| Quantum communication based on the properties of non-measurability and nonclonability is theoretically considered to be absolutely secure and has broad application prospects in fields with high confidentiality requirements such as military operations.Because the polarization state of photons is easy to be manipulated and measured,it is often used in engineering to implement quantum communication.The quantum communication between satellite and ground compensates for the defect that optical fibers cannot be laid in mountainous and other scenarios.The development of the quantum communication is helpful for deploying a global secure communication network.At present,the quantum communication links between satellite and ground generally only have good stability on clear nights.But under adverse channel conditions such as daytime,rainy and snowy day,the link is prone to interruption,and the communication links between satellite-ground transceivers may not even be able to be established.To solve this problem and increase the duration of communication links under adverse weather or daytime scenarios as much as possible,it is necessary to conduct in-depth research on the channel characteristics of satellite-ground quantum communication and analyze the impact of the atmospheric channel environment on the polarization state of photons.The atmospheric channel factors that affect quantum communication between satellites and ground mainly include absorption,scattering,turbulence,and background light.Currently,research on this channel mainly focuses on turbulence factors,while analysis of background light factors is limited,and there is a lack of experimental data on the daily variation of the polarization state of light.In view of the above problems,this paper first analyzed the influence of the channel on the intensity of polarized light from the two aspects including absorption,scattering and turbulence of the satellite-ground atmospheric channel,and then studyed the background light intensity and polarization characteristics of the channel.Secondly,the influence of channel scattering on the degree of polarization was analyzed by vector Monte Carlo method.Thirdly,an experiment about all-day polarized light was performed.Finally,according to the experimental data,a daily variation trend prediction model of polarization degree was proposed.The main work of this paper is following :(1)The effects of atmospheric channels on polarization light signal attenuation are analyzed,at the same time,the background light intensity in different channels is estimated.The variation of channel attenuation coefficients under different visibility conditions is analyzed,and the differences in laser attenuation at different wavelengths under different visibility conditions are discussed.The radiation intensity of background light at different wavelengths is also studied.(2)Based on Mie theory,the influence of atmospheric scattering channel between satellite and ground on the transmission characteristics of polarized light is studied by vector Monte Carlo method.The influence of different refractive indices of scattering media on polarization degree is analyzed,and the differences in polarization degree under different particle sizes of scattering media are studied.The polarization retention of different polarized lights in scattering channels is discussed and compared.(3)A full-time polarization light outdoor transmission experiment was performed.The daily variation patterns of turbulence and background light in the two channels are analyzed.The daily variation patterns of the received power of polarization light and polarization degree are discussed.(4)A trend prediction model for polarization degree daily variation was proposed and validated.Initially,an initial model for predicting polarization degree daily variation trend was proposed.Then,the initial model was optimized based on experimental data,and the accuracy of the model was verified,demonstrating its effectiveness in trend prediction. |
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