Research On Sensing Networks And Demodulation Technology Of Fiber Gratings

There is universal attention on fiber gratings and its application to fiber sensors and fiber communications. Fiber gratings offer many important advantages, especially they are very suitable to form the fiber array, by means of writing them into a fiber continuously. With themselves be pasted on or into the material, the fiber grating array can multipoint measured the properties, such as temperature, strain and so on, of the material, and the sensor array has wide prospect for detecting the properties of the huge buildings and dangerous situations, such as the dam, bridge, shuttle, mine, oil field, oilcan, and so on. In the dissertation, the fiber Bragg gratings(FBG) is taken as the sensing element, and the experiments and theories of sensing and demodulating of a FBG and FBG array. The main contents are taken as follows:1. The fundamental theory of the fiber gratings is introduced, the spectra of the FBG and long period grating(LPG) are analyzed by the coupling-mode theory, and the coupling-mode theory and the transmission matrix is used to explain the spectrum of the chirped fiber grating.2. Taken a FBG as the sensing element, the theory and experiment of the single-point senor are resolved. The experimental temperature properties of the FBG are carried out, where the FBG is covered by two different kinds of material. Due to the driving effect of the polymer substrate, the enhanced pressure sensitivity is more than 6.9 times and 13.5 times than that of a bare fiber grating.3. The cross-sensitivity of fiber grating sensors is studied. A new approach for displacement sensing based on chirp effect of fiber Bragg grating under strain-gradient is proposed. Strain gradient chirp of fiber Bragg grating is realized by attaching the grating slantways on a side face of a simple cantilever beam. The strain gradient, which is formed along the grating when the free of the beam is curved, produces a linear variation in the grating pitch. Because bandwidth of the grating is temperature-insensitive, the cross talk between displacement and temperature is avoided.4.A direct current and voltage sensor based on all-fiber Mach-Zehnder interferometer were demonstrated. The phases of interferometric lights of the interferometer was modulated by heating the fiber of one arm when the current is through a thin metal tube. The charactersistics of current sensing are studied experimentally. Adopting the wavelength scale method, in the case of elimination of environmental perturbation, the...