High-sensitivity liquid level sensor based on single mode-coreless-seven core-coreless-single mode fiber structure

A liquid level sensor based on single mode-coreless-seven core-coreless-single mode fiber structure is proposed, in which two short sections of coreless fibers are utilized as fiber couplers, so as to improve the coupling effi-ciency between the single mode fiber and the seven core fiber, thus enhance the mode interference perception of external liquid level. Experimental results reveal that the liquid level sensitivities of the sensors with seven core fiber length of 16 mm, 18 mm and 20 mm, are-0. 3163 nm/mm,-0.2687 nm/mm and-0.2471 nm/mm in the liquid level ranges of 16 mm, 18 mm and 20 mm, respectively. In addition, stability test is performed and the maximum instability is 0.04 nm with a standard error of 0.16 mm. The sensor possesses advantages of robustness, low fabrication cost, high sensitivity and good stability, indicating it has a prospective potential in petrochemical and biological applications for liquid level sensing.