A fibre-optic temperature sensor based on the deposition of a thermochromic material on an adiabatic taper

Abstract

A fibre-optic sensor has been developed for the measurement of temperature, especially of liquids. The device is conceived as part of an all-optical CTD probe for the control of the physical parameters of a marine medium. The dependence on temperature of the optical properties (specifically, absorbance) of a thermochromic material, namely lophine (2,4,5-triphenylimidazole), is the basis of the sensor. The sensor presents some significant differences with respect to other similar sensors proposed in the literature: the use of adiabatic, long, tapered optical fibres with adjustable geometric parameters; the use of LED illumination in the 800 nm range; improvements in the deposition technique, etc. The sensors show a linear behaviour over the desired temperature range, and their sensitivity is high. Also, the dependence of the response of the sensor with variations of the geometry of the tapers is discussed. Specifically, we have performed measurements with different diameters of the taper waist, and we show the dependence of the slope of the response curve with that parameter.