Research On Dynamic Fiber Bragg Grating Sensing System Based On Virtual Instrument Technology

The sensing system based on fiber gratings has a wide range of applications in civil and military fields, including architecture and manufacture industry as well as research work. As the needs of many industries keep varying, the potential usage of this kind of sensing system is still promising and need to be developed. In our work, based on a tunable fiber Fabry-Perot filter, a fiber Bragg grating (FBG) sensing system is established using Virtual Instrument Technology. Theoretically, we deduce the FBG reflective spectra model using Transfer Matrix theory. An applicable encapsulation method is described. Experiments are used to validate the feasibility of strain measurement of the established system. Two methods are proposed independently to correct the nonlinear characteristics of the tunable fiber Fabry-Perot filter. A novel demodulation algorithm is proposed and compared with other traditional algorithms based on the FBG sensing system.The major achievements in this thesis are:1. Model coupling theory and transfer matrix method are described in this work. The FBG reflective spectrum model is deduced using transfer matrix method, and the spectrum characteristics of the uniform FBG are obtained. The theoretical models of strain sensing and temperature sensing are established. The synchronous demodulation method for strain and temperature parameters is proposed.2. A dynamic FBG sensing system based on a tunable FP filter is established. A applicable encapsulation method is described. The feasibility of strain measurement of the established system is validated by experiments. Dynamic and static FBG sensing systems are compared and generalized. And the corresponding applicable fields are also defined.3. The spectrum characteristics of the tunable FP filter are tested using instruments controlling technology. The nonlinear facts of the moving of filter window center wavelength versus driving voltage are observed and the corresponding principle is analyzed. Two methods for correcting the nonlinear fact are proposed independently and validated by experiments.4. Various data processing methods for the demodulation of FBG sensing system are introduced. A novel demodulation algorithm based on cross-correlation is proposed independently. Traditional algorithms and correlation algorithms are used to process the experimental data and comparisons are made among those algorithms. Strain resolutions of 0.4μεand 1.5μεin high reflective gratings and low reflective gratings respectively are reported using proposed algorithm. Moreover, in the presence of low reflected power of FBG sensor, the proposed algorithm produces significantly better results than those of other algorithms. This makes the proposed algorithm perform well even in a low SNR system or with a long scanning wavelength step and thus can save the system cost to a large extent.