A method and system for submarine cable scour detection based on brillouin dynamic grating

Abstract

The application discloses a kind of based on Brillouin dynamic grating submarine cable scour detection method and system, it is related to submarine cable monitoring technical field, to realize accurately submarine cable state detection.The technical points of the present application include: the measuring optical fiber is wound and laid on submarine cable;The frequency interval of scanning pump light and the wavelength of probe light, the wide-band signal of Brillouin dynamic grating is collected using transverse pressure detection device;The wide-band signal is processed, and the pressure brought by ocean current scour submarine cable is obtained.The present application measures the transverse pressure generated by the scour of sea current to the surface of the optical fiber body wrapped outside submarine cable, to judge the pressure intensity of submarine cable affected by the scour of sea current.The present application has the advantages of high precision, real-time and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of submarine cable monitoring, and particularly relates to a submarine cable scouring detection method and system based on Brillouin dynamic grating. BACKGROUND

[0002] With the development of ocean clean energy and offshore wind power, submarine cables become an important channel connecting the ocean and the land. Submarine cables are installed underwater and laid on the seabed, and are long-term exposed to complex and changeable marine environment, corroded and scoured by high-salinity seawater, which easily causes the submarine cables to be exposed and suspended, and seriously threatens the mechanical and electrical properties of the submarine cables, and affects the long-term reliable operation of the submarine cables. Therefore, it is necessary to establish an online detection system for the health status of submarine cables in view of the operation of the submarine cables.

[0003] At present, there are few monitoring means for the submarine cable burial depth and the suspension of some sections caused by external forces such as ocean current scouring, and the existing submarine cable burial depth detection method has problems of long cycle, high cost and low detection efficiency. When the submarine cable is scoured by the ocean current, it is subjected to the pressure of the fluid perpendicular to the acting surface, and the change of the flow rate will change the pressure, so that the current ocean flow rate can be indirectly obtained by measuring the pressure. The pressure measurement of the submarine cable subjected to the scouring of the ocean current can be converted into the measurement of the lateral pressure generated on the surface of the submarine cable.

[0004] In recent years, with the continuous development of distributed optical fiber measurement technology, the use of optical fiber as a sensing element in the measurement system has become the main way of submarine cable monitoring. The use of optical fiber as a sensing unit for lateral pressure measurement has many advantages: first, it can effectively avoid electromagnetic interference and obtain more accurate measurement results; second, optical fiber has the characteristics of small size and light weight, and can be applied to more working environments; third, optical fiber is resistant to high temperature, has stable transmission, high sensitivity and fast response speed, and can realize distributed measurement. At present, the ocean flow rate lateral pressure optical fiber sensor is mainly based on various optical fiber interferometers and optical fiber gratings, but they are all point sensors and cannot realize large-scale and continuous distributed measurement. Some researchers have also used Brillouin optical time domain analysis technology to realize distributed measurement of fluid pressure, but the measurement accuracy is very low and far cannot meet the current application requirements. SUMMARY

[0005] In view of the above problems, the present application provides a submarine cable scouring detection method and system based on Brillouin dynamic grating to realize accurate submarine cable state detection.

[0006] According to an aspect of the present application, a submarine cable scouring detection method based on Brillouin dynamic grating is provided, which comprises:

[0007] The measurement fiber is wound and laid on the submarine cable;

[0008] The frequency interval of the scanning pump light and the wavelength of the probe light are scanned, and a wide-band signal of the Brillouin dynamic grating is collected by using a transverse pressure detection device;

[0009] The wide-band signal is processed to obtain the pressure caused by the ocean current scouring the submarine cable.

[0010] In one possible implementation, the measurement fiber includes a bow-tie polarization maintaining fiber, a panda polarization maintaining fiber or a photonic crystal fiber.

[0011] In one possible implementation, the transverse pressure detection device includes a narrow-line-width tunable laser 1, a first single-mode fiber coupler 2, a second single-mode fiber coupler 3, a first polarization controller 4, a first electro-optic modulator 5, a first erbium-doped fiber amplifier 6, a second polarization controller 7, a second erbium-doped fiber amplifier 8, a second electro-optic modulator 9, a third polarization controller 10, a fourth polarization controller 11, a third erbium-doped fiber amplifier 12, a third electro-optic modulator 13, a fifth polarization controller 14, a fourth electro-optic modulator 15, a fourth erbium-doped fiber amplifier 16, a sixth polarization controller 17, a polarization beam splitter 18, a circulator 19, a photodetector 20 and a data acquisition card 21.

[0012] The output end of the narrow-line-width tunable laser 1 is connected to the input end of the first single-mode fiber coupler 2, the output end of the first single-mode fiber coupler 2 is connected to the input end of the second single-mode fiber coupler 3 and the fourth polarization controller 11 respectively, the output end of the second single-mode fiber coupler 3 is connected to the input end of the first polarization controller 4 and the second erbium-doped fiber amplifier 8 respectively, the output end of the first polarization controller 4 is connected to the input end of the first electro-optic modulator 5, the output end of the first electro-optic modulator 5 is connected to the input end of the first erbium-doped fiber amplifier 6, the output end of the first erbium-doped fiber amplifier 6 is connected to the input end of the second polarization controller 7, the output end of the second polarization controller 7 is connected to one end of the measurement fiber, the other end of the measurement fiber is connected to one end of the polarization beam splitter 18, the output end of the second erbium-doped fiber amplifier 8 is connected to the input end of the second electro-optic modulator 9, the output end of the second electro-optic modulator 9 is connected to the input end of the third polarization controller 10, the output end of the third polarization controller 10 is connected to one end of the polarization beam splitter 18.

[0013] The output end of the fourth polarization controller 11 is connected with the input end of the third erbium-doped fiber amplifier 12; the output end of the third erbium-doped fiber amplifier 12 is connected with the input end of the third electro-optic modulator 13, the output end of the third electro-optic modulator 13 is connected with the input end of the fifth polarization controller 14; the output end of the fifth polarization controller 14 is connected with the input end of the fourth electro-optic modulator 15, the output end of the fourth electro-optic modulator 15 is connected with the input end of the fourth erbium-doped fiber amplifier 16, the output end of the fourth erbium-doped fiber amplifier 16 is connected with the input end of the sixth polarization controller 17, the output end of the sixth polarization controller 17 is connected with the 1 port of the circulator 19, the 2 port of the circulator 19 is connected with one end of the polarization beam splitter 18; the 3 port of the circulator 19 is connected with the input end of the photoelectric detector 20, the output end of the photoelectric detector 20 is connected with the input end of the data acquisition card 21.

[0014] In one possible implementation, the acquiring, by the lateral pressure detection device, a wide-band signal of the Brillouin dynamic grating includes:

[0015] The continuous light output by the narrow-linewidth tunable laser 1 is divided into two paths of light through the 90%:10% first single-mode fiber coupler 2;

[0016] The first path is: the 90% power light is divided into the upper continuous pump light and the lower pump light through the 50%:50% second single-mode fiber coupler 3, the 50% power upper continuous pump light generates a frequency-reduced Brillouin frequency shift after passing through the first polarization controller 4 and the first electro-optic modulator 5, and is amplified in power through the first erbium-doped fiber amplifier 6 to serve as the low-frequency pump light for exciting the Brillouin dynamic grating; then the upper continuous pump light is modulated into the polarization in the x direction through the second polarization controller 7 and then enters the measurement fiber; the other 50% power lower pump light is amplified in optical signal through the second erbium-doped fiber amplifier 8, then is modulated into the pump pulse light through the second electro-optic modulator 9 to serve as the high-frequency pump light for exciting the Brillouin dynamic grating, then the polarization state of the high-frequency pump light is modulated into the polarization in the x direction through the third polarization controller 10, and then the high-frequency pump light enters the polarization beam splitter 18 and then enters the measurement fiber; the upper and lower pump lights are input from the two ends of the measurement fiber in opposite directions, meet in the fiber to generate stimulated Brillouin scattering, and form the moving Brillouin dynamic grating;

[0017] The second path is: 10% power light as probe light, after the polarization state is modulated by the fourth polarization controller 11, the optical signal is amplified by the third erbium-doped fiber amplifier 12; then the probe light is modulated to be higher than the frequency difference between the high-frequency pump light and the low-frequency pump light by the third electro-optic modulator 13; then the polarization state is adjusted by the fifth polarization controller 14, and the probe pulse light is modulated by the fourth electro-optic modulator 15 with a pulse generator; then the optical signal is amplified by the fourth erbium-doped fiber amplifier 16 again, and then the polarization is modulated to be the y direction by the sixth polarization controller 17, and then injected through the 1 port of the circulator 19, and then output through the 2 port into the polarization beam splitter 18, and then into the measurement optical fiber; the probe pulse light is reflected after passing through the Brillouin dynamic grating, and the reflected broadband signal has a Brillouin frequency shift from the frequency of the incident probe pulse light;

[0018] The reflected broadband signal enters the photodetector 20 through the 3 port of the circulator 19 for photoelectric conversion, and then enters the data acquisition card 21 for acquisition.

[0019] In one possible implementation, the processing of the broadband signal to obtain the pressure caused by the ocean current scouring the submarine cable includes:

[0020] Fitting the acquired broadband signal to obtain the frequency shift of the Brillouin dynamic grating;

[0021] Calculating the birefringence frequency distribution of the optical fiber according to the frequency shift of the Brillouin dynamic grating;

[0022] Obtaining the pressure caused by the ocean current scouring the submarine cable according to the birefringence frequency distribution; wherein the birefringence frequency distribution and the pressure are in a linear relationship.

[0023] In one possible implementation, the birefringence frequency distribution δ(Δv) of the optical fiber is calculated according to the following formula:

[0024]

[0025] In the formula, Δv represents the frequency shift change amount of the Brillouin dynamic grating; δ represents the average value of the frequency shift change amount; B represents the birefringence of the optical fiber; c represents the speed of light in vacuum; n represents the average refractive index of the optical fiber; and λ represents the wavelength of the incident light.

[0026] According to another aspect of the present application, a submarine cable scouring detection system based on a Brillouin dynamic grating is provided, which comprises:

[0027] The signal acquisition module is configured to wind the measurement optical fiber on the submarine cable; scan the frequency interval of the pump light and the wavelength of the probe light, and acquire the broadband signal of the Brillouin dynamic grating by using the transverse pressure detection device;

[0028] A signal processing module configured to process the wide-band signal to obtain the pressure caused by the ocean current scouring the submarine cable.

[0029] In one possible implementation, the measurement fiber used includes a bow-tie polarization maintaining fiber, a panda polarization maintaining fiber or a photonic crystal fiber.

[0030] In one possible implementation, the processing of the wide-band signal in the signal processing module to obtain the pressure caused by the ocean current scouring the submarine cable includes:

[0031] Fitting the collected wide-band signal to obtain the frequency shift of the Brillouin dynamic grating;

[0032] Calculating the birefringence frequency distribution of the fiber according to the frequency shift of the Brillouin dynamic grating;

[0033] Obtaining the pressure caused by the ocean current scouring the submarine cable according to the birefringence frequency distribution; wherein the birefringence frequency distribution and the pressure are in a linear relationship.

[0034] In one possible implementation, the signal processing module calculates the birefringence frequency distribution of the fiber according to the following formula:

[0035]

[0036] In the formula, Δv represents the change amount of the frequency shift of the Brillouin dynamic grating; δ represents the average value of the change amount of the frequency shift; B represents the birefringence of the fiber; c represents the speed of light in vacuum; n represents the average refractive index of the fiber, and λ represents the wavelength of the incident light.

[0037] The present application has the following beneficial technical effects:

[0038] The present application provides a submarine cable scouring detection method and system based on a Brillouin dynamic grating. First, a measurement fiber is wound and laid on a submarine cable. Then, the frequency interval of the pump light and the wavelength of the probe light are scanned, and the wide-band signal of the Brillouin dynamic grating is collected by a transverse pressure detection device. Then, the wide-band signal is processed to obtain the pressure caused by the ocean current scouring the submarine cable. By measuring the transverse pressure generated by the ocean current scouring the surface of the fiber body wrapped outside the submarine cable, the strength of the pressure acting on the submarine cable due to the ocean current scouring is determined. The present application has the following advantages:

[0039] 1) High precision: By using the fiber Brillouin dynamic grating technology, the pressure caused by the ocean current scouring the submarine cable is obtained, and the current ocean flow rate is indirectly obtained according to the pressure, so that the ocean flow rate can be monitored in real time, and high-precision ocean flow rate measurement results can be provided.

[0040] 2) Real-time: The ocean flow rate information can be obtained in real time to provide timely detection results.

[0041] 3) The lateral pressure detection device for collecting signals has the advantage of distributed pressure measurement, which can continuously measure the lateral pressure in a long distance range. BRIEF DESCRIPTION OF DRAWINGS

[0042] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which a number of embodiments of the application are shown by way of example, and in which:

[0043] Figure 1 is a flow chart of a submarine cable scour detection method based on Brillouin dynamic grating according to an embodiment of the present application.

[0044] Figure 2 is a schematic diagram of a submarine cable model according to an embodiment of the present application; wherein: 1 - oil duct; 2 - copper conductor; 3 - oil paper insulation; 4 - lead sheath; 5 - PP buffer layer; 6 - armored steel wire; 7 - optical unit; 8 - polypropylene outer layer.

[0045] Figure 3 is a structural schematic diagram of a lateral pressure detection device according to an embodiment of the present application.

[0046] Figure 4 is a structural schematic diagram of a submarine cable scour detection system based on Brillouin dynamic grating according to an embodiment of the present application. DETAILED DESCRIPTION

[0047] The principles and spirits of the present application will be described below with reference to a number of exemplary embodiments. It should be understood that these embodiments are given only to enable those skilled in the art to better understand and implement the present application, and do not limit the scope of the present application in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0048] An embodiment of the present application proposes a submarine cable scour detection method based on Brillouin dynamic grating, as shown in Figure 1 The method comprises:

[0049] S1, winding and laying a measurement optical fiber on a submarine cable;

[0050] S2, scanning the frequency interval of the pump light and the wavelength of the probe light, and collecting the wide-band signals of the Brillouin dynamic grating by using a lateral pressure detection device;

[0051] S3, processing the wide-band signals to obtain the pressure caused by the ocean current scouring the submarine cable.

[0052] The method starts at S1. In S1, the measurement fiber is wound and laid on the submarine cable.

[0053] According to the embodiment of the present application, the measurement fiber is wound or laid longitudinally on the outside of the polypropylene outer sheath of the submarine cable while laying the submarine cable. The submarine cable model is shown in Figure 2 The measurement fiber used in the present application can be a bow-tie polarization maintaining fiber, a panda polarization maintaining fiber or a photonic crystal fiber.

[0054] Then S2 is performed, in which the frequency interval of the pump light and the wavelength of the probe light are scanned, and the wide-band signals of the Brillouin dynamic grating are collected by the lateral pressure detection device.

[0055] According to the embodiment of the present application, when the ocean current washes the submarine cable and the measurement fiber, the submarine cable and the fiber are subjected to external lateral pressure, and the birefringence frequency of the measurement fiber changes with the external pressure. Since the Brillouin dynamic grating is sensitive to the change of the birefringence of the fiber, the change of the birefringence frequency shift of the fiber caused by the external lateral pressure is measured by exciting and detecting the Brillouin dynamic grating in the measurement fiber, so as to demodulate the position and size of the lateral pressure on the fiber, and obtain the size of the washing effect of the submarine cable by the ocean current, and further judge the health status of the submarine cable.

[0056] The frequency interval of the pump light and the wavelength of the probe light are scanned, and the wide-band signals of the Brillouin dynamic grating are collected by the lateral pressure detection device. The frequency shift of the Brillouin dynamic grating can be calculated by analysis and Lorentz fitting. Since the frequency shift of the Brillouin dynamic grating is sensitive to the birefringence frequency value, the birefringence distribution of the fiber can be obtained, and the lateral pressure on the surface of the fiber is obtained, so as to obtain the pressure caused by the ocean current washing the submarine cable.

[0057] In the embodiment, as shown in Figure 3 The lateral pressure detection device includes a narrow-line-width tunable laser 1, a first single-mode fiber coupler 2, a second single-mode fiber coupler 3, a first polarization controller 4, a first electro-optic modulator 5, a first erbium-doped fiber amplifier 6, a second polarization controller 7, a second erbium-doped fiber amplifier 8, a second electro-optic modulator 9, a third polarization controller 10, a fourth polarization controller 11, a third erbium-doped fiber amplifier 12, a third electro-optic modulator 13, a fifth polarization controller 14, a fourth electro-optic modulator 15, a fourth erbium-doped fiber amplifier 16, a sixth polarization controller 17, a polarization beam splitter 18, a circulator 19, a photodetector 20, and a data acquisition card 21.

[0058] The output end of the narrow line width tunable laser 1 is connected with the input end of the first single-mode fiber coupler 2, the output end of the first single-mode fiber coupler 2 is connected with the input end of the second single-mode fiber coupler 3 and the fourth polarization controller 11 respectively; the output end of the second single-mode fiber coupler 3 is connected with the input end of the first polarization controller 4 and the second erbium-doped fiber amplifier 8 respectively; the output end of the first polarization controller 4 is connected with the input end of the first electro-optic modulator 5, the output end of the first electro-optic modulator 5 is connected with the input end of the first erbium-doped fiber amplifier 6, the output end of the first erbium-doped fiber amplifier 6 is connected with the input end of the second polarization controller 7, and the output end of the second polarization controller 7 is connected with one end of a measuring optical fiber, and the other end of the measuring optical fiber is connected with one end of a polarization beam splitter 18; the output end of the second erbium-doped fiber amplifier 8 is connected with the input end of the second electro-optic modulator 9, the output end of the second electro-optic modulator 9 is connected with the input end of the third polarization controller 10, and the output end of the third polarization controller 10 is connected with one end of the polarization beam splitter 18;

[0059] The output end of the fourth polarization controller 11 is connected with the input end of the third erbium-doped fiber amplifier 12; the output end of the third erbium-doped fiber amplifier 12 is connected with the input end of the third electro-optic modulator 13, the output end of the third electro-optic modulator 13 is connected with the input end of the fifth polarization controller 14; the output end of the fifth polarization controller 14 is connected with the input end of the fourth electro-optic modulator 15, the output end of the fourth electro-optic modulator 15 is connected with the input end of the fourth erbium-doped fiber amplifier 16, the output end of the fourth erbium-doped fiber amplifier 16 is connected with the input end of the sixth polarization controller 17, and the output end of the sixth polarization controller 17 is connected with the 1 port of a circulator 19, the 2 port of the circulator 19 is connected with one end of the polarization beam splitter 18; the 3 port of the circulator 19 is connected with the input end of a photoelectric detector 20, and the output end of the photoelectric detector 20 is connected with the input end of a data acquisition card 21.

[0060] The working principle of the signal acquisition is that the continuous light with a frequency of v output by the narrow line width tunable laser 1 is divided into two paths through the 90%:10% first single-mode fiber coupler 2;

[0061] The first path is: 90% power light passes through the 50%:50% second single-mode fiber coupler 3 to divide into the upper continuous wave pump light and the lower pump light, 50% power of the upper continuous wave pump light passes through the first polarization controller 4 and the first electro-optic modulator 5 to generate a frequency down-converted Brillouin frequency shift, and then passes through the first erbium-doped fiber amplifier 6 to be amplified as the low-frequency pump light of the stimulated Brillouin dynamic grating; then the low-frequency pump light passes through the second polarization controller 7 to be modulated into the x-direction polarization and then enters the measurement fiber; the other 50% power of the lower pump light passes through the second erbium-doped fiber amplifier 8 to be amplified, and then passes through the second electro-optic modulator 9 to be modulated into the pump pulse light as the high-frequency pump light of the stimulated Brillouin dynamic grating, and then passes through the third polarization controller 10 to modulate the polarization state of the high-frequency pump light into the x-direction polarization, and then enters the polarization beam splitter 18 and then enters the measurement fiber; the upper and lower pump lights are input from the two ends of the measurement fiber in opposite directions, meet in the fiber to generate stimulated Brillouin scattering, and form the moving Brillouin dynamic grating;

[0062] The second path is: 10% power light as probe light passes through the fourth polarization controller 11 to modulate the polarization state, and then passes through the third erbium-doped fiber amplifier 12 to be amplified; then the probe light passes through the third electro-optic modulator 13 to be modulated into the probe pulse light with a frequency higher than the frequency difference Δf of the high-frequency pump light and the low-frequency pump light, and the frequency of the probe light is v probe = v + Δf; then the probe light passes through the fifth polarization controller 14 to adjust the polarization state, and then passes through the fourth electro-optic modulator 15 with the pulse generator to be modulated into the probe pulse light; then the probe pulse light passes through the fourth erbium-doped fiber amplifier 16 to be amplified, and then passes through the sixth polarization controller 17 to be modulated into the y-direction polarization, and then enters the 1-port of the circulator 19, and then is output from the 2-port to enter the polarization beam splitter 18 and then enters the measurement fiber; then the probe pulse light is reflected after passing through the Brillouin dynamic grating, and the reflected broadband signal has a Brillouin frequency shift from the frequency of the incident probe pulse light;

[0063] The reflected broadband signal enters the photodetector 20 through the 3-port of the circulator 19 to be converted into an electrical signal, and then enters the data acquisition card 21 to be collected.

[0064] In the above signal acquisition process, the low-frequency pump light and the high-frequency pump light enter the optical fiber from both ends, interact in the optical fiber, and if the frequency difference between the two is close to the Brillouin frequency shift of the optical fiber, stimulated Brillouin scattering occurs in the optical fiber, the energy of the high-frequency pump light is transferred to the low-frequency pump light, and a Brillouin dynamic grating is formed in the optical fiber. The probe light pulse is reflected after passing through the Brillouin dynamic grating, and the reflected light also has a Brillouin frequency shift from the incident probe light pulse. When collecting, the frequency difference between the two pump lights is set to the Brillouin frequency shift of the optical fiber, and the wavelength of the probe light pulse is scanned to measure the Brillouin dynamic grating spectrum. The wide-band signal obtained by the data acquisition card 21 is the rate of change of light intensity with time, and the light intensity represents the signal intensity reflected by the Brillouin dynamic grating. Since a pulse is used as a signal trigger, the time information obtained by the data acquisition card is the time of flight of the pulse, which is equivalent to the position.

[0065] Then, by performing Lorentz fitting on the Brillouin dynamic grating spectrum, the Brillouin dynamic grating frequency shift can be obtained; since the Brillouin dynamic grating frequency shift is sensitive to the birefringence of the optical fiber, the birefringence distribution of the optical fiber can be obtained, and the relationship between the birefringence and the frequency shift is shown in formula (1). When the surface of the optical fiber is subjected to transverse pressure, the birefringence of the optical fiber will change, and by measuring the birefringence, the pressure caused by the ocean current scouring the submarine cable can be obtained, wherein the birefringence frequency distribution is linearly related to the pressure.

[0066]

[0067] Wherein, Δv represents the frequency shift change of the Brillouin dynamic grating; δ represents the average value of the frequency shift change; B is the birefringence of the optical fiber, c is the speed of light in vacuum, n is the average refractive index of the optical fiber, and λ is the wavelength of the incident light.

[0068] The Brillouin frequency shift is related to the refractive index, Young's modulus E, fiber density ρ, Poisson's ratio k and other parameters of the optical fiber, and the frequency shift v can be obtained B :

[0069]

[0070] Another embodiment of the present application provides a submarine cable scouring detection system based on a Brillouin dynamic grating, as shown in Figure 4 The system comprises:

[0071] The signal acquisition module 410 is configured to wind the measurement optical fiber on the submarine cable; scan the frequency interval of the pump light and the wavelength of the probe light, and use the transverse pressure detection device to acquire the wide-band signal of the Brillouin dynamic grating;

[0072] The signal processing module 420 is configured to process the wide-band signal to obtain the pressure caused by the ocean current scouring the submarine cable.

[0073] Optionally, in the embodiment, the measurement fiber comprises a bow-tie polarization maintaining fiber, a panda polarization maintaining fiber or a photonic crystal fiber.

[0074] Optionally, in the embodiment, the signal processing module 420 processes the wideband signal to obtain the pressure on the submarine cable caused by the ocean current scouring.

[0075] The collected wideband signal is fitted to obtain the frequency shift of the Brillouin dynamic grating;

[0076] The birefringence frequency distribution of the fiber is calculated according to the frequency shift of the Brillouin dynamic grating;

[0077] The pressure on the submarine cable caused by the ocean current scouring is obtained according to the birefringence frequency distribution; wherein the birefringence frequency distribution and the pressure are in linear relationship.

[0078] Optionally, in the embodiment, the signal processing module 420 calculates the birefringence frequency distribution of the fiber according to the following formula:

[0079]

[0080] In the formula, Δv represents the frequency shift variation of the Brillouin dynamic grating; δ represents the average value of the frequency shift variation; B represents the birefringence of the fiber; c represents the speed of light in vacuum; n represents the average refractive index of the fiber, and λ represents the wavelength of the incident light.

[0081] The function of the submarine cable scouring detection system based on the Brillouin dynamic grating in the embodiment can be explained by the aforementioned submarine cable scouring detection method based on the Brillouin dynamic grating, and therefore, the part not described in detail in the embodiment can be referred to the aforementioned method embodiment.

[0082] Although the operations of the method of the present application are described in a particular order in the drawings, this does not require or imply that the operations must be performed in that particular order, or that all of the illustrated operations must be performed to achieve the desired results. Additionally or alternatively, certain steps can be omitted, combined, performed simultaneously, and / or performed in a different order.

[0083] Although the spirit and principles of the present application have been described with reference to several specific embodiments, it should be understood that the present application is not limited to the disclosed specific embodiments, and the division of aspects does not mean that the features in these aspects cannot be combined to benefit. The division is only for the convenience of expression. The present application is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims.

Claims

1. A method for detecting scour of submarine cables based on a Brillouin dynamic grating, characterized in that, include: The measuring optical fiber is wound and laid on the submarine cable; The frequency interval of the pump light and the wavelength of the probe light are scanned, and the broadband signal of the Brillouin dynamic grating is acquired using a transverse pressure detection device. Processing the broadband signal to obtain the pressure caused by ocean currents scouring the submarine cable; including: The frequency shift of the Brillouin dynamic grating is obtained by fitting the acquired wideband signal. The birefringence frequency distribution of the optical fiber is obtained by calculating the frequency shift of the Brillouin dynamic grating, and then calculated according to the following formula. ( ): ； In the formula, This represents the frequency shift change of the Brillouin dynamic grating; λ represents the average value of the frequency shift change; B represents the birefringence of the optical fiber; c represents the speed of light in a vacuum; n represents the average refractive index of the optical fiber; and λ represents the wavelength of the incident light. The pressure caused by ocean currents scouring the submarine cable is obtained based on the birefringence frequency distribution; wherein, the birefringence frequency distribution and the pressure have a linear relationship.

2. The method for detecting submarine cable scour based on a Brillouin dynamic grating according to claim 1, characterized in that, The measuring optical fiber includes bowtie polarization-maintaining fiber, panda polarization-maintaining fiber, or photonic crystal fiber.

3. The method for detecting submarine cable scour based on a Brillouin dynamic grating according to claim 1, characterized in that, The transverse pressure detection device includes: a narrow linewidth tunable laser (1), a first single-mode fiber coupler (2), a second single-mode fiber coupler (3), a first polarization controller (4), a first electro-optic modulator (5), a first erbium-doped fiber amplifier (6), a second polarization controller (7), a second erbium-doped fiber amplifier (8), a second electro-optic modulator (9), a third polarization controller (10), a fourth polarization controller (11), a third erbium-doped fiber amplifier (12), a third electro-optic modulator (13), a fifth polarization controller (14), a fourth electro-optic modulator (15), a fourth erbium-doped fiber amplifier (16), a sixth polarization controller (17), a polarization beam splitter (18), a circulator (19), a photodetector (20), and a data acquisition card (21). Among them, the output end of the narrow linewidth tunable laser (1) is connected to the input end of the first single-mode fiber coupler (2), and the output end of the first single-mode fiber coupler (2) is connected to the input ends of the second single-mode fiber coupler (3) and the fourth polarization controller (11), respectively; the output end of the second single-mode fiber coupler (3) is connected to the input ends of the first polarization controller (4) and the second erbium-doped fiber amplifier (8), respectively; the output end of the first polarization controller (4) is connected to the input end of the first electro-optic modulator (5), and the output end of the first electro-optic modulator (5) is connected to the first erbium-doped fiber amplifier (8). The input end of the erbium-doped fiber amplifier (6) is connected to the input end of the second polarization controller (7), the output end of the second polarization controller (7) is connected to one end of the measuring fiber, and the other end of the measuring fiber is connected to one end of the polarization beam splitter (18); the output end of the second erbium-doped fiber amplifier (8) is connected to the input end of the second electro-optic modulator (9), the output end of the second electro-optic modulator (9) is connected to the input end of the third polarization controller (10), and the output end of the third polarization controller (10) is connected to one end of the polarization beam splitter (18); The output of the fourth polarization controller (11) is connected to the input of the third erbium-doped fiber amplifier (12); the output of the third erbium-doped fiber amplifier (12) is connected to the input of the third electro-optic modulator (13), the output of the third electro-optic modulator (13) is connected to the input of the fifth polarization controller (14); the output of the fifth polarization controller (14) is connected to the input of the fourth electro-optic modulator (15), the output of the fourth electro-optic modulator (15) is connected to the input of the fourth erbium-doped fiber amplifier (16), the output of the fourth erbium-doped fiber amplifier (16) is connected to the input of the sixth polarization controller (17), the output of the sixth polarization controller (17) is connected to port 1 of the circulator (19), port 2 of the circulator (19) is connected to one end of the polarization beam splitter (18); port 3 of the circulator (19) is connected to the input of the photodetector (20), and the output of the photodetector (20) is connected to the input of the data acquisition card (21).

4. The method for detecting submarine cable scour based on a Brillouin dynamic grating according to claim 3, characterized in that, The method of acquiring broadband signals of Brillouin dynamic gratings using a lateral pressure detection device includes: The narrow linewidth tunable laser (1) outputs continuous light, which is split into two beams by a first single-mode fiber coupler (2) with a ratio of 90%:10%. The first path consists of: 90% power light passing through a 50%:50% second single-mode fiber coupler (3) to split into an upper continuous pump light and a lower pump light. The 50% power upper continuous pump light, after passing through a first polarization controller (4) and a first electro-optic modulator (5), generates a Brillouin frequency shift with a decreasing frequency. After being amplified by a first erbium-doped fiber amplifier (6), it serves as the low-frequency pump light to excite the Brillouin dynamic grating. Subsequently, it is modulated into x-direction polarization by a second polarization controller (7) before entering the measurement fiber; the other 50%... The power of the lower pump light is amplified by the second erbium-doped fiber amplifier (8), and then modulated into pump pulse light by the second electro-optic modulator (9) as the high-frequency pump light to excite the Brillouin dynamic grating. Then, the polarization state of the high-frequency pump light is modulated to the x-direction polarization by the third polarization controller (10) and then enters the polarization beam splitter (18) and then enters the measurement fiber. The upper and lower pump lights are input from the two ends of the measurement fiber respectively, meet in the fiber and generate stimulated Brillouin scattering to form a moving Brillouin dynamic grating. The second path is as follows: 10% power light is used as probe light. After the polarization state is modulated by the fourth polarization controller (11), the light signal is amplified by the third erbium-doped fiber amplifier (12). Then, it is modulated by the third electro-optic modulator (13) into probe light with a higher frequency difference than that between the high-frequency pump light and the low-frequency pump light. After the polarization state is adjusted by the fifth polarization controller (14), it is modulated into probe pulse light by the fourth electro-optic modulator (15) with a pulse generator. Then, the light signal is amplified by the fourth erbium-doped fiber amplifier (16). After being modulated into y-direction polarization by the sixth polarization controller (17), it is injected through port 1 of the circulator (19) and output through port 2 into the polarization beam splitter (18), and then into the measurement fiber. The probe pulse light is reflected after passing through the Brillouin dynamic grating. The frequency of the reflected broadband signal is different from that of the incident probe pulse light by a Brillouin frequency shift. The reflected broadband signal enters the photodetector (20) through port 3 of the circulator (19) for photoelectric conversion, and then enters the data acquisition card (21) for acquisition.

5. A submarine cable scour detection system based on a Brillouin dynamic grating, characterized in that, include: The signal acquisition module is configured to wrap and lay the measuring optical fiber on the submarine cable; scan the frequency interval of the pump light and the wavelength of the probe light, and acquire the broadband signal of the Brillouin dynamic grating using the lateral pressure detection device. A signal processing module, configured to process the broadband signal to obtain the pressure exerted by the ocean current scouring the submarine cable, includes: The frequency shift of the Brillouin dynamic grating is obtained by fitting the acquired wideband signal. The birefringence frequency distribution of the optical fiber is obtained by calculating the frequency shift of the Brillouin dynamic grating; the birefringence frequency distribution of the optical fiber is calculated according to the following formula: ； In the formula, This represents the frequency shift change of the Brillouin dynamic grating; λ represents the average value of the frequency shift change; B represents the birefringence of the optical fiber; c represents the speed of light in a vacuum; n represents the average refractive index of the optical fiber; and λ represents the wavelength of the incident light. The pressure caused by ocean currents scouring the submarine cable is obtained from the birefringence frequency distribution; wherein the birefringence frequency distribution and the pressure have a linear relationship.

6. The submarine cable scour detection system based on a Brillouin dynamic grating according to claim 5, characterized in that, The measuring optical fiber includes bowtie polarization-maintaining fiber, panda polarization-maintaining fiber, or photonic crystal fiber.

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