High Accuracy Distributed Static Strain Sensing Based on Relative Phase Method With Cyclic Shift and Wavelet Denoising in OFDR

In this paper, the cyclic shift method is provided to solve the phase wrapping problem of relative phase due to the initial wavelength error by a pure theoretical algorithm in optical frequency domain reflectometry (OFDR) system. The method reduces the experimental equipment requirements and can be extended to all the system uses relative phase demodulation system. The Hilbert-Euclidean distance substitution method is presented to solve the phase wrapping problem in the strain area with complete preservation of all phase information. What's more, the wavelet denoising two-dimensional weighted relative phase map is proposed, which is able to measure the strain with the spatial resolution of 9.07 mm, the accuracy of 0.5 μϵ and the maximum error of 0.225 μϵ in the range of 36 m, based on eight measurements. This method has lower error than the cross-correlation method and the relative phase averaging method, and it can make full use of multiple sets of relative phase information in every point, which solves the problem of high spatial resolution and high accuracy static strain measurement in the medium measurement distance.