We present results on the operation of a high sensitivity semi‐insulating multiple quantum well device for optical image processing. This device operates in the visible spectrum using II‐VI CdZnTe/ZnTe multiple quantum well structures. Incident light creates charge carriers that screen an applied ac electric field modulating the absorption and refractive index of the structure through the quantum confined Stark effect. In this way, an incident intensity pattern is recorded as an absorption and refractive index variation. The semi‐insulating nature of the material eliminates the need for pixelation. In a wave‐mixing experiment, a peak diffraction efficiency of 0.25% was observed from 2.25 &mgr;m active layer of the device. Two‐beam‐coupling gain coefficients of ∼500 cm−1at wavelengths longer than the exciton absorption peak should be possible.