Research Of High Sensitivity Optical Fiber Vibration Sensor Based On φ-OTDR

As the distributed optical fiber sensing technology can achieve a wide range field of information measurement, it has been widely used nowadays, such as distributed stress sensor, which can be used for dams, bridges and other large public facilities of safety inspection; And distributed temperature sensor, which can be used in the temperature measurement of transformer and generator set; And distributed vibration sensor,which can be used for long distance oil pipeline leak detection and anti intrusion alarm system of important territory. This thesis is mainly devoted to high sensitivity optical fiber vibration sensor based on φ-OTDR.The main work in this thesis is the analysis and discussion on high-accuracy, high sensitivity and multi-point detection of optical fiber vibration sensor system based on φ-OTDR. Firstly, reviews of the theoretical model and research status of distributed optical fiber vibration sensor based on backward Rayleigh scattering, Raman scattering, Brillouin scattering and interference principle have been made. And we described the scientific significance and development status of φ-OTDR distributed fiber optical sensing system. Then From the backward Rayleigh scattering phenomenon, we elaborated the working principle of OTDR systems, and established the mathematical model of signal transmission of φ-OTDR system. Of course,researches on the main performance parameters of φ-OTDR system have also been made.The analysis based on φ-OTDR system of different vibration signal demodulation and extraction schemes have also been made, and a further comparison between their advantages and disadvantages is also carried out. Then a new extraction scheme of vibration position and frequency information at the same time based on two-dimensional signal matrix of the Fourier transform method is raised. On this basis, we established the experiment system of φ-OTDR.Through simulation and experimental verification, we successfully extracted the multi-point vibration signal location and frequency information at the same time by using the method of Fourier transform of two-dimensional signal matrix, and signal processing efficiency is also improved. By using the noise elimination method, we achieved the high sensitivity detection of vibration signals in φ-OTDR system.At the end of the thesis, we preliminary studied how to further enhance the sensitivity of φ-OTDR system through introducing the ultra weak fiber Bragg grating(FBG) array into the sensing fiber, and made a simply simulation to demonstrate it.