Research On Optical Fiber Positioning System Based On DPSK And Spread Spectrum Technology

With the rapid development of fiber communication technique,the fiber optic network has been widely used due to its excellent characteristics,including long transmission distance,fast speed,large capacity and strong anti-interference ability.However,optical fiber networks are mostly located in various buildings,or in underground,underwater and other complex environments.It is more difficult to monitor the optical fiber network,as well as to locate and maintain the location of events.Optical Time Domain Reflectometer(OTDR)is an important tool for analyzing fiber quality.But,the contradiction between the dynamic range of OTDR and the spatial resolution limits the further improvement of its performance.In order to improve the above problems,this paper proposes a novel optical fiber positioning system based on the Differential Phase Shift Keying(DPSK)modulation format and spread spectrum technology.DPSK modulation format is suitable for longdistance transmission and requires low signal-to-noise ratio of receiver,and the spread spectrum technology has the characteristics on reducing noise jamming.The structure is studied by theoretical analysis,simulation and experimental verification.The main contents of this paper are as follows:Firstly,the background and development status of OTDR are introduced,the advantages of DPSK modulation and demodulation and spread spectrum technology are expounded.The principle and implementation method of related technology are explained,which lays the theoretical foundation for the subsequent content.Secondly,the shortcomings of traditional demodulation scheme of DPSK system are analyzed,and then a novel Mach-Zehnder(M-Z)interferometer structure is designed.The interference principle and demodulation principle of the novel M-Z structure are described in detail.Through the contrast experiment by using photoelectric simulation software,it is proved that the novel DPSK system has good temperature stability,high tolerance for interference arm length mismatching and low requirement for linewidth parameters of light source.Thirdly,an optical multiplier is designed to solve the “electronic bottleneck” problem.The working principle of the optical multiplier is analyzed,and it is applied to spread spectrum system and spread spectrum ranging system.Through simulation experiment,the feasibility of the spread spectrum ranging system based on optical multiplier is verified,and the ranging distance and accuracy are consistent with the theory.Finally,the experimental prototypes of novel DPSK modulation and demodulation system and optical fiber positioning system based on novel M-Z interferometer structure and optical multiplier are built respectively.The location of the testing points of 460 m optical fiber and the end face of 12.3038 km long-distance fiber are tested.The feasibility of the optical fiber positioning system is proved by experiments.With further improvement and perfection,it can be applied to optical fiber fence,boundary detection,geological variation monitoring and other fields,and has broad development prospects.