Low-Cost and High-Performance Optical Fiber-Based Sensor for Liquid Level Monitoring

Liquid level sensing is nowadays a relevant issue in a broad range of applications, forcing the sensors performance and cost to be evaluated in parallel. This paper proposes a fiber optic-based liquid level sensor system using a fiber Fabry-Pérot interferometer (FPI) embedded into a polyurethane resin diaphragm. The FPI is based on microcavities generated upon catastrophic fuse effect, enabling the fiber recycling and sensors fabrication in a cost-effective way, compared to traditional methods. To enable the simultaneous temperature control, a fiber Bragg grating was used as thermal reference sensor to compensate the temperature cross-sensitivity. The sensor prototype was tested in a field application, using two different configurations, an open chamber configuration, where the diaphragm is in contact with the atmosphere, and a closed chamber configuration revealing the sensitivities of 4.4 ± 0.1 pm/mm and 1.57 ± 0.04 pm/mm, respectively. These sensitivity values are within the figures of merit for diaphragm-based sensors as reported recently.