Stability Analysis And Control Technology Research On Fiber-Based Quantum Key Distribution

With the Internet becoming an important part of human life, its reliability is becoming absolutely essential. Quantum key distribution (QKD) has attracted a lot of attention in resent years with the discovery that it can provide absolute security for communications. In quantum cryptograohy absolute security is ensured by two fundamental aspects of quantum mechanics, which are the no-cloning theorem and the uncertainty principle. Along with the research on QKD technology becoming deeper and deeper, QKD is desired for using on networks for quantum secrecy communication. So it is necessary to maintain the system's high stability for achieving the real-commercial communication system.In this paper, two parts are mainly focused on. One for the factors which influence the system's stability. The other for the control system for our QKD experiment. It is implemented on USB and FPGA and the details are discussed. A control circuit for driving phase modulator is also presented using high-speed and high-frequency analog switch.First introduced the concept of cryptography, modern cryptography security and the current international research trends on QKD. Then the principle of QKD was discussed in detail together with an introduction on the mainstream of QKD protocol and the latest QKD network research.In chapter 3, the factors which affect the system's stability are discribed, taking the Mach-Zehnder interferometer system,the improved interference structures—"Plug&Play" set-up and Sagnac circular-type interferometer, which can enhance the stability of the system, for an example, from the temperature, polarization and other aspects effects on the quantum bit error rate(QBER). These architectures are all with phase-encoded and the improved interference structures can achieve the max. transmission distance now.The fourth chapter focuses on QKD control technology implementatio-n. A control circuit for driving phase modulator is presented, as well as the system control technology with USB. Simulation results show that the driver output voltage pulse width can be less than 10ns, adjustable between 20ns-200ns, voltage adjustable between 0.0V-10.0V, ripple peak jitter is less than 1%, which can be well applied to QKD system. The feasibility and reliability of the scheme are verified through theoretical analysis and experiment results. Control system includes two modules, hardware and software. The hardware part includes USB interface, FPGA master chip, phase modulation, power supply voltage conversion circuit and digital pulse delay circuit. The field programmable gate array FPGA is used as the core chip and QuantusII is used for hardware design, VHDL programming and so on. Finally, the hardware circuit boards are produced by the printed circuit board(PCB)documents. The control system circuit works well under the control of software and can be well applied to QKD system.In chapter 5, QKD network model is introduced as well as the present three major quantum communication networks in the international.Chapter 6 is a full summary of our research work.