Highly sensitive liquid-level sensor based on an optical reflective microfiber probe

Increasing the sensitivity and miniaturizing the size of liquid-level sensors are crucial for confined installation space. Here we propose and demonstrate a highly sensitive liquid-level sensor based on a compact optical reflective microfiber probe. By tracking the resonant wavelength shift of the in-line Mach-Zehnder interferometer generated between the HE11 and HE12 modes, liquid-level sensing can be realized. Through optimizing the structure parameters of the microfiber probe, an ultra-high sensitivity of similar to 367.644 nm/mm is achieved in experiment, which is two to three orders of magnitude higher than other reported liquid-level sensors, to the best of our knowledge. Considering the high sensitivity and compact structure of the sensor, it has great potential in real-time intelligent monitoring of tiny changes in the liquid level such as small autonomous drones and micro-channels. (C) 2019 Optical Society of America