Differential EIT-EIA signal-based CPT magnetometer magnetic measurement signal-to-noise ratio improving method and device

Abstract

The invention relates to the field of quantum measurement, and provides a CPT magnetometer magnetic measurement signal-to-noise ratio improving method and device based on a differential EIT-EIA signal. The CPT magnetometer solves the problem that a traditional CPT magnetometer is low in magnetic measurement signal-to-noise ratio due to the influence of environment temperature noise, laser stability and atomic gas chamber buffer gas. According to the main scheme, the CPT magnetometer comprises a laser generation module, a reference correction module, a differential detection module, a non-magnetic heating module and a signal processing module. The laser generation module generates reference / measurement double beams through the laser and the polarization regulation and control assembly; the reference correction module performs polarization conversion and optical path regulation and control on the reference light; the differential detection module divides the measurement light into two paths by adopting polarization beam splitting, the first path is subjected to polarization state conversion through an interference light path after frequency modulation, the second path is converted into circularly polarized light after optical fiber transmission, the two paths of light are coupled and then enter an atomic gas chamber for interaction, and differential detection is realized through a polarization beam splitting detector; and the non-magnetic heating module accurately controls the temperature of the air chamber by using a non-contact photo-thermal conversion technology.

Description

Technical Field

[0001] The present invention relates to the field of quantum precision sensing and measurement, and provides a method and device for improving the magnetic measurement signal-to-noise ratio of a CPT magnetometer based on differential EIT-EIA signals. Background Art

[0002] Traditional geomagnetic measurement methods (such as proton precession magnetometers and optically pumped magnetometers) have many limitations. The proton precession magnetometer measures based on the Larmor precession frequency of hydrogen protons in the geomagnetic field, and needs to polarize a liquid to excite proton spin. The corresponding device needs to be equipped with a high-power radio frequency coil and a liquid container, which is not only bulky but also has a poor dynamic response. The optically pumped magnetometer uses the Zeeman splitting effect of alkali metal atoms (such as rubidium and cesium) in a magnetic field and relies on optical pumping and radio frequency resonance. Its disadvantage is that it needs to maintain a specific density of atomic vapor (typical temperature 80-150 °C) by heating or cooling, and has a low-temperature dependence. At the same time, the optically pumped magnetometer also has a dead zone effect, that is, a signal blind area will appear when the radio frequency field is coupled with the optical pumping frequency, and complex feedback control is required. In the fields of geospace magnetic field detection, unmanned aerial vehicle applications, and magnetic anomaly space navigation, the temperature environment adaptation range of the above methods is insufficient. The CPT (Coherent Population Trapping Magnetometer) atomic magnetometer based on alkali metal two-photon spectral resonance is a highly sensitive magnetic sensor that can be chip-sized, which overcomes the disadvantages of the above two magnetometers, but still has the deficiency that the measurement error is affected by the environmental temperature, laser stability, and buffer gas in the atomic cell. To sum up, realizing a CPT magnetometer that reduces the influence of environmental noise and has a higher signal-to-noise ratio of the output signal is of great significance for geospace magnetic field detection applications and accelerating the localization and independent control of geomagnetic field magnetometers. Summary of the Invention

[0003] The present invention aims to solve the problem of low magnetic measurement signal-to-noise ratio of traditional CPT magnetometers caused by environmental temperature noise, laser stability, and buffer gas in the atomic cell by means of differential processing of complementary signals of EIT (Electromagnetically Induced Transparency) and EIA (Electromagnetically Induced Absorption), so as to improve the accuracy and anti-interference ability of geomagnetic field measurement.

[0004] To achieve the above object, the present invention adopts the following technical means:

[0005] The present invention provides a CPT magnetometer device, comprising:

[0006] A laser generation module, including a laser and a polarization control component, for generating and splitting into a reference beam and a measurement beam;

[0007] Reference calibration module, including a reference optical path component and a reference signal detection component, for performing polarization conversion and optical path regulation on the reference beam;

[0008] Differential detection module, including:

[0009] Polarization beam splitting component, for splitting the measurement beam into a first detection light and a second detection light;

[0010] Modulation transmission component, including a frequency modulator and an optical fiber transmission unit, for performing frequency modulation and transmission on the two detection lights respectively;

[0011] Interference optical path component, for performing polarization state conversion on the first detection light and forming an interference optical path;

[0012] Polarization conversion component, for converting the second detection light into circularly polarized light and coupling it with the output of the interference optical path;

[0013] Spectral splitting detection component, including an atomic gas cell and a polarization spectral splitting detector, for performing atomic interaction and polarization spectral splitting detection on the coupled light;

[0014] Non-magnetic heating module, including a heating light source and a heat conduction component, for controlling the temperature of the atomic gas cell in a non-contact manner;

[0015] Signal processing module, including a signal amplification unit and a data processing unit, constituting a closed-loop feedback control link.

[0016] In the above solution, in the laser generation module:

[0017] The laser is a DBR laser, and its output end is sequentially connected to a first half-wave plate and a first polarization beam splitter;

[0018] The first polarization beam splitter divides the incident light into two paths of a reference beam and a measurement beam, where the reference beam is transmitted to the reference calibration module and the measurement beam is transmitted to the differential detection module.

[0019] In the above solution, the reference calibration module includes:

[0020] A third polarization beam splitter, a reference gas cell, a first quarter-wave plate, and a mirror arranged in sequence along the propagation direction of the reference beam;

[0021] The mirror reflects the transmitted light to the first photodetector to form a closed-loop reference optical path.

[0022] In the above solution, in the differential detection module:

[0023] The polarization beam splitting component includes a second polarization beam splitter, and a first quarter-wave plate is arranged at its input end;

[0024] The modulation transmission component includes:

[0025] The first branch is sequentially connected to a first acousto-optic modulator, a first fiber optic coupling mirror, and a first fiber optic transmission.

[0026] The second branch is sequentially connected to a corner reflector, a fourth reflector, a second acousto-optic modulator, and a second fiber optic coupling mirror.

[0027] In the above solution, the interference optical path component includes:

[0028] The first detection light output by the first fiber optic collimator sequentially forms an interference optical path through a first reflector, a second quarter-wave plate, a third quarter-wave plate, and a first laser beam splitter.

[0029] A reflector and a fifth quarter-wave plate are arranged at the output end of the interference optical path for generating orthogonally circularly polarized light.

[0030] In the above solution, the beam splitting and detection component includes:

[0031] The second detection light output by the second fiber optic collimator is converted into circularly polarized light through a fifth quarter-wave plate.

[0032] The circularly polarized light and the orthogonally circularly polarized light are spatially coupled through a second laser beam splitter and then incident on 87 an Rb atomic gas cell;

[0033] A second half-wave plate, a fourth polarization beam splitter, a second photodetector, and a third photodetector are sequentially arranged at the output end of the atomic gas cell.

[0034] In the above solution, the non-magnetic heating module includes:

[0035] The heating laser is connected to a multimode fiber through a third fiber optic transmission.

[0036] The multimode fiber is connected to 87 the graphene heating layer of the Rb atomic gas cell in a tangential coupling manner to form an annular photo-thermal conversion structure.

[0037] In the above solution, in the signal processing module:

[0038] The first photodetector, the second photodetector, and the third photodetector are connected to a transimpedance amplifier through coaxial cables.

[0039] The output end of the transimpedance amplifier is connected to a lock-in amplifier and a data acquisition and processing device to form three differential signal processing channels.

[0040] The present invention also provides a method for measuring magnetic field by a CPT magnetometer based on differential EIT-EIA signals, including the following steps:

[0041] Step S1: Heat the Rb atomic gas cell to a predetermined temperature by using heating laser that is detuned from the pumping laser wavelength through a multimode optical fiber. 87 Rb atomic gas cell to a predetermined temperature;

[0042] Step S2: Generate a laser beam containing a frequency modulation signal through a DBR laser, and form a forward optical path and a reference optical path after polarization splitting.

[0043] Step S3: The reference optical path is reflected by the reference gas cell and then received by the first photodetector, and the wavelength of the DBR laser is feedback-controlled through phase-locked amplification and signal processing.

[0044] Step S4: The forward optical path generates orthogonally polarized I_EIT beam and I_EIA beam through a quarter-wave plate and a polarization beam splitter.

[0045] Step S5: Acousto-optically modulate the I_EIT beam and the I_EIA beam respectively to achieve the zero Raman detuning condition.

[0046] Step S6: The modulated I_EIT beam generates orthogonally circularly polarized light through a Michelson interferometer, and the I_EIA beam is converted into circularly polarized light through a quarter-wave plate.

[0047] Step S7: Integrate the orthogonally polarized I_EIT and I_EIA beams to the 87 Rb atomic gas cell through a laser beam splitter;

[0048] Step S8: Detect the transmitted I_EIT and I_EIA signals respectively, and obtain an enhanced resonance peak through differential calculation.

[0049] Step S9: According to the resonance peak frequency difference Δv, calculate the magnetic field strength through the formula where μ B is the Bohr magneton, g F is the Landé g-factor, B is the magnetic field strength, represents the reduced Planck constant.

[0050] The CPT magnetometer system and sensor probe design based on differential EIT / EIA signals of the present invention achieve the following remarkable advantages through innovative technical solutions:

[0051] 1. Improvement in signal-to-noise ratio and anti-interference ability: By simultaneously detecting the complementary EIT and EIA signals in the double-Λ four-level system and performing differential processing, the common-mode interferences such as temperature drift, laser frequency fluctuation, and environmental electromagnetic noise are effectively suppressed, and the signal-to-noise ratio of magnetic field measurement is significantly enhanced. The differential signal processing mechanism can eliminate the systematic error of the ground state frequency, reduce the influence of atomic collision broadening and buffer gas pressure fluctuation on the measurement accuracy, thereby improving the stability and reliability of magnetic field detection.

[0052] 2. Magnetic-free Heating and Low-noise Design: By adopting laser heating technology that is detuned from the pumping / detection laser wavelength and directly acting on the gas cell through optical fibers, magnetic noise introduced by traditional electrical heating methods is avoided, achieving true magnetic-free heat source control. This design not only reduces the magnetic field interference in the probe part but also improves the temperature control uniformity and response speed, enabling the atomic gas cell to maintain a high-density atomic vapor at a stable temperature and further optimizing the two-photon resonance condition.

[0053] 3. Structural Simplification and Miniaturization: The all-optical excitation scheme abandons the radio-frequency coil and complex feedback circuits, and realizes the physical isolation of the optical path and the electronic system through optical fiber coupling technology, significantly reducing the probe volume and power consumption. The probe module can suppress environmental magnetic field interference without magnetic shielding. Combining the micron-scale optical excitation region and the integrated optical path design provides a technical basis for the miniaturization and chip integration of the magnetometer.

[0054] 4. Environmental Adaptability and Application Expansion: The system adopts a multi-layer permalloy shielded reference gas cell and combines with an all-optical fiber transmission architecture, enabling high-precision magnetic field measurement in a non-shielded environment and adapting to complex working conditions such as temperature and vibration. This technology is particularly suitable for fields such as airborne magnetic detection of unmanned aerial vehicles, marine magnetic anomaly monitoring, and space navigation, meeting the engineering requirements of high sensitivity, wide dynamic range, and low power consumption.

[0055] 5. Enhanced Measurement Stability: Through phase-locked amplification, dynamic frequency modulation tracking, and double gas cell calibration mechanisms, the laser wavelength drift and environmental magnetic field disturbance are compensated in real time to ensure the consistency of long-term measurement. Compared with traditional CPT magnetometers, this solution can still maintain the high-precision magnetic field scalar calculation ability in a wide temperature range and harsh electromagnetic environment.

[0056] In summary, through the collaborative optimization of differential signal processing, magnetic-free heating, and all-optical architecture, the present invention improves the comprehensive performance of the magnetometer while solving the bottleneck problems such as volume, noise, and environmental adaptability in traditional technologies, providing an innovative solution for high-precision geomagnetic field detection. Brief Description of the Drawings

[0057] Figure 1 It is the overall structural diagram of a CPT magnetometer device based on differential EIT / EIA signals for implementing the present invention.

[0058] The reference numerals are listed as follows: 1 - Power drive control; 2 - DBR laser; 3 - First half-wave plate; 4 - First polarization beam splitter; 5 - First quarter-wave plate; 6 - Second polarization beam splitter; 7 - First acousto-optic modulator; 8 - First fiber optic coupling mirror; 9 - First fiber optic transmission; 10 - First fiber optic collimator; 11 - First reflector; 12 - Second quarter-wave plate; 13 - Third quarter-wave plate; 14 - First laser beam splitter; 15 - Second reflector; 16 - Third reflector; 17 - Fourth quarter-wave plate; 18 - Reference gas cell; 19 - Third polarization beam splitter; 20 - First photodetector; 21 - Fourth reflector; 22 - Second acousto-optic modulator; 23 - Second fiber optic coupling mirror; 24 - Second fiber optic transmission; 25 - Second fiber optic collimator; 26 - Fifth quarter-wave plate; 27 - Sixth quarter-wave plate; 28 - 87 Rb gas cell; 29 - Second half-wave plate; 30 - Fourth polarization beam splitter; 31 - Second photodetector; 32 - Data acquisition and signal processing; 33 - Lock-in amplifier; 34 - Transimpedance amplifier; 35 - Corner reflector; 36 - Heating laser; 37 - Third fiber optic transmission; 38 - Second laser beam splitter; 39 - Multimode fiber; 40 - Third photodetector; 41 - System optical path and control processing system; 42 - Probe. Detailed implementation mode

[0059] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific implementation modes, it should be noted that the present invention is not limited to these implementation modes only. On the contrary, any modifications or equivalent replacements made to the present invention should be covered within the scope of the claims of the present invention.

[0060] In addition, for better illustration of the present invention, numerous specific details are given in the following detailed implementation modes. Those skilled in the art will understand that the present invention can also be implemented without these specific details.

[0061] The present invention aims to propose a device and sensor probe design of a CPT magnetometer based on differential EIT / EIA signals for measuring the geomagnetic field and magnetic anomaly fluctuations. The method is based on quantum effects and the Zeeman effect, using two-photon resonance to measure the magnetic field. By irradiating with electromagnetic radiation of different frequencies, alkali metal atoms in the sensor atomic cell can be tuned and excited. Under the condition of an external magnetic field, the atomic energy levels will undergo Zeeman energy level splitting. The difference in the transition frequencies of the split energy levels depends on the external magnetic field. This energy level splitting will cause a decrease in the absorption rate of the probe light by the atoms at a certain resonance frequency, that is, EIT (Electromagnetically Induced Transparency), and the opposite effect to EIT is EIA (Electromagnetically Induced Absorption). Among them, the peak value of the transmission peak of EIT is upward, and the peak value of the absorption peak of EIA is downward, and the two can form a pair of complementary signals. In the D1 line of alkali metal atoms, one of the four electric dipole moments involved in the double-Λ four-level system has the opposite sign to the other three electric dipole moments. Therefore, EIT and EIA resonances can be generated simultaneously in this double-Λ energy level system. EIT and EIA signals can be detected to exist simultaneously under the condition of zero Raman detuning, that is, the deviation between the actual two-photon resonance frequency difference and the ideal resonance frequency is zero. By measuring the signal values of the EIT and EIA resonance peaks and subtracting them at the output end, an output signal with enhanced amplitude and suppressed common-mode noise is finally generated, and then the magnetic field strength is measured.

[0062] The magnetometer detection system designed based on this principle can eliminate the influence of systematic errors in the ground state frequency and reduce the influence of factors such as environmental temperature noise, pressure noise, and laser stability on the magnetic field measurement signal. The obvious advantage of all-optical resonance compared with radio frequency excitation is that optical fibers can be used to transmit the excitation radiation to the sample, which can keep all magnetic and electronic components away from the measurement probe, greatly improving the sensitivity of the magnetometer. At the same time, compared with the centimeter-sized excitation region in radio frequency excitation, the optical excitation in the micron range makes it possible to miniaturize and micro-miniaturize the sensor and even develop a chip atomic magnetometer. In addition, a temperature control method of heating the atomic cell with a laser is adopted, and the laser is transmitted through an optical fiber, effectively reducing the interference of the heating device on the magnetic field around the probe. The present invention can meet the detection requirements in various space magnetic field detection fields such as unmanned aerial vehicle magnetic measurement, ocean magnetic field, and magnetic anomaly detection.

[0063] Figure 1 It is the overall structure diagram of a CPT magnetometer device based on differential EIT / EIA signals for implementing the present invention. As shown in the reference drawings, a specific implementation method of a CPT magnetometer device system and sensor probe design based on differential EIT / EIA signals includes the following steps:

[0064] Step 1: Start the heating laser 36, set the power, transmit it through the multimode optical fiber 39, and heat the atomic gas cell 28 to a predetermined temperature range (~55 °C).

[0065] Step 2: The power supply drive control 1 first sets the DBR laser 2 to the static operating current point, and then the power supply drive control 1 controls the DBR laser 2 to generate a laser frequency modulation signal.

[0066] Step 3: The laser emitted by the DBR laser 2 carrying the frequency modulation signal passes through the first half-wave plate 3 and the first polarization beam splitter 4, and then one beam of light propagates along the forward optical path, and the other beam of light enters the reference gas cell 18 through the third polarization beam splitter 19, and is reflected by the fourth quarter-wave plate 17 and the third mirror 16 and enters the first photodetector 20. The frequency modulation spectrum and the demodulated value of the electrical signal are obtained through the transimpedance amplifier 32, the phase-locked amplifier 33, the data acquisition and signal processing device 34, and the output of the power supply drive control 1 is adjusted to control the wavelength of the DBR laser 2, so that the wavelength of the DBR laser 2 tracks the fine structure transition of the 133Cs atomic D1 line and suppresses the drift of the frequency modulation spectrum.

[0067] Step 4: The co-frequency light beam in the forward optical path passes through the first quarter-wave plate 5 to generate two orthogonally polarized light beams that enter the second polarization beam splitter 6, namely I_EIT and I_EIA.

[0068] Step 5: The light beam I_EIT is transmitted to the first acousto-optic modulator 7 to achieve fine frequency tuning, and the light beam I_EIA passes through the corner reflector 35 and the fourth mirror 21 and then is transmitted to the second acousto-optic modulator 22 to achieve fine frequency tuning. The final effect of this frequency modulation is to make the deviation between the actual two-photon resonance frequency difference and the ideal resonance frequency zero under the condition of zero Raman detuning.

[0069] Step 6: The light beam I_EIT passes through the first optical fiber transmission 9 device composed of the first optical fiber coupling mirror 8 and the first optical fiber collimator 10 and then enters the Michelson interferometer device jointly composed of the first mirror 11, the second quarter-wave plate 12, the third quarter-wave plate 13, the first laser beam splitter 14, the second mirror 15, and the sixth quarter-wave plate 27. By adjusting the distance between the first mirror 11 and the second quarter-wave plate 12 in the Michelson interferometer, a new circularly polarized light beam orthogonal to the original light beam is generated. The light beam I_EIA passes through the second optical fiber transmission 24 device composed of the second optical fiber coupling mirror 23 and the second optical fiber collimator 25 and then forms circularly polarized light through the fifth quarter-wave plate 26.

[0070] Step 7: The mutually orthogonal I_EIT light beam and I_EIA light beam are integrated onto the same optical path through the BS laser beam splitter 38 and then injected into 87 the Rb gas cell 28.

[0071] Step 8, after the splitting of light by the second half-wave plate 29 and the fourth polarization beam splitter 30, the I_EIT beam and the I_EIA beam carrying magnetic field information enter the second photodetector 31 and the third photodetector 40 respectively. The frequency resonance peaks of EIT and EIA are obtained through the transimpedance amplifier 34, lock-in amplification 33, and data acquisition and signal processing device 32. Then, by differential calculation, the EIT / EIA differential frequency resonance peak with enhanced signal-to-noise ratio can be output. By recording the frequencies of the pump light and the probe light, the frequency difference Δv between the two can be obtained. The magnetic field magnitude is calculated using the formula:

[0072]

[0073] Calculate the scalar value of the magnetic field magnitude, where μ B is the Bohr magneton, g F is the Landé factor, B is the magnetic field strength, represents the reduced Planck constant.

Claims

1. A CPT magnetometer device, characterized in that, Comprising: A laser generation module, including a laser and a polarization regulation component, for generating and splitting into a reference beam and a measurement beam; A reference correction module, including a reference optical path component and a reference signal detection component, for performing polarization conversion and optical path regulation on the reference beam; A differential detection module, including: A polarization beam splitting component, for splitting the measurement beam into a first detection light and a second detection light; A modulation transmission component, including a frequency modulator and an optical fiber transmission unit, for respectively performing frequency modulation and transmission on the two detection lights; An interference optical path component, for performing polarization state conversion on the first detection light and forming an interference optical path; A polarization conversion component, for converting the second detection light into circularly polarized light and coupling it with the output of the interference optical path; A spectroscopic detection component, including an atomic gas cell and a polarization spectroscopic detector, for performing atomic interaction and polarization spectroscopic detection on the coupled light; A non-magnetic heating module, including a heating light source and a heat conduction component, for controlling the temperature of the atomic gas cell in a non-contact manner; A signal processing module, including a signal amplification unit and a data processing unit, constituting a closed-loop feedback control link.

2. The CPT magnetometer device according to claim 1, characterized in that, In the laser generation module: The laser is a DBR laser (2), and its output end is sequentially connected to a first half-wave plate (3) and a first polarization beam splitter (4); The first polarization beam splitter (4) splits the incident light into two paths, a reference beam and a measurement beam, where the reference beam is transmitted to the reference correction module and the measurement beam is transmitted to the differential detection module.

3. The CPT magnetometer device according to claim 1, wherein, The reference correction module includes: A third polarization beam splitter (19), a reference gas cell (18), a first quarter-wave plate (17), and a mirror (16) sequentially arranged along the propagation direction of the reference beam; The mirror (16) reflects the transmitted light to a first photodetector (20) to form a closed-loop reference optical path.

4. The CPT magnetometer device according to claim 1, characterized in that, In the differential detection module: The polarization beam splitting component includes a second polarization beam splitter (6), and a first quarter-wave plate (5) is arranged at its input end; The modulation transmission component includes: A first branch is sequentially connected to a first acousto-optic modulator (7), a first fiber optic coupler (8), and a first fiber optic transmission (9); A second branch is sequentially connected to a corner reflector (35), a fourth mirror (21), a second acousto-optic modulator (22), and a second fiber optic coupler (23).

5. The CPT magnetometer device according to claim 1, characterized in that, The interference optical path component includes: The first detection light output by the first fiber optic collimator (10) sequentially passes through a first mirror (11), a second quarter-wave plate (12), a third quarter-wave plate (13), and a first laser beam splitter (14) to form an interference optical path; A mirror (15) and a fifth quarter-wave plate (27) are arranged at the output end of the interference optical path for generating orthogonally circularly polarized light.

6. The CPT magnetometer device according to claim 1, characterized in that, The spectroscopic detection component includes: The second detection light output by the second fiber optic collimator (25) is converted into circularly polarized light by a fifth quarter-wave plate (26); The circularly polarized light and the orthogonally circularly polarized light are spatially coupled by a second laser beam splitter (38) and then incident on 87 the Rb atomic gas cell (28); At the output end of the atomic gas cell, a second half-wave plate (29), a fourth polarization beam splitter (30), a second photodetector (31), and a third photodetector (40) are sequentially arranged.

7. The CPT magnetometer device according to claim 1, wherein, The non-magnetic heating module includes: A heating laser (36) is connected to a multimode fiber (39) through a third fiber optic transmission (37); The multimode optical fiber (39) is connected in a tangential coupling manner 87 The graphene heating layer of the Rb atomic gas cell (28) forms an annular photothermal conversion structure.

8. The CPT magnetometer device according to claim 1, characterized in that, In the said signal processing module: The first photodetector (20), the second photodetector (31) and the third photodetector (40) are connected to a transimpedance amplifier (34) through coaxial cables; The output end of the transimpedance amplifier (34) is connected to a lock-in amplifier (33) and a data acquisition and processing device (32), forming three differential signal processing channels.

9. A magnetic measurement method for a CPT magnetometer based on differential EIT-EIA signals, characterized in that, It includes the following steps: Step S1: Heat the Rb atomic gas cell (28) to a predetermined temperature by using a heating laser that is detuned from the pumping laser wavelength through a multimode optical fiber. 87 ​ Step S2: Generate a laser beam containing a frequency-modulated signal through a DBR laser (2), and form a forward optical path and a reference optical path after polarization splitting; Step S3: The reference optical path is reflected by a reference gas cell (18) and then received by the first photodetector (20), and the wavelength of the DBR laser is controlled through lock-in amplification (33) and signal processing feedback; Step S4: The forward optical path generates an orthogonally polarized I_EIT beam and an I_EIA beam through a quarter-wave plate and a polarization beam splitter; Step S5: Acousto-optic modulation is respectively performed on the I_EIT beam and the I_EIA beam to achieve the zero Raman detuning condition; Step S6: The modulated I_EIT beam generates orthogonally circularly polarized light through a Michelson interferometer, The I_EIA beam is converted into circularly polarized light through a quarter-wave plate; Step S7: Integrate the orthogonally polarized I_EIT and I_EIA beams into 87 the Rb atomic vapor cell; Step S8: The transmitted I_EIT and I_EIA signals are respectively detected, and an enhanced resonance peak is obtained through differential calculation; Step S9. According to the resonance peak frequency difference Δv, calculate the magnetic field strength through the formula where μ B is the Bohr magneton, g F is the Lande factor, B is the magnetic field strength, represents the reduced Planck constant.

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