Numerical Modeling of Fcy OTDR Sensing Using a Refractive Index Perturbation Approach

Phase-sensitive optical time domain reflectometry (ΦOTDR) is an important tool for distributed fiber sensing. In order to optimize system performance, the influence on sensing performance of factors such as laser frequency drift and variations in ambient conditions need to be understood. While theoretical models can facilitate such understanding, to the best of our knowledge there is only one numerical model for ΦOTDR dynamic sensing, focusing on one particular detection scheme. In this article we propose a simple generic model for simulating the response characteristics of static and dynamic ΦOTDR systems. In the model, the sensing fiber is treated as a unidimensional waveguide, consisting of inhomogeneities with randomly generated refractive indices. Environmental perturbations are represented by modulations in the refractive index profile that produce equivalent phase shifts. The model is applied in the simulation of a ΦOTDR sensor for static measurements and the simulation of two different dynamic ΦOTDR sensor configurations. The model is used to analyze the experimentally observed phase drift in a ΦOTDR sensor, the model confirmed that observed drift was consistent with expected variations in the ambient temperature and laser frequency drift.