Fast Strain Measurement in OFDR With the Joint Algorithm of Wavelength Domain Differential Accumulation and Local Cross-Correlation

A joint algorithm of wavelength domain differential accumulation (WDDA) and local cross-correlation is proposed in an optical frequency domain reflectometry (OFDR) for fast strain measurement along the sensing fiber. Among this, the WDDA is used to realize rapid strain positioning first, then the local cross-correlation is operated to the strain region only for fast strain computation. Thus, the processing time is substantially decreased. The mathematical principle of WDDA is theoretically derived and verified by numerical simulation. Meanwhile, the time complexity of WDDA is demonstrated to be reduced from O(
nlogn
) to O(
n
) by theoretical analysis and experimental verification, compared with the traditional whole-region cross correlation. Experiments are carried out to verify the effectiveness of this method. In experiments, we exerted the same strain region over 10.6, 35.0, 63.5, and 113.3 m long fibers. The strain greater than 10 μϵ can be identified by the WDDA. Compared with the traditional cross-correlation method in OFDR, the processing speed is increased by 5.3, 6.1, 6.3 and 6.4 times, respectively.