Theoretical study of self-starting gratings in photorefractive multiple-quantum-well structures

Abstract

A model of wave mixing is developed for photorefractive multiple-quantum-well structures in quantum-confined Stark effect geometry. This optical model takes into account both absorption and index gratings and is based on the nonlocal character of the optical nonlinearity in the direction of the applied electric field. A coupling gain is defined that depends only on the imaginary part of the relative permittivity grating. It is shown that self-starting gratings can appear when a certain threshold condition on the coupling gain is verified, with this condition being similar to the threshold condition for double phase-conjugate mirror operation in bulk photorefractive materials. The possibility of obtaining with actual devices the relatively high optical nonlinearity necessary to reach the threshold is discussed. Double phase conjugation with multiple-quantum-well structures in a two-zone configuration is envisaged.