Dual-Wavelength Differential Cross Multiplication Method for Dynamic Cavity Length Interrogation of Fiber-Optic Fabry-Perot Vibration Sensors

A new dual wavelength differential cross multiplication (DWDCM) method for the large range dynamic cavity length demodulation of fiber-optic Fabry-Perot (FP) vibration sensors was proposed. A DWDCM demodulation system based on the combination using of a wideband light source and two fiber Bragg gratings (FBGs) was proposed and a DWDCM algorithm was accordingly given. The method firstly filters out two optical signals with different wavelengths by the using of two FBGs and normalizes them, then synthesizes the two signals by differential cross multiplication to generate a synthetic signal with a rather large synthetic wavelength, based on which, the cavity length demodulation range can be significantly expanded. Experiment for a 161.12-µm FP cavity by the using of two optical wavelengths 1553 and 1547 nm shows a good resolution of 6.3 nm for a vibration amplitude of 5.5 µm. The DWDCM method shows advantages of large dynamic demodulation range, high demodulation accuracy, and fast demodulation rate.