A high SNR system for intensity demodulation of fiber Bragg grating based on phase-locked loop

Abstract

The intensity demodulation technology of fiber Bragg gratings (FBG) is typically realized by detecting the output light power. Traditional methods, such as DC power detection, have a low signal-to-noise ratio and sensitivity. Thus, a novel intensity demodulation system based on the phase-locked loop is proposed in this study. Theoretical analysis and experiments show that the system has a high signal-to-noise ratio, linearity, and stability with a low-temperature sensitivity of the FBG sensor head. Compared to traditional light power detection, the proposed system increases the signal-to-noise ratio by more than 24 dB. According to the repeated temperature experimental results, the proposed sensor with an accuracy of ± 0.5 °C has a repeatability error of 1.8%, alinearity error of 3%, and ahysteresis error of 1.5% in the temperature range from 10 to 90 °C, which indicates that the system is of high-sensitivity and high-precision.