These devices are essential for continued advancement in the effort to transform information storage and transmission from the electrical to the optical regime. The promise of NLO polymers lies in their fortuitous combination of exceptional optical qualities, low cost, and ease of fabrication into device structures. This juxtaposition of technologically favorable characteristics has led to considerable research into the development of NLO polymers for commercial applications. A material suitable for widespread industrial use has yet to be synthesized, however. One of the most interesting and technologically promising phenomenon applicable to some of these materials is the light-induced modulation of the index of refraction of the material through the photorefractive effect.
Photorefractive materials combine photoconductivity and the electro-optic effect.
Photorefractive nonlinear optics is by far the most efficient technique for causing beams of light to interact. Holograms can be written and erased in photorefractive media with low power lasers, and the intrinsic phase shift in the holographic grating can lead to energy exchange between the writing beams. With the growing use of fiber optics and optical communications technologies, photorefractive materials have become prime candidates for all-optical data processing applications. They are expected to be used for high density optical data storage, associative image processing techniques including dynamic holography and image amplification, spatial light modulation, programmable interconnections in integrated optics and simulations of neural networks and associative memories with parallel signal processing. Polymers and liquid crystals have emerged in recent years as exceptional candidates for photorefraction, but much work in material development and characterization remains to be done.