Fiber laser and magnetic field measurement method

Abstract

The invention discloses an optical fiber laser and a magnetic field measurement method. The optical fiber laser comprises a pumping source, an annular structure resonant cavity and a magnetic field sensing area which are in light path connection in sequence, a wavelength division multiplexer, an erbium-doped gain fiber, a polarization controller, an optical fiber polarizer, a polarization independent isolator and an optical fiber coupler are sequentially arranged in the annular structure resonant cavity in the laser propagation direction. The wavelength division multiplexer, the erbium-doped gain fiber, the polarization controller, the optical fiber polarizer, the polarization independent isolator and the optical fiber coupler are connected in sequence to form an annular optical path structure; laser excited by the pumping source passes through the annular structure resonant cavity to generate a beat frequency signal, the beat frequency signal is influenced by an external magnetic field to generate beat frequency offset when passing through the magnetic field sensing area, and magnetic field change measurement information is obtained based on the beat frequency offset. The system has the advantages of being simple and compact in structure, high in sensitivity and low in cost, and the signal-to-noise ratio and the resolution ratio of the optical fiber magnetic field sensor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical sensors, and in particular to a fiber laser and a magnetic field measurement method. Background Art

[0002] Due to its advantages of small size, anti-electromagnetic interference, corrosion resistance and low cost, optical fiber magnetic field sensors have emerged in fields such as earth exploration, vehicle navigation and aviation, becoming an important detection technology. Since the main component of optical fiber, silicon dioxide, is insensitive to magnetic fields, most optical fiber magnetic field sensors need to rely on the combination of magnetostrictive and magneto-optical materials to detect magnetic fields. Among them, magnetostrictive materials can deform along the direction of the magnetic field when affected by a magnetic field. Due to its excellent characteristics such as fast response and magneto-strain, magnetostrictive materials have been favored by scientists in recent years.

[0003] At present, many different types of magnetic field sensors based on magnetostrictive materials have been proposed and developed, mainly including fiber Bragg grating type, fiber interferometer and other structures. However, most of the existing detection methods use passive detection, resulting in low signal-to-noise ratio and low resolution.

[0004] Therefore, the prior art needs to be improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is that, in view of the defects of the prior art, the present invention provides a fiber laser and a magnetic field measurement method to solve the problems of low signal-to-noise ratio and low resolution in the existing magnetic field sensors and detection methods.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: In a first aspect, the present invention provides a fiber laser for magnetic field measurement, comprising: A pump source, a ring-shaped structure resonant cavity and a magnetic field sensing area connected by an optical path are sequentially formed; The ring-shaped resonant cavity is provided with a wavelength division multiplexer, an erbium-doped gain optical fiber, a polarization controller, an optical fiber polarizer, a polarization-independent isolator and an optical fiber coupler in sequence along the propagation direction of the laser; The wavelength division multiplexer, the erbium-doped gain optical fiber, the polarization controller, the optical fiber polarizer, the polarization-independent isolator and the optical fiber coupler are connected in sequence to form a ring optical path structure; The laser excited by the pump source generates a beat frequency signal through the ring structure resonant cavity. The beat frequency signal is affected by the external magnetic field when passing through the magnetic field sensing area to generate a beat frequency offset. The measured magnetic field change information is obtained based on the beat frequency offset.

[0007] In one implementation, a single-mode optical fiber and a magnetostrictive sleeve are disposed in the magnetic field sensing area, and the single-mode optical fiber is encapsulated in the magnetostrictive sleeve.

[0008] In one implementation, the magnetostrictive sleeve is Tb 0.3 Dy 0.6 Nd 0.1 (Fe 0.8 Co 0.2 ) 1.93 Telescopic sleeve of material.

[0009] In one implementation, the magnetostrictive sleeve generates telescopic deformation under the change of the external magnetic field, and the single-mode optical fiber generates corresponding telescopic deformation under the deformation of the magnetostrictive sleeve.

[0010] In one implementation, the mode locking mechanism of the fiber laser is a nonlinear polarization rotation mechanism.

[0011] In a second aspect, the present invention provides a method for measuring a magnetic field of a fiber laser, comprising: Adjusting the power of the pump source according to a preset power parameter so that the pump source generates a laser pulse signal; Adjust the cavity length of the ring-shaped resonant cavity according to the preset optical path parameters, and generate a beat frequency signal under any two longitudinal mode states in the ring-shaped resonant cavity; Adjusting the size of the external magnetic field to control the magnetostrictive sleeve in the magnetic field sensing area to drive the single-mode optical fiber to generate a telescopic deformation, so as to shift the beat frequency signal and obtain a beat frequency offset; The magnetic field variation of the external magnetic field is measured based on the beat frequency offset, and the magnetic field variation information of the external magnetic field is acquired by calculation.

[0012] In one implementation, a beat frequency signal is generated in any two longitudinal modes in the ring structure resonant cavity. for: ; in, is an integer, is the speed of light in vacuum, is the effective refractive index of the optical fiber, is the total cavity length of the resonant cavity.

[0013] In one implementation, the beat frequency offset is: ; in, is the change in length of the single-mode optical fiber, is the magnetostriction coefficient, is the magnetic field variation, is the original length of the magnetostrictive material.

[0014] In one implementation, the method further includes: The corresponding fiber laser sensitivity is obtained by adjusting the size of the beat frequency signal.

[0015] In one implementation, the fiber laser sensitivity for: .

[0016] The present invention adopts the above technical solution to achieve the following effects: 1) The fiber laser provided by the present invention adopts a fiber laser sensing solution, and the generated beat frequency signal has a higher signal-to-noise ratio and resolution due to the direct deformation response of the magnetostrictive material.

[0017] 2) The fiber laser provided by the present invention can provide a clearer and more stable measurement signal, and can ensure high-precision magnetic field measurement even in the presence of external noise sources.

[0018] 3) The mode-locking mechanism of the fiber laser provided by the present invention can effectively reduce the impact of environmental interference (such as temperature changes, mechanical vibrations, etc.) on the laser output frequency, improve the stability and accuracy of the system, and make the magnetic field measurement results more reliable, especially in scenarios requiring high-precision long-term monitoring, which has obvious advantages.

[0019] 4) The laser scheme adopted in the present invention has more longitudinal modes, which can keep the beat frequency signal in a high-quality state at high frequencies. It has the advantages of simple structure, compact structure, high sensitivity, and no need for complicated demodulation process and expensive optical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0021] Figure 1 It is a structural schematic diagram of a fiber laser in the present invention.

[0022] Figure 2 It is a flow chart of a method for measuring a magnetic field of a fiber laser in the present invention.

[0023] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Exemplary Devices Due to its advantages of small size, anti-electromagnetic interference, corrosion resistance and low cost, optical fiber magnetic field sensors have emerged in fields such as earth exploration, vehicle navigation and aviation, becoming an important detection technology. Since the main component of optical fiber, silicon dioxide, is insensitive to magnetic fields, most optical fiber magnetic field sensors need to rely on the combination of magnetostrictive and magneto-optical materials to detect magnetic fields. Among them, magnetostrictive materials can deform along the direction of the magnetic field when affected by a magnetic field. Due to its excellent characteristics such as fast response and magneto-strain, magnetostrictive materials have been favored by scientists in recent years.

[0026] At present, many different types of magnetic field sensors based on magnetostrictive materials have been proposed and developed, mainly including fiber Bragg grating type, fiber interferometer and other structures. However, most of the existing detection methods use passive detection, resulting in low signal-to-noise ratio and low resolution.

[0027] In view of the above technical problems, an embodiment of the present invention provides a fiber laser for magnetic field measurement, including a 980nm pump source, a ring-structured resonant cavity and a magnetic field sensing area; the ring-structured resonant cavity includes a wavelength division multiplexer, an erbium-doped gain fiber, a polarization controller, a fiber polarizer, a polarization-independent isolator, and a fiber coupler along the propagation direction of light; the magnetic field sensing area is a section of single-mode optical fiber encapsulated in a magnetostrictive sleeve. The laser scheme used in the embodiment of the present invention has more longitudinal modes, which can keep the beat frequency signal in a high-quality state at high frequencies; compared with other laser sensing schemes, the fiber laser provided in the embodiment of the present invention has the advantages of simple structure, compact structure, high sensitivity, no need for cumbersome demodulation process and expensive optical devices, etc., which improves the signal-to-noise ratio and resolution of the fiber magnetic field sensor.

[0028] like Figure 1 As shown, an embodiment of the present invention provides a fiber laser for magnetic field measurement, comprising: a pump source 1, a ring-structured resonant cavity and a magnetic field sensing area 8 which are sequentially connected by an optical path.

[0029] Among them, a wavelength division multiplexer 2, an erbium-doped gain fiber 3, a polarization controller 4, an optical fiber polarizer 5, a polarization-independent isolator 6 and an optical fiber coupler 7 are arranged in sequence in the ring-structure resonant cavity along the propagation direction of the laser; the wavelength division multiplexer 2, the erbium-doped gain fiber 3, the polarization controller 4, the optical fiber polarizer 5, the polarization-independent isolator 6 and the optical fiber coupler 7 are connected in sequence to form a ring-shaped optical path structure.

[0030] In this embodiment, the pump source 1 adopts a 980 nm pump source. In order to achieve magnetic field measurement, in this embodiment, a single-mode optical fiber and a magnetostrictive sleeve are arranged in the magnetic field sensing area 8, and the single-mode optical fiber is encapsulated in the magnetostrictive sleeve.

[0031] In this embodiment, the magnetostrictive sleeve is Tb 0.3 Dy 0.6 Nd 0.1 (Fe 0.8 Co 0.2 ) 1.93 The telescopic sleeve of the material has low magnetocrystalline anisotropy, a saturated magnetostriction of up to 930 ppm, and a linear magnetostriction of up to 670 ppm within a range of 3 kOe. Therefore, the magnetostrictive sleeve can produce telescopic deformation under changes in the external magnetic field, and at the same time, the single-mode optical fiber can produce corresponding telescopic deformation under the deformation of the magnetostrictive sleeve.

[0032] In this embodiment, the mode locking mechanism of the optical fiber laser is a nonlinear polarization rotation mechanism.

[0033] In order to realize the above fiber laser structure setting, in this embodiment, a fiber fusion splicer is first used to fusion-splice each device according to Figure 1 The fiber laser system is then carefully debugged. Specifically, the debugging process is as follows: Turn on the pump source, connect the external output end of the OC cavity (optical resonant cavity) to the spectrometer, oscilloscope and spectrum analyzer and record the current mode-locking state. While adjusting the power of the pump source 1, carefully adjust the PC end and observe the output state of the fiber laser to ensure a stable mode-locking state. In terms of the magnetic field, two parallel electromagnets are used to generate the required magnetic field. Place the magnetic field sensing area 8 of the fiber laser at the center of the two electromagnets, and use a Gaussmeter to measure the magnetic field strength in real time to calibrate the magnetic field. The size of the magnetic field is precisely controlled by adjusting the drive current.

[0034] In this embodiment, a section of single-mode optical fiber encapsulated in a magnetostrictive sleeve is placed in the magnetic field sensing area 8 of the optical fiber laser. Therefore, under the influence of the external magnetic field change, the magnetostrictive material will deform, thereby driving the single-mode optical fiber attached to the magnetostrictive material to deform.

[0035] The principle of the magnetic field measurement of the fiber laser in this embodiment is: A 980nm laser is excited by a pump source 1, and the laser excited by the pump source 1 generates a beat frequency signal through the ring structure resonant cavity. When the beat frequency signal passes through the magnetic field sensing area 8, it is affected by the external magnetic field and generates a beat frequency offset. The measured magnetic field change information is obtained based on the calculation of the beat frequency offset.

[0036] As an example, in the actual magnetic field measurement process of this embodiment, the power of the 980nm pump source 1 is first adjusted to 200 mW to ensure the saturation amplification effect of the gain medium so that the laser can effectively generate pulse output. Subsequently, the state of the polarization controller 4 is continuously fine-tuned to obtain a stable mode-locked state output. Because a section of single-mode optical fiber encapsulated in a magnetostrictive sleeve is placed in the magnetic field sensing area 8 of the fiber laser. Therefore, under the influence of the external magnetic field change, the magnetostrictive material will deform, thereby driving the single-mode optical fiber pasted on the magnetostrictive material to deform. Among them, the external magnetic field is generated by two parallel electromagnets to generate the required magnetic field, and the size of the magnetic field can be accurately controlled by adjusting the driving current. When the magnetic field intensity gradually increases, the length of the single-mode optical fiber pasted on the magnetostrictive material increases accordingly, resulting in a longer laser cavity length. When the structure of the ring structure resonant cavity is adjusted so that the cavity length of the ring structure resonant cavity increases, the mode spacing in the laser cavity decreases, which means that the frequency of the beat signal is reduced.

[0037] Therefore, any two longitudinal modes in the ring structure resonant cavity generate a beat frequency signal for: ; in, is an integer, is the speed of light in vacuum, is the effective refractive index of the optical fiber, is the total cavity length of the resonant cavity; because, Only integers are accepted Optical Path The change in magnetic field will cause the length of the magnetostrictive material to changes, that is, the length of the single-mode optical fiber pasted on the magnetostrictive material changes, and its size is Therefore, the effect of the magnetic field on the length of the magnetic field stretching material will cause the shift of the beat frequency signal, that is, It can be expressed as: ; in, is the deformation caused by magnetostrictive effect, if we assume , the above formula can be simplified to ; in, is the magnetostriction coefficient, is the magnetic field variation, is the original length of the magnetostrictive material. It can be seen that there is a good linear relationship between the beat frequency offset and the magnetic field change. Therefore, the measured magnetic field change information can be obtained by converting the magnetic field change into the beat frequency offset.

[0038] Among them, the sensitivity of fiber laser It can be expressed as: ; When measuring the magnetic field, since the sensitivity of the fiber laser is related to the size of the selected monitored beat frequency signal, a higher sensitivity can be obtained by changing the monitored beat frequency signal.

[0039] As an example, assuming that the total laser cavity length of the fiber laser is 12 m and the fundamental repetition frequency is 17 MHz, by monitoring the changes in the beat frequency signal at different frequencies (for example, 5 GHz and 10 GHz), the impact of the magnetic field on the laser can be evaluated, and the measured magnetic field performance of the fiber laser can be understood, thereby optimizing the design.

[0040] Specifically, when measuring the magnetic field in this embodiment, the corresponding frequency signals that change with the magnetic field are recorded at the beat frequency signals of 5 GHz and 10 GHz respectively. The light output by the optical fiber resonant cavity is transmitted to the electronic spectrum analyzer (ESA) via the PD (photodetector), and finally the measured beat frequency signal is transmitted to the computer for accurate data processing.

[0041] As the magnetic field gradually increases, the deformation of the single-mode optical fiber in the magnetic field sensing area 8 also increases, resulting in a red shift in the laser beat frequency spectrum position, that is, a beat frequency signal offset. By using the origin (function plotting software) data processing software, the relationship between the magnetic field change and the laser beat frequency offset can be accurately determined in this embodiment. This innovative sensing scheme has great flexibility, so beat frequency signals of different frequencies can be used as needed to customize the magnetic field sensitivity of the proposed magnetic field sensing scheme. Through this set of precise experimental procedures and data processing methods, accurate and reliable magnetic field sensing results can be obtained.

[0042] The present invention adopts the above technical solution to achieve the following effects: Compared with the traditional optical fiber magnetic field sensor, the device for magnetic field measurement provided in this embodiment adopts an optical fiber laser sensing scheme, and the generated beat frequency signal has a higher signal-to-noise ratio and resolution due to the direct deformation response of the magnetostrictive material. Traditional sensors may rely on changes in light intensity or phase, and these signals are easily interfered by noise, resulting in reduced measurement accuracy. The device can provide a clearer and more stable measurement signal, and can still ensure high-precision magnetic field measurement even in the presence of external noise sources. This has important advantages for applications requiring a high signal-to-noise ratio, such as precision scientific experiments, geological exploration and other fields. In addition, the mode-locking mechanism can effectively reduce the impact of environmental interference (such as temperature changes, mechanical vibrations, etc.) on the laser output frequency, improve the stability and accuracy of the system, and make the magnetic field measurement results more reliable, especially in scenarios requiring high-precision long-term monitoring, which has obvious advantages. At the same time, compared with ordinary optical fiber lasers, the laser scheme adopted in the present invention has more longitudinal modes, which can keep the beat frequency signal in a high-quality state at high frequencies. Compared with other laser sensing schemes, the system of the present invention has the advantages of simple structure, compact structure, high sensitivity, no need for cumbersome demodulation process and expensive optical devices. These characteristics make fiber laser sensing technology have great application potential in the field of magnetic field sensing.

[0043] Exemplary Methods Based on the above embodiments, an embodiment of the present invention further provides a magnetic field measurement method of a fiber laser, which is used to measure magnetic field change information and obtain accurate and reliable magnetic field sensing results.

[0044] like Figure 2 As shown, an embodiment of the present invention provides a method for measuring the magnetic field of a fiber laser, comprising the following steps: Step S100, adjusting the power of the pump source according to a preset power parameter so that the pump source generates a laser pulse signal; Step S200, adjusting the cavity length of the ring structure resonant cavity according to a preset optical path parameter, and generating a beat frequency signal in any two longitudinal mode states in the ring structure resonant cavity; Step S300, adjusting the size of the external magnetic field, controlling the magnetostrictive sleeve in the magnetic field sensing area to drive the single-mode optical fiber to generate a telescopic deformation, so as to shift the beat frequency signal to obtain a beat frequency offset; Step S400: obtaining a magnetic field variation of the external magnetic field based on the beat frequency offset measurement, and obtaining magnetic field variation information of the external magnetic field by calculation.

[0045] In this embodiment, a fiber optic fusion splicer is first used to fusion-splice each device. Figure 1 The fiber laser system is then carefully debugged. Specifically, the debugging process is as follows: Turn on the pump source, connect the external output end of the OC cavity (optical resonant cavity) to the spectrometer, oscilloscope and spectrum analyzer and record the current mode-locking state. While adjusting the power of the pump source 1, carefully adjust the PC end and observe the output state of the fiber laser to ensure a stable mode-locking state. In terms of the magnetic field, two parallel electromagnets are used to generate the required magnetic field. Place the magnetic field sensing area 8 of the fiber laser at the center of the two electromagnets, and use a Gaussmeter to measure the magnetic field strength in real time to calibrate the magnetic field. The size of the magnetic field is precisely controlled by adjusting the drive current.

[0046] In this embodiment, a section of single-mode optical fiber encapsulated in a magnetostrictive sleeve is placed in the magnetic field sensing area 8 of the optical fiber laser. Therefore, under the influence of the external magnetic field change, the magnetostrictive material will deform, thereby driving the single-mode optical fiber attached to the magnetostrictive material to deform.

[0047] The principle of the magnetic field measurement of the fiber laser in this embodiment is: The power of the pump source 1 is adjusted to excite a 980nm laser. Thereafter, the laser excited by the pump source 1 generates a beat frequency signal through the ring structure resonant cavity. When the beat frequency signal passes through the magnetic field sensing area 8, it is affected by the external magnetic field and generates a beat frequency offset. The measured magnetic field change information is obtained by calculation based on the beat frequency offset.

[0048] As an example, in the actual magnetic field measurement process of this embodiment, the power of the 980nm pump source 1 is first adjusted to 200 mW (that is, the preset power parameter is 200 mW) to ensure the saturation amplification effect of the gain medium so that the laser can effectively generate pulse output. Subsequently, the state of the polarization controller 4 is continuously fine-tuned to obtain a stable mode-locked state output.

[0049] In this embodiment, before fine-tuning the state of the polarization controller 4, the optical path parameter (i.e., the total cavity length of the resonant cavity) can be pre-set according to the measured magnetic field environment and the required sensitivity, so as to set the initial value of the total cavity length of the resonant cavity to meet the sensitivity requirements of the on-site magnetic field measurement; wherein the optical path parameter can be set according to the required frequency, for example, at a frequency of 5 GHz, the required total cavity length of the resonant cavity is 12 m.

[0050] Because, in this embodiment, a section of single-mode optical fiber encapsulated in a magnetostrictive sleeve is placed in the magnetic field sensing area 8 of the fiber laser. Therefore, under the influence of the external magnetic field change, the magnetostrictive material will deform, thereby driving the single-mode optical fiber pasted on the magnetostrictive material to deform. Among them, the external magnetic field is generated by two parallel electromagnets to generate the required magnetic field, and the size of the magnetic field can be accurately controlled by adjusting the driving current. When the magnetic field intensity gradually increases, the length of the single-mode optical fiber pasted on the magnetostrictive material increases accordingly, resulting in a longer laser cavity length; conversely, when the magnetic field intensity gradually decreases, the length of the single-mode optical fiber pasted on the magnetostrictive material decreases accordingly, resulting in a shorter laser cavity length. Therefore, when the structure of the ring-structure resonant cavity is adjusted so that the cavity length of the ring-structure resonant cavity increases, the mode spacing in the laser cavity decreases, which means that the frequency of the beat signal decreases.

[0051] Therefore, any two longitudinal modes in the ring structure resonant cavity generate a beat frequency signal for: ; in, is an integer, is the speed of light in vacuum, is the effective refractive index of the optical fiber, is the total cavity length of the resonant cavity; because, Only integers are accepted Optical Path The change in magnetic field will cause the length of the magnetostrictive material to changes, that is, the length of the single-mode optical fiber pasted on the magnetostrictive material changes, and its size is Therefore, the effect of the magnetic field on the length of the magnetic field stretching material will cause the shift of the beat frequency signal, that is, It can be expressed as: ; in, is the deformation caused by magnetostrictive effect, if we assume , the above formula can be simplified to ; in, is the magnetostriction coefficient, is the magnetic field variation, is the original length of the magnetostrictive material. It can be seen that there is a good linear relationship between the beat frequency offset and the magnetic field change. Therefore, the measured magnetic field change information can be obtained by converting the magnetic field change into the beat frequency offset, that is, the magnetic field change is quantified by calculating the beat frequency offset, thereby obtaining the magnetic field change information.

[0052] In this embodiment, in order to adapt to different magnetic field measurement environments and meet the requirements of different measurement scenarios, the corresponding fiber laser sensitivity can be obtained by adjusting the size of the beat frequency signal; wherein the sensitivity of the fiber laser It can be expressed as: ; When measuring the magnetic field, since the sensitivity of the fiber laser is related to the size of the selected monitored beat frequency signal, a higher sensitivity can be obtained by changing the monitored beat frequency signal.

[0053] As an example, assuming that the total laser cavity length of the fiber laser is 12 m and the fundamental repetition frequency is 17 MHz, by monitoring the changes in the beat frequency signal at different frequencies (for example, 5 GHz and 10 GHz), the impact of the magnetic field on the laser can be evaluated, and the measured magnetic field performance of the fiber laser can be understood, thereby optimizing the design.

[0054] Specifically, when measuring the magnetic field in this embodiment, the corresponding frequency signals that change with the magnetic field are recorded at the beat frequency signals of 5 GHz and 10 GHz respectively. The light output by the optical fiber resonant cavity is transmitted to the electronic spectrum analyzer (ESA) via the PD (photodetector), and finally the measured beat frequency signal is transmitted to the computer for accurate data processing.

[0055] As the magnetic field gradually increases, the deformation of the single-mode optical fiber in the magnetic field sensing area 8 also increases, resulting in a red shift in the laser beat frequency spectrum position, that is, a beat frequency signal offset. By using the origin (function plotting software) data processing software, the relationship between the magnetic field change and the laser beat frequency offset can be accurately determined in this embodiment. This innovative sensing scheme has great flexibility, so beat frequency signals of different frequencies can be used as needed to customize the magnetic field sensitivity of the proposed magnetic field sensing scheme. Through this set of precise experimental procedures and data processing methods, accurate and reliable magnetic field sensing results can be obtained.

[0056] This embodiment achieves the following technical effects through the above technical solution: The magnetic field measurement method of the fiber laser provided in this embodiment can provide a clearer and more stable measurement signal, and can still ensure high-precision magnetic field measurement even in the presence of external noise sources. This has important advantages for applications requiring a high signal-to-noise ratio, such as precision scientific experiments, geological exploration and other fields. In addition, the mode-locking mechanism in this embodiment can effectively reduce the impact of environmental interference (such as temperature changes, mechanical vibrations, etc.) on the laser output frequency, improve the stability and accuracy of the system, and make the magnetic field measurement results more reliable, especially in scenarios requiring high-precision long-term monitoring. It has obvious advantages. At the same time, compared with ordinary fiber lasers, the laser scheme adopted in this embodiment has more longitudinal modes, which can keep the beat frequency signal in a high-quality state at high frequencies. Compared with other laser sensing schemes, the system of this embodiment has the advantages of simple structure, compact structure, high sensitivity, no need for cumbersome demodulation process and expensive optical devices. These characteristics make fiber laser sensing technology have great application potential in the field of magnetic field sensing.

[0057] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the computer program can be stored in a non-volatile storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided by the present invention can include non-volatile and volatile memory.

[0058] In summary, the present invention provides a fiber laser and a magnetic field measurement method, including: a pump source, a ring-shaped resonant cavity and a magnetic field sensing area connected by an optical path in sequence; a wavelength division multiplexer, an erbium-doped gain fiber, a polarization controller, a fiber polarizer, a polarization-independent isolator and a fiber coupler are sequentially arranged in the ring-shaped resonant cavity along the propagation direction of the laser; the wavelength division multiplexer, the erbium-doped gain fiber, the polarization controller, the fiber polarizer, the polarization-independent isolator and the fiber coupler are sequentially connected to form a ring-shaped optical path structure; the laser excited by the pump source passes through the ring-shaped resonant cavity to generate a beat frequency signal, and the beat frequency signal is affected by the external magnetic field when passing through the magnetic field sensing area to generate a beat frequency offset, and the measured magnetic field change information is obtained based on the beat frequency offset. The system of the present invention has the characteristics of simple structure, compactness, high sensitivity and low cost, and improves the signal-to-noise ratio and resolution of the optical fiber magnetic field sensor.

[0059] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A fiber laser for magnetic field measurement, characterized in that: include: A pump source, a ring-shaped structure resonant cavity and a magnetic field sensing area connected by an optical path are sequentially formed; The ring-shaped resonant cavity is provided with a wavelength division multiplexer, an erbium-doped gain optical fiber, a polarization controller, an optical fiber polarizer, a polarization-independent isolator and an optical fiber coupler in sequence along the propagation direction of the laser; The wavelength division multiplexer, the erbium-doped gain optical fiber, the polarization controller, the optical fiber polarizer, the polarization-independent isolator and the optical fiber coupler are connected in sequence to form a ring optical path structure; The laser excited by the pump source generates a beat frequency signal through the ring structure resonant cavity. The beat frequency signal is affected by the external magnetic field when passing through the magnetic field sensing area to generate a beat frequency offset. The measured magnetic field change information is obtained based on the beat frequency offset.

2. The fiber laser according to claim 1, characterized in that: A single-mode optical fiber and a magnetostrictive sleeve are arranged in the magnetic field sensing area, and the single-mode optical fiber is encapsulated in the magnetostrictive sleeve.

3. The fiber laser according to claim 2, characterized in that: The magnetostrictive sleeve is Tb 0.3 Dy 0.6 Nd 0.1 (Fe 0.8 Co 0.2 ) 1.93 Telescopic sleeve of material.

4. The fiber laser according to claim 2, characterized in that: The magnetostrictive sleeve generates telescopic deformation under the change of the external magnetic field, and the single-mode optical fiber generates corresponding telescopic deformation under the deformation of the magnetostrictive sleeve.

5. The optical fiber laser according to any one of claims 1 to 4, characterized in that: The mode locking mechanism of the optical fiber laser is a nonlinear polarization rotation mechanism.

6. A method for measuring the magnetic field of a fiber laser, characterized in that: include: Adjusting the power of the pump source according to a preset power parameter so that the pump source generates a laser pulse signal; Adjust the cavity length of the ring-shaped resonant cavity according to the preset optical path parameters, and generate a beat frequency signal under any two longitudinal mode states in the ring-shaped resonant cavity; Adjusting the size of the external magnetic field to control the magnetostrictive sleeve in the magnetic field sensing area to drive the single-mode optical fiber to generate a telescopic deformation, so as to shift the beat frequency signal and obtain a beat frequency offset; The magnetic field variation of the external magnetic field is measured based on the beat frequency offset, and the magnetic field variation information of the external magnetic field is acquired by calculation.

7. The method for measuring the magnetic field of a fiber laser according to claim 6, characterized in that: The beat frequency signal is generated in any two longitudinal modes in the ring structure resonant cavity for: ； in, is an integer, is the speed of light in vacuum, is the effective refractive index of the optical fiber, is the total cavity length of the resonant cavity.

8. The method for measuring the magnetic field of a fiber laser according to claim 6, characterized in that: The beat frequency offset is: ； in, is the change in length of the single-mode optical fiber, is the magnetostriction coefficient, is the magnetic field variation, is the original length of the magnetostrictive material.

9. The method for measuring the magnetic field of a fiber laser according to claim 6, characterized in that: The method further comprises: The corresponding fiber laser sensitivity is obtained by adjusting the size of the beat frequency signal.

10. The method for measuring the magnetic field of an optical fiber laser according to claim 9, characterized in that: The fiber laser sensitivity for: 。

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