Design of dual-zone freeform holographic optical elements

Freeform holographic optical elements (HOEs), which combine the merits of HOEs and freeform surfaces, can provide high degrees of freedom for aberration correction. To achieve flexible phase modulation, the representation of the flexible phase profiles of freeform HOEs becomes crucial. In this paper, we propose a method to design dual-zone freeform HOEs that can provide higher degrees of freedom compared to traditional designs. The dual-zone freeform HOE includes two individual subregions. The phase profile of each subregion is represented by an individual polynomial, and the two subregions are jointly designed by taking both aberration correction and diffraction efficiency into account. An example is given, and comprehensive comparisons are made to validate the proposed method. Compared to the conventional design, the resolution is increased from 8 to 14 lp/mm at a modulation transfer function value of 0.2, the average diffraction efficiency across the whole field-of-view was increased from 75.58% to 95.37%, and the diffraction efficiency uniformity was improved by a factor of 5.7, showing the effectiveness of the proposed method.