Atomic magnetometer based on homodyne and differential detection

Abstract

The atom magnetometer based on homodyne and differential detection is provided for the first time, detection light is divided into signal light and reference light through a 1 * 2 polarization-maintaining optical fiber coupler, and the signal light enters a gas chamber and interacts with polarized alkali metal atoms to induce magnetic field information; the reference light is subjected to high-frequency phase modulation and then subjected to homodyne coherent frequency mixing with the signal light to generate orthogonal phase signals, magnetic field information is extracted from the two paths of orthogonal signals through a homodyne and differential fusion detection mechanism, response signals are improved, low-frequency noise is suppressed, and the measurement precision, signal response and low-frequency sensitivity of the atom magnetometer are improved. Compared with a traditional single differential detection method, the phase sensitivity characteristic of homodyne detection and the common-mode noise suppression capability of differential detection are innovatively combined, and enhancement and high-fidelity extraction of detection signals and suppression of low-frequency noise are achieved through coherent demodulation and differential processing of double-path polarization modulation signals.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement instrument technology in magnetic field measurement, and particularly to an atomic magnetometer based on zero-difference detection and differential detection. The detection light is split into signal light and reference light through a 1×2 polarization-maintaining fiber coupler. The signal light enters the gas cell and interacts with polarized alkali metal atoms to induce magnetic field information. The reference light is subjected to high-frequency phase modulation and then coherently mixed with the signal light with zero-difference to generate orthogonal phase signals. The magnetic field information is then extracted from the two orthogonal signals through a zero-difference and differential fusion detection mechanism, which is beneficial to improving the measurement accuracy, signal response and low-frequency sensitivity of the atomic magnetometer. Background Technology

[0002] With the development of quantum technology, various scientific instruments based on quantum effects are constantly and significantly breaking through the measurement limits of traditional instruments. Atomic magnetometers are quantum instruments that use the interaction between light, magnetism, and atoms to precisely measure weak magnetic fields by detecting the size of the Zeeman splitting of atoms. Compared to other types of magnetometers, they have unparalleled advantages in performance indicators and represent an important development direction for next-generation ultra-high sensitivity magnetometers. The basic principle of atomic magnetometers using differential detection is that when linearly polarized light interacts with alkali metal atoms in a specific excited state, its polarization direction changes, generating a magneto-optical rotation angle signal. By measuring this rotation angle, information about the interaction between atoms and light can be calculated. However, the single differential detection method is susceptible to low-frequency noise such as laser intensity fluctuations, circuit noise, and environmental interference, resulting in poor low-frequency sensitivity. Zero-difference detection uses a fiber optic EOM (Electro-optic modulator) for high-frequency phase modulation, and simultaneously combines differential detection to amplify and demodulate two orthogonal signals, suppressing the influence of low-frequency noise and significantly improving the extraction accuracy of the magnetic field signal, system response, and low-frequency sensitivity. In view of the above, the inventors have completed this invention. Summary of the Invention

[0003] The problem solved by this invention is to overcome the shortcomings of the prior art and provide an atomic magnetometer based on zero-difference and differential detection. The detection light is split into signal light and reference light by a 1×2 polarization-maintaining fiber coupler. The signal light enters the gas cell and interacts with the polarized alkali metal atoms to induce magnetic field information. The reference light is subjected to high-frequency phase modulation and then coherently mixed with the signal light with zero-difference to generate orthogonal phase signals. The magnetic field information is then extracted from the two orthogonal signals through a zero-difference and differential fusion detection mechanism, which improves the response signal and suppresses low-frequency noise, thereby improving the measurement accuracy, signal response and low-frequency sensitivity of the atomic magnetometer.

[0004] The technical solution provided by this invention is as follows:

[0005] An atomic magnetometer based on zero-difference and differential detection is characterized by comprising a 1×2 polarization-maintaining fiber coupler. The input end of the 1×2 polarization-maintaining fiber coupler is connected to a detection laser. The 1×2 polarization-maintaining fiber coupler splits the detection light into a signal light and a reference light. The first output end of the 1×2 polarization-maintaining fiber coupler outputs the signal light, and the second output end of the 1×2 polarization-maintaining fiber coupler outputs the reference light. The signal light enters a gas cell and interacts with polarized alkali metal atoms in the gas cell to induce magnetic field information before exiting and passing through a half-wave plate into the first output of a depolarizing beam splitter. On the input side, the reference light passes sequentially through the fiber EOM and the second fiber collimator before entering the second input side of the depolarization beam splitter. The output side of the depolarization beam splitter outputs a combined beam generated by zero-difference coherent mixing of the transmitted signal light from the first input side and the reflected reference light from the second input side. The combined beam is then passed through a lateral displacement polarization beam splitter to generate orthogonal phase signals, which enter a photodetector. The photodetector is connected to a measurement and control circuit system via a differential circuit. The measurement and control circuit system extracts magnetic field information based on a zero-difference and differential fusion detection mechanism formed by the two orthogonal signals.

[0006] The measurement and control circuit system includes a function generation module, a transimpedance amplification module, a modulation and demodulation module, a low-pass filter module, and a data acquisition module. The output of the data acquisition module is connected to a computer, and the input of the data acquisition module is connected to the output of the low-pass filter module. The input of the low-pass filter module is connected to the output of the modulation and demodulation module, the input of the modulation and demodulation module is connected to the output of the transimpedance amplification module, and the input of the transimpedance amplification module is connected to the output of the differential circuit.

[0007] The air chamber is located inside the oven, which is located inside the triaxial coil, and the triaxial coil is connected to the function generating module.

[0008] The triaxial coil is equipped with a first fiber collimator, a third fiber collimator, a second fiber collimator, and a differential circuit. The input end of the first fiber collimator is connected to the first output end of the 1×2 polarization-maintaining fiber coupler in sequence through a polarization-maintaining fiber and a fiber flange. The output end of the first fiber collimator is connected to the signal light input side of the gas cell through a linear polarizer. The input side of the third fiber collimator is connected to the pump laser, and the output side of the third fiber collimator is connected to the pump light incident side of the gas cell through a combined prism.

[0009] Including the following expressions:

[0010]

[0011] δ=βsin(ω m t),

[0012] Where E sig ω is the electric field vector of the transmitted signal light, E0 is the initial amplitude of the detection light vector, η is the transmittance of the detection light through the gas chamber glass each time, e is the natural constant, i is the imaginary unit, ω is the frequency of the transmitted signal light, t is time, φ is the phase change of the signal light after passing through the gas chamber due to the magnetic field, OD is the optical depth, and θ is the optical rotation angle. It is the x-axis component label. It is the y-axis component label;

[0013] E ref δ is the electric field vector of the reflected reference light, β is the phase difference applied by the fiber EOM, β is the modulation depth, and ω is the electric field vector of the reflected reference light. m The modulation frequency.

[0014] Including the following expressions:

[0015]

[0016] V=GI out ,

[0017] Among them I out It is the light intensity detected by the photodetector. It is the complex amplitude of the orthogonal electric field vector along the x-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector, It is the complex amplitude of the orthogonal electric field vector along the y-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector is given by I0, the initial incident detection light intensity is given by V, the atomic magnetometer response signal output by the modulation and demodulation module is given by G, and the conversion coefficient is given by G.

[0018] The technical effects of this invention are as follows: This invention proposes for the first time an atomic magnetometer based on zero-difference and differential detection. The detection light is split into two beams by a 1×2 polarization-maintaining fiber coupler, which serve as the signal light and the reference light, respectively. The signal light enters the gas cell and interacts with the polarized alkali metal atoms to induce magnetic field information. The reference light is subjected to high-frequency phase modulation using an electro-optic modulator (EOM) and then coherently mixed with the signal light with zero-difference to generate orthogonal phase signals. At the same time, differential detection is combined to compare the amplitudes of the two orthogonal signals. The magnetic field response signal is amplified and demodulated by a transimpedance amplification module and a modulation and demodulation module, suppressing low-frequency noise such as laser intensity fluctuations, circuit noise, and environmental interference. This is beneficial to improving the measurement accuracy, signal response, and low-frequency sensitivity of the atomic magnetometer. This invention, when used in a spin-exchange relaxation-free (SERF) atomic magnetometer, can optimize the magnetic field sensitivity to the sub-Femtotes level and significantly improve the system's robustness and long-term stability. It is suitable for ultra-high precision weak magnetic sensing needs in fields such as extremely weak magnetic measurement, biomedical magnetic imaging, and ultra-low field nuclear magnetic resonance.

[0019] The advantages of this invention compared to the prior art are:

[0020] (1) Conventional atomic magnetometers use differential detection to extract magnetic field information, but can only extract the amplitude information of the magnetic field; while the zero-difference-differential fusion detection mechanism can extract the amplitude and phase information of the magnetic field, improving the measurement accuracy and response signal.

[0021] (2) Conventional atomic magnetometers using differential detection methods are susceptible to low-frequency noise such as laser intensity fluctuations, circuit noise and environmental interference, resulting in poor low-frequency sensitivity. However, the zero-difference-differential fusion detection mechanism effectively suppresses low-frequency noise and improves the low-frequency sensitivity of the system by using the interference of high-frequency phase-modulated reference light and signal light.

[0022] (3) In this invention, a 1×2 polarization-maintaining fiber coupler is used to split the detection light and an optical fiber EOM is used to achieve high-frequency phase modulation of the detection reference light. No additional external optical path is required, and it is easy to miniaturize. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an atomic magnetometer structure based on zero difference and differential detection according to the present invention.

[0024] Figure 2 This is a schematic diagram illustrating the relationship between the meter system, laser system, and measurement and control circuit system of the present invention.

[0025] The reference numerals in the attached figures are explained as follows: 1-First fiber collimator; 2-Linear polarizer; 3-Half-wave plate; 4-Depolarizing beam splitter; 5-Lateral displacement polarizing beam splitter; 6-Photodetector; 7-Differential circuit; 8-Second fiber collimator; 9-Third fiber collimator; 10-Combined prism; 11-Gas cell; 12-Oven; 13-Triaxial coil; 14-Pump laser; 15-Detection laser; 16-1×2 polarization-maintaining fiber coupler; 17-Fiber EOM (Electro-optic) 18-Electro-optic modulators; 19-Fiber optic flange; 20-Polarization-maintaining fiber; 21-Measurement and control circuit system (including function generation module, transimpedance amplification module, modulation and demodulation module, low-pass filter module, and data acquisition module); 22-Computer; xyz-Cartesian coordinate system (i.e., x-axis, y-axis, and z-axis); I-Meter system (with zero-difference optical path structure); II-Laser system; III-Measurement and control circuit system, In-Input terminal; Out-Output terminal. Detailed Implementation

[0026] The following is in conjunction with the attached diagram ( Figures 1-2 The invention will be described in the following sections and examples.

[0027] Figure 1 This is a schematic diagram of an atomic magnetometer based on zero-difference and differential detection according to the present invention. Figure 2 This is a schematic diagram illustrating the relationship between the meter system, laser system, and measurement and control circuit system of the present invention. (Reference) Figures 1 to 2 As shown, an atomic magnetometer based on zero-difference and differential detection includes a 1×2 polarization-maintaining fiber coupler 16. The input end of the 1×2 polarization-maintaining fiber coupler 16 is connected to a detection laser 15. The 1×2 polarization-maintaining fiber coupler 16 splits the detection light into a signal light and a reference light. The first output end of the 1×2 polarization-maintaining fiber coupler 16 outputs the signal light, and the second output end of the 1×2 polarization-maintaining fiber coupler 16 outputs the reference light. The signal light enters a gas cell 11 and interacts with polarized alkali metal atoms in the gas cell 11 to induce magnetic field information. After being emitted, it passes through a half-wave plate 3 and enters the first output of a depolarizing beam splitter 4. On the input side, the reference light passes sequentially through fiber EOM17 and the second fiber collimator 8 before entering the second input side of the depolarization beam splitter 4. The output side of the depolarization beam splitter 4 outputs a combined beam generated by zero-difference coherent mixing of the transmitted signal light from the first input side and the reflected reference light from the second input side. The combined beam enters the photodetector 6 through the orthogonal phase signal generated by the lateral displacement polarization beam splitter 5. The photodetector 6 is connected to the measurement and control circuit system 20 through the differential circuit 7. The measurement and control circuit system 20 extracts magnetic field information based on the zero-difference and differential fusion detection mechanism formed by the two orthogonal signals.

[0028] The measurement and control circuit system 20 includes a function generation module, a transimpedance amplification module, a modulation and demodulation module, a low-pass filter module, and a data acquisition module. The output of the data acquisition module is connected to the computer 21, and the input of the data acquisition module is connected to the output of the low-pass filter module. The input of the low-pass filter module is connected to the output of the modulation and demodulation module, and the input of the modulation and demodulation module is connected to the output of the transimpedance amplification module. The input of the transimpedance amplification module is connected to the output of the differential circuit 7. The air chamber 11 is located inside the oven 12, and the oven 12 is located inside the triaxial coil 13, which is connected to the function generation module. The triaxial coil 13 is equipped with a first fiber collimator 1, a third fiber collimator 9, a second fiber collimator 8, and a differential circuit 7. The input end of the first fiber collimator 1 is connected to the first output end of the 1×2 polarization-maintaining fiber coupler 16 in sequence through a polarization-maintaining fiber 19 and a fiber flange 18. The output end of the first fiber collimator 1 is connected to the signal light input side of the gas cell 11 through a linear polarizer 2. The input side of the third fiber collimator 9 is connected to the pump laser 14, and the output side of the third fiber collimator 9 is connected to the pump light incident side of the gas cell 11 through a combined prism 10.

[0029] Including the following expressions:

[0030]

[0031] δ=βsin(ω m t),

[0032] Where E sig ω is the electric field vector of the transmitted signal light, E0 is the initial amplitude of the detection light vector, η is the transmittance of the detection light through the gas chamber glass each time, e is the natural constant, i is the imaginary unit, ω is the frequency of the transmitted signal light, t is time, φ is the phase change of the signal light after passing through the gas chamber due to the magnetic field, OD is the optical depth, and θ is the optical rotation angle. It is the x-axis component label. It is the y-axis component label; E ref δ is the electric field vector of the reflected reference light, β is the phase difference applied by the fiber EOM, β is the modulation depth, and ω is the electric field vector of the reflected reference light. m The modulation frequency.

[0033] Including the following expressions:

[0034]

[0035] V=GI out ,

[0036] Among them I out It is the light intensity detected by the photodetector. It is the complex amplitude of the orthogonal electric field vector along the x-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector, It is the complex amplitude of the orthogonal electric field vector along the y-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector is given by I0, the initial incident detection light intensity is given by V, the atomic magnetometer response signal output by the modulation and demodulation module is given by G, and the conversion coefficient is given by G.

[0037] This invention proposes an atomic magnetometer based on null-difference and differential detection. Conventional atomic magnetometers utilize differential detection technology to extract magnetic field signals. This method has a simple optical path and can effectively suppress common-mode noise, but it suffers from high noise levels in the low-frequency range due to interference from laser intensity fluctuations and electrical noise. This invention proposes a method and apparatus for implementing an atomic magnetometer based on null-difference and differential detection. This method innovatively combines the phase sensitivity of null-difference detection with the common-mode noise suppression capability of differential detection. Through coherent demodulation and differential processing of dual-path polarization modulation signals, it achieves signal enhancement, high-fidelity extraction, and low-frequency noise suppression. In practice, the linearly polarized laser beam is split into a detection signal beam and a reference beam. The signal beam, after passing through an atomic gas cell, carries magnetic field information caused by spin precession. This signal beam is then coherently mixed with the reference beam, which has been high-frequency modulated by an electro-optic modulator (EOM), to generate orthogonal phase signals. Simultaneously, differential detection is used to compare the amplitudes of the two orthogonal signals. The magnetic field response signal is amplified and demodulated using a transimpedance amplification module and a modulation / demodulation module, suppressing the effects of low-frequency noise such as laser intensity fluctuations, circuit noise, and environmental interference. Compared to traditional single differential detection methods, this invention, through a zero-difference-differential fusion detection mechanism, significantly improves the extraction accuracy of the magnetic field signal and the system's signal and low-frequency sensitivity.

[0038] An atomic magnetometer based on zero-difference and differential detection is disclosed, comprising a meter system (I), a laser (II), and a measurement and control circuit system (III). Specifically, it includes a first fiber collimator (1), a linear polarizer (2), a half-wave plate (3), a depolarizing beam splitter (4), a lateral displacement polarizing beam splitter (5), a photodetector (6), a differential circuit (7), a second fiber collimator (8), a third fiber collimator (9), a combined prism (10), a gas chamber (11), an oven (12), a triaxial coil (13), a pump laser (14), a detection laser (15), a 1×2 polarization-maintaining fiber coupler (16), a fiber electro-optic modulator (17), a fiber flange (18), a polarization-maintaining fiber (19), a measurement and control circuit board (20), and a computer (21).

[0039] The meter head system (I) includes a pump optical path, a detection optical path, a three-dimensional magnetic compensation coil, an alkali metal gas chamber, and a non-magnetic electric heating module. The pump optical path uses optical devices to realize left-hand circularly polarized light; the detection optical path uses a polarization-maintaining fiber beam splitter to generate two detection beams with the same frequency, namely the signal beam and the reference beam, which, combined with zero-difference and differential detection, enhance the response signal and improve low-frequency sensitivity; the three-dimensional magnetic compensation coil is used to compensate for the residual magnetism of the magnetometer's three axes and provide calibration signals; the alkali metal gas chamber is the core sensitive element of the magnetometer; the non-magnetic electric heating module is used to heat the gas chamber. The laser system (II) includes a pump laser and a detection laser. The measurement and control circuit system (III) includes a signal generation module, a transimpedance amplification module, a modulation and demodulation module, a low-pass filter module, and a data acquisition module.

[0040] The pump laser (14) emits pump light through the polarization-maintaining fiber (19) and the third collimator (9). The pump light is converted into left-hand circularly polarized light by the combined prism (10) and enters the gas cell to polarize alkali metal atoms. The detection laser (15) splits the detection light into two beams through the 1×2 polarization-maintaining fiber coupler (16) as signal light and reference light respectively. The signal light enters the meter system through the fiber flange (18), the polarization-maintaining fiber (19) and the first fiber collimator (1), and then enters the gas cell (11) through the linear polarizer (2) to become linearly polarized light. It interacts with the polarized alkali metal atoms to induce magnetic field information, and then passes through the half-wave plate (3) and the depolarizing beam splitter (4) to be combined with the reference light. The reference light is phase-modulated by the fiber electro-optic modulator (17) and then enters the meter system through the fiber flange (18), the polarization-maintaining fiber (19) and the second fiber collimator (8). It is then combined with the signal light by the depolarizing beam splitter (4). The combined signal light and the reference light interfere with each other. Then, the lateral displacement polarization beam splitter (5) splits the light into two parts with mutually perpendicular polarization directions and emits them. The magnetic field signal is then received by the photodetector (6) and the differential circuit (7).

[0041] It also includes the oven (12) and the three-dimensional coil (13) in the meter system (I). The purpose of the oven (12) is to heat the gas chamber to achieve a higher number density of alkali metal atoms; the purpose of the three-axis coil (13) is to use in-situ magnetic compensation technology to compensate the magnetic field felt by the atoms in the alkali metal gas chamber (11), so that the magnetic field felt by the atoms is approximately 0, and to apply a calibration signal.

[0042] The measurement and control circuit system (III) consists of a measurement and control circuit board (20). The measurement and control circuit board (20) includes a function generation module, a transimpedance amplification module, a modulation and demodulation module, a low-pass filter module, and a data acquisition module. The function generation module, transimpedance amplification module, modulation and demodulation module, low-pass filter module, and data acquisition module amplify, demodulate, filter, and acquire data of the magnetometer response signal obtained from the meter system. The measurement and control circuit board (20) inputs the response signal output by the meter system into the computer (21) through a USB interface, and obtains the final magnetic field sensitivity after data processing.

[0043] The pump laser (14) passes through a combined prism (10) consisting of a reflecting prism and a λ / 4 waveplate, which converts the pump light into left-hand circularly polarized light and enters the alkali metal gas chamber (11) to polarize the alkali metal atoms.

[0044] The signal light and reference light emitted from the detection laser (15) through the 1×2 polarization-maintaining fiber coupler (16) are linearly polarized light with an angle of 45° to the x-axis. The signal light passes through the linear polarizer (2) to change its polarization direction to the x-axis, and then passes through the gas cell (11) to interact with the polarized alkali metal atoms to induce magnetic field information. The reference light passes through the fiber electro-optic modulator (17) to perform high-frequency modulation on its phase, and then passes through the depolarization beam splitter (4) to interfere with the signal light beam. After passing through the lateral displacement polarization beam splitter (5), it is split into two parts with mutually perpendicular polarization directions and emitted. Then, the magnetic field signal is extracted by the photodetector (6) and the differential circuit (7).

[0045] The splitting ratio of the 1×2 polarization-maintaining fiber coupler (16) is 50:50; the fiber electro-optic modulator (17) modulates the phase of the reference detection light at high frequency, and through zero-difference coherent demodulation and differential processing of the dual-path polarization modulation signal, it realizes the enhancement and high-fidelity extraction of the optical rotation angle signal (magnetic field signal) and the suppression of low-frequency noise.

[0046] This invention extracts magnetic field information through a zero-difference-differential fusion detection mechanism, wherein the DC component and the second harmonic component contain the amplitude information of the magnetic field, and the first harmonic component contains the phase information of the magnetic field, which significantly improves the extraction accuracy of the magnetic field signal and the low-frequency sensitivity of the system.

[0047] When the magnetometer is in operation, the changes in the optical signal detected by the optical path are as follows:

[0048] 1. The detection laser (15) emits detection signal light through a 1×2 polarization-maintaining fiber coupler (16) and a first fiber collimator (1). The signal light is converted into horizontally polarized (x-axis) linearly polarized light through a linear polarizer (2). Then, it interacts with the polarized atomic ensemble through the gas cell (11) to generate the optical rotation angle signal θ as follows. After passing through a 1 / 2 wave plate (3), the electric field vector of the signal light is as follows.

[0049]

[0050] In the formula, n is the atomic number density, l is the optical path length of the detection light interacting with polarized alkali metal atoms, and r e Let f be the classical electron radius, c be the speed of light in a vacuum, and f be the speed of light in a vacuum. D1 Γ represents the oscillation intensity of the D1 line of alkali metal atoms, Δν is the detection optical detuning frequency, and Γ is the frequency of the oscillation. D1 For alkali metal D1 line pressure broadening, S0 is the steady-state polarizability, γ e B is the gyromagnetic ratio of electrons. y η is the magnitude of the magnetic field along the y-axis, T2 is the transverse relaxation rate, η is the transmittance of the detection light through the glass of the air chamber each time, E0 is the initial amplitude of the detection light vector, Φ is the phase change of the signal light after passing through the air chamber due to the magnetic field, e is the natural index, and OD is the optical depth.

[0051] 2. The detection laser emits a detection reference light through a 1×2 polarization-maintaining fiber coupler, a fiber EOM, and a second fiber collimator (8). The electric field vector of the reference light is:

[0052]

[0053] In the formula, δ=βsin(ω m t) represents the phase difference applied by the fiber EOM, β represents the modulation depth, and ω represents the phase difference applied by the EOM. m The modulation frequency.

[0054] 3. The light intensity obtained after the detection signal light and reference light are combined and interfered by the depolarization beam splitter (4) and then passed through the lateral displacement polarization beam splitter (5) and photodetector (6) is as follows (θ << 1, φ << 1).

[0055]

[0056] In the formula, and The complex amplitude of the orthogonal electric field vector obtained after interference and passing through a lateral displacement polarization beam splitter is given. and Let I be the corresponding conjugate electric field vector, and I0 be the initial incident detection light intensity.

[0057] 4. After passing through the differential circuit (7) and the transimpedance amplification and modulation / demodulation module in the measurement and control circuit system (IV), the response signal of the atomic magnetometer is obtained as V = GI. out , where G is the conversion coefficient.

[0058] See Figure 1 and Figure 2 This invention provides an atomic magnetometer based on zero-difference and differential detection, such as... Figure 1 and Figure 2 As shown, the atomic magnetometer based on zero-difference and differential detection includes a meter system I, a laser II, and a measurement and control circuit system III, specifically including: a first fiber collimator 1, a linear polarizer 2, a half-wave plate 3, a depolarizing beam splitter 4, a lateral displacement polarizing beam splitter 5, a photodetector 6, a differential circuit 7, a second fiber collimator 8, a third fiber collimator 9, a combined prism 10, a gas chamber 11, an oven 12, a triaxial coil 13, a pump laser 14, a detection laser 15, a 1×2 polarization-maintaining fiber coupler 16, a fiber EOM 17, a fiber flange 18, a polarization-maintaining fiber 19, a measurement and control circuit board 20, and a computer 21.

[0059] like Figure 1 and Figure 2 As shown, the specific implementation steps of the present invention are as follows:

[0060] (1) First, the initial orientation of the fast axis of the linear polarizer, half-wave plate, and fiber EOM is set. The transmission axis of the linear polarizer and the fast axis of the EOM are along the x-axis, and the angle between the fast axis of the half-wave plate and the x-axis is 22.5°. The pump optical path uses the combined prism 10 to achieve the polarization of the alkali metal atom ensemble by the left-hand circularly polarized light. The detection optical path uses a 1×2 polarization-maintaining fiber coupler 16 to achieve 1:1 beam splitting of the detection signal light and the detection reference light, and uses fiber EOM 17 to achieve high-frequency phase modulation of the reference light, thus completing the construction of the optical path system.

[0061] (2) The alkali metal gas chamber 11 is located at the center of the triaxial coil 13 and the triaxial coil 13 is used to compensate for the remaining magnetic field; the oven 12 heats the alkali metal gas chamber 11 to ensure that the alkali metal atomic density in the gas chamber is high.

[0062] (3) The laser frequency output by the pump laser 14 is adjusted to be near the D1 line of the alkali metal atom. The polarization-maintaining fiber 19 and the third fiber collimator 9 are used to couple the laser into the atomic magnetometer probe. Then, the left-hand circularly polarized light is used to polarize the alkali metal atom ensemble in the gas chamber 11 through the combined prism 10.

[0063] (4) The laser direction output by the detection laser 15 is set to make an angle of 45° with the x-axis. A 1×2 polarization-maintaining fiber coupler 16 is used to achieve a 1:1 beam split between the detection signal light and the detection reference light. The signal light is transmitted through the polarization-maintaining fiber 19 to the first fiber collimator 1 and coupled into the atomic magnetometer probe. After passing through the linear polarizer 2, it becomes linearly polarized light and enters the gas cell 11, where the linear polarization angle changes (optical rotation angle θ), thus detecting the atomic precession signal. It then passes through the half-wave plate 3 and reaches the depolarizing beam splitter prism 4, where it interferes with the reference light beam. The optical rotation angle θ and the electric field vector of the signal light are expressed as follows:

[0064]

[0065] n is the atomic number density, l is the optical path length for detecting the interaction between light and polarized alkali metal atoms, and r e Let f be the classical electron radius, c be the speed of light in a vacuum, and f be the speed of light in a vacuum. D1 Γ represents the oscillation intensity of the D1 line of alkali metal atoms, Δν is the detection optical detuning frequency, and Γ is the frequency of the oscillation. D1 For alkali metal D1 line pressure broadening, S0 is the steady-state polarizability, γ e B is the gyromagnetic ratio of electrons. y η is the magnitude of the magnetic field along the y-axis, T2 is the transverse relaxation rate, η is the transmittance of the detection light through the glass of the air chamber each time, E0 is the initial amplitude of the detection light vector, Φ is the phase change of the signal light after passing through the air chamber due to the magnetic field, e is the natural index, and OD is the optical depth.

[0066] (5) After being high-frequency modulated by fiber EOM 17, the reference light is transmitted through polarization-maintaining fiber 19 to the second fiber collimator 8 and coupled into the atomic magnetometer probe. It then interferes with the signal light beam after passing through the depolarization beam splitter 4. The electric field vector of the reference light is:

[0067]

[0068] In the formula, δ=βsin(ω m t) represents the phase difference applied by the fiber EOM, β represents the modulation depth, and ω represents the phase difference applied by the EOM. m The modulation frequency.

[0069] (6) The light intensity obtained after the detection signal light and the reference light pass through the depolarization beam splitter 4 and then through the lateral displacement polarization beam splitter 5 and the photodetector 6 is as follows (θ << 1, φ << 1).

[0070]

[0071] (7) The response signal of the atomic magnetometer obtained after passing through the differential circuit 7 and the transimpedance amplification and modulation / demodulation module in the measurement and control circuit system IV is:

[0072]

[0073] In the formula, G is the conversion coefficient, and I0 is the initial incident detection light intensity. Let be an i-th order Bessel function.

[0074] In summary, the atomic magnetometer based on zero-difference and differential detection of this invention has a simple structure and is easy to manufacture, assemble, and miniaturize. The zero-difference-differential fusion detection mechanism extracts the amplitude and phase information of the magnetic field, improving measurement accuracy and response signal strength. Simultaneously, the interference between the reference light and signal light using high-frequency phase modulation of the fiber optic EOM effectively suppresses low-frequency noise, improving the system's low-frequency sensitivity.

[0075] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. An atomic magnetometer based on zero-difference and differential detection, characterized in that, The system includes a 1×2 polarization-maintaining fiber coupler. The input of the 1×2 polarization-maintaining fiber coupler is connected to a detection laser. The 1×2 polarization-maintaining fiber coupler splits the detection light into a signal light and a reference light. The first output of the 1×2 polarization-maintaining fiber coupler outputs the signal light, and the second output output outputs the reference light. The signal light enters a gas cell and interacts with polarized alkali metal atoms in the gas cell to induce magnetic field information. It then exits and passes through a half-wave plate to enter the first input side of a depolarizing beam splitter. The reference light sequentially passes through… After passing through the fiber EOM and the second fiber collimator, the light enters the second input side of the depolarization beam splitter. The output side of the depolarization beam splitter outputs a combined beam generated by zero-difference coherent mixing of the transmitted signal light from the first input side and the reflected reference light from the second input side. The combined beam is then passed through a lateral displacement polarization beam splitter to generate orthogonal phase signals, which enter a photodetector. The photodetector is connected to a measurement and control circuit system via a differential circuit. The measurement and control circuit system extracts magnetic field information based on a zero-difference and differential fusion detection mechanism formed by the two orthogonal signals.

2. The atomic magnetometer based on zero-difference and differential detection according to claim 1, characterized in that, The measurement and control circuit system includes a function generation module, a transimpedance amplification module, a modulation and demodulation module, a low-pass filter module, and a data acquisition module. The output of the data acquisition module is connected to a computer, and the input of the data acquisition module is connected to the output of the low-pass filter module. The input of the low-pass filter module is connected to the output of the modulation and demodulation module, the input of the modulation and demodulation module is connected to the output of the transimpedance amplification module, and the input of the transimpedance amplification module is connected to the output of the differential circuit.

3. The atomic magnetometer based on zero-difference and differential detection according to claim 2, characterized in that, The air chamber is located inside the oven, which is located inside the triaxial coil, and the triaxial coil is connected to the function generating module.

4. The atomic magnetometer based on zero difference and differential detection according to claim 3, characterized in that, The triaxial coil is equipped with a first fiber collimator, a third fiber collimator, a second fiber collimator, and a differential circuit. The input end of the first fiber collimator is connected to the first output end of the 1×2 polarization-maintaining fiber coupler in sequence through a polarization-maintaining fiber and a fiber flange. The output end of the first fiber collimator is connected to the signal light input side of the gas cell through a linear polarizer. The input side of the third fiber collimator is connected to the pump laser, and the output side of the third fiber collimator is connected to the pump light incident side of the gas cell through a combined prism.

5. The atomic magnetometer based on zero-difference and differential detection according to claim 1, characterized in that, Including the following expressions: δ=βsin(ω m t), Where E sig ω is the electric field vector of the transmitted signal light, E0 is the initial amplitude of the detection light vector, η is the transmittance of the detection light through the gas chamber glass each time, e is the natural constant, i is the imaginary unit, ω is the frequency of the transmitted signal light, t is time, φ is the phase change of the signal light after passing through the gas chamber due to the magnetic field, OD is the optical depth, and θ is the optical rotation angle. It is the x-axis component label. It is the y-axis component label; E ref δ is the electric field vector of the reflected reference light, β is the phase difference applied by the fiber EOM, β is the modulation depth, and ω is the electric field vector of the reflected reference light. m The modulation frequency.

6. The atomic magnetometer based on zero difference and differential detection according to claim 1, characterized in that, Including the following expressions: V=GI out , Where I out It is the light intensity detected by the photodetector. It is the complex amplitude of the orthogonal electric field vector along the x-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector, It is the complex amplitude of the orthogonal electric field vector along the y-axis obtained through a lateral displacement polarization beam splitter. yes The conjugate electric field vector is given by I0, the initial incident detection light intensity is given by V, the atomic magnetometer response signal output by the modulation and demodulation module is given by G, and the conversion coefficient is given by G.

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