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.

中文翻译：

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一种基于单模-锥形-细芯-锥形-单模光纤结构的高灵敏度液位传感器

提出并实验证明了一种基于细芯光纤 (TCF) 的光纤内马赫-曾德尔干涉仪 (MZI) 用于液位传感。传感头由单模-锥形-细芯-锥形-单模光纤结构熔接而成。其工作原理依赖于对液位变化敏感的模间干扰，其采用锥形作为耦合器构成。实验结果表明，透射光谱随着液位从 0 到 15 mm 发生线性红移，并且对 1.3352 的液体 RI 实现了 0.6853 nm/mm、0.9062 nm/mm 和 1.2416 nm/mm 的增强灵敏度，分别为 1.3491 和 1.3698。进行温度实验，温度引起的最大测量误差为-0.017 mm/℃，