Research On The Back Brillouin Scattering Sensing Technology In Optical Fiber

The distributed optical fiber sensor based on Brillouin scattering is a novel smart skin technology. Because of many advantages such as large dynamic rang, long sensing distance, high spatial resolution and accuracy, and it has been the focus and leading edge topics in the optical fiber sensing field in recent years.Based on the results of previous studies and referring to the relevant literatures, the distribution of Brillouin scattering along the long distance optical fiber is analyzed and calculated in the steady state, and the pump pulse effect to Brillouin scattering in transient state is investigated. The signal detection principle, preferences and the system performance are discussed in optical fiber Brillouin sensing system based on microwave heterodyne technique. The intensity demodulation distributed optical fiber Brillion temperature sensing system is founded, and the design of the system light source, the Brillouin scattering signal separation, optical receiver and data conversion, the temperature demodulation method and experiment test are studied. The method which can improve the system dynamic rang by using the coded pump pulse and correlation algorithm is analyzed theoretically, and feasibility is demonstrated by the simulation. With the discussing and investigation above, and the following results have been obtained:(1) The steady state Brillouin scattering in a long single mode optical fiber is analyzed, and the analytical solutions with the attenuation coefficient have been obtained for the first time to our best knowledge. It can be used to describe the power distribution of the pump wave and the Stokes wave accurately, and it will provide a more accurate theoretical model for the analysis and calculation in long distance fiber.(2) In the distributed Brillouin sensing system based on direct detection, the FBG Sagnac loop is used as a filter for the first time, and it can separate the backscattered spontaneous Brillouin from Rayleigh effectively. However, it provides a novel method for the signal separation in the direct detection Brillouin sensing system, and it can simplify the system structure also.(3) The temperature demodulation methods by using the last known temperature curve or several known temperature curves are presented respectively. By using the demodulation methods, the high temperature resolution with±0.08K has been obtained in the experiment test.(4) The comparison is made among several methods which can improve the distributed Brillouin system dynamic rang. The method by using the coded pump pulse and correlation algorithm is presented, which has been proved to improving the system dynamic rang effectively by the simulation and experiment.