Optical fiber cavity optical force magnetic field sensor, direct current / alternating current magnetic field measurement system and method

Abstract

The application relates to the technical field of magnetic field measurement, in particular to an optical fiber cavity optical force magnetic field sensor, a direct current / alternating current magnetic field measurement system and a method. The optical fiber cavity optical force magnetic field sensor comprises an optical fiber grating, capillary tubes are fixedly sleeved at two ends of the optical fiber grating, two capillary tubes are respectively located on two sides of a grating area on the optical fiber grating, a magnetic field response component is arranged below the optical fiber grating, positions of the two capillary tubes close to two ends of the magnetic field response component are respectively fixedly connected with the two ends of the magnetic field response component, the magnetic field response component is made of a material with a magnetostrictive effect, and an axis of the optical fiber grating is parallel to a magnetostrictive direction of the magnetic field response component. The application combines the advantages of cavity optics and optical fiber sensing, uses a grating area of an optical fiber grating as an optical cavity and a magnetic field response component as a mechanical resonator, and significantly improves the direct current / alternating current magnetic field measurement sensitivity through a strain amplification mechanism.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnetic field measurement, in particular to a kind of optical fiber cavity optical force magnetic field sensor, DC / AC magnetic field measurement system and method. BACKGROUND

[0002] With the continuous progress of society, magnetic field detection technology shows its indispensable value in national security, health care, engineering construction and other industries. However, traditional magnetic field measurement techniques, such as inductive coils, Hall sensors, etc., although widely used, have significant limitations in sensitivity, response speed and cost.

[0003] In recent years, in order to overcome these challenges, researchers have proposed a variety of new magnetic field measurement techniques, among which schemes based on superconducting quantum interferometer, atomic magnetometer and sensors based on magnetostrictive materials have made significant progress in magnetic field measurement. However, these technologies still face problems such as complex operating environment, high cost or insufficient integration in practical applications.

[0004] Cavity optical force magnetometer as a new magnetic field measurement technology, it mainly uses the resonance enhancement effect of optical cavity and mechanical mode, has high sensitivity and wide dynamic range etc. characteristics. Because the current cavity optical force magnetometer mainly uses microchip ring cavity and other on-chip optical whispering gallery mode, the preparation process is complex, special processing equipment is needed, and low-cost mass production cannot be realized, which limits the practical application.

[0005] Optical fiber magnetometer as another potential magnetic field measurement technology, by directly bonding fiber grating on the surface of magnetostrictive material, using the length change of magnetostrictive material under the action of magnetic field, affecting the phase or amplitude of light field transmission in optical fiber, to infer the change of magnetic field strength. Optical fiber magnetometer has the advantages of anti-electromagnetic interference, ultra-high electrical insulation, fireproof, explosion-proof, small size, low cost, light weight, corrosion resistance, etc., so it has been widely used in various fields of social production and life. However, since the fiber grating is directly bonded on the magnetostrictive material, the upper limit of the physical properties of the saturation magnetostriction coefficient of these materials limits the further improvement of the magnetic field measurement sensitivity. SUMMARY

[0006] The present application aims to solve the problem that the current optical fiber magnetometer cannot achieve high magnetic field measurement sensitivity due to the physical properties of magnetostrictive materials. The present application provides an optical fiber cavity optical force magnetic field sensor, DC / AC magnetic field measurement system and method, which combines the advantages of cavity optics and optical fiber sensing, realizes high sensitivity magnetic field measurement, uses the grating area of fiber grating as optical cavity, and uses the magnetic field response component as mechanical resonator. Through strain amplification mechanism, the magnetic field measurement sensitivity is significantly improved, while the cost is low and the distributed test scalability is good.

[0007] To achieve the above object, the present application adopts the following technical solutions:

[0008] An optical fiber cavity optical force magnetic field sensor comprises a fiber grating, both ends of the fiber grating are fixedly sleeved with capillary tubes, two capillary tubes are respectively located on both sides of a grating area on the fiber grating, a magnetic field response component is arranged below the fiber grating, both ends of the two capillary tubes close to the magnetic field response component are fixedly connected with both ends of the magnetic field response component, the magnetic field response component is made of a material with a magnetostrictive effect, and an axis of the fiber grating is parallel to a magnetostrictive direction of the magnetic field response component.

[0009] Further, the fiber grating is any one of a fiber Bragg grating, a phase-shift fiber grating, a long-period fiber grating, a chirped fiber grating, and a fiber Bragg grating pair.

[0010] Still further, an inner diameter of the capillary tube is 10-30 microns larger than a diameter of the fiber grating, so as to ensure that the fiber grating can be smoothly inserted without being damaged, and a material of the capillary tube is any one of quartz, metal, alloy, and plastic.

[0011] Still further, a material of the magnetic field response component is any one of pure nickel, iron oxide, iron-gallium alloy, iron-cobalt-vanadium alloy, iron-nickel alloy, terbium-dysprosium-iron alloy, and iron-gallium-boron alloy, and a shape of the magnetic field response component is any one of a solid cylinder, a hollow cylinder, a solid cuboid, and a hollow cuboid.

[0012] A direct-current magnetic field measurement system comprises a broadband light source, a fiber ring, a spectrometer, an optical fiber cavity optical force magnetic field sensor, a direct-current solenoid, and a direct-current power supply, the direct-current solenoid is connected with the direct-current power supply, the optical fiber cavity optical force magnetic field sensor is located in the direct-current solenoid, the fiber ring is connected with the broadband light source, the spectrometer, and the optical fiber cavity optical force magnetic field sensor through a fiber connector, the broadband light source is used to provide an optical signal covering a working waveband range of the optical fiber cavity optical force magnetic field sensor, the fiber ring is used for input of the optical signal of the broadband light source and output of a fiber grating reflected optical signal, the spectrometer is used to read changes of a reflected spectrum of the fiber grating through the fiber connector under different external direct-current magnetic fields, a magnetic field intensity of a calibration direct-current magnetic field generated by the direct-current solenoid is adjusted by changing an output current of the direct-current power supply, and a direct-current magnetic field test sensitivity of the optical fiber cavity optical force magnetic field sensor is tested by using the calibration direct-current magnetic field.

[0013] An alternating current magnetic field measurement system comprises a continuous tunable light source, a fiber coupler, a fiber loop, an optical attenuator, a balanced optical detector, an oscilloscope, a spectrum analyzer, a fiber-optic cavity optomechanical magnetic field sensor, an alternating current solenoid and a low noise signal generator, the alternating current solenoid is connected with the low noise signal generator, the fiber-optic cavity optomechanical magnetic field sensor is located in the alternating current solenoid, the fiber loop is connected with the fiber coupler, the balanced optical detector and the fiber-optic cavity optomechanical magnetic field sensor through fiber connectors, the optical attenuator is connected with the continuous tunable light source and the balanced optical detector respectively, the oscilloscope and the spectrum analyzer are connected with the balanced optical detector through coaxial cables, the continuous tunable light source is used to provide an optical signal, the fiber coupler is used to divide the optical signal emitted by the continuous tunable light source into two beams, one of which enters the fiber loop and the other of which enters the optical attenuator, the fiber loop is used for input of the optical signal of the continuous tunable light source and output of the fiber grating reflected optical signal, the optical attenuator is used to adjust the optical power of one of the two beams entering the balanced optical detector so as to perform effective balanced detection, the balanced optical detector is used to convert the optical signal into an electrical signal, the oscilloscope is used to record the reflection spectrum of the fiber grating output by the balanced optical detector or to monitor the level values of the two electrical signals output by the monitoring end of the balanced optical detector, and the spectrum analyzer is used to perform frequency spectrum analysis on the alternating current component electrical signal output by the radio frequency end of the balanced optical detector to obtain the frequency domain response of the fiber-optic cavity optomechanical magnetic field sensor to the external alternating current magnetic field.

[0014] Further, the relationship between the frequency of the low noise signal generator and the characteristic mechanical resonance frequency of the magnetic field response component in the fiber-optic cavity optomechanical magnetic field sensor is that the resonance frequency corresponding to the strongest vibration mode of the magnetic field response component is within the frequency range of the sine signal output by the low noise signal generator.

[0015] A direct current magnetic field measurement method comprises the following steps:

[0016] A broadband optical signal is output by a broadband light source, the broadband optical signal enters a fiber loop and then enters a fiber-optic cavity optomechanical magnetic field sensor, the reflected light of the fiber-optic cavity optomechanical magnetic field sensor is detected by a spectrum analyzer after passing through the fiber loop, the direct current solenoid generates magnetic fields of different intensities in the axial direction by changing the size of the direct current output by a direct current power supply, the reflected spectrum detected by the spectrum analyzer under different intensity magnetic fields is recorded, and the direct current magnetic field test sensitivity of the fiber-optic cavity optomechanical magnetic field sensor is obtained by dividing the wavelength drift of the reflected spectrum center by the change in the magnetic field intensity.

[0017] An alternating current magnetic field measurement method comprises the following two stages:

[0018] In the first stage, the reflected spectrum of the fiber grating under the action of the non-calibrated alternating current magnetic field is tested:

[0019] The continuous variable optical signal is output by a continuously tunable light source, the spectral bandwidth range of the optical signal needs to cover the reflection spectrum of the fiber cavity optical force magnetic field sensor, the optical signal enters the fiber cavity optical force magnetic field sensor through the optical fiber circulator, is reflected by the fiber grating in the fiber cavity optical force magnetic field sensor, and enters the balanced optical detector again through the optical fiber circulator, the balanced optical detector converts the optical signal into an electrical signal and outputs to an oscilloscope, and the reflection spectrum level value of the fiber grating is recorded by the oscilloscope.

[0020] In the second stage, the AC magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor is tested.

[0021] The continuously tunable light source outputs a specific single wavelength optical signal, the level values of the two-way electrical signals output by the balanced optical detector monitoring end displayed on the reference oscilloscope are used to adjust the optical attenuator, and the optical power entering one of the two ways of the balanced optical detector through the optical fiber beam splitter is adjusted to perform effective balanced detection; the balanced optical detector performs balanced detection through the two-way optical signal channels, subtracts the background optical noise of the continuously tunable light source, and the two monitoring ends are used to output the electrical signals converted from the two-way optical signals, and the radio frequency end is used to output the AC component electrical signal after balanced detection, which is used for analyzing the frequency domain response of the fiber cavity optical force magnetic field sensor; the size of the continuously variable AC current output by the low-noise signal generator is changed, and the strength of the AC magnetic field generated by the AC solenoid is changed; the frequency spectrum analysis of the AC component electrical signal output by the radio frequency end of the balanced optical detector is performed by the spectrum analyzer, and the frequency domain response of the fiber cavity optical force magnetic field sensor to the external AC magnetic field is obtained; the frequency spectrum curve of the fiber cavity optical force magnetic field sensor when the AC magnetic field is applied and the frequency spectrum curve of the device when the AC magnetic field is not applied are mathematically operated, and the AC magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor is obtained.

[0022] Further, the specific wavelength output by the continuously tunable light source in the second stage refers to one of the two wavelength values corresponding to the one quarter power intensity of the fiber grating reflection spectrum under linearized power intensity.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] The application combines the advantages of cavity optomechanics and fiber sensing, uses the grating area of the fiber grating as an optical cavity, and uses a magnetic field response component as a mechanical resonator, thereby significantly enhancing the AC magnetic field test sensitivity in a specific frequency range; when the external magnetic field changes, the magnetic field response component generates a corresponding mechanical deformation, which is transmitted to the fiber grating through two capillary tubes, so that the fiber grating generates axial strain and internal normal stress; since the reflection spectrum of the fiber grating will drift with the change of the normal stress, the drift amount is proportional to the size of the normal stress, so the change of the magnetic field intensity can be measured by monitoring the change of the reflection spectrum of the fiber grating; in particular, the application introduces a strain amplification mechanism to enhance the sensitivity to the change of the magnetic field, and specifically, the two capillary tubes in the application are located on both sides of the grating area of the fiber grating; since the cross-sectional area difference between the fiber grating and the capillary tube is large, the normal stress is concentrated in the grating area part of the fiber grating with smaller cross-sectional area, thereby enhancing the sensitivity of the grating area part to the change of the magnetic field.

[0025] The application uses the fiber grating as a sensing medium, and compared with the existing on-chip cavity optomechanics magnetic field measurement system, the application has the advantages of simple manufacturing process, low cost, easy integration and higher test sensitivity.

[0026] The application can be used without low temperature and without shielding the magnetic field, and has excellent application scenarios.

[0027] The application can realize multi-point or even grid magnetic field / strain / temperature measurement by cascading multiple fiber cavity optical force magnetic field sensors with different center wavelengths. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Fig. 1 is a structural schematic diagram of the fiber cavity optical force magnetic field sensor of the application;

[0029] Figure 2 Fig. 2 is a structural schematic diagram of the DC magnetic field measurement system of the application;

[0030] Figure 3 Fig. 3 is a structural schematic diagram of the AC magnetic field measurement system of the application;

[0031] Figure 4 Fig. 4 is a comparison diagram of measurement results of different devices under a DC magnetic field;

[0032] Figure 5 Fig. 5 is a comparison diagram of spectral curves of different devices under the condition of applying an AC magnetic field and not applying an AC magnetic field;

[0033] Figure 6 Fig. 6 is a spectral curve diagram of different devices under the condition of not applying an AC magnetic field;

[0034] Figure 7 Fig. 7 is a schematic diagram of specific wavelengths output by the continuously tunable light source in the second stage;

[0035] In the figure, broadband light source 1, optical fiber circulator 2, optical spectrum analyzer 3, optical fiber cavity optical force magnetic field sensor 4, direct current solenoid 5, direct current power supply 6, continuous tunable light source 7, optical fiber beam splitter 8, optical attenuator 9, balanced optical detector 10, oscilloscope 11, spectrum analyzer 12, alternating current solenoid 13, low noise signal generator 14, optical fiber grating 401, capillary tube 402, grating region 403, magnetic field responsive component 404. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical solutions of the present application, the present application will be further described below through examples.

[0037] An optical fiber cavity optical force magnetic field sensor, comprising an optical fiber grating 401, capillary tubes 402 are fixedly sleeved at both ends of the optical fiber grating 401, the two capillary tubes 402 are respectively located on both sides of a grating region 403 on the optical fiber grating 401, a magnetic field responsive component 404 is arranged below the optical fiber grating 401, the positions of the two capillary tubes 402 close to both ends of the magnetic field responsive component 404 are respectively fixedly connected with both ends of the magnetic field responsive component 404, the magnetic field responsive component 404 is made of a material having a magnetostrictive effect, and the axis of the optical fiber grating 401 is parallel to the magnetostrictive direction of the magnetic field responsive component 404. The optical fiber grating 401 is any one of a fiber Bragg grating, a phase-shifted fiber grating, a long-period fiber grating, a chirped fiber grating and a fiber Bragg grating pair. The inner diameter of the capillary tube 402 is 10-30 microns larger than the diameter of the optical fiber grating 401, so as to ensure that the optical fiber grating 401 can be smoothly inserted without being damaged, and the material of the capillary tube 402 is any one of quartz, metal, alloy and plastic. The material of the magnetic field responsive component 404 is any one of pure nickel, iron oxide, iron-gallium alloy, iron-cobalt-vanadium alloy, iron-nickel alloy, terbium-dysprosium-iron alloy and iron-gallium-boron alloy; and the shape of the magnetic field responsive component 404 is any one of a solid cylinder, a hollow cylinder, a solid cuboid or a hollow cuboid.

[0038] The direct current magnetic field measurement system comprises a broadband light source 1, a fiber loop 2, a spectrometer 3, a fiber cavity optical force magnetic field sensor 4, a direct current solenoid 5 and a direct current power supply 6, the direct current solenoid 5 is connected with the direct current power supply 6, the fiber cavity optical force magnetic field sensor 4 is located in the direct current solenoid 5, the fiber loop 2 is connected with the broadband light source 1, the spectrometer 3 and the fiber cavity optical force magnetic field sensor 4 through fiber connectors, the broadband light source 1 is used to provide the fiber cavity optical force magnetic field sensor 4 with an optical signal covering the working waveband range thereof, the fiber loop 2 is used for the input of the optical signal of the broadband light source 1 and the output of the reflected optical signal of the fiber grating 401, the spectrometer 3 is used to read the change of the reflected spectrum of the fiber through the fiber connector grating under different external direct current magnetic fields, the output current size of the direct current power supply 6 is changed to adjust the magnetic field intensity of the calibration direct current magnetic field generated by the direct current solenoid 5, and the direct current magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor 4 is tested by using the calibration direct current magnetic field. The broadband light source 1 is any one of a fluorescent lamp, an incandescent lamp, a halogen lamp, an LED array, an ultra-continuous light source, a broadband laser, a broadband LED light source and a continuous tunable laser. The spectrometer 3 is any one of a grating spectrometer, a Fourier transform spectrometer and a prism spectrometer.

[0039] The AC magnetic field measurement system comprises a continuous tunable light source 7, a fiber coupler 8, a fiber loop 2, an optical attenuator 9, a balanced optical detector 10, an oscilloscope 11, a spectrum analyzer 12, a fiber cavity optical force magnetic field sensor 4, an AC solenoid 13 and a low noise signal generator 14. The AC solenoid 13 is connected with the low noise signal generator 14, the fiber cavity optical force magnetic field sensor 4 is located in the AC solenoid 13, the fiber loop 2 is connected with the fiber coupler 8, the balanced optical detector 10 and the fiber cavity optical force magnetic field sensor 4 through fiber connectors, the optical attenuator 9 is connected with the continuous tunable light source 7 and the balanced optical detector 10 respectively, the oscilloscope 11 and the spectrum analyzer 12 are connected with the balanced optical detector 10 through coaxial cables, the continuous tunable light source 7 is used for providing an optical signal, the fiber coupler 8 is used for dividing the optical signal emitted by the continuous tunable light source 7 into two beams, one of which enters the fiber loop 2 and the other of which enters the optical attenuator 9, the fiber loop 2 is used for inputting the optical signal of the continuous tunable light source 7 and outputting the reflected optical signal of the fiber grating 401, the optical attenuator 9 is used for adjusting the optical power of one of the two beams entering the balanced optical detector 10 so as to perform effective balanced detection, the balanced optical detector 10 is used for converting the optical signal into an electrical signal, the oscilloscope 11 is used for recording the reflection spectrum of the fiber grating 401 output by the balanced optical detector 10 or for monitoring the level values of the two electrical signals output by the monitoring end of the balanced optical detector 10, and the spectrum analyzer 12 is used for performing frequency spectrum analysis on the AC component electrical signal output by the radio frequency end of the balanced optical detector 10 to obtain the frequency domain response of the fiber cavity optical force magnetic field sensor 4 with respect to the external AC magnetic field. The relationship between the frequency of the low noise signal generator 14 and the characteristic mechanical resonance frequency of the magnetic field response component 404 in the fiber cavity optical force magnetic field sensor 4 is that the resonance frequency corresponding to the strongest vibration mode of the magnetic field response component 404 is located in the frequency range of the sine signal output by the low noise signal generator 14. The optical attenuator 9 is any one of a mechanical adjustable optical attenuator, a thermo-optic adjustable attenuator, an electro-optic adjustable attenuator, a magneto-optic adjustable attenuator, an acousto-optic adjustable attenuator and a liquid crystal adjustable attenuator. The continuous tunable light source 7 is any one of a semiconductor tunable laser, an optical parametric oscillator, a tunable fiber laser, a tunable vertical cavity surface emitting laser and an electro-absorption modulated laser.

[0040] The DC magnetic field measurement method comprises the following steps:

[0041] A broadband light signal is output by a broadband light source 1, and the broadband light signal enters a fiber cavity optical force magnetic field sensor 4 through a fiber circulator 2. The reflected light of the fiber cavity optical force magnetic field sensor 4 is detected by a spectrometer 3 after passing through the fiber circulator 2. The strength of the magnetic field in the axial direction of a direct-current solenoid 5 is changed by changing the size of the direct-current output by a direct-current power supply 6. The reflected spectrum detected by the spectrometer 3 under different strength magnetic fields is recorded. The direct-current magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor 4 is obtained by dividing the center wavelength drift of the reflected spectrum by the change in the magnetic field strength.

[0042] An alternating-current magnetic field measurement method includes the following two stages.

[0043] In the first stage, the reflected spectrum of the fiber grating 401 under the action of the uncalibrated alternating-current magnetic field is tested.

[0044] A continuously tunable light source 7 outputs a continuously changing light signal. The spectral bandwidth range of the light signal needs to cover the reflected spectrum of the fiber cavity optical force magnetic field sensor 4. The light signal enters the fiber cavity optical force magnetic field sensor 4 through the fiber circulator 2. After being reflected by the fiber grating 401 in the fiber cavity optical force magnetic field sensor 4, the light signal enters a balanced optical detector 10 again through the fiber circulator 2. The balanced optical detector 10 converts the light signal into an electrical signal and outputs the electrical signal to an oscilloscope 11. The reflected spectrum level value of the fiber grating 401 is recorded by the oscilloscope 11.

[0045] In the second stage, the alternating-current magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor 4 is tested.

[0046] The continuous tunable light source 7 outputs a specific single wavelength light signal, the balanced optical detector 10 displays the level values of the two output electrical signals on the reference oscilloscope 11, the optical attenuator 9 is adjusted, the optical power entering one of the two balanced optical detectors 10 through the optical fiber splitter 8 is adjusted, and effective balanced detection is performed; the balanced optical detector 10 performs balanced detection through the two optical signal channels, the background optical noise of the continuous tunable light source 7 is subtracted, the two monitoring ends are used to output the electrical signals converted from the two optical signals, the radio frequency end is used to output the alternating component electrical signal after balanced detection, and the frequency domain response of the fiber cavity optical force magnetic field sensor 4 is analyzed; the frequency of the alternating current output by the low-noise signal generator 14 is changed, the strength of the alternating magnetic field generated by the alternating solenoid 13 is changed; the spectrum analyzer 12 is used for spectrum analysis on the alternating component electrical signal output by the radio frequency end of the balanced optical detector 10, the frequency domain response of the fiber cavity optical force magnetic field sensor 4 with the change of the external alternating magnetic field is obtained; the spectrum curve of the fiber cavity optical force magnetic field sensor 4 when the alternating magnetic field is applied and the spectrum curve of the device when the alternating magnetic field is not applied are mathematically operated, and the alternating magnetic field test sensitivity of the fiber cavity optical force magnetic field sensor 4 is obtained. The specific wavelength output by the continuous tunable light source 7 in the second stage refers to one of the two wavelength values corresponding to the linearized power intensity of the reflected light spectrum of the fiber grating 401 and the quarter power intensity.

[0047] In the structural design of the embodiment, the grating area 403 of the fiber grating 401 is exposed between the two capillary tubes 402, and the length of the exposed fiber is L1; the two capillary tubes 402 are fixed on the magnetic field response component by glue, and the distance between the two glues is defined as L2, and the structural proportion factor Θ=L2 / L1 related to L1 and L2.

[0048] The structural proportion factor Θ related to L1 and L2 is calculated by using the direct-current magnetic field measurement system in the embodiment.

[0049] As shown in the figure, Figure 4 The No. 0 device has no related structure, the fiber grating is directly bonded on the magnetic field response component, and Θ=1; the No. 1 device and the No. 2 device adopt the fiber cavity optical force magnetic field sensor structure of the application, wherein the Θ of the No. 1 device is 7.71; the Θ of the No. 2 device is 15.75;

[0050] The left side is the spectrum drift test condition, and the right side is the drift condition of the center wavelength. The direct-current magnetic field test sensitivities of the No. 0, No. 1 and No. 2 devices are calculated as 0.58 pm / Gs, 5.17 pm / Gs and 8.47 pm / Gs respectively.

[0051] The structural proportion factor Θ related to L1 and L2 is calculated by using the alternating-current magnetic field measurement system in the embodiment.

[0052] Figure 5 The upper curve is the spectrum curve test chart of different devices under the condition of applying AC magnetic field, and the lower curve is the spectrum curve test chart under the condition of not applying AC magnetic field, Figure 6 The figure is the calculated AC magnetic field test sensitivity curve of the No. 0, No. 1 and No. 2 devices, which is the highest at the characteristic mechanical resonance frequency 11.25 kHz of the magnetic field response component, and the highest AC magnetic field test sensitivity of the three devices is 31.79 pT / Hz 1 / 2 , 5.05 pT / Hz 1 / 2 and 4.35 pT / Hz 1 / 2 , respectively. The calculation results of the AC magnetic field test sensitivity are shown in Figure 6 .

[0053] The main features and advantages of the present application are shown and described above, and it is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0054] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A fiber optic cavity optical force and magnetic field sensor, characterized in that: The fiber optic grating (401) includes capillary tubes (402) fixedly sleeved at both ends of the fiber optic grating (401). The two capillary tubes (402) are located on both sides of the grating region (403) on the fiber optic grating (401). The grating region (403) of the fiber optic grating (401) is exposed between the two capillary tubes (402). The length of the exposed optical fiber is L1. A magnetic field response component (404) is provided below the fiber optic grating (401). The two capillary tubes (402) are fixedly connected to the two ends of the magnetic field response component (404) by adhesive. The distance between the two adhesives is defined as L2. The structural scaling factor Θ related to L1 and L2 is L2 / L1, and L2 is greater than L1. The magnetic field response component (404) is made of a material with magnetostrictive effect. The axis of the fiber optic grating (401) is parallel to the magnetostrictive direction of the magnetic field response component (404).

2. The fiber optic cavity optical force and magnetic field sensor according to claim 1, characterized in that: The fiber Bragg grating (401) is any one of the following: fiber Bragg grating, phase-shifted fiber Bragg grating, long-period fiber Bragg grating, chirped fiber Bragg grating, and fiber Bragg grating pair.

3. The fiber optic cavity optical force and magnetic field sensor according to claim 1, characterized in that: The inner diameter of the capillary (402) is 10-30 micrometers larger than the diameter of the fiber grating (401) to ensure that the fiber grating (401) can be smoothly inserted without being damaged. The capillary (402) is made of any one of quartz, metal, alloy, or plastic.

4. The fiber optic cavity optical force and magnetic field sensor according to claim 1, characterized in that: The magnetic field response component (404) is made of any one of pure nickel, iron oxide, iron-gallium alloy, iron-cobalt-vanadium alloy, iron-nickel alloy, terbium-dysprosium-iron alloy, and iron-gallium-boron alloy; the shape of the magnetic field response component (404) is any one of solid cylinder, hollow cylinder, solid cuboid, or hollow cuboid.

5. A DC magnetic field measurement system based on the fiber optic cavity optical force and magnetic field sensor of claim 1, characterized in that: The system includes a broadband light source (1), an optical fiber circulator (2), a spectrometer (3), an optical fiber cavity optical magnetic field sensor (4), a DC solenoid (5), and a DC power supply (6). The DC solenoid (5) is connected to the DC power supply (6). The optical fiber cavity optical magnetic field sensor (4) is located in the DC solenoid (5). The optical fiber circulator (2) is connected to the broadband light source (1), the spectrometer (3), and the optical fiber cavity optical magnetic field sensor (4) through an optical fiber connector. The broadband light source (1) is used to provide the optical fiber cavity optical magnetic field sensor (4) with an optical signal covering its operating wavelength range. The optical fiber circulator (2) is used for the optical signal input of the broadband light source (1) and the output of the reflected optical signal of the fiber optic grating (401). The spectrometer (3) is used to read the changes in the reflected spectrum of the optical fiber through the fiber optic connector grating under different external DC magnetic fields. The magnetic field strength of the calibration DC magnetic field generated by the DC solenoid (5) is adjusted by changing the output current of the DC power supply (6). The DC magnetic field test sensitivity of the optical fiber cavity optical magnetic field sensor (4) is tested using this calibration DC magnetic field.

6. An AC magnetic field measurement system based on the fiber optic cavity optical force and magnetic field sensor of claim 1, characterized in that: The system includes a continuously tunable light source (7), an optical fiber beam splitter (8), an optical fiber circulator (2), an optical attenuator (9), a balanced photodetector (10), an oscilloscope (11), a spectrum analyzer (12), an optical cavity photomagnetic sensor (4), an AC solenoid (13), and a low-noise signal generator (14). The AC solenoid (13) is connected to the low-noise signal generator (14). The optical cavity photomagnetic sensor (4) is located in the AC solenoid (13). The optical fiber circulator (2) is connected to the optical fiber beam splitter (8), the balanced photodetector (10), and the optical cavity photomagnetic sensor (4) via optical fiber connectors. The two ends of the optical attenuator (9) are connected to the continuously tunable light source (7) and the balanced photodetector (10), respectively. The oscilloscope (11) and the spectrum analyzer (12) are both connected to the balanced photodetector (10) via coaxial cables. The continuously tunable light source (7) is used to provide optical signals. The optical fiber beam splitter... The device (8) is used to split the optical signal emitted by the continuously tunable light source (7) into two beams, one of which enters the fiber optic circulator (2) and the other enters the optical attenuator (9). The fiber optic circulator (2) is used for the input of the optical signal from the continuously tunable light source (7) and the output of the reflected optical signal from the fiber optic grating (401). The optical attenuator (9) is used to adjust the optical power of one of the beams entering the balanced photodetector (10) so as to perform effective balanced detection. The balanced photodetector (10) is used to convert the optical signal into an electrical signal. The oscilloscope (11) is used to record the reflection spectrum of the fiber optic grating (401) output by the balanced photodetector (10) or to monitor the level values ​​of the two electrical signals output by the monitoring end of the balanced photodetector (10). The spectrum analyzer (12) is used to perform spectrum analysis on the AC component electrical signal output by the radio frequency end of the balanced photodetector (10) to obtain the frequency domain response of the fiber cavity optical magnetic field sensor (4) as the external AC magnetic field changes.

7. The AC magnetic field measurement system according to claim 6, characterized in that: The relationship between the frequency of the low-noise signal generator (14) and the characteristic mechanical resonant frequency of the magnetic field response component (404) in the fiber cavity optical magnetic field sensor (4) is as follows: the resonant frequency corresponding to the strongest mode of the magnetic field response component (404) is located within the frequency range of the sinusoidal signal output by the low-noise signal generator (14).

8. A method for measuring a DC magnetic field based on the DC magnetic field measurement system of claim 5, characterized in that: Includes the following steps: A broadband optical signal is output through a broadband light source (1). The broadband optical signal enters the fiber cavity optical magnetic field sensor (4) through the fiber optic circulator (2). The reflected light of the fiber cavity optical magnetic field sensor (4) is detected by the spectrometer (3) after passing through the fiber optic circulator (2). By changing the magnitude of the DC current output by the DC power supply (6), the DC solenoid (5) generates magnetic fields of different intensities in the axial direction. The spectrometer (3) detects the reflected spectrum under different magnetic field intensities. The DC magnetic field test sensitivity of the fiber cavity optical magnetic field sensor (4) is obtained by dividing the center wavelength shift of the reflected spectrum by the change in magnetic field intensity.

9. An AC magnetic field measurement method based on the AC magnetic field measurement system of claim 6, characterized in that: It includes the following two stages: In the first stage, the reflection spectrum of the fiber grating (401) under the action of an uncalibrated AC magnetic field was obtained: A continuously changing optical signal is output through a continuously tunable light source (7). The spectral bandwidth of the optical signal needs to cover the reflection spectrum of the fiber cavity optical magnetic field sensor (4). The optical signal enters the fiber cavity optical magnetic field sensor (4) through the fiber circulator (2). After being reflected by the fiber grating (401) in the fiber cavity optical magnetic field sensor (4), it enters the balanced photodetector (10) through the fiber circulator (2) again. The balanced photodetector (10) converts the optical signal into an electrical signal and outputs it to the oscilloscope (11). The oscilloscope (11) records the reflection spectral level value of the fiber grating (401). In the second stage, the AC magnetic field sensitivity of the fiber optic cavity optical magnetic field sensor (4) was tested: A specific single-wavelength optical signal is output through a continuously tunable light source (7). Referring to the levels of the two electrical signals output from the monitoring end of the balanced photodetector (10) displayed on the oscilloscope (11), the optical attenuator (9) is adjusted to regulate the optical power of one of the optical signals entering the balanced photodetector (10) through the fiber optic splitter (8), thus performing effective balanced detection. The balanced photodetector (10) performs balanced detection through two optical signal channels, subtracting the background optical noise of the continuously tunable light source (7). The two monitoring ends are used to output the electrical signals converted from the two optical signals, and the radio frequency end is used to output the AC component electrical signal after balanced detection, used for optical-magnetic transmission in the fiber cavity. Analysis of the frequency domain response of the sensor (4); by changing the magnitude of the alternating current with continuously changing frequency output by the low-noise signal generator (14), the strength of the alternating magnetic field generated by the alternating solenoid (13) is changed; by performing spectrum analysis on the alternating component electrical signal output by the radio frequency terminal of the balanced photodetector (10) using the spectrum analyzer (12), the frequency domain response of the fiber cavity optical magnetic field sensor (4) with the change of the external alternating magnetic field is obtained; by performing mathematical operations on the spectrum curve of the fiber cavity optical magnetic field sensor (4) when the alternating magnetic field is applied and the spectrum curve of the device when the alternating magnetic field is not applied, the AC magnetic field test sensitivity of the fiber cavity optical magnetic field sensor (4) is obtained.

10. The method for measuring alternating magnetic fields according to claim 9, characterized in that: The specific wavelength output by the continuously tunable light source (7) in the second stage refers to one of the two wavelength values ​​corresponding to a quarter power intensity under the linearized power intensity of the fiber grating (401) reflection spectrum.

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