Highly sensitive liquid level sensor based on an optical fiber Michelson interferometer with core-offset structure

A highly sensitive liquid level sensor based on an optical fiber Michelson interferometer with core-offset structure has been proposed and demonstrated. The sensor was fabricated by offset splicing a section of single-mode fiber (SMF) between another two SMFs and coated the reflection film at the end-face of the pigtail. This sensor was then used to measure liquid level and the dip of the measured reflection spectra caused by Michelson interference shifted obvious when the sensor is immersed in pure water. A good linear relationship between the liquid level and spectrum dip wavelength shift was detected (R-2 = 0.9971), while the dip intensity of the interference fringes fluctuates very little. The measured sensitivity up to 77 pm/mm was shown when the water level changed from 0 to 40 mm. In summary, this optical fiber sensing system would be appreciated in applications to liquid level measurement due to its good linearity, sensitivity, simple structure, and low cost.