Research On Dynamic Polarization Coupling In Polarization Maintaining Fiber Based On White Light Interferometer

The distributed polarization coupling(DPC)system based on white light interferometer(WLI)are widely used in the measurement of stress,strain,twist,position,temperature and other physical parameters due to its large dynamic range,high spatial resolution and accuracy.In practical applications,the external stresses are usually time-varying.Therefore,it is more significant to study the dynamic stress sensing.Based on the previous research,we develop the distributed polarization coupling(DPC)system to measure the frequencies of dynamic stresses.We simulated the white light interferograms when polarization maintaining fiber(PMF)subjects to dynamic stresses,and conducted experiments to measure the frequency of dynamic stresses in two ways.The completed works is shown below:1.According to the polarization coupling mode,principles of photo elastic and elasticity,we deduced and analyzed the coupling strength when the PMF subjects to a transversal stress,simulated the white light interferograms when PMF subjects to dynamic stresses,and compared the interferograms of static and dynamic stresses.Two methods are proposed to measure the frequency of dynamic stress.2.We deployed the DPC system to measure the interferograms of dynamic stresses.By extracting the interference fringe of dynamic coupling point from the interferogram,extracting the envelop,fast Fourier transform,we can demodulate the frequency of dynamic stress.We achieved sinusoidal stresses of 10 Hz-180 Hz,sawtooth wave stress,square wave stress measurements and two sinusoidal stresses simultaneous measurement.The root-mean-square errors of sinusoidal stresses measurements are less than 0.46 Hz.We deduced the frequency measurement range,which is 5.95 Hz-381 Hz in our system,and came up with several methods to enlarge the frequency range.3.We deployed the discrete polarization coupling system to measure the sinusoidal signals,sawtooth signal,square signal,chirp signal and frequency-shift keying signal.The measurement errors of periodical signals are less than 1.11 Hz.This method achieved the monitoring of dynamic stresses in real time and the measurement of kHz sinusoidal signal.