Working Principle

Among the different sensing and multiplexing techniques available, the sensor development focuses on Fiber Bragg Grating technology along with the corresponding multiplexing technique. Fiber Bragg Gratings (FBGs) are diffracting elements printed in the Germanium-doped core of an optical fiber. FBGs consist in a periodical modulation of the core refractive index along a short length. They behave like selective filters which reflect in the fiber core the spectral components λ of a propagating packet according to the Bragg relation λ = 2 n·Λ, with n being the core mean refractive index and Λ the FBG step or the spatial period of the refractive index modulation. If the temperature varies, n is accordingly modulated through the thermo-optic effect. If the FBG is strained along the fiber axis, is λ modulated. As a result, the FBG (or Bragg) wavelength is shifted, which is a measure for the parameter under investigation.