The force results in deformation and strain of the cantilever
beam. As strain is applied to the FBG, the Bragg grating
pitch will change accordingly, which leads to the Bragg wavelength
shift of the spectrum. As well, the change of the liquid
level would induce the shift of Bragg wavelength. Therefore,
the liquid level can be sensed by monitoring the shift of Bragg
wavelength from an optical spectrum analyzer.