The Technology Of Compensating For Polarization In The QKD System On Polarization States Encoded By Phase Modulation

With the rapid development of Information technology, information and communication security become more and more important. Quantum cryptography is the combination of quantum mechanics and cryptography. It is a new kind of cryptography, which is based on the Heisenberg's uncertainty principle and the no-cloning theorem of unknown quantum state. It can be theoretically proved to be unconditionally secure. Thanks to its absolute security, quantum cryptography will have wide practical use in many fields, such as military, diplomacy, communication and Electronic Commerce. However, the polarization and phase states of photons in the fiber will change according to the environmental changes. Though such changes are not serious in a short instance, they cannot be ignored in the long distance transmission. So it adds the quantum bit error rate and as a result limits the communication distance.In this thesis, the compensating technology of the polarization fluctuation in the s Quantum key Distribution (QKD) system is discussed, and a new setup of quantum key distribution system based on phase modulation polarization coding technology is introduced. The polarization fluctuation compensating technology is theoretically analyzed. And the experimental results are given to prove the theoretical result and they show good coherence.The thesis is consisted of 5 chapters. The complete content as follows:Chapter1: This chapter introduces the existing problem in the classical cryptography, the origin and development of quantum cryptography, and current research status.Chapter2: This chapter introduces the compensating technology of the polarization fluctuation in the QKD system, and analyzes theirs existing problem.Chapter3: This chapter discusses the quantum cryptography system based on phase modulation polarization coding technology in details. It analyzes the four states quantum coding and encoding, communication process and polarization compensationin theory with optic matrix.Chapter4: The key component-phase polarization controller is designed. We prove the characteristic of phase modulate and produce all kinds of polarization states with phase polarization controller. It achieved some good experimental results.Chapter 5: Summarize this thesis, and give an expectation for the future development.