Composite optical fiber vibration sensing system based on phi-OTDR

Abstract

The invention relates to a composite optical fiber vibration sensing system, which realizes optical fiber remote sensitivity by using a multimode optical fiber and a single-mode optical fiber as sensitive elements on the basis of taking the single-mode optical fiber as a sensing medium. According to a sensing process, high-power laser pulses are incident to the multimode optical fiber through thecirculator and then flow into the single-mode optical fiber through the mode converter, so that the sensing medium effectively prevents high-power detection pulses from directly flowing into the single-mode optical fiber to cause unstable modulation, stimulated Brillouin effect and other non-linear effects to cause insensitivity of the detection distance; in addition, insensitivity of a front endarea of the front end of the detection distance due to saturation of the photoelectric detector can be avoided, short transmission distance due to the fact that only the multimode optical fiber is used is avoided, and 30km remote sensitivity is achieved based on the composite multimode-single mode optical fiber.

Description

technical field [0001] The present invention relates to the technical field of distributed reflective sensing, in particular to a composite optical fiber vibration sensing system. Background technique [0002] Compared with other sensing technologies, distributed optical fiber sensors have the advantages of long detection distance, high sensitivity and fast response speed. Therefore, it is widely used in perimeter security, oil and gas pipeline monitoring, rail transit and many other fields, and has become an ideal non-destructive testing technology for large-scale facilities. [0003] At present, the most widely used distributed optical fiber sensing technology is mainly phase-sensitive optical time domain reflectometer, which uses the Rayleigh scattered light of the detection pulse in the optical fiber for distributed sensing. Perturbation signals are sensed by detecting the phase change of scattered light, which has been applied in distributed vibration sensing. Howev...

AI Technical Summary

Problems solved by technology

However, as the sensing distance increases, the simple single-mode fiber sensing distance is limited, resulting in insufficient sensing distance

High-power pulses will lead to an insensitive area at the front end of the detection range due to the saturation phenomenon of the photodetector; high-power pulses will also cause nonlinear effects of single-mode fiber sensing, and the detection range will appear insensitive areas, which cannot be measured Front-end disturbance signal

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