Highly sensitive and temperature-insensitive liquid level sensor based on fiber Bragg grating

A simple and novel design strategy, to our knowledge, of developing a temperature-insensitive, all-optical liquid level sensor based on Archimedes' law of buoyancy employing fiber Bragg gratings (FBGs) is proposed and demonstrated experimentally. The sensing approach relies on mapping the liquid level variation to the shift in wavelength difference between two FBGs. The main objective of this work is to enhance the sensitivity toward liquid level variation while achieving a very large dynamic range. Comprehensive analysis is carried out while investigating the sensor response. The proposed sensor is characterized with a significantly enhanced sensitivity of 77.5 pm/cm, with an excellent resolution of 0.006 cm [<0.020% of the full-scale reading (FSR)] and accuracy of <0.03% of FSR over the designed dynamic range of 30 cm. Moreover, this sensor exhibits a very high level of reversibility and repeatability following an excellent agreement with the theoretical response. These attributes make the proposed sensor highly significant for real-life applications.