Measurements of liquid surface tension and refractive index using a tapered microfiber

Abstract

In this letter, a tapered microfiber (TMF) liquid surface tension (LST) sensor is proposed and demonstrated. Due to the strong evanescent field and weak stiffness of the TMF, the LST can be measured. The processse of the TMF immersion into liquid and leaching from the liquid are divided into multiple stages, and the dip wavelength shifts at different stages of the immersion process are attributed to refractive index (RI) and bending changes, but those of the process of leaching only are attributed to bending change. By both theory and experiment, it is found that the sensitivity has a obvious response to the waist diameter of the TMF. In addition, the RI of solutions can be measured by monitoring the variation of the wavelength difference of the TMF in liquid and in air. Experimental results show that the RI and LST sensitivity are 14.56 pm/(N/m) and 211.51 nm/RIU, respectively. By using the known RI and LST of the liquid as reference, the RI of the unknown solutions can be obtained and the LST of them can be qualitatively estimated by measurement of wavelength shifts.