Binary square spiral zone plates trimmed with quasi-random dots for single-order focusing

How to realize a square spiral zone plates with a single focus is still plagued by the trade-off between structural complexity and fabrication difficulty. Here, we propose a new single optical element, named Quasi-random dots Square Spiral Zone Plates (QDSSZPs), to suppress high-order foci. The key idea of this design is to reshape the structure of a square spiral zone plates using a quasi-random distribution of rectangular dots to make it sinusoidal in transmittance. Numerical simulations and experimental results show that the QDSSZPs has a good single-order focus characteristic and can effectively suppress undesired high-order foci, which is almost consistent with the theoretical prediction. The characteristic of suppressing high-order foci in the QDSSZPs has broad applications in imaging and microscopy.