COTDR (coherent detection based optical time-domain reflectometry) fused long-distance coherent detection brilouin optical time-domain analyzer

Abstract

The invention discloses a COTDR (coherent detection based optical time-domain reflectometry) fused long-distance coherent detection brilouin optical time-domain analyzer which comprises a narrow-linewidth laser, two couplings, a microwave signal source, an electro-optic modulator, an isolator, a long-distance sensing optical fiber, an optical circulator, a 3 db coupling, a pulse modulator, an Er-doped fiber amplifier, a scrambler, a pulse signal generator, a balancing photoelectric detector, an electrical frequency spectrum analyzer, a data processing module and an acousto-optic modulator. According to the invention, the signal-to-noise ratio of BOTDA (brilouin optical time domain analysis) is improved by using a coherent detection method, a non-local effect of a BOTDA system is reduced in a double-sideband detection mode, and the sensing distance is more than 70 km under the condition of no light amplification such as raman; and according to the invention, the COTDR is fused to a coherent detection based BOTDA system, and the system can run in a breakpoint testing mode, so that the defect that the traditional BOTDA can not run when a sensing fiber has breakpoints and can not carry out positioning on breakpoints is effectively overcome, thereby enhancing the adaptability and practicability of the sensing system.

Description

technical field [0001] The invention relates to a long-distance coherent detection Brillouin optical time domain analyzer integrated with COTDR, which is mainly used in the technical field of optical fiber sensing. Background technique [0002] In addition to high sensitivity, large dynamic range, anti-electromagnetic interference, corrosion resistance, and a wide range of measurement objects (such as temperature, strain, humidity, displacement, pressure, electromagnetic field, etc.), distributed optical fiber sensors also have the ability to combine transmission and sensing media The advantage of this is that the entire laid optical fiber can be used as a sensitive element, and because the optical fiber transmission loss is small, it can realize fully distributed measurement on the entire optical fiber length of tens or even hundreds of kilometers, which greatly reduces the cost and is widely used. Health monitoring and measurement for large civil engineering, tunnels, brid...

AI Technical Summary

Problems solved by technology

In order to increase the sensing distance of BOTDA, various methods have been proposed. Among them, BOTDA based on Raman amplification technology can obtain an effective sensing length of hundreds of kilometers, but the BOTDA system based on Raman amplification has a complex structure and introduces relative intensity noise. and other nonlinear effects, which affect the performance and measurement accuracy of the sensing system; BOTDA based on encoding technology and pre-amplification can also obtain a sensing length of hundreds of kilometers, but this method increases the complexity of the control system and subsequent data processing degree and measurement time

In addition, BOTDA requires double-ended access, which means that when a breakpoint occurs in the optical fiber link, BOTDA will not work. This is a fatal shortcoming of BOTDA, which greatly limits the application of BOTDA

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