Electric field controlled switching of an optical vortex charge with a liquid crystal cell

Relations between the topological charge l of the optical vortex and the topological strengths of the nematic defect generating it are discussed. A voltage-driven effect switching the optical vortex charge from 1l1 = 1 to 1l1 = 2 for a nematic cell assembled from substrates providing circular and linear planar alignment of the nematic director is reported. The switching of the optical vortex charge is evidenced by the transformations of two into four extinction brushes in the optical polarization texture and of the single-spiral into the double-spiral pattern in the Mach-Zehnder interferograms.