A new approach for the fabrication of diffractive optical elements with rotationally symmetric phase distribution

Diffractive optical elements (DOEs), especially those used in imaging systems, often have phase distributions of rotational symmetry. A metal mask is designed such that it has different open slit angles on different radii, and the angle on a specific radius is inversely proportional to the phase magnitude there. The substrate is placed immediately under this mask and rotated relative to it during ion etching. The amount of etching on different radii of the substrate is thus modulated by the mask, and the DOE is produced in a single step. Experiments show that this is a practical and low-cost manufacture method when the phase variation along the radius is not too rapid.