Electronic Control System For Quantum Key Distribution

Cryptography is the subject study of the secure communication. Quantum cryptography(QC) is the combination of classical cryptography and quantum mechanics. The characteristics of quantum mechanics, such as no-cloning theorem and Heisenberg's uncertainty principle, provide the perfect secrecy for quantum cryptographic communication. Being the first application of quantum physics, quantum key distribution(QKD) has been developed very fast experimentally in recent years. It would impact thoroughly the existing secure communication, especially in military affairs, e-banking and so on.In this paper, the principle of the QKD was discussed in detail together with an the introduction of classical cryptographic communication. Then we present description of our QKD experiment setup based on B92 protocal. The paper is focused on the control system of our QKD apparatus.The control system includes two modules, one named the input module which acquires data digitally, and the other, named the output module, controls the emission of the laser, the gating function of the single photon counting module(SPCM) and the synchronization of the input and output modules. Each of them uses a complex programmable logic device(CPLD) as the core component, and is devided into three parts: the hardware circuit, the programming logic circuit and the software. The hardware circuit boards are produced by a laser photoplotter according to the Gerber files gererated from the schematic(SCH) documents and the printed circuit board(PCB) documents. The CPLDs, programmed with the Verilog Hardware Description Language (Verilog HDL), were completed after four steps: design, simulation, synthesis and fit. The software is developed with C language using direct I/O to communicate with the device through the ISA bus computer interface. The output module can set the interval of the laser pulse to change from 50ns to 3.2ms in steps of 50ns, and the frequency from 500Hz to 100kHz in steps of 1Hz. It can control well the SPCM and the input module. Because of the embeded soft core, the function of the control system can change with varying demands of the application. That makes it possible to integrate the quantum communication algorithm into one chip.