Displacement Monitoring Based On Low-coherence Michelson Interferometer

Landslide is the most serious geological disaster.Because of its unique topography,China is the country with the most landslide disasters in the world.Landslide disasters can cause serious consequences,such as road and bridge damaged,traffic disruption,electric power,water conservancy equipment failure and huge economic losses.Some large landslides can cause heavy casualties.Therefore,the monitoring of landslides is particularly important.After decades of development,the methods of monitoing of landslides are developing from the traditional methods such as geodetic method,inclinometer and GPS image method to the field of optical fiber sensing.At present,there are many slope monitoring technologies based on optical fiber sensor,such as BOTDR,OTDR,fiber grating and so on.In this paper,a Michelson interferometer based on broadband scanning laser source is used to monitor the displacement of landslide:A low coherence Michelson interferometer based on sm125-500 type fiber Bragg grating sensor demodulator is setted up.The interference signal is output by three spline interpolation to realize the frequency domain interval sampling,denoised by Hanning filter,and normalizated by Hilbert transform,which eliminated the influence of light source spectrum.The demodulation technique of spectrum domain is deeply analyzed.After searching and comparing the single peak tracking method,Shuangfeng tracking method and fast Fourier transform method,the fast Fourier transform method is chosen as the demodulation method of the system.The use of optical fiber drawing device to simulate the optical fiber sensing arm stretching from actual slope sliding,and the displacement monitoring experiment,the experimental results show that the low coherence measurement of Michelson interferometer system maximum value is 42 mm,the highest resolution can reach 45 ?m.After analysising of the polarization experiment system and method of eliminating polarization fading,selected Faraday rotation mirror method to eliminating polarization fading of the system.Experimental results show that the maximum measurement of low coherence interferometer Michelson low polarization fading 45 mm as the value of the system,the high resolution can reach 27 ?m.