Research On And Implementation Of The Key Technologies Of A Kind Of Communication System Based On Quantum Cryptography

Nowadays, quantum key distribution has been paid much attention in the field of communications due to its absolute security in theory. In this thesis, we work toward to build a experimental quantum key distribution system.Firstly, based on the analysis of some implementations of BB84 protocol, we developed a scheme of quantum key distribution by using polarization encoding and only one single photon detector. Secondly, the sender is designed and implemented. A narrow electric pulse whose effective width is approximate 700ps is produced by time-delay chip, high-speed logic chip and broadband amplifier. A laser-diode is driven by this narrow pulse and is attenuated to simulate single-photon source. Then the polarization state of a photon to 0°, 90°, 45°, and ? 45°is adjusted by polarization controller. In addition, a clock signal is propagated in the same long fiber but in different wavelength. Thirdly, the receiver is designed and implemented. In the receiver, the trigger signal for single photon detector is produced based on synchronization, and the transmission channel of light signal is divided into four ones with different delay. According to BB84 protocol, the basis choice, bit error rate checking, data correction and privacy amplification is implemented by a PC. So the final key is produced. In addition, we achieved the polarization feedback control at receiving end for the stable transmission of photon pulse. Finally, the test result of this experimental system shows that the sender and the receiver attain our design object and work well.