Optimum Design And Experimental Research On EOM Of Rayleigh BOTDA Sensing System

In this dissertation, the development trend of distributed optical fiber sensing technology in recent years is firstly summarized, then the present research state of Rayleigh Brillouin optical time domain analysis(R-BOTDA) system is described in detail. Theoretically, the technical principle of BOTDA system is analyzed, the steady and transient coupled wave equations of stimulated Brillouin scattering(SBS) are analyzed and the relationship between the Brillouin frequency shift and temperature and strain are studied.The relationship between pump energy depletion and fiber length and probe power in BOTDA system that affected by nonlocal effect is studied and analyzed quantitatively. The simulation study of SMF fiber shows that nonlocal effect can bring the temperature error of 1.5 ? and the strain error of 30 ?? when the fiber length is 2000 m. A pulse pre-pump Rayleigh BOTDA sensing system is constructed to reduce the nonlocal effect. Rayleigh scattering light of the pre-pump pulse 1st order sideband is used as the probe light, so that the stimulated Brillouin scattering(SBS) interaction takes place between Rayleigh scattering light and 0-order baseband of pre-pump pulse and sensing pulse respectively. Finally, the temperature and strain information of the fiber is obtained by detecting the Rayleigh light signal.In this paper, the mathematical model of the SBS interaction between pre-pulse pump and sensing pulse is established, the optimal design of step pulse is made. Matlab software simulation shows that the SBS effect's natural Brillouin gain line-width is 34 MHz under transient condition when sensing pulses is 50 mw, 6ns and pre-pump pulse is 500 mW, 100 ns, which the requirement of Rayleigh scattering light in the PPP-RBOTDA system can be obtained and effectively reduces the broadening effect of FWHM and improves the spectrum resolution of the system.The optimum design of the step pulse synthesized by EOM of PPP-RBOTDA is carried out and the OptiSystem software simulation has been conducted to verify that the pre-pump modulated by EOM contains both 0-order baseband and first-order sidebands signal. The step pulse is synthesized in the experimental system. After the acquisition and processing of Rayleigh scattering signal, the Brillouin loss spectrum curve is fitted successfully by sweeping operation.