Thermally stable optical fibre Bragg grating wavelength reference

The inherent temperature dependence of optical fibre Bragg gratings is caused mainly by the positive thermo-optic effect of the fibre core material, and it results in an increase of Bragg wavelength with temperature. Special mounting techniques may be designed in order to compensate this thermo-optic effect by counter-acting effects: decreasing mechanical strain, as well as a decreasing effective refractive index for the guided light wave by evanescent field interaction with a liquid of negative thermo-optic effect. Because of the non-linear interaction characteristics, exact temperature compensation is obtained for a certain temperature, which depends on the design parameters. Such stabilised fibre Bragg gratings find application as wavelength references in Bragg grating sensor networks.

Research Highlights
► Special mounting and embedding techniques have been designed in order to stabilise Bragg wavelength of fibre-optic Bragg gratings.
► With increasing temperature, both, decreasing mechanical strain, as well as a decreasing effective refractive index of an ambient liquid may compensate for the positive thermo-optic effect in silica-based optical fibre.
► Because of the non-linear characteristic of thermo-optic effect, exact temperature compensation is obtained for a certain temperature only, which can be adjusted by design parameters.