An optical fiber liquid level sensor based on two twisted polymer optical fibers twining around a racetrack column is demonstrated\nin this study. The side-coupling power of the passive fiber is modulated by the refractive index (RI) of the environment medium and\ndecreases while the liquid level increases. The variation patterns of the side-coupling power in the bent section and the straight\nsection form a step attenuation, which can improve the measurement range with a superior sensitivity and distinguish liquids\nwith different RIs. Furthermore, the cost-effective sensor also shows good reversibility and low temperature-dependent properties.
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