Enhancement Of Spatial Resolution In Distributed Brillouin Optical Time Domain Analysis Using Deconvolution Method

Due to the ability of measuring stress or temperature changes in sensing optical fiber according to Brillouin center frequency shift, distributed Brillouin Optical Time Domain Analysis(BOTDA) system is widely used in health monitoring of roads and bridges. Conventional BOTDA system uses a rectangular pulse as the pump pulse, a continues wave as the probe wave. The detecting process is to sweep the frequency of the probe wave and record stimulated Brillouin scattering signal generated in the sensing fiber. The center frequency shift of Brillouin gain spectrum in scattering signal can be used to determine the change of temperature or stress in different location of the fiber. The longer the sensing distance is, the wider the pump pulse is required, and the lower the spatial resolution is. There will be a broad application space for a high spatial resolution BOTDA system in long-distance transmission.This thesis provides a method of improving the spatial resolution of BOTDA system by deconvolution algorithm. Without increasing the complexity of the experimental device and simply launching single pump pulse, the deconvolution algorithm is used to eliminate the broadening of the scattered signal by signal processing technique. This paper contents are as follows:Firstly, the Stokes waves signals are obtained in different stress in the fiber by using of the simulation of stimulated Brillouin scattering three-wave coupling equations. The Stokes lights deconvoluted with the pump light, and the feasibility and limits of improving spatial resolution through deconvolution method are analyzed.Secondly, a BOTDA experimental platform is built for the study of the resolution limit of overlapping peaks. Two sections of the sensing fiber are under stress with a section in their between without stress. The scattering signals of different pump pulse width are recorded. the experimental data through the deconvolution algorithm are processed and are compared with theory.the experiment results show that there are two useful methods of deconvolution in BOTDA system, one is RL deconvolution algorithm under the condition of accurate observation of the pump pulse, the other is time domain sharpening method under the condition of inaccurate observation to eliminate the p ulse broadening of signal caused by the pump pulse. Both methods can improve spatial resolution more than 1.75 times.