Research On Disturbance Monitoring Technology Of Cross-relay Optical Cable Based On OFDR

Compared with other distributed optical fiber sensing technologies,Optical Frequency Domain Reflectometry(OFDR)has been widely used in vibration measurement due to its unique advantages in terms of large dynamic range and high signal-to-noise ratio.It is a relatively new type of optical fiber sensing technology.Whereas,the OFDR technology still has shortages when applied to long-distance fiber vibration measurement.Moreover,it also faces problems such as long test time,poor sensitivity when measuring vibration signals,and no way to accurately locate vibration signals.This article conducts research and analysis on OFDR system with these problems.The main contents of this paper are as follows:1.Introducing the basic principles of Rayleigh scattering and optical heterodyne detection technology firstly.Then,researching the theoretical model and signal model of the OFDR system,the expression of the beat signal light intensity is derived in detail.After that,introducing the generation and influence of the nonlinear tuning effect and polarization fading effect of the light source by studying some important parameters of the tunable light source.More importantly,finishing the analysis of effective solutions to suppress polarization fading in-depth,in which the polarization hierarchical receiving technology is mainly studied and did the necessary formula derivations.2.Analyzing and selecting the relevant components of the OFDR system,and completing the construction of the test system by reasonably designing the optical path of the system.After that,the corresponding vibration experiment test was set:PZT is used to simulate the external vibration source and the spectrum broadening phenomenon related to vibration is observed from the experimental results.The experimental results show that the devices used in the OFDR system can satisfy the experimental requirements of this paper,and prove that the system can detect external vibrations.3.This paper presents an improved algorithm for automatic detection of vibration signal based on OFDR.In this algorithm,we define a judgment threshold accordingly.When the cross-correlation coefficient is less than the threshold,the vibration can be detected and located.In order to show the experimental effect,the collected beat signal was processed and analyzed by the algorithm and the spectral difference method respectively.Then through the establishment of an experimental platform for experimental verification,the PZT vibration at 26.96 km was successfully located,which verified the effectiveness of the algorithm.4.In order to achieve a longer measurement distance,this article also improves the OFDR system.Based on the improved system,we use the remote pump fiber amplifier technology to design a non-relay fiber optic cable vibration detection system that can detect 200km in one direction and 400km in two directions.Starting with the experiment of OFDR fiber vibration within 112km on the experimental platform firstly.Then detect the OFDR fiber vibration from 112km to 223km.After the experiments,the PZT vibration at 110.9km and 220.9km was located,which verified the feasibility of the optical fiber vibration detection system with a detection distance of 400km.