Liquid Level Sensor With High Sensitivity Based on Hetero Core Structure

In this paper, a novel liquid level sensor with high sensitivity is proposed. The proposed sensor is configured by multimode fiber-No-core fiber-multimode fiber (MMF-NCF-MMF) hetero core structure (MNM-HCS). The sensor is composed of two MMF structures spliced on both ends of NCF, in which NCF is used as a sensing unit, and the MMF at both ends excites higher cladding modes to improve the sensitivity of the sensor to the external environment. Interference occurs when light is transmitted from MMF to NCF. Experimental results show that the compact sensor with a length of 12.2 mm has a high liquid level sensitivity of 1034 pm/mm in the water level (RI
$=$
1.333) range of 0-10 mm. The temperature sensitivity is 20 pm/°C in the range of 35-
$95^{\circ }\text{C}$
. The temperature-liquid level cross sensitivity of the proposed sensor is 0.019 mm/°C. Due to the advantages of high sensitivity, good linearity and stable performance, MNM-HCS has potential application potential application prospects in the field of high sensitivity liquid level measurement.