High sensitivity distributed static strain sensing based on all grating optical fiber in optical frequency domain reflectometry

We present a distributed high sensitivity static strain sensing method based on all grating optical fiber in optical frequency domain reflectometry (OFDR).Through the use of all grating optical fiber, the backscattered light can be greatly improved, which increases the signal-to-noise ratio. A higher signal-to-noise ratio can help to obtain more accurate distance domain information, thereby obtaining better segmented optical frequency domain information for cross-correlation. Therefore, in the same cross-correlation method, our system obtains even larger range of FUT information due to the signal with higher signal-to-noise ratio. Using this system, we measured the change of strain at the end of a total 200 m FUT. The minimum measurable strain variation is 5 με and the spatial resolution of the system is 10cm. It should be noted that we use interpolation zero padding method on the basis of cross-correlation to obtain higher strain accuracy. In addition, we verified the stability of the system by fitting the results of different strains. The linearity of the fitting results is extremely high, and the R-square can reach more than 0.9. Compared with the OFDR system using the single mode fiber, the OFDR system using all grating optical fiber can provide a better sensing performance of measuring a minor strain variation under the same sensing spatial resolution. This is of great significance for the improvement of OFDR measurement applications.