Preservation of Optical Vortex OAM after Distortion by a Diaphragm

Abstract

In this study, we theoretically and numerically show that the normalized orbital angular momentum (OAM) and the topological charge (TC) of superposition of optical Gaussian vortices with symmetric OAM-spectrum are equal to TC of the middle constituent vortex. It is also shown that after passing a sector-shaped aperture, the symmetric superposition preserves the OAM, with the TC becoming fractional and proportional to the angle of the sector aperture. As it further propagates in free space after the sector aperture, the TC of the superposition becomes integer albeit indefinite due to the aperture edges generating a multitude of extra optical vortices with positive and negative unit TC, irregularly arranged across the beam.