Deformation of Optical Vortex Beam by Off-axis Incident-beam from Spiral Phase Plate Center

An optical vortex beam (OVB) is obtained when a Gaussian beam is transmitted through an appropriately designed spiral phase plate (SPP). The OVB can be deformed by displacements of the optical axis of the incident Gaussian beam from the center of the SPP. We calculated the deformation of OVB using theoretical simulations and discussed the results. When the incident-beam optical axis is shifted from the SPP center, the dark hole is shifted from the output-beam center. The far-field optical intensity distribution of a doughnut shape is changed to a crescent pattern and finally becomes to a Gaussian beam according to the dark hole shift. These results are important for fabrication of a SPP integrated laser.