Brillouin Fiber Sensing Based On Lossless Separation Of Stokes And Anti-stokes Scattering

The Brillouin distributed optical fiber sensing technology not only has the advantages of small size,high accuracy,and strong immunity to electromagnetic interference,but also continuously senses the distribution and change of physical parameters at each point on the optical fiber transmission line.This paper analyzes the use of Brillouin scattering in the existing distributed Brillouin fiber-optic sensor system,and conducts related research on the issue of discarding anti-Stokes scattering and remaining Stokes scattering.The research work is as following:1)A new method for lossless separation of Stokes scattering and anti-Stokes scatteringt based on orthogonal optical coherent reception is proposed.This technique preserves the phase information of the optical field and hence Stokes and anti-Stokes Brillouin scatterings can be arranged in coherent addition or cancellation in different outputs,realizing separation of the two symmetrical scattering lights.2)Using the electro-optic modulator to generate double-sideband with suppressing the carrier or single-sideband signals to simulate Stokes scattering and anti-Stokes scattering.Building an experimental platform to verify the sideband separation effect.Experimental results show that the output signal power and the corresponding input signal power remain a good linear relationship with a the crosstalk less than-25 d B after separation.3)To maximize the use of separated Stokes scattering and anti-Stokes scattering,a signal acquisition system based on NI PXle162 high-speed data acquisition card and a data processing system based on Matlab software are designed.And the coding algorithm optimization and the repeated comparison of experimental results ensure the feasibility and correctness of the system.4)Building a Brillouin Optical Time Domain Reflectometry(BOTDR)system to collect Stokes scattering and anti-Stokes scattering respectively,and conducting the fiber-optic sensing research on Brillouin frequency shift and power.The experimental results show that the frequency shift of both Brillouin Stokes scattering and anti-Stokes scattering maintain the same positive linear relationship with the temperature.And the Brillouin scattering signal power increases with the increase of temperature,but Stokes scattering have more sensitivity to temperature than anti-Stokes scattering.The relationship between the ratio of Stokes scattering and anti-Stokes scattering power and the temperature also verifies the effect of sideband separation.