Phase Demodulation Of Rayleigh Scattering Light In The Fiber

Due to the inhomogeneity of the fiber, Rayleigh scattering takes place during the transmission of light waves in optical fiber. Distributed optical fiber sensing (DAS) technology based on Rayleigh scattering has played an important role in fields like perimeter security, pipelines, such as high-speed structural safety and health monitoring. As a new type of DAS system, phase-sensitive optical time-domain reflectometry (Φ-OTDR) based on the phase demodulation has become a hotspot owing to the applications in the petroleum exploration and geological structure analysis.In this paper, by introducing a new way of phase demodulation is introduced in Φ-OTDR using 90° hybrid, and the distributed acoustic sensor based on the phase demodulation of the Rayleigh scattering light is demonstrated. The work is summarized as follows:1. This paper introduces the theories of Rayleigh scattering in the fiber, and Φ-OTDR.2. Phase demodulation of Rayleigh scattering light on the 90° hybrid is proposed in this paper, and the demodulation principle is introduced.3. Distributed acoustic sensor based on the new phase demodulation using heterodyne detection is demonstrated in the paper.4. Distributed acoustic sensor based on the new phase demodulation using homodyne detection is demonstrated in the paper.5. This article compares the phase demodulation scheme based on 90° optical hybrid and other several existing phase demodulation schemes. It is concluded that the phase demodulation based on 90° optical hybrid owns several advantages such as stability, high real-time performance, and high sensitivity.