Highly sensitive liquid level and temperature sensors based on all-fiber intermodal interferometers

Abstract Fiber optic-based precise measurements of liquid level and temperature are crucial for remote controlling in pharmaceutics, chemistry, and bromatology. Thus, it is essential to monitor liquid level and temperature simultaneously. In this paper, we propose all-fiber intermodal interferometers for highly sensitive liquid level and temperature measurements. We fabricated two different structures of single mode fiber-no core fiber-single mode fiber (SMF-NCF-SMF). One of them was used to measure the liquid level when the liquid soaked the NCF, and the other one was further coated with polydimethylsiloxane(PDMS) thermal-optic material and utilised to detect temperature. The measurement sensitivity of liquid level was 580 pm/mm within the range of 0–20 mm, while that of temperature was 1 nm/°C within the range of 28 °C–51 °C. A matrix was finally obtained by demodulating the measurements of liquid level and temperature. The proposed liquid level and temperature sensors, exhibiting the merits of high sensitivity, easy fabrication, and low cost, could be a candidate for precise and remote monitoring of liquid levels.