Determination of thermo-optic coefficient of ethanol-water mixtures with optical fiber tip sensor

In this work, the thermo-optic coefficient (TOC) of ethanol-water mixtures, through refractive index and temperature measurements are determined using an etched optical fiber tip based on a multimode interferometer. The proposed probe is fabricated by fusion-splicing a 5.2 mm long coreless fiber section to a single mode fiber. To reduce the sensor dimensions and improve its sensitivity towards external medium variations, the fiber tip is subjected to wet chemical etching using a solution of 40% hydrofluoric acid, presenting a final diameter of 24.4 μm. The TOC of each solution is estimated and, in the case of deionized water and pure ethanol, its value is of −1.128 × 10−4 °C−1 and −3.117 × 10−4 °C−1, respectively.