Research on the Conversion Coefficient in Coherent Φ-OTDR and Its Intrinsic Impact on Localization Accuracy

Abstract

Phase-sensitive optical time domain reflectometry (Φ-OTDR) plays a crucial role in localizing and monitoring seismic waves, underwater structures, etc. Accurate localization of external perturbations along the fiber is essential for addressing these challenges effectively. The conversion coefficient, which links the detected phase signal to the perturbation signal on the fiber, has a significant impact on localization accuracy. This makes the characteristic of parameters relative to the conversion coefficient in Φ-OTDR a subject of deep research. Based on the coherent Φ-OTDR mathematical model, parameters like the modulus, the statistical phase, the phase change, and the peak difference are analyzed with and without the static region, respectively. When perturbations are homogeneously distributed along the fiber, the absence of static region on the phase change-fiber length plane leads to a nonlinear phase change relationship. This deviation from the expected linear relationship in the presence of static region means that the static region is essential for higher localization accuracy. The absence of static region results in a standard deviation of 0.042263 m for the localization deviation value, which could be theoretically reduced by a new sensor design with a static region. These findings underscore the importance of the conversion coefficient and the relevance of the static region in Φ-OTDR to achieving accurate and effective localization.