Portable Optical Fiber Sensor for Continuous Liquid Level Sensing Using Commercially Available POF

This article presents a portable optical fiber sensor (OFS) design for continuous liquid level measurement, fabricated using two pieces of bare polymer optical fibers (POFs). The proposed sensor design utilizes the twisted coupling technique, where two optical fibers are twisted and coupled, leading to power coupling from the illumination fiber (IF) to the coupled fiber. The casing is fabricated through a 3-D printing method. The 3D-printed casing is utilized to mount the sensor onto a smartphone, facilitating the connection of the fibers to both the flashlight and the camera. The flashlight serves as the light source, while the camera records the intensity variations. The liquid level sensing relies on the coupling loss, where the light is transmitted to the IF, and the twisted coupled fiber couples the power, exhibiting intensity variations with changing liquid levels. The proposed liquid level sensor can measure depths up to 120 mm with a sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.053~\pm ~0.002$ </tex-math></inline-formula>% per mm and an impressive resolution of 0.05 mm. The experimental findings indicate that the proposed sensor has excellent stability and reliability. The sensor’s straightforward, comprehensive, and cost-effective design enables its application in chemical, petroleum, and many other industries.