A liquid level optical fiber sensor with refractive index compensation through cascading double multi-mode interferences

Abstract

A liquid level (Li-Le) optical fiber sensor with refractive index (RI) compensation through cascading double multi-mode interferences (MMIs) sensors was experimentally investigated. Previous researches showed that the sensitivities of Li-Le sensor were interfered by the variation in liquid RIs significantly, which illustrated the necessity of RI compensation in Li-Le sensors. In this work, we designed a Li-Le sensor by cascading a Li-Le sensor and a RI sensor, where the RI sensor was used for the RI compensation in Li-Le detection. The sensitivity of Li-Le sensor varied with the increase of liquid RI. The RI sensor could achieve the RI compensation in the RI range of 1.333–1.370. A contour map was plotted to effectively determine the Li-Le from the disturbing of liquid RI. The maximum sensitivity of Li-Le was 875 pm/mm when the liquid RI was 1.4164, which was higher than most of the previous works. This designed RI compensation Li-Le sensor could become a competitive candidate in the field of accurate detection of Li-Le for the advantages of high sensitivity, simple structure, and RI compensation.