Optimization and application of hybrid-level binary zone plates

The binary zone plate (BZP) is a diffractive optical element whose wide-ranging development is expected to have a strong effect on fields such as optical communications and information processing. With the increasing demand for more-compact systems and devices the BZP needs to be efficient as well as small. It is well known that fabrication errors strongly influence the characteristics of BZPs. To mitigate the influence of fabrication errors and obtain an efficient BZP with a high numerical aperture, we propose a design, called the hybrid-level BZP (HBZP), that combines zones with different numbers of phase levels. A method to correct the phase mismatch generated by such a combination is described. We furthermore discuss the optimum design of HBZPs in the presence of fabrication errors and report on its experimental evaluation.