Phase quantization of a grating without altering the diffraction pattern

Quantization of the phase-delay profile of a diffractive optical element often leads to unwanted deviations of considerable extent in the diffraction pattern. A method for avoiding this flaw for periodic phase gratings is described. The idea is to forgo strict periodicity and use the new degrees of freedom thus obtained to compensate for quantization-related deviations. The method is demonstrated for Fourier-array illuminator gratings designed with an iterative Fourier-transform algorithm.