Brillouin Scattering Distributed Optical Fiber Sensor Theoretical Analysis And Related Technologies

Many large scale projects such as tunnels, viaducts, river bridges, riverbanks and irrigation works hinge et al., there use time are as long as several decades or even centuries. We had brought forward the idea of health inspect for them for a long time. These good-sized structures will happen distortions in different degree when they under diversified loads and external envitronments. However, these distortions are very faintness in early time, and they have the characteristics as①big range and long distance,②too ulterior to be measured,③Real-time,④distributed et. al. So traditional inspect means are hard to competent.To realize the distributed fiber sensing for temperature and strain, this paper introduces and discusses some distributed fiber sensing technique which are studied broadly at present, especially the headway and the developing direction of the Brillouin scattering distributed optic fiber sensor(BOTDR). Combining our studied emphases, we make deeply theoretic analysis for the theoretics of spontaneous brillouin scattering in fiber and the mechanism of its sensing for temperature and strain. Based on this, we bring forward a availability and viable distributed fiber sensing for temperature and strain system that based on spontaneous Brillouin scattering, Coherent Self-Heterodyne BOTDR, and done part experimental study.Be different with other BOTDR systems, the Coherent Self-Heterodyne BOTDR system uses only one consecutive laser. The light from consecutive laser is divided into two beams, the detecting light and the reference light, by a coupler. At the same time, it uses a frequency translator to obtain a frequency shift, which is equal to the brillouin frequency in fiber. Then the detecting pulsed light and the cw reference light can coherent. This method greatly improved the system's sensitive and signal to noise ratio (SNR). More, this paper discusses some important performance parameters of the Coherent Self-Heterodyne BOTDR system, such as dynamic ranges, spatial resolution, minimum detectable change. For the importance of the AO frequency translator loop, the mechanism of AO frequency shift and the loop are analysed detailedly, and done the experiment of this part. For the frequency shifter used has no fiber input and output...