Dependence of the contrast ratio on crystal thickness in an electroabsorptive spatial light modulator that uses GaAs

The contrast ratio of an optically addressed spatial light modulator that u ses electroabsorption in a GaAs single crystal is discussed experimentally and theoretically. The modulator has the same structure as a Pockels readou t optical modulator. The contrast ratio depends strongly on the change in t he absorption coefficient and on the thickness of the GaAs crystal. From th e experimental results and from theoretical investigations of the Franz-Kel dysh effect, the change in the absorption coefficient is estimated by use o f the quadratic equation of an applied electric field that is not excessive ly strong. Under this condition, an optimum thickness of the GaAs crystal p late that will yield the maximum contrast ratio can be determined. (C) 1998 Optical Society of America.