A diffraction grating for which the intensity and/or direction of the diffracted light is electronically modulated using the electrophoresis of an index-modifying species. Index-modifying dye ions are dissolved in an electrophoretic medium maintained adjacent the diffraction grating. Application of a voltage across the medium moves many of the ions into the region adjacent the grating such that the ions absorb the incident light or otherwise modify the local index of refraction so as to change the optical characteristics of the diffracted light. Application of an opposite voltage across the medium moves many of the ions away from the grating, allowing light rays to diffract in a different manner when encountering the grating.