The Research On The Subcarrier Multiplexing Quantum Key Distribution System Based On Single Photon Phase Modulation

Quantum key distribution (QKD) has received worldwide attention since it was proposed due to its unique security. By using the phase modulation in the quantum key distribution could encode the key in the phase which be modulated by the single photon modulation, and obtain the key which be carried by the single photon through demodulation at the receiving. And because of the single photon’s action was completely conforms to the theorem of quantum mechanics, it is absolutely safe by the single photon acts as a communication carrier in the quantum key distribution. The single photon modulation quantum key distribution used in high frequency modulation and has very good signal-to-noise ratio (SNR), and it has a high practical value in the optical fiber quantum communication. Based on the single photon modulation subcarrier multiplexing quantum key distribution (SCM-QKD) can effectively improve the system’s key rate. But in the practical application, due to the outside noise and the limitation of experimental conditions, the improvement of signal-to-noise ratio and the capacity analysis of the system need to be solved.In this paper, we study the single photon modulation spectrum characteristics in the experiment and realize the rapid lock-in of the system. We analyze the single photon phase modulation subcarrrier multiplexing quantum key distribution system in the theory. And we realize the response of the multiple channels in the experiment. According to the problems in the single photon modulation subcarrier multiplexing quantum key distribution existing in the system we did the following work:First, we present a robust method of single-photon modulation. Compared with the’conventional photon counting modulation technique, the single-photon modulation spectrum shows that the method could not only realize higH-frequency modulation but also obtain higher signal-to-noise ratio The signal-to-noise ratio is as high as 122 in the experiment and we realized the rapid lock-in.Second, we study the capability of the subcarrier multiplexing quantum key distribution system considering the quantum bit error rate and the useful key rate. The impacts of the typical experimental values and theoretical limit values on the system capability are discussed. We realize the response of the multiple channels and prove when the modulation index is 0.02, and multiple channels didn’t influence between each other.