Transmission Properties Of Off-axis Vortex Beam

Optical vortex, which has a special spiral wave front structure, has a special advantage in the field of particle manipulation and communication. Research on the vortex beams are of great significance to application of vortex beams. In this dissertation, a research has been made on the propagation properties of off-axis vortex beams was investigated based on the Fresnel diffraction integral and Fourier transform.The analytical expression for the propagation of off-axis vortex beams with topological charge±1through a single slit diffraction is derived based on the Fresnel diffraction integral, which is used to study the propagation of central phase singularity of off-axis vortex beams by using Mathematica software to numerical simulation. The simulation results show that when the off-axis vortex beam passes through a single slit diffraction, its spatial distribution of phase singularities depends on propagation distance, the half-width of a single slit and off-axis parameter. Then, the anisotropic elliptical vortex beams were analyzed. The analytical expression for the propagation of off-axis elliptical vortex beams with different topological charges in free space is derived, which is used to study the intensity distribution and propagation of phase singularity of off-axis elliptical vortex beams in detail by using Mathematica software to numerical simulation. The results show that in the case of off-axis the intensity distributions of beams will change significantly while propagation. And the position of phase singularity is always changes. The spatial distribution of phase singularities depends on propagation distance, off-axis parameter and the ratio of minor axis to major axis of ellipse. There are some different changes for different topological charges.The results obtained in this paper would be useful for a deep understanding of the propagation of off-axis phase singularity in the diffracted field, and provide guidance for the beam aligning.