High Sensitivity Distributed Static Strain Sensing Based on Differential Relative Phase in Optical Frequency Domain Reflectometry

We present a novel distributed high sensitivity static strain sensing method based on differential relative phase in optical frequency domain reflectometry (OFDR). By performing two separate tests of the measurement and the reference states, distributed strain sensing can be achieved by acquiring differential relative phase between these two states, which can reduce common-mode residual nonlinear phase in OFDR greatly and favor phase unwrapping, thanks to decreasing wrapped phase change rate as a function of the length of fiber under test (FUT). In addition, an all grating optical fiber that has a stronger backscattering than that of a standard single-mode fiber is used as FUT in the presented OFDR system. In the experiment, the measurement range of static strain variation is 0 to 25 μϵ, the sensing spatial resolution is 4.35 cm, and the minimum measurable strain variation is 0.25 μϵ along with a total 36 m FUT. Compared with the widely-used Rayleigh backscattering spectra shift cross-correlation method using the same data, the presented method can provide a better sensing performance of measuring a minor strain variation under the same sensing spatial resolution.