Vector magnetic field measuring device and method based on Bell-Bloom vector magnetometer

Abstract

The invention discloses a vector magnetic field measurement device and method based on a Bell-Bloom vector magnetometer, and relates to the field of magnetic field measurement, and the device comprises a light source module, an electro-optical modulator, an adjustment module, a beam splitting and direction adjustment module, an atomic gas chamber, a balance detector, a first lock-in amplifier and a data processing module. And the data processing module adopts the trained artificial neural network to determine the external magnetic field angle based on the atomic spin projection amplitude and the atomic spin polarization phase. The precision and reliability of vector magnetic field measurement can be improved.

Description

Technical Field

[0001] The present application relates to the field of magnetic field measurement, and in particular to a vector magnetic field measurement device and method based on a Bell-Bloom vector magnetometer. Background Art

[0002] Optically pumped (OPM) magnetometers are widely used in various fields due to their superior accuracy and high sensitivity. The high sensitivity of OPM to scalar magnetic fields offers great potential for a variety of magnetometer applications. However, accurate vector magnetic field information is also crucial in many applications, especially in biomagnetism, Earth sensing, and geomagnetic navigation. To this end, various methods for measuring vector magnetic field information using OPM have been proposed, but these technologies all suffer from low measurement accuracy. Summary of the Invention

[0003] The purpose of this application is to provide a vector magnetic field measurement device and method based on a Bell-Bloom vector magnetometer, which can improve the accuracy and reliability of vector magnetic field measurement.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a vector magnetic field measurement device based on a Bell-Bloom vector magnetometer, comprising:

[0006] A light source module, used for emitting pump light and detection light;

[0007] an electro-optical modulator, arranged on the outgoing light path of the light source module, for modulating the pump light;

[0008] an adjustment module, arranged on an outgoing light path of the electro-optical modulator, for adjusting the polarization direction of the pump light and adjusting the pump light to circularly polarized pump light;

[0009] A beam splitting and direction adjustment module is provided on the outgoing light path of the light source module, and is used to split the detection light into two beams, and adjust the two detection light beams into detection light in the x-axis direction and detection light in the y-axis direction;

[0010] an atomic gas chamber, arranged on the outgoing light path of the adjustment module and the beam splitting and direction adjustment module, and arranged in a three-axis Helmholtz coil, wherein the three-axis Helmholtz coil is used to apply an external magnetic field. After the atoms in the atomic chamber receive the circularly polarized pump light, the atomic spins are modulated by the external magnetic field;

[0011] A balanced detector for converting optical signals of atomic spin projections detected by the detection light in the x-axis direction and the detection light in the y-axis direction into electrical signals;

[0012] a first lock-in amplifier, connected to the balanced detector, for extracting the atomic spin projection amplitude and the atomic spin polarization phase from the electrical signal of the atomic spin projection; the atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; the atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction;

[0013] A data processing module is connected to the first lock-in amplifier and is used to determine the external magnetic field angle based on the atomic spin projection amplitude and the atomic spin polarization phase using a trained artificial neural network.

[0014] In a second aspect, the present application provides a vector magnetic field measurement method based on a Bell-Bloom vector magnetometer, the vector magnetic field measurement method being applied to the above-mentioned vector magnetic field measurement device, the vector magnetic field measurement method comprising:

[0015] The external magnetic field is applied via a triaxial Helmholtz coil;

[0016] Applying circularly polarized pump light in the z-axis direction, detection light in the x-axis direction, and detection light in the y-axis direction to the atomic gas cell; after the atoms in the atomic cell receive the circularly polarized pump light, the atomic spins are modulated by the external magnetic field;

[0017] The atomic spin projection is detected by the detection light in the x-axis direction and the detection light in the y-axis direction;

[0018] Extracting an atomic spin projection amplitude and an atomic spin polarization phase based on the atomic spin projection; the atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; the atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction;

[0019] Based on the atomic spin projection amplitude and the atomic spin polarization phase, a trained artificial neural network is used to determine the external magnetic field angle.

[0020] According to the specific embodiments provided in this application, this application has the following technical effects:

[0021] This application provides a vector magnetic field measurement device and method based on a Bell-Bloom vector magnetometer. This device combines artificial neural networks (ANNs) with dual-beam phase detection technology. The trained ANNs can identify the complex relationship between phase and external magnetic field angle, enabling the Bell-Bloom vector magnetometer to independently correct phase errors, significantly improving the accuracy and reliability of vector magnetic field measurements. Furthermore, blind spots can be essentially eliminated by inputting the atomic spin projection amplitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 A schematic diagram of a vector magnetic field measurement device based on a Bell-Bloom vector magnetometer provided in one embodiment of the present application;

[0024] Figure 2 Schematic diagram of the light source of the vector Bell-Bloom magnetometer. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] Currently, the most direct approach to measuring vector magnetic field information is to use coils to compensate for the external magnetic field, using the optical phase shift (OPM) as a zero (or specific value) magnetic field indicator. The directional components of the external magnetic field can be derived from the coil drive current. Various methods have been developed to achieve vector zero-field indication, including the Hanle effect and parametric resonance. Similarly, a modulated magnetic field can be introduced to demodulate the vector components through the relationship between the vector and scalar fields. Despite these numerous approaches, those involving additional magnetic fields often suffer from crosstalk when using multiple sensors to measure magnetic field gradients or tensors, and their accuracy relies on the stability of the coils. A more ideal approach is to implement vector OPM based on light-atom interactions. For example, Patton et al. proposed an all-optical vector OPM that replaces magnetic field modulation with an AC Stark shift introduced by a circularly polarized laser beam, capable of detecting magnetic fields in the yz plane. Cox et al. reported an electromagnetically induced transparency (EIT) vector magnetometer based on the dependence of the EIT resonance amplitude on the direction of the external magnetic field. However, these methods are susceptible to drift and experimental interference from factors that affect the resonance amplitude. A major breakthrough in this field was proposed in 2020 by Cai et al., who introduced a dual-optical pump beam into an all-optical Bell-Bloom vector magnetometer. This method extracts vector angle information through dual-phase detection and, through precise phase measurement, enables the bandwidth of the vector magnetometer to be the same as that of a traditional Bell-Bloom magnetometer, theoretically suppressing drift. However, when the magnetic field strength is insufficient to distinguish the Larmor frequency difference between the 85Rb and 87Rb isotopes, the bandwidth of the vector measurement is limited. In addition, the additional phase error in the experimental setup is difficult to measure accurately, which also reduces the accuracy of the system to a certain extent.

[0027] In this application, a vector magnetic field measurement device and method based on a Bell-Bloom vector magnetometer are proposed. By adopting a dual-detection beam configuration, it is possible to simultaneously monitor the atomic spin projections in the x-axis and y-axis directions. The determination of the external magnetic field angle depends on the precise analysis of the phase of the atomic spin projection signal. An important advancement in this application is the integration of an artificial neural network (ANN), which can identify the complex relationship between the phase and the direction (i.e., angle) of the external magnetic field. This integration enables the Bell-Bloom vector magnetometer to independently correct the phase error, greatly improving the accuracy of the system and effectively eliminating blind spots. It is worth noting that previous similar studies usually faced challenges in sensitive areas and required additional error mitigation techniques, while the ANN in this application achieved comprehensive angle measurement capabilities in almost all directions.

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0029] In an exemplary embodiment, Figure 1 As shown, a vector magnetic field measurement device based on a Bell-Bloom vector magnetometer is provided, comprising: a light source module 1, an electro-optical modulator 2, an adjustment module 3, a beam splitting and direction adjustment module 4, an atomic gas chamber 5, a balanced detector 7, a first phase-locked amplifier 8 and a data processing module (not shown in the figure).

[0030] The light source module 1 is used to emit pump light and probe light. The light source module 1 includes a pump laser 11 and a probe laser 12 .

[0031] The electro-optical modulator 2 is provided in the output optical path of the light source module 1 and is used to modulate the pump light. Specifically, the electro-optical modulator 2 is provided in the output optical path of the pump laser 11. After the pump light with a wavelength of 894 nm is emitted from the pump laser 11, it is modulated by the electro-optical modulator (EOM) 2. The modulated reference signal is provided by the second lock-in amplifier 9. The electro-optical modulator 2 sinusoidally modulates the amplitude of the pump light to minimize additional phase error.

[0032] Adjustment module 3, located in the output optical path of electro-optic modulator 2, is used to adjust the polarization direction of the pump light and convert it into circularly polarized pump light. Adjustment module 3 includes a first half-wave plate 31 and a quarter-wave plate 32. The pump light passes through first half-wave plate 31 to adjust its polarization direction. Then, through quarter-wave plate 32, the linearly polarized pump light is converted into circularly polarized pump light. The circularly polarized pump light is directed along the z-axis, causing the atoms in atomic chamber 5 to be polarized along the z-axis by the intensity-modulated pump light.

[0033] The beam splitting and direction adjustment module 4 is disposed on the output optical path of the light source module 1 and is used to split the probe light into two beams and adjust the two probe light beams into probe light in the x-axis direction and probe light in the y-axis direction. The beam splitting and direction adjustment module 4 includes: a second half-wave plate 41, a polarization beam splitter 42, a third half-wave plate 43, a reflector assembly consisting of a reflector 44 and a reflector 45, and a fourth half-wave plate 46. The polarization beam splitter 41 is disposed on the output optical path of the probe laser 12.

[0034] After being emitted by detection laser 12, the 852nm probe light passes through a second half-wave plate 41 to adjust its polarization direction. The polarization beam splitter (PBS) 42 then splits the linearly polarized light perpendicular to the PBS's optical axis into two beams. One beam passes through a third half-wave plate 43 to adjust its polarization along the x-axis, while the other beam passes through a reflector 44, a reflector 45, and a fourth half-wave plate 46 to adjust its polarization along the y-axis. The x-axis and y-axis probe lights are used to monitor the atomic spin projections along the x- and y-axes.

[0035] Atomic gas chamber 5 is located in the outgoing light path of adjustment module 3 and beam splitting and direction adjustment module 4. The atoms within atomic gas chamber 5 exhibit spin polarization and Larmor precession through interaction with light. After being exposed to circularly polarized pump light, the spins of the atoms are modulated by the external magnetic field, and the external magnetic field is measured by monitoring changes in the spin projection. In this embodiment, the atoms within atomic gas chamber 5 are cesium atoms, which are placed in a spherical bubble coated with paraffin wax with a diameter of 2.5 cm.

[0036] The atomic gas cell 5 is precisely placed in the center of the triaxial Helmholtz coil 6 and is not heated. The triaxial Helmholtz coil 6 is used to apply an external magnetic field and is enclosed in a five-layer magnetic shield.

[0037] The balanced detector is used to convert the optical signals of the atomic spin projections detected by the probe light in the x-axis direction and the probe light in the y-axis direction into electrical signals. In this application, two balanced detectors 7 are used to convert the optical signals of the two probe beams into electrical signals. The probe light detects the atomic spin projections through the Faraday rotation effect.

[0038] First lock-in amplifiers 8 are connected to balanced detectors 7 and are used to extract the atomic spin projection amplitude and atomic spin polarization phase from the electrical signal of the atomic spin projection. The atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; the atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction. First lock-in amplifiers 8 can improve the system's signal-to-noise ratio through high-sensitivity phase detection, thereby enabling the system to accurately measure magnetic fields.

[0039] The data processing module is connected to the first lock-in amplifier 8 and is used to determine the external magnetic field angle based on the atomic spin projection amplitude and the atomic spin polarization phase using a trained artificial neural network.

[0040] An artificial neural network (ANN) is integrated into the data processing module, which can identify the complex relationship between the signal and the direction of the magnetic field. This integration enables the magnetometer to independently correct phase errors, greatly improving the accuracy of the system and effectively eliminating blind spots.

[0041] With respect to the above-mentioned vector magnetic field measurement device based on the Bell-Bloom vector magnetometer, based on the same inventive concept, the embodiment of the present application also provides a vector magnetic field measurement method based on the Bell-Bloom vector magnetometer. Specifically, it includes:

[0042] S1: Apply an external magnetic field via a triaxial Helmholtz coil.

[0043] S2: Circularly polarized pump light in the z-axis direction, detection light in the x-axis direction, and detection light in the y-axis direction are applied to the atomic gas cell; after the atoms in the atomic cell receive the circularly polarized pump light, the atomic spins are modulated by the external magnetic field.

[0044] S3: Detect the atomic spin projection using the detection light in the x-axis direction and the detection light in the y-axis direction.

[0045] S4: Extract the atomic spin projection amplitude and atomic spin polarization phase based on the atomic spin projection; the atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; the atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction.

[0046] S5: Based on the atomic spin projection amplitude and atomic spin polarization phase, the trained artificial neural network is used to determine the external magnetic field angle.

[0047] The artificial neural network (ANN) consists of four hidden layers. The input layer includes three features: the phase φ of the atomic spin polarization in the x-axis direction x , the phase of atomic spin polarization in the y-axis direction φ y and the atomic spin projection amplitude A′(A x or A y ). The network architecture is designed to map these input features to the target output, which is the angle between the external magnetic field and the z-axis. The angle θ between the projection of the external magnetic field on the xy plane and the y-axis xy The ANN's hidden layers are configured with 20, 40, 20, and 10 neurons, respectively. These neurons are the computational units through which the network learns patterns and relationships in the input features. The number of neurons in each layer was determined experimentally to balance the model's ability to learn complex mappings while avoiding overfitting. Each neuron in the hidden layer uses a ReLU (rectified linear unit) as its activation function, introducing nonlinearity to enhance the model's expressiveness.

[0048] During training, the triaxial Helmholtz coils are precisely calibrated to generate an external magnetic field with known direction and strength. These coils are typically used to compensate for external magnetic fields and provide a stable and controllable magnetic field environment to more accurately detect and measure changes in atomic spins.

[0049] The training sample data of the artificial neural network is determined by the following method:

[0050] like Figure 2As shown, the atoms are polarized by the intensity-modulated pump light in the z-axis direction, while the spin projections in the x- and y-axis directions are monitored by two probe beams. The external magnetic field B is in an arbitrary direction. The optical pumping rate generated by the pump light modulated with frequency ω can be expressed as R op =a0+a1cos(ωt). A coordinate system x'y'z' can be established, where z' is along the B direction and y' is in the zz' plane. The solution for spin polarization in the x'y' plane is:

[0051] P x' +iP y' =Ae -iωt (1)

[0052] Among them, P x' and P y' They represent the projections of the atomic spin polarization on the x' and y' axes, respectively, represent the components of the atomic spin, A represents the magnitude of the atomic spin polarization vector, and ω represents the frequency of spin precession in the system.

[0053]

[0054] where ω L Represents the Larmor precession frequency of the atom, R = a0 + R d represents the relaxation rate in the absence of optical pumping. The atomic spin projection detected by the probe light can be derived from formula (1).

[0055] For the x-axis:

[0056] P x =A x sin(ωt+φ x )(3)

[0057] Among them, P x A represents the component of the atomic spin polarization vector along the x-axis, x It's P x The amplitude projected on the x-axis, φ x It represents the phase of the atomic spin polarization in the x-axis direction.

[0058]

[0059] Among them, θ xy It represents the angle between the projection of the external magnetic field B on the xy plane and the y-axis.

[0060] For the y-axis:

[0061] P y =A y sin(ωt+φ y )(6)

[0062] Among them, Py A represents the component of the atomic spin polarization vector along the y-axis, y It's P y The amplitude projected on the x-axis, φ y Represents the phase of the atomic spin polarization in the y-axis direction.

[0063]

[0064] The mapping relationship between the phase and the external magnetic field angle can be derived from formulas (4) and (7):

[0065]

[0066] Among them, A′ is the atomic spin projection amplitude, A′ is A x or A y .

[0067] The mapping relationship between the phase and the external magnetic field angle can be derived from formulas (5) and (8):

[0068]

[0069] In this way, an external magnetic field B in any direction in space can be obtained by demodulating the two detection beams to obtain the phase information φ of the two detection beam directions. x and φ y And the atomic spin projection amplitude A′. x 、φ y and A′ can determine the two angles of the external magnetic field in any direction in space and θ xy .

[0070] By training a large amount of experimental data, the artificial neural network can automatically correct the phase offset caused by optoelectronic devices, path errors, etc. The trained artificial neural network is used to map the atomic spin projection amplitude and phase to the external magnetic field angle respectively. The trained artificial neural network converts the phase signal φ x and φ y Mapping to magnetic field direction and θ xy , thereby automatically correcting the phase error. In addition, by combining the amplitude information A′, the influence of the blind zone can also be suppressed.

[0071] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A vector magnetic field measuring device based on a Bell-Bloom vector magnetometer, characterized in that: include: A light source module, used for emitting pump light and detection light; an electro-optical modulator, arranged on the outgoing light path of the light source module, for modulating the pump light; an adjustment module, arranged on an outgoing light path of the electro-optical modulator, for adjusting the polarization direction of the pump light and adjusting the pump light to circularly polarized pump light; A beam splitting and direction adjustment module is provided on the outgoing light path of the light source module, and is used to split the detection light into two beams, and adjust the two detection light beams into detection light in the x-axis direction and detection light in the y-axis direction; an atomic gas chamber, arranged on the outgoing light path of the adjustment module and the beam splitting and direction adjustment module, and arranged in a three-axis Helmholtz coil, wherein the three-axis Helmholtz coil is used to apply an external magnetic field. After the atoms in the atomic chamber receive the circularly polarized pump light, the atomic spins are modulated by the external magnetic field; A balanced detector for converting optical signals of atomic spin projections detected by the detection light in the x-axis direction and the detection light in the y-axis direction into electrical signals; a first lock-in amplifier, connected to the balanced detector, for extracting the atomic spin projection amplitude and the atomic spin polarization phase from the electrical signal of the atomic spin projection; the atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; The atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction; A data processing module is connected to the first lock-in amplifier and is used to determine the external magnetic field angle based on the atomic spin projection amplitude and the atomic spin polarization phase using a trained artificial neural network.

2. The vector magnetic field measuring device based on Bell-Bloom vector magnetometer according to claim 1, characterized in that: The light source module includes a pump laser for emitting pump light and a detection laser for emitting detection light.

3. The vector magnetic field measuring device based on Bell-Bloom vector magnetometer according to claim 2 is characterized in that: The electro-optical modulator is arranged on an outgoing optical path of the pump laser, and a modulation reference signal when the electro-optical modulator modulates the pump light is generated by a second lock-in amplifier.

4. The vector magnetic field measuring device based on Bell-Bloom vector magnetometer according to claim 1, characterized in that: The adjustment module includes: A first half-wave plate is provided on the output light path of the electro-optical modulator and is used to adjust the polarization direction of the pump light; The 1 / 4 half-wave plate is arranged on the outgoing light path of the first half-wave plate and is used to adjust the pump light into circularly polarized pump light.

5. The vector magnetic field measuring device based on Bell-Bloom vector magnetometer according to claim 2, characterized in that: The beam splitting and direction adjustment module includes: a second half-wave plate, a polarization beam splitter, a third half-wave plate, a reflector group and a fourth half-wave plate; the polarization beam splitter is arranged on the outgoing light path of the detection laser; After the detection light is emitted by the detection laser, it passes through the second half-wave plate to adjust the polarization direction, and then passes through the polarization beam splitter to split the detection light into two beams. One beam of detection light passes through the third half-wave plate to adjust the polarization direction to obtain the detection light in the x-axis direction, and the other beam of detection light passes through the reflector group and the fourth half-wave plate to adjust the polarization direction to obtain the detection light in the y-axis direction.

6. The vector magnetic field measuring device based on Bell-Bloom vector magnetometer according to claim 1, characterized in that: The atoms in the atomic gas chamber are cesium atoms, which are placed in a spherical bubble coated with paraffin wax; the three-axis Helmholtz coil is encapsulated in a five-layer magnetic shield.

7. A method for measuring a vector magnetic field based on a Bell-Bloom vector magnetometer, characterized in that: The vector magnetic field measurement method is applied to the vector magnetic field measurement device according to any one of claims 1 to 6, and the vector magnetic field measurement method includes: The external magnetic field is applied via a triaxial Helmholtz coil; Applying circularly polarized pump light in the z-axis direction, detection light in the x-axis direction, and detection light in the y-axis direction to the atomic gas cell; after the atoms in the atomic cell receive the circularly polarized pump light, the atomic spins are modulated by the external magnetic field; The atomic spin projection is detected by the detection light in the x-axis direction and the detection light in the y-axis direction; Extracting an atomic spin projection amplitude and an atomic spin polarization phase based on the atomic spin projection; the atomic spin projection amplitude is the amplitude of the atomic spin projection in the x-axis direction or the amplitude of the atomic spin projection in the y-axis direction; the atomic spin polarization phase includes the phase of the atomic spin polarization in the x-axis direction and the phase of the atomic spin polarization in the y-axis direction; Based on the atomic spin projection amplitude and the atomic spin polarization phase, a trained artificial neural network is used to determine the external magnetic field angle.

8. The method for measuring a vector magnetic field based on a Bell-Bloom vector magnetometer according to claim 7, wherein: The trained artificial neural network is used to map the atomic spin projection amplitude and the phase to the external magnetic field angle respectively.

9. The method for measuring a vector magnetic field based on a Bell-Bloom vector magnetometer according to claim 8, wherein: The mapping relationship between the atomic spin projection amplitude and the external magnetic field angle is: Among them, A′ is the atomic spin projection amplitude, A is the atomic spin polarization vector, is the angle between the external magnetic field and the z-axis, θ xy It represents the angle between the projection of the external magnetic field on the xy plane and the y-axis.

10. The method for measuring a vector magnetic field based on a Bell-Bloom vector magnetometer according to claim 9, wherein: The mapping relationship between phase and external magnetic field angle is: Among them, φ x is the phase of atomic spin polarization in the x-axis direction, φ y Represents the phase of the atomic spin polarization in the y-axis direction.

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