ABSTRACT
The index of refraction of a material possessing both photoconductivity and electro-optic (EO) response can be modulated when the material is subjected to nonuniform optical illumination. This is the so-called photorefractive (PR) effect. Its origin is the Pockels effect that is in response to the photoinduced space-charge field. Several features of the PR effect are attractive and interest ing, including the characteristic that the refractive index change is reversible. A second feature is that the magnitude of the index modulation is indepen dent of the illumination intensity and a saturated refractive index modulation is achievable under the illumination of a low-power laser source. In contrast, light intensity affects the speed of the PR response. In addition, it is a nonlocal effect; the largest index change does not occur at the brightest region. There is a nonzero phase-shift of the resultant index grating with respect to the light intensity distribution.
