Resolving the problem of cross sensitivity in fiber Bragg grating sensor based on the principle of polarized-light interference

Abstract

The article introduces an advanced approach of fiber grating strain demodulation based on the principle of polarized-light interference. This method can solve the problem of cross sensitivity in fiber Bragg grating sensor. As for the yttrium vanadate (YVO₄) crystal polarized-light interferometer, if there are two different fiber Bragg gratings that have a ? rad phase difference, one is used for strain sensor and the other is used for temperature compensating. Then the problem of cross sensitivity can be overcome. The analyses of the strain demodulation resolution show that with a decrease in crystal thickness the resolution increases. The experiment shows that when the thickness of YVO₄ crystal is 0.5 mm, the effect of cross-sensitivity will be reduced to 0.13 µε/?C, which is 1.6% of the effect used by only one fiber Bragg grating for strain measure. And when the thickness is 0.1 mm the cross-sensitivity will be reduced to 0.006 7 µε/?C, which is less than 0.08%. Less thickness of crystal is beneficial for the resolution of strain measure, but the machining of small thickness crystal is difficult. To solve this problem, a new scheme of polarized-light interferometer with the structure of double layer crystal was analyzed.