| 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-Placzek Ratio(LPR), the intensity ratio of the Rayleigh scattering to Brillouin scattering, and using heterodyne detection of Brillouin scattering, has been presented. The LPR is used to eliminate influnce of fiber attenuation, bending loss and splice loss. The system, composed of optical transmission subsystem, pulse modulation subsystem, Brillouin heterodyne receiver subsystem, frequency down-converter subsystem and data acquisition and signal processing subsystem, has been designed. The system performances such as measurement accuracy, dynamic range, and spatial resolution have been analyzed and calculated theoretically. Finally, the experimental study of performance electro-optical modulator and backscatter light is conducted. |
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