Intensity effects in Bragg grating sensors scanned by a tunable filter

The fact that the wavelength shift in fiber Bragg grating sensors is insensitive to intensity fluctuations has made them superior to other intensity-based or phase-based sensors. However, the intensity variations in the light source, the bending on lead/in-out fibers, and a tunable filter can cause signal deviations when a tunable filter scans the Bragg grating sensors. In this paper, the spectrum analysis is used in the Bragg grating sensing system for characterizing the signal deviation by intensity effects. The intensity effects are quantitatively analyzed by assuming approximate Gaussian distributions of spectra in a Bragg grating and a single-loop transmitted mode of a tunable Fabry-Perot filter in the spectrum analysis. It is concluded that the intensity effects from the light source or the macrobending on lead-in/out fibers need to be considered in high-frequency harsh environments. Thus, a cancellation method is introduced to compensate intensity variations in the Bragg grating sensing system. Experimental data shows a good agreement compared with the analytical predication in compensating intensity variations. A cancellation technique, therefore, can be effectively applied in the high-frequency harsh environments, especially in explosive tests.