Study on improving the dynamic range of demodulation signals in fiber Bragg grating sensing system using digital matched filter

A Method to realize signal demodulation of fiber Bragg grating (FBG) sensing system using non-balanced fiber Mach-Zehnder interferometer based on phase generated carrier (PGC) technique is proposed. A detecting scheme to realize phase carrier modulation using PZT phase modulator and to realize demodulation of detected signal using Bessel function and Fourier analysis is presented. The results of the analysis show that the upper limitation of the dynamic range in fiber Mach-Zehnder interferometer is limited by the frequency of the carrier and the cut-off frequency of the low pass filter. In order to enhance the function of filtering wave in phase generated carrier signal demodulation, we use digital matched filter (DMF) in place of low pass filter. The filter can be used to recover the useful signals from signals of a low signal-to-noise ratio. The wavelength detection accuracy of this demodulation scheme is 1.8pm, and the dynamic range of the FBG sensing system has been also improved. The theoretical analysis shows that the scheme can effectively suppress effect of random interference signals on the measurement accuracy and can demodulate the dynamic signal with high resolution.