A Fiber Bragg Grating Vibration Interrogation System Based on a Cascaded Long-Period Fiber Grating

A fiber Bragg grating (FBG) vibration interrogation system based on a cascaded long-period fiber grating (CLPG) was designed and demonstrated in this article. The light of broad optical source was reflected by the FBG, and then the reflected light entered the CLPG. The intensity of reflected light of the FBG after being modulated by the CLPG would change, so the static and dynamic signal monitoring of the FBG was realized by detecting the transmission power at the resonant wavelength of the FBG. The interrogation system was calibrated by temperature-measuring experiment firstly, and then the FBG was mounted on the surface of an aluminium specimen to interrogate the vibration signal. The acquired vibration signal and its fast Fourier transform (FFT) by the experiments are analysed and agree with the signal of an eddy current displacement gauge. Experimental results have proved that the interrogation system has a good performance on the measurement of vibration. It is hopeful that the FBG wavelength demodulation based on a CLPG is used to monitor more than 1 KHz dynamic signal.