Research On Generation And Detection Of Orbital Angular Momentum

Orbital Angular Momentum(OAM)is a fundamental physical quantity of classical and quantum mechanics.It is a natural property of spiral phase ray beams.Further research results show that there are OAM states in electron beams,radio frequencies,X-rays,light waves and sound waves.The large capacity of a single OAM state and the mutual orthogonality among different OAM states make OAM state more suitable for information reuse and become a new type of freedom of loadable information,which is one of the research hotpoints in quantum optics and modern communication.Although the generation method of OAM has been relatively mature,it cannot be mass-produced and used,and there is no convenient and practical detection method for OAM.At the same time,considering that when OAM beam is transmitted in atmospheric space,atmospheric turbulence in free space will have an impact on OAM state.In this paper,the generation and detection of OAM states are studied,and the main work and achievements are as follows:(1)Based on the basic theory of Daman gratings,a method to generate multiple coaxial orbital angular momentum states is proposed by designing circular array Daman gratings.In this method,gauss light from a laser comes from after collimator collimating light to produce multiple coaxial orbital angular momentum on the improvement of circular array shanmugaratnam grating,the shanmugaratnam grating phase structure in horizontal direction and vertical direction,and radial distribution into a cycle,use of grating,and the characteristics of the fork grating,Different modes of OAM beams can be obtained on the diffraction order array,and the energy distribution of OAM beams corresponding to each diffraction order is equal or controllable,so as to realize the simultaneous generation of multiple coaxial orbital angular momentum beams.The simulation results show that the scheme has good performance of coaxial mode generation,and the intensity distribution of each ring is equal,and the energy is concentrated.(2)According to the basic principle of Fourier transform,a method of detecting orbital angular momentum based on Fourier transform is proposed by modulating the incident OAM beam through phase shift and Hadama beam.In this method,for the incident OAM beam,different phase shifts and Hadamar structures are given to modulate the beam,and the intensity of the center point of the Fourier plane is measured.Through calculation,the detection of the OAM state without reference is obtained.Simulation results verify the effectiveness of the method under different topological load and different radial parameters.At the same time,the feasibility of the proposed OAM state detection method under the disturbance of atmospheric turbulence is further studied,in which the atmospheric turbulence is simulated by a random phase screen.