ON PIXEL-ORIENTED STRUCTURE PARAMETRIZATION FOR DESIGN OF DIFFRACTIVEELEMENTS

In two dimensions the design of paraxially operating diffractive eleme nts is typically based on a pixel-oriented parametrization of the stru cture of the element. Various algorithms have been suggested to optimi ze such a set of parameters in order to obtain a diffractive element w ith satisfying optical properties. In particular projection-type algor ithms such as the iterative Fourier transform algorithm have been prov en to be well adapted to this kind of parametrization. Because of the significant progress which has been made in the availability of comput er memory the number of pixels is no longer a serious bottleneck of a pixel-oriented parametrization and therefore the benefit of projection -type algorithms has been increased in recent years. This is demonstra ted by comparing designs of diffractive elements as they can be obtain ed by different methods. Moreover, an additional constraint for projec tion-type algorithms is described and implemented which allows the con trol of the minimum feature size of the structure of the diffractive e lement independent of the chosen pixel size. In general this is necess ary to maintain the validity of the scalar approximation for a design which is based on the pixel-oriented parametrization.