Study On Quantum Fiber Channel And Relevant Technique

The ongoing booms of modern communications require the development of new methods and techniques to secure data transmission, but current cryptography implementations provide only conditional security. Quantum key distribution provides a way to distribute a secret key between two distant parties. The security of this new way of key distribution has been proved to be unconditional because its security is guaranteed by the laws of quantum mechanics. The main problem in quantum key distribution via fiber is the polarization variation of single photon during its propagation in quantum fiber channel.This dissertation investigates quantum key distribution in both the performance of fiber channel and the restoration of polarization.1.The model of BB84 is eslablished and the relationship between the length of fiber and the efficiency of channel transmission and dark current is analyzed. The numerical analysis shows the dark current has nothing to do with the performance of channel.The theoretical model of polarization encoded and phase encoded on fiber is established.2.The polarization encoded scheme of BB84 is analyzed with the model of phase variation when filber is affected by briefingence.The result shows the little curvature bend should be avoid when laying fiber, and stress birefringence has more affection on quantum bit than core ellipticity. A QBER model under polarization mode dispersion is built and numerical analysis is made. The QBER model under magneto-optic effect is built and numerical analysis shows the variantion of polarization will lead to system error.3.The QBER model of collapsed M-Z interferometer with changing temperature is built and analyzed. The result shows the fluctuations of error probability varying with the change of temperature. The impact of transversal pressure on collapsed M-Z interferometer scheme is analysed and the result shows transversal pressure will decrease the efficiency of QKD.The model of the effection of magnetic field on 'Plug&Play'scheme is built. The result shows whether'Plug&Play'scheme will work depends on magnetic field around the fiber. And the theoretical analysis shows slow-varying of environmental factors have no effect on Sangac model.4.A method of polarization auto-compensation is presented.The analysis shows this method can eliminate the effect of biefriengence, but the efficiency of transmission will decrease.