Research On The Vibration Sensing Technology Based On φ-OTDR

The research state of the φ-OTDR vibration sensing technology has been introduced in this paper, Rayleigh scattering in the optical fiber are analyzed, the interference principle of backscattering light in the optical fiber and the relationship between phase of scattering optical field and optical fiber strain have been investigated theoretically, and the relationship between Rayleigh backscattering power and phase difference of optical interference field and the relationship between phase difference of optical interference field and optical fiber strain have been derived in this article, which provides theoretical support for research of the φ-OTDR system. The system based on φ-OTDR and Mach-zehnder interferometer is used, mathematical model of vibration sensing system is founded, and phase demodulation methods have been introduced. The performances parameter of φ-OTDR and Mach-zehnder interferometer system such as spatial resolution, the sensitivity, the sensing distance, strain measurement range, frequency measurement range have been analyzed.The cause and manifestation of phase ambiguity are analyzed, and the influence of the phase ambiguity for system performance as well as the relationship between maximum detectable strain and spatial resolution have been research theoretically and demonstrated by simulation. The results shows that the phase ambiguity is the main factor which limiting the strain measurement range of the system. The phase ambiguity not only make mistakes in the measurement of vibration frequency and amplitude, but also fail to report for large strain information. Because the traditional phase unwrapping algorithm has problems such as low reliability and time-consuming, it has a poor suitability in terms of vibration sensor, two ways to improve strain maximum detection range have been proposed. The scattering curve along with the change of optical fiber strain have been obtained by simulation, the existence of phase ambiguity phenomenon is verified, analyses the system maximum detectable strain range and the spatial resolution of the constraint relationship are analyzed, and backward Rayleigh scattering curve simulation program structure is introduced. The φ- OTDR system is built preliminarily, and the noise of the system components and solution are anaylaed.