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...