The Development of an $\Phi $ -OTDR System for Quantitative Vibration Measurement

Phase sensitive optical time domain reflectometry is suitable for vibration detection due to its high sensitivity. However, for conventional amplitude-measuring method, the strain-amplitude relation is nonlinear and the monotonic interval of strain-amplitude transfer function is very small (corresponding to less than $2\pi $ phase shift in light duration). Thus, the vibration detection is qualitative and it is difficult to distinguish different kinds of vibrations. In this letter, a quantitative vibration measurement by analyzing the differential phase in the interrogated fiber separation is proposed. A statistics calculating method is present to suppress the uncertainty in phase-measuring. Dynamic strain of 400 $\text{n}\varepsilon $ (peak-to-peak, corresponding to phase shift of 17 rad) was reproduced with high quality by proposed method.