Investigation on nonlinear polarization coupling in quantum key distribution

Because of the effect of nonlinear polarization of transmission fiber, coupling ratio between local oscillator and quantum signal in a quantum key distribution system is decreased, signal jitters which leads to polarization multiplexing is increased, and security and stability of the system are decreased. To enhance technical performance of polarization encodement of quantum optics, after theoretical analysis and numerical simulation, operational experiment scheme was proposed to solve the polarization jitters caused by nonlinear polarization coupling of fiber. The results show that signal stability of polarization multiplexing enhances and transmission capacity of quantum key distribution increases to 61% by using feedback of spectral test results to control fiber nonlinear polarization coupling ratio between local oscillator and quantum signal. The research is helpful for practical application of polarization coding technology in quantum key distribution.