Research Of Atmosphere Turbulence Simulation In Free Space Optical Communication

Free space optical communication(FSO)is a kind of wireless communication method which employs laser light as carrier to transmit information in free space.Compared with the traditional wireless radio communication method,it has the advantages of wider bandwidth,small size in terminal volume,light weight,lower cost and high flexibility so it is gaining popularity in commercial,civilian applications and so on.It has been a long time in the researches of principle and technologies of FSO for domestic and foreign scholars,and gratifying achievements have been made.With the developments of the related research,atmosphere turbulence effects cause scholars' attention.It has been verified by amounts of experiments and theories that the transmission process in atmospheric medium of laser will be disturbed by turbid and turbulent atmosphere.Among them,the latter is the main interference source.The turbulence consists of a series of air vortexes with various radius and density size and mainly distributes in the junction of troposphere and stratosphere.They move desultorily with radius changing randomly and power distributing unequally,which makes the index of refractive changes irregularly.Laser transmitting through them will meet optical intensity,focus shifting,defocus,spherical aberration and astigmatism problems.So the studies of the characters of turbulence channel are the significant point in FSO research field.This paper will introduce the research achievements of turbulence simulations from the principle of FSO,turbulence channel properties and channel modeling.The main research works are as follows:First,we give the transmission process and various damage effects of FSO.Based on the wireless communication principles,we introduce the system structure and the main interference factors.Second,we will introduce the turbulence channel properties.Based on the Kolmogorov turbulence theory,we study the formation process,turbulent motion,the refractive index perturbation,refraction and scattering effects of turbulence to obtain the statistical properties of refractive index in turbulent channel.Finally,we do the turbulent channel modeling and simulation.The methods for simulations can be divided into two kinds---non-numerical and numerical methods.We introduce them and focus on the spatial light modulator numerical method to give the modeling process and simulation results.This method bases on some certain theories and several algorithms.We apply the common used theories and algorithms---the Kolmogorov and Von Karman theory models and the Fourier transformation,Zernike polynomials and Subharmonic algorithms.Then we give the phase screen,Gaussian optical distortion pictures,spectra,phase structure function and probability density function of the methods mentioned above to compare and analyze the accurateness of the methods and theories and the performance of complete frequency phase screens and two compensation methods.