Phase Compensation Method Of Phase Encoding QKD

As the communication demand evolving continually day by day, quantum cryptography communication as an emerging discipline is taken seriously by researchers. Quantum communication is based on quantum physics and cryptography, which combines the Heisenberg’s uncertainty principle and the no-cloning theorem of unknown quantum state. Quantum cryptography communication provides new ideas and solutions for the secure transfer of information due to its large capacity, high safety, eavesdropping detection and so on. Quantum key distribution (QKD) as the first quantum communication technology from laboratory to real life, has great application value. Quantum key distribution will have wide practical use in many fields, such as military, electronic commerce and so on. The stability of quantum key distribution system is easily affected by environmental and other interference source. How to maintain the stability of the system, effectively monitor the eavesdroppers and ensure the smooth completion of the information transmission has been one of the important problems for the quantum key distribution system. In this paper, the stability factors and the corresponding solutions will be researched for the polarization encoded QKD system and the phase encoded QKD system. Main works are summarized as follows:1、According to the theory of quantum key distribution, two common modulation and encoded structure of the QKD systems will be introduced. The advantages and disadvantages of the two systems are compared. Birefringence, polarization mode dispersion, phase drift and other factors are researched to the polarization encoded QKD system and the phase encoded QKD system.2、the solutions of the QKD system stability issues are studied. To polarization encoded QKD system, a polarization feedback control system for the birefringence is proposed. To phase encoded QKD system, there are some kinds of methods to solve the phase drift problem. Such as the plug-and-play structure of faraday mirror compensation, the strict method of thermal and mechanical isolation, the single photon scanning compensation method,"five phase" scanning compensation method and so on. The advantages and disadvantages of various schemes are analyzed and compared.3、Phase drift is the main sources of error in phase encoded QKD. The traditional compensation methods have many shortcomings such as large amount of calculation, low accuracy and complex system. In this paper, a kind of active phase compensation method based on least square algorithm is proposed. Scanning a little amount of phase points under the condition of single photon, applying the least square algorithm then phase compensation parameters are derived. The experimental simulation shows that the method can gain phase drift parameter in a shorter time and complete the real-time active compensation. The performance and efficiency of QKD are improved.