Abstract: A new method is presented to detect the wavelength shift on in fiber Bragg gratings.The system employs a series of in fiber Bragg gratings,having the same parameters as the sensing in fiber Bragg gratings,as filter elements.Furthermore,the system tracks the maximum wavelength of the reflected spectrum of in fiber Bragg gratings through dithering and doubling the frequency.A grating with high sensitivity is used to read the output of the system.The non linearity and hysteresis of PZT have been erased thoroughly,so the accuracy of the system is improved a lot.