CN116449268A - High-sensitivity magnetic field detection device and method - Google Patents
High-sensitivity magnetic field detection device and method Download PDFInfo
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- 239000011521 glass Substances 0.000 claims description 21
- 239000004973 liquid crystal related substance Substances 0.000 claims description 21
- 238000010408 sweeping Methods 0.000 claims description 6
- 239000004988 Nematic liquid crystal Substances 0.000 claims description 3
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- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 claims description 3
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- 229910052771 Terbium Inorganic materials 0.000 description 3
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- 229910052733 gallium Inorganic materials 0.000 description 3
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Abstract
The invention discloses a high-sensitivity magnetic field detection device and a method, wherein the device comprises a narrow-linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens, a Fabry-Perot cavity and a detection calculation module which are sequentially arranged along the light propagation direction, wherein a magneto-optical crystal surrounding a magnetic field coil is arranged in the Fabry-Perot cavity, the narrow-linewidth tunable light source emits signal light with elliptical polarization, the polarized light forming module forms the signal light into linear polarized light with a preset angle, the Fabry-Perot cavity and the incident linear polarized light form resonance, the incident linear polarized light is emitted from the cavity into light beams with two modes after passing through the magneto-optical crystal, the detection calculation module comprises a detection unit and a calculation unit, the detection unit receives the light beams with the two modes, and the calculation unit calculates a magnetic field applied to the magneto-optical crystal according to the frequency difference of the two modes. The invention has simple structure, simple operation, wide application range and high sensitivity.
Description
Technical Field
The invention relates to a magnetic field measurement technology, in particular to a high-sensitivity magnetic field detection device and a method.
Background
The magnetic field sensor has wide application and plays an important role in the fields of industrial detection, national defense construction, astronomy, resource exploration, medical health, scientific research and the like. Currently, magnetic sensors that are widely used mainly include coils, hall elements, magnetoresistive elements, magneto-optical crystals, and the like. Among them, the coil is used to detect a change in magnetic flux, so that measurement cannot be performed for a static magnetic field or a case where the change in magnetic flux is slow, and a magnetic sensor based on the hall effect is generally not sufficiently sensitive. Magneto-optical crystal materials have been widely used in recent years as magnetic sensing fields due to their stable properties, and are easy to integrate due to their high electron density, which is a solid. The principle adopted by the magneto-optical crystal for magnetic sensing is that the magneto-optical Faraday effect is adopted, when linearly polarized light passes through the magneto-optical crystal, the linearly polarized light can be regarded as superposition of left-handed and right-handed circularly polarized light with equal amplitude, and the two beams of light have different refractive indexes due to the magneto-optical effect, so that the linearly polarized light passing through plasma deflects after passing through the same distance. For weak magnetism, the deflection angle is small, the error in the measuring process is large, the measuring range is small, and the accuracy is not high. Therefore, the magnetic sensor using the magneto-optical effect also faces the problem that the sensitivity needs to be improved.
In summary, it can be known from analysis how to improve the sensitivity of magnetic sensing and reduce the measurement error in the existing magnetic sensing technology, so as to develop a magnetic sensor device with simple principle, convenient operation, easy integration and wide application range.
Disclosure of Invention
The invention aims to: aiming at the problems existing in the prior art, the invention provides the high-sensitivity magnetic field detection device and the method which are simple in principle, convenient to operate, beneficial to integration and wide in application range.
The technical scheme is as follows: the high-sensitivity magnetic field detection device comprises a narrow-linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens, a Fabry-Perot cavity and a detection calculation module which are sequentially arranged along the light propagation direction, wherein a magneto-optical crystal surrounding a magnetic field coil is arranged in the Fabry-Perot cavity, the narrow-linewidth tunable light source emits signal light with elliptical polarization, the polarized light forming module forms the signal light into linearly polarized light with a preset angle, the Fabry-Perot cavity and the incident linearly polarized light form resonance, the incident linearly polarized light is emitted from the cavity after passing through the magneto-optical crystal, the detection calculation module comprises a detection unit and a calculation unit which are connected, the detection unit receives the light beams with the two modes, and the calculation unit calculates a magnetic field applied to the magneto-optical crystal according to the frequency difference of the two modes.
Further, the polarized light forming module comprises a 1/4 wave plate, a first half wave plate, a polarized beam splitter and a second half wave plate which are sequentially arranged along the light propagation direction.
Further, the fabry-perot cavity comprises a first concave cavity mirror and a second concave cavity mirror which are arranged along the light propagation direction, the incidence surface of the first concave cavity mirror is a plane, the emergent surface is a concave surface, the incidence surface of the second concave cavity mirror is a concave surface, and the emergent surface is a plane. The planes of the first concave cavity mirror and the second concave cavity mirror are plated with high-transmittance antireflection films, and the concave surfaces are plated with high-reflectivity reflection films.
Furthermore, the two ends of the magnetic field coil are connected with constant current power supplies, and the size and the direction of the magnetic field to be measured are changed by changing the size and the direction of current.
Further, the detection unit comprises a 1/4 wave plate, a polarization beam splitter positioned behind the 1/4 wave plate, a first photoelectric detector for receiving the reflected light beam output by the polarization beam splitter, and a second photoelectric detector for receiving the transmitted light beam output by the polarization beam splitter.
As an alternative, a liquid crystal cell with adjustable attenuation difference can be arranged in the fabry-perot cavity and behind the magneto-optical crystal, and the detection unit is in particular a photodetector. The liquid crystal box comprises a box body and a first glass sheet and a second glass sheet which are arranged in the box body and are vertically placed in parallel, wherein an antireflection film is plated on the outer sides of the first glass sheet and the second glass sheet, an indium tin oxide conductive layer and a polyimide orientation layer are plated on the inner sides of the first glass sheet and the second glass sheet, nematic liquid crystal molecules are filled in the liquid crystal box, the orientation of the liquid crystal molecules is in a vertical direction, the conductive layers of the first glass sheet and the second glass sheet are connected with a signal generator, alternating current voltage is provided by the signal generator, and the attenuation difference delta kappa of the liquid crystal box to horizontal and vertical linearly polarized light is changed by changing the size of the alternating current voltage.
The invention provides a high-sensitivity magnetic field detection method, which comprises the following steps:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and magneto-optical crystals surrounding a magnetic field coil are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity;
(3) Scanning the frequency of the narrow linewidth tunable light source to ensure that the Fabry-Perot cavity outputs stable light beams with a left-handed mode and a right-handed mode in a frequency sweeping range;
(4) Changing the current of the magnetic field coil, and setting a polarized magnetic field;
(5) The detection unit is used for receiving light beams with a left-handed mode and a right-handed mode and comprises a 1/4 wave plate, a polarization beam splitter positioned behind the 1/4 wave plate, a first photoelectric detector for receiving reflected light beams output by the polarization beam splitter and a second photoelectric detector for receiving transmitted light beams output by the polarization beam splitter;
(6) A calculation unit is used to calculate the magnetic field applied to the magneto-optical crystal from the frequency difference between the left-handed mode and the right-handed mode.
The invention also provides another high-sensitivity magnetic field detection method, which comprises the following steps:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and a magneto-optical crystal surrounding a magnetic field coil and a liquid crystal box with adjustable attenuation difference are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity;
(3) Scanning the frequency of the narrow linewidth tunable light source to ensure that the Fabry-Perot cavity outputs stable light beams with two modes in a frequency sweeping range;
(4) The magnetic field coil is not added with current, and the attenuation difference delta kappa is regulated to the liquid crystal box;
(5) Changing the current of the magnetic field coil to find a magnetic field corresponding to the singular point;
(6) A detection unit is adopted to receive light beams with two modes, and the detection unit is specifically a photoelectric detector;
(7) Changing the current of a magnetic field coil to obtain Fabry-Perot cavity output light beams under different magnetic fields nearby a singular point magnetic field;
(8) The calculating unit obtains the frequency difference delta omega of the two modes by utilizing the output light beam of the Brinell-Hercules cavity by the double Lorentz function fitting method, and calculates the magnetic field applied to the magneto-optical crystal according to the delta omega.
The beneficial effects are that: compared with the prior art, the invention has the remarkable advantages that: the device is simple in principle, convenient to operate, high in measurement sensitivity, wide in application, beneficial to integration, and expected to be used for high-sensitivity detection of extremely weak magnetic fields and serving the fields of future medicine, geological exploration, national defense, aerospace and the like.
Drawings
FIG. 1 is a system block diagram of one embodiment of a high sensitivity magnetic field detection apparatus provided by the present invention;
fig. 2 is a system block diagram of another embodiment of the high sensitivity magnetic field detection device provided by the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The embodiment provides a high-sensitivity magnetic field detection device, which works in an hermite system, as shown in fig. 1, and comprises a narrow linewidth tunable light source 1, a polarized light forming module, a first convex lens 3-1, a second convex lens 3-2, a fabry-perot cavity and a detection computing module, wherein the narrow linewidth tunable light source, the polarized light forming module, the first convex lens 3-1, the second convex lens 3-2, the fabry-perot cavity and the detection computing module are sequentially arranged along the light propagation direction, a magneto-optical crystal 5 surrounding a magnetic field coil 6 is arranged in the fabry-perot cavity, and the detection computing module comprises a detection unit 7 and a computing unit (not shown) which are connected.
The narrow linewidth tunable light source 1 is specifically a narrow linewidth light source with a central wavelength of 795nm, and the linewidth is smaller than 100kHz.
The polarized light forming module forms the signal light into linearly polarized light with a preset angle, and specifically comprises a 1/4 wave plate 2-1, a first half wave plate 2-2, a polarized beam splitter 2-3 and a second half wave plate 2-4, wherein the 1/4 wave plate 2-1 is sequentially arranged along the light propagation direction, the signal light emitted by the narrow-linewidth tunable light source 1 is adjusted into linearly polarized light, the first half wave plate 2-2 is used for adjusting the linearly polarized light into a horizontal direction, the polarized beam splitter 2-3 is used for further purifying the horizontally linearly polarized light, and the second half wave plate 2-4 is used for adjusting the horizontally linearly polarized light into 45-degree linear polarization or other angle linear polarization.
The focal length of the first convex lens 3-1 and the second convex lens 3-2 is 100mm, the first convex lens and the second convex lens are fixed on a one-dimensional displacement table, the adjusting direction is parallel to the light propagation direction, and the distance between the first convex lens and the second convex lens is adjusted to enable the laser beam waist to be matched with the Fabry-Perot cavity mode.
The Fabry-Perot cavity comprises a first concave cavity mirror 4-1 and a second concave cavity mirror 4-2 which are arranged along the light propagation direction, the incident surface of the first concave cavity mirror 4-1 is a plane, the emergent surface is a concave surface, the incident surface of the second concave cavity mirror 4-2 is a concave surface, the emergent surface is a plane, the planes of the first concave cavity mirror 4-1 and the second concave cavity mirror 4-2 are plated with an antireflection film with 99.9% transmittance, the concave surfaces are plated with a reflection film with 99% reflectance, the focal lengths of the two concave cavity mirrors are 100mm, and the Fabry-Perot cavity with the cavity length of 200mm is formed. The light output by the polarized light forming module enters the Fabry-Perot cavity, the output light with a left-handed mode and a right-handed mode is emitted after passing through the magneto-optical crystal, and the laser light field and the Fabry-Perot cavity form resonance.
The magneto-optical crystal 5 is a Terbium Gallium Garnet (TGG) crystal with the length of 18mm, the clear aperture is 3mm, the center of the TGG coincides with the beam waist position of the Fabry-Perot cavity, 99.8% antireflection films are plated on two sides of the TGG, the center of the magneto-optical crystal coincides with the cavity beam waist position, the magnetic field coil 6 surrounds the magneto-optical crystal 5, the two ends of the magnetic field coil 6 are connected with constant current power supplies, and when in use, the bias magnetic field applied to the magneto-optical crystal 5 is changed by adjusting the current of the magnetic field coil 6.
The detection unit 7 includes a 1/4 wave plate 7-1, a polarizing beam splitter 7-2 located behind the 1/4 wave plate 7-1, a first photodetector 7-3 receiving the reflected light beam output from the polarizing beam splitter 7-2, and a second photodetector 7-4 receiving the transmitted light beam output from the polarizing beam splitter 7-2. The optical signals of the left-hand mode and the right-hand mode output by the Fabry-Perot cavity are respectively converted into horizontal linearly polarized light and vertical linearly polarized light through a 1/4 wave plate 7-1, the horizontal linearly polarized light is respectively transmitted and reflected from a polarization beam splitter 7-2, the vertical linearly polarized light is respectively detected by a second photoelectric detector 7-4 and a first photoelectric detector 7-3 and input to an oscilloscope (not shown in the figure) for display, a calculating unit obtains the frequency difference delta omega of the left-hand polarization mode and the right-hand polarization mode according to the obtained output spectral line, and then calculates the magnetic field strength according to the frequency difference delta omega, and the calculating principle is as follows: the device works in an hermite system, when the magnetic field intensity is B, the frequency difference of the left-hand circular polarization and the right-hand circular polarization output by the Fabry-Perot cavity is expressed as:
Δω＝2gB
g is the coupling constant, and the calculating unit can calculate the magnetic field strength according to the above formula.
The embodiment also provides a magnetic field measuring method based on the device, which comprises the following steps:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and magneto-optical crystals surrounding a magnetic field coil are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity; the specific adjusting method comprises the following steps: the 1/4 wave plate 2-1 and the first half wave plate 2-2 are adjusted, the maximum light intensity of the light beam is obtained through the polarization beam splitter 2-3 by rotating the angles of the first 1/4 wave plate and the first half wave plate, and the angle of the second half wave plate 2-4 is adjusted, so that the light beam is linearly polarized at 45 degrees;
(3) Scanning the frequency of the narrow linewidth tunable light source to ensure that the Fabry-Perot cavity outputs stable light beams with a left-handed mode and a right-handed mode in a frequency sweeping range;
(4) Changing the current of the magnetic field coil, and setting a polarized magnetic field;
(5) The detection unit is used for receiving light beams with a left-handed mode and a right-handed mode and comprises a 1/4 wave plate, a polarization beam splitter positioned behind the 1/4 wave plate, a first photoelectric detector for receiving reflected light beams output by the polarization beam splitter and a second photoelectric detector for receiving transmitted light beams output by the polarization beam splitter;
(6) A calculation unit is used to calculate the magnetic field applied to the magneto-optical crystal from the frequency difference between the left-handed mode and the right-handed mode.
Example two
The present embodiment provides another high-sensitivity magnetic field detection device, which works in a non-hermite system, and is different from the first embodiment in that a liquid crystal box 8 capable of adjusting attenuation difference delta kappa is further arranged behind a magneto-optical crystal in a fabry-perot cavity, and the detection unit 7 is specifically a photoelectric detector. Since the eigenstates near the singular point of the non-hermite are no longer left-right-hand polarization modes, the lines of the two eigenmodes cannot be separated by the 1/4 wave plate and the polarizing beam splitter shown in fig. 1.
Wherein, the inside of the liquid crystal box 8 is provided with a first glass sheet 8-1 and a second glass sheet 8-2 which are arranged in parallel, the outside of the first glass sheet 8-1 and the outside of the second glass sheet 8-2 are plated with 99.9 percent of antireflection films, the inside is plated with an indium tin oxide conductive layer and a polyimide alignment layer, nematic liquid crystal molecules E7 are filled in the liquid crystal box, the alignment of the liquid crystal molecules is in the vertical direction, the conductive layers of the two glass sheets are connected with any signal generator, the signal generator provides square wave alternating voltage of 1KHz, and the attenuation difference delta kappa of the liquid crystal box to horizontal and vertical linearly polarized light is changed by changing the magnitude of the alternating voltage.
The calculation unit calculates the magnetic field intensity according to the data frequency difference delta omega, and the calculation principle is as follows: the device is operated in a non-herm system, and when the magnetic field strength is B and the attenuation difference between the horizontal and vertical polarization modes is delta kappa, the frequency difference is expressed as:
g is the coupling constant, when delta kappa is not equal to 0, the device operates in a non-hermitian system,at the same time, for the singular point, a small magnetic field disturbance is measured in the vicinity of the singular point, i.e. b=b 0 +ΔB，ΔB＜＜B 0 Then
Due to DeltaB < B 0 ，ΔB 2 Can be ignored, thus
Compared with the output signal Δω and Δb of the hermitian system (Δκ=0), the output signal Δω is greatly improved for the same weak magnetic field signal Δb. The calculation unit may calculate the magnetic field on the magneto-optical crystal according to the above formula from Δω.
The embodiment also provides a magnetic field measuring method based on the device, which comprises the following steps:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and a magneto-optical crystal surrounding a magnetic field coil and a liquid crystal box with adjustable attenuation difference are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity; the specific adjusting method comprises the following steps: the 1/4 wave plate 2-1 and the first half wave plate 2-2 are adjusted, the maximum light intensity of the light beam is obtained through the polarization beam splitter 2-3 by rotating the angles of the first 1/4 wave plate and the first half wave plate, and the angle of the second half wave plate 2-4 is adjusted, so that the light beam is linearly polarized at 45 degrees;
(3) Scanning the frequency of the narrow linewidth tunable light source, so that the Fabry-Perot cavity outputs stable light beams with horizontal linearly polarized light and vertical linearly polarized light in a frequency sweeping range;
(4) The magnetic field coil is not added with current, and the attenuation difference delta kappa is regulated to be about 2MHz by the liquid crystal box;
(5) Changing the current of the magnetic field coil to find a magnetic field corresponding to the singular point;
(6) A detection unit is adopted to receive light beams with horizontal linearly polarized light and vertical linearly polarized light, and the detection unit is specifically a photoelectric detector;
(7) Changing the current of a magnetic field coil to obtain Fabry-Perot cavity output light beams under different magnetic fields nearby a singular point magnetic field;
(8) The calculating unit obtains the frequency difference delta omega of the two modes by utilizing the output light beam of the Brinell-Hercules cavity by the double Lorentz function fitting method, and calculates the magnetic field applied to the magneto-optical crystal according to the delta omega.
The above embodiments are merely preferred embodiments of the present invention, and the scope of the claims should not be limited thereto. The angle of the linearly polarized light incident into the cavity is set to 45 degrees in the embodiment, but is not limited to 45 degrees, and can be-45 degrees or any other angle; the magneto-optical crystal is selected from Terbium Gallium Garnet (TGG) of 18mm, but is not limited to terbium gallium garnet, and may be other magneto-optical crystals such as Terbium Scandium Aluminum Garnet (TSAG) or Yttrium Iron Garnet (YIG). In the second embodiment, the attenuation difference Δκ between the horizontal and vertical polarization modes is set to 2MHz, but is not limited to 2MHz, and may be other attenuation differences, which are all equivalent changes according to the claims of the present invention, and still fall within the scope of the present invention.
Claims (10)
1. A high-sensitivity magnetic field detection device is characterized in that: the device comprises a narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens, a Fabry-Perot cavity and a detection calculation module, wherein the narrow linewidth tunable light source, the polarized light forming module, the first convex lens, the second convex lens, the Fabry-Perot cavity and the detection calculation module are sequentially arranged along the light propagation direction, a magneto-optical crystal surrounding a magnetic field coil is arranged in the Fabry-Perot cavity, the narrow linewidth tunable light source emits signal light with elliptical polarization, the polarized light forming module forms the signal light into linearly polarized light with a preset angle, the Fabry-Perot cavity and the incident linearly polarized light form resonance, the incident linearly polarized light emits light beams with two modes from the cavity after passing through the magneto-optical crystal, the detection calculation module comprises a detection unit and a calculation unit, the detection unit receives the light beams with the two modes, and the calculation unit calculates a magnetic field applied to the magneto-optical crystal according to the frequency difference of the two modes.
2. The high sensitivity magnetic field detection device according to claim 1, wherein: the polarized light forming module comprises a 1/4 wave plate, a first half wave plate, a polarized beam splitter and a second half wave plate which are sequentially arranged along the light propagation direction.
3. The high sensitivity magnetic field detection device according to claim 1, wherein: the Fabry-Perot cavity comprises a first concave cavity mirror and a second concave cavity mirror which are arranged along the light propagation direction, wherein the incidence surface of the first concave cavity mirror is a plane, the emergent surface is a concave surface, the incidence surface of the second concave cavity mirror is a concave surface, and the emergent surface is a plane.
4. A high sensitivity magnetic field detection device according to claim 3, wherein: the planes of the first concave cavity mirror and the second concave cavity mirror are plated with high-transmittance antireflection films, and the concave surfaces are plated with high-reflectivity reflection films.
5. The high sensitivity magnetic field detection device according to claim 1, wherein: the two ends of the magnetic field coil are connected with constant current power supplies, and the size and the direction of the magnetic field to be measured are changed by changing the size and the direction of current.
6. The high sensitivity magnetic field detection device according to claim 1, wherein: the detection unit comprises a 1/4 wave plate, a polarization beam splitter positioned behind the 1/4 wave plate, a first photoelectric detector for receiving a reflected light beam output by the polarization beam splitter, and a second photoelectric detector for receiving a transmitted light beam output by the polarization beam splitter.
7. The high sensitivity magnetic field detection device according to claim 1, wherein: the liquid crystal box capable of adjusting attenuation difference is arranged in the Fabry-Perot cavity and behind the magneto-optical crystal, and the detection unit is specifically a photoelectric detector.
8. The high sensitivity magnetic field detection device according to claim 7, wherein: the liquid crystal box comprises a box body and a first glass sheet and a second glass sheet which are arranged in the box body and are vertically placed in parallel, wherein an antireflection film is plated on the outer sides of the first glass sheet and the second glass sheet, an indium tin oxide conductive layer and a polyimide orientation layer are plated on the inner sides of the first glass sheet and the second glass sheet, nematic liquid crystal molecules are filled in the liquid crystal box, the orientation of the liquid crystal molecules is in a vertical direction, the conductive layers of the first glass sheet and the second glass sheet are connected with a signal generator, alternating current voltage is provided by the signal generator, and the attenuation difference delta kappa of the liquid crystal box to horizontal and vertical linearly polarized light is changed by changing the size of the alternating current voltage.
9. A method of high sensitivity magnetic field detection, comprising:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and magneto-optical crystals surrounding a magnetic field coil are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity;
(3) Scanning the frequency of the narrow linewidth tunable light source to ensure that the Fabry-Perot cavity outputs stable light beams with a left-handed mode and a right-handed mode in a frequency sweeping range;
(4) Changing the current of the magnetic field coil, and setting a polarized magnetic field;
(5) The detection unit is used for receiving light beams with a left-handed mode and a right-handed mode and comprises a 1/4 wave plate, a polarization beam splitter positioned behind the 1/4 wave plate, a first photoelectric detector for receiving reflected light beams output by the polarization beam splitter and a second photoelectric detector for receiving transmitted light beams output by the polarization beam splitter;
(6) A calculation unit is used to calculate the magnetic field applied to the magneto-optical crystal from the frequency difference between the left-handed mode and the right-handed mode.
10. A method of high sensitivity magnetic field detection, comprising:
(1) A narrow linewidth tunable light source, a polarized light forming module, a first convex lens, a second convex lens and a Fabry-Perot cavity are sequentially arranged along the light propagation direction, and a magneto-optical crystal surrounding a magnetic field coil and a liquid crystal box with adjustable attenuation difference are arranged in the Fabry-Perot cavity;
(2) Turning on a narrow linewidth tunable light source, and adjusting a polarized light forming module to convert the signal light into linear polarized light with a preset angle and maximum light intensity;
(3) Scanning the frequency of the narrow linewidth tunable light source to ensure that the Fabry-Perot cavity outputs stable light beams with two modes in a frequency sweeping range;
(4) The magnetic field coil is not added with current, and the attenuation difference delta kappa is regulated to the liquid crystal box;
(5) Changing the current of the magnetic field coil to find a magnetic field corresponding to the singular point;
(6) A detection unit is adopted to receive light beams with two modes, and the detection unit is specifically a photoelectric detector;
(7) Changing the current of a magnetic field coil to obtain Fabry-Perot cavity output light beams under different magnetic fields nearby a singular point magnetic field;
(8) The calculating unit obtains the frequency difference delta omega of the two modes by utilizing the output light beam of the Brinell-Hercules cavity by the double Lorentz function fitting method, and calculates the magnetic field applied to the magneto-optical crystal according to the delta omega.
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