Single Photons Phase Interference Quantum Key Distribution And Information Transmission

The goal of secure communication is that the legal users could deliver the secret information safely,and at the same time the eavesdroppers could not get any useful information.The secure communication plays an important role in the area such as national defense ? finance and so on.The communication security of classical cryptosystem is guaranteed by the computational complexity.That is to say,the eavesdroppers couldn't solve the complex mathematical problems by taking advantage of the limited resources within a period of time.For example,the security of the classical RSA cryptosystem is guaranteed by the computational complexity of factorizing the large integers into its prime number.With the development of efficient algorithm and quantum computation,the security of the classical communication takes the huge risks.One-time pad cryptosystem is proved to be absolutely secure.It requires that the each secret key must be generated randomly,the each secret key could be used only one time,and the secret key have the same length with the plaintext,at this time the security of communication system depends on the secret key.For the quantum key distribution,the security of secret key is guaranteed by the fundamental principle of quantum mechanics,and secure communication could be achieved by the combination of one-time pad and quantum key distribution.So people have paid more and more attention to the quantum key distribution.Since the C.Bennett and G.Brassard proposed the first complete quantum key distribution protocol(BB84 protocol)in 1984,quantum key distribution has been developed at high speed.For the single photons sidebands interference quantum key distribution system,the single photon sidebands are produced by phase modulating the classical laser,the secure keys are transmitted by use of the single photons sidebands.The characteristics of this system are as follows:(1)Interferometer structure with the delayed path is not used,and this makes phase matching between the two communication parties easy.High stability of the system is achieved;(2)Sidebands interference results only depend on the phase of the radio frequency signal,for the frequency of the radio frequency signal is five orders magnitude lower than that of the optical signal,so it is easy to control and synchronize;(3)Multiple sidebands could be used to transmit the secret keys at the same time by use of subcarrier multiplexed technology.The system key generation rate is improved,which is applicable to the network communication.In this dissertation,relative research work is done about the single photons phase interference quantum key distribution and information transmission.By modulating the detection probability of single photons,and directly demodulating the discrete digital pulses by use of the phase sensitive detection in order to obtain the derivative signal,the 1550 nm laser is locked to the narrow linewidth transmission peak of ? phase-shifted fiber Bragg grating.The fiber Bragg grating frequency fluctuations induced by strong laser photothermal effect is eliminated with single photons incident light.The 1/f frequency noise at low frequency band of the laser is suppressed effectively by use of the feedback loop,and single photons transmission coherence is enhanced.The optical properties of the PSFBG-F-FBG resonant cavity are theoretically analyzed by means of transfer matrix method,it is found that the resonant cavity have a narrow linewidth impedence matching cavity mode.A PSFBG-F-FBG fiber resonant cavity is formed experimentally by use of the tunable ? phase-shifted fiber Bragg grating,and the experimental spectrum is consistent with the theoretical spectrum.The PSFBG-F-FBG fiber resonant can be used as the optical filter to remove the noise photons generated from the nonlinear optical process when the laser transmits through the optical fiber,and the single photons interference visibility is improved.Single photons counting value of polarization feedback reference light is used as the feedback standard,and the single photons polarization drift is compensated in real time by squeezing the optical fiber with the four channels polarization controller controlled by the optimized genetic algorithm.Single photons interference counting value from the phase feedback reference light time-multiplexed with the signal light is regarded as the feedback standard,and single photons phase drift is compensated continuously and reset-freely by adjusting the digital phase shifter based on the negative feedback process.Single photons interference visibility is optimized in real time over the 25 km single mode optical fiber,and influence on the quantum key distribution from the random disturbance of external environment is eliminated.Stable working sidebands interference quantum key distribution system is formed.By frequency modulating the single photons,the information is encoded to the different modulation frequency,and Fourier transform of the discrete digital signals and frequency spectrum analysis are used to extract the modulation frequency information.The impact on the information transmission resulting from the channel loss and noise are overcome,and the information transmission is achieved by use of the single photons frequency modulation coding.The innovations of this paper are as follows:1.The fiber Bragg grating frequency drift resulting from the laser irradiation photothermal effect is eliminated by using single photons incident light.By applying the single photons modulation technology,the 1550 nm laser is locked to the ? phase-shifted fiber Bragg grating.The frequency fluctuation of the frequency stabilized laser source is compressed to 3 MHz,and the laser frequency noise at low frequency band is suppressed effectively.The single photons transmission coherence is enhanced.A PSFBG-F-FBG passive fiber resonant cavity is constructed by means of the tunable ? phase-shifted fiber Bragg grating.So far the narrowest linewidth(3 MHz)impedence matching cavity mode from the passive fiber resonant cavity is obtained by use of the cavity enhanced effect and impedence self-matching effect.The resonant cavity can be used as the optical filter to remove the noise photons in order to improve the single photons interference visibility.2.A method to optimize the single photons interference visibility in real time is proposed.The single photons polarization drift is compensated in real time with the four channels polarization controller controlled by the optimized genetic algorithm,and the single photons phase drift is compensated continuously and reset-freely by adjusting the digital phase shifters based on the negative feedback process.The optimized single photons interference visibility reaches to 98.6% over the 25 km single mode optical fiber.3.An information transmission scheme based on single photons is proposed.Information transmission is achieved by use of the single photons frequency modulation,and the influence of loss and noise from the channel are overcome.The color image transmission is achieved by means of the multi-channels frequency modulation coding with the error rate lower than 10-5.The method about single photons used for information transmission provides a feasible scheme that the classical information could be directly transmitted over the quantum key distribution channel.