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Influence of temperature on the refractive index sensitivities of fiber Bragg gratings refractometers

In this work, the cross-sensitivity between temperature and refractive index (RI) in etched fiber Bragg grating inscribed in multi-mode fiber (MMF) is studied. The refractive index sensitivities of different modes are used to obtain a linear response and the temperature dependence. It was verified that the absolute average RI sensibility reduces from 0.97Â Â±Â 0.05Â nm/RIU to 0.76 Â± 0.07 nm/RIU when the temperature increases from 15 o C up to 35 o C, respectively. Due the fact of this MMF fiber Bragg grating has low RI sensitivity; the effect of temperature increasing on the RI sensitivity is not marginal and thus, must be considered in the calibration curves in order to improve the precision during the RI measures. This temperature effect on the refractive index sensitivity is related with the increasing difference between the fiber and surrounding RI, which results in a decrease of the evanescent field and consequently reduced surrounding RI sensitivity.