Variable-step diffractive element and preparation method thereof

The invention provides a variable-step diffractive element and a preparation method thereof. The preparation method plans the number of steps according to the annular tape width of different zones, thereby solving a contradiction between the processing capability limit of the processing equipment and the diffraction efficiency of the diffractive element. For the central region of the diffractive element, a larger number of steps are designed in comparison with that in a peripheral region. Due to the increase in the number of steps, the diffraction efficiency of the region is increased, therebyimproving the diffraction efficiency of the entire diffractive element. Further, a laser direct writing machine is used to expose the step region in different stages of the diffraction elements in batches, and an ion beam etching apparatus is used to perform ion beam etching processing on a substrate, so as to realize the design and fabrication of diffraction elements with higher diffraction efficiency without loss of pr