An optical liquid level sensor based on polarization-maintaining fiber modal interferometer

A novel optical liquid level sensor based on polarization-maintaining fiber (PMF) modal interferometer with waist enlarge splicing is proposed. A length of 35 mm PMF is spliced between two single-mode fibers (SMF) to construct an all-fiber modal interferometer. The results show that the transmission spectrum has a red shift with the increasing level of liquid, and the higher sensitivity is acquired for the higher refractive index liquid. The sensitivities for the liquids with indices of 1.335, 1.363 and 1.382 are 0.279 nm/mm, 0.437 nm/mm and 0.516 nm/mm respectively. At the same time, the temperature effect of the sensor has been measured and discussed.