Depth of focus enhancement of a modified imaging quasi-fractal zone plate

We propose a new parameter w for optimization of foci distribution of conventional fractal zone plates (FZPs) with a greater depth of focus (DOF) in imaging. Numerical simulations of DOF distribution on axis directions indicate that the values of DOF can be extended by a factor of 1.5 or more by a modified quasi-FZP. In experiments, we employ a simple object–lens–image-plane arrangement to pick up images at various positions within the DOF of a conventional FZP and a quasi-FZP, respectively. Experimental results show that the parameter w improves foci distribution of FZPs in good agreement with theoretical predictions.

► The paper proposes a new parameter w named Quasi-FZP with a greater depth of focus (DOF) in imaging.
► Theory and numerical simulations show the values of DOF can be extended by a factor of 1.5 or more.
► The imaging experiments with parallel light and letters are provided to verify the theory.
► The experiments show great agreements with theoretical predictions.