Application Of Optical Pulse Coding Technique In Phase Sensitive Optical Time Domain Reflectometry

Because of the advantages of anti-electromagnetic interference,corrosion resistance,and long-distance sensing,distributed optical fiber sensing systems(DOFS)have good prospects in defense,building safety monitoring,and geological exploration.Among them,the ?-OTDR system based on Rayleigh scattering is favored by researchers due to its high sensitivity and fast dynamic response.But due to the inherent characteristics of the system,there is an inherent contradiction between the sensing distance and the system resolution.So the traditional ?-OTDR system extends the sensing distance at the expense of the spatial resolution of the system.Researchers have proposed many solutions to this contradiction,in which optical pulse coding solves this contradiction very effectively in other distributed optical fiber sensing.However,(p-OTDR limits the application of this technology in its system due to the nonlinear nature of the system.This paper analyzes the characteristics of the ?-OTDR system and linearizes the ?-OTDR system through a series of compensation measures.For the first time in this field,coherent demodulation intensity coding ?-OTDR is implemented on this system,which greatly improves system performance and effectively solves the contradiction between sensing distance and spatial resolution.Using optical pulse coding technology to achieve sub-meter spatial resolution and nano-strain resolution at lOKm sensing distance.The specific work of this paper is introduced one by one.(1)The principle and application of fiber-optic sensing technology are introduced in general and the current research status of ?-OTDR at domestic and foreign are introduced.Several hotspot technologies to solve the contradiction between sensing distance and spatial resolution are introduced in detail,and the application prospect of optical pulse coding technology is analyzed.(2)The working mechanism of the coding ?-OTDR system is introduced in detail including:the mathematical model of ?-OTDR based on Rayleigh scattering is established by analyzing the Rayleigh scattering in the fiber;the phase demodulation technology based on I/Q is deduced;the system characteristics of ?-OTDR,and the method of linearizing ?-OTDR are proposed;introduces the application of Golay in a linear system and improves the performance of the system.(3)The coding ?-OTDR experiment based AOM modulator was built.The experiment is mainly a verification experiment.First of all,verify the correctness of the theory proposed in this paper,and then verify that the coding improves the system performance.(4)The coding ?-OTDR experiment based on I/Q modulator was built.The modulation based on I/Q can realize flexible heterodyne experiment and high spatial resolution sensing experiment.Experimental study includes four parts,the first part based on rotation vector summation to eliminate fading point of the experiment;second coding system is studied for complex frequency spectrum signal demodulation performance improvement;the third test the coding system can realize linear measurement of external disturbances.Finally,the application of coding in the long distance spatial resolution system is studied.The experimental results show that coding can effectively extend the sensing distance and improve the system performance...