The Study On High-performance Sensor Of Brilouin Optical Time Domain Analysis

Distributed Optical-fiber Sensor (DOFS) has the advantages of electromagnetic interference resistance, corrosion resistance and electrical insulation just like optical fiber sensor, also can get on a path along the fiber optical measurement field in time and space distribution of continuous information. The technology based on back scattering includes: based on Rayleigh scattering, based on Raman’s effect, based on Brillouin’s effect, etc. In these sensing mechanism Brillouin DOFS can realize the temperature and stain measurement. With the characteristic of the strong SBS signal, Brillouin optical time domain analyzer avoid the disadvantage of Raman and BOTDR sensor in a certain extent, and become a most popular research item and application.In the system of BOTDA, stimulated Brillouin scattering signal which produced by the interaction of pulse pump and CW probe light should be detected. According to the frequency difference between two optical waves, BOTDA systems can be made as two types. One is the gain-mechanism, whose frequency of the pump pulse light is higher than the CW probe, and the other is the loss-mechanism, the frequency of the pump pulse light is lower than the CW probe. In the gain-mechanism BOTDA, the sensing distance and the Signal-to-Noise ratio is limited for the loss of pulse pump by the Brillouin interaction. In this paper, the loss-mechanism BOTDA has been studied by comparing the gain-mode BOTDA. At first, we analysis the characteristic of gain/loss mechanism BOTDA in the theoretical way, point out the advantage of the loss-mechanism. Then based on MATLAB and Optsim, we demonstrate the former viewpoint in the experimental way. It is found that the loss-mechanism BOTDA has better sensing distance and detecting performance than the gain-mechanism, and the worst SNR of the loss-mechanism is above10dB larger than the gain gain-mechanism under the same distance. So, the loss-mechanism BOTDA is a better choice for the long-range distributed optical-fiber sensing. At last, we have compared several methods of polarization controlling, and propose a suitable way to the loss-mechanism BOTDA.