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In order to improve the detection accuracy of wavelength, the filtering and curve fitting technologies were applied in the FBG wavelength demodulation system based on tunable F-P filter. These methods could realize the accurate peak-location of output signals of the photo detector. According to the characteristics of noise, the FIR low-pass filter was designed to filter the obtained light power signals so as to provide the input signals with high SNR for the peak-detection algorithms. By analyzing and comparing several typical peak-searching algorithms, the algorithm of Gauss formula nonlinear curve fitting (L-M) was chosen to fit the digitized light power signals. The experimental results show that L-M fitting algorithm reduces the mean square error by 7.5% compared with the Gauss fitting algorithm. For the Gauss signal in the wavelength demodulation system designed in the paper, the L-M algorithm has lower mean square error than other peak-searching algorithms. This algorithm is suitable for FBG wavelength demodulation system based on tunable F-P filter. It can efficiently raise the accuracy of wavelength demodulation system.

Long Period Fiber Grating (LPFG) sensors have wide range of potential applications; low-cost and high-sensitivity demodulation technology is the key of its practical applications. In this paper, an interferometer is comprised of an all-fiber loop mirror and two identical LPFGs, a tunable F-P filter is used to perform wavelength scanning one of the interference peaks, two negative pulse interval formed by signal light in the drive signal period are measured by means of detector and oscilloscope to realize signal demodulation. This demodulation system was used to detect the temperature parameter. The results showed that the sensing sensitivity of this system was demonstrated to be 0.08349 ms/°C, experimentally, which was 2.3 times higher than a single LPFG using the same demodulation technology.