A Mach-Zehnder-like interferometer based on cascaded long period gratings with palladium silver (Pd-Ag) film coating
is developed for monitoring the hydrogen concentration. The visibility of fringes is measured using Fourier analysis. The
basic theory was given and preliminary experiment had been proved that this sensor can used to monitor the hydrogen
concentration. The sensor showed a good response.
Theoretical and experimental aspects of the extrinsic Fabry-Perot(FP) interferometric(EFPI) optical fiber sensor are
studied. For a low-finesse EFPI sensor, the change of cavity length will influence the visibility of the interference fringes
reflected back into the fiber. In this paper, an analysis on the fringe visibility of EFPI sensors based on the power
distribution is presented. The effect that the cavity length and the source bandwidth play in the fringe visibility of EFPI
sensors interrogated with a broadband light source which makes the sensor immune to source fluctuations is explored.
The analysis may provide useful guidance for sensor design.
An extrinsic Fabry-Perot interferometric (EFPI) optical fiber hydrogen sensor based on palladium silver (Pd-Ag) film is
designed for hydrogen leakage detection. A modified cross correlation signal processing method for an optical fiber
EFPI hydrogen sensor is presented. As the applying of a special correlating factor which advises the effect on the fringe
visibility of the gap length and wavelength, the cross correlation method has a high accuracy which is insensitive to light
source power drift or changes in attenuation in the fiber, and the segment search method is employed to reduce
computation and demodulating speed is fast. The Fabry-Perot gap length resolution of better than 0.2nm is achieved in a
certain concentration of hydrogen.
An extrinsic Fabry-Perot interferometric (EFPI) optical fiber hydrogen sensor based on palladium silver (Pd-Ag) film is
designed for hydrogen leakage detection. The sensing mechanism of such a sensor is based on the mechanical stress that
is induced in the Pd-Ag film when it absorbs hydrogen. The sensor system which is portable and suitable for field
detection is formed by a conventional coupler, a low-power LED operating at 850 nm, and a high resolution miniature
spectrometer. To obtain the absolute length of the EFPI air gap, a cross-correlation signal processing method is
introduced.The sensor is suitable for monitoring concentrations of hydrogen below the lower explosive limit.
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