Research On Optical Communication Based On Orbital Angular Momentum

With the continuous development of the Internet and big data industries,the amount of data continues to increase,and people's demand for the amount of communication data is also increasing.The development of 5G technology has brought huge changes to the communication industry.As an important carrier in the communication process,compared with traditional mobile communication and microwave communication,optical communication has a larger bandwidth and can transmit a huge amount of data.Therefore,optical communication is the key to improving long-distance and large-capacity communication.The field of communication is mainly focused on the multiplexing of basic dimensions such as wavelength,frequency,and polarization.With the increase in data transmission demand,space division multiplexing,wavelength division multiplexing,frequency division multiplexing and other methods to increase communication capacity have been widely used.The discovery of orbital angular momentum has brought brand-new changes to the field of communication.The new multiplexing dimension has brought new challenges to optical communication.In recent years,it has become a hot research direction in the field of optical communication.The orthogonality of modals can bring infinite communication capacity.Compared with all communication methods,the cost of free-space optical communication is relatively low,so the research in this article is focused on freespace orbital angular momentum optical communication,using the unique physical properties of orbital angular momentum beams.The main contents of this article are as follows:1.The spatial light modulator is used to generate different vortex beams,mainly using the method of computational holography and the method of loading spiral phase maps,which can produce high-quality vortex beams and vortex light arrays,and compare the vortices generated by the two methods.The beam gives a theoretical analysis.2.The coding and decoding schemes of coaxial multiplexed vortex beams are proposed,and the coding method based on superposition and multiplexing of conjugate vortex light beams and the coding method of dual-channel multiplex vortex beam multiplexing are studied.Puts forward a practical and feasible coding scheme,and combines the coding to give a feasible decoding scheme.3.In order to further improve the capacity of the communication system,a new encoding and decoding scheme of the vortex optical array is proposed,which mainly uses the different modal information of the vortex beam and the spatial position information of the vortex beam for encoding.Three different types are proposed.The first type of dual-vortex optical array coding uses two vortex lights distributed symmetrically in space for encoding,and uses angle and vortex light modal information.The second method is to provide an encoding scheme under a four-vortex optical array,using two vortex beams of different modes for encoding,and provide experimental verification.The third type is the multi-layer vortex optical array coding,which gives a theoretically feasible coding scheme,and also gives the experimental results and analyzes the results.4.The method of vortex beam mode recognition is given.The first is to use plane wave and spherical wave interference detection method,and the second is to use circular grating diffraction method to produce different light intensity fringes.The difference in light intensity pattern generated by interference and diffraction solves the vortex optical mode information.Identify difficult problems.5.Combining the theoretical basis of image recognition,a convolutional neural network method is given to more conveniently identify the multiplexed light intensity map of the vortex beam to determine the information carried by the vortex beam.At the same time,the influence of atmospheric turbulence on the vortex beam is considered,and theoretical analysis and verification are carried out.6.Combining theory with experiments,the basic communication process of vortex beams is studied.On the basis of theoretical research,combined with experimental optical links,experiments are carried out,and feasible solutions are given in contrast to theoretical research,and the shortcomings of the experiment are put forward.What needs to be improved in the experiment.7.A method of using two convex mirrors to change the distance between the convex mirrors is proposed to solve the problem of far-field interference of the array vortex beam,and the feasibility is verified through experiments.