Liquid level measurement based on a no-core fiber with temperature compensation using a fiber Bragg grating

• A novel sensor for simultaneous liquid level and temperature measurement based on a combination of a NCF and a FBG is proposed.
• The related theory is explained and the experiment results are analyzed.
• The liquid level sensor has advantages of simple fabrication and temperature compensated.

An optical fiber sensor for simultaneous measurement of liquid level and temperature is proposed and experimentally demonstrated. The sensor is formed by the integration of a no-core fiber (NCF) with a fiber Bragg grating (FBG).When the liquid level is changed, the interference fringe of the NCF would shift while the Bragg wavelength of the FBG remains the same. On the other hand, the interference fringe of the NCF and the Bragg wavelength of the FBG would shift simultaneously with the variation of temperature. Thus the liquid level sensor with dynamic temperature compensation can be easily achieved by using the temperature sensing property of FBG. For 10 pm wavelength resolution, the resolution of the sensor is 0.046 cm and 1.1 °C in liquid level and temperature, respectively. The fabrication of the proposed sensor is very simple and it is characterized by the dynamic temperature compensation, which makes it desirable in liquid level measurement.