Simulation Of Partially Coherent Light Propagation In Atmospheric Turbulence By Controlling Beam Parameters

When the laser beam as the information carrier is propagated in the atmosphere,the effect of atmospheric turbulence will cause the decrease of signal-to-noise ratio(SNR)and the increase of bit error rate(BER),and seriously affects the performance of the communication system.A large number of studies have shown that partially coherent light is less affected by atmospheric turbulence than fully coherent light,therefore,it is extremely significance to explored the propagation characteristics of partially coherent light.Due to the high cost and inconvenient operation of the field test,indoor transmission simulation technology has gradually become a research hotspot.In this paper,liquid crystal on Silicon Modulator(LC-SLM)is applied to laser transmission system.The beam parameters of the initial light source are adjusted by the phase modulation principle of LC-SLM to simulate the propagation of partially coherent light with different coherence in atmospheric turbulence.Firstly,the coherence characteristics of light waves and the basic principle of modulating the coherence length of light beams by LC-SLM are studied.The partially coherent beams with coherence of 3 mm and 30 mm are generated experimentally,and their coherence is detected,It is proved that LC-SLM can high accurately generate partially coherent beams.Secondly,the dynamic atmospheric turbulence simulation technology based on LC-SLM is studied.the turbulence phase screen is generated by power spectrum inversion method,and superposition of four-stage low-frequency harmonics to construct the indoor dynamic atmospheric turbulence channel simulation platform.Compared with the theoretical values,the atmospheric coherence length is retrieved by measuring the variance of angle-of-arrival fluctuations of light beams affected by turbulence.Compared with the theoretical values,the atmospheric coherence length is retrieved by measuring the variance of angle-of-arrival fluctuations of light beams affected by turbulence.the root mean square error of the system is 0.0121 m,which proves that the LC-SLM has the ability to simulate turbulence with high precision.Finally,a composite control technique based on LC-SLM for partially coherent optical in atmospheric turbulence is proposed.The offset of the centroid of the spot and the intensity of the flicker factor and the degree of beam expansion of the partially coherent and fully coherent light after turbulence through the atmosphere are analyzed statistically.The experimental results can be concluded that the partial coherent light is less affected by turbulence than the fully coherent light,and the smaller the coherence length of the beam is,the smaller the influence is.Through the above analysis and experiments,the feasibility and effectiveness of partial coherent optical atmospheric turbulence transmission simulation technology based on LC-SLM are verified.In summary,the subject studied in this paper provides a simulation method for studying the propagation of partially coherent light in atmospheric turbulence;secondly,the experimental results of this subject can also be used in the experimental design of the communication system of partially coherent light,and which can provide a reference for optimizing the communication light source.