Large-range liquid level sensor based on an optical fibre extrinsic Fabry-Perot interferometer

We propose an efficient approach to develop large-range liquid level sensors based on an extrinsic Fabry-Perot optical fibre interferometer with an all fused-silica structure and CO2 laser heating fusion bonding technology. The sensor exhibits signatures of a high sensitivity of 5.3 nm/kPa (36.6 nm/psi), a resolution of 6.8 Pa (9.9×10−4 psi) and an extreme low temperature dependence of 0.013 nm/°C. As a result, a high resolution of the water level measurement of approximately 0.7 mm on the length scale of 5 m and small errors of the water pressure measurement induced by the temperature dependence within 0.0025 kPa/°C (0.00036 psi/°C, water level 0.25 mm/°C) are achieved, thus providing useful applications for the detection of the large-range liquid level in harsh environments.