Experimental Research of the Identification of Topological Charges for Vortex Beams

An optical vortex beam has attracted more and more attention in several fields such as optical communication and quantum information. Generally, the vortex beam carries orbital angular momentum (OAM) and the topological charges (TCs). Measuring and identifying TCs of vortex beams is a key issue in many applications. In this study, the polarization status has been introduced into the interferometric procedure for identifying TCs of vortex beams. The influence of polarization states on the TC identification has been demonstrated experimentally. Furthermore, we demonstrate the satisfactory robustness for the interferometric method during identifying the TCs of vortex beams. When the reference and signal beam do not perfectly overlap in a Mach-Zehnder (M-Z) interferometer, i.e. there is a small tilt angle between two beams, a petal-like interference pattern can still be maintained with good visibility and be used for estimating the magnitude and sign of the TC. Our results might provide reference significance for the long-distance optical communication using vortex beams in the near future.