Research On The Characteristics Of Satellite-to-Ground Quantum Key Distribution

As a research hotspot of quantum communication,quantum key distribution(QKD)can make up for the shortcomings of short transmission distance and weak flexibility of quantum key distribution in optical fiber and free space,and is of great significance to the construction of global communication network.In the transmission process of light quantum signal,it will inevitably be affected by background light,atmospheric effect,zenith angle and other factors,resulting in the increase of quantum bit error rate and the decrease of security key rate.In practice,different signal light wavelengths are affected differently by background light,atmospheric effects and other factors.Therefore,this paper takes satellite-to-ground quantum key distribution based on low orbit downlink as the research background,The performance of satellite-to-ground quantum communication at different wavelengths is studied.The main research contents are as follows:Firstly,the satellite-to-ground QKD channel transmission model related to zenith angle is established.Considering the atmospheric refraction effect,the troposphere and stratosphere of the atmosphere are linearly stratified.The refractive index of each layer is calculated by using the temperature and pressure values of each layer,so as to obtain the actual transmission link distance of optical quantum signal under different zenith angles,this link distance is used to study the performance of satellite-to-ground quantum key distribution.Secondly,the theoretical model of quantum bit error rate caused by background light under BB84 protocol is established,and the influence of background light noise on the performance of satellite-to-ground QKD is systematically studied.Various conditions are considered in the research process,including three signal light wavelengths of 810 nm,1550nm and 3800 nm,and three common background light conditions of clear day,full moon and no moon.The relationship between bit error rate caused by background light and parameters such as zenith angle,beam divergence angle and tracking error angle is analyzed,and some methods to suppress background light noise are discussed.Finally,considering the influence of various factors such as atmospheric effect,dark count and background light count on the satellite-to-ground bit error rate and security key rate,based on the established layered channel transmission model,considering the different atmospheric turbulence intensity of each layer,the calculation formulas of satellite-to-ground QKD quantum bit error rate and security key rate based on decoy state BB84 protocol are improved.Then,the relationship between quantum bit error rate and security key rate with zenith angle of three wavelength signals under different background light conditions is simulated and analyzed.At the same time,the influence of detector dark count on quantum communication performance is also studied,the relationship between security key rate and the value range of the best average photon number is analyzed,and the suggestions of wavelength selection in the actual satellite-to-ground QKD system are given.