Self-heterodyne φ-otdr system with free multi-spatial resolution

Abstract

The invention discloses a self-heterodyne φ-OTDR system with free multi-spatial resolution, characterized in that the φ-OTDR system includes a narrow linewidth laser source, a 1×3 coupler, three acousto-optic Modulator, 3×1 coupler, two delay fibers, erbium-doped fiber amplifier, circulator, photodetector, electric amplifier, three filters, digital acquisition card, pulse signal generator and drive module. The present invention uses multiple acousto-optic modulators with the same drive to couple the detection lights with different pulse intervals and different frequency shifts and then inject them into the optical fiber, thereby realizing a self-heterodyne and multi-spatial resolution detection structure, which can effectively suppress coherent fading noise , Optical background noise such as phase noise introduced by frequency drift of the light source, PRN, etc., and solve the problem of spatial resolution matching.

Description

technical field [0001] The invention relates to the technical field of distributed optical fiber sensing, in particular to a self-heterodyne φ-OTDR system with free multi-spatial resolution. Background technique [0002] Distributed Optical Fiber Sensor (DOFS) uses the entire optical fiber as the sensing medium and sensing unit of the signal, which can continuously measure the parameter changes along the optical fiber in real time. It has anti-electromagnetic interference, high sensitivity, high temperature and high pressure resistance, etc. Advantages, it is very suitable for structural health detection of large-scale and long-distance large-scale infrastructure, and is more and more widely used in infrastructure and fields such as power cables, tunnels, oil and gas pipelines, and perimeter security. [0003] Currently, (phase-sensitive Optical Time Domain Reflectometry) is the most mature and widely used distributed optical fiber sensing technology based on Rayleigh back...

AI Technical Summary

Problems solved by technology

[0005] However, since the position and reflectivity of the Rayleigh scattering points are random, the phase and amplitude of the RBS are also randomly distributed, so the coherent fading effect will occur during the superposition of the RBS, resulting in a detection dead zone and reducing the sensing System Detection Performance

In addition, the frequency drift of the laser and the polarization state of the reference light will introduce phase noise and optical background noise such as PRN to the system, which will reduce the signal-to-noise ratio of the sensing system and limit the application of distributed optical fiber vibration sensors.

Secondly, the spatial resolution is one of the important indicators of the distributed optical fiber vibration sensing system, but in practical applications, the length of action of the vibration signal cannot be predicted in advance, and too low or too high spatial resolution will reduce the signal-to-noise ratio of the system. Affects the overall performance of the sensing device

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