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Research Of Sensor And Demodulation Technology Based On Fiber Grating

Posted on:2010-03-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:J L ZhangFull Text:PDF
GTID:1118360308462202Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
The technology of fiber sense is an intersectant science of multiply subjects which obtains information from nature, processes and recognizes it using a sensor, and it constitutes there backbones associated with the communication and computer technology. This technology mainly refers to fiber optics, nonlinear optics, and corresponding technologies of laser, electron, computer, communication, and signal processing, and so on. With further investigation and application of sense technology, the technology of fiber grating sense is developing toward the direction of network, intelligence and practicality. Therefore, the technology of sense and demodulation also will necessarily develop toward the direction of measuring at high speed, high precision and distribution.This paper probes into the characteristics of fiber sense and its applications in the field of military affairs and civilization applications as well as research progress at home and abroad, and the investigation on Fiber Bragg Grating Sensor is carried out: analyzing the technology advantage and disadvantage of sense and demodulation of fiber grating, the further direction of investigation and technology difficulties unsolved; investigating the optical characteristics and sense mechanism of fiber grating based on coupling-mode theory; summarizing the classification and fabrication techniques of fiber grating; studying a number of schemes of sense and demodulation of fiber grating theoretically and experimentally; designing some structures of sense and demodulation and constructing network of wireless sense based on fiber grating successfully. The innovative works are primarily as follows:A kind of structure with gradient strength and double-triangle cantilever for investigating the compensation mechanism of temperature on tuning of fiber grating is designed aiming at cross-sensitive issues in actual use of sense technology of fiber grating. The linear and chirp-free tuning and temperature compensation of this structure on fiber grating are verified experimentally. The stress and temperature sensing parameters are measured in one grating at the same time using Fiber Bragg Grating with gradient strength, double-triangle cantilever structure through measuring the two peak locations of reflection spectrum of grating. The sensitivities of stress and temperature sense are KF=0.125nm/N and KT=0.0124nm/℃,respectively.Having designed and achieved the shift-sensor based on chirp fiber grating of bandwidth detection, the measurement of shift is implemented through determining the reflection spectrum of chirp grating, and the sensitivity of shift sensing can achieve up to K=0.05 nm/mm.Having designed and achieved the shift-sensor based on chirp fiber grating of light intensity detection, this system enhances precision of measurement and reduces cost through utilizing circuit method to determine light intensity, and the sensitivity of shift sensing can achieve up to K=0.58pm/mm.Having developed the FBG sensor of chemical concentration, the concentration of propylene glycol solution is measured experimentally, and the influence of temperature-sensitivity on chemical concentration and the method of eliminating sensitivity are analyzed. The detection of concentration is achieved by measuring changes in the refractive index of solution.Having designed and achieved the demodulation system of the phase-locked fiber grating sensor based on cross-phase modulation (XPM) technology, the uses of mechanical structures such as PZT, and so on are avoided because of XPM technology, the speed and repeat of system are greatly enhanced, and the precision of measurement on temperature can achieve up to 0.1℃.Furthermore, the influence of surrounding environment on the structure of M-Z is analyzed, and the improved scheme for overcoming the influence of temperature on parts of an apparatus of interference based on LiNbO3 waveguide devices is put forward.Having designed the system of wavelength-demodulation based on the loop mirror with polarization-keeping fiber, the distribution characteristics between the input wavelengths and output powers is analyzed with the numerical simulation being carried out, and the demodulation is established. Moreover, the scope of measurement and resolution of system are controlled through adjusting the length of polarization-keeping fiber, the coupling coefficient of coupling devices, and the main-axis angles of polarization-keeping fiber with the structure parameters being determined by software. The resolution and precision of demodulation system are less than 1pm and±1pm in a much wider scope of above 1nm, respectively.Having designed the schemes of sense and demodulation of establishing interferometer based on polarization-keeping fiber and polarization beam-splitter, the influences of structure parameters of system on the corresponding relationship of output light intensities and wavelengths are simulated numerically, and the experimental system is established. The scope of measurement and resolution of system are controlled through adjusting the length of polarization-keeping fiber, and the main-axis angles of polarization-keeping fiber. The resolution and precision of demodulation system are less than lpm and±1pm within 1nm, respectively.Having developed controllable software for sense and demodulation of fiber grating aiming at different schemes of sense and demodulation based on Lab VIEW platform, and apply successfully it to the determination of structure parameters, data processing and display of two dimension image of FBG sensor with different principles and structures. This software is crucial for sense system to depart from lab and enter into the field of application.Finally, all works investigated are summarized, and the further direction of study is indicated.
Keywords/Search Tags:fiber Bragg grating (FBG), chirped fiber grating, sense and demodulation, fiber loop mirror, polarization beam-splitter, LabVIEW
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