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

Abstract

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.

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“…Therefore, exists a ratio between and SRI. In order to enhance the sensibility of the SMS structures it is necessary to increase the intensity of the evanescent wave by the increase of , this can be achieved reducing the diameter in the sensitive region [15]. The application of corrosive materials makes possible to reduce the section of MMF-NC (typically HF is used).…”

“…The duration of the etching process is dependent of parameters such as: percentage concentration of HF and temperature. When the values of both parameters increase, minor will be the time of the process [15,16].…”

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“…Nano-coated optical fiber sensors have been developed; however, this process is difficult because it involves an etching process [15][16][17][18][19][20][21]. Wet etching can be performed using a cheap method for removing optical fiber silica coated with harmful chemicals, such as hydrofluoric acid [22][23][24][25]. Dry etching and inexpensive processes can be conducted mechanically using sandpaper; however, this method is only suitable for polymer fiber optics [26].…”