Passive temperature compensation package for fiber Bragg grating

The reflecting wavelength shift of fiber Bragg grating (FBG) can be caused by the variations of both strain and temperature, and such a so-called cross sensitivity is a "bottle-neck" which limits the FBG sensing and measuring technique to put into practical application. The measurement error is caused by the temperature change to measure the strain-inducing Bragg wavelength shift. The basic theory of temperature compensation of fiber Bragg gratings is presented according to the physical mechanisms of the strain and temperature cross sensitivity. A passive compact package for compensating the temperature dependence of FBG, based on the use of two materials with different thermal expansion coefficients, has been demonstrated. Two ends of the tensioned fiber grating are attached to the organic glass with epoxy resin. As the temperature rises and the strain is progressively released, it compensates the temperature dependence of the Bragg wavelength. The relation between temperature and wavelength in different compensation condition and in different strain is given. And the reason of undercompensation or overcompensation of the FBG is also analyzed. The Bragg wavelength shift over the temperature range of-19 degrees C to 60 degrees C is 0.79 nm for the uncompensated FBG, and that of the compensated FBG is only 0.035 nm for uncompensated FBG, which is 1/22 of that of the uncompensated FBG.