real-time hologram recording devices, phase conjugation wave mixing, optical correlators, optical laser systems for adaptive correction of ultrashort light pulses. Photo-induced absorption make possible to develop and produce ô light-lightö type of optical devices such as optical modulators, switches etc. The fabrication Sillenite Oxide thin-film crystal structures by different technique permits the development of a long list of devices including optical waveguides, integrated optical devices. The use of waveguide optical structures based on Sillenites allows to achieve uniform illumination (normally to the plane of waveguide ) in a wide spectral range.
     The relatively large electrooptic and Faraday effect of Sillenite Oxides makes them useful for optical fiber electric/magnetic fields sensors.
     Strontium-Barium Niobate (SrxBa(1-x)Nb2O6) SBN is an excellent optical and photorefractive material. Nominally pure and doped by Ce, Cr, Co, Fe. SBN crystals of different compositions are used in elecro-optics, acousto-optics, photorefractive non-linear optics. A new growing technique provides excellent optical quality single crystals, free of growth striations, inclusions and other inhomogeneities, as well as definite cross section and linear dimensions up to 80mm. SBN crystalline elements meet the requirements for different applications. Based on this unique crystal growing technique, large high quality SBN optical elements and photorefractive cells are available.Fe:LiNbO3 (other dopants are available).
     Iron doped Lithium Niobate crystal (Fe:LiNbO3) is a kind of common used photorefractive materials with high electro-optical (EO) coefficients, high photorefractive sensitivity and diffraction efficiency. Compared to BaTiO3 series photorefractive crystals, it has some outstanding advantages, such as easy operation and storage, low cost and large size availability, which make it more suitable for volume fabrication and practical devices. Therefore, Fe:LiNbO3 crystal will forecast a wide range applications.

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