A liquid-crystal phase modulator for large-screen projection

The substitution of a liquid-crystal phase modulator for the electrically deformable oil film used for image generation in some large-screen projectors is studied. The liquid crystal causes a voltage-dependent phase shift to the incident light, which is converted into amplitude-modulated light by means of a schlieren optical system. A cell configuration in which the phase shift is about equal for both polarization directions, so that no polarizers are necessary and therefore optical efficiency can be increased, was found. The diffraction properties of the resulting rectangular phase grid were investigated. When used with a thin-film transistor array or a wafer-scale MOS transistor array as drivers, a gray scale projection is possible