| Free Space Optical(FSO)communication is a kind of wireless communications with light as the carrier and atmosphere as the transmission channel.Due to its advantages of large bandwidth,strong confidentiality and no need for frequency permission,it has become a research hotspot in the field of optical communications.It is widely used in satellite communications,ground communications and national defense.However,due to the existence of atmospheric turbulence,the refraction index of the channel is unstable,which will damage the quality of transmitted optical signals,increase the bit error rate and decrease the signal-to-noise ratio.The adaptive optical technology for atmospheric turbulence compensation is studied in this paper.The main works are as follows:1.In view of the technical challenges in the FSO communication system,the channel compensation technology and turbulence mitigation technology for FSO communication are investigated,including diversity reception technology,aperture averaging technology,adaptive optics technology and so on.At the same time,the research status at home and abroad is investigated.2.The basic theory of turbulent channel modeling are studied.The propagation properties of light in turbulence are studied by means of geometrical optics,wave optics and Fourier optics.The turbulence model based on Kolmogorov theory is studied.The light intensity distribution under atmospheric turbulence was modeled based on log-normal model and gamma-gamma model.3.Dynamic turbulence is simulated by using a spatial light modulator.This part includes two aspects:Firstly,common methods of dynamic turbulence simulation is investigated.The method based on Taylor turbulence freezing theory is investigated.Secondly,dynamic turbulence simulation is studied experimentally.A dynamic turbulence simulation system based on spatial light modulator was established to simulate dynamic turbulence under laboratory conditions.Simulation experiments of dynamic turbulence under different wind speed and turbulence intensity were carried out,the experimental results were analyzed and discussed.4.Experimental study on space-to-fiber coupling of FSO system based on adaptive optics.The working principle of adaptive optics technology and SPGD algorithm is studied,and the adaptive optics experimental platform was built.The indoor simulation experiments have been conducted,including the coupling of space to single-mode fiber and space to few-mode fiber.The experimental results were analyzed,the SPGD algorithm was used to improve the coupling efficiency,and the SPGD algorithm was optimized. |
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