Polarization Properties Of Brillouin Scattering And Interferometry In Optical Fibers And Their Applications On Distributed Fiber Sensing

Fiber birefringence is one of the dominating factors that limit the performance ofoptical fiber systems, including fiber communication and sensing systems. Thepolarization issues induced by fiber birefringence lead to several unsolved problemsin those systems. In this dissertation, the polarization properties of Brillouinscattering and interferometry caused by fiber birefringence in single mode fibers areanalyzed, and their applications on distributed fiber sensing are further investigated,including the distributed fiber birefringence measurement and the influence of fiberbirefringence on the performance of distributed fiber sensors.The polarization properties of Brillouin spectrum in single mode fibers are firstlyinvesitigated, including the spatial evolution of Brillouin gain and the polarizationdependence of Brillouin linewidth and peak frequency. A theoretical model on thespatial evolution of Brillouin gain over fiber length is established by using wave platemodel; the polarization dependence of Brillouin linewidth and peak frequency isobserved for the first time in single mode fibers, and theoretical analysis shows thatboth fiber birefringence and sound velocity variation contribute to this effect.Based on the theoretical model of Brillouin gain evolution and the polarizationproperty of Brillouin peak frequency, two novel methods for the distributedbirefringence measurement are developed in single mode fibers, which are verified bynumerical simulation and experimental results. Those mothods can be applied onsingle mode fibers with elliptical birefringence.Based on the polarization properties of Brillouin spectrum, the influence of fiberbirefringence on the measurement resolution of distributed fiber temperature andstrain sensor is further investigated. The suppression effect of the commonly appliedpolarization scrambler on the polarization dependence of Brillouin spectrum isanalyzed, and both theoretical analysis and experimental results show that themeasurement uncertainty caused by fiber birefringence and sound velocity variationprovides another limit of the temperature and strain measurement resolution of thesensor; the measurement resolutions are further compared in detail when usingdifferent types of sensing fibers and using single-end and double-end accessconfigurations. The influence of polarization fading effect on the positioning error of distributedfiber interferometric vibration sensor is finally invetigated. The properties ofpolarization fading induced visibility and phase noises are analyzed by using theequivalent birefringent model of fiber interferometry; a positioning error estimationand prediction method is established, which indicates the contribution of polarizationfading induced noises on the positioning error of the sensor; a novel method forsuppressing the influence of polarization fading is further developed and verifiedbased on the established model.