A new designed FBG and Φ-OTDR hybrid system for vibration and temperature sensing

We have proposed and experimentally demonstrated a distributed vibration and temperature sensing system based on the hybrid of phase-sensitive optical time domain reflectometry (Φ-OTDR) and fiber Bragg grating (FBG). An interrogation technique has been proposed by treating the low reflectivity Gaussian-shaped FBGs pair as an edge filter that linearly translates the wavelength shift into reflection intensity variation. Closely spaced identical low reflectivity Gaussian-shaped FBGs was embedded into the sensing fiber, so that the same narrow line-width laser used in Φ-OTDR could be employed to pump the FGBs. The experimental results have shown that this designed hybrid sensing system could realize fully distributed vibration sensing along a 20.4km long fiber with 10m spatial resolution, and the perturbation events of 81 Hz can be obviously distinguished with a remarkable signal-to-noise ratio (SNR) of 7.5dB. And multipoint temperature sensing could be obtained at the same time with a resolution superior to 0.12°C.