Resonance Energy Leakage in Hollow Core Fiber for Sensitive Liquid Level Measurement

A sensitive liquid-level sensor based on energy leakage of anti-resonant reflecting guidance in a hollow core fiber is proposed and experimentally demonstrated. It is constructed by splicing a 15mm-long hollow core fiber with a cladding thickness of 40 μm to single mode fibers. Since the leakage of resonance energy is sensitive to surrounding liquids, liquid level is measured by pushing sensor transversely against the liquid surface to efficiently change the proportion of fiber circumference in liquid. Based on the variation of transmission power at resonant wavelengths, liquid-level measurement was achieved with sensitivity up to 7.64 dB/mm, which is several times higher than that of normal sensors immersed vertically into the liquid.