光纤耦合对量子密钥分配系统光子探测的影响

借助量子密码术和卫星可以实现全球性的保密通信网络。但使用现有的单光子探测模块搭建星地量子密钥分配(QKD)系统,接收端就面临着空间光-多模光纤耦合的技术挑战。空间光-多模光纤耦合条件对星地量子密钥分配系统的跟瞄精度提出了严格要求。理论分析和定量计算表明,跟瞄精度ε与光束发散角θdiv的比值ε/dθiv≤0.5时,星地量子密钥分配系统的光子探测概率较高,系统可以正常工作;ε/dθiv≤0.1时,系统处于量子密钥产生速率为几kb/s的更理想状况。采用短波长更有利于满足空间光-多模光纤耦合条件,同时有利于系统获得更高的密钥产生速率。

Effect of Fiber Coupling on Photon-Detection Probability of Quantum Key Distribution Systems

Global secure communication networks could become ture by use of quantum cryptography and satellite. However, satellite-to-ground quantum key distribution (QKD) systems by using of commercial single photon counting module (SPCM) are facing a challenge of spatial-light-to-multimode-fiber coupling on the receiver end. Spatial light-to-multimode-fiber coupling qualification puts strict restricts on pointing and tracking precision of satellite-to-ground QKD systems. It is indicated by theoretical analysis and quantificational calculation that QKD systems work normally with a high photon detection probability when the ratio of tracking error ε to beam divergence θdiv is below 0.5, and that QKD systems could work better when ε/θdiv≤0.1 with a quantum key rate of a few kb/s. Light with shorter wavelength is more favorable to spatial-light-to-multimode-fiber coupling, and to achieve a higher quantum key production rate as well.