Demodulation Theory And Experiment Research On White Light Polarization Interferometry System

Besides the merits of white light polarization interferometer （e.g. large dynamic range,high sensitivity, absolute measuring ability, simple and flexible structures）, white lightpolarization interferometer makes it possible to test polarizing devices and sense moreinformation via polarized light interference. Based on the former achievements of ourseminar, the thesis further addresses the problems of the time-domain polarizationinterference system, and preliminary theory studies on the frequency-domain interferencesystem model as well as the demodulation experiments are carried out.The main achievements are as follows:1、 Based on the polarization coupling measurement instrument of PolarizationMaintaining Fiber （PMF）, research on the dynamic dispersion compensation isconducted theoretically and experimentally, making the space resolution increase from62.85cm to6.03cm at the position of1000m, and the birefringence dispersioncoefficient△D=0.0116×10^-9ps/（nm·km） is obtained simultaneously. The envelopebroadening phenomenon caused by the birefringence dispersion is settled, whichestablished a foundation for the long distance sensing;2、 Before compensating the birefringence dispersion, the widened envelopes of two closecoupling points will overlap with each other, resulting in multi-splitting peaks in theoverlap region. Theoretical analysis and verification tests are carried out to demonstratethis phenomenon, which solve the misjudgment on the position of two close couplingpoints as well as the distance between them, and then improve the space resolution of thesystem;3、 In order to reduce the noise level and enhance the detectability of weak coupling points,modulation with PZT is employed to make the sample mirror of the demodulationinterferometer vibrate back and forth when collecting the interference fringe, whichenables the background noise to be decreased by7dB;4、 Based on the distributed polarization coupling, a self-adaptive method for PolarizationExtinction Ratio （PER） measurement is put forward. In the method, the thresholdcoupling intensity and the non-uniform iteration step are dynamically determinedaccording to the polarization maintaining ability of the polarizing device, and thenincreasing numbers of contributive coupling points are selectively extracted out for PER calculation, making the measurement more flexible and accurate;5、 The spectral transform function of the white light polarization interferometer is deducedvia Jones Matrix, which is used to analyze the distributed polarization coupling of thesystem and guide the test model construction of Y-waveguide as well. Verification testson PER of Y-waveguide are also carried out and the measured value is36dB;6、 Based on the multi-scale characteristic and self-adaptive ability of the Empirical ModeDecomposition （EMD）, the Ensemble Empirical Mode Decomposition （EEMD）&EMDis applied to the data demodulation of the interference spectrum. Mode-mixing isinhibited and signal-noise ratio of the interference spectrum is increased by4.02dBsimultaneously.