An Ultrafine No-Core Fiber-Based Sensor for Simultaneous Liquid Level and Temperature Measurement

In this article, a section of ultrafine no-core fiber (UNCF) is fused between two sections of single-mode fiber (SMF) to form a multimode interference (MMI)-based sensor, which enables dual-parameter measurement of liquid level and temperature. The effect of UNCF diameter on the liquid-level sensing performance is analyzed theoretically and experimentally, and the results show that the sensitivity can be improved by reducing the UNCF diameter. When the UNCF diameter is reduced to 30 mu m, the sensitivity of the sensor is 1008.2 pm/mm for water with a refractive index (RI) of 1.333 in the liquid-level range of 0-30 mm. Its temperature sensitivity is -221.02 pm/degrees C over a detection range of 5 degrees C-60 degrees C. Attractively, the sensor shows almost no response to pressure variation. When applied to the liquid-level measurement of a water cooler, the sensitivity is 1898 pm/mm. The sensor has the advantages of high sensitivity, good repeatability and stability, and satisfactory anti-interference ability. It has great potential for applications in the health management of lasers, chips, transformers, and other instruments.