Research On OAM Multiplexed Optical Communication And Performance Improvement Based On Orthogonal Polarization

With the advent of the information age,higher standards for the definition of ultra-highspeed and large-capacity communication have been proposed.In particular,the development of the Internet of Things and the emergence of various intelligent scenarios will make the future an era of high-speed and high-density communication for the interconnection of all things.The current communication capacity and communication rate cannot meet future needs.However,most of the existing communication technologies have reached the bottleneck,and it is difficult to achieve significant capacity growth.The orbital angular momentum(OAM)multiplexed optical communication technology can increase the communication capacity several times or even dozens of times based on the existing communication capacity,so it has attracted the attention of many researchers since it was proposed.The beam carrying orbital angular momentum is a beam with a special spiral phase structure.The different phase structures constitute different modes of the OAM beam.The number of modes is theoretically unlimited.And these different modes of OAM beams are orthogonal to each other in space,so they can be completely separated after coaxial transmission in space,which is equivalent to multiplexing and demultiplexing of communication channels.When these different modes of OAM beams carry different information,OAM multiplexed optical communication is realized.The advantages of applying OAM in the field of optical communication are not only that OAM beams have rich channel resources,but also that OAM multiplexed optical communication technologies have backward compatibility and security.However,in actual communication,OAM multiplexed spatial optical communication has to consider the impact of the atmospheric environment.Atmospheric attenuation and turbulence effects will cause the intensity reduced and phase distortion of the OAM beam,resulting in channel crosstalk,reducing the demultiplexing quality and efficiency at the receiving end,and seriously affecting the communication performance of the OAM multiplexed optical communication system.Therefore,how to reduce the influence of the spatial channel on the OAM beam,so that the multi-modal OAM beam can stably and effectively transmit information through the spatial channel is the research focus of the OAM multiplexed optical communication technology.Aiming at the problems mentioned above,firstly,this article studies the OAM beam theory and the main source of noise in the space channel-the theory of atmospheric turbulence;then further explores the random distortion of the phase and intensity of the OAM beam caused by atmospheric turbulence,and these turbulence effects’ influence on the performance of OAM multiplexed optical communication system.Finally,considering that polarization is not sensitive to turbulence and the successful application of orthogonal polarization in multiplexed optical communication,an OAM multiplexed optical communication scheme based on orthogonal polarization is proposed to improve the communication performance of the system,and then the proposed scheme is simulated and experimentally studied.The work of this paper is mainly divided into two parts:(1)Numerical simulation research on the performance of OAM multiplexing optical communication system based on orthogonal polarization.A power spectrum inversion method was used to construct a turbulent equivalent phase screen based on the Hill power spectrum model.Then,changes in intensity,phase,and channel-crosstalk power of two OAM beams under orthogonal circular polarization,orthogonal linear polarization,and parallel linear polarization were studied after passing through the turbulent equivalent phase screen.Afterwards the performance of OAM multiplexed optical communication systems under three polarization combinations is analyzed.(2)OAM multiplexing optical communication experiment based on orthogonal polarization.A QPSK(Quadrature Phase Shift Keying,QPSK)-OAM multiplexed coherent optical communication experimental system with a transmission rate of 100 Gbit/s was established.OAM multiplexed beams with orthogonal circular polarization,orthogonal linear polarization,and parallel linear polarization are equipped with 50Gbit/s QPSK signal,coaxial transmission in space,which make the system transmission rate reach 100Gbit/s.The experimental results are discussed,and the demultiplexing quality,channel crosstalk,and system error performance of the two OAM channels under three polarization combinations are analyzed.The innovation of the OAM multiplexing optical communication scheme based on orthogonal polarization proposed in this article is reflected in the following: the scheme only uses the polarization properties of the beam itself.As long as the polarization of the OAM multiplexed beam is adjusted to orthogonal polarization at the transmitting end,there is no need to add additional processing at the receiving end,which can achieve the purpose of improving the performance of the OAM multiplexed optical communication system.The scheme is simple in principle,easy to implement,and low in cost.OAM multiplexing optical communication technology is of great significance for the development of large-capacity ultra-high-speed optical communication in the future,and has great potential in the development of future communication technology.The continuous improvement of the performance of the OAM multiplexed optical communication system is the key to promote the OAM multiplexed optical communication from the laboratory to practical applications.