A high sensitivity liquid level sensor based on single mode -taper-thin core - taper- single mode fiber structure

An optical in-fiber Mach-Zehnder interferometer (MZI) based on thin core fiber (TCF) for liquid level sensing is proposed and experimentally demonstrated. The sensor head is formed by single mode -taper-thin core - taper- single mode fiber structure via fusion splicing. The operation principle relies on the intermodal interference is sensitive to liquid level variation, which constructed by employing tapers as couplers. Experimental results reveal that the transmission spectrum has a linearly red-shift with the liquid level changing from 0 to 15 mm, and achieves enhanced sensitivities of 0.6853 nm/mm, 0.9062 nm/mm, and 1.2416 nm/mm for liquid RIs of 1.3352, 1.3491 and 1.3698, respectively. The temperature experiment is carried out and the maximum measurement error induced by temperature is -0.017 mm/℃, which indicates the sensor has a good practical prospect.