A Multipoint Liquid Level Sensor Based on Two Twisted Polymer Optical Fibers in a Race-Track Helical Structure

A multipoint liquid level sensor based on the RI modulation of macrobend polymer optical fiber (POF) couplers is proposed. By twinning two twisted POFs around a race-track column, a series of U-shaped sensing heads are achieved. The output power in the passive fiber declines in a step form while the sensing heads are immersed into liquid in turn. The introduction of UV optical cement in the gap between two POFs improves the side-coupling ratio, increasing the attenuation per step. For the measurement range of 100 cm, the resolution is 2 cm. The sensor can differentiate different liquids with low temperature dependence