The ground deformation observation is the method that estimates the ground deformation according to the displacement
change of work spot measured periodically. By using the repeatability of the mechanical transducer and the reliability of
the wavelength modulation, the differential fiber Bragg grating settlement gauge reduces availably the disturbance of the
artificial causation and the weather. In this scheme, the drive rod converts the displacement of settlement block into the
strain of beam, and causes the Bragg wavelength shifts of the sensing gratings mounted on the top and bottom surfaces
of the beam, on which the temperature-compensated is achieved by the differential operation of the shifts of Bragg
wavelengths. Because the collapse of slope is caused by the cutting slippage as the shearing strength in the soil body of
slope exceeded the anti-shearing intensity, the slide prevention pier is the regular retaining structure for treating slope.
The differential fiber Bragg grating settlement gauge is developed and fixed on the pier, which converts the settlement of
the observation point into the Bragg wavelength shifts of the sensing gratings. Applied in Bai Ni-jing Slope, the
measurement precision between the settlement gauges and Wild N3 precise level is 0.03, which is satisfied with the
engineering order measure precision 0.05~0.1. By subtract the displacement-induced settlement deviation, the corrected
precision between the settlement gauges compensated by Leica J2 theodolite and the precise level is improved to 0.007,
which is satisfied with the scientific research order measure precision 0.01~0.05.
A scanned Talbot interferometer based on shifting phase mask and fiber is developed to change the inscribed Bragg
wavelength. In the scanned Talbot interferometer with scan translation platform and fiber translation platform, the ±1
order diffraction light beams form the interference fringe in the far field, thereinto, the fiber translation platform drives
the fiber exposing in the interference fringe, and the scan translation platform causes the fiber shifting in the interference
fringe to point-by-point write grating in the fiber. Followed the size of interference fringe is decreases from 10 mm to
about fraction of a mm, the coherence length of light beams is reduced distinctly. It is important that the length of mirror
could be reduced to the size of interference fringe. Additionally, the pulse energy of light source is also reduced
evidently.
Multi-parameter measurement is important for building health monitoring. In this paper, we use fiber Bragg grating (FBG) and extrinsic Fabry-Perot interferometer (EFBI) sensor to realize the measurement of strain, temperature and vibration. A universal demodulate method, which combines the low coherence interference demodulation of EFBI and fiber Fourier transform demodulation of FBG, is proposed. Thus it is possible to extract the signals from FBG and EFBI parallely with only a Michelson interferometer. A data fusion model is established to process the origin data to get more precise results and distinguish the different parameters. The system is tested on a equi-intensity cantilever, and the results of experiment show that strain and temperature can be obtained efficiently.
A wedge-adjusted Talbot interferometer is presented to change the inscribed Bragg wavelength of fiber Bragg gratings. In this system, the grating is written by UV interference stripes of 193 nm derived from two combined mirrors, where a phase mask is used as a beamsplitter of ±1 order of diffraction light. It is noteworthy that the adjustor transforms the shift of wedge into the rotation of the two mirrors, and alters the mutual angle of two interfering beams in writing fiber Bragg gratings.
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