Studying On Detecting Topological Charge Number And Conversing System Of Vortex Beam

Vortex beam is one of the unusual beams, which is of circular intensity distribution, spiral structure of wave front and the feature of OAM (orbital angular momentum). These especially nature made it cause the high attention of academia, and have potential application in areas such as optical tweezers, quantum communication and information transmission. The study of the optical vortex has become a research focus in optical frontiers. In recent years, researchers aimed on producing method and measuring method of vortex beam. In this paper, our main work is list below.The development history, present situation and application of vortex light are introduced in this paper. The main components and software used here are mentioned.We elaborate the basic theory of vortex beam and the common ways of producing vortex beam in the laboratory. The principle of producing vortex beam is analyzed, and the corresponding simulation results are given. The methods we adopted in this paper, such as making the hologram, designing the experimental light path are introduced detailedly. The experimental results are consistent with the theory.The basic theory of interference and diffraction was illustrated. And the methods and devices of measuring the topological charge number, which were designed based on the theory above, were further illustrated in the paper.The methods which are commonly used to measure topological charge number of vortex beam, include the diffraction method of an annular aperture and the diffraction method of an annular triangle aperture. By analyzing, optical-path designing and simulating these methods, the results in agreement with the principle were obtained. By summarizing the previous researches’ work, another method that based on the diffraction method of an annular pentagram aperture was put forward. The theoretical of the method was derived, the light path was designed and simulated, the simulation results obtained prove that this method can be used to judge the topological charge number. In addition, the existing device which is to measure topological charge number by using the method of the Yong’s double slit interference was improved. We first consider the influence of isophase line distortion. By combining Mach-Zehnder interferometer and double slit interference,the impact of isophase line distortion was greatly reduced.the simulation results showed that the method can be used to quickly judge the topological charge number.A conversion system of vector beam based on the Magneto-optic modulation effect was put forward in this paper. It can realize the conversion between the radially polarized beam and angularly polarized beam. The basic theories of Magneto-optic modulation and vector beam were introduced, the experimental light path was designed, the simulation result was obtained.This paper systematically studied the producing, detecting and conversing of vortex beam, put forward two method to detecting the topological charge number of vortex beam, one is the diffraction method of an annular pentagram aperture, the other is the Yong’s double slit interference method of Mach-Zehnder interferometer. The characteristics of the diffraction field of the bended vortex beams through a double slit were discussed, it may help to predict the experimental results and analysis the phenomenon. In addition, a conversion system of vector beam that based on the Magneto-optic modulation effect, which can realize the conversion between the radially polarized beam and angularly polarized beam was put forward.