The Design Of Several Electronic Modules In Quantum Key Distribution System

Information, as a resource and its universality, sharing, value-added, treatable and versatility, make its particular importance for human lives. Information security is a big problem which any country, governments, departments, industry must pay attention to. And it is a national security strategy that can not be ignored.The Quantum key distribution theory, based on quantum physics and modern Informatics, is the most powerful means to information security.Quantum key distribution theory is based on the Heisenberg uncertainty principle and quantum no-cloning theorem in the fundamental theorem of quantum mechanics. The fundamental theorem in quantum mechanics guarantees the quantum cryptography with unconditional security in physics level. It can defense any attack including the ways with quantum computer. Due to the importance and great prospects of quantum key distribution, every government pays much attention to the design and achievement of quantum key distribution. Since Bennett and Brassard proposed the first quantum key distribution protocol, the BB84 protocol, the quantum key distribution has been modified and improved by Numerous countries, laboratories and communications cooperation and has been becoming Practical. Chinese government has paid great attention to quantum key distribution either. Now the Quantum Physics and Quantum Information Laboratory in the University of Science and Technology of China has finished the practicality of quantum key distribution first and is attempt to build a quantum metro communication network.The design and achievement of the synchronization-delay plugin and the DC high voltage plugin as well as the high-speed single photon source in the quantum key distribution system based on decoy state coded designed by the Quantum Physics and Quantum Information Laboratory in the University of Science and Technology of China is introduced.The quantum key distribution system is generally divided into two parts, the transmitter (Alice) and the receiver (Bob). The transmitter transmits the information of quantum state to receiver by fiber and the receiver obtain the information of quantum state by a single photon detector. For keeping a low dark count rate detected by the single photon detector, the detector works at a gate-controlled model. It means that the detector opens the"time gate"to count when the single photon coming. The width of the gate set by the detector and the width should be as narrow as possible. The time that photon comes is associated with the synchronization signal. But after a distance of fiber transmission, the phase relationship between them may be changed. Therefore, the receiver needs a programmable delay circuit which could change delay in time to adjust the phase relationship and making the photon count rate detected by the single photon detector more accurate. The final solution of the design takes the way that the coarse delay and the fine delay could be controlled separately. The value of delay is controlled by a MCU and determining the value by scanning.The coding that the quantum key distribution takes is polarization coding. Controlling the polarization coding mainly depends on controlling the polarization modulator. Tens volt of DC high voltage is needed when the polarization modulator is working. Because of the environmental interference, the voltage cannot be fixed. So a controllable DC high voltage module is needed to control the polarization modulator and the module is a single plugin. The solution of design takes a MCU to control the DAC and the voltage which the DAC outputs is DC enlarged and transmits to the polarization modulator.With the high speed development of quantum key distribution technology, the development direction of quantum key distribution system is high speed, long distance and network. Therefore we carried out an experiment with high speed and long distance quantum key distribution. We designed a kind of single photon source with 520MHz repetition frequency. A kind of narrow pulse shaping technology base on SerDes is taken in the solution of design. The width of the pulse is about 300ps.The synchronization-delay plugin and the DC high voltage plugin works normally in the first prototype in the quantum metro communication network in Hefei. They achieved the requirement of industrialization and commoditization.