Accurate Determination of the Temperature Sensitivity of UV-Induced Fiber Bragg Gratings

Over the past 18 months, we have performed hundreds of temperature characterizations of fiber Bragg gratings inscribed in different germanium-doped silica glass fibers. Under the experimental conditions, the main conclusions, are: the temperature dependence of the “temperature gauge factor” or the normalized temperature sensitivity, KT, was found to be quadratic in the −¬¬50–200 ºC range while it may be considered linear for the −20–100 ºC range; KT values at 20 ºC varies from 5.176 x 10-6 K-1, for a B/Ge co-doped fiber up to 6.724 x 10-6 K-1, for a highly Ge-doped fiber; KT does not depend on the hydrogen-loading process or the gratings coupling strength; KT is essentially independent on wavelength in the 1500–1600 nm range being its value accurately determined with a relative error ~ 0.2%; gratings produced by femtosecond-laser radiation and UV-laser radiation exhibit comparable values of KT. The previous achievements allows, by having knowledge of KT for a single grating, the accurate determination of the temperature dependence of the Bragg wave-length for any other grating inscribed in the same fiber; the presented methodology enables one to determine the “unknown” gratings temperature sensitivity, typically, with an error of 0.01 pm/ºC, being, therefore, very useful in research labs and computer simulations; thus, expressions for the temperature dependence of KT for gratings inscribed in several fibers are given. We have also fully analyzed the potential sources of error in KT determination.