Alternative interrogation method for a dual laser sensor based on fiber Bragg gratings to measure temperature using the fundamental beating frequency intensity

Abstract In this work we present an alternative interrogation method for a dual sensor based on a fiber laser used to measure temperature in two remote locations simultaneously. The dual laser consisted of two Fabry–Perot cavities each conformed by two fiber Bragg gratings (FBG). For each cavity, one FBG was used as the reference and the other one as a sensing element. The sensing element interrogation was performed by the quantification of the fundamental beating frequency (FBF) intensity, which was calculated using the fast Fourier transform algorithm. The laser emissions were centered at 1549 and 1556 nm, while the lengths of cavities were of 300 and 400 m, which corresponds to FBFs of 334 and 258 kHz, respectively. The quantification of the temperature was calculated from the difference between the FBF values of both cavities. Such difference describes a geometrical plane in function of the two sensing FBGs temperatures. Consequently, it was possible to achieve temperature measurements in a range of 25–28 °C for the two sensors.

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