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高速深空通信是深空探测的关键技术之一,具备单光子灵敏度的激光通信系统将大大提高现有的深空通信速度.然而,单光子条件下的激光通信不仅需要考虑传输环境的影响,还需要考虑实际单光子探测器性能和光子数量子态的分布.本文在不考虑大气湍流影响的情况下,以光电探测模型为基础,引入超导纳米线单光子探测器(SNSPD)系统的探测效率和暗计数,建立了反应系统差错性能的数学模型,提出了系统误码率的计算公式.先对公式中的光强和激光脉冲重复频率对误码率的影响进行仿真,再通过实验结果验证仿真模型.结果表明,光强对误码率的影响最明显,随着光强从0.01光子/脉冲到1000光子/脉冲的增加,误码率从10~(-1)到10~(-7)量级明显下降;激光脉冲重复频率对误码率的影响受到不同光强的制约,但都随着脉冲重复频率的增加呈下降趋势.与此同时,当增加光强或者提高速度时,误码率高于仿真结果,约在10~(-4)量级,其原因可能是实际通信中调制光信号的消光比不足和光纤引入背景噪声提高了系统暗计数.以上模型和实验结果为进一步开展基于SNSPD的月球-地球、火星-地球等高速深空激光通信奠定了基础.
High speed deep space communication is one of the key technologies in deep space exploration, and the single photon sensitivity laser communication system will greatly improve the existing deep space communication speed.However, the laser communication in single photon condition not only needs to consider the influence of transmission environment, It is also necessary to consider the actual single-photon detector performance and the distribution of photon quantum states.In this paper, without considering the influence of atmospheric turbulence, based on the photodetection model, the detection of the superconducting nanowire single photon detector (SNSPD) system is introduced Efficiency and dark count, a mathematical model of the error performance of the reaction system is established, and the formula for calculating the bit error rate of the system is proposed. The influence of the light intensity and the repetition frequency of the laser pulse on the error rate is simulated first, The simulation results show that the light intensity has the most obvious impact on the bit error rate, with the light intensity increasing from 0.01 photon / pulse to 1000 photons / pulse, the bit error rate is from 10 -1 to 10 ~ 7) decreased obviously, the influence of laser pulse repetition frequency on the bit error rate was restricted by different light intensity, but all decreased with the increase of pulse repetition frequency. At the same time, The error rate is higher than the simulation result by about 10 ~ (-4), which may be due to the insufficient extinction ratio of the modulated optical signal in the actual communication and the introduction of the background noise in the optical fiber, which increases the system dark counting.The above model and The experimental results lay a foundation for further SNSPD-based deep-space laser communications in the Moon-Earth, Mars-Earth and other high-speed areas.