Square optical vortices generated by binary spiral zone plates

Binary phase square spiral zone plates (BPSSZPs), a special type of binary phase vortex lenses, are introduced to generate focused optical vortices showing square symmetry. The numerical solution and fabrication method, as well as the experimental results are given. Different from conventional vortex lenses, these BPSSZPs produce focused vortices with small topological charge following a modulo-4 transmutation rule. In addition, the central diffracted image rotates in the vicinity of the focal plane. These interesting properties suggest that BPSSZPs might become key components for many potential applications such as optical image processing and quantum computation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581044]