Research On Key Technologies Of Photon Orbital Angular Momentum Multiplexed Optical Wave

In recent years, with the development of social informationization and the deepening of the Internet, cloud computing and Internet technology, the world of network traffic and bandwidth for communication the capacity of the system demand also grow with each passing day. To this end, people in the field of optical communication explore a variety of multiplexing modulation techniques to cope with the current capacity crisis. A basic and most direct way is to make use of the different degrees of freedom or dimension of the beam. As people go deep into the study, most of the technology is close to the limitation of scalability, which puts forward higher requirements for the transmission network of optical communication. Space division multiplexing is a new milestone in the development of optical communication, and it will become an effective means to deal with the capacity crisis. Photon orbital angular momentum(OAM) multiplexing is a kind of space division multiplexing. In recent years,it has received extensive attention and become the current research focus.OAM modes can form an infinite dimensional Hilbert space, so that the information capacity of the communication system can be significantly improved. However, the free space OAM multiplexing communication system is vulnerable to the influence of atmospheric turbulence, which causes the OAM crosstalk seriously and affects the communication performance of the system. This paper takes free space optical communication based orbital angular momentum as the center, and researches a variety of vortex beam, the atmospheric turbulence model and system performance based on OAM. The main research work is as follows:(1) Free space communication system based on photon orbital angular momentum multiplexing was established. We discussed the vortex beams carrying orbital angular momentum of the generation and detection methods. Advantages and disadvantages of the vortex beam generation scheme were analyzed and compared;(2) The atmospheric turbulence intensity, transmission distance and other factors to influence the performance of free space optical communication system based on orbital angular momentum were researched, and we compared the different transport properties of vortex beams carrying orbital angular momentum through simulation. This provided a theoretical basis for the orbital angular momentum optical wavelength division multiplexing technology widely used in free space optical communication;(3) In view of the influence of atmospheric turbulence, two schemes are adopted to improve the performance of the system: 1.Using discontinuous OAM mode coding, we evaluated system channel capacity under the influence of the atmospheric turbulence. It is shown that the discontinuous OAM mode coding method can effectively reduce the crosstalk between the OAM multiplexing channels, so as to improve the channel capacity of the system. This method is simple and efficient, and the cost is relatively low. 2.By using the Zernike polynomial simulation of adaptive optics technology, OAM model of wavefront phase distortion caused by atmosphere turbulence was corrected. Simulation proved that this method can effectively suppress the effects of atmospheric turbulence,greatly enhance the capacity of the system, and make channel capacity more close to the ideal curve.