Liquid-level monitoring sensor systems using fiber Bragg grating embedded in cantilever

A fiber-optic liquid-level sensor based on the bending of a fiber Bragg grating (FBG) is proposed. The FBG embedded in a cantilever rod such that the elongation and contraction of the Bragg grating indicate a liquid-level change. The shift in the Bragg wavelength has a good linear response to the bending of the cantilever. An optical bandpass filter is used to determine the Bragg wavelength by converting the wavelength shift to an intensity demodulation. The relative power measured by a photo-detector is also linearly proportional to the liquid-level variation. The sensitivity is approximately 0.1 dB/cm. To eliminate the temperature dependence of the FBG sensor, we suggest that the tuning of the optical bandpass filter should take into account the temperature variation. The operating principle is described in detail.