The fiber Bragg grating(FBG) vibration system demodulated by double-long period fiber grating(LPFG) is proposed based on the edge filter analysis.The double-LPFG is adopted as filter after the transmission spectra super positioned,in order to improve the demodulation sensitivity.The static experiments illustrate that the demodulated sensitivities using single-and double-LPFG as filter are-1.196 5 dB/nm and-2.483 6 dB/nm,respectively.The demodulation sensitivity of the double-LPFG filter is about...