The Research Of The Distributed Sensing Technique Based On Brillouin Scatting

The fiber sensor technology has been froming with the optical fiber communication,and the fiber sensor has many advantages which can't be found in ordinary sensors.Distributed optical fiber sensor is the use of light in the fiber transmission characteristics,the length direction of optical fiber sensor is continuously measured temperature and pressure,so it has been paid great attention in the current scientific research. Among all the distributed fiber sensing system, the disrtibuted fiber sensing system based on Brillouin scattering can realize simultaneous temperature and strain long length, big dynamic range, high accuracy sensing. Because distributedoptical fiber sensing technology which based on optical time domain reflectometer(OTDR)technology has been perfecting. Butbased on Brillouin optical time domain reflectometry(BOTDR) distributed optical fiber sensing technology is still in-depth study, so it has wide using area and development space.The research condition of Brillouin distributed optical fiber sensing technology, the dependances of Brillouin distributed shift and intensity on temperature and strain are investigated theoretically are introduced in this thesis. The principle of distributed fiber-optic sensing technique based on Brillouin scattering has been discussed roundly. The characteristics of Brillouin scattering induced by pulses in fiber and the sensing mechanism of temperature and strain have been analyzed thoroughly, and the temperature and strain dependences of Brillouin spectrum have been founded. On this basis, a simultaneous measurement system of temperature and strain based on Landau-Placezek Ratio(LPR), the intensity ratio of the Rayleigh scattering to Brillouin scattering, and using heterodyne detection of the Brillouin scattering has been presented. The LPR is used to eliminate influnce of fiber attention, bending loss and splice loss. Introduces two ways of echo signal of the system for testing and introduced their respective advantages and disadvantages respectively, Finally in this system, we select the coherent detection heterodyne detection for echo signal detection, this system have a good detection effect and improve the detection precision of the system for echo signal.In this thsis, we will make MATLAB sumulation to BOTDR analog signals with gaussian white noise, respectively introduce the theories of the digital average accumulative technology and the wavelet transform, Using MATLAB to the simulation of the noise reduction effect, finally we use the method combined digital average accumulative and the wavelet transform to make a detect signal noise reduction processing simulation, obtained a very good denoising effect and improve the test precision of the system. Sensing system performance has made the detailed analysis. According to the theory of the system calculated the signal-to-noise ratio, and the resolution of temperture and strain. At last, this paper do a detailed analysis and research about the spatial resolution of the sensor system, dynamic range and measuring the time.