Dual Sensing Points Mach–Zehnder Interferometer for Refractive Index and Discrete Liquid Level Sensing

An in-line all-fiber Mach-Zehnder interferometer (MZI) based on the combination of etched single mode fiber (ESMF) and double cladding fiber (DCF) is proposed for refractive index and discrete liquid level sensing. In the proposed structure, two sensing points are devised using two ESMF section of length. The two sections are separated by a refractive index insensitive region formed by DCF section. The sensor may be deployed to measure refractive index in single- or dual-point configuration. The experimental work revealed maximum refractive index (RI) sensitivity at - 37.2 nm/RIU for 1.305-1.335 RI range, with 1 mm compact sensor size. Additionally, the sensor performed as a two-point liquid level sensor with wavelength shift ranging between 0.84 nm and 1.44 nm. The proposed sensor displayed great potential to be deployed in liquid chemical storage to monitor liquid quality and level.