| There are turbulent motions in the atmosphere near earth's ground,that affect the optical refractive index fluctuation of the air,and the fluctuation causes phenomena of light intensity scintillation,beam drift,beam broadening and angle-of-arrival fluctuation after the optical beam propagates through them,and those phenomena usually have a negative impact on the actual optical transmission engineering system performance.In order to assess the severity of this negative impact,it is necessary to study quantitatively statistics parameters of optical wave after transmitted through atmospheric turbulence.Methods to study parameters of optical wave include theoretical analysis,experimental measurement and computer simulation.When using the theoretical analysis,it is necessary to make certain assumptions so that the theoretical model established is only valid under certain conditions.Experimental measurement method is not flexible and not easy to obtain a comprehensive measurement results due to the restrictions of a variety of environmental and engineering conditions.Computer simulation is essentially the use of Monte Carlo method to generate random samples of optical field,and then the statistical analysis of the sample to obtain quantitatively statistical parameters of optical wave,the method can flexibly change transmission parameters,and can provides more comprehensive data support for the design of optical transmission engineering systems.According to domestic and foreign literatures,the random phase screen model of atmospheric turbulence,the method of numerical generation of random phase screen and the spatial sampling constraints of optical wave transmission for computer simulation are studied.Through the comprehensive analysis of the existing research results,the numerical experiment modeling;computer simulation of optical wave propagation in atmospheric turbulence,the confidence of the simulation experiment for optical wave propagation in atmospheric turbulence,the pulse time broadening algorithm for the horizontal transmission of optical pulses in the anisotropic atmospheric turbulence and the optical wave atmosphere,CUDA Simulation experiment algorithms for optical wave propagation in atmospheric turbulence have been completed.The main research contents and conclusions are summarized as follows:(1)Aiming at the Monte Carlo computer simulation of optical wave propagation in atmospheric turbulence,a method of determining the sample and hold area of optical grid based on the average optical intensity distribution is proposed.Then a parallel cluster simulation scheme is designed to significantly reduce the number of samples required to store the optical field samples Storage space,effectively reducing the length of the computer simulation time.Through simulation examples,the problem that the average optical intensity of collimated Gaussian beams propagating in atmospheric turbulence and the spatial mode composition of Laguerre-Gaussian beams propagating in atmospheric turbulence is studied.The results show that for the horizontal transmission case,compared with the high-order moment matching method,the zero-moment matching method can be used to determine the atmospheric coherent parameters of the random phase plate to obtain higher simulation accuracy.The atmospheric turbulence leads to the Laguerre-Gaussian beam generation module Scattering,the intensity of which depends on the absolute turbulence intensity and the beam emission plane parameters,radial and azimuth indices.(2)Based on the Monte Carlo computer simulation method of optical wave propagation in atmospheric turbulence,the two-frequency mutual coherence function of the collimated ultrashort optical pulse transmitted by the weak turbulent horizontal path with a length of 3 km was simulated and compared with 100 sets of numerical data Compared.The results show that under the conditions of weak turbulence and narrow band approximation,the computer simulation results of the two-frequency mutual function of the previous data are consistent with the theoretical analysis results.The larger the difference between the two frequencies is,the lower the degree of coherence can be maintained.Verify the correctness of the computer simulation.(3)A new expression for the two-frequency mutual coherence function propagating along a horizontal path based on the Huygens-Fresnel principle in strongly anisotropic atmospheric turbulence is proposed.According to the obtained expression,the approximation expression of mean square temporal pulse width of strongly anisotropic atmospheric turbulence can be derived by time matrix method,and the numerical analysis is carried out.Based on the theoretical results obtained,the time broadening of the optical pulse transmitted along the horizontal path in strongly anisotropic atmospheric turbulence can be easily determined.Therefore,the theoretical basis for computer simulation of the anisotropy of optical pulse propagation behavior is established.(4)In this study,to measure the speed of computer simulation of optical wave propagation in atmospheric turbulence,a method of block processing based on the number of grid samples of phase screen and a zero copy method of reducing CPU and GPU communication traffic are proposed,and a parallel algorithm based on CUDA is designed.The distribution of optical intensities,phases and optical spots of collimated Gaussian beams propagating in atmospheric turbulence is studied.The analysis results show that when the sampling number of Fourier transform mode based on Monte Carlo is less than 1024 × 1024,the speeds are almost the same measured by the CPU-based serial computation method and the CUDA-based parallel computation method;but when the number of samples is more than 1024 × 1024,as the increase of sampling points,the time-consuming of the two methods is clearly distinguished.For sparse spectrum model based on Monte Carlo simulation,the optimization of CUDA parallel computing method,compared with the calculation method based on CPU serial,the acceleration of the former is significantly higher than the latter. |
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