Enhancing sensitivity of photonic crystal fiber interferometric humidity sensor by the thickness of SnO2 thin films

In order to improve the sensitivity of an interferometric humidity sensor based on a photonic crystal fiber with a sputtered SnO2 nanocoating, a study of the effect of its thickness on the sensitivity is presented in this paper. Sensors with coatings of different thickness were performed by applying distinct sputtering times in order to obtain an optimal thickness: the resulting nanofilms ranged from 470 to 1800 nm. Sensors were tested increasing the relative humidity from 20% to 90%, finding that the thickness was a key parameter which has to be optimized at nanometer scale to get the best sensitivity. The study points that there is an optimal thickness and higher or lower thicknesses worsen the sensitivity of the sensor. The optimal sensor showed a humidity resolution of 0.067%HR, a wavelength shift of 67 nm and a negligible sensitivity with the temperature. (C) 2017 Elsevier B.V. All rights reserved.