High sensitivity liquid level sensor based on a hollow core fiber structure

Abstract

A high sensitivity liquid level sensor formed by using a 15-mm-long hollow core fiber sandwiched between two single mode fibers is proposed and experimentally demonstrated. The sensing principle bases on the leakage of resonant light propagating in cladding of the hollow core fiber when the sensor is partially immersed in the measured liquid in a horizontal manner. High sensitivity of 7.64 and 9.74 dB/mm are achieved for liquid level measurements of water and ethanol, respectively. The maximum measurement range is 2.2 mm for water, which is limited but much larger than diameter of the fiber due to the effect of liquid surface tension. The high sensitivity property makes the proposed sensor a potential candidate for discrete liquid level measurement, especially for some flammable and explosive liquids.