Liquid level sensor based on PM-MD fiber structure loop mirror

Abstract

A fiber-optics liquid level sensor based on a PM-MD structure fiber loop mirror is proposed and demonstrated experimentally. The PM-MD structure is fabricated by core-to-core splicing a section of polarization-maintaining fiber (PMF) with a segment of multimode D-shaped fiber (MDF). Then the PM-MD structure is built into a Sagnac loop using a 3 dB coupler. The liquid level measuring characteristic of the sensor has been investigated experimentally by using the deionized water, ethyl alcohol, and different concentrations of NaCl solutions. The results show that the sensor has different liquid level response to the liquid with different refractive index (RI), and the highest sensitivity can reach 0.573 nm/mm for the ethyl alcohol with the RI of 1.3567. The proposed sensor has the advantages of simple structure, easy fabrication and low-cost. The liquid level measurement range can be freely customized according to the actual application by setting the polishing length of the D-shaped fiber. Furthermore, the proposed sensor has high sensitivity in the liquid level measurement and can distinguish the type of liquid base on the sensitivity, which may find the potential applications in chemical, biological, and biochemical fields.