Miniaturized optically pumped atomic magnetometer based on resonant metasurface

Abstract

The application discloses a miniaturized optical pumping atomic magnetometer based on a resonant metasurface, which comprises a plasmonic metasurface module arranged between a linear polarizer and a pumping light incident side of an alkali metal cell, wherein a metasurface in the plasmonic metasurface module is composed of periodically arranged orthogonal silver nanocolumns, and a phase difference of about 90 degrees is realized at a wavelength of 795 nm by accurately designing the asymmetric size of the nanocolumns, so that linearly polarized light is efficiently converted into high-purity circularly polarized light. The device is ultrathin, easy to integrate and high in efficiency, and can be directly embedded in a pumping light path of the optical pumping atomic magnetometer to replace a traditional bulk optical quarter-wave plate and integrated in the pumping light path of the optical pumping atomic magnetometer. The system is combined with a magnetic shielding layer and a magnetic field coil to effectively suppress environmental interference and realize precise magnetic field control, thereby significantly improving the measurement sensitivity, stability and miniaturization degree of the atomic magnetometer, and providing key technical support for miniaturized and high-performance atomic magnetic sensing.

Description

Technical Field

[0001] This invention relates to the fields of micro-nano photonic devices and optical polarization modulation technology, and in particular to a miniaturized optically pumped atomic magnetometer based on a resonant metasurface. Background Technology

[0002] Weak magnetic fields at the nanoterascale level and below contain rich information and are crucial in basic scientific research, public safety, and national strategy. Their precise measurement is a core support for the development of multiple disciplines and technological innovation: in basic science, they can unlock the laws of nature; in public safety, they can build a strong protective barrier; and in national strategy, they can strengthen core competitiveness. With the development of quantum precision measurement technology, devices based on alkali metal atoms (such as rubidium and cesium), such as atomic magnetometers, atomic gyroscopes, and atomic clocks, have placed higher demands on optical polarization control. In these systems, linearly polarized light typically needs to be converted to circularly polarized light for atomic polarization and detection, or vice versa for signal extraction. However, due to their weak intensity, large size of the measurement equipment, and complex manufacturing processes, they are difficult to integrate and chip-based, especially for wearable devices requiring portable magnetic field testing for heart and brain health. The bulky structure of existing magnetometers greatly limits their application range. Traditional optical waveplates (such as λ / 4 waveplates) are large, difficult to integrate, and have limited bandwidth and efficiency near specific atomic line wavelengths (such as the Rb D1 line at 795nm).

[0003] In recent years, metasurfaces, as two-dimensional artificial electromagnetic materials, have provided a new approach to realizing compact polarization devices by flexibly controlling the amplitude, phase, and polarization of light fields through subwavelength structural units. In particular, plasmon resonance-based metallic nanostructures can achieve significant polarization conversion effects within deep subwavelength thicknesses. In the process of polarization conversion of incident light, most methods still employ traditional waveplate cascades, requiring adjustment of the angle between the fast axis of the polarizer and the quarter-wave plate to convert the linearly polarized light into the desired polarization state. This multi-layered cascaded polarization conversion device is not only large in size and incompatible with nanofabrication technology, making it very unfavorable for system miniaturization and integration; it also has limited controllability, making it difficult to guarantee high-precision polarization conversion, thus affecting the photon spin angular momentum component carried by the laser along the pump light direction, consequently affecting pump efficiency, and ultimately impacting the magnetometer's scaling coefficient and signal-to-noise ratio.

[0004] Therefore, it is necessary to design a metasurface polarization conversion device that is highly efficient, has a wide bandwidth, and is easy to integrate near the atomic line wavelength to meet the optical polarization control requirements of quantum sensor devices. Summary of the Invention

[0005] This invention provides a miniaturized optically pumped atomic magnetometer based on a resonant metasurface. By designing the geometric parameters and spatial orientation of subwavelength metallic silver nanostructures on a plasma metasurface module, it is possible to achieve efficient circular polarization conversion of incident linearly polarized light in the 795nm band, replacing the traditional bulk optical quarter-wave plate, thereby improving the miniaturization, environmental stability and polarization control accuracy of the optically pumped atomic magnetometer.

[0006] The technical solution of the present invention is as follows:

[0007] A miniaturized optically pumped atomic magnetometer based on a resonant metasurface is characterized by comprising a plasma metasurface module disposed between a linear polarizer and the pump light incident side of an alkali metal gas cell, wherein the plasma metasurface module is used to convert the input linearly polarized light into the output circularly polarized light at a working wavelength of 795 nm.

[0008] The plasma metasurface module includes a metasurface substrate on which periodically arranged metasurface units are distributed. Each metasurface unit has silver nanopillars oriented in a first direction and silver nanopillars oriented in a second direction. The first and second directions are orthogonal. The relevant geometric parameters are as follows: P, L1, W1, L2, W2, G, H, and H1, where P is the unit period, L1 is the length of the silver nanopillars oriented in the first direction, W1 is the width of the silver nanopillars oriented in the first direction, L2 is the length of the silver nanopillars oriented in the second direction, W2 is the width of the silver nanopillars oriented in the second direction, G is the gap between the silver nanopillars oriented in the first and second directions, H is the height of the silver nanopillars, and H1 is the thickness of the metasurface substrate.

[0009] P=500nm×500nm; L1=205nm; W1=110nm; L2=150nm; W2=165nm; G=50nm; H=40nm; H1=100nm.

[0010] The metasurface substrate is a transparent dielectric silicon dioxide substrate, and the metasurface unit is prepared by electron beam lithography or focused ion beam process.

[0011] The first-oriented silver nanopillars are used to generate a first transmission phase response for linearly polarized light components along the first orthogonal polarization direction, and the second-oriented silver nanopillars are used to generate a second transmission phase response for linearly polarized light components along the second orthogonal polarization direction. By designing the geometric dimensions of the two sets of silver nanopillars in a non-uniform ratio, they are in different detuned states at the plasma resonance frequency at the 795nm working wavelength, so that the two orthogonal linearly polarized light components have basically equal amplitudes and a phase difference of π / 2 after transmission.

[0012] The transport characteristics of the plasma metasurface module conform to the following expression:

[0013]

[0014] Where T is the transmission matrix, r is the transmission amplitude, and i is the imaginary unit.

[0015] Including the following expressions:

[0016]

[0017] in It is the surface admittance tensor of the metasurface unit. It is free-space wave impedance. .

[0018] The linear polarizer is connected to an acousto-optic modulator via a collimation component for beam shaping. The acousto-optic modulator is connected to a laser and a lock-in amplifier, respectively. The lock-in amplifier is connected to a data processing unit and a transimpedance amplifier, respectively. The detection light emission side of the alkali metal gas cell is connected to the transimpedance amplifier via a photodetector. The collimation component, the linear polarizer, the plasma metasurface module, the alkali metal gas cell, and the photodetector are all located within a magnetic field coil, which is located within a magnetic shielding layer. The acousto-optic modulator, the laser, the data processing unit, the lock-in amplifier, and the transimpedance amplifier form an integrated circuit functional module area.

[0019] A highly sensitive magnetic field measurement method is characterized by employing the aforementioned miniaturized optically pumped atomic magnetometer based on a resonant metasurface.

[0020] Includes the following steps:

[0021] Step 1: The laser outputs 795nm laser light, which is shaped by the collimation component and then converted into high-purity linearly polarized light by the linear polarizer.

[0022] Step 2: Adjust the polarization direction of the high-purity linearly polarized light so that it is incident on the plasma metasurface module at a 45° angle to the axis of the metallic silver nanopillars.

[0023] Step 3: The metasurface in the plasma metasurface module is based on the plasma resonance effect, and different phase delays are applied to the two orthogonal polarization components respectively to achieve a π / 2 phase difference at 795nm and output high-purity circularly polarized light.

[0024] Step 4: The high-purity circularly polarized light enters the alkali metal gas cell and undergoes optical pumping with the alkali metal atoms, polarizing the atomic spins;

[0025] Step 5: The external magnetic field induces atomic spin precession, modulating the polarization state of the detection light. The detection light signal emitted from the alkali metal gas cell is received by a photodetector and converted into an electrical signal.

[0026] Step 6: The electrical signal is processed by a transimpedance amplifier and a lock-in amplifier, and the magnetic resonance frequency is extracted by the data processing unit to achieve high-sensitivity magnetic field measurement.

[0027] The technical effects of this invention are as follows: This invention is a miniaturized optically pumped atomic magnetometer based on a resonant metasurface. It includes a plasmonic metasurface module positioned between a linear polarizer and the pump light incident side of an alkali metal gas cell. The metasurface in the plasmonic metasurface module is composed of periodically arranged orthogonal silver nanopillars. By precisely designing the asymmetric dimensions of the nanopillars, a phase difference of approximately 90° is achieved at a wavelength of 795 nm, thereby efficiently converting linearly polarized light into high-purity circularly polarized light. The device is ultra-thin, easily integrated, and highly efficient. It can be directly embedded in the pump optical path of the optically pumped atomic magnetometer, replacing the traditional bulk optical quarter-wave plate. The system combines a magnetic shielding layer and a magnetic field coil to effectively suppress environmental interference and achieve precise magnetic field control, significantly improving the measurement sensitivity, stability, and miniaturization of the atomic magnetometer, providing key technical support for miniaturized, high-performance atomic magnetic sensing.

[0028] The plasma metasurface module proposed in this invention achieves high performance with a circular polarization conversion efficiency of over 85% and a polarization purity of over 0.9 at a working wavelength of 795 nm. It also possesses an ultra-thin and compact characteristic with a total thickness of only about 140 nm, far superior to traditional bulk optical waveplates, and is easily integrated into miniaturized atomic sensors. The plasma metasurface module is fabricated using electron beam lithography or focused ion beam processes, is compatible with existing semiconductor processes, has good system integration, and can be directly embedded in the pump optical path of an optically pumped atomic magnetometer to replace traditional waveplates. Its physical mechanism is based on a clear theory of plasma resonance phase modulation, with a complete model and high degree of design freedom, providing a reliable technical foundation for achieving high-precision atomic sensing. Attached Figure Description

[0029] Figure 1 is a schematic diagram of the three-dimensional structure of the plasma metasurface module unit involved in the miniaturized optically pumped atomic magnetometer based on resonant metasurface of the present invention.

[0030] Figure 2 is Figure 1 A top-view structural diagram. Figure 2The planar geometric parameters include: P, L1, W1, L2, W2, and G. P is the unit period, P = 500 nm × 500 nm; L1 is the length of the silver nanopillars oriented in the first direction, L1 = 205 nm; W1 is the width of the silver nanopillars oriented in the first direction, W1 = 110 nm; L2 is the length of the silver nanopillars oriented in the second direction, L2 = 150 nm; W2 is the width of the silver nanopillars oriented in the second direction, W2 = 165 nm; and G is the gap between the silver nanopillars oriented in the first and second directions, G = 50 nm. These planar geometric parameters are the core structural dimensions for achieving plasmonic resonance and polarization modulation functions.

[0031] Figure 3 is Figure 1 A schematic diagram of the cross-sectional side view structure. Figure 3 The cross-sectional side view includes the following geometric parameters: H and H1, where H is the height of the silver nanopillars (the silver nanopillars oriented in the first direction and the silver nanopillars oriented in the second direction have the same height), H = 40 nm; and H1 is the thickness of the metasurface substrate, H1 = 100 nm. This cross-sectional side view clearly defines the longitudinal structural hierarchy and dimensions of the metasurface, and clarifies the spatial relationship between the nanostructure and the metasurface substrate.

[0032] Figure 4 is a schematic diagram of the optical path and circuit integration structure of the optical polarization control system involved in the miniaturized optically pumped atomic magnetometer based on a resonant metasurface of the present invention.

[0033] The reference numerals in the attached figures are explained as follows: 1- Metasurface substrate (silicon dioxide, serving as a support for the nanostructure); 2- Silver nanopillars oriented in the first direction (i.e., silver nanopillars arranged along the x-direction); 3- Silver nanopillars oriented in the second direction (i.e., silver nanopillars arranged along the y-direction, with the first and second directions orthogonal); 4- Collimation component for beam shaping; 5- Linear polarizer; 6- Plasma metasurface module; 7- Alkali metal gas cell; 8- Photodetector; 9- Magnetic shielding layer; 10- Magnetic field coil; 11- Circuit functional module integration area (including acousto-optic modulator, laser, data processing unit, lock-in amplifier, transimpedance amplifier, etc.). Detailed Implementation

[0034] The following is in conjunction with the attached diagram ( Figures 1-4 The present invention will be described in conjunction with the examples.

[0035] Figure 1 is a schematic diagram of the three-dimensional structure of the plasma metasurface module unit involved in the miniaturized optically pumped atomic magnetometer based on a resonant metasurface of the present invention. Figure 2 is... Figure 1 A top-view structural diagram. Figure 3 is... Figure 1Figure 4 is a schematic diagram of the cross-sectional side view structure of the optical path and circuit integration structure of the optical polarization modulation system involved in the miniaturized optically pumped atomic magnetometer based on a resonant metasurface of the present invention. (Reference) Figures 1 to 4 As shown, a miniaturized optically pumped atomic magnetometer based on a resonant metasurface includes a plasma metasurface module 6 disposed between the pump light incident side of a linear polarizer 5 and an alkali metal gas cell 7. The plasma metasurface module 6 is used to convert the input linearly polarized light into the output circularly polarized light at a working wavelength of 795 nm.

[0036] The plasma metasurface module 6 includes a metasurface substrate 1 on which periodically arranged metasurface units are distributed. Each metasurface unit has silver nanopillars 2 oriented in a first direction and silver nanopillars 3 oriented in a second direction. The first and second directions are orthogonal. The relevant geometric parameters are as follows: P, L1, W1, L2, W2, G, H, and H1, where P is the unit period, L1 is the length of the silver nanopillars 2 oriented in the first direction, W1 is the width of the silver nanopillars 2 oriented in the first direction, L2 is the length of the silver nanopillars 3 oriented in the second direction, W2 is the width of the silver nanopillars 3 oriented in the second direction, G is the gap between the silver nanopillars 2 and 3 oriented in the first direction, H is the height of the silver nanopillars, and H1 is the thickness of the metasurface substrate 1.

[0037] P=500nm×500nm; L1=205nm; W1=110nm; L2=150nm; W2=165nm; G=50nm; H=40nm; H1=100nm.

[0038] The metasurface substrate 1 is a transparent dielectric silicon dioxide substrate, and the metasurface unit is prepared by electron beam lithography or focused ion beam process.

[0039] The first-oriented silver nanopillars 2 are used to generate a first transmission phase response for linearly polarized light components along the first orthogonal polarization direction, and the second-oriented silver nanopillars 3 are used to generate a second transmission phase response for linearly polarized light components along the second orthogonal polarization direction. By designing the geometric dimensions of the two sets of silver nanopillars in a non-uniform ratio, they are in different detuned states at the plasma resonance frequency at the 795nm working wavelength, so that the two orthogonal linearly polarized light components have basically equal amplitudes and a phase difference of π / 2 after transmission.

[0040] The transport characteristics of the plasma metasurface module 6 conform to the following expression:

[0041]

[0042] Where T is the transmission matrix, r is the transmission amplitude, and i is the imaginary unit.

[0043] Including the following expressions:

[0044]

[0045] in It is the surface admittance tensor of the metasurface unit. It is free-space wave impedance. .

[0046] The linear polarizer 5 is connected to the acousto-optic modulator via the collimation component 4 for beam shaping. The acousto-optic modulator is connected to the laser and the lock-in amplifier, respectively. The lock-in amplifier is connected to the data processing unit and the transimpedance amplifier, respectively. The detection light emission side of the alkali metal gas cell 7 is connected to the transimpedance amplifier via the photodetector 8. The collimation component, the linear polarizer, the plasma metasurface module, the alkali metal gas cell, and the photodetector are all located within the magnetic field coil 10, which is located within the magnetic shielding layer 9. The acousto-optic modulator, the laser, the data processing unit, the lock-in amplifier, and the transimpedance amplifier form a circuit functional module integration area 11.

[0047] A highly sensitive magnetic field measurement method employs the aforementioned miniaturized optically pumped atomic magnetometer based on a resonant metasurface.

[0048] The process includes the following steps: Step 1, a 795nm laser output from a laser is shaped by a collimating component and then converted into high-purity linearly polarized light by a linear polarizer; Step 2, the polarization direction of the high-purity linearly polarized light is adjusted so that it is incident on a plasma metasurface module at a 45° angle to the axis of the silver nanopillars; Step 3, the metasurface in the plasma metasurface module, based on the plasma resonance effect, applies different phase delays to the two orthogonal polarization components, achieving a π / 2 phase difference at 795nm, and outputting high-purity circularly polarized light; Step 4, the high-purity circularly polarized light enters the alkali metal gas cell and undergoes optical pumping with alkali metal atoms, polarizing the atomic spins; Step 5, an external magnetic field induces atomic spin precession, modulating the polarization state of the detection light, and the detection light signal emitted from the alkali metal gas cell is received by a photodetector and converted into an electrical signal; Step 6, the electrical signal is processed by a transimpedance amplifier and a lock-in amplifier, and the magnetic resonance frequency is extracted by a data processing unit to achieve high-sensitivity magnetic field measurement.

[0049] This invention provides a linear-to-circular polarization converter based on a metal plasmonic metasurface and its application system and method in an optically pumped atomic magnetometer. By designing the geometric parameters and spatial orientation of the subwavelength metallic silver nanostructure, it achieves efficient circular polarization conversion of incident linearly polarized light in the 795 nm band, replacing the traditional bulk optical quarter-wave plate, thereby improving the miniaturization, environmental stability and polarization control accuracy of the optically pumped atomic magnetometer system.

[0050] The metal-plasma metasurface polarization modulation device includes: a transparent dielectric substrate; and an array of silver nanopillars disposed on the surface of the transparent dielectric substrate. The silver nanopillar array is composed of multiple periodically arranged metasurface units, each metasurface unit including at least two sets of orthogonally oriented anisotropic silver nanopillar structures in a plane. The length, width, and height of the silver nanopillars are all smaller than the operating wavelength, and the overall thickness of the metasurface is much smaller than the 795 nm operating wavelength. The silver nanopillars oriented in the first direction are used to generate a first transmission phase response for linearly polarized light components along the first orthogonal polarization direction; the silver nanopillars oriented in the second direction are used to generate a second transmission phase response for linearly polarized light components along the second orthogonal polarization direction. By designing the geometric dimensions of the two sets of silver nanopillars in a non-uniform ratio, they are placed in different detuned states at the plasma resonant frequency at the 795 nm operating wavelength, thereby ensuring that the two orthogonally polarized components have essentially equal amplitudes and a phase difference of approximately π / 2 after transmission.

[0051] A plasma metasurface polarization conversion device for atomic magnetometers, comprising:

[0052] A transparent dielectric substrate; an array of silver nanopillars disposed on the surface of the transparent dielectric substrate; the array of silver nanopillars is composed of multiple periodically arranged metasurface units, each metasurface unit including two sets of anisotropic silver nanopillar structures orthogonally oriented in the plane; the length, width, and height of the silver nanopillars are all smaller than the working wavelength, and the overall thickness of the metasurface is much smaller than the working wavelength; the silver nanopillars oriented in the first direction are used to generate a first transmission phase response for linearly polarized light components along the first orthogonal polarization direction; the silver nanopillars oriented in the second direction are used to generate a second transmission phase response for linearly polarized light components along the second orthogonal polarization direction.

[0053] By designing the geometric dimensions of the two sets of silver nanopillars in a non-uniform manner, they are placed in different detuned states at the plasma resonance frequency at the working wavelength, so that the two orthogonal polarization components have basically equal amplitudes and a phase difference of about π / 2 after transmission.

[0054] Furthermore, the specific dimensions of the metasurface unit are as follows:

[0055] Unit period: 500nm × 500nm; First silver nanopillar (along the x-direction): length L1 = 205nm, width W1 = 110nm; Second silver nanopillar (along the y-direction): length L2 = 150 nm, width W2 = 165nm; Inter-pillar gap: G = 50nm; Silver nanopillar height: H = 40nm; Substrate thickness: H1 = 100 nm, material is silicon dioxide.

[0056] The metasurface operates at a wavelength of 795 nm, corresponding to the D1 line of Rb atoms, making it suitable for optically pumped atomic magnetometer systems. Furthermore, when the incident linearly polarized light is polarized at a 45° angle to the orientation of the silver nanopillars, the transmitted light is converted from a linearly polarized state to an approximately circularly polarized state.

[0057] In atomic magnetometers, the spin polarization efficiency of alkali metal atoms is positively correlated with the circular polarization degree of the pump light, and its polarization efficiency satisfies the following relationship:

[0058]

[0059] in, For atomic polarization efficiency, For circular polarization degree, and These are the parameters representing light intensity and circular polarization components in the Stokes parameters, respectively. Higher circular polarization indicates more complete atomic spin polarization, narrower magnetic resonance lines, and higher sensitivity in magnetic field measurements. At the subwavelength scale, when incident light interacts with the plasma metasurface, the light field acquires an additional phase abrupt change at the interface introduced by the structure. This phase abrupt change satisfies the generalized refraction and reflection conditions, expressed as:

[0060]

[0061] in, Vacuum wavelength, and These are the refractive indices of the media on either side of the interface. and These are the incident angle and the transmission angle, respectively. This refers to the spatial phase distribution introduced at the interface of the metasurface.

[0062] The transmission characteristics of the metasurface polarization conversion device can be described by a transmission matrix:

[0063]

[0064] It is the complex amplitude transmission coefficient, "Indicates the linear polarization direction of the transmitted light," "Indicates the linear polarization direction of the incident light, Including amplitude transmittance and phase delay This is the core of achieving phase manipulation on metasurfaces. Because orthogonal structures have no cross-coupling, Linearly polarized light is converted into circularly polarized light upon incident incidence, which requires satisfying the transmission light... The component amplitudes are equal and the component phase difference is ,Right now , The corresponding transfer matrix can be written as:

[0065]

[0066] Furthermore, the surface admittance tensor of the metasurface can be expressed as:

[0067]

[0068] in For free-space wave impedance, this form satisfies the electromagnetic constitutive relation of linear-to-circular deflection transformation.

[0069] A polarization conversion system for an atomic magnetometer based on the aforementioned metasurface includes:

[0070] A laser source outputs linearly polarized light with a wavelength of 795 nm; a linear polarizer is used to further improve the linear polarization purity; the plasma metasurface device is placed after the linear polarizer and before the alkali metal gas cell to convert the linearly polarized light into circularly polarized light; the alkali metal gas cell receives the circularly polarized light and performs atomic polarization; and a signal detection and processing system is used to extract magnetic resonance signals.

[0071] Includes the following steps:

[0072] Step 1: Integrate the metasurface device into the optical path of the atomic magnetometer, located between the linear polarizer and the alkali metal gas cell;

[0073] Step 2: Adjust the polarization direction of the incident light to form a 45° angle with the orientation of the metasurface nanopillars;

[0074] Step 3: After the incident light passes through the metasurface, the two orthogonally polarized components acquire a phase difference of approximately π / 2 and have equal amplitudes, resulting in the output of circularly polarized light;

[0075] Step 4: Circularly polarized light enters the alkali metal gas cell, achieving atomic spin polarization for magnetic field sensing.

[0076] A polarization conversion system for an atomic magnetometer based on an orthotropic plasmonic metasurface, reference Figures 1 to 4 This embodiment provides an atomic magnetometer polarization conversion system with integrated plasma metasurface, which includes optical components, metasurface module, gas cell and signal processing circuit.

[0077] 1. Metasurface Structure Design

[0078] like Figure 1 As shown, the unit three-dimensional structure of the plasma metasurface module of the present invention includes a silicon dioxide substrate (i.e., metasurface substrate 1) and two orthogonally arranged silver nanopillars on it: silver nanopillar 1 arranged along the x-direction (i.e., metallic silver nanopillar 2 oriented in the first direction) and silver nanopillar 2 arranged along the y-direction (i.e., metallic silver nanopillar 3 oriented in the second direction). This orthogonal anisotropic structure is the core for realizing the conversion of linearly polarized light to circularly polarized light.

[0079] like Figure 2 As shown in the top view of the unit cell planar dimensions, the following key geometric parameters are clearly defined: unit cell period P = 500 nm × 500 nm; length L1 = 205 nm and width W1 = 110 nm for silver nanopillar 1; length L2 = 150 nm and width W2 = 165 nm for silver nanopillar 2; gap G = 50 nm between the two nanopillars. Figure 3 As shown, the longitudinal structural parameters are marked in the side view of the unit cross-section: the height of the silver nanopillar H = 40 nm; the substrate thickness H1 = 100 nm. This structure was fabricated using electron beam lithography and metal evaporation. Near a wavelength of 795 nm, this structure achieves a high-efficiency linear-to-circular polarization conversion by generating a phase difference of approximately π / 2 between two orthogonal polarization directions through asymmetric dimensional design.

[0080] 2. System optical path and circuit integration

[0081] like Figure 4 As shown, the system's optical path and circuit integration structure includes the following components: system integration and optical path layout. The system is integrated in the following order: Laser (located in the circuit functional module integration area 11): generates 795nm continuous laser. Collimation component (4): collimates and expands the laser beam. Linear polarizer (5): generates linearly polarized light. Plasma metasurface module (6): receives linearly polarized light and converts it into circularly polarized light. Alkali metal gas chamber (7): contains rubidium atomic vapor, where circularly polarized light polarizes atomic spins. Photodetector (8): receives the emitted light signal modulated by atoms. Magnetic shielding layer (9): wraps around the entire sensing core (gas chamber, coil, etc.) to shield against geomagnetic and environmental magnetic field interference. Magnetic field coil (10): surrounds the gas chamber to generate a precisely controllable bias magnetic field or modulated magnetic field. Circuit functional module integration area (11): includes a transimpedance amplifier (converts photocurrent into voltage), a lock-in amplifier (extracts magnetic resonance frequency signals), and a data processing unit (completes magnetic field calculation and system control). Optionally, an acousto-optic modulator can also be integrated into the system to modulate the laser.

[0082] 3. Work Process

[0083] Step 1: The laser outputs 795nm laser light, which is shaped by the collimation component (4) and then becomes high-purity linearly polarized light through the linear polarizer (5).

[0084] Step 2: Adjust the polarization direction of the linearly polarized light so that it is incident on the plasma metasurface module at a 45° angle to the axis of the metasurface nanopillar (6).

[0085] Step 3: Based on the plasmon resonance effect, the metasurface applies different phase delays to the two orthogonal polarization components, achieving a phase difference of about 90° at 795nm, and outputting high-purity circularly polarized light.

[0086] Step 4: Circularly polarized light enters the alkali metal gas cell (7) and undergoes optical pumping with the alkali metal atoms, polarizing the atomic spins.

[0087] Step 5: The external magnetic field causes the atomic spin precession, modulating the polarization state of the probe light. This signal is received by the photodetector (8) and converted into an electrical signal.

[0088] Step 6: The electrical signal is processed by a transimpedance amplifier and a lock-in amplifier, and the magnetic resonance frequency is extracted by the data processing unit to achieve high-sensitivity magnetic field measurement.

[0089] 4. Performance Characteristics

[0090] During operation, 795nm linearly polarized light is incident on the metasurface at a 45° angle to the axis of the nanopillars. Due to the resonant detuning of the two sets of nanopillars, the x and y polarization components in the light field acquire a phase difference of about 90° and have approximately equal amplitudes, resulting in high-purity circularly polarized light. This circularly polarized light efficiently polarizes rubidium atoms in the gas chamber. In the silent environment created by the magnetic shielding layer (9), the required magnetic field is applied through the magnetic field coil (10). The combined effect of the magnetic field to be measured and the magnetic field of the coil causes the atomic spins to precess at a specific Larmor frequency, thereby modulating the polarization or intensity of the probe light. This modulated signal is received by the photodetector (8), and after being processed by lock-in amplification, the external magnetic field value can be accurately deduced. The overall system has high integration, small size, and is suitable for miniaturized atomic magnetometers, atomic gyroscopes, and other quantum sensing devices.

[0091] A plasma metasurface polarization conversion device for an atomic magnetometer includes: a transparent dielectric substrate (i.e., metasurface substrate 1); periodically arranged metasurface units disposed on the surface of the substrate, each unit comprising two orthogonally arranged metallic silver nanopillars in a plane (i.e., metallic silver nanopillars 2 oriented in a first direction and metallic silver nanopillars 3 oriented in a second direction); the metasurface unit has a period of 500 nm × 500 nm; the first silver nanopillar (i.e., metallic silver nanopillars 2 oriented in the first direction) has a length of 205 nm and a width of 110 nm along the x-direction; the second silver nanopillar (i.e., metallic silver nanopillars 3 oriented in the second direction) has a length of 150 nm and a width of 165 nm along the y-direction; the gap between the two nanopillars is 50 nm; the height of the silver nanopillars is 40 nm; the substrate thickness is 100 nm; the device (i.e., plasma metasurface module) converts incident X-polarized light into circularly polarized light at a working wavelength of 795 nm.

[0092] The transparent substrate is silicon dioxide.

[0093] The material of the metallic silver nanopillars is silver.

[0094] The metasurface units are fabricated using electron beam lithography or focused ion beam processes.

[0095] The transmission matrix of the device satisfies:

[0096]

[0097] Where r is the transmission amplitude.

[0098] An atomic magnetometer system based on the aforementioned plasma metasurface polarization conversion device is characterized by comprising: a laser that outputs a 795 nm wavelength laser; a collimation component (4) for collimating and shaping the laser; a linear polarizer (5) for adjusting the incident light to be linearly polarized; a plasma metasurface module (6) for converting the linearly polarized light into circularly polarized light; an alkali metal gas cell (7) for receiving circularly polarized light to polarize atomic spins; a photodetector (8) for detecting optical signals and converting them into electrical signals; and a signal processing circuit including a transimpedance amplifier, a lock-in amplifier, and a data processing unit for extracting and processing magnetic field signals.

[0099] The signal processing circuit also includes an acousto-optic modulator for modulating the laser output characteristics.

[0100] A polarization conversion method based on the aforementioned plasma metasurface polarization conversion device includes the following steps: placing the metasurface device between a linear polarizer (5) and an alkali metal gas cell (7); adjusting the polarization direction of the incident light to form a 45° angle with the axis of the metasurface nanopillar; after the incident light passes through the metasurface, the two orthogonal polarization components obtain a phase difference of approximately π / 2 and have equal amplitudes, outputting circularly polarized light; the circularly polarized light enters the alkali metal gas cell, realizing atomic spin polarization.

[0101] The circularly polarized light is used for atomic polarization in an optically pumped atomic magnetometer, thereby enabling magnetic field sensing.

[0102] It also includes coating the metasurface with a protective layer to enhance environmental stability and maintaining a constant operating temperature of the device through a temperature control device.

[0103] Contents not described in detail in this specification are existing technologies 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 the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essence of the present invention fall within the scope of protection of the present invention.

Claims

1. A miniaturized optically pumped atomic magnetometer based on a resonant metasurface, characterized in that, The invention includes a plasma metasurface module disposed between the linear polarizer and the pump light incident side of the alkali metal gas cell. The plasma metasurface module is used to convert the input linearly polarized light into the output circularly polarized light at a working wavelength of 795 nm.

2. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 1, characterized in that, The plasma metasurface module includes a metasurface substrate on which periodically arranged metasurface units are distributed. Each metasurface unit has silver nanopillars oriented in a first direction and silver nanopillars oriented in a second direction. The first and second directions are orthogonal. The relevant geometric parameters are as follows: P, L1, W1, L2, W2, G, H, and H1, where P is the unit period, L1 is the length of the silver nanopillars oriented in the first direction, W1 is the width of the silver nanopillars oriented in the first direction, L2 is the length of the silver nanopillars oriented in the second direction, W2 is the width of the silver nanopillars oriented in the second direction, G is the gap between the silver nanopillars oriented in the first and second directions, H is the height of the silver nanopillars, and H1 is the thickness of the metasurface substrate.

3. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 2, characterized in that, P=500nm×500nm; L1=205nm; W1=110nm; L2=150nm; W2=165nm; G=50nm; H=40nm; H1=100nm.

4. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 2, characterized in that, The metasurface substrate is a transparent dielectric silicon dioxide substrate, and the metasurface unit is prepared by electron beam lithography or focused ion beam process.

5. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 2, characterized in that, The first-oriented silver nanopillars are used to generate a first transmission phase response for linearly polarized light components along the first orthogonal polarization direction, and the second-oriented silver nanopillars are used to generate a second transmission phase response for linearly polarized light components along the second orthogonal polarization direction. By designing the geometric dimensions of the two sets of silver nanopillars in a non-uniform ratio, they are in different detuned states at the plasma resonance frequency at the 795nm working wavelength, so that the two orthogonal linearly polarized light components have basically equal amplitudes and a phase difference of π / 2 after transmission.

6. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 1, characterized in that, The transport characteristics of the plasma metasurface module conform to the following expression: Where T is the transmission matrix, r is the transmission amplitude, and i is the imaginary unit.

7. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 2, characterized in that, Including the following expressions: in It is the surface admittance tensor of the metasurface unit. It is free-space wave impedance. .

8. The miniaturized optically pumped atomic magnetometer based on a resonant metasurface according to claim 1, characterized in that, The linear polarizer is connected to an acousto-optic modulator via a collimation component for beam shaping. The acousto-optic modulator is connected to a laser and a lock-in amplifier, respectively. The lock-in amplifier is connected to a data processing unit and a transimpedance amplifier, respectively. The detection light emission side of the alkali metal gas cell is connected to the transimpedance amplifier via a photodetector. The collimation component, the linear polarizer, the plasma metasurface module, the alkali metal gas cell, and the photodetector are all located within a magnetic field coil, which is located within a magnetic shielding layer. The acousto-optic modulator, the laser, the data processing unit, the lock-in amplifier, and the transimpedance amplifier form an integrated circuit functional module area.

9. A high-sensitivity magnetic field measurement method, characterized in that, A miniaturized optically pumped atomic magnetometer based on a resonant metasurface, as described in any one of claims 1-8 above.

10. The high-sensitivity magnetic field measurement method according to claim 9, characterized in that, Includes the following steps: Step 1: The laser outputs 795nm laser light, which is shaped by the collimation component and then converted into high-purity linearly polarized light by the linear polarizer. Step 2: Adjust the polarization direction of the high-purity linearly polarized light so that it is incident on the plasma metasurface module at a 45° angle to the axis of the metallic silver nanopillars. Step 3: The metasurface in the plasma metasurface module is based on the plasma resonance effect, and different phase delays are applied to the two orthogonal polarization components respectively to achieve a π / 2 phase difference at 795nm and output high-purity circularly polarized light. Step 4: The high-purity circularly polarized light enters the alkali metal gas cell and undergoes optical pumping with the alkali metal atoms, polarizing the atomic spins; Step 5: The external magnetic field induces atomic spin precession, modulating the polarization state of the detection light. The detection light signal emitted from the alkali metal gas cell is received by a photodetector and converted into an electrical signal. Step 6: The electrical signal is processed by a transimpedance amplifier and a lock-in amplifier, and the magnetic resonance frequency is extracted by the data processing unit to achieve high-sensitivity magnetic field measurement.

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