Research Of Adaptive Optics Technique In Atmospheric Optical Communications

In recent years,the demand of atmospheric laser communication for communication bandwidth and speed is growing rapidly.Laser communication has the advantages of high bandwidth,high speed,flexible laying and low laying cost.However,the influence of atmospheric turbulence on the beam propagation characteristics will reduce the coupling efficiency of the fiber.In order to reduce turbulence interference,adaptive optics is usually used for real-time correction.In this dissertation,the relationship between the parameters of the adaptive optics system and the coupling efficiency under the influence of turbulence is analyzed and studied.The adaptive optics system for horizontal laser communication is designed,and the indoor static aberration correction experiment and the outdoor correction experiment are carried out.The related work is as follows:In this dissertation,the composition and model of atmospheric turbulence are introduced,the characteristics of characteristic parameters of atmospheric turbulence are summarized,and the Zernike polynomial expression of wavefront distortion under the influence of turbulence is analyzed,and the wavefront variance after correcting the number of Zernike modes of different orders is given.The relationship between atmospheric turbulence and the coupling efficiency of singlemode fiber is studied.Based on the analysis of the mode field of single-mode fiber,the quantitative relationship between the bandwidth of adaptive optics system,the number of correction modes and the coupling efficiency under different turbulence intensities is obtained,and the relevant parameters of turbulence are numerically simulated.According to the results of numerical simulation,the optical path and key components of the system are determined,and the adaptive optics system for horizontal laser communication is designed and built.After the system alignment,the indoor static aberration correction experiment is carried out,and the wavefront distortion with wavefront aberration of 0.35?(?=830nm)is corrected by adaptive optics.After correction,the RMS value is less than 0.05?,and the coupling efficiency of single-mode fiber is improved to more than 45%.Finally,a 1km horizontal atmospheric laser communication adaptive correction experiment is carried out,and the coupling efficiency and RMS before and after adaptive optics correction are compared and analyzed.Before the closed-loop correction of adaptive optics,the RMS value of wavefront distortion caused by turbulence is 0.25-0.39?,and the coupling efficiency of single-mode fiber is 4%-7%.After the closed-loop correction of the adaptive optics system,the RMS value is reduced to 0.1-0.16?,and the single-mode fiber coupling efficiency is improved to 10%-27%,which verifies the correction effect of the adaptive optics system on atmospheric turbulence.At the same time,the variation curves of atmospheric turbulence coherence length and atmospheric refractive index structure constant in 16 hours a day are measured and recorded,and the influence of adaptive optics system on laser communication performance under different turbulence intensity and weather conditions is analyzed,which has certain reference significance in practical application.