Numerical simulation and design of an apodized diffractive optical element composed of open-ring zones and pinholes.

In this paper, we investigate the relationship between open-ring zones of the Fresnel zone plate and the pinhole rings of photon sieves (PSs). Numerical simulations show that the normalized diffraction fields near the focal point of an individual pinhole ring and the circular open-ring zone are the same. It is confirmed that the maximum diffraction efficiency of an open-ring zone is higher than that of the traditional pinhole ring. Meanwhile, pinhole rings have more flexibility for apodization filtering. Based on these key findings, we propose the design theory of an apodized diffractive optical element comprised of open-ring zones and pinholes. To validate the theory, we developed a design example. Compared with traditional apodized PSs, the new apodized diffractive element has a 50.19% higher energy efficiency, and the minimum pinhole size is enlarged by 30.77%.