Performance Analysis Of Free Space Quantum Communication System With Different Wavelengths

Free-space quantum communication system has become an important way to realize global quantum communication network due to its advantages,such as small transmission loss,strong flexibility,and the ability to transmit distances of thousands of kilometers at a time.The performance of the space quantum communication system is unavoidably affected by atmospheric effects and weather conditions,since the light quantum travels in free space.And the various signal light wavelengths lead to different affection at the same condition.Therefore,it is necessary to study the effects of atmospheric effects and different weather conditions to the quantum communication systems with different wavelengths.An entanglement-based continuous variable quantum key distribution transmission model is established,and the effects of atmospheric characteristics and weather conditions to the quantum signals with different wavelengths is investigated.The above study has reference value for the design of practical free space quantum communication systems.First,the security key rate of free-space quantum communication system with different wavelengths signals is studied.In the case of individual attack and collective attack,the security key rate are formulated when Bob uses homodyne detection and heterodyne detection respectively.The impact analysis is carried out according to the transmittance fluctuations,communication interruptions,and excess noise.Also,the relationship between the security key rate and the transmission distance of free-space quantum communication systems with different wavelengths is investigated.Secondly,in the case of rain,snow and haze,it is important to analyze the effects of security key rate to the free-space quantum communication systems with different signal wavelengths.Specificly,the model consists of snowfall intensity,rainfall intensity and haze particle concentration.The relationship between the security key rate and the transmission distance are simulated under various conditions,such as,different weather conditions and levels,quantum signal with different wavelengths,different attack types and different detection modes.Finally,since the communication interruptions is affected by the atmospheric turbulence,the problem of simulating atmospheric turbulence phase screen is investigated.Then an improved subharmonic method to generate atmospheric turbulence phase screen is introduced to design low frequency phase screen,which achieves adequately sampling in low frequency portion of power spectrum.Numerical simulation of atmospheric turbulence phase screen using this method,the phase structure function and relative error function are employed to evaluate the accuracy of the proposed method.The impact of the subharmonics and the sampling points on the accuracy of simulated phase screen is investigated.In addition,comparison between the improved subharmonic method and other four phase screen generation methods is also carried out.