Design And Implementation Of Single Beam Coherent Optical Communication System

The distribution of the continuous variable quantum key using the coherent optical communication is a safe secret key transmission method.The protocol of distribute the secret key is not only compatible with existing optical communication technologies,but also has advantages such as low cost,high detection efficiency,and large capacity compared to discrete variable quantum key distribution technology..In present work,the distribution of the continuous variable quantum key is based on the principle of Mach-Zehnder interferometer transmission,which has lower stability and reliability on the experiment,because of this protocol separates the signal light and the vibration light in different beam to transmission in the free space,the two beams are affected by different environment noise,and it is extreme difficult to coupling,the two light beams into one light at the receiving terminal.However,the method of the single beam coherent optical communication based on Stokes parameters overcome the drawbacks that the above protocol we mentioned welled,because of the signal light and the local oscillator light belong to the two different polarized components of the same light beam,they,present the signal light and vibration light respectively.In this thesis,we construct a control system to achieve the protocol of distribute the continuous variable quantum key based on the single beam coherent optical communication with Stokes parameters,According to the requirements of the system,each module is designed and optimized.The detail works of this thesis are as follows:1.According to the acousto-optic effect,the control unit of the acousto-optic modulator was designed,and which can chop the continuous laser beam with time to,generate the pulse light that the duty and frequency are controllable.The pulse light can be used as the carrier of the light source to be modulated,and the pulse jump is used as a synchronization signal to trigger the decoder operation,distinguish the sequence of transmitted/received signals.Also the encoder and decoder based on the principle of the electro-optic effect of crystal are designed.By imbedded a program-controlled gain module with a three-stage gain adaptive homodyne detection circuit is designed to expand the measurement range and improve the resolution.The inertia weight of the particle swarm optimization algorithm is calculated by the nonlinear equation of the threshold power function.Under the premise of ensuring the calculation accuracy,the number of iterations is reduced and the calculation efficiency is improved.For the creep of the encoder device and the error introduced by the installation,the generalized regression neural network is used to compensate the output of encoder,and eliminate the error.2.According to the requirements of the single-beam coherent optical communication system,the logical relationship between each modules in the system were analyzed,and established a communication control system by a protocol of time-sharing control.We set up a control system with the dominant of ARM-PC as the main control unit,it control the generation of the puled light,the transmission of modulated signals,the decoding and acquisition of the signals.The control system is mainly divided into two different work modes,one is initialization mode that is use to calibrate and adjust the optical path of communication system to meet the requirements of communication.The other is the communication mode,in which the transmission side is controlled by the control system to encode the pulse light,and the generated modulation signal is transmitted through the free space.The receiving side decodes the modulated signal under the control of the control system.Meanwhile,the correction control scheme is enabled to correct the drift working point and return to the normal working state,so that the system can communicate normally.3.Finally,the actual communication experimental system of coherent optical communication is built according to the system architecture.The system first runs the initialization mode to initialize the system,and then implement the actual communication experiment.The problem of drift of the working point is solved by the designed correction control scheme.The experimental results show that the system has certain self-adjusting ability,good stability and high speed,and can be used for continuous variable quantum key distribution.