Detection of Liquid Level With an MI-Based Fiber Laser Sensor Using Few-Mode EMCF

This letter firstly and experimentally demonstrated a fiber laser sensing system using Michelson interferometer (MI) based on few-mode elliptical multilayer-core fibers (EMCFs) for liquid level and refractive index (RI) measurement. The fiber sensing system has high optical signal-to-noise ratio (~45 dB) and narrow 3-dB bandwidth (<;0.1 nm). Four water-glycerin solutions of different RI are used for this experiment, and the higher sensitivity is acquired for the higher RI liquid. The sensitivities for the liquids with indices of 1.333, 1.353, 1.373, and 1.393 are 30.5, 35.6, 41.1, and 50.6 pm/mm within a depth range of 0-45 mm, respectively. Moreover, the RI of liquid can also be measured, and a sensitivity of 329.222 pm/mm/RIU is experimentally achieved.

I. Introduction

Fiber-optics sensor technology [1] has been attracting much attention for liquid level measurements in electric conductive, explosive or chemical flammable environments, attributed to its distinctive advantages, such as high sensibility, anti-erosion, immune to electromagnetic interference and low-cost owing to its easy fabrication, etc. The liquid level fiber sensors can apply to more wide areas than electrical ones. In modern industry and daily life, multiple liquid level fiber sensors have been proposed and experimentally demonstrated using various sensing techniques including long-period fiber gratings (LPGs) [2], fiber taper technology [3], fiber Bragg gratings (FBGs) [4], [5] and Michelson interferometry, etc. Up to now, singlemode-multimode-singlemode-film (SMSF) fiber structure based Michelson interferometer (MI) for liquid level measurement [6], [7] has attracted much attention with the merits of easy fabrication and high sensitivity.