Research On Optical Fiber Grating Sensor Demodulation Technology

Optical fiber grating is the optic fiber component of rapid development in the recent years. With thecontinuous perfection of the read-in and demodulation techniques, the optical fiber grating has graduallybeen applied in life. The rapid and accurate demodulation of the grating signals is one of the key problemsof the sensor system design. The sensing information of optical fiber grating sensor measurement isreceived by the demodulation system in the form of wavelength encoded. The mobile sensor signals can bereceived according to by measuring the changes of the wavelength. Therefore, how to detect tiny changesof fiber optic Bragg grating wavelength, i.e., the signal demodulation on the wavelength coded is a keyproblem for the application and research of fiber Bragg grating sensors.In order to make wavelength interference demodulation with higher stability and higher precision, thisarticle firstly intrduces the basic sensing mechanism and demodulation principle of the fiber Bragg gratingsensors. Then, on the problems of how to improve the optical fiber grating sensor demodulation technologyand how to optimize the performance of demodulation system, this article has carried out in-depth research.The main research contents of this paper are as follows:Firstly, it expounds thoroughly the sensing mechanism and sensing properties of the optical fibersensors and fiber Bragg grating sensors.At the same time, the two types of sensor are analyzed andcompared to sum up their respective advantages and disadvantages.Secondly, in view of the existing various kinds of optical fiber grating sensor demodulationtechnologies, the thorough research is respectively given to the sensor principles of them. Thecharacteristics, advantages, disadvantages and their use scope are also analysised and discussed thoroughly. Thirdly, it designs the structure of the polarization-maintaining optical fiber loop mirror and putsforward fiber Bragg grating sensor demodulation scheme based on this structure. Then, the model isestablished on the basis of coupling mode theory, and numerical simulation analysis is made by Matlab7.0to verify the correctness of the theory.Forthly, on the basis of theoretical guidance, optical path module is built by Optisystem7.0which isthe optical system simulation software, to process system simulations and optical path analog. The opticalsignal transmission process in the system is understandly simulated to further verify the feasibility of thedemodulation scheme..Fifthly, demodulation system is set up and the measured experimental datas are analyzed respectivelyon the basis of numerical simulation by Matlab7.0and optical path system simulation by Optisystem7.0.The distribution characteristics of the input light wavelength and output optical power are discussed.Theinfluence of structure parameters on the system demodulation precision is also discussed. At last, itanalyses the optimal range of parameters for the length of polarization maintaining fiber, the couplingcoefficient of coupler and the phase difference of the two polarization states in FBG sensor demodulationmodel. The results show that the system has good stability, wide applicability and high detectionsensitivity.Sixly, after researcheing the application of the Polarization beam splitter (PBS) in the wavelengthdemodulation, it puts forward the second demodulation scheme which is optical fiber grating sensordemodulation scheme based on PBS. Using the principle of polarization-maintaining fiber polarizationinter-modal interference of PBS, the theoretic model is set up. The transmission process of light path isanalyzed by the matrix optics theory. The influence of temperature on the output light power at the twooutput arms of PBS is researched. Seventhly, on the basis of the optical fiber grating sensor demodulation scheme based on PBS, thelight path system is established.The circuit model which is applied to various fabric parameters and theparameter metrical software based on LabVIEW are also designed to process the experimental verification.The experimental results and the emulation results are both accordant with the theoretic analysis. In thedemodulation range greater than1nm, the average precision of the wavelength demodulation will be lowerthan1pm (equals to0.1℃).