An annular beam with segmented phase gradients generated by a modified spiral zone plate

A modified spiral zone plate (MSZP) is proposed to produce an annulus with a tailored radius and multiple segments of phase gradients at the focal plane. The MSZP can be fabricated simply and cost-effectively, and remove the inner redundant spiral zones. The tailorable radii of generated annuli are independent of topological charges and corresponding segmented phase gradients can be shown by the different kinds of petals with phase gradients. Moreover, the topological charges for the segmented phase gradients of annuli can be identified by the number of different kinds of fringes generated by the corresponding interference phases of MSZPs. The construction method and focusing property of the proposed zone plate are illustrated and studied in the simulations, respectively. It is also proved in the simulations and experiments that the annulus generated by the proposed zone plate has a tailored radius and multiple segments of phase gradients. The proposed zone plate can be applied to rotate the trapped particles at different speeds and have potential applications in optical communication. (paper)