CN104165644B - The pinpoint Brillouin's distributed optical fiber sensing method of testing of a kind of energy - Google Patents

Abstract

The invention provides a Brillouin fully distributed optical fiber sensing testing method capable of precise positioning, and relates to the technical field of distributed sensors or methods. It connects fiber gratings in series at key positions on the sensing fiber, and uses the characteristics of the same direction and large difference in optical power between the back reflected light of the fiber grating and the back Brillouin scattered light to obtain the reflection events of the fiber grating; The reflection peak of the fiber grating in the Liouin scattered light spectrum is used as a positioning indicator tool to determine the position of the grating, and then accurately determine the spatial position of the structural information mutation event through the relative position of the structural information mutation event and the grating position, so as to realize the fully distributed Precise positioning for Brillouin sensing tests. The invention can realize the precise positioning of the structural mutation position, has scientific principle and simple application, and can be practically applied in the field of optical fiber sensing and testing.

Description

A Brillouin Fully Distributed Optical Fiber Sensing Test Method Capable of Accurate Positioning

technical field

The invention relates to the technical field of distributed sensors or methods.

Background technique

In the multi-sensor information fusion system, both centralized and distributed structures are often used. In the centralized data fusion structure, the sensor information is directly sent to the data fusion center for processing, which has the advantage of small information loss, but the data interconnection is complicated, the reliability is poor, and the requirements for computing and communication resources are also high. In the distributed fusion structure, each sensor can process its own information independently, and then send each decision result to the data fusion center for fusion. With the rapid development and maturity of communication technology, embedded computing technology and sensor technology, micro sensors with perception, computing and communication capabilities have begun to be applied. Distributed Sensor Network (Distributed Sensor Network, DSN) has become an important research field in recent years.

Brillouin fully distributed sensing is to use the Brillouin scattered light generated by the interaction of phonons and light wave systems in optical fibers to realize fully distributed measurement of structures. Optical fiber Brillouin sensing has the advantages of full-scale continuity, long distance, large capacity, low cost, intelligent network, anti-electromagnetic interference, small size, and light weight. It is currently a promising optical fiber sensing testing technology. It will have broad application prospects in the field of optical fiber sensing and testing.

In Brillouin fully distributed sensing technology, the most important technology is Brillouin Time Domain Analysis Technology (BOTDA). This technology obtains the spatial distance of the optical fiber by measuring the optical power of the backscattered Rayleigh light in the optical fiber and the time it takes from the transmitted signal to the returned signal. Long-distance and full distribution are the outstanding advantages of the Brillouin sensing test method. However, due to the sensitivity of the optical fiber to temperature and strain, the length of the optical fiber changes with the temperature, strain or other external parameters. The spatial position data obtained by the test method will also change, resulting in the same position of the structure under different environments, the test position data is indeed quite different, resulting in the inability to accurately locate the structural mutation event. Due to the inability to realize the precise positioning of structural mutations, it seriously affects its application in the field of optical fiber sensing. Therefore, there is an urgent need for a positioning method that can realize Brillouin fully distributed sensing testing.

Regarding the method of optical fiber positioning, the general method in the world is: by setting a section of optical fiber in the optical fiber line that does not change with external information such as ambient temperature and strain, and obtaining the position of the optical fiber before and after the change by comparing the Brillouin spectrum, and then Determine the location of the structural mutation. However, this method is used in engineering applications due to: Strict requirements on the environment; It is impossible to determine the size of the length change, so the Brillouin spectrum comparison is complicated and difficult; For large-scale engineering structures, due to the large range of fiber deployment and the change of fiber length in different parts, it is necessary to lay a large number of comparison fiber segments, which is even more difficult for engineering applications. Therefore, this positioning method is difficult to apply to engineering practice. Up to now, no method has been found to realize the precise positioning of the mutation position of the Brillouin fully distributed sensing test structure, which seriously affects the application of the Brillouin fully distributed sensing in the field of optical fiber sensing and testing. The above-mentioned defects or deficiencies have become a technical problem that people have always wanted to solve but have not been resolved for a long time.

Contents of the invention

The technical problem solved by the present invention is to provide a Brillouin fully distributed optical fiber sensing test method capable of precise positioning, which uses the reflected light through the fiber grating as the spatial position indicator, and use the invariance principle of fiber grating and structural information mutation event space position to realize the precise positioning of the structure. This method can realize the precise positioning of the structural mutation position, and the principle is scientific and easy to use. practical application in the field.

The technical solution of the present invention is: a Brillouin fully distributed optical fiber sensing test method capable of precise positioning, which is characterized in that: a fiber grating is connected in series at a key position on the sensing fiber, and the backreflected light of the fiber grating is used Obtain the reflection event of the fiber grating due to the characteristics of the same direction as the back Brillouin scattered light and a large difference in optical power; by testing the reflection peak of the fiber Bragg grating in the Brillouin scattered light spectrum as a positioning indicator tool, the position of the grating can be determined , and then accurately determine the spatial position of the structural information mutation event through the relative position of the structural information mutation event and the grating position, so as to realize the precise positioning of the fully distributed Brillouin sensing test;

Preferably, at least 2 fiber gratings are connected in series at a certain length interval at a key position on the sensing fiber (one can also be positioned, but it is best to set at least two so that there are references when measuring), including fiber grating 1 and fiber grating 2. When the external environment such as temperature and strain changes, the spatial position of the Brillouin test of the fiber Bragg grating 1 changes from L1 to L2; the spatial position of the fiber Bragg grating 2 test changes from L3 to L4 ; At this time, if there is an information mutation event in the structure, the spatial position that passes the Brillouin time domain test is L6, and if the external environment does not change, the original position is L5, using the principle of invariance of the distance between the grating and the structural information mutation position before and after the change , L6-L2 or L4-L6 is the relative position to the fiber grating, that is, through the position data of the fiber grating before and after the environmental change, the spatial relative position of the structural mutation event can be accurately measured, and the fully distributed sensing can be used to measure the structural strain or other The precise positioning of the fully distributed Brillouin sensing test is realized while measuring the physical parameters.

Preferably, the selection of the wavelength of the fiber grating avoids using a grating with the same wavelength as that of the BOTDA light source; at the same time, the wavelength of the fiber grating is not too far from the wavelength of the BOTDA light source.

Preferably, the reflectivity of the optical fiber grating is selected such that the reflected optical power of the grating does not exceed the upper limit of the detected optical power of the BOTDA test instrument.

Preferably, the fiber grating uses a single-mode fiber.

Preferably, the single-mode optical fiber uses a Bragg grating. Other types of gratings can also be used, aiming to obtain a sharp reflection spectrum.

Preferably, the fiber grating layout interval should be such that the change in the length of the fiber in the fiber grating layout is smaller than the positioning accuracy.

The positioning principle of the fiber Bragg grating of the present invention is: using the characteristics that the direction of the fiber Bragg grating (FBG) back reflection light is the same as that of the back Brillouin scattered light and the optical power is large, the reflection event of the fiber Bragg grating can be clearly obtained, and the test layout The optical power of the fiber grating reflection peak in the Rieouin scattered light spectrum realizes the determination of the grating position, and the spatial position of the structural information mutation event is precisely determined by the relative position of the structural information mutation event and the grating position.

The positive effect of the present invention is: the present invention solves the technical problem that people have been trying to solve for a long time but has not been solved well, can realize the precise positioning of the structural mutation position, and has a scientific principle, easy to use, simple and convenient layout, and can The implementation of the application in the project can make the Brillouin fully distributed sensing test actually applied in the field of optical fiber sensing test, effectively solving the technical problem that people have been trying to solve for a long time but have not been able to solve.

The following will be further described in detail in conjunction with the embodiments and accompanying drawings, but not as a limitation to the present invention.

Description of drawings

Fig. 1 is a schematic diagram of the positioning principle of the fiber grating in the method of the present invention.

Fig. 2 is a structural diagram of a sensing fiber with a fiber grating applied in the method of the present invention.

Fig. 3 is the Brillouin loss power spectrum of the fiber grating at different temperatures by the method of the present invention.

Figures 4 to 6 are comparison diagrams of positioning data of the present invention at different temperatures and different test spatial resolutions, wherein:

Fig. 4 is the spatial positioning data map of the present invention at different temperatures [(a) 5.1°C, (b) 25.8°C, (c) 45.8°C] and 20cm test spatial resolution;

Fig. 5 is the spatial positioning data map of the present invention at different temperatures [(a) 5.1°C, (b) 25.8°C, (c) 45.8°C] and 50cm test spatial resolution;

Fig. 6 is a map of spatial positioning data of the present invention at different temperatures [(a) 5.1°C, (b) 25.8°C, (c) 45.8°C] and 100cm test spatial resolution.

detailed description

Example 1:

See Figures 1 to 6. This Brillouin fully distributed optical fiber sensing test method capable of precise positioning is characterized in that: a fiber grating is connected in series at a key position on the sensing fiber as a position indicator, and the optical fiber grating is used to reflect the light backward and backward The Brillouin scattered light has the same direction and large difference in optical power to obtain the reflection events of the fiber Bragg grating; the position of the grating can be determined by testing the reflection peak of the fiber Bragg grating in the Brillouin scattered light spectrum, and then through the structural information mutation event and the grating The relative position of the position precisely determines the spatial position of the structural information mutation event, thus enabling the precise positioning of the fully distributed Brillouin sensing test. The selection of the wavelength of the optical fiber grating avoids using the grating with the same wavelength as the BOTDA light source; at the same time, the wavelength of the optical fiber grating is not too far from the wavelength of the BOTDA light source. The reflectivity of the optical fiber grating is selected so that the reflected light of the grating does not exceed the upper limit of the detection light power of the BOTDA test instrument. The fiber grating uses single-mode fiber. The single-mode optical fiber uses a Bragg grating.

The specific method is: the fiber grating at least includes a fiber grating 1 and a fiber grating 2, the spatial position of the Brillouin test of the fiber grating 1 changes from L1 to L2; the spatial position of the test of the fiber grating 2 Change from L3 to L4; at this time, if there is an information mutation event in the structure, the spatial position that passes the Brillouin time-domain test is L6. If the external environment does not change, the original position is L5. Use the grating and structural information before and after the mutation position changes The principle of invariance of distance, L6-L2 or L4-L6 is the relative position to the fiber grating, that is, through the position data of the grating before and after the environmental change, the spatial relative position of the structural mutation event can be accurately measured (as shown in Figure 1), which can realize Fully distributed sensing measures the structural strain (temperature) or other physical parameters while realizing the precise positioning of the fully distributed Brillouin sensing test.

In order to ensure the feasibility of the experiment to verify the positioning of FBGs, a sensing fiber with FBGs was fabricated. The fiber string contains three gratings. The performance parameters are shown in Table 1 below.

surface Fiber Bragg Grating Performance Parameters

wavelength(nm) Reflectivity(%) Bandwidth (nm) Grating interval (m) 1514.80, 1519.79, 1524.8 90.98,90.68,89.50 0.22,0.23,0.22 8.015,8.01m

It can be seen from Table 2 and Figure 3 that when the temperature changes by 40°C, the position of the grating changes by about 30cm, which indicates that the ambient temperature of the 1km optical fiber changes by 40°C and the length changes by 30cm. In engineering applications, the length of the optical fiber is generally tens of kilometers, and the length changes by tens of meters when the environment changes by 40°C. At the same time, different optical fiber lengths vary in length, and the changing length has a lot to do with the protective layer outside the optical fiber. Different optical fiber protective layers have different length changes, which also brings great impact on engineering applications. challenge. From the perspective of the relative position of the grating and the grating, it remains basically unchanged. Compared with the grating interval measured by the ruler, the positioning accuracy is about 4cm.

The spatial position changes of the fiber gratings tested at different temperatures are shown in Table 2 and Figure 3 below. It can be clearly seen from Figure 3 that there are three peaks, corresponding to three gratings. As the ambient temperature increases, the spatial position of the grating (the test result of BOTDA) gradually becomes larger.

surface Fiber Bragg Grating Spatial Positioning Data

From Figure 4 to Figure 6, it can be seen that the positioning error of the positioning data at different temperatures and different test spatial resolutions is about 10cm, and the positioning error has basically no relationship with temperature and spatial resolution. This means that the positioning error of this method will not change much if measured with a larger spatial resolution.

Suppose the external input signal is z. , The sensor output signal y. input to the local detector. Local detectors according to y. As a result, the local decision u is made using the corresponding decision criterion, and the data fusion center takes the received decision u of each local detector as its observation value. Since the observations of each sensor are statistically independent, and assuming that there is no data interaction between the local detectors, the local decisions are also statistically independent. According to the classical reasoning theory, the fusion center can obtain a joint probability density function based on multi-sensor decision-making, and then make the final decision u according to certain criteria. That is, a distributed multi-sensor system includes a series of sensor nodes and corresponding processing units, as well as a communication network connecting different processing units. Each processing unit is connected to one or more sensors, and the data is transmitted from the sensor to the processing unit connected to it, and data integration is performed at the processing unit. Finally, the processing units are fused with each other to obtain the best evaluation of the environment. Since the Brillouin fully distributed sensing test can accurately locate the position of each structural mutation, it is also accurate to integrate the final processing units to obtain the best evaluation of the environment.

The invention is not only applicable to the BOTDA fully distributed optical fiber sensing test method, but also can serve as a reference for other fully distributed sensing test methods.

The method of the invention can be applied not only in the field of optical fiber sensing, but also in occasions requiring precise positioning in the field of communication.

All deformations, replacements, etc. based on the principles of the method of the present invention fall within the scope of the protection law of the present invention.

Claims (6)

1. A Brillouin fully distributed optical fiber sensing test method capable of precise positioning is characterized in that: a fiber grating is connected in series at a key position on the sensing fiber, and a fiber grating is used to reflect back light and backward Brilliant grating The Brillouin scattered light has the same direction and large difference in optical power to obtain the reflection events of the fiber grating; the position of the grating can be determined by testing the reflection peak of the fiber grating in the Brillouin scattered light spectrum, and then through the structural information mutation event and the grating position The relative position of the structure information can accurately determine the spatial position of the mutation event, and realize the precise positioning of the fully distributed Brillouin sensing test; At least two fiber gratings are connected in series at a certain length interval at a key position on the sensing fiber, including fiber grating 1 and fiber grating 2. When the external environment changes, the space for the Brillouin test of the fiber grating 1 The position changes from L1 to L2; the test spatial position of the fiber grating 2 changes from L3 to L4; at this time, if there is an information mutation event in the structure, the spatial position passed through the Brillouin time domain test is L6, if the external environment does not change, the original position is L5, using the principle of invariance of the distance between the grating and the structural information before and after the sudden change, L6 - L 2 or L4 - L6 is the relative position to the fiber grating, that is, the position before and after the environment changes through the fiber grating Data, accurately measure the spatial relative position of the structural mutation event, realize the fully distributed sensing measurement of structural strain or other physical parameters, and realize the precise positioning of the fully distributed Brillouin sensing test. 2. a kind of Brillouin fully distributed optical fiber sensing testing method capable of precise positioning according to claim 1, is characterized in that: the wavelength selection of described fiber grating avoids using the grating of identical wavelength with BOTDA light source; Simultaneously , the wavelength of the fiber grating is not too far from the wavelength of the BOTDA light source. 3. A kind of Brillouin fully distributed optical fiber sensing test method capable of precise positioning according to claim 1, characterized in that: the reflectivity selection of the fiber grating makes the reflected light power of the grating no more than the BOTDA test The upper limit of the detection optical power of the instrument. 4. A Brillouin fully distributed optical fiber sensing testing method capable of precise positioning according to claim 1, characterized in that: said optical fiber grating uses a single-mode optical fiber. 5. A Brillouin fully distributed optical fiber sensing testing method capable of precise positioning according to claim 4, characterized in that: said single-mode optical fiber uses a Bragg grating. 6. A Brillouin fully distributed optical fiber sensing testing method capable of precise positioning according to claim 1, characterized in that: the fiber grating layout interval and the change in the length of the intermediate fiber between the fiber gratings is less than the positioning accuracy.