High-Sensitivity Micro-Liquid-Level Sensor Based on Balloon-Like Core-Offset Structure

Based on Mach-Zehnder interference (MZI) principle, we propose a balloon-like optical fiber micro-liquid-level sensor and verify its performance through experiments. The sensor can accurately measure the liquid level of different liquids. The structure of the sensor is to bend into a balloon-like after the single-mode optical fiber core-offset fusion. The core-offset fusion stimulates the cladding mode. The cladding mode and the core mode interfere with each other to form MZI. The liquid surface tension is used to change the bending radius of the sensor structure, so as to realize the measurement of the liquid level. The liquid-level sensitivity of the proposed sensor is 7300 pm/mm, corresponding to a liquid-level resolution of about $2.74~\boldsymbol {\mu }$ m. In addition, the temperature sensitivity of the sensor is 91 pm/°C, and the temperature cross crosstalk sensitivity is 0.012 mm/°C. The sensor has significant advantages of good repeatability, high sensitivity, high linearity, and low cost. So, the sensor has broad application prospects in the fields of aerospace, energy and power, and biomedicine and scientific research.