A novel double-edged filter wavelength interrogation technology for FBGs

A novel double-edged filter wavelength interrogation scheme for FBGs is designed based on mechanical-induced long period gratings MI-LPGs.Two LPGs,which have symmetrical overlap resonant sideband,the same resonant peak and bandwidth,are fabricated as filters under different parameters.When FBG reflection signals get through different spectral characteristic filters,the demodulation system will output two intensity different lights.Logarithmic algorithm is adopted due to the ratio between the two output lights.Experiments show that FBG sensing signals interrogation can be realized stability and accurately.And the demodulation dynamic range is up to 5 nm.The mean square between demodulation system linear fitting calculated wavelength value and Spectrometer measurement value is 6 pm.Excellent Linearity and high precision of designed system is proved.