Optical vibration sensor using FBG Fabry-Perot interferometer with wavelength scanning and Fourier analysis

An in-fiber Fabry-Perot interferometer with fiber Bragg grating mirrors (FBG-FPI) yields extremely narrow transmission peaks within the FBG reflection wavelength range. Periodical scanning of the laser light source wavelength produces a train of optical pulses and the occurrence time of the pulse is modulated as the FBG-FPI is under influence of strain. When dynamic strain due to mechanical vibration is applied to the FBG-FPI, the detected signal of the pulse train is Fourier transformed and processed to reproduce the waveform of the vibration-induced strain. A high signal-to-noise ratio interrogation is possible with high resolution and a wide range of vibration frequency can be analyzed since the laser wavelength can be easily scanned at high frequency. Furthermore, an inexpensive DFB laser can be utilized as a light source because the narrowness of the transmission peaks does not require broad wavelength scanning.