Fiber Bragg grating cladding mode resonance liquid-level sensor

Abstract

A Fiber-optic liquid-level sensor based on etched fiber Bragg grating (FBG) cladding mode resonance is proposed and demonstrated both theoretically and experimentally. The theoretical model of the FBG cladding mode liquid-level sensor is built under a three-layer step-index fiber geometry. Response of cladding mode resonance spectra to the variation of ambient liquid level are studied and simulated numerically with couple mode theory and transmission matrix method. In the experiments, a chemical etching method is adopted to diminish the fiber cladding diameter and increase the sensitivity of cladding mode resonances to the ambient refractive index change. Dependences of FBG cladding mode resonance spectra on the liquid-level variation are measured and the experiments data match the model well.