Application Of Sensing Transverse Stress And Temperature With Polarization Maintaining Fiber Based On Distributed Polarization Crosstalk Analysis

Because of the high spatial resolution in long distance sensing conditions and the sensitivity to transverse stress,distributed polarization crosstalk analysis(DPXA)technique has great potential applications in distributed fiber sensing field.In this paper,the response characteristic of the DPXA system,the sensing characteristic of polarization maintaining fiber(PMF)as well as effects of fiber coating in a measuring process are studied.On this basis,a sensing tape of measuring liquid level,two schemes of measuring transverse stress and temperature simultaneously are proposed.Moreover,in these processes,a new technique of fixing the most sensitive angle of PMF is used to achieve a best sensing result.The major contents and innovations of this dissertation are as follow:1.The sensitivity of the DPXA system and its capability to sensing transverse stress are demonstrated experimentally.A PMF under test is fixed on a tape at the most sensitive angle using the layout process and the result suggests that the minimum response stress of the DPXA system is 4 N/m.For simulating distributed transverse stress sensing,eight test points are set along a PMF.The experimental data shows their performances have a high degree of uniformity.2.For the first time,the influences of fiber coating in the case of sensing transverse stress are experimentally studied using a DPXA system.Two types of Panda PMFs with polyacrylate coating and one Bow-tie PMF with polyimide coating are employed as experimental samples.The results suggest that the common fiber coating will increase the sensitivity of transverse stress sensing and induce additional recovery time of the transverse stress induced polarization crosstalk while polyimide fiber coating can reduce even eliminate these negative effects,however,this new fiber coating will enhance the noise level of polarization crosstalk.This work will be very useful for designing a DPXA-based distributed sensing system or evaluating the coating process.3.A DPXA-based liquid pressure sensing system and the relative calibration method are proposed.For experimentally demonstrating the quasi-distributed sensing capability of this system,five sensing units are set along the sensing tape after the layout process.Every unit exhibits a good sensing sensitivity when the depth of water varies from 100 cm to 190 cm.Furthermore,a nonlinear calibration method by fitting the experimental data with thetheoretical curve is shown and its reliability is verified by a set of experiments.4.The feasibility of simultaneously sensing transverse stress and temperature is verified theoretically,and in the process of making sensing tape,the fixed-axis layout process is applied to obtain a high sensing sensitivity.The capability of this sensing type to simultaneously sensing transverse stress and temperature is demonstrate experimentally.The results suggest that the sensing type can realize distributed temperature sensing with a 2 m spatial resolution and its measurement error of temperature no more than 6.84?.What is more,a series of analysis and discussion are proposed on the basis of the experimental data.