ABSTRACT
The photorefractive (PR) effect refers to the light-induced change of refractive index in an electro-optic optically sensitive doped semiconductor. Since its first discovery by Ashkin et al. (1966), a tremendous amount of research has been carried out to study the PR effect and apply it to real-time image processing, beam amplification, self-pumped phase conjugation, four-wave mixing, optical computing, etc. (Yeh, 1993). When two coherent plane waves of light intersect in a PR material, they form an intensity interference pattern comprising bright and dark regions. In a PR material that is predominantly n-doped, electrons migrate from bright to dark regions, thus creating an approximately sinusoidal charge distribution. This diffusioncontrolled PR effect in turn creates an electrostatic space charge field which is ideally phase-shifted from the intensity pattern by 90j and modulates the refractive index of the material via the electro-optic effect. A grating is thus induced in the PR material. The incident plane waves are, in turn, scattered by the grating in a way that one wave may have constructive recombination, while the other may encounter a destructive recombination. This effect leads to energy coupling between the beams through what is commonly referred to as the two-beam coupling effect (Yeh, 1993).
