Fabrication of Multiple Superimposed Fiber Bragg Gratings for Multiple Parameter Sensing

Multiple superimposed fiber Bragg gratings (FBGs) are fabricated based on a non-uniform single-core As2Se3-Poly methyl methacrylate (PMMA) tapered fiber, by which superimposition of up to nine chirped FBGs is achieved. Multiple superimposed uniform FBGs are first inscribed on the nonuniform waveguide and multiple superimposed chirped FBGs are obtained by stretching the non-uniform waveguide. Simultaneous measurement of temperature and strain is realized based on two superimposed chirped FBGs at wavelengths of 1540 nm (FBG1) and 1550 nm (FBG2), respectively. The central wavelength shifts and bandwidth changes of the two superimposed chirped FBGs, when temperature and strain change, are measured, respectively. Four matrices are defined to predict the temperature and strain change, and the one defined by measuring the bandwidth change of FBG1 and the central wavelength shift of FBG2 gives the most accurate measurement with the sensitivities of 29.1 pm/degrees C for temperature measurement and 0.373 pm/mu e for strain measurement by measuring the bandwidth change of FBG1, and 75.1pm/degrees C for temperature measurement and 0.245 pm/mu e for strain measurement by measuring the central wavelength shift of FBG2, respectively. The resolutions for temperature and strain measurement are enhanced by more than a factor of 10, respectively, compared with those using the matrix defined by measuring the wavelength shifts of FBG1 and FBG2. A large strain change from 0 to 22000 mu e is achieved due to the low stiffness of As2Se3-PMMA taper, which is far beyond the operating range of silica materials.