Distributed Optical Fiber Acoustic-vibration Sensor

Optical fiber sensing technology is a measurement technology that uses optical fiber as the sensing medium and uses the optical signal propagating through the optical fiber as the sensing signal to detect environmental variables such as temperature changes,pressure changes,and vibration information around the sensing medium.With the advantages of anti-electromagnetic interference,high sensitivity,small size,stable performance,long service life,fiber optic sensing has a wide range of application prospects in transportation,industry,construction,aviation,aerospace,medical and other fields.Distributed optical fiber sensing technology,including distributed optical fiber acoustic vibration sensing,is a kind of optical fiber sensing technology with unique advantages in the field of long-distance sensing technology,and has important applications in oil and gas pipelines,rail transportation,defense and military fields value.In this article,Distributed Acoustic-vibration Sensor(DAS)was built which is based on the principle of phase-sensitive Rayleigh Scattering,and phase demodulation scheme of 3×3coupler was introduced into the traditional phase-sensitive distributed optical fiber vibration sensor.The simulation based on theoretical design was carried out,a complete DAS hardware system was built,a matching software system was developed,and corresponding experimental research was conducted.Finally,the experimental data was analyzed.The main work and research results of this paper are as follows:1.The research on the technical background and research status of DAS was carried out,and the relative merits of various technical solutions were comprehensively analyzed.The DAS system was designed based on the traditional phase-sensitive distributed optical fiber vibration sensor and then a phase demodulation scheme based on a 3×3 coupler was introduced into that theory.The amplitude and phase output principle of the 3×3 coupler wasshown in detail,and the calculation method and principle of the 3×3 coupler demodulation method are analyzed.2.A theoretical simulation model of DAS was established.The model of DAS is composed of narrow linewidth laser pulse,sensing fiber module,data acquisition module and3×3 coupler phase demodulation module.According to the corresponding optical function of each module,the numerical model of the mathematical formula is given,and the internal factors of the system such as the pulse width and wavelength of the light source,the length of the optical fiber,Rayleigh scattering and the vibration imposed by the outside are represented in a clear mathematical form.The simulation of the established DAS theoretical simulation model verifies that the designed DAS can have the ability to detect external acoustic vibrations.3.In the article,a complete DAS hardware system was built,and the corresponding software system was developed.The sensing distance,spatial resolution,demodulation of loading signals,and system stability of the DAS were studied.The experimental results show that the studied DAS can achieve a maximum sensing distance of 10 kilometers,a minimum spatial resolution of 1.6 meters,and a vibration sensing frequency range of 100 Hz to 1.5 KHz.The DAS has been tested for 5 hours and has a good stability.