The paper develops a statistical model for the signals received in phase-sensitive optical time domain reflectometry (OTDR) probed by highly coherent sources. The backscattering process is modelled by a set of discrete scatterers with properly chosen parameters. Explicit equations for calculating the amplitude and the phase of the backscattered signal are obtained. The developed model predicts spectral and autocorrelation characteristics of the amplitude signals that are validated by experimental results. Characteristics of the phase signals, practicable for studying the sensing applications of the OTDR system, are presented and studied as well, demonstrating good correspondence with experiment. A more detailed modelling of distributed vibration sensing systems and their response to disturbances along an optical fiber will be possible as an extension of the developed formalism. Index Terms-Optical fiber devices, optical fiber sensors, Rayleigh scattering, reflectometry, time domain analysis. 0733-8724

An intermodal fiber interferometer with an optical frequency scanning light source is considered to attain two main goals: signal fading elimination and achieving a linear response to external fiber perturbations. It is demonstrated that the interferometric signal traces repeatedly generated by the laser frequency scans can be used to average the target signal by calculating their autocorrelation function. A correlation approach is studied for signal processing, and various correlation function modifications are proposed and theoretically analyzed to achieve complete signal reconstruction. In particular, the relation between the autocorrelation function and the averaged amplitude characteristic is demonstrated. The efficiency of the proposed interferometer’s scheme and the correlative signal processing are confirmed experimentally for the case of a sine-shaped fiber length modulation. We believe that the proposed method will be useful in real-time sensing applications.

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