Fiber-optic Quantum Key Distribution System Theoretical And Experimental Study

The research of quantum information has shown that if one encodesmessages onto quantum state, he will be able to achieve a perfectcryptographic communication whose security is unconditionally guaranteedby the well-known uncertainty principle of quantum mechanics. Thistechnique is called quantum cryptography or quantum key distribution.The main purpose of this work is to explore novel schemes for potentiallypractical quantum cryptography. And the experimental work here isconcentrated on building up a long-distance quantum cryptosystem withlong-term stability. Main contents of this paper are as follows:1. Designed an intensity modulator on the basis of phase-polarizationmodulator, which is employed as laser source of differential phase shiftquantum key distribution system to generate coherent pulse train.2. Presented an improved differential phase shift quantum key distributionscheme which features auto-compensation, high efficiency, and excellentpracticality. Alice modulates continuous laser using an intensity modulatorbased on polarization to generate coherent pulse train. Bob employs aFraday-Michelson interferometer instead of a traditional M-Z interferometer,which automatically compensates the polarization mode dispersion caused bythe changes of environment and improves the stability of the interferencevisibility. The present scheme not only has a simpler configuration, but alsooffers a higher key creation efficiency than traditional schemes. Furthermore,it enhances the security of the system. With the proposed experimental setup,a stable quantum key distribution was performed.3. Studied the phase drift mechanism of double M-Z interferometer system.By tracking phase drift and distributing key at suitable times, the quantum keydistribution based on double M-Z interferometer was performed through thelocal-area network. The scheme has made progress in the practical application.