Overhead cable icing monitoring method and device based on chaotic Brillouin dynamic grating

Abstract

The invention relates to the technical field of electric power overhaul and distributed optical fiber sensing, and discloses an overhead cable icing monitoring method and device based on a chaotic Brillouin dynamic grating, and the method comprises the following steps: dividing the chaotic laser outputted by the same chaotic laser into two beams, and then carrying out the frequency deviation and polarization adjustment; the first pump light and the second pump light have the same polarization direction, and the frequency difference is Brillouin frequency shift; the first pump light and the second pump light are respectively injected into two ends of a sensing optical fiber in the optical fiber composite overhead ground wire to form a chaotic Brillouin dynamic grating; injecting detection light which has the same incident direction as the first pump light, is orthogonal in polarization and has a positive / negative birefringence frequency shift frequency difference into the sensing optical fiber; measuring to obtain a gain spectrum and a reflection spectrum; and determining a Brillouin frequency shift and a birefringence frequency shift according to the gain spectrum and the reflection spectrum, and determining the thickness of the ice layer. According to the invention, both the spatial resolution and the sensing distance can be considered, and the accuracy of the icing monitoring result can be improved.

Description

Technical Field

[0001] This invention relates to the fields of power maintenance and distributed optical fiber sensing technology, specifically to a method and device for monitoring icing of overhead cables based on chaotic Brillouin dynamic gratings. The method and device monitor icing of overhead cables by measuring the fiber strain when the overhead cables are iced using chaotic Brillouin dynamic gratings. Background Technology

[0002] Overhead cables are prone to freezing rain and ice buildup. This ice not only increases the weight of the conductors, putting cable towers at risk of collapse, but also alters their original aerodynamics, causing the cables to swing wildly and even break through the insulation layer, resulting in short circuits and serious economic losses.

[0003] Distributed fiber optic sensing technology, with its advantages of resistance to electromagnetic interference and long-distance measurement, has already found important applications in monitoring icing on overhead cables. Traditional Brillouin scattering distributed fiber optic sensing methods invert icing loads by measuring fiber strain changes, offering advantages such as direct measurement and high accuracy. However, since both temperature and strain information affect the Brillouin frequency shift, ambient temperature can severely impact the monitoring results of icing on overhead cables (a method for monitoring the icing status of high-voltage transmission networks, CN202011492487.1). In contrast, Brillouin dynamic grating distributed fiber optic sensing technology employs a simultaneous measurement method of gain and reflection spectra, introducing decoupled measurement of temperature parameters while measuring strain, effectively avoiding the influence of temperature on the monitoring results of icing on overhead cables. Currently, Brillouin dynamic grating distributed fiber optic sensing technology mainly includes time-domain systems and correlation-domain systems. Time-domain systems have high sensing distance, but their spatial resolution is limited by the pulse width of the probe light (CN201210059817.7); correlation-domain systems have high spatial resolution, but the periodic generation of Brillouin dynamic gratings on the optical fiber leads to ambiguity in the sensing distance (IEEE Sensors Journal, 2014, 14(1): 244-248).

[0004] To address the challenge of simultaneously achieving both spatial resolution and sensing distance in traditional distributed fiber optic sensing technology based on Brillouin dynamic gratings, improvements are needed to the structure and methods of the sensing system to adapt it to the requirements of monitoring icing on overhead cables. Summary of the Invention

[0005] To address the problem that traditional Brillouin dynamic grating distributed fiber optic sensing technology cannot simultaneously achieve both spatial resolution and sensing distance, thus making it unsuitable for monitoring icing on overhead cables, this invention proposes a method and device for monitoring icing on overhead cables based on chaotic Brillouin dynamic gratings.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for monitoring icing of overhead cables based on chaotic Brillouin dynamic gratings, comprising the following steps: Step 1: The chaotic laser output from the same chaotic laser is split into two beams and then frequency shifted and polarization adjusted to become the first pump light and the second pump light with the same polarization direction and a frequency difference of Brillouin frequency shift. The first pump light and the second pump light are injected into the two ends of the sensing fiber in the fiber-optic composite overhead ground wire, respectively, so that the first pump light and the second pump light meet in the sensing fiber and stimulated Brillouin scattering occurs to generate an acoustic wave field, forming a chaotic Brillouin dynamic grating. Simultaneously, probe light with the same incident direction as the first pump light, orthogonal polarization, and a frequency difference of positive / negative birefringence frequency shift is injected into the sensing fiber. Step 2: Fix the frequency of the probe light, sweep the frequency of the second pump light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the frequency of the second pump light to obtain the gain spectrum. Step 3: Fix the frequency of the second pump light, scan the frequency of the probe light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the probe light frequency to obtain the reflection spectrum; Step 4: Determine the Brillouin frequency shift and birefringence frequency shift based on the gain spectrum and reflection spectrum, calculate the strain and temperature when the overhead cable is covered with ice, and determine the ice thickness based on the strain magnitude.

[0007] In step 1, the first pump light and the second pump light are incident along the slow axis of the sensing fiber, and the probe light is incident along the fast axis of the sensing fiber. The frequency difference between the injected probe light and the first pump light is a birefringence frequency shift.

[0008] In step 1, the first pump light and the second pump light are incident along the fast axis of the sensing fiber, and the probe light is incident along the slow axis of the sensing fiber. The frequency difference between the first pump light and the injected probe light is a birefringence frequency shift.

[0009] The method for monitoring icing of overhead cables based on chaotic Brillouin dynamic gratings further includes the following steps: Step 5: Change the optical path difference between the first pump light and the second pump light, adjust the position of the chaotic Brillouin dynamic grating, and repeat steps 2-4 to obtain the ice layer thickness along the overhead cable.

[0010] In addition, the present invention also provides an overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating, used to implement the aforementioned monitoring method, comprising: a chaotic laser, a coupler, a first polarization adjustment unit, a polarization beam splitter, a first single-sideband modulator, a second polarization adjustment unit, a narrow linewidth laser, a pulse modulator, a circulator, a photodetector, a lock-in amplifier, and a host computer. The chaotic laser output from the chaotic laser enters the coupler. The chaotic laser signal from the first output end of the coupler is polarized by the first polarization adjustment unit and then enters the sensing fiber as the first pump light after passing through the polarization beam splitter. The chaotic laser output from the second output end of the coupler is frequency-shifted by the first single-sideband modulator and then polarized by the second polarization adjustment unit, and then enters the sensing fiber as the second pump light from the other end of the sensing fiber. The laser output from the narrow linewidth laser is pulse-modulated by a pulse modulator and then used as probe light. It is incident on the polarization beam splitter through a circulator, and after passing through the polarization beam splitter, it is combined with the first pump light and enters the sensing fiber. The reflected light formed by the probe light being reflected by the chaotic Brillouin dynamic grating is received by the photodetector after passing through the polarization beam splitter and circulator. After photoelectric conversion, the gain spectrum and reflection spectrum are collected by the lock-in amplifier and then sent to the host computer.

[0011] The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating further includes a first optical amplifier, a second optical amplifier, and a third optical amplifier. The first optical amplifier is disposed between the first output end of the coupler and the first polarization adjustment unit, and is used to amplify the chaotic laser signal at the first output end of the coupler. The second optical amplifier is disposed at the output end of the first single-sideband modulator, and is used to amplify the low-frequency single-sideband optical signal output by the first single-sideband modulator. The third optical amplifier is disposed between the pulse modulator and the circulator, and is used to amplify the pulse probe light.

[0012] The first polarization adjustment unit includes a first polarization controller and a first polarizer arranged in sequence; the second polarization adjustment unit includes a second polarization controller and a second polarizer arranged in sequence.

[0013] The overhead cable icing monitoring device based on chaotic Brillouin dynamic grating further includes an optical isolator, which is disposed between the output end of the chaotic laser and the coupler.

[0014] The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating further includes an optical delay line, which is disposed between a second optical amplifier and a second polarization controller to adjust the optical path difference between the first pump light and the second pump light, thereby enabling the chaotic Brillouin dynamic grating to move along the entire sensing fiber.

[0015] The overhead cable icing monitoring device based on chaotic Brillouin dynamic grating further includes a microwave signal source and a pulse signal generator. The microwave signal source is used to output a microwave signal to drive the first single-sideband modulator to perform low-frequency single-sideband modulation to obtain a single-sideband with a lower frequency. The pulse signal generator is used to drive the pulse modulator to perform pulse modulation to obtain a pulsed probe light.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention provides a method and apparatus for monitoring icing of overhead cables based on chaotic Brillouin dynamic gratings. By using chaotic light as pump light to generate a chaotic Brillouin dynamic grating with a unique position in the optical fiber, sub-centimeter spatial resolution measurement can be achieved in monitoring icing of overhead cables. Moreover, the sensing distance is not limited by the periodic characteristics of the pump light. Therefore, this invention overcomes the problem that traditional Brillouin dynamic grating distributed optical fiber sensing technology cannot simultaneously achieve both spatial resolution and sensing distance.

[0017] 2. This invention obtains two parameters, Brillouin frequency shift and birefringence frequency shift, by simultaneously acquiring the reflection spectrum and gain spectrum, thereby achieving decoupling of temperature and strain, improving the accuracy of icing monitoring results, and overcoming the crosstalk problem of temperature on strain monitoring in traditional Brillouin scattering distributed optical fiber overhead cable icing monitoring. Attached Figure Description

[0018] Figure 1 This is a flowchart of the overhead cable icing monitoring method based on chaotic Brillouin dynamic grating provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating provided in Embodiment 2 of the present invention. In the diagram: 1-chaotic laser, 2-optical isolator, 3-coupler, 4-first optical amplifier, 5-first polarization controller, 6-first polarizer, 7-polarization beam splitter, 8-sensing fiber, 9-single-sideband modulator, 10-microwave signal source, 11-second optical amplifier, 12-optical delay line, 13-second polarization controller, 14-second polarizer, 15-narrow linewidth laser, 16-second single-sideband modulator, 17-second microwave signal source, 18-acousto-optic modulator, 19-pulse signal generator, 20-third optical amplifier, 21-circulator, 22-photodetector, 23-locked-in amplifier, 24-host computer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 like Figure 1 As shown, Embodiment 1 of the present invention provides a method for monitoring icing of overhead cables based on a chaotic Brillouin dynamic grating, comprising the following steps: Step 1: The chaotic laser output from the same chaotic laser is split into two beams and then frequency-shifted and polarized to become a first pump light and a second pump light with the same polarization direction and a Brillouin frequency shift. The first pump light and the second pump light are injected into the two ends of the sensing fiber in the fiber-optic composite overhead ground wire, respectively, so that the first pump light and the second pump light meet in the sensing fiber and undergo stimulated Brillouin scattering to generate an acoustic wave field, forming a chaotic Brillouin dynamic grating. At the same time, a probe light with the same incident direction as the first pump light, orthogonal polarization, and a frequency difference of positive / negative birefringence frequency shift is injected into the sensing fiber.

[0021] Specifically, in step 1 of this embodiment, the first pump light and the second pump light are incident along the slow axis of the sensing fiber, and the probe light is incident along the fast axis of the sensing fiber. The frequency difference between the injected probe light and the first pump light is a birefringence frequency shift.

[0022] Furthermore, in step 1 of this embodiment, the first pump light and the second pump light can be incident along the fast axis of the sensing fiber, and the probe light can be incident along the slow axis of the sensing fiber; at this time, the frequency difference between the first pump light and the injected probe light is a birefringence frequency shift.

[0023] Step 2: Fix the frequency of the probe light, sweep the frequency of the second pump light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the frequency of the second pump light to obtain the gain spectrum.

[0024] When the probe light frequency is fixed and the second pump light frequency sweep changes, the returned reflected light power characterizes the intensity of the Brillouin dynamic grating under different frequencies of the second pump light, that is, the gain of the second pump light under the first pump light when the stimulated Brillouin response occurs. Since the intensity of the Brillouin dynamic grating is the largest when the frequencies of the first and second pump lights are equal to the Brillouin frequency shift, the gain spectrum that reflects the change of reflected light power with the frequency of the second pump light reflects the intensity of the Brillouin dynamic grating. Therefore, the center frequency of the gain spectrum is the Brillouin frequency shift.

[0025] Step 3: Fix the frequency of the second pump light, scan the frequency of the probe light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the probe light frequency to obtain the reflection spectrum.

[0026] When the frequency of the second pump light is fixed and the frequency of the probe light changes, the power of the returned reflected light characterizes the reflection intensity of the Brillouin dynamic grating for probe light of different frequencies. Since the intensity of the reflected light is the greatest when the frequency difference between the probe light and the first pump light is equal to the birefringence frequency shift, the reflection spectrum of the reflected light power changing with the frequency of the probe light reflects the difference between the frequency difference between the probe light and the first pump light and the birefringence frequency shift. Therefore, the center frequency of the reflection spectrum is the birefringence frequency shift.

[0027] Step 4: Determine the Brillouin frequency shift and birefringence frequency shift based on the gain spectrum and reflection spectrum, calculate the strain and temperature when the overhead cable is covered with ice, and determine the ice thickness based on the strain magnitude.

[0028] When overhead cables are covered with ice, the load on the conductors increases, causing tensile deformation, and the sensing optical fiber is subjected to tensile strain. Simultaneously, due to the low temperature of the ice layer, the sensing optical fiber is also affected by temperature. When the sensing optical fiber is subjected to strain, the Brillouin frequency shift and the birefringence frequency shift both increase with increasing strain; when the sensing optical fiber is affected by temperature, the Brillouin frequency shift increases with increasing temperature, while the birefringence frequency shift decreases with increasing temperature.

[0029] By measuring the Brillouin and birefringence frequency shifts along the sensing fiber, the strain and temperature of the overhead cable when it is covered with ice are demodulated. Combined with the Young's modulus and thermal expansion coefficient of the cable, the stress on the cable is calculated, thereby enabling the monitoring of ice thickness. In practice, the relationship between fiber strain and ice thickness is calibrated experimentally.

[0030] Furthermore, the overhead cable icing monitoring method based on chaotic Brillouin dynamic grating in this embodiment includes the following steps: Step 5: Change the optical path difference between the first and second pump lights, adjust the position of the chaotic Brillouin dynamic grating, and repeat steps 2-4 to obtain the ice thickness along the overhead cable. Specifically, the optical path difference between the two pump lights can be adjusted by setting an optical delay line.

[0031] Example 2 like Figure 2As shown, Embodiment 2 of the present invention provides an overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating, used to implement a monitoring method described in Embodiment 1, comprising: a chaotic laser 1, a coupler 3, a first polarization adjustment unit, a polarization beam splitter 7, a first single-sideband modulator 9, a second polarization adjustment unit, a narrow linewidth laser 15, a pulse modulator 18, a circulator 21, a photodetector 22, a lock-in amplifier 23, and a host computer 24.

[0032] The chaotic laser output from the chaotic laser 1 enters the coupler 3. The chaotic laser signal from the first output end of the coupler 3 is polarized by the first polarization adjustment unit and then passes through the polarization beam splitter 7 as the first pump light into the sensing fiber 8 in the fiber-optic composite overhead ground wire (OPGW). The chaotic laser output from the second output end of the coupler 3 is frequency-shifted by the first single-sideband modulator 9 and then polarized by the second polarization adjustment unit as the second pump light, which enters from the other end of the sensing fiber 8.

[0033] The laser output from the narrow linewidth laser 15 is pulse-modulated by the pulse modulator 18 and then used as probe light. It is incident on the polarization beam splitter 7 through the circulator 21. After passing through the polarization beam splitter 7, it is combined with the first pump light and enters the sensing fiber 8. The reflected light formed by the probe light being reflected by the chaotic Brillouin dynamic grating passes through the polarization beam splitter 7 and the circulator 21 and is received by the photodetector 22. After photoelectric conversion, the gain spectrum and reflection spectrum are collected by the lock-in amplifier 23 and then sent to the host computer 24.

[0034] Furthermore, the overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating in this embodiment also includes a first optical amplifier 4, a second optical amplifier 11, and a third optical amplifier 20; the first optical amplifier 4 is disposed between the first output end of the coupler 3 and the first polarization adjustment unit, and is used to amplify the chaotic laser signal at the first output end of the coupler 3; the second optical amplifier 11 is disposed at the output end of the first single-sideband modulator 9, and is used to amplify the low-frequency single-sideband optical signal output by the first single-sideband modulator 9; the third optical amplifier 20 is disposed between the pulse modulator 18 and the circulator 21, and is used to amplify the pulse probe light.

[0035] Specifically, in this embodiment, the first polarization adjustment unit includes a first polarization controller 5 and a first polarizer 6 arranged in sequence; the second polarization adjustment unit includes a second polarization controller 13 and a second polarizer 14 arranged in sequence. The first polarization controller 5 and the second polarization controller 13 are used to adjust the incident light into linearly polarized light, and the first polarizer 6 and the second polarizer 14 are used to adjust the polarization direction of the linearly polarized light so that it is along the fast axis or slow axis of the sensing fiber 8.

[0036] Furthermore, the overhead cable icing monitoring device based on chaotic Brillouin dynamic grating in this embodiment also includes an optical isolator 2, which is disposed between the output end of the chaotic laser 1 and the coupler 3 to isolate stray light in the optical path from disturbing the chaotic laser 1.

[0037] Furthermore, the overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating in this embodiment also includes an optical delay line 12. The optical delay line 12 is disposed between the second optical amplifier 11 and the second polarization controller 13 and is used to adjust the optical path difference between the first pump light and the second pump light, thereby realizing the movement of the chaotic Brillouin dynamic grating along the entire sensing fiber 8. Thus, the icing thickness along the overhead cable can be detected through the optical delay line 12.

[0038] Furthermore, the overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating in this embodiment also includes a microwave signal source 10 and a pulse signal generator 19. The microwave signal source 10 is used to output a microwave signal to drive the first single-sideband modulator 9 to perform low-frequency single-sideband modulation to obtain a frequency-downshifted single-sideband. The pulse signal generator 19 is used to drive the pulse modulator 18 to perform pulse modulation to obtain a pulsed probe light. Furthermore, the pulse signal generator 19 is also used to output a trigger signal to the lock-in amplifier 23 to achieve the acquisition of the gain spectrum and reflection spectrum.

[0039] Specifically, in this embodiment, the pulse modulator 18 can be an acousto-optic modulator. The coupler 3 is a 1×2 fiber optic coupler, the sensing fiber 8 is a single-mode or polarization-maintaining fiber, and the circulator 21 is a fiber optic circulator.

[0040] Specifically, in this embodiment, the various optical devices are connected by fiber optic patch cords.

[0041] Furthermore, this embodiment also includes a second single-sideband modulator 16 and a second microwave signal source 17. The second single-sideband modulator 16 is disposed between the narrow linewidth laser 15 and the pulse modulator 18 to realize frequency scanning of the probe light. In addition, the second single-sideband modulator 16 can be used to perform high-frequency shift or low-frequency shift on the laser output by the narrow linewidth laser 15 so that the frequency difference between the probe light and the first pump light is a positive / negative birefringence frequency shift.

[0042] In this embodiment, the frequency scanning of the probe light is achieved by scanning the driving frequency of the second single-sideband modulator 16. Alternatively, it can be achieved by scanning the driving current of the narrow-linewidth laser 15.

[0043] Specifically, in this embodiment, the lock-in amplifier 23 is used to extract the reflected light signal that is in phase and frequency with the probe light, thereby improving the signal-to-noise ratio of the test signal; the host computer 24 determines the Brillouin frequency shift and birefringence frequency shift through the gain spectrum and reflection spectrum, and calculates the strain and temperature when the overhead cable is covered with ice, and determines the ice thickness according to the strain magnitude. In addition, the host computer is also used for signal storage and display.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring icing of overhead cables based on chaotic Brillouin dynamic gratings, characterized in that, Includes the following steps: Step 1: The chaotic laser output from the same chaotic laser is split into two beams and then frequency shifted and polarization adjusted to become the first pump light and the second pump light with the same polarization direction and a frequency difference of Brillouin frequency shift. The first pump light and the second pump light are injected into the two ends of the sensing fiber in the fiber-optic composite overhead ground wire, respectively, so that the first pump light and the second pump light meet in the sensing fiber and stimulated Brillouin scattering occurs to generate an acoustic wave field, forming a chaotic Brillouin dynamic grating. Simultaneously, probe light with the same incident direction as the first pump light, orthogonal polarization, and a frequency difference of positive / negative birefringence frequency shift is injected into the sensing fiber. Step 2: Fix the frequency of the probe light, sweep the frequency of the second pump light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the frequency of the second pump light to obtain the gain spectrum; Step 3: Fix the frequency of the second pump light, scan the frequency of the probe light, and measure the change in intensity of the reflected light formed after the probe light is reflected by the chaotic Brillouin dynamic grating as a function of the probe light frequency to obtain the reflection spectrum; Step 4: Determine the Brillouin frequency shift and birefringence frequency shift based on the gain spectrum and reflection spectrum, calculate the strain and temperature when the overhead cable is covered with ice, and determine the ice thickness based on the strain magnitude.

2. The method for monitoring icing of overhead cables based on a chaotic Brillouin dynamic grating according to claim 1, characterized in that, In step 1, the first pump light and the second pump light are incident along the slow axis of the sensing fiber, and the probe light is incident along the fast axis of the sensing fiber. The frequency difference between the injected probe light and the first pump light is a birefringence frequency shift.

3. The method for monitoring icing of overhead cables based on a chaotic Brillouin dynamic grating according to claim 1, characterized in that, In step 1, the first pump light and the second pump light are incident along the fast axis of the sensing fiber, and the probe light is incident along the slow axis of the sensing fiber. The frequency difference between the first pump light and the injected probe light is a birefringence frequency shift.

4. The method for monitoring icing of overhead cables based on a chaotic Brillouin dynamic grating according to claim 1, characterized in that, It also includes the following steps: Step 5: Change the optical path difference between the first pump light and the second pump light, adjust the position of the chaotic Brillouin dynamic grating, and repeat steps 2-4 to obtain the ice layer thickness along the overhead cable.

5. An overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating, used to implement the monitoring method described in any one of claims 1-4, characterized in that, include: Chaotic laser (1), coupler (3), first polarization adjustment unit, polarization beam splitter (7), first single-sideband modulator (9), second polarization adjustment unit, narrow linewidth laser (15), pulse modulator (18), circulator (21), photodetector (22), lock-in amplifier (23), host computer (24); The chaotic laser output from the chaotic laser (1) enters the coupler (3). The chaotic laser signal from the first output end of the coupler (3) is polarized by the first polarization adjustment unit and then enters the sensing fiber (8) as the first pump light after passing through the polarization beam splitter (7). The chaotic laser output from the second output end of the coupler (3) is frequency-shifted by the first single-sideband modulator (9) and then polarized by the second polarization adjustment unit and enters the sensing fiber (8) as the second pump light from the other end. The laser output from the narrow linewidth laser (15) is pulse-modulated by the pulse modulator (18) and then used as probe light. It is incident on the polarization beam splitter (7) through the circulator (21). After passing through the polarization beam splitter (7), it is combined with the first pump light and enters the sensing fiber (8). The reflected light formed by the probe light being reflected by the chaotic Brillouin dynamic grating passes through the polarization beam splitter (7) and the circulator (21) and is received by the photodetector (22). After photoelectric conversion, the gain spectrum and reflection spectrum are collected by the lock-in amplifier (23) and sent to the host computer (24).

6. The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating according to claim 5, characterized in that, It also includes a first optical amplifier (4), a second optical amplifier (11) and a third optical amplifier (20); the first optical amplifier (4) is located between the first output end of the coupler (3) and the first polarization adjustment unit, and is used to amplify the chaotic laser signal at the first output end of the coupler (3); the second optical amplifier (11) is located at the output end of the first single-sideband modulator (9), and is used to amplify the low-frequency single-sideband optical signal output by the first single-sideband modulator (9); the third optical amplifier (20) is located between the pulse modulator (18) and the circulator (21), and is used to amplify the pulse probe light.

7. The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating according to claim 5, characterized in that, The first polarization adjustment unit includes a first polarization controller (5) and a first polarizer (6) arranged in sequence; the second polarization adjustment unit includes a second polarization controller (13) and a second polarizer (14) arranged in sequence.

8. The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating according to claim 5, characterized in that, It also includes an optical isolator (2), which is disposed between the output end of the chaotic laser (1) and the coupler (3).

9. The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating according to claim 5, characterized in that, It also includes an optical delay line (12), which is set between the second optical amplifier (11) and the second polarization controller (13) to adjust the optical path difference between the first pump light and the second pump light, thereby realizing the movement of the chaotic Brillouin dynamic grating along the entire sensing fiber (8).

10. The overhead cable icing monitoring device based on a chaotic Brillouin dynamic grating according to claim 5, characterized in that, It also includes a microwave signal source (10) and a pulse signal generator (19). The microwave signal source (10) is used to output a microwave signal to drive the first single-sideband modulator (9) to perform low-frequency single-sideband modulation to obtain a single-sideband with a lower frequency. The pulse signal generator (19) is used to drive the pulse modulator (18) to perform pulse modulation to obtain a pulsed probe light.

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