Spiral phase elements obtained by use of discrete space-variant subwavelength gratings

The formation of spiral phase elements producing helical beams with different topological charges is presented. The elements consist of discrete space-variant subwavelength dielectric gratings. We demonstrate our approach by fabricating elements for circularly polarized laser radiation with a wavelength of 10.6 μm. The resulting helical phases, as well as the birefrigent parameters of the element, are measured by analyzing the polarization-dependency of the elements along with the self-interference characteristics of the emerging beams.