Diffraction Properties of Rectangular Phase Gratings in a Liquid Crystal Phase Modulator

Abstract The diffraction properties of rectangular phase gratings in a schlieren optical system are analysed. Those gratings are in a good approximation produced by liquid crystal control layers especially designed for phase modulation. In a first step, the dependence of the diffraction efficiency on the geometrical parameters of the control layer is investigated and optimum parameters for good efficiency and linearity are defined. In the second step, the influence of the schlieren optical system itself is analyzed, where the extension of the light source is taken into account. The optimum values for good contrast are evaluated. The problem of the tradeoff between contrast and intensity for high resolution can be solved by subdivision of the pixels which keeps the number of active addressing elements constant but produces a higher carrier frequency. The contrast can nearly be doubled in this case without loss of intensity.