Strain Measurement Range Extension of OFDR based on Self-correcting Two-dimensional Cross-correlation

In this study, a wide strain measurement range optical frequency domain reflectometry (OFDR) system based on self-correcting two-dimensional (2D) cross-correlation is proposed and experimentally demonstrated. Large strain events can lead to spatial mismatch caused by overstretching of the fiber, resulting in inaccurate demodulation of the cross-correlation spectrum during conventional OFDR data processing. The degradation of signal similarity due to spatial mismatch can be mitigated by creating a 2D array of reference signals in frequency domain with different positional deviations and performing a 2D cross-correlation operation with the measurement signal in frequency domain. In addition, based on the obvious trend difference between the main peak and the rest of the 2D cross-correlation result with positional deviation points, a self-correcting dictionary is constructed based on the standard deviation, which further improves the demodulation accuracy of the spectrum shift. In experiments, the strain gradient information from 1000με to 8000με is reconstructed free of outliers with a spatial resolution of 3mm located at the end of 50-m-long sensing fiber. The mean absolute error (MAE) is reduced from 14.12pm to 6.12pm, and the standard deviation is reduced from 13.09pm to 4.56pm compared to the conventional method. This novel and simple strain measurement range extension technique will provide new ideas for the development of economical, reliable, and practical large strain measurement systems.