The Distributed Optical Fiber Srtain Sensor System Based On OFDR Design And Key Techniques Of Data Demodulation

With the advent of 5G,a world in which all things are interconnected on the internet is forming,and sensors,as eyes that perceive outside information,are under unprecedented attention.Optical frequency domain reflectometry(OFDR)is one of the distributed optical fiber sensing technologies.Compared with other distributed sensing technologies,it has good performance in terms of spatial resolution,sensing accuracy,sensitivity,and signal-to-noise ratio,so it has great application value in the fields of modern military,intelligent transportation,large buildings and so on.Because OFDR can achieve ultra-high spatial resolution,it can accurately monitor small components.The current OFDR distributed system has poor sensing stability and is seriously affected by laser performance,which greatly limits its development,so we need to carry out further research.In order to solve the problems existing in the current OFDR distributed system,we study the principle of back-scattering Rayleigh scattering sensing,nonlinear sweep frequency effect of tunable light source,polarization fading effect,data demodulation algorithm,etc.We designed the OFDR distributed strain sensing system with high spatial resolution,and completed the experimental verification.The system achieved a mm-level spatial resolution.The main contents of this article are as follows:1.We designed an overall OFDR system based on the hardware-compensated nonlinear sweep frequency effect of the light source.The beat signal of the auxiliary interferometer is used as the trigger signal of the acquisition card,which eliminates the influence of the nonlinear sweep effect of the light source on the positioning accuracy and spatial resolution.The PBS diversity reception method is used to divide the signal into orthogonal P light and S light,which compensates for the deterioration of the sensitivity caused by the polarization fading effect.2.We designed a joint control scheme for the transmission and reception of lasers and acquisition cards.Combined with the laser synchronous signal and the external trigger of the acquisition card,we have completed the synchronous acquisition of the laser sweep and acquisition card.We have proposed a solution to eliminate reflection signal anomalies using soldering,which optimizes the reflected signal waveform and improves system stability.3.We developed a data demodulation process and completed the sensor validation.We designed a data demodulation algorithm based on cross-correlation to calculate the strain value on the entire sensing link.In addition,we completed sensing experiments on sensing length,sensing accuracy,and spatial resolution,and verified the linear relationship between strain magnitude and wavelength shift.