| Quantum secure communication has been proved theoretically to be unconditionally safe, and quantum key distribution(QKD) has been studied intensively and applied widely in quantum communication field. In the past thirty years, QKD has been experimentally demonstrated and stepping into real-world implementation stage. Basing on QKD experimental system, this paper focuses on automatic polarization control schemes to ensure the efficiency and reliability of communication.Firstly, some quantum mechanical theories guaranteeing unconditional security of QKD are introduced in this paper, the present situation of quantum communication and QKD is reviewed. In addition, corresponding to our research, typical QKD protocols such as BB84 protocol and B92 protocol, some basic concepts about optical polarization are also described.In the following chapter, with Jones vector and Poincare representations, squeeze-fiber PC has been modeled and analyzed in this thesis. Basing on the workflow of traditional genetic algorithm(GA), its application to polarization control has been simulated, then we find some shortcomings. In this thesis, an improved GA basing on divided-and-conquer has been proposed, post-processing the optimal solution with simulated annealing algorithm. Some parameters related to the improved GA have been determined with the assistance of simulation analysis. The simulation results show that the improved GA has a better performance in smoothing sampling data and overcoming premature convergence.In chapter 4, the polarization encoded B92 QKD experimental platform is introduced. Focusing on automatic polarization control at the receiver, main functional modules have been studied in detail. Basing on the improved GA proposed in previous chapter, we redesign the automatic polarization control schemes in QKD system. Thus, the proposed GA has been applied to experimental system. Experimental results show that with the improved GA, better feasibility and higher reliability can be achieved. |
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