System and method for distributed optical fibre sensing measurement based on Brillouin scattering

Abstract

The invention discloses a system and a method for distributed optical fibre sensing measurement based on Brillouin scattering. According to the invention, the laser of the system outputs two continuous laser lights having a wavelength difference of greater than 15 nm, and the laser lights are split into a detection light and a local oscillation light via a wave combiner and a coupler; the detection light enters sensing optical fibres via an electro-optical modulator and a circulator which are connected with a pulse signal generator, and a self-excited Brillouin scattering light is accessed into the 3 dB coupler via the circulator; and the local oscillation light is accessed into the 3 dB coupler as well, and the output of the 3 dB coupler is connected with a balance detector and a data acquisition and processing unit which stores associated programs and formulas. The measurement method comprises the following steps that: the double-wavelength detection light is modulated into a detection light pulse so as to generate self-excited Brillouin scattering in the sensing optical fibres, and subjected to coherent frequency mixing with the local oscillation light; the data acquisition and processing unit performs a frequency-sweep measurement on the difference-frequency electric signal of the balance detector so as to obtain Brillouin scattering frequency spectrums and Brillouin frequency shifts along different points of the optical fibres, and calculates to obtain the change amounts of a temperature and a strain. Via the system and the method disclosed by the invention, simultaneous measurement for the temperature and the strain is realized, and the measurement accuracy is improved.

Description

technical field [0001] The invention relates to the technical field of optical fiber sensors, in particular to a distributed optical fiber sensing measurement system and measurement method based on Brillouin scattering. Background technique [0002] The safety and health inspection of large-scale infrastructure and the timely detection of hidden failures are of great significance to disaster prevention and mitigation, ensuring the safety of people's lives and national property. Especially with the continuous construction and commissioning of high-speed railways, large-scale bridges and tunnels, oil pipelines, power communication networks, and large-scale nuclear power plants, the demand for safety and health monitoring of large-scale infrastructure continues to increase. [0003] The structural health monitoring of large-scale projects has long-distance, high-precision, and distributed requirements, and traditional detection methods and point sensors are not competent. Dist...

AI Technical Summary

Problems solved by technology

However, because the Brillouin frequency shift in the optical fiber is affected by both temperature and strain, there is a problem of cross sensitivity, that is, it is impossible to distinguish whether the frequency shift is caused by temperature or strain only by the Brillouin frequency shift, and it is difficult to realize multi-parameter Simultaneous sensing of the BOTDR limits the usefulness of

At present, there are three main methods to solve the BOTDR cross-sensitivity problem. The first method is to measure the Brillouin scattered light intensity and Brillouin frequency shift at the same time. The self-published Brillouin scattered power to be measured is weak, and the actual power in the system is always Certain fluctuations, so the measurement accuracy is not high; the second method is to use the frequency shift of multiple Brillouin peaks in special fibers (such as large effective area dispersion-shifted single-mode fibers), which requires special fibers, so the cost The third method is to distinguish temperature and strain using different physical effects, such as the method of combining Raman and spontaneous Brillouin scattering effects, which can also be called the method of combining other physical effects, and also requires the use of special optical fibers, and Combining two sets of sensing and measuring devices makes the system structure more complicated and the cost higher

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