On pixel-oriented structure parametrization for design of diffractive elements

Abstract

In two dimensions the design of paraxially operating diffractive elements is typically based on a pixel-oriented parametrization of the structure of the element. Various algorithms have been suggested to optimize such a set of parameters in order to obtain a diffractive element with satisfying optical properties. In particular projection-type algorithms such as the iterative Fourier transform algorithm have been proven to be well adapted to this kind of parametrization. Because of the significant progress which has been made in the availability of computer 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 demonstrated by comparing designs of diffractive elements as they can be obtained by different methods. Moreover, an additional constraint for projection-type algorithms is described and implemented which allows the control of the minimum feature size of the structure of the diffractive element independent of the chosen pixel size. In general this is necessary to maintain the validity of the scalar approximation for a design which is based on the pixel-oriented parametrization.