A High-Resolution Liquid-Level Sensor Based on Fabry–Perot Interferometer With Fiber Laser Intracavity Sensing

High-resolution monitoring of liquid levels over a wide range has always been a great challenge. In this article, a fiber ring laser (FRL) sensor system with Fabry-Perot interferometer (FPI) is proposed for the high-resolution measurement of liquid level. The FPI fabricated with a polyimide film is embedded in an FRL for intracavity sensing. It is used as a reflective sensing head, which generates different reflection losses at different liquid levels to modulate the output power of the FRL. With the intracavity sensing, the resolution of the liquid-level sensing system has been significantly improved from 37.5 to 1.5 mm. The measurement range of the liquid-level sensing system is obtained as 0.6 m. The output stability and measurement error of the sensing system have been discussed. The sensor has a compact structure and a broad application prospect in the field of wide-range and high-resolution liquid-level monitoring, such as in chemical and marine applications.