A Tracking-Based High-Speed Demodulation Method for Fiber Bragg Grating Sensing System Based on Wavelength-Tunable Laser in Space Application

The vibration measurement of spacecraft structures in space applications has raised higher requirements for the demodulation frequency of the fiber Bragg grating (FBG) demodulator. In this article, a tracking-based high-speed demodulation method for FBG sensing systems based on the wavelength-tunable laser is proposed. The wavelength-tunable laser only scans wavelengths near the latest wavelength of each FBG sensor. The scanning range is constantly updated to achieve wavelength tracking, and the FBG demodulator continuously outputs the center wavelengths of the FBG sensors. The influence of multiple parameters on the demodulation frequency is simulated for the traditional full wavelength range scanning demodulation method and the proposed method. An FBG sensing system for measuring vibration was established. The demodulation frequencies are 14 and 560 Hz when using these two methods, which coincide with the simulation results. The FBG sensing system can accurately measure vibration frequency below 200 Hz with a maximum error of 0.528 Hz. Thus, the proposed method significantly increases the demodulation frequency by 40 times compared to the traditional method and provides an effective approach to achieve high-speed demodulation of the FBG demodulator.