Photorefraktive

Photorefraktive refers to photorefractive materials and effects, a class of optical media whose refractive index can be modulated by patterned light. This capability enables the formation of volume holograms and dynamic diffraction gratings that can be written, read, and, in some cases, erased in a relatively simple optical setup.

The underlying mechanism involves photoexcitation of charge carriers, migration by diffusion and drift, and trapping in hidden states to create a space-charge field. This internal field then induces a refractive-index change through the electro-optic effect, producing a refractive-index modulation proportional to the light pattern. The resulting hologram can diffract light or serve as a waveguide. The process typically requires two or more beams to form an interference pattern, and the grating can be persistent or transient depending on the material and illumination conditions. Erasure is possible with uniform illumination, heating, or exposure to certain wavelengths.

Materials commonly exhibiting photorefractive behavior include inorganic crystals such as lithium niobate (LiNbO3), strontium barium niobate (SBN), and barium titanate, as well as bismuth silicon oxide and related compounds. Organic and hybrid systems, including photorefractive polymers and polymer-dispersed liquid crystals, have been developed to improve sensitivity, processing ease, and operation at different wavelengths.

Applications span holographic data storage, all-optical signal processing, image recognition and correlation, adaptive optics, and waveguide writing for integrated photonic circuits. While offering high diffraction efficiency and wavelength selectivity, photorefractive materials can require relatively high light intensities and show temperature sensitivity; ongoing research aims to broaden material choices and reduce operating power.