Etched optical fiber for measuring concentration and refractive index of sucrose solutions by evanescent waves

The study of the reduction of an optical fiber by chemical etching has been suggested to determine the concentrations of sucrose in water and their refractive indices by evanescent waves using a coherent infrared source. The cladding of a single-mode optical fiber was removed at a rate of ∼3.27 µm min⁻¹ using hydrofluoric acid until it reached a diameter of 7.3 µm, similar to the core of the fiber. This fiber was used to characterize sucrose solutions at different amounts employing a continuous wave infrared laser source at 1550 nm. The sucrose was dissolved in water to evaluate the quantitative sensor response based on the transmission relationship. The experimental results showed that the refractive indices obtained by the evanescent absorbance were in the range of 1.31–1.44 for concentrations of sucrose between 0% (water) to 65%. Additionally, it was determined that for concentrations higher than 65% of sucrose, the refractive index of the solution is similar to the core of the fiber, and therefore the total internal reflection was not possible. The results obtained in this work suggest that the etched optical fiber can be used as a refractive index sensor, which may play an important role in chemical applications. (paper)