Extension of the measurable strain range in OFDR using overlapping and averaging method

Optical Frequency Domain Reflectometry (OFDR) has been widely used for many applications thanks to its high strain accuracy and high spatial resolution. In OFDR, cross-correlation between reference and measured Rayleigh Scattering Spectrum (RSS) is calculated, and strain is obtained from the peak shift of the cross-correlation. As strain increases, the similarity between reference and measured RSS is degraded and correct calculation of the peak shift is consequently difficult. In this paper, to avoid such misdetection of correlation peak, we propose an algorithm that suppresses undesired correlation coefficients. In this method, multiple cross-correlation functions are calculated for overlapped sub windows. The peak shift of the correlation is calculated based on the averaged value of the cross-correlation functions over all sub windows. Despite simple calculation, the ratio between true peak and undesired correlation coefficients is improved. In our experiments, the measurable range could be extended from 2,500 με to 4,500 με under the condition with a spatial resolution of 5 centimeters and a wavelength sweep range of 8 nano meters. To the best of our knowledge, this is the first time that the extension of the measurable strain range by using overlapping approach.