Enhancement of a Continuous Liquid Level Sensor Based on a Macro-Bend Polymer Optical Fiber Coupler

An approach to improve the side-coupling ratio of the macro-bend polymer optical fiber (POF) coupler is proposed in this paper. Two naked POFs are twisted and twined around a cylinder to achieve continuous liquid level sensing. Through filling the gap between the two twisted POFs with UV optical cement, both the sensitivity and the measurement range are increased substantially. The reversibility is also improved since the gap is eliminated, and little liquid can exist in the structure with the liquid level decreasing. The design turns out to be a good method to enhance the performance, and could also be applied in the displacement or stress sensing field.