CN115508754A - Optical fiber magnetic field sensor and method based on stimulated Brillouin scattering - Google Patents
Optical fiber magnetic field sensor and method based on stimulated Brillouin scattering Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 121
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- 238000000691 measurement method Methods 0.000 claims description 3
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- 229910000859 α-Fe Inorganic materials 0.000 claims description 3
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- 229910000990 Ni alloy Inorganic materials 0.000 claims 1
- 238000002360 preparation method Methods 0.000 claims 1
- 230000004044 response Effects 0.000 abstract description 7
- 238000001228 spectrum Methods 0.000 description 12
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
- 229910001329 Terfenol-D Inorganic materials 0.000 description 6
- 238000005086 pumping Methods 0.000 description 6
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- G01R33/032—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
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Abstract
The invention belongs to the technical field of optical devices, and particularly discloses an optical fiber magnetic field sensor and an optical fiber magnetic field sensing method based on stimulated Brillouin scattering. The method comprises the following steps: the magnetostrictive coating is arranged on the periphery of a cladding of the single-mode optical fiber and drives the single-mode optical fiber to generate axial length change under the action of an external magnetic field; the pump light source is connected with the incident end of the single-mode fiber through the fiber circulator, the pump light input to the single-mode fiber by the pump light source generates stimulated Brillouin scattering and is converted into reverse SBS light, and the SBS light is subjected to frequency shift due to the change of the axial length of the single-mode fiber; the spectrometer is connected with the incident end of the single-mode optical fiber through the optical fiber circulator and is used for measuring the frequency shift quantity of SBS light in real time; and the controller is used for acquiring the size and the variation of the magnetic field according to the axial length change of the single-mode fiber and the frequency shift quantity of the SBS light. The invention has the advantages of simple structure, high response speed and the like.
Description
Technical Field
The invention belongs to the technical field of optical devices, and particularly relates to an optical fiber magnetic field sensor and an optical fiber magnetic field sensing method based on stimulated Brillouin scattering.
Background
The magnetic field sensor has important application value in the fields of geological survey, biomedicine, national defense safety and the like. The optical fiber magnetic field sensor using light waves as sensing signals has the advantages of plasticity, electromagnetic interference resistance, corrosion resistance, low cost, easiness in real-time monitoring, integration and multiplexing and the like, and is widely concerned at home and abroad. Among them, the optical fiber magnetic field sensor based on the magnetostrictive effect has the properties of fast response, magnetostrictive strain property and the like, has a simple structure and high reliability, and becomes an optical fiber magnetic field sensor with higher attention at present.
Under the action of an external magnetic field, a material with magnetostrictive property will stretch along the magnetization direction, and this phenomenon is called magnetostrictive effect. In 1980, A Yariv et al plated magnetostrictive material nickel on optical fiber, and the measurement of weak magnetic field was realized for the first time. With the development of magnetostrictive materials, it has been found that rare earth materials such as TbDyFe alloy (also known as Terfenol-D) have a magnetostrictive coefficient of 10 -3 The magnitude of the magnetic field sensor is 40-50 times that of a nickel-based material, and the development of the optical fiber magnetic field sensor based on the magnetostrictive effect is greatly promoted. In 2009, yang et al first applied magnetron sputtering technology to deposit Terfenol-D film on fiber Bragg grating, and the resonant wavelength of the grating was measuredMove to achieve magnetic field measurements. In 2013, wuhan university proposes that the cladding of the FBG is processed into a compact spiral shape with uniform period by femtosecond, and then a Terfenol-D film is plated on the outer surface of the cladding of the FBG. As the magnetic field changes, the Terfenol-D film deforms, thereby modulating the FBG's reflection spectrum. In 2015, zhang et al proposed a device combining Terfenol-D material with an optical fiber Fabry-Perot interferometer, and realized ultra-high sensitivity magnetic field measurement. In addition, magnetic field sensors based on single-mode-multimode-single-mode fiber and magnetostrictive sleeve structures have also been proposed in succession. The size of the magnetic field is obtained by measuring the drift amount of the wave trough position of the interference transmission spectrum, namely, the optical fiber magnetic field sensor in the prior art is mostly based on two principles of an optical fiber Bragg grating and an optical fiber Fabry-Perot interferometer, and the structure and the manufacturing process are complex.
Disclosure of Invention
In view of the above-mentioned drawbacks and needs of the prior art, the present invention provides a fiber magnetic field sensor and method based on stimulated brillouin scattering, in which a magnetostrictive coating is attached to a surface of an optical fiber in a tubular shape, pump light is injected from one end of the optical fiber, and SBS light generated due to the stimulated brillouin scattering is reversely emitted from an incident end of the optical fiber. When an external magnetic field or a magnetic field component parallel to the axial direction of the optical fiber exists, the magnetostrictive coating drives the optical fiber to axially expand and contract, so that the SBS gain spectrum frequency shift is caused. The size and the variation of the magnetic field can be obtained by measuring the frequency shift quantity of the SBS gain spectrum, so that the magnetic field sensing function is realized. The device has the advantages of simple structure, high response speed and the like.
To achieve the above object, according to one aspect of the present invention, there is provided a fiber magnetic field sensor based on stimulated brillouin scattering, comprising: the magnetostrictive coating is arranged on the periphery of a cladding of the single-mode optical fiber and drives the single-mode optical fiber to generate axial length change under the action of an external magnetic field; the pump light source is connected with the incident end of the single-mode fiber through the fiber circulator, the pump light input to the single-mode fiber by the pump light source generates stimulated Brillouin scattering and is converted into reverse SBS light, and the SBS light is subjected to frequency shift due to the change of the axial length of the single-mode fiber; the spectrometer is connected with the incident end of the single-mode optical fiber through the optical fiber circulator and is used for measuring the frequency shift quantity of SBS light in real time; and the controller is used for acquiring the size and the variation of the magnetic field according to the axial length change of the single-mode fiber and the frequency shift quantity of the SBS light.
More preferably, the SBS light has a frequency shift amount of:
wherein, the first and the second end of the pipe are connected with each other,
is the amount of frequency shift of the SBS light,
is a coefficient of a dimensionless quantity,
is the axial length variation of the single-mode optical fiber.
As a further preferred, the controller is integrated with a graph of the axial length change of the single-mode optical fiber and the magnitude of the external magnetic field;
the relation graph is obtained by placing the optical fiber magnetic field sensor into standard magnetic fields with different sizes according to the size of the magnetic field and the frequency shift quantity of SBS light.
As a further preferred, the magnetostrictive coating is: one of ferrite magnetostrictive material, metal or alloy magnetostrictive material or rare earth giant magnetostrictive material is mixed with epoxy resin and polyamide curing agent according to a certain proportion to prepare the material.
As a further preference, the metal or alloy magnetostrictive material comprises one of a Ni-Co-Cr alloy, a Fe-Al alloy, a Fe-Ni alloy or a Ni metal;
the rare earth giant magnetostrictive material comprises Tb-Dy-Fe magnetostrictive alloy.
According to another aspect of the present invention, there is also provided a measurement method of a fiber optic magnetic field sensor based on stimulated brillouin scattering, including the steps of:
s11, injecting pump light into an incident end of the single-mode fiber, adjusting the power of the pump light to enable the optical power of the pump light to exceed an SBS threshold value, generating stimulated Brillouin scattering, converting the incident pump light into reverse SBS light, and emitting the reverse SBS light from the incident end in a reverse direction;
s12, placing the single mode fiber wrapped with the magnetostrictive coating into a magnetic field to be measured, wherein the magnetostrictive coating drives the single mode fiber to generate axial length change under the action of an external magnetic field;
s13, the SBS light is subjected to frequency shift due to the axial length change of the single-mode optical fiber, and the frequency shift quantity of the SBS light is measured in real time;
and S14, acquiring the size and the variation of the magnetic field according to the axial length variation of the single-mode fiber and the frequency shift quantity of the SBS light.
Preferably, before measurement, the optical fiber magnetic field sensor needs to be calibrated to obtain a relationship diagram between the axial length change of the single-mode optical fiber and the external magnetic field, which is specifically as follows:
the optical fiber magnetic field sensor is placed in standard magnetic fields with different strengths, the frequency shift quantity of SBS light under the magnetic fields with different strengths is obtained by changing the strength of the standard magnetic field, the axial length change of the single-mode optical fiber is obtained according to the frequency shift quantity of the SBS light and the size and the variable quantity of the strength of the standard magnetic field, and a relational graph of the axial length change of the single-mode optical fiber and the size of an external magnetic field is drawn according to the axial length change of the single-mode optical fiber.
Preferably, the arrangement direction of the optical fiber magnetic field sensor is changed, and steps S12 and S13 are repeated to obtain the frequency shift amount of the plurality of sets of SBS light, so as to calculate the magnitude and the variation amount of the magnetic field.
According to another aspect of the present invention, there is also provided a method for manufacturing an optical fiber magnetic field sensor based on stimulated brillouin scattering, comprising the steps of:
s21, combining a magnetostrictive composite material with a cladding of a single-mode optical fiber by a coating and adhesion method, orienting the magnetostrictive composite material by a weak magnetic field, and waiting for a period of time to solidify the magnetostrictive composite material to form a magnetostrictive coating wrapped on the cladding of the single-mode optical fiber;
s22, a pump light source is connected with the incident end of the single-mode fiber through a fiber circulator, a spectrometer is connected with the incident end of the single-mode fiber through the fiber circulator and used for measuring the frequency shift quantity of SBS light in real time, and a controller is connected with the spectrometer and the pump light source.
As a further preferable mode, combining the magnetostrictive composite material with the cladding of the single-mode optical fiber by coating and adhesion methods, and orienting the magnetostrictive composite material by a weak magnetic field specifically includes:
uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; placing and fixing the single-mode optical fiber in a chassis track engraved on a chassis; pouring the prepared magnetostrictive composite material mixture into a chassis track to submerge the single-mode optical fiber; placing a solenoid along the outside of the chassis rail, and placing the chassis rail in the center of the solenoid; connecting the solenoid coil with power supply, applying current via the switch on the power supply to produce weak magnetic field in the center of the solenoid coil to orient the composite magnetostrictive material, curing the composite magnetostrictive material after 2-16 hr and cutting off the current from the solenoid coil.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. the magnetostrictive coating is attached to the surface of the optical fiber in a tubular shape, pumping light is injected from one end of the optical fiber, stimulated Brillouin scattering is generated when the light power exceeds an SBS threshold, and incident light is converted into reverse SBS light with lower energy and is reversely emitted from an incident end. When the axial direction of the optical fiber is parallel to the direction of the magnetic field to be measured or the component of the magnetic field to be measured, the length of the magnetostrictive coating outside the optical fiber changes in the axial direction due to the existence of the magnetic field, so that the axial strain of the optical fiber (the ratio of the axial length change amount to the total length of the optical fiber) is brought, and the SBS gain spectrum is subjected to frequency shift. The size and the variation of the magnetic field can be obtained by measuring the frequency shift quantity of the SBS gain spectrum, so that the precise sensing of the magnetic field is realized.
2. The invention is based on the stimulated Brillouin scattering of the optical fiber, does not need complex processes such as grating inscription and the like, only needs to plate a layer of magnetostrictive film outside the common optical fiber, and has simple structure.
3. The invention uses a spectrometer to measure the frequency shift of the SBS gain spectrum, thereby obtaining the magnitude of the external magnetic field. The response speed of the sensor to the change of the magnetic field is determined by the shrinkage response speed of the magnetostrictive coating outside the optical fiber, and can reach microsecond magnitude, so that the real-time magnetic field monitoring of MHz bandwidth can be realized. The sensor has high response speed to the change of the magnetic field and can realize real-time monitoring.
Drawings
Fig. 1 is a schematic structural diagram of an optical fiber magnetic field sensor based on stimulated brillouin scattering according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a fiber optic magnetic field sensor based on stimulated brillouin scattering according to another embodiment of the present invention;
FIG. 3 is a diagram showing the variation of the magnetic field intensity with the strain amount of the magnetostrictive layer obtained in the test.
In all the figures, the same reference numerals denote the same features, in particular: 1-pump light, 2-SBS light, 3-fiber circulator, 4-single-mode fiber, 5-magnetostrictive coating and 6-spectrometer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the respective embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1 and fig. 2, an optical fiber magnetic field sensor based on stimulated brillouin scattering according to an embodiment of the present invention includes: the single-mode fiber 4 and the magnetostrictive coating 5 are arranged on the periphery of a cladding of the single-mode fiber 4, and the magnetostrictive coating 5 drives the single-mode fiber 4 to generate axial length change under the action of an external magnetic field; the pump light source is connected with the incident end of the single-mode fiber 4 through the fiber circulator 3, the pump light input to the single-mode fiber 4 by the pump light source generates stimulated Brillouin scattering and is converted into reverse SBS light, and the SBS light is shifted in frequency due to the change of the axial length of the single-mode fiber 4; the spectrometer 6 is connected with the incident end of the single-mode optical fiber 4 through the optical fiber circulator 3 and is used for measuring the frequency shift quantity of SBS light in real time; and the controller is used for acquiring the size and the variation of the magnetic field according to the axial length change of the single-mode optical fiber 4 and the frequency shift quantity of the SBS light.
Optionally, the frequency shift amount of the SBS light is:
wherein the content of the first and second substances,
is the amount of frequency shift of the SBS light,
the coefficient is a coefficient without dimension,
is the axial length variation of the single mode optical fiber 4.
Optionally, the controller is integrated with a graph of the axial length change of the single-mode optical fiber 4 and the magnitude of an external magnetic field; the relation graph is obtained by placing the optical fiber magnetic field sensor into standard magnetic fields with different sizes according to the size of the magnetic field and the frequency shift quantity of SBS light. More specifically, in the invention, the optical fiber magnetic field sensor is placed in standard magnetic fields with different sizes, meanwhile, the magnetic field lines of the magnetic fields are arranged in parallel with the axial direction of the optical fiber magnetic field sensor, and the frequency shift quantity of the SBS light is obtained by adjusting the size of the standard magnetic field. Therefore, in the measurement process of the later sensor, the frequency shift quantity of the SBS light can be obtained by adjusting the direction of the sensor, so that the axial length change of the optical fibers in different directions can be obtained, and the strength and the direction of the magnetic field can be obtained through space coordinates.
In a preferred embodiment of the present invention, said magnetostrictive coating 5 is: one of ferrite magnetostrictive material, metal or alloy magnetostrictive material or rare earth giant magnetostrictive material is mixed with epoxy resin and polyamide curing agent according to a certain proportion.
In a preferred embodiment of the present invention, the metal or alloy magnetostrictive material comprises one of a Ni-Co-Cr alloy, a Fe-Al alloy, a Fe-Ni alloy or a Ni metal; the rare earth giant magnetostrictive material comprises Tb-Dy-Fe magnetostrictive alloy.
According to another aspect of the present invention, there is also provided a measurement method of a fiber optic magnetic field sensor based on stimulated brillouin scattering, including the steps of:
s11, pumping light is injected into the incident end of the single-mode optical fiber, the power of the pumping light is adjusted, the optical power of the pumping light exceeds an SBS threshold value, stimulated Brillouin scattering is generated, and the incident pumping light is converted into reverse SBS light and is reversely emitted from the incident end.
In this step, before measurement, the optical fiber magnetic field sensor needs to be calibrated to obtain a relationship diagram between axial length change of the single-mode optical fiber and an external magnetic field, which is specifically as follows:
the optical fiber magnetic field sensor is placed in standard magnetic fields with different strengths, the frequency shift quantity of SBS light under the magnetic fields with different strengths is obtained by changing the strength of the standard magnetic field, the axial length change of the single-mode optical fiber is obtained according to the frequency shift quantity of the SBS light and the size and the variable quantity of the standard magnetic field strength, and a relational graph of the axial length change of the single-mode optical fiber and the size of an external magnetic field is drawn according to the axial length change of the single-mode optical fiber.
S12, placing the single-mode optical fiber wrapped with the magnetostrictive coating into a magnetic field to be detected, wherein the magnetostrictive coating drives the single-mode optical fiber to generate axial length change under the action of an external magnetic field;
s13, the SBS light is subjected to frequency shift due to the axial length change of the single-mode optical fiber, and the frequency shift quantity of the SBS light is measured in real time;
and S14, acquiring the size and the variation of the magnetic field according to the axial length variation of the single-mode fiber and the frequency shift quantity of the SBS light.
According to another aspect of the present invention, there is also provided a method for manufacturing an optical fiber magnetic field sensor based on stimulated brillouin scattering, comprising the steps of:
s21, combining the magnetostrictive composite material with the cladding of the single-mode optical fiber through a coating and adhesion method, orienting the magnetostrictive composite material through a weak magnetic field, and waiting for a period of time to solidify the magnetostrictive composite material to form a magnetostrictive coating wrapped on the cladding of the single-mode optical fiber. In the step, combining the magnetostrictive composite material with the cladding of the single-mode optical fiber by a coating and adhesion method, and orienting the magnetostrictive composite material by a weak magnetic field specifically comprises the following steps:
uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; placing and fixing the single mode fiber in a chassis track carved on a chassis; pouring the prepared magnetostrictive composite material mixture into a chassis track to submerge the single-mode optical fiber; placing a solenoid along the outside of the chassis rail, and placing the chassis rail in the center of the solenoid; connecting the solenoid coil with power supply, applying current via the switch on the power supply to produce weak magnetic field in the center of the solenoid coil to orient the composite magnetostrictive material, curing the composite magnetostrictive material after 2-16 hr and cutting off the current from the solenoid coil.
S22, a pump light source is connected with the incident end of the single-mode fiber through the fiber circulator, the spectrometer is connected with the incident end of the single-mode fiber through the fiber circulator and used for measuring the frequency shift amount of SBS light in real time, and the controller is connected with the spectrometer and the pump light source.
In one embodiment of the invention, the fiber optic magnetic field sensor comprises in major part: optical fiber, magnetostrictive coating, pump light and SBS light. The magnetostrictive coating is attached to the surface of the optical fiber in a tubular shape, pumping light is injected from one end of the optical fiber, stimulated Brillouin scattering is generated when the light power exceeds an SBS threshold, and incident light is converted into reverse SBS light with lower energy and is reversely emitted from an incident end. When the optical fiber is placed in parallel to the axial direction of the magnetic field to be measured, the length of the magnetostrictive coating outside the optical fiber changes in the axial direction due to the existence of the magnetic field, so that the axial strain of the optical fiber (the ratio of the axial length change amount to the total length of the optical fiber) is caused, and the SBS gain spectrum is subjected to frequency shift. The size and the variation of the magnetic field can be obtained by measuring the frequency shift quantity of the SBS gain spectrum, so that the precise sensing of the magnetic field is realized.
The optical fiber SBS gain spectrum approximately satisfies the lorentzian profile, and the brillouin gain can be expressed as:
wherein
Is the peak brillouin gain factor,
is the line width of the Brillouin line,
namely the brillouin frequency shift. Under the action of an external magnetic field, the molecular structure in the magnetostrictive coating changes to drive the optical fiber to generate axial length contraction, and when the magnetic field is weaker (less than 0.1T), the optical fiber strain brought by the magnetostrictive coating and the external magnetic field approximately satisfy the linear relation:
wherein the coefficientCIn relation to the magnetostriction coefficient of the material,His the intensity of the external magnetic field. When strain exists, the Brillouin frequency shift is changed, and the change amount is
Wherein
，
Is the amount of change in the strain of the optical fiber. By measuring the SBS gain spectrum frequency shift in real time
The magnitude and the variation of the external magnetic field can be calculated.
In another embodiment of the present invention, a fiber optic magnetic field sensor based on stimulated brillouin scattering includes: pump light 1, SBS light 2, fiber circulator 3, single mode fiber 4, magnetostrictive coating 5, spectrometer 6 and controller. In the embodiment, a powder Terfenol-D material is deposited outside a cladding of a single-mode optical fiber 4 by using a sputtering coating method to obtain a magnetostrictive coating 5, and a molecular structure in the magnetostrictive coating 5 is rearranged under the action of an external magnetic field to drive the single-mode optical fiber 4 to generate axial length change. The magnetostrictive coating 5 has a uniform magnetic strain under a uniform magnetic field, especially at lower magnetic field strengths (< 0.1T), the magnetic strain and magnetic field strength satisfying a nearly linear relationship, as shown in fig. 3. Natural linewidth of SBS gain spectrum in common single mode fiber
About 35 MHz, and the axial length strain of the single mode fiber 4 due to the magnetostrictive coating 5 is about 3X 10 when the magnetic field is 0.05T -4 The resulting brillouin shift is about 17 MHz. When an external magnetic field changes, the contraction response speed of the magnetostrictive coating 5 reaches microsecond magnitude, and the external magnetic field can be sensed in real time by measuring the Brillouin frequency of the SBS gain spectrum in real time through the spectrometer 6.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An optical fiber magnetic field sensor based on stimulated Brillouin scattering, comprising:
a single-mode optical fiber (4),
the magnetostrictive coating (5) is arranged on the periphery of the cladding of the single-mode optical fiber (4), and the magnetostrictive coating (5) drives the single-mode optical fiber (4) to generate axial length change under the action of an external magnetic field;
the pump light source is connected with the incident end of the single-mode fiber (4) through the fiber circulator (3), the pump light input into the single-mode fiber (4) by the pump light source generates stimulated Brillouin scattering and is converted into reverse SBS light, and the SBS light is shifted in frequency due to the change of the axial length of the single-mode fiber (4);
the spectrometer (6) is connected with the incident end of the single-mode optical fiber (4) through the optical fiber circulator (3) and is used for measuring the frequency shift quantity of SBS light in real time;
and the controller is used for acquiring the size and the variation of the magnetic field according to the axial length change of the single-mode optical fiber (4) and the frequency shift quantity of the SBS light.
2. The optical fiber magnetic field sensor based on stimulated brillouin scattering according to claim 1, wherein the SBS light is shifted by an amount of:
wherein the content of the first and second substances,
is the amount of frequency shift of the SBS light,
the coefficient is a coefficient without dimension,
the axial length variation of the single-mode optical fiber (4) is adopted.
3. The stimulated brillouin scattering-based optical fiber magnetic field sensor according to claim 1, wherein the controller is integrated with a graph of axial length change of the single mode optical fiber (4) versus magnitude of an external magnetic field;
the relation graph is obtained by placing the optical fiber magnetic field sensor into standard magnetic fields with different sizes according to the size of the magnetic field and the frequency shift quantity of SBS light.
4. The stimulated brillouin scattering-based optical fiber magnetic field sensor according to claim 1, wherein the magnetostrictive coating (5) is: one of ferrite magnetostrictive material, metal or alloy magnetostrictive material or rare earth giant magnetostrictive material is mixed with epoxy resin and polyamide curing agent according to a certain proportion to prepare the material.
5. The optical fiber magnetic field sensor based on stimulated brillouin scattering according to claim 2, wherein the metal or alloy magnetostrictive material comprises one of Ni-Co-Cr alloy, fe-Al alloy, fe-Ni alloy or Ni metal;
the rare earth giant magnetostrictive material comprises Tb-Dy-Fe magnetostrictive alloy.
6. A measuring method of an optical fiber magnetic field sensor based on stimulated Brillouin scattering is characterized by comprising the following steps:
s11, injecting pump light into an incident end of the single-mode fiber (4), adjusting the power of the pump light to enable the optical power of the pump light to exceed an SBS threshold value, generating stimulated Brillouin scattering, converting the incident pump light into reverse SBS light, and reversely emitting the reverse SBS light from the incident end;
s12, placing the single-mode optical fiber (4) wrapped with the magnetostrictive coating (5) into a magnetic field to be measured, wherein the magnetostrictive coating (5) drives the single-mode optical fiber (4) to generate axial length change under the action of an external magnetic field;
s13, the SBS light is subjected to frequency shift due to the change of the axial length of the single-mode optical fiber (4), and the frequency shift quantity of the SBS light is measured in real time;
and S14, acquiring the size and the variation of the magnetic field according to the axial length change of the single-mode fiber (4) and the frequency shift of the SBS light.
7. The measurement method according to claim 6, wherein before measurement, the fiber optic magnetic field sensor needs to be calibrated to obtain a relationship diagram of the axial length change of the single mode fiber (4) and the magnitude of the external magnetic field, which is as follows:
the optical fiber magnetic field sensor is placed in standard magnetic fields with different strengths, the frequency shift quantity of SBS light under the magnetic fields with different strengths is obtained by changing the strength of the standard magnetic field, the axial length change of the single-mode optical fiber (4) is obtained according to the frequency shift quantity of the SBS light and the size and the variable quantity of the standard magnetic field, and a relational graph of the axial length change of the single-mode optical fiber (4) and the size of an external magnetic field is drawn according to the axial length change of the single-mode optical fiber (4).
8. The method according to claim 6, wherein the orientation of the fiber-optic magnetic field sensor is changed, and steps S12 and S13 are repeated to obtain the frequency shift of the SBS light, thereby calculating the magnitude and variation of the magnetic field.
9. A preparation method of an optical fiber magnetic field sensor based on stimulated Brillouin scattering is characterized by comprising the following steps:
s21, combining a magnetostrictive composite material with a cladding of a single-mode optical fiber (4) through a coating and adhesion method, orienting the magnetostrictive composite material through a weak magnetic field, waiting for a period of time to solidify the magnetostrictive composite material, and forming a magnetostrictive coating (5) wrapping the cladding of the single-mode optical fiber (4);
s22, a pump light source is connected with an incidence end of the single-mode fiber (4) through the fiber circulator (3), a spectrometer (6) is connected with the incidence end of the single-mode fiber (4) through the fiber circulator (3) and used for measuring the frequency shift quantity of SBS light in real time, and a controller is connected with the spectrometer (6) and the pump light source.
10. The method of claim 9, wherein the step S21 of bonding the magnetostrictive composite material with the cladding of the single-mode optical fiber (4) by coating and adhesion, and orienting the magnetostrictive composite material by a weak magnetic field specifically comprises:
uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; uniformly mixing and stirring the magnetostrictive composite material according to the proportion, and discharging bubbles in the mixture; placing the single-mode optical fiber (4) in a chassis track engraved on the chassis and fixing; pouring the prepared magnetostrictive composite material mixture into a chassis track to submerge the single-mode optical fiber (4); placing a solenoid along the outside of the chassis rail, and placing the chassis rail in the center of the solenoid; connecting a solenoid coil wound outside the solenoid coil with a power supply, applying current through a switch on the power supply so as to generate a weak magnetic field in the center of the solenoid coil to orient the magnetostrictive composite material, and curing the magnetostrictive composite material after 2-16 hours and disconnecting the current on the solenoid coil.
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