Very-low-frequency atom magnetometer environmental interference suppression method based on polarization selective receiving

Abstract

The invention provides a very-low-frequency atom magnetometer environment interference suppression method based on polarization selection receiving. A main magnetic field coil applies precession main magnetic fields Be and-Be in the front area and the rear area of an air chamber in the z direction and the-z direction respectively; detecting precession of spin projection signals of atoms in Be and-Be regions in the x direction by using detection laser in the x direction; an external very-low-frequency signal interacts with atoms polarized in the z direction to enable the atoms to generate precession signals on an xOy plane, so that the external very-low-frequency signal is detected by detection light; when an external signal is linearly polarized, atomic precession signals in Be and-Be regions are mutually offset according to a selection rule of angular momentum conservation, so that the system does not respond to the linear polarization signal, and for a circular polarization signal, only atoms in the Be or-Be region have precession signals, thereby realizing detection of the circular polarization signal. By applying the technical scheme of the invention, the technical problem of environmental magnetic noise interference caused by a very-low-frequency atom magnetometer in an actual application scene in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the field of quantum sensing technology, and in particular to a method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception. Background Art

[0002] In recent years, with the continuous development of quantum precision measurement technology, atomic magnetometer technology based on the atomic spin precession effect has achieved remarkable achievements in the field of high-sensitivity measurement of weak magnetic fields, especially in the field measurement of femtometers. Compared with its competitor, the superconducting quantum interference device (SQUID), atomic magnetometers have outstanding advantages in engineering applications such as small volume integration and room temperature operation, while not lagging behind in measurement sensitivity. They have shown great potential application value in the fields of communication, exploration, and magnetic imaging, especially in the field of very low frequency communication. Compared with traditional very low frequency magnetic induction coil technology, the sensitivity of very low frequency atomic magnetometers can be 3 orders of magnitude higher under the same effective sensing volume. The very low frequency atomic magnetometer technology based on atomic magnetometers will bring revolutionary development to this field. However, the performance test of very low frequency atomic magnetometers is more realized in the heavily shielded environment under the laboratory, such as in a multi-layer magnetic shielding room. In non-shielded environment applications such as very low frequency atomic magnetometers, the influence of environmental magnetic field noise will limit their performance. Therefore, noise suppression technology in non-shielded environments is an important issue that needs to be solved in the application of very low frequency atomic magnetometers. Summary of the invention

[0003] The present invention provides a method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception, which can solve the technical problem of environmental magnetic noise interference caused by the very low frequency atomic magnetometer in actual application scenarios in the prior art.

[0004] According to one aspect of the present invention, a method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception is provided. The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception comprises: using a driving laser to polarize alkali metal atoms in an atomic gas chamber along the driving laser direction (z direction); the external magnetic field at the atomic gas chamber is compensated by a three-axis magnetic field coil and a three-axis magnetic sensor to provide a zero field environment, and the main magnetic field B e Coil and main magnetic field-B e The coil applies a precession main magnetic field B of equal magnitude and opposite direction in the z direction and -z direction in the front and rear regions of the air chamber. e and -B e ; In the x direction, the detection laser is used to simultaneously detect B e with -B eThe precession of the spin projection signal of the atoms in the region in the x direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as the external very low frequency signal. The atoms are manipulated by the pump laser and the detection laser. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF=+1, under the action of the circularly polarized pump laser, the atoms will be pumped to m f =F max The magnetic quantum number is the largest quantum state, thereby realizing polarization. The system quantization axis points along the driving laser, and the polarized atomic spin points to the positive z direction. For the main magnetic field B e In the region, the polarized atomic spins point to the same direction as B e Same, along the positive z direction, for the main magnetic field is -B e In the region, the polarized atomic spins are directed in the same direction as -B e On the contrary, also along the positive z direction, the very low frequency electromagnetic signal propagating in the z direction and vibrating in the xy plane will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency of γBe, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and the frequency is greatly detuned from the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroism effect plays a dominant role. The detection laser signal will change with the precession of the atomic spin. When the received very low frequency signal is a linearly polarized signal, according to the transition selection rule, the polarized atoms in the two magnetic field regions can absorb the electromagnetic signal, thereby generating precession. Since the directions of the precession magnetic fields in the two regions are opposite, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite, so the precession of the detection light after passing through the two regions will cancel each other, and finally appear as no signal. When the received signal is σ - For circularly polarized signals, according to the transition selection rule, only B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, -B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e Area B will be detected e The atomic precession in the region can detect the very low frequency signal; when the received signal is σ + For circularly polarized signals, according to the transition selection rule, only -B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e After the area will be detected -B e The atomic precession in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization selective reception.

[0005] Furthermore, the pumping laser generated by the pumping light laser sequentially passes through the first Glan Taylor prism and the quarter wave plate before entering the atomic gas chamber, and polarizes the alkali metal atoms by interacting with the alkali metal atoms in the atomic gas chamber; the detection laser generated by the detection light laser sequentially passes through the second half wave plate, the second Glan Taylor prism and the second reflector before entering the atomic gas chamber, and the detection laser emitted from the atomic gas chamber is reflected by the first reflector and then passes through the first half wave plate and the Wollaston prism before entering the balanced zero-beat detector, and the signal collected by the balanced zero-beat detector is output to the data acquisition and control system; a three-axis magnetic field coil, a three-axis flux gate, and a main magnetic field B are arranged outside the atomic gas chamber. e Coil and main magnetic field-B e Coil, main magnetic field B e The coil is used to generate the main magnetic field B in the positive z direction. e , main magnetic field-B e The coil is used to generate e The main magnetic field in the opposite negative z direction - B e .

[0006] Furthermore, since the Faraday rotation angle θ of light is proportional to the polarization projection size P of the spin ensemble in the x direction x , that is: θ∝P x The detection laser passes through two atomic ensembles with opposite main magnetic fields successively, and the signal output by the balanced zero-beat detector is proportional to the polarization projection size P of the spin ensemble in the x direction. x , P x =M1cos(ωt)-M2cos(ωt), where the amplitude M1 is the B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, the amplitude M1 is equal to the amplitude M2, so the system does not respond to linearly polarized very low frequency signals; for σ + Circularly polarized VLF signal, only the main magnetic field is B e The regional response, the main magnetic field is -B e The area does not respond, that is, M2 = 0, so the final detection signal is proportional to: M1cos(ωt); for σ - Circularly polarized VLF signal, only the main magnetic field is -B e There is a precession signal in the atomic region, so M1=0, and the final output is proportional to: -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

[0007] Furthermore, for circularly polarized signals, the phase difference of the signal received by the system is 180°, so the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization; through polarization selective reception, the interference of environmental linear polarization noise can be effectively suppressed, and at the same time, a communication technology with stronger anti-interference can be realized based on specific polarization.

[0008] Furthermore, the Faraday rotation angle θ can be calculated according to Calculate and obtain, where I1 is the light intensity of the first laser output by the Wollaston prism, I2 is the light intensity of the second laser output by the Wollaston prism, I0=I1+I2, and I0 is the total light intensity of the two laser beams.

[0009] According to another aspect of the present invention, a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception is provided. The very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception as described above to perform very low frequency atomic magnetometer environmental interference suppression.

[0010] Furthermore, the environmental interference suppression system of the very low frequency atomic magnetometer based on polarization selective reception includes a pumping light laser, a first Glan-Taylor prism, a quarter wave plate, an atomic gas chamber, a first reflector, a first half wave plate, a Wollaston prism, a balanced zero-beat detector, a data acquisition and control system, a detection light laser, a second half wave plate, a second Glan-Taylor prism, a second reflector, a three-axis magnetic field coil, a three-axis fluxgate, and a main magnetic field B. e Coil and main magnetic field-B e Coil, the pumping laser generated by the pumping light laser passes through the first Glan Taylor prism and the quarter wave plate in sequence and then enters the atomic gas chamber, and realizes the polarization of the alkali metal atoms by interacting with the alkali metal atoms in the atomic gas chamber; the detection laser generated by the detection light laser passes through the second half wave plate, the second Glan Taylor prism and the second reflector in sequence and then enters the atomic gas chamber, the detection laser emitted by the atomic gas chamber is reflected by the first reflector, and then passes through the first half wave plate and the Wollaston prism and enters the balanced zero-beat detector, and the signal collected by the balanced zero-beat detector is output to the data acquisition and control system; three-axis magnetic field coil, three-axis fluxgate, main magnetic field B e Coil and main magnetic field-B e The coil is set outside the atomic gas chamber, and the main magnetic field B e The coil is used to generate the main magnetic field B in the positive z direction. e , main magnetic field-B e The coil is used to generate e The main magnetic field in the opposite negative z direction - B e .

[0011] The technical solution of the present invention is applied to provide a very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception. The method can detect very low frequency magnetic field signals. At the same time, by cleverly using the quantum mechanics law of conservation of angular momentum, the very low frequency atomic magnetometer selectively receives the polarization state of the radio frequency magnetic signal in a novel way, thereby realizing a new very low frequency atomic magnetometer design that can suppress environmental noise, and providing a new way to suppress environmental noise of very low frequency atomic magnetometers in non-shielded environments, thereby realizing efficient wireless communication technology based on this. Therefore, compared with the prior art, the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception provided by the present invention can realize polarization selective reception of very low frequency signals and separate detection of specific circularly polarized signals; it can effectively suppress the interference of linear polarization noise in the environment; based on specific polarized electromagnetic waves, efficient anti-interference communication can be realized. In addition, on the basis of selectively receiving circularly polarized electromagnetic waves, the invention can further judge the polarity of circular polarization through phase information to realize two circularly polarized signals; the method and system are simple, and it is easy to realize the miniaturization integration of sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 A schematic structural diagram of a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception according to a specific embodiment of the present invention is shown;

[0014] Figure 2a The method according to the specific embodiment of the present invention shows that when the received very low frequency signal is a linearly polarized signal, the magnetic field B e and -B e Schematic diagram of the precession signal generated when

[0015] Figure 2b The example of the embodiment of the present invention shows that when the received very low frequency signal is σ - When circularly polarized, it passes through magnetic field B e and -B e Schematic diagram of the precession signal generated when

[0016] Figure 2c The example of the embodiment of the present invention shows that when the received very low frequency signal is σ + When the circularly polarized signal passes through the magnetic field B e and -Be Schematic diagram of the precession signal generated when .

[0017] The above drawings include the following reference numerals:

[0018] 10. Pumping laser; 20. First Glan-Taylor prism; 30. Quarter wave plate; 40. Atomic gas chamber; 50. First reflector; 60. First half wave plate; 70. Wollaston prism; 80. Balanced zero-beat detector; 90. Data acquisition and control system; 100. Detection laser; 110. Second half wave plate; 120. Second Glan-Taylor prism; 130. Second reflector; 140. Three-axis magnetic field coil; 150. Three-axis fluxgate; 160. Main magnetic field B e Coil; 170, main magnetic field-B e Coil. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0021] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0022] like Figure 1 to Figure 2c As shown, according to a specific embodiment of the present invention, a very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception is provided, and the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception comprises: using a driving laser to polarize the alkali metal atoms in the atomic gas chamber along the driving laser direction (z direction); the external magnetic field at the atomic gas chamber is compensated by a three-axis magnetic field coil and a three-axis magnetic sensor to provide a zero field environment, and the main magnetic field B e Coil 160 and main magnetic field-B e The coil 170 applies a precession main magnetic field B of equal magnitude and opposite direction in the front and rear regions of the atomic gas chamber along the z direction and the -z direction respectively. e and -B e ; In the x direction, the detection laser is used to simultaneously detect B e with -B e The precession of the spin projection signal of the atoms in the region in the x direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as the external very low frequency signal. The atoms are manipulated by the pump laser and the detection laser. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF=+1, under the action of the circularly polarized pump laser, the atoms will be pumped to m f =F max The magnetic quantum number is the largest quantum state, thereby realizing polarization. The system quantization axis points along the driving laser, and the polarized atomic spin points to the positive z direction. For the main magnetic field B e In the region, the polarized atomic spins point to the same direction as B e Same, along the positive z direction, for the main magnetic field is -B e In the region, the polarized atomic spins are directed in the same direction as -B eOn the contrary, also along the positive z direction, the very low frequency electromagnetic signal propagating in the z direction and vibrating in the xy plane will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency of γBe, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and the frequency is greatly detuned from the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroism effect plays a dominant role. The detection laser signal will change with the precession of the atomic spin. When the received very low frequency signal is a linearly polarized signal, according to the transition selection rule, the polarized atoms in the two magnetic field regions can absorb the electromagnetic signal, thereby generating precession. Since the directions of the precession magnetic fields in the two regions are opposite, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite, so the precession of the detection light after passing through the two regions will cancel each other, and finally appear as no signal. When the received signal is σ - For circularly polarized signals, according to the transition selection rule, only B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, -B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e Area B will be detected e The atomic precession in the region can detect the very low frequency signal; when the received signal is σ + For circularly polarized signals, according to the transition selection rule, only -B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e After the area will be detected -B e The atomic precession in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization selective reception.

[0023] By applying this configuration, a method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception is provided. Considering that in wireless communication, the use of polarization selective reception can improve the selectivity and anti-interference ability of the signal and effectively suppress the interference of noise. For example, in wireless communication, since the signal may be subject to various interferences during the propagation process, the use of a polarization selective receiving antenna can effectively distinguish and select the required signal, and effectively filter out signals of other polarization states, thereby improving the purity of the received signal and achieving the purpose of improving the communication quality. For example, in satellite communication, the interference caused by atmospheric and ground reflections can be reduced by selecting a specific polarization state; in radar systems, polarization characteristics can be used to distinguish targets from clutter and improve the accuracy of target detection; in wireless networks, signal attenuation and interference can be reduced by polarization selection in a multipath propagation environment. Based on this, the present invention aims at the noise suppression problem of the very low frequency atomic magnetometer in a non-shielded environment, designs a polarization selective receiving dual-channel very low frequency atomic magnetometer solution, which can detect very low frequency magnetic field signals, and at the same time, by cleverly using the quantum mechanics law of conservation of angular momentum, the very low frequency atomic magnetometer selectively receives the polarization state of the radio frequency magnetic signal in a novel way, thereby realizing a new very low frequency atomic magnetometer design that can suppress environmental noise, and provides a new way to suppress environmental noise of the very low frequency atomic magnetometer in a non-shielded environment, thereby realizing efficient wireless communication technology based on this. Therefore, compared with the prior art, the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception provided by the present invention can realize polarization selective reception of very low frequency signals, realize separate detection of specific circularly polarized signals; can effectively suppress the interference of linear polarization noise in the environment; based on specific polarized electromagnetic waves, can realize efficient anti-interference communication. In addition, on the basis of selectively receiving circularly polarized electromagnetic waves, the invention can further judge the polarity of circular polarization through phase information, and realize two circularly polarized signals; the method and system are simple, and it is easy to realize the miniaturization integration of sensors.

[0024] Furthermore, the pumping laser generated by the pumping light laser 10 passes through the first Glan Taylor prism 20 and the quarter wave plate 30 in sequence and then enters the atomic gas chamber 40, and polarizes the alkali metal atoms by interacting with the alkali metal atoms in the atomic gas chamber 40; the detection laser generated by the detection light laser 100 passes through the second half wave plate 110, the second Glan Taylor prism 120 and the second reflector 130 in sequence and then enters the atomic gas chamber 40, and the detection laser emitted from the atomic gas chamber 40 is reflected by the first reflector 50 and then passes through the first half wave plate 60 and the Wollaston prism 70 and then enters the balanced zero-beat detector 80, and the signal collected by the balanced zero-beat detector 80 is output to the data acquisition and control system 90; a three-axis magnetic field coil 140, a three-axis flux gate 150, and a main magnetic field B are arranged outside the atomic gas chamber 40. e Coil 160 and main magnetic field-Be Coil 170, main magnetic field B e Coil 160 is used to generate a main magnetic field B in the positive z direction. e , main magnetic field-B e Coil 170 is used to generate e The main magnetic field in the opposite negative z direction - B e When detecting the very low frequency signal, the data acquisition and control system first controls the ambient magnetic field of the air chamber according to the real-time measurement information of the three-axis flux gate, so that the magnetic fields in the x, y and z directions are 0; on this basis, the main magnetic field B e Coil and main magnetic field-B e The coil applies a resonant main magnetic field B of equal magnitude and opposite direction along the z direction in two different regions of the air chamber. e and -B e .

[0025] Specifically, in the present invention, since the Faraday rotation angle θ of light is proportional to the polarization projection size P of the spin ensemble in the x direction x , that is: θ∝P x , the Faraday rotation angle θ can be calculated according to Calculate and obtain, where I1 is the intensity of the first laser output by the Wollaston prism 70, I2 is the intensity of the second laser output by the Wollaston prism 70, I0 = I1 + I2, I0 is the sum of the intensities of the two lasers. The detection laser passes through two atomic ensembles with opposite main magnetic fields in succession, and the signal output by the balanced zero-beat detector 80 is proportional to the polarization projection size P of the spin ensemble in the x direction. x , P x =M1cos(ωt)-M2cos(ωt), where the amplitude M1 is the B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, the amplitude M1 is equal to the amplitude M2, so the system does not respond to linearly polarized very low frequency signals; for σ + Circularly polarized VLF signal, only the main magnetic field is B e The regional response, the main magnetic field is -B e The area does not respond, that is, M2 = 0, so the final detection signal is proportional to: M1cos(ωt); for σ - Circularly polarized VLF signal, only the main magnetic field is -B e There is a precession signal in the atomic region, so M1=0, and the final output is proportional to: -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

[0026] In the present invention, for circularly polarized signals, the phase difference of the signal received by the system is 180°, so the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization; through polarization selective reception, the interference of environmental linear polarization noise can be effectively suppressed, and at the same time, a communication technology with stronger anti-interference can be realized based on a specific polarization.

[0027] According to another aspect of the present invention, a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception is provided. The very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception as described above to perform very low frequency atomic magnetometer environmental interference suppression.

[0028] By applying this configuration, a very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception is provided. The system can realize polarization selective reception of very low frequency signals and separate detection of specific circular polarization signals; it can effectively suppress the interference of linear polarization noise in the environment; based on specific polarized electromagnetic waves, efficient anti-interference communication can be achieved. In addition, based on the selective reception of circularly polarized electromagnetic waves, the invention can further determine the polarity of circular polarization through phase information and realize two circular polarization signals; the method and system are simple and easy to realize miniaturized integration of sensors.

[0029] Specifically, Figure 1 As shown, the environmental interference suppression system of the very low frequency atomic magnetometer based on polarization selective reception includes a pumping light laser 10, a first Glan-Taylor prism 20, a quarter wave plate 30, an atomic gas chamber 40, a first reflector 50, a first half wave plate 60, a Wollaston prism 70, a balanced zero-beat detector 80, a data acquisition and control system 90, a detection light laser 100, a second half wave plate 110, a second Glan-Taylor prism 120, a second reflector 130, a three-axis magnetic field coil 140, a three-axis fluxgate 150, and a main magnetic field B e Coil 160 and main magnetic field-B e Coil 170, the pumping laser generated by the pumping light laser 10 passes through the first Glan Taylor prism 20 and the quarter wave plate 30 in sequence and then enters the atomic gas chamber 40, and realizes the polarization of the alkali metal atoms by interacting with the alkali metal atoms in the atomic gas chamber 40; the detection laser generated by the detection light laser 100 passes through the second half wave plate 110, the second Glan Taylor prism 120 and the second reflector 130 in sequence and then enters the atomic gas chamber 40, and the detection laser emitted from the atomic gas chamber 40 is reflected by the first reflector 50, and then passes through the first half wave plate 60 and the Wollaston prism 70 and enters the balanced zero beat detector 80, and the signal collected by the balanced zero beat detector 80 is output to the data acquisition and control system 90; the three-axis magnetic field coil 140, the three-axis flux gate 150, the main magnetic field Be Coil 160 and main magnetic field-B e The coil 170 is disposed outside the atomic gas chamber 40, and the main magnetic field B e Coil 160 is used to generate a main magnetic field B in the positive z direction. e , the main magnetic field - Be coil 170 is used to generate the B e The main magnetic field in the opposite negative z direction - B e .

[0030] In order to further understand the present invention, the following Figure 1 2 and FIG. 3 illustrate in detail the method and system for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception provided by the present invention.

[0031] like Figure 1 As shown in FIG2 , in order to solve the problem of environmental magnetic noise interference caused by very low frequency atomic magnetometers in actual application scenarios, the present invention designs a dual-channel destructive very low frequency atomic magnetometer method and system based on the transition selection rule caused by the conservation of angular momentum, so as to realize polarization selective reception of very low frequency radio signals. Based on this, specific radio polarization states can be used for transmission and reception, thereby effectively suppressing the interference of environmental noise.

[0032] The technical solutions adopted to achieve the above objectives are as follows: (1) the alkali metal atoms in the atomic gas chamber are polarized along the driving laser direction (z direction) by using a driving laser; (2) the external magnetic field in the gas chamber is compensated by a three-axis magnetic coil and a three-axis magnetic sensor to provide a zero-field environment, and the main magnetic field coil applies a precession main magnetic field B in the front and rear areas of the gas chamber along the z direction and -z direction respectively. e and -B e ; (3) In the x direction, use the detection laser to simultaneously detect B e with -B e The precession of the spin projection signal of the atoms in the region in the x direction is detected. The precession amplitude is proportional to the amplitude of the external VLF signal, and the frequency is the same as the external VLF signal, thereby realizing the detection of the VLF signal; (4) The external VLF signal interacts with the atoms polarized in the z direction to generate a precession signal in the xOy plane, which is then detected by the detection light. When the external signal is linearly polarized, according to the selection rule of conservation of angular momentum, B e and -B e The atomic precession signals in the B region cancel each other out, so the system does not respond to linear polarization signals. e or -B e The atoms in the area will have precession signals, thereby realizing the detection of circular polarization signals.

[0033] The beneficial effects of the present invention are: it can realize polarization selective reception of very low frequency signals and separate detection of specific circularly polarized signals; it can effectively suppress the interference of linear polarization noise in the environment; and based on specific polarized electromagnetic waves, it can realize efficient anti-interference communication.

[0034] Additional beneficial effects: Based on the selective reception of circularly polarized electromagnetic waves, the present invention can further determine the polarity of circular polarization through phase information, thereby realizing two circularly polarized signals; the method and system are simple and easy to realize miniaturized integration of sensors.

[0035] The specific implementation principle of this solution is as follows:

[0036] The very low frequency atomic magnetometer uses the Larmor precession of atomic spins under the resonance of the main magnetic field to detect the magnetic field component of the very low frequency radio signal, thereby receiving the very low frequency radio signal. The present invention uses the superposition of the precession signals of the atomic spin ensemble in the opposite direction of the main magnetic field to realize polarization selective reception. The basic principle is shown in the figure. The atoms are manipulated by the pumping light and the detection light. The pumping light is σ + Circularly polarized light resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = +1, under the action of circularly polarized pump light, the atoms will be pumped to m f =F max The magnetic quantum number is the largest quantum state, thus achieving polarization, the system quantization axis points along the driving light, and the polarized atomic spin points to the positive z direction. e The polarized atomic spins point to the same direction as B e Same, along the positive z direction. For, the main magnetic field is -B e In the region, the polarized atomic spins are directed in the same direction as -B e On the contrary, it is also in the positive z direction. The very low frequency electromagnetic signal propagating in the z direction and vibrating in the xy plane will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to revolve around the z axis at a frequency of γB e Precession, γ is the gyromagnetic ratio of the alkali metal atoms. The detection laser is linearly polarized, and its frequency is greatly detuned from the resonance frequency of the alkali metal atoms, so that the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroic effect plays a dominant role. The detection light signal will change with the precession of the atomic spin. When the received very low frequency signal is a linearly polarized signal (as shown in Case 1 in the figure), according to the transition selection rule, the polarized atoms in the two magnetic field regions can absorb the electromagnetic signal, thereby generating precession. Since the directions of the precession magnetic fields in the two regions are opposite, according to the right-hand rule, the precession directions of the atoms in the two regions are also opposite, so the precession of the detection light after passing through the two regions will cancel each other, and ultimately appear as no signal. When the received signal is σ - In the case of circular polarization (as shown in case 2 in the figure), according to the transition selection rule, only B eThe atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal represented by -B e There is no atomic precession signal in the area, and the detection light passes through B e with -B e Area B will be detected e The atomic precession in the region can detect the very low frequency signal. + Circular polarization signal (as shown in case 3 in the figure), similarly only -B e The regional atoms will interact with it, thereby realizing the detection of the polarization signal.

[0037] Physical Implementation

[0038] A typical physical implementation structure is as follows Figure 1 As shown, the system mainly includes pumping laser, detection laser, quarter wave plate, half wave plate, Glan Taylor prism, Wollaston prism, three-axis magnetic compensation coil, three-axis flux gate, B e Main magnetic field coil, -B e It consists of main magnetic field coil, atomic gas chamber, reflector, balanced zero-beat detector, data acquisition and control system.

[0039] Function of each component

[0040] Pumping laser: generates pumping laser; Detection laser: generates detection laser; Quarter wave plate: changes laser polarization, mainly used to convert linear polarized light into circular polarized light; Half wave plate: changes laser polarization, mainly used to change the polarization direction of linear polarized light; Glan Taylor prism: performs polarization splitting on the light beam, used here to purify the polarization of the transmitted laser to ensure that it is horizontally polarized (polarized in the x direction); Wollaston prism: performs polarization splitting on the light beam, so that the vertical (y direction) and horizontal (x direction) polarized light are separated in spatial propagation; Three-axis magnetic field coil: generates a magnetic field in three directions, which is controlled by the acquisition and control system to offset the interference of the ambient magnetic field; Three-axis fluxgate: used to detect the size of the ambient magnetic field in the gas chamber in real time, and the result is input into the acquisition and control system as a feedback variable; Main magnetic field B e Coil: used to generate the main magnetic field B in the positive z direction e ; Main magnetic field-B e Coil: used to generate B e The main magnetic field in the opposite negative z direction - B e ; Atomic gas chamber: the core working device, providing an atomic ensemble for detecting very low frequency signals; reflector: changes the direction of the light beam; balanced zero-beat detector: converts the precession information detected by the detection light into a differential electrical signal for output; data acquisition and control system: collects and processes data, and performs feedback control on the system.

[0041] How it works

[0042] After the pump laser generated by the pump laser is polarized and purified by the Glan-Taylor prism, the transmitted light polarized in the x direction is transformed into the circularly polarized laser required by the very low frequency atomic magnetometer system through a quarter wave plate and then emitted into the gas cell, where it interacts with the alkali metal atoms in the gas cell to polarize them.

[0043] The laser beam emitted from the detection light laser is polarized and purified by the Glan Taylor mirror, and then enters the gas chamber through the reflector in the polarization state of linear polarization in the x direction. The transmitted light through the gas chamber is adjusted by a half-wave plate, and then divided into two laser beams with orthogonal polarization directions by the Wollaston prism. The light intensity of the two laser beams is related to the Faraday rotation angle after passing through the gas chamber, which can be specifically expressed as:

[0044]

[0045] Where I0=I1+I2 is the sum of the light intensities of the two laser beams, I1 is the light intensity of laser 1, and I2 is the light intensity of laser 2. θ is the Faraday rotation angle after the laser passes through the gas cell, which is related to the polarization intensity of the atoms in the gas cell in the direction of laser propagation. The light intensities of the two laser beams are received by the two photodetectors of the balanced zero-beat detector behind them. The Faraday rotation angle can be obtained from the signals of the two photodetectors:

[0046]

[0047] Therefore, the differential result (I2-I1) output by the balanced zero-beat detector is directly proportional to the Faraday rotation angle θ. When detecting the very low frequency signal, the data acquisition and control system first controls the ambient magnetic field of the air chamber according to the real-time measurement information of the three-axis flux gate, so that the magnetic field in the x, y and z directions is 0; on this basis, the main magnetic field B e Coil and main magnetic field-B e The coil applies a resonant main magnetic field B of equal magnitude and opposite direction along the z direction in two different regions of the air chamber. e and -B e Since the Faraday rotation angle θ of light is proportional to the polarization projection size P of the spin ensemble in the x direction x , that is: θ∝P x Since the detection light passes through two atomic ensembles with opposite main magnetic fields, the signal output by the balanced zero-beat detector is proportional to: P x =M1cos(ωt)-M2cos(ωt), where the amplitudes M1 and M2 are the B of the atom under the action of the very low frequency signal. e Main magnetic field area and -B eThe amplitude of the atomic precession signal in the main magnetic field region. For linearly polarized VLF signals, according to the above principle, M1=M2, so the system does not respond to linearly polarized VLF signals. For circularly polarized VLF signals, according to the above principle, for σ + Polarization, only the main magnetic field is B e The regional response, the main magnetic field is -B e The area does not respond, that is, M2 = 0, so the final detection signal is proportional to: M1cos(ωt). Similarly, for σ - Circular polarization, only the main magnetic field is -B e There is a precession signal in the atomic region, so M1=0, so the final output is proportional to: -M2cos(ωt), thus achieving selective reception of circularly polarized signals. Furthermore, for circularly polarized signals, the phase difference of the signal received by the system is 180°, so the polarization of the detected signal can be determined by the phase information, thereby further achieving circular polarization resolution. Through polarization selective reception, the interference of environmental linear polarization noise can be effectively suppressed, and at the same time, a communication technology with stronger anti-interference can be achieved based on a specific polarization.

[0048] In summary, in order to solve the problem of environmental magnetic noise interference caused by very low frequency atomic magnetometers in actual application scenarios, the present invention designs a dual-channel destructive very low frequency atomic magnetometer method and system based on the transition selection rule caused by the conservation of angular momentum, so as to realize polarization selective reception of very low frequency radio signals. Based on this, specific radio polarization states can be used for transmission and reception, effectively suppressing the interference of environmental noise.

[0049] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0050] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception, characterized in that: The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception comprises: The driving laser is used to polarize the alkali metal atoms in the atomic gas chamber along the driving laser direction (z direction); the external magnetic field in the atomic gas chamber is compensated by the three-axis magnetic field coil and the three-axis magnetic sensor to provide a zero-field environment. e Coil (160) and main magnetic field-B e The coil (170) applies a precession main magnetic field B of equal magnitude and opposite direction in the front and rear regions of the atomic gas chamber respectively along the z direction and the -z direction. e and -B e ; In the x direction, the detection laser is used to simultaneously detect B e with -B e The precession of the spin projection signal of the atoms in the region in the x direction is detected. The precession amplitude is proportional to the amplitude of the external very low frequency signal, and the frequency is the same as the external very low frequency signal. The atoms are manipulated by pump laser and probe laser. The pump laser is σ+ circularly polarized light, which resonates with the D1 line of alkali metal atoms. Due to the transition selection rule ΔF = +1, the atoms will be pumped to m under the action of circularly polarized pump laser. f =F max The magnetic quantum number is the largest quantum state, thereby realizing polarization. The system quantization axis points along the driving laser, and the polarized atomic spin points to the positive z direction. For the main magnetic field B e In the region, the polarized atomic spins point to the same direction as B e Same, along the positive z direction, for the main magnetic field is -B e In the region, the polarized atomic spins are directed in the same direction as -B e On the contrary, also along the positive z direction, the very low frequency electromagnetic signal propagating in the z direction and vibrating in the xy plane will be absorbed by the polarized atoms, causing the polarization vector to deviate from the z direction and begin to precess around the z axis at a frequency of γBe, where γ is the gyromagnetic ratio of the alkali metal atom. The detection laser is linearly polarized, and the frequency is greatly detuned from the resonance frequency of the alkali metal atom. Therefore, the absorption of the detection laser by the atomic ensemble can be ignored, and the dichroic effect plays a dominant role. The detection laser signal will change with the precession of the atomic spin. When the received VLF signal is a linearly polarized signal, according to the transition selection rule, the polarized atoms in the two magnetic field regions can absorb the electromagnetic signal, thereby generating precession. Since the precession magnetic fields in the two regions are in opposite directions, the precession directions of the atoms in the two regions are also opposite according to the right-hand rule. Therefore, the precession of the detection light after passing through the two regions will cancel each other out, and finally appear as no signal. When the received signal is σ - For circularly polarized signals, according to the transition selection rule, only B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, -B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e Area B will be detected e The atomic precession in the region can detect the very low frequency signal; when the received signal is σ + For circularly polarized signals, according to the transition selection rule, only -B e The atoms in the region will interact with the electromagnetic field under this polarization, thus generating a precession signal, B e There is no atomic precession signal in the area, and the detection laser passes through B e with -B e After the area will be detected -B e The atomic precession in the region enables the detection of very low frequency signals, thereby completing the environmental interference suppression of the very low frequency atomic magnetometer based on polarization selective reception.

2. The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception according to claim 1, characterized in that: The pumping laser light generated by the pumping light laser (10) passes through a first Glan Taylor prism (20) and a quarter wave plate (30) in sequence and then enters an atomic gas chamber (40), and polarizes the alkali metal atoms in the atomic gas chamber (40) by interacting with the alkali metal atoms in the atomic gas chamber (40); the detection laser light generated by the detection light laser (100) passes through a second half wave plate (110), a second Glan Taylor prism (120) and a second reflecting mirror (130) in sequence and then enters the atomic gas chamber (40); the detection laser light emitted from the atomic gas chamber (40) is reflected by a first reflecting mirror (50) and then passes through a first half wave plate (60) and a Wollaston prism (70) and then enters a balanced zero beat detector (80); the signal collected by the balanced zero beat detector (80) is output to a data acquisition and control system (90); a three-axis magnetic field coil (140), a three-axis flux gate (150), and a main magnetic field B are arranged outside the atomic gas chamber (40); e Coil (160) and main magnetic field-B e Coil (170), the main magnetic field B e The coil (160) is used to generate a main magnetic field B in the positive z direction. e , the main magnetic field-B e The coil (170) is used to generate a e The main magnetic field in the opposite negative z direction - B e .

3. The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception according to claim 2, characterized in that: Since the Faraday rotation angle θ of light is proportional to the polarization projection size P of the spin ensemble in the x direction x , that is: θ∝P x The detection laser passes through two atomic ensembles with opposite main magnetic fields in sequence, and the signal output by the balanced zero-beat detector (80) is proportional to the polarization projection size P of the spin ensemble in the x direction. x , P x =M1cos(ωt)-M2cos(ωt), where the amplitude M1 is the B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region, M2 is the -B of the atom under the action of the very low frequency signal e The amplitude of the atomic precession signal in the main magnetic field region; for linearly polarized very low frequency signals, the amplitude M1 is equal to the amplitude M2, so the system does not respond to linearly polarized very low frequency signals; for σ + Circularly polarized VLF signal, only the main magnetic field is B e The regional response, the main magnetic field is -B e The area does not respond, that is, M2 = 0, so the final detection signal is proportional to: M1cos(ωt); for σ - Circularly polarized VLF signal, only the main magnetic field is -B e There is a precession signal in the atomic region, so M1=0, and the final output is proportional to: -M2cos(ωt), thereby achieving selective reception of circularly polarized signals.

4. The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception according to claim 3, characterized in that: For circularly polarized signals, the phase difference of the signal received by the system is 180°, so the polarization of the detected signal can be determined by the phase information, thereby further realizing the resolution of circular polarization; through polarization selective reception, the interference of environmental linear polarization noise can be effectively suppressed, and at the same time, a communication technology with stronger anti-interference can be realized based on specific polarization.

5. The method for suppressing environmental interference of a very low frequency atomic magnetometer based on polarization selective reception according to claim 3, characterized in that: The Faraday rotation angle θ can be calculated according to Calculate and obtain, wherein I1 is the light intensity of the first laser output by the Wollaston prism (70), I2 is the light intensity of the second laser output by the Wollaston prism (70), I0=I1+I2, and I0 is the total light intensity of the two laser beams.

6. A very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception, characterized in that: The very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception uses the very low frequency atomic magnetometer environmental interference suppression method based on polarization selective reception as described in claims 1 to 5 to suppress the very low frequency atomic magnetometer environmental interference.

7. The very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception according to claim 6, characterized in that: The very low frequency atomic magnetometer environmental interference suppression system based on polarization selective reception comprises a pumping light laser (10), a first Glan-Taylor prism (20), a quarter wave plate (30), an atomic gas chamber (40), a first reflector (50), a first half wave plate (60), a Wollaston prism (70), a balanced zero-beat detector (80), a data acquisition and control system (90), a detection light laser (100), a second half wave plate (110), a second Glan-Taylor prism (120), a second reflector (130), a three-axis magnetic field coil (140), a three-axis fluxgate (150), a main magnetic field B e Coil (160) and main magnetic field-B e A coil (170), wherein the pumping laser light generated by the pumping light laser (10) sequentially passes through the first Glan Taylor prism (20) and the quarter wave plate (30) and then enters the atomic gas chamber (40), and polarizes the alkali metal atoms by interacting with the alkali metal atoms in the atomic gas chamber (40); The detection laser light generated by the detection light laser (100) is reflected by the second half wave plate (110), the second Glan Taylor prism (120) and the second reflector (130) in sequence and then enters the atomic gas chamber (40). The detection laser light emitted by the atomic gas chamber (40) is reflected by the first reflector (50), and then enters the balanced zero-beat detector (80) after passing through the first half wave plate (60) and the Wollaston prism (70). The signal collected by the balanced zero-beat detector (80) is output to the data acquisition and control system (90). The three-axis magnetic field coil (140), the three-axis fluxgate (150) and the main magnetic field B e Coil (160) and the main magnetic field-B e The coil (170) is arranged outside the atomic gas chamber (40), and the main magnetic field B e The coil (160) is used to generate a main magnetic field B in the positive z direction. e , the main magnetic field-B e The coil (170) is used to generate a e The main magnetic field in the opposite negative z direction - B e .

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