Novel Technique for Meniscus Height Measurement of Liquids Using Optical Fibers

A novel technique was designed to measure the meniscus height (MH) of liquids on a standard single mode fiber (SMF) using fiber optics. Once the MH is known, the contact angle could be calculated, and the surface tension of liquids can be determined. In this paper, the MH is measured using a cleaved and side polished optical fiber attached to a SMF with a known separation distance between their fiber tips. When the liquid reaches the SMF, the liquid meniscus rises on the vertical wall of the SMF, which also causes a variation in mass (measured by a μg scale). At this point, the liquid moves upwards until the liquid meniscus touches the side polished fiber, which registers a variation of the reflected optical power. The MH seems to increase as the surface tension decreases, and the variation of the mass measured by the scale increase with the increase of the surface tension. This sensor was also used to measure the interfacial surface tension of the air-liquid and liquid-liquid interface since the contact angle could be measured. In addition, the small dimension of the sensor is adequate for applications where using small amounts of liquid is critical, i.e., biomedical applications.