Coefficient compensation device and method for correcting Brillouin gain spectrum distortion of BOTDA

Abstract

The invention relates to the technical field of optical fiber sensing, and provides a coefficient compensation device and method for correcting Brillouin gain spectrum distortion of a BOTDA (Brillouin Optical Time Domain Analysis). The compensation device comprises a laser and a coupler, the probe light branch optical path emits probe light into the sensing optical fiber, the pump branch optical path emits pump light into the sensing optical fiber, a stimulated Brillouin scattering effect is generated in the sensing optical fiber, and a probe light signal carrying Brillouin scattering information is obtained; the optical fiber Bragg grating filters an incoming detection light signal to obtain a first single side band signal; the detector converts the first single side band signal into a Brillouin scattering signal and inputs the Brillouin scattering signal into the processing module; the industrial personal computer is used for acquiring power fluctuation characteristics of the probe light under different frequencies when the coefficient compensation device does not generate the stimulated Brillouin scattering effect so as to calculate a compensation coefficient; and when the stimulated Brillouin scattering effect occurs, compensating the Brillouin scattering signal output by the detector by using the compensation coefficient to obtain the compensated Brillouin scattering signal.

Description

Technical Field

[0001] The present invention relates to the field of fiber optic sensing technology, and in particular, to a coefficient compensation device and method for correcting the distortion of Brillouin gain spectrum in BOTDA. Background Art

[0002] The statements in this section merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] With its superior characteristics such as anti-electromagnetic interference, anti-radiation, small size, light weight, high sensitivity, and long-distance transmission ability, fiber optic sensing technology has been widely used in the field of structural health monitoring of large-scale infrastructure, such as key engineering facilities like submarine optical cables, roads, bridges, tunnels, and aircraft. Among them, Brillouin optical time domain analysis (BOTDA) based on stimulated Brillouin scattering (SBS) is one of the most representative solutions in distributed fiber optic sensing technology. Compared with other fiber optic sensing technologies, BOTDA has the advantages of long sensing distance, high signal gain, and high measurement accuracy, making it of important application value in the fields of large-scale, long-distance, and high-precision sensing.

[0004] In a BOTDA system, a high-power pulsed pump light and a continuous probe light are transmitted in opposite directions in the sensing fiber. In the probe light optical path, different frequency radio frequency signals are sent by a microwave source (MWG) to apply modulation signals to an electro-optic modulator (EOM), so as to achieve the output of different frequency suppressed carrier double-sideband modulation signals. When the frequency difference between the two is close to the Brillouin frequency shift (BFS) of the fiber, SBS occurs, resulting in the transfer of energy between the probe light and the pump light, and forming the maximum gain when the frequency difference is equal to the BFS. By detecting the Brillouin scattering signal, the Brillouin gain spectrum (BGS) distributed along the entire fiber can be obtained. Through fitting and analyzing the BGS, the distributed measurement of temperature and strain can be realized. However, factors such as the symmetry, line width, and signal-to-noise ratio of the measured BGS have a significant impact on the measurement accuracy.

[0005] Signal processing methods can improve the tolerance to BGS distortion to a certain extent. For example, the following several existing technologies: (1) Using algorithms such as anisotropy to reduce system noise, suppress noise, and improve BGS, so as to improve the fitting accuracy of BFS and measurement stability; (2) For the change of the pump pulse light energy along the sensor optical fiber caused by Brillouin scattering, based on the energy exchange relationship between the pulse and the continuous light with position change, the integral method is used to restore the pulse energy change, so as to correct the system error caused by Brillouin gain; (3) For the problem of BGS distortion caused by the non-local effect in BOTDA, after modeling the non-local effect BGS distortion, a correction method based on deep learning is used for correction; However, these methods cannot eliminate the BGS distortion problem caused by hardware.

[0006] Generally, bench-top microwave sources have high performance. However, in a small integrated BOTDA system, the commonly used small microwave sources have the problem of unstable radio frequency signal power. Moreover, the electro-optic modulator (EOM) is easily affected by the stability of the bias voltage such as the environment, resulting in the drift of its operating point and further affecting the output probe optical signal power. In addition, the power of the actual Fiber Bragg Grating (FBG) is not completely flat within the 3dB bandwidth, and there are also differences in the flatness between different FBGs. The limited bandwidth of the microwave module, electro-optic modulator, and optical FBG filter will also affect the detected optical power value. The above factors will cause the detected optical power to be unstable during the frequency sweep process, thus triggering BGS spectral distortion and ultimately affecting the fitting accuracy of BFS. In BOTDA, since the Brillouin scattering signal is in the same propagation direction as the probe light, it will cause BGS distortion and ultimately affect the measurement accuracy of BFS. Therefore, during the frequency sweep process, the stability of the detected optical power is crucial for the accuracy of the BOTDA system. Summary of the Invention

[0007] In order to solve the problem of BGS distortion caused by the fluctuation of the detected optical power caused by non-ideal devices in the BOTDA system, the present invention provides a coefficient compensation device and method for correcting the Brillouin gain spectrum distortion of BOTDA. When the SBS effect does not occur in the device, the compensation coefficient is calculated; when the SBS effect occurs, the Brillouin gain spectrum is compensated by the compensation coefficient, so as to reduce the influence of power fluctuation on BFS fitting. The present invention does not require additional modification of the hardware and can directly improve the measurement accuracy of the existing BOTDA system.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a coefficient compensation device for correcting the Brillouin gain spectrum distortion of BOTDA.

[0009] A coefficient compensation device for correcting the Brillouin gain spectrum distortion of BOTDA includes: a laser, a coupler, a probe light branch optical path, a pump branch optical path, a sensing optical fiber, a fiber Bragg grating, a detector, and an industrial control computer; The continuous light generated by the laser generates the detection light and the pump light through the coupler; The detection light branch optical path injects the detection light into the sensing optical fiber, and the pump branch optical path injects the pump light into the sensing optical fiber, and a stimulated Brillouin scattering effect occurs in the sensing optical fiber, thereby obtaining a detection light signal carrying Brillouin scattering information; The fiber Bragg grating filters the incoming detection light signal to obtain a first single-sideband signal; The detector converts the first single sideband signal into a Brillouin scattering signal and inputs the signal into a processing module; The industrial computer is used to obtain the detection light power fluctuation characteristics at different frequencies to calculate the compensation coefficient when the stimulated Brillouin scattering effect does not occur in the coefficient compensation device; when the stimulated Brillouin scattering effect occurs, the compensation coefficient is used to compensate the Brillouin scattering signal output by the detector to obtain the compensated Brillouin scattering signal.

[0010] Furthermore, the detection light branch optical path includes an electro-optic modulator, a microwave source and an optical isolator. The microwave source applies a modulation signal to the electro-optic modulator, and the modulated detection light is emitted into the sensing optical fiber through the optical isolator.

[0011] Furthermore, the situation in which the coefficient compensation device does not undergo stimulated Brillouin scattering effect refers to: the pump branch optical path is not connected to the coefficient compensation device, the detection light is emitted into the detection light branch optical path, the microwave source applies a modulation signal in a first set frequency range to the electro-optical modulator, and the modulated detection light is emitted into the fiber Bragg grating via the optical isolator and the sensing optical fiber for filtering to obtain a second single-sideband signal.

[0012] Furthermore, the calculation compensation coefficient is expressed by the following formula:

[0013]

[0014] in, Indicates continuous j The second single sideband signal of the frequency, in dBm, express i The detection optical power at the frequency, in mW, express i The compensation coefficient under frequency, N represents the difference between the maximum value and the minimum value in the first set frequency range, and the difference is divided according to 1 frequency step to obtain the number of frequencies, which is N.

[0015] Furthermore, the pump branch optical path includes a pulse modulator, an erbium-doped fiber amplifier and a random polarization scrambler. The pump light is modulated by the pulse modulator to obtain pulse light. The pulse light is amplified by the erbium-doped fiber amplifier and then enters the random polarization scrambler to randomize the polarization.

[0016] Further, the situation where the coefficient compensation device generates the stimulated Brillouin scattering effect means that: the pump branch optical path is connected to the coefficient compensation device, the probe light is injected into the probe light branch optical path, the microwave source applies a modulation signal within a second set frequency range to the electro-optic modulator, and the modulated probe light is injected into the sensing optical fiber through the optical isolator; the pump light is injected into the sensing optical fiber through the pump branch optical path; the stimulated Brillouin scattering effect occurs in the sensing optical fiber to obtain a probe light signal carrying Brillouin scattering information; and after filtering by the fiber Bragg grating, a first single-sideband signal is obtained. Wherein, the second set frequency range is less than the first set frequency range, and the first set frequency range includes the second set frequency range.

[0017] Further, compensating the Brillouin scattering signal output by the detector with a compensation coefficient to obtain a compensated Brillouin scattering signal; which is represented by the following formula:

[0018] Wherein, represents the compensated Brillouin scattering signal, represents the Brillouin scattering signal, represents the compensation coefficient, represents the frequency value within the second set frequency range, represents the minimum value within the first set frequency range.

[0019] Further, a first circulator and a second circulator are also provided between the sensing optical fiber and the fiber Bragg grating, and the probe light signal carrying Brillouin scattering information emitted from the sensing optical fiber is injected into the fiber Bragg grating through the first circulator and the second circulator.

[0020] Further, the coefficient compensation device further includes a spectrometer and a data acquisition card, both the spectrometer and the data acquisition card are connected to the industrial control computer, the spectrometer is used to collect the second single-sideband signal obtained by filtering the fiber Bragg grating and upload it to the industrial control computer when the coefficient compensation device does not generate the stimulated Brillouin scattering effect; the data acquisition card is used to collect the Brillouin scattering signal and upload it to the industrial control computer.

[0021] The second aspect of the present invention provides a coefficient compensation method for correcting the distortion of the Brillouin gain spectrum of BOTDA.

[0022] A compensation method based on the coefficient compensation device for correcting the distortion of the Brillouin gain spectrum of BOTDA described in the first aspect includes: Turn off the erbium-doped fiber amplifier in the pump branch optical path, and set the sweep frequency range of the microwave source in the probe light branch optical path to the first set frequency range; Change the frequency of the microwave source in each iteration to obtain the power values of the second single-sideband signals at each frequency until the first set frequency range is traversed; Linearly transform the power values of all the second single-sideband signals to obtain the detected optical powers at all frequency points; calculate the average value of the detected optical powers at all frequency points, and obtain a compensation coefficient according to the ratio of the average value to the detected optical power at a single frequency point; Turn on the erbium-doped fiber amplifier in the pump branch optical path, and set the sweep frequency range of the microwave source in the detected optical branch optical path to the second set frequency range; Change the frequency of the microwave source in each iteration, multiply the Brillouin scattering signal output by the detector by the compensation coefficient at the corresponding frequency to obtain the compensated Brillouin scattering signal at that frequency; until the second set frequency range is traversed.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a coefficient compensation device and method for correcting the distortion of the Brillouin gain spectrum of BOTDA. When the SBS effect does not occur in the system, the fluctuation characteristics of the detected optical power at different frequencies are obtained, and the compensation coefficient is calculated. During the optical fiber sensing process, the BGS distortion is corrected by this compensation coefficient, so as to achieve a more stable Brillouin gain spectrum form, higher measurement accuracy, and more reliable distributed optical fiber sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0025] Figure 1 is a structural diagram of the coefficient compensation device for correcting the distortion of the Brillouin gain spectrum of BOTDA shown in the embodiment of the present invention; Figure 2 is a flowchart of obtaining the power compensation coefficient shown in the embodiment of the present invention; Figure 3 is a flowchart of compensating with the compensation coefficient shown in the embodiment of the present invention; Figure 4 is a comparison diagram of the BGS after normalization and the compensation coefficient at different temperatures shown in the embodiment of the present invention; FIG. 5(a) is a schematic diagram of the 2D-BGS at 30°C before correction shown in the embodiment of the present invention; FIG. 5(b) is a schematic diagram of the 2D-BGS at 70°C before correction shown in the embodiment of the present invention; FIG. 5(c) is a schematic diagram of the 2D-BGS at 30°C after correction shown in the embodiment of the present invention; Figure 5(d) is a schematic diagram of the corrected 2D-BGS at 70°C shown in the embodiment of the present invention; Figure 6 is a schematic diagram of the linear relationship between temperature and BFS shown in the embodiment of the present invention; wherein, 1. laser, 2. coupler, 3. electro-optic modulator, 4. microwave source, 5. optical isolator, 6. sensing optical fiber, 7. first circulator, 8. second circulator, 9. fiber Bragg grating, 10. detector, 11. spectrometer, 12. data acquisition card, 13. industrial control computer, 14. pulse modulator, 15. erbium-doped fiber amplifier, 16. random polarization scrambler. Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise clearly specified in the context, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] To facilitate the understanding of the technical solution of the present invention, some technical terms related to the present invention will be introduced below.

[0030] Embodiment 1 As Figure 1 shown, this embodiment provides a coefficient compensation device for correcting the distortion of the Brillouin gain spectrum of BOTDA, including: a laser 1, a coupler 2, a detection light branch optical path, a pump light branch optical path, a sensing optical fiber 6, a fiber Bragg grating 9, a detector 10, and an industrial control computer 13; The continuous light generated by the laser 1 generates detection light and pump light through the coupler 2; The detection light branch optical path injects the detection light into the sensing optical fiber 6, and the pump light branch optical path injects the pump light into the sensing optical fiber 6. The stimulated Brillouin scattering effect occurs in the sensing optical fiber 6 to obtain a detection light signal carrying Brillouin scattering information; The fiber Bragg grating 9 filters the incoming detection light signal to obtain a first single-sideband signal; The detector 10 converts the first single-sideband signal into a Brillouin scattering signal and inputs it into the processing module; An industrial control computer 13 is configured to obtain the detection optical power fluctuation characteristics at different frequencies to calculate a compensation coefficient when the stimulated Brillouin scattering effect does not occur in the coefficient compensation device; and when the stimulated Brillouin scattering effect occurs, compensate the Brillouin scattering signal output by the detector 10 with the compensation coefficient to obtain a compensated Brillouin scattering signal.

[0031] In some embodiments, the detection optical branch optical path includes an electro-optic modulator 3, a microwave source 4, and an optical isolator 5. The microwave source 4 applies a modulation signal to the electro-optic modulator 3, and the modulated detection light is incident on the sensing optical fiber 6 through the optical isolator 5.

[0032] In some embodiments, the situation where the stimulated Brillouin scattering effect does not occur in the coefficient compensation device means that the pump branch optical path is not connected to the coefficient compensation device, the detection light is incident on the detection optical branch optical path, the microwave source 4 applies a modulation signal within a first set frequency range to the electro-optic modulator 3, and the modulated detection light is incident on the fiber Bragg grating 9 through the optical isolator 5 and the sensing optical fiber 6 for filtering to obtain a second single-sideband signal.

[0033] In some embodiments, the pump branch optical path includes a pulse modulator 14, an erbium-doped fiber amplifier 15, and a random polarization scrambler 16. The pump light is modulated by the pulse modulator 14 to obtain pulsed light, and the pulsed light is amplified by the erbium-doped fiber amplifier 15 and then enters the random polarization scrambler 16 to randomize the polarization.

[0034] In some embodiments, a first circulator 7 and a second circulator 8 are further provided between the sensing optical fiber 6 and the fiber Bragg grating 9. The detection optical signal carrying Brillouin scattering information emitted from the sensing optical fiber 6 is incident on the fiber Bragg grating 9 through the first circulator 7 and the second circulator 8.

[0035] Specifically, both the first circulator 7 and the second circulator 8 have three ports, namely port 1, port 2, and port 3. The optical signal input from port 1 is output from port 2, and the optical signal input from port 2 is output from port 3.

[0036] In some embodiments, the situation where the stimulated Brillouin scattering effect occurs in the coefficient compensation device means that the pump branch optical path is connected to the coefficient compensation device, the detection light is incident on the detection optical branch optical path, the microwave source 4 applies a modulation signal within a second set frequency range to the electro-optic modulator 3, and the modulated detection light is incident on the sensing optical fiber 6 through the optical isolator 5; the pump light is incident on the sensing optical fiber 6 through the pump branch optical path; the stimulated Brillouin scattering effect occurs in the sensing optical fiber 6 to obtain a detection optical signal carrying Brillouin scattering information; and after filtering by the fiber Bragg grating 9, a first single-sideband signal is obtained. Among them, the second set frequency range is smaller than the first set frequency range, and the first set frequency range includes the second set frequency range.

[0037] In some embodiments, the coefficient compensation device further includes a spectrometer 11 and a data acquisition card 12. Both the spectrometer 11 and the data acquisition card 12 are connected to an industrial control computer 13. The spectrometer 11 is configured to collect the second single-sideband signal filtered by the fiber Bragg grating 9 when the coefficient compensation device does not undergo stimulated Brillouin scattering effect, and upload it to the industrial control computer 13; the data acquisition card 12 is configured to collect the Brillouin scattering signal and upload it to the industrial control computer 13.

[0038] In addition, the industrial control computer 13 is also connected to a laser 1, an electro-optic modulator 3, a microwave source 4, a detector 10, a pulse modulator 14, etc., to control the working processes of these components.

[0039] The working principle of the coefficient compensation device is as follows: First, turn off the erbium-doped fiber amplifier 15 and set the pump optical power to zero (that is, when the coefficient compensation device does not undergo stimulated Brillouin scattering effect). The laser 1 with a central wavelength of 1550 nm divides the optical path into two branches, namely the probe light and the pump light, through the coupler 2. In the probe light branch optical path, a modulation signal with a first set frequency range (F1min~F1max) and a step of 1 MHz is applied to the electro-optic modulator 3 by the microwave source 4. The current microwave source 4 sets the frequency f to perform double-sideband suppressed carrier modulation on the probe light signal. The modulation signal enters the sensing fiber 6 through the optical isolator 5. Then it enters the fiber Bragg grating 9 through the first circulator 7 and the second circulator 8 for filtering to obtain a single-sideband signal. The reflected light reaches the spectrometer 9 through the 3-port of the second circulator 8, and the spectrometer 11 collects the single-sideband signals at different scanning frequencies. Repeat the above process, and jump out of the loop when f>F1max to complete the spectral acquisition of all sweep points. Calculate the power compensation coefficient through formulas (1) and (2). In one embodiment, F1min can be taken as 8 GHz and F1max can be taken as 12 GHz, which is not limited in this embodiment.

[0040] (1) (2) Among them, represents continuous j second single-sideband signals of frequencies, in units of dBm, i represents the probe optical power at frequency, in units of mW, iThe compensation coefficient at the frequency, N represents the difference between the maximum and minimum values in the first set frequency range. The difference is divided by one frequency step to obtain the number of frequencies, which is N.

[0041] During the sensing process (i.e., when the stimulated Brillouin scattering effect occurs in the coefficient compensation device), the erbium-doped fiber amplifier 15 is turned on. In the pump light branch, the continuous light is modulated into pulsed light by the pulse modulator 14, and the optical power is amplified by the erbium-doped fiber amplifier 15. The polarization state is randomized by the random polarization scrambler 16. Finally, it is injected into the sensing fiber 6 through the first circulator 7. In the probe light branch, in order to obtain a complete Brillouin gain signal, the sweep frequency range of the microwave source 4 is set to the actual fiber Brillouin range, that is, the second set frequency range (F2min~F2max), with a step of 1 MHz. The modulation signals at different frequencies f modulate a continuous suppressed-carrier double-sideband probe optical signal through the electro-optic modulator 3. The counter-propagating continuous probe light and pump light generate the stimulated Brillouin scattering effect in the sensing fiber 6. The Brillouin scattering signal passes through the first circulator 7 and the second circulator 8 and is filtered by the fiber Bragg grating 9 to obtain a single-sideband signal. The Brillouin scattered optical signal is converted into an electrical signal by the detector 10, and the signal G is sampled by the data acquisition card 12. Finally, it is input into the industrial control computer 13, and then the signal G is multiplied by the compensation coefficient Pcofficent(f) consistent with the current frequency f of the microwave source 4, as shown in formula (3), to obtain the compensated Brillouin scattering signal. When f>F2max, the loop is exited, and the coefficient compensation for all sweep frequency points is completed. In one embodiment, F2min can be taken as 10.7 GHz, and F2max can be taken as 11 GHz. This embodiment is not limited herein.

[0042] (3) Among them, represents the compensated Brillouin scattering signal, represents the Brillouin scattering signal, represents the compensation coefficient, represents the frequency value in the second set frequency range, represents the minimum value in the first set frequency range.

[0043] When the SBS effect does not occur in the system of the present invention, the fluctuation characteristics of the probe optical power at different frequencies are obtained, and the compensation coefficient is calculated. During the fiber sensing process, the BGS distortion is corrected by this compensation coefficient, so as to achieve a more stable Brillouin gain spectrum shape, higher measurement accuracy, and more reliable distributed fiber sensing.

[0044] Embodiment 2 Such as Figure 2 、 Figure 3As shown, this embodiment provides a coefficient compensation method for correcting the distortion of the Brillouin gain spectrum of BOTDA, which is applied to the coefficient compensation device for correcting the distortion of the Brillouin gain spectrum described in Embodiment 1, and includes: Turn off the erbium-doped fiber amplifier in the pump branch optical path, and set the sweep frequency range of the microwave source in the probe light branch optical path to the first set frequency range; Change the frequency of the microwave source iteratively each time, and obtain the power value of the second single-sideband signal at each frequency until the first set frequency range is traversed; Linearly convert the power values of all the second single-sideband signals to obtain the probe light power at all frequency points; calculate the average value of the probe light power at all frequency points, and obtain the compensation coefficient according to the ratio of the average value to the probe light power at a single frequency point; Turn on the erbium-doped fiber amplifier in the pump branch optical path, and set the sweep frequency range of the microwave source in the probe light branch optical path to the second set frequency range; Change the frequency of the microwave source iteratively each time, multiply the Brillouin scattering signal output by the detector by the compensation coefficient at the corresponding frequency to obtain the compensated Brillouin scattering signal at that frequency; until the second set frequency range is traversed.

[0045] In this embodiment, convert the power values of all the second single-sideband signals to linear coordinates to obtain the probe light power at all frequency points; which is expressed by the following formula:

[0046] In this embodiment, calculate the average value of the probe light power at all frequency points (as the reference value for power flatness), and obtain the compensation coefficient according to the ratio of the average value to the probe light power at a single frequency point; which is expressed by the following formula:

[0047] Wherein, Represents the second single-sideband signals of consecutive j Frequencies, Represents i The probe light power at the Frequency, i Represents the compensation coefficient at the i Frequency, N represents the difference between the maximum value and the minimum value in the first set frequency range, and the difference is divided according to 1 frequency step to obtain the number of frequencies, which is N.

[0048] In this embodiment, change the frequency of the microwave source iteratively each time, multiply the Brillouin scattering signal output by the detector by the compensation coefficient at the corresponding frequency to obtain the compensated Brillouin scattering signal at that frequency; which is expressed by the following formula:

[0049] Among them, represents the compensated Brillouin scattering signal, represents the Brillouin scattering signal, represents the compensation coefficient, represents the frequency value in the second set frequency range, represents the minimum value in the first set frequency range.

[0050] To verify the effectiveness of the method of the present invention, a temperature sensing experiment was carried out. In the temperature sensing experiment, a 9.85 km long single-mode sensing optical fiber of model G.625.D was used. 20 meters of the sensing optical fiber at the end of the optical fiber was kept loose. Among them, 10 m of the sensing optical fiber near the end was loose outdoors, and the other 10 m was wound into a ring with a diameter of 30 cm and placed in a constant temperature oven. The constant temperature oven precisely controlled the heating temperature from 20 °C to 70 °C, and the step temperature was 10 °C.

[0051] To analyze the influence of the detection optical power fluctuation on the BGS distortion, the present invention selects the BGS at the 9835 m position in the constant temperature oven and the 500 m position of the normal temperature optical fiber section at the temperature of 70 °C under different temperatures. To visually present how the detection optical power fluctuation affects the BGS, the BGS is normalized and compared with the compensation coefficient, as Figure 4 shown. At the temperatures of 30 °C and 70 °C, the detection optical power of the BGS mutates at the frequencies of 10.85 GHz and 10.90 GHz, causing the gain to rapidly decrease, resulting in the narrowing of the BGS, and further affecting the accurate fitting of the BFS. After being corrected by the compensation coefficient, this abnormal point is significantly corrected, making the shape of the BGS restore symmetry. For the BGS under other temperature conditions, since the detection optical power is relatively stable within its frequency range, the BGS is overall good. However, there is a slow change in the detection optical power, which will also have a certain impact on the actually measured BGS, and further cause the measurement accuracy to decrease. And by the coefficient compensation method for correcting the BGS, the BGS distortion can be effectively improved.

[0052] Figures 5(a) - 5(d) are the two-dimensional BGS before and after correction by coefficient compensation of the entire optical fiber when the temperature in the constant temperature oven is 30 °C and 70 °C. The color in the figure represents the amplitude of the Brillouin gain energy. It can be clearly seen that the distortion line caused by the power mutation disappears in the BGS of the normal temperature area after correction.

[0053] Take the BFS data of the test optical fiber in the constant temperature oven and calculate the linear relationship between the temperature and the BFS, as Figure 6As shown. There are mutation points in the optical power at 30 °C and 70 °C, which will cause large differences in the BFS value and deviate from the linear fitting curve. The optical power changes slowly from 40 °C to 60 °C and does not cause large deviations. Overall, when no compensation is performed, the determination coefficient R of the temperature-BFS linear fitting 2 is 0.9975. After being corrected by the coefficient compensation method, R 2 is increased to 0.99904. This result shows that the compensation method proposed by the present invention can effectively reduce this influence, make the linear relationship between temperature and BFS more accurate, and improve the measurement accuracy and reliability of the BOTDA system.

[0054] When the SBS effect does not occur in the device of the present invention, the compensation coefficient is calculated; when the SBS effect occurs, the Brillouin gain spectrum is compensated by the compensation coefficient, thereby reducing the influence of power fluctuation on the BFS fitting. The present invention does not require additional modification of the hardware and can directly improve the measurement accuracy of the existing BOTDA system.

[0055] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coefficient compensation device for correcting the distortion of the Brillouin gain spectrum of BOTDA, characterized in that Comprising: A laser, a coupler, a detection light branching optical path, a pump branching optical path, a sensing optical fiber, a fiber Bragg grating, a detector, and an industrial control computer; The continuous light generated by the laser generates detection light and pump light through the coupler; The detection light branching optical path injects the detection light into the sensing optical fiber, and the pump branching optical path injects the pump light into the sensing optical fiber. The stimulated Brillouin scattering effect occurs in the sensing optical fiber to obtain a detection light signal carrying Brillouin scattering information; The fiber Bragg grating filters the incoming detection light signal to obtain a first single-sideband signal; The detector converts the first single-sideband signal into a Brillouin scattering signal and inputs it to the processing module; The industrial control computer is used to obtain the detection light power fluctuation characteristics at different frequencies to calculate the compensation coefficient when the stimulated Brillouin scattering effect does not occur in the coefficient compensation device; When the stimulated Brillouin scattering effect occurs, the compensation coefficient is used to compensate the Brillouin scattering signal output by the detector to obtain a compensated Brillouin scattering signal.

2. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 1, characterized in that The detection light branching optical path includes an electro-optic modulator, a microwave source, and an optical isolator. The microwave source applies a modulation signal to the electro-optic modulator, and the modulated detection light is injected into the sensing optical fiber through the optical isolator.

3. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 2, wherein The situation where the stimulated Brillouin scattering effect does not occur in the coefficient compensation device means that the pump branching optical path is not connected to the coefficient compensation device, the detection light is injected into the detection light branching optical path, the microwave source applies a modulation signal within a first set frequency range to the electro-optic modulator, and the modulated detection light is injected into the fiber Bragg grating through the optical isolator and the sensing optical fiber for filtering to obtain a second single-sideband signal.

4. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 3, wherein The calculation of the compensation coefficient is expressed by the following formula: Among them, represents the second single-sideband signal of j consecutive frequencies, represents i the detected optical power at the frequency, and i represents the compensation coefficient at the frequency. N represents the difference between the maximum and minimum values in the first set frequency range. The difference is divided by one frequency step to obtain the number of frequencies, which is N.

5. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 3, characterized in that, The pump branching optical path includes a pulse modulator, an erbium-doped fiber amplifier, and a random polarization scrambler. The pump light is modulated by the pulse modulator to obtain pulsed light, and the pulsed light is amplified by the erbium-doped fiber amplifier and then enters the random polarization scrambler to randomize the polarization.

6. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 3, wherein The situation where the stimulated Brillouin scattering effect occurs in the coefficient compensation device means that the pump branching optical path is connected to the coefficient compensation device, the detection light is injected into the detection light branching optical path, the microwave source applies a modulation signal within a second set frequency range to the electro-optic modulator, and the modulated detection light is injected into the sensing optical fiber through the optical isolator; the pump light is injected into the sensing optical fiber through the pump branching optical path; The stimulated Brillouin scattering effect occurs in the sensing optical fiber to obtain a detection light signal carrying Brillouin scattering information; After filtering by the fiber Bragg grating, a first single-sideband signal is obtained; Wherein, the second set frequency range is less than the first set frequency range, and the first set frequency range includes the second set frequency range.

7. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 6, wherein The compensation coefficient is used to compensate the Brillouin scattering signal output by the detector to obtain a compensated Brillouin scattering signal; It is expressed by the following formula: Among them, represents the compensated Brillouin scattering signal, represents the Brillouin scattering signal, represents the compensation coefficient, represents the frequency value in the second set frequency range, represents the minimum value in the first set frequency range.

8. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 1, wherein A first circulator and a second circulator are also provided between the sensing optical fiber and the fiber Bragg grating. The detection light signal carrying Brillouin scattering information emitted from the sensing optical fiber is injected into the fiber Bragg grating through the first circulator and the second circulator.

9. The coefficient compensation device for correcting the Brillouin gain spectrum distortion according to claim 1, wherein The coefficient compensation device further includes a spectrometer and a data acquisition card. Both the spectrometer and the data acquisition card are connected to an industrial control computer. The spectrometer is used to collect the second single-sideband signal obtained by filtering the fiber Bragg grating when the stimulated Brillouin scattering effect does not occur in the coefficient compensation device and upload it to the industrial control computer. The data acquisition card is used to collect the Brillouin scattering signal and upload it to the industrial control computer.

10. A compensation method for a coefficient compensation device that corrects the Brillouin gain spectrum distortion according to any one of claims 1-9, characterized in that, Comprising: Turn off the erbium-doped fiber amplifier in the pump branch optical path, and set the frequency sweep range of the microwave source in the probe light branch optical path to a first set frequency range; Change the frequency of the microwave source in each iteration to obtain the power value of the second single-sideband signal at each frequency until the first set frequency range is traversed; Linearly convert the power values of all the second single-sideband signals to obtain the probe light power at all frequency points; calculate the average value of the probe light power at all frequency points, and obtain the compensation coefficient according to the ratio of the average value to the probe light power at a single frequency point; Turn on the erbium-doped fiber amplifier in the pump branch optical path, and set the frequency sweep range of the microwave source in the probe light branch optical path to a second set frequency range; Change the frequency of the microwave source in each iteration, multiply the Brillouin scattering signal output by the detector by the compensation coefficient at the corresponding frequency to obtain the compensated Brillouin scattering signal at that frequency; until the second set frequency range is traversed.

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