Temperature-insensitive fiber Bragg grating liquid-level sensor based on bending cantilever beam

A temperature insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflection optical power change with the liquid level and they are insensitive to spatially uniform temperature variations. For a liquid level variation of 500 mm and a temperature range from 0°C to 80°C, the measured liquid level fluctuates less than 2% without any temperature compensation. By optical power detection via a pin photodiode, the liquid-level sensor avoids complex demodulation process and potentially costs low.