A high-sensitivity magnetic field detection device and method

Abstract

The application discloses a kind of high-sensitivity magnetic field detection device and method, device includes sequentially arranged in light propagation direction narrow line width tunable light source, polarized light formation module, first convex lens, second convex lens, Fabry-Perot cavity and detection calculation module, the Fabry-Perot cavity is equipped with the magneto-optical crystal that circled magnetic field coil, wherein, narrow line width tunable light source emits elliptically polarized signal light, polarized light formation module is formed into linearly polarized light of preset angle by signal light, Fabry-Perot cavity is formed with the linearly polarized light of resonance by injection, and linearly polarized light is shot from the cavity after being incident with two modes of light beam after magneto-optical crystal, detection calculation module includes connected detection unit and calculation unit, detection unit receives two modes of light beam, and calculation unit calculates the magnetic field applied to magneto-optical crystal according to the frequency difference of two modes.The application simple structure, simple operation, wide use, high sensitivity.

Description

Technical Field

[0001] This invention relates to magnetic field measurement technology, and more particularly to a highly sensitive magnetic field detection device and method. Background Technology

[0002] Magnetic field sensors have a wide range of applications, playing a vital role in industrial monitoring, national defense, astronomy, resource exploration, medical and health care, and scientific research. Currently, the most commonly used magnetic sensors include coils, Hall elements, magnetoresistive elements, and magneto-optical crystals. Coils are used to detect changes in magnetic flux, so they cannot measure static magnetic fields or slowly changing magnetic flux. Hall effect-based magnetic sensors typically lack sufficient sensitivity. Magneto-optical crystals, due to their stable properties, have been widely used in magnetic sensing in recent years. Furthermore, being solid, they have high electron density, making integration easy. The principle behind using magneto-optical crystals for magnetic sensing is the magneto-optical Faraday effect. When linearly polarized light passes through a magneto-optical crystal, it can be considered as a superposition of left-handed and right-handed circularly polarized light of equal amplitude. Due to the magneto-optical effect, these two beams have different refractive indices, resulting in different phases after traveling the same distance, thus deflecting the linearly polarized light passing through the plasma. However, for weak magnetic fields, the deflection angle is very small, leading to large measurement errors, a small measurement range, and low accuracy. Therefore, magnetic sensors utilizing the magneto-optical effect also face the challenge of improving sensitivity.

[0003] In summary, the analysis shows that, in the existing magnetic sensing technology, how to improve the sensitivity of magnetic sensing, reduce measurement errors, and thus develop a magnetic sensor device that is simple in principle, easy to operate, easy to integrate, and has a wide range of applications is an urgent technical problem to be solved. Summary of the Invention

[0004] Purpose of the invention: This invention addresses the problems existing in the prior art by providing a highly sensitive magnetic field detection device and method that is simple in principle, easy to operate, easy to integrate, and has a wide range of applications.

[0005] Technical Solution: The high-sensitivity magnetic field detection device of the present invention includes a narrow-linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, a Fabry-Borro cavity, and a detection calculation module arranged sequentially along the light propagation direction. The Fabry-Borro cavity contains a magneto-optical crystal surrounding a magnetic field coil. The narrow-linewidth tunable light source emits elliptically polarized signal light. The polarization light forming module forms the signal light into linearly polarized light at a preset angle. The Fabry-Borro cavity resonates with the incident linearly polarized light and, after passing through the magneto-optical crystal, emits a beam with two modes from within the cavity. The detection calculation module includes a connected detection unit and a calculation unit. The detection unit receives the beam with two modes, and the calculation unit calculates the magnetic field applied to the magneto-optical crystal based on the frequency difference between the two modes.

[0006] Furthermore, the polarization light forming module includes a quarter-wave plate, a first half-wave plate, a polarization beam splitter, and a second half-wave plate arranged sequentially along the light propagation direction.

[0007] Furthermore, the Fabry-Borne cavity includes a first concave cavity mirror and a second concave cavity mirror arranged along the light propagation direction. The first concave cavity mirror has a planar incident surface and a concave exit surface, while the second concave cavity mirror has a concave incident surface and a planar exit surface. Both the planar surfaces of the first and second concave cavity mirrors are coated with a high-transmittance anti-reflection film, and both concave surfaces are coated with a high-reflectance reflective film.

[0008] Furthermore, a constant current power supply is connected to both ends of the magnetic field coil, and the magnitude and direction of the magnetic field to be measured are changed by changing the magnitude and direction of the current.

[0009] Furthermore, the detection unit includes a quarter-wave plate, a polarization beam splitter located behind the quarter-wave plate, a first photodetector that receives the reflected beam output from the polarization beam splitter, and a second photodetector that receives the transmitted beam output from the polarization beam splitter.

[0010] As an alternative, an adjustable attenuation difference liquid crystal cell can be provided within the Fabry-Borro cavity and behind the magneto-optical crystal, and the detection unit is specifically a photodetector. The liquid crystal cell includes a cell body and a first glass plate and a second glass plate placed vertically side-by-side within the cell body. Both the first and second glass plates are coated with an anti-reflection film on their outer surfaces and with an indium tin oxide conductive layer and a polyimide alignment layer on their inner surfaces. The liquid crystal cell is filled with nematic liquid crystal molecules oriented vertically. The conductive layers of the first and second glass plates are connected to a signal generator, which provides an AC voltage. By changing the magnitude of the AC voltage, the attenuation difference Δκ of the liquid crystal cell for horizontally and vertically polarized light is changed.

[0011] This invention provides a highly sensitive magnetic field detection method, comprising:

[0012] (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil is placed inside the Fabry-Borro cavity.

[0013] (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module to convert the signal light into linearly polarized light with the maximum light intensity at a preset angle;

[0014] (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with both left-hand and right-hand modes in the frequency sweep range;

[0015] (4) Change the current in the magnetic field coil to set the polarization magnetic field;

[0016] (5) A detection unit is used to receive a beam with left-handed and right-handed modes. The detection unit includes a quarter-wave plate, a polarization beam splitter located behind the quarter-wave plate, a first photodetector that receives the reflected beam output by the polarization beam splitter, and a second photodetector that receives the transmitted beam output by the polarization beam splitter.

[0017] (6) The magnetic field applied to the magneto-optical crystal is calculated by the calculation unit based on the frequency difference between the left-hand and right-hand modes.

[0018] This invention also provides another highly sensitive magnetic field detection method, comprising:

[0019] (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil and a liquid crystal cell with adjustable attenuation difference are placed in the Fabry-Borro cavity.

[0020] (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module to convert the signal light into linearly polarized light with the maximum light intensity at a preset angle;

[0021] (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with two modes in the frequency sweep range;

[0022] (4) No current is applied to the magnetic field coil, and the attenuation difference Δκ is adjusted in the LCD cell.

[0023] (5) Change the current in the magnetic field coil to find the magnetic field corresponding to the singularity point;

[0024] (6) A detection unit is used to receive a light beam with two modes, wherein the detection unit is specifically a photodetector;

[0025] (7) Change the current in the magnetic field coil to obtain the output beam of the Fabry-Borre cavity under different magnetic fields near the singular point magnetic field;

[0026] (8) The computing unit uses the double Lorentz function to fit the output beam of the Fabry-Borne cavity to obtain the frequency difference Δω between the two modes, and calculates the magnetic field applied to the magneto-optical crystal based on Δω.

[0027] Beneficial effects: Compared with the prior art, the significant advantages of this invention are: the device of this invention is simple, the principle is simple, the operation is convenient, the measurement sensitivity is high, the applicability is wide, and it is easy to integrate. It is expected to be used for highly sensitive detection of extremely weak magnetic fields, and will serve the future fields of medicine, geological exploration, national defense, and aerospace. Attached Figure Description

[0028] Figure 1This is a system block diagram of one embodiment of the high-sensitivity magnetic field detection device provided by the present invention;

[0029] Figure 2 This is a system block diagram of another embodiment of the highly sensitive magnetic field detection device provided by the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment provides a highly sensitive magnetic field detection device that operates in a Hermitian system, such as... Figure 1 As shown, the system includes a narrow-linewidth tunable light source 1, a polarization light forming module, a first convex lens 3-1, a second convex lens 3-2, a Fabry-Borro cavity, and a detection and calculation module arranged sequentially along the light propagation direction. The Fabry-Borro cavity contains a magneto-optical crystal 5 surrounding a magnetic field coil 6. The detection and calculation module includes a connected detection unit 7 and a calculation unit (not shown).

[0033] Specifically, the narrow linewidth tunable light source 1 is a narrow linewidth light source with a center wavelength of 795nm and a linewidth of less than 100kHz.

[0034] The polarization light forming module forms the signal light into linearly polarized light at a preset angle. Specifically, it includes a quarter-wave plate 2-1, a first half-wave plate 2-2, a polarization beam splitter 2-3, and a second half-wave plate 2-4 arranged sequentially along the light propagation direction. The quarter-wave plate 2-1 adjusts the signal light emitted by the narrow linewidth tunable light source 1 into linearly polarized light. The first half-wave plate 2-2 adjusts the linearly polarized light to the horizontal direction. The polarization beam splitter 2-3 further purifies the horizontally linearly polarized light. The second half-wave plate 2-4 adjusts the horizontally linearly polarized light to 45-degree linear polarization or other angle linear polarization.

[0035] The first convex lens 3-1 and the second convex lens 3-2 have a focal length of 100mm and are fixed on a one-dimensional displacement stage. The adjustment direction is parallel to the light propagation direction. The distance between the two is adjusted so that the laser beam waist matches the Fabry-Borre cavity mode.

[0036] The Fabry-Borne cavity includes a first concave cavity mirror 4-1 and a second concave cavity mirror 4-2 arranged along the light propagation direction. The first concave cavity mirror 4-1 has a flat incident surface and a concave exit surface, while the second concave cavity mirror 4-2 has a concave incident surface and a flat exit surface. The flat surfaces of both the first and second concave cavity mirrors 4-1 and 4-2 are coated with an anti-reflection film with a transmittance of 99.9%, and the concave surfaces are coated with a reflective film with a reflectivity of 99%. The focal length of both concave cavity mirrors is 100mm, forming a Fabry-Borne cavity with a cavity length of 200mm. The light output from the polarization light forming module enters the Fabry-Borne cavity, passes through a magneto-optical crystal, and is emitted as output light with left-hand and right-hand rotation modes. The laser light field resonates with the Fabry-Borne cavity.

[0037] The magneto-optical crystal 5 is a terbium gallium garnet (TGG) crystal with a length of 18 mm and a light-transmitting aperture of 3 mm. The center of the TGG coincides with the waist of the Fabry-Royce cavity. Both sides are coated with 99.8% anti-reflection film to make the center of the magneto-optical crystal coincide with the waist of the cavity. The magnetic field coil 6 is wrapped around the magneto-optical crystal 5. The two ends of the magnetic field coil 6 are connected to a constant current power supply. During use, the bias magnetic field applied to the magneto-optical crystal 5 is changed by adjusting the current of the magnetic field coil 6.

[0038] The detection unit 7 includes a quarter-wave plate 7-1, a polarization beam splitter 7-2 located behind the quarter-wave plate 7-1, a first photodetector 7-3 that receives the reflected beam output from the polarization beam splitter 7-2, and a second photodetector 7-4 that receives the transmitted beam output from the polarization beam splitter 7-2. The left-hand and right-hand circular polarization light signals output from the Fabry-Borro cavity are converted into horizontally and vertically linearly polarized light by the quarter-wave plate 7-1, respectively, and transmitted and reflected by the polarization beam splitter 7-2. The transmitted beam is horizontally linearly polarized light, and the reflected beam is vertically linearly polarized light. These are detected by the second photodetector 7-4 and the first photodetector 7-3, respectively, and displayed on an oscilloscope (not shown in the figure). The calculation unit calculates the frequency difference Δω between the left-hand and right-hand circular polarization modes based on the obtained output spectrum, and then calculates the magnetic field strength based on the frequency difference Δω. The calculation principle is as follows: the device operates in a Hermitian system. When the magnetic field strength is B, the frequency difference between the left-hand and right-hand circular polarization outputs of the Fabry-Borro cavity is expressed as:

[0039] Δω=2gB

[0040] g is the coupling constant, and the calculation unit can calculate the magnetic field strength according to the above formula.

[0041] This embodiment also provides a magnetic field measurement method based on the above-described device, including the following steps:

[0042] (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil is placed inside the Fabry-Borro cavity.

[0043] (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module so that the signal light is converted into linearly polarized light with the maximum light intensity at a preset angle. The specific adjustment method is as follows: adjust the 1 / 4 wave plate 2-1 and the first half-wave plate 2-2. By rotating the angle of the first 1 / 4 wave plate and the first half-wave plate, the beam obtains the maximum light intensity after passing through the polarization beam splitter 2-3. Adjust the angle of the second half-wave plate 2-4 so that the beam is linearly polarized at 45 degrees.

[0044] (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with both left-hand and right-hand modes in the frequency sweep range;

[0045] (4) Change the current in the magnetic field coil to set the polarization magnetic field;

[0046] (5) A detection unit is used to receive a beam with left-handed and right-handed modes. The detection unit includes a quarter-wave plate, a polarization beam splitter located behind the quarter-wave plate, a first photodetector that receives the reflected beam output by the polarization beam splitter, and a second photodetector that receives the transmitted beam output by the polarization beam splitter.

[0047] (6) The magnetic field applied to the magneto-optical crystal is calculated by the calculation unit based on the frequency difference between the left-hand and right-hand modes.

[0048] Example 2

[0049] This embodiment provides another highly sensitive magnetic field detection device, operating in a non-Hermitian system. The difference from Embodiment 1 is that an adjustable attenuation difference Δκ liquid crystal cell 8 is provided behind the magneto-optical crystal within the Fabry-Borre cavity. The detection unit 7 is specifically a photodetector. Since the eigenstates near the singularity point in a non-Hermitian system are no longer left- or right-handed polarization modes, it is impossible to utilize... Figure 1 The quarter-wave plate and polarization beam splitter shown separate the spectral lines of the two eigenmodes.

[0050] The liquid crystal cell 8 has a first glass sheet 8-1 and a second glass sheet 8-2 arranged side by side on its inner side. The outer sides of the first glass sheet 8-1 and the second glass sheet 8-2 are coated with a 99.9% anti-reflection film, and the inner sides are coated with an indium tin oxide conductive layer and a polyimide alignment layer. The liquid crystal cell is filled with nematic liquid crystal molecules E7, and the liquid crystal molecules are oriented vertically. The conductive layers of the two glass sheets are connected to an arbitrary signal generator, which provides a 1KHz square wave AC voltage. By changing the magnitude of the AC voltage, the attenuation difference Δκ of the liquid crystal cell for horizontal and vertical linearly polarized light is changed.

[0051] The calculation unit calculates the magnetic field strength based on the frequency difference Δω. The calculation principle is as follows: the device operates in a non-Hermitian system. When the magnetic field strength is B and the attenuation difference between the horizontal and vertical linear polarization modes is Δκ, the frequency difference is expressed as:

[0052]

[0053] g is the coupling constant. When Δκ≠0, the device operates as a non-Hermitian system. When is a singular point, a tiny magnetic field disturbance is measured near the singular point, i.e., B = B0 + ΔB, where ΔB << B0.

[0054]

[0055] Since ΔB << B0, ΔB 2 Negligible, therefore

[0056]

[0057]

[0058] Compared to the Hermitian system (Δκ=0), where the output signal Δω∝ΔB, the output signal Δω is significantly improved for the same weak magnetic field signal ΔB. The computing unit can calculate the magnetic field on the magneto-optical crystal based on Δω using the above formula.

[0059] This embodiment also provides a magnetic field measurement method based on the above-described device, including the following steps:

[0060] (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil and a liquid crystal cell with adjustable attenuation difference are placed in the Fabry-Borro cavity.

[0061] (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module so that the signal light is converted into linearly polarized light with the maximum light intensity at a preset angle. The specific adjustment method is as follows: adjust the 1 / 4 wave plate 2-1 and the first half-wave plate 2-2. By rotating the angle of the first 1 / 4 wave plate and the first half-wave plate, the beam obtains the maximum light intensity after passing through the polarization beam splitter 2-3. Adjust the angle of the second half-wave plate 2-4 so that the beam is linearly polarized at 45 degrees.

[0062] (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with both horizontal and vertical linear polarization in the frequency sweep range.

[0063] (4) No current is applied to the magnetic field coil, and the attenuation difference Δκ of the LCD cell is adjusted to about 2MHz.

[0064] (5) Change the current in the magnetic field coil to find the magnetic field corresponding to the singularity point;

[0065] (6) A detection unit is used to receive a beam of light with horizontal linear polarization and vertical linear polarization, wherein the detection unit is specifically a photodetector;

[0066] (7) Change the current in the magnetic field coil to obtain the output beam of the Fabry-Borre cavity under different magnetic fields near the singular point magnetic field;

[0067] (8) The computing unit uses the double Lorentz function to fit the output beam of the Fabry-Borne cavity to obtain the frequency difference Δω between the two modes, and calculates the magnetic field applied to the magneto-optical crystal based on Δω.

[0068] The above Embodiments 1 and 2 correspond to magnetic field measurement devices and methods operating in Hermitian and non-Hermitian systems, respectively. These are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. In these embodiments, the angle of the linearly polarized light incident into the cavity is set to 45 degrees, but is not limited to 45 degrees; it can also be -45 degrees or any other arbitrary angle. The magneto-optical crystal is selected as 18mm terbium gallium garnet (TGG), but is not limited to terbium gallium garnet; it can also be terbium scandium aluminum garnet (TSAG) or yttrium iron garnet (YIG), or other magneto-optical crystals. In Embodiment 2, the attenuation difference Δκ between the horizontal and vertical linear polarization modes is set to 2MHz, but is not limited to 2MHz; it can also be other attenuation differences. In short, any equivalent variations made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A highly sensitive magnetic field detection device, characterized by: The device includes a narrow-linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, a Fabry-Borne cavity, and a detection and calculation module, arranged sequentially along the light propagation direction. The Fabry-Borne cavity contains a magneto-optical crystal surrounding a magnetic field coil. The narrow-linewidth tunable light source emits elliptically polarized signal light. The polarization light forming module shapes the signal light into linearly polarized light at a preset angle. The Fabry-Borne cavity resonates with the incident linearly polarized light, and after passing through the magneto-optical crystal, the incident linearly polarized light exits from the cavity as a beam with two modes. The detection and calculation module includes a connected detection unit and a calculation unit. The detection unit receives the beam with two modes, and the calculation unit calculates the magnetic field applied to the magneto-optical crystal based on the frequency difference between the two modes. In this case, the high-sensitivity magnetic field detection device operates in a Hermitian system, and the magnetic field calculation formula is: , is the coupling constant, is the magnetic field strength, denotes the frequency difference between the two modes.

2. The high-sensitivity magnetic field detection device according to claim 1, characterized in that: The polarization light forming module includes a quarter-wave plate, a first half-wave plate, a polarizing beam splitter, and a second half-wave plate arranged sequentially along the light propagation direction.

3. The high-sensitivity magnetic field detection device according to claim 1, characterized in that: The Fabry-Borne cavity includes a first concave cavity mirror and a second concave cavity mirror arranged along the light propagation direction. The first concave cavity mirror has a plane incident surface and a concave exit surface, while the second concave cavity mirror has a concave incident surface and a plane exit surface.

4. The high-sensitivity magnetic field detection device according to claim 3, characterized in that: The first and second concave cavity mirrors both have antireflective coatings with high transmittance on their flat surfaces and reflective coatings with high reflectivity on their concave surfaces.

5. The high-sensitivity magnetic field detection device according to claim 1, characterized in that: The magnetic field coil is connected to a constant current power supply at both ends, and the magnitude and direction of the magnetic field to be measured are changed by changing the magnitude and direction of the current.

6. The high-sensitivity magnetic field detection device according to claim 1, characterized in that: The detection unit includes a quarter-wave plate, a polarization beam splitter located behind the quarter-wave plate, a first photodetector that receives the reflected beam output from the polarization beam splitter, and a second photodetector that receives the transmitted beam output from the polarization beam splitter.

7. The high-sensitivity magnetic field detection device according to claim 1, characterized in that: Within the Fabry-Bohr cavity and behind the magneto-optical crystal, there is a liquid crystal cell with adjustable attenuation difference. The detection unit is specifically a photodetector, and the liquid crystal cell attenuation difference... and initial value of magnetic field strength satisfy At this time, the high-sensitivity magnetic field detection device operates in a non-Hermitian system, and the magnetic field calculation formula is: , This is a magnetic field disturbance.

8. The high-sensitivity magnetic field detection device according to claim 7, characterized in that: The liquid crystal cell includes a cell body and a first glass sheet and a second glass sheet arranged vertically side-by-side within the cell body. Both the first and second glass sheets are coated with an anti-reflection film on their outer surfaces and with an indium tin oxide conductive layer and a polyimide alignment layer on their inner surfaces. The liquid crystal cell is filled with nematic liquid crystal molecules oriented vertically. The conductive layers of the first and second glass sheets are connected to a signal generator, which provides an alternating current voltage. By changing the magnitude of the alternating current voltage, the attenuation difference of the liquid crystal cell for horizontally and vertically polarized light is altered. .

9. A highly sensitive magnetic field detection method, characterized in that... include: (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil is placed inside the Fabry-Borro cavity. (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module so that the signal light is converted into linearly polarized light with the maximum light intensity at a preset angle; (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with both left-hand and right-hand modes in the frequency sweep range; (4) Change the current in the magnetic field coil to set the polarization magnetic field; (5) A detection unit is used to receive a beam with left-handed and right-handed modes. The detection unit includes a quarter-wave plate, a polarization beam splitter located behind the quarter-wave plate, a first photodetector that receives the reflected beam output by the polarization beam splitter, and a second photodetector that receives the transmitted beam output by the polarization beam splitter. (6) The magnetic field applied to the magneto-optical crystal is calculated using a computing unit based on the frequency difference between the left-hand and right-hand modes; at this time, it is operating in a Hermitian system, and the magnetic field calculation formula is: , The coupling constant is... The magnetic field strength, This represents the frequency difference between the two modes.

10. A highly sensitive magnetic field detection method, characterized in that... include: (1) A narrow linewidth tunable light source, a polarization light forming module, a first convex lens, a second convex lens, and a Fabry-Borro cavity are arranged sequentially along the light propagation direction. A magneto-optical crystal surrounded by a magnetic field coil and a liquid crystal cell with adjustable attenuation difference are placed in the Fabry-Borro cavity. (2) Turn on the narrow linewidth tunable light source and adjust the polarization light forming module so that the signal light is converted into linearly polarized light with the maximum light intensity at a preset angle; (3) Scan the frequency of the narrow linewidth tunable light source so that the Fabry-Borro cavity outputs a stable beam with two modes in the frequency sweep range; (4) No current is applied to the magnetic field coil, and the attenuation difference is adjusted by setting the LCD cell. ; (5) Change the current in the magnetic field coil to find the magnetic field corresponding to the singular point, and the attenuation difference. and the initial value of the magnetic field strength at this time satisfy , The coupling constant; (6) A detection unit is used to receive a light beam with two modes, wherein the detection unit is specifically a photodetector; (7) Change the current in the magnetic field coil to obtain the output beam of the Fabry-Borre cavity under different magnetic fields near the singular point magnetic field; (8) The computational unit uses the dual Lorentz function to fit the output beam of the Fabry-Borre cavity to obtain the frequency difference between the two modes. ,according to The magnetic field applied to the magneto-optical crystal is calculated; since it is operating in a non-Hermitian system, the formula for calculating the magnetic field is: ， This represents the frequency difference between the two modes. This is a magnetic field disturbance.

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