Optical atom magnetic sensor four-channel polarization decoupling detection method based on metasurface

Abstract

The invention discloses a metasurface-based optical atom magnetic sensor four-channel polarization decoupling detection method, and aims to solve the problems that a detection end of a single-beam atom magnetometer is large in size and is easily interfered by pump light ellipticity fluctuation. The technical scheme of the invention is as follows: a four-channel focusing metasurface device integrated with a sub-aperture pseudo-random spatial multiplexing nano-pillar array is utilized to replace a discrete component in a traditional detection light path, and a single beam of detection light carrying magnetic field information is directly separated in space and is focused into four independent light spots of left rotation, right rotation, 45 degrees and 135 degrees at the same time; common-caliber uniform sampling of the Gaussian beam cross section is realized through pseudo-random arrangement; the signal processing system inverts the ellipticity of the pump light in real time by using a circular polarization channel, extracts a magnetic field signal by using a linear polarization channel, and performs dynamic correction through a full-polarization decoupling algorithm. According to the invention, chip-level integration of the magnetometer is facilitated, and high-sensitivity and high-stability anti-interference measurement is realized.

Description

Technical Field

[0001] This invention relates to the fields of quantum precision measurement, micro-nano optics and signal processing, and in particular to a four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces. Background Technology

[0002] Optical atomic magnetic sensors, with their theoretical sensitivity surpassing that of superconducting quantum interference devices (SQUIDs), have become the core sensors in the field of extremely weak magnetic field measurement, showing great application potential in biomagnetic imaging such as magnetoencephalography (MEG) and magnetocardiography (MCG), as well as in deep space exploration and geomagnetic navigation.

[0003] With the expansion of application scenarios, there is an urgent need for the miniaturization, integration, and arraying of optical atomic magnetic sensors. Among the many magnetometer configurations, the single-beam elliptical polarization optical atomic magnetic sensor (SB-EPAM) is an ideal solution for miniaturization due to its relatively simple optical path structure (only one beam of light is needed to simultaneously perform pumping and detection). However, in the actual engineering process of SB-EPAM, the integration of the detection optical path has become one of the core bottlenecks restricting its further reduction in size.

[0004] To accurately extract the magnetic field signal and suppress optical path noise, traditional SB-EPAM detectors typically require a complete analysis of the polarization state of the emitted light. In conventional optical architectures, this necessitates a complex combination of discrete optical components: typically including a quarter-wave plate (QWP) for converting the circularly polarized component, a polarizing beam splitter (PBS) or Wollaston prism for separating the linearly polarized component, and a focusing lens for coupling the beam to the detector. These conventional optical components suffer from the following significant drawbacks:

[0005] 1. Large size and difficult to integrate: Waveplates, prisms and lenses usually have large physical dimensions (millimeters to centimeters) and require long optical paths for beam separation, making it difficult to compress the size of the probe.

[0006] 2. Complex assembly and poor stability: Multiple discrete components require extremely high precision mechanical alignment and assembly. Any slight mechanical vibration or thermal deformation can cause optical path misalignment and affect measurement stability.

[0007] 3. Limited functionality: Traditional components have limited functionality, making it difficult to achieve synchronous control and acquisition of multiple polarization states of the light field using a single component.

[0008] Therefore, how to abandon bulky traditional discrete optical components and use a single integrated device to achieve efficient separation and focusing of the full polarization state of the probe light, thereby breaking through the miniaturization bottleneck of optical atomic magnetic sensors, is a technical problem that urgently needs to be solved. Summary of the Invention

[0009] This invention aims to solve the technical problems of existing single-beam optical atomic magnetic sensors having a large number of optical elements at the detection end, large size, and difficulty in achieving chip-level integration, and provides a four-channel polarization decoupling detection method for optical atomic magnetic sensors based on metasurfaces.

[0010] The technical solution of the present invention is as follows:

[0011] A four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces, characterized by comprising the following steps:

[0012] Step 1: Set up a four-channel focusing metasurface device between the alkali metal gas cell detector light output side in the photoelectric detection array and the magnetic probe assembly;

[0013] Step 2: Using the four-channel focusing metasurface device, the light emitting side probe carrying magnetic field information is directly separated in space and simultaneously focused into the following four independent light spots: left-hand circularly polarized focusing light spot, right-hand circularly polarized focusing light spot, 45-degree linearly polarized focusing light spot, and 135-degree linearly polarized focusing light spot.

[0014] Step 3: Simultaneously collect the following four parameters using the photoelectric detection array: , , , , It is the light intensity of the left-handed circularly polarized focused spot. It is the light intensity of the right-hand circularly polarized focused spot. It is the light intensity of the 45-degree linearly polarized focused spot. It is the light intensity of the 135-degree linearly polarized focused spot;

[0015] Step 4, based on the principle of light polarization, using , , ,and Calculate respectively and , It is a monitoring signal characterizing the real-time ellipticity of the pump light. It is the original signal that characterizes magnetic field information;

[0016] Step 5, using right Decoupling corrections are performed to eliminate ellipticity interference, and the inversion is obtained. , It is the rotation angle of the magnetic field.

[0017] Step 4 includes the following expression:

[0018]

[0019]

[0020]

[0021]

[0022] in It is the pump light ellipticity.

[0023] Step 5 includes the following expression:

[0024]

[0025] The above expression eliminates the ellipticity term. The modulation effect can be accurately obtained. value, It is proportional to the strength of the magnetic field being measured.

[0026] In step 1, the four-channel focusing metasurface device adopts a "sub-aperture pseudo-random spatial multiplexing" design method to ensure uniform sampling of the Gaussian beam cross section. Specifically, this includes: dividing the metasurface aperture logic into several tiny sub-aperture units; within each sub-aperture unit, nanopillar focusing units that respond to left-hand circular polarization, right-hand circular polarization, and linear polarization are set according to a preset ratio; the positions of the nanopillars within the sub-aperture units are determined by a pseudo-random algorithm, so that each functional unit presents a uniform mixed distribution on the macroscopic aperture.

[0027] The preset ratio is 1:1:1, meaning that within each sub-aperture unit, the number of nanopillars responding to left-handed circular polarization, right-handed circular polarization, and linear polarization is equal.

[0028] The nanopillar focusing unit, responding to left-handed and right-handed circular polarization, performs wavefront modulation based on the geometric phase principle. The nanopillar has fixed length and width dimensions and is configured as a half-wave plate structure at the operating wavelength to maximize polarization conversion efficiency. The polarization conversion efficiency is maximized by changing the rotation angle of the nanopillar in the plane. To introduce the required focusing phase And satisfy , (as a sign factor related to rotation), thereby enabling independent focusing of left-handed and right-handed circularly polarized light respectively.

[0029] The nanopillar focusing unit with linear polarization response is a dual-function multiplexing unit, which is configured to have a dual phase response: when the incident light is linearly polarized at 45 degrees, it generates a focusing phase pointing to the 45° channel focus; when the incident light is linearly polarized at 135 degrees, it generates a focusing phase pointing to the 135° channel focus; thus, a single nanopillar can be used to simultaneously detect two orthogonally linearly polarized channels.

[0030] The four-channel polarization decoupling detection device based on metasurface optical atomic magnetic sensor is characterized by employing the above-mentioned four-channel polarization decoupling detection method based on metasurface optical atomic magnetic sensor.

[0031] The device includes a four-channel focusing metasurface device with an anisotropic nanopillar array integrated on its surface. The photodetector array is located on the focal plane of the four-channel focusing metasurface device and contains four independent photosensitive units, each corresponding to one of the four focusing channels. The photodetector array is sequentially connected to a TIA transimpedance amplifier, a LIA lock-in amplifier, and a PC. The LIA lock-in amplifier is connected to a coil in a magnetic probe assembly. The alkali metal gas cell in the magnetic probe assembly is connected to a laser source assembly via a collimation and polarization state preparation lens group.

[0032] The technical advantages of this invention are as follows: This invention boasts extremely high integration, utilizing a single-chip metasurface with a thickness of only a few micrometers to replace the traditional bulky discrete optical component array, facilitating the integration and manufacturing of chip-level magnetometers. This invention achieves high-precision measurement with strong anti-interference capabilities. Through full polarization state decoupling at the physical model level, common-mode noise caused by pump light ellipticity fluctuations is completely eliminated, solving the problem of poor long-term stability in traditional single-beam magnetometers.

[0033] This invention has excellent beam sampling capability. Through pseudo-random spatial multiplexing design, it solves the sampling distortion problem of metasurface when processing non-uniform beams (Gaussian beams), and ensures high fidelity and high signal-to-noise ratio of multi-channel signals. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure and optical path of the device involved in the four-channel polarization decoupling detection method of the optical atomic magnetic sensor based on metasurface of this invention.

[0035] Figure 2 This is a schematic diagram of the pseudo-random spatial multiplexing arrangement of sub-apertures and the nanopillar screening principle of the four-channel focusing metasurface device in this invention. Figure 2 Figure (a) shows the local equilibrium arrangement logic inside the sub-aperture unit. Figure 2 Figure (b) shows the pseudo-random mixing effect of the macroscopic array. LCP is left-handed circularly polarized light. RCP is right-handed circularly polarized light.

[0036] Figure 3 This is a schematic diagram illustrating the wavefront modulation and focusing principle of the light field by the metasurface structure in this invention. Figure 3 It demonstrates how anisotropic nanopillars can transform a single incident beam of light into four spatially separated focused beams.

[0037] The reference numerals in the attached figures are explained as follows: 1-Laser source assembly; 2-Collimation and polarization state preparation lens group; 3-Magnetic probe assembly (including magnetic shielding and coil system, alkali metal gas chamber); 4-Four-channel focusing metasurface device; 5-Photodetector array; 6-Signal processing system (including TIA transimpedance amplifier, LIA lock-in amplifier, and PC terminal, PC stands for Personal Computer, LIA stands for lock-in amplifier, and TIA stands for Trans-Impedance Amplifier). ①-Incident probe light carrying magnetic field information; ②-Four-channel focusing metasurface; ③-Left-hand circularly polarized focusing spot; ④-Right-hand circularly polarized focusing spot; ⑤-45° linearly polarized focusing spot; ⑥-135° linearly polarized focusing spot; ⑦-Photodetector array receiving surface located at the focal plane. Detailed Implementation

[0038] The following is in conjunction with the attached diagram ( Figures 1-3 The present invention will be described in conjunction with the examples.

[0039] Figure 1 This is a schematic diagram of the overall structure and optical path of the device involved in the four-channel polarization decoupling detection method of the optical atomic magnetic sensor based on metasurface of this invention. Figure 2 This is a schematic diagram of the pseudo-random spatial multiplexing arrangement of sub-apertures and the nanopillar screening principle of the four-channel focusing metasurface device in this invention. Figure 3 This is a schematic diagram illustrating the wavefront modulation and focusing principle of the light field by the metasurface structure in this invention. (Reference) Figures 1 to 3 As shown, the four-channel polarization decoupling detection method of the optical atomic magnetic sensor based on metasurface includes the following steps: Step 1, a four-channel focusing metasurface device is set between the light-emitting side of the alkali metal gas cell in the photodetector array and the magnetic probe assembly; Step 2, the four-channel focusing metasurface device is used to directly separate and simultaneously focus the light emitting side probe carrying magnetic field information (i.e., the incident probe ① carrying magnetic field information is irradiated onto the four-channel focusing metasurface ②) in space into the following four independent light spots: left-handed circularly polarized focusing spot ③, right-handed circularly polarized focusing spot ④, 45-degree linearly polarized focusing spot (i.e., 45° linearly polarized focusing spot ⑤), and 135-degree linearly polarized focusing spot (i.e., 135° linearly polarized focusing spot ⑥); Step 3, the photodetector array is used to synchronously acquire the following four parameters: , , , , It is the light intensity of the left-handed circularly polarized focused spot. It is the light intensity of the right-hand circularly polarized focused spot. It is the light intensity of the 45-degree linearly polarized focused spot. It is the light intensity of the 135-degree linearly polarized focused spot; Step 4, based on the principle of light polarization, using... , , ,and Calculate respectively and , It is a monitoring signal characterizing the real-time ellipticity of the pump light. It is the original signal characterizing magnetic field information; Step 5, using right Decoupling corrections are performed to eliminate ellipticity interference, and the inversion is obtained. , It is the rotation angle of the magnetic field.

[0040] Step 4 includes the following expression:

[0041]

[0042]

[0043]

[0044]

[0045] in It is the pump light ellipticity.

[0046] Step 5 includes the following expression:

[0047]

[0048] The above expression eliminates the ellipticity term. The modulation effect can be accurately obtained. value, It is proportional to the strength of the magnetic field being measured.

[0049] In step 1, the four-channel focusing metasurface device employs a "sub-aperture pseudo-random spatial multiplexing" design method to ensure uniform sampling of the Gaussian beam cross-section. Specifically, this involves: logically dividing the metasurface aperture into several tiny sub-aperture units; within each sub-aperture unit, nanopillar focusing units responding to left-handed circular polarization, right-handed circular polarization, and linear polarization are set according to a preset ratio; the positions of the nanopillars within the sub-aperture unit are determined by a pseudo-random algorithm, resulting in a uniform mixed distribution of functional units across the macroscopic aperture. The preset ratio is 1:1:1, meaning that the number of nanopillars responding to left-handed circular polarization, right-handed circular polarization, and linear polarization is equal within each sub-aperture unit.

[0050] The nanopillar focusing unit, responding to left-handed and right-handed circular polarization, performs wavefront modulation based on the geometric phase principle. The nanopillar has fixed length and width dimensions and is configured as a half-wave plate structure at the operating wavelength to maximize polarization conversion efficiency. The polarization conversion efficiency is maximized by changing the rotation angle of the nanopillar in the plane. To introduce the required focusing phase And satisfy , (The sign factor is related to the rotation), thereby enabling independent focusing of left-handed and right-handed circularly polarized light respectively. The nanopillar focusing unit responding to linear polarization is a dual-function multiplexing unit, which is configured to have a dual phase response: when the incident light is linearly polarized at 45 degrees, it generates a focusing phase pointing to the 45° channel focus; when the incident light is linearly polarized at 135 degrees, it generates a focusing phase pointing to the 135° channel focus; thus, a single nanopillar can simultaneously detect two orthogonally linearly polarized channels.

[0051] The four-channel polarization decoupling detection device based on metasurface optical atomic magnetic sensors employs the aforementioned four-channel polarization decoupling detection method based on metasurface optical atomic magnetic sensors. It includes a four-channel focusing metasurface device 4 with an anisotropic nanopillar array integrated on its surface. A photodetector array 5 is located on the focal plane of the four-channel focusing metasurface device 4 (the photodetector array receiving surface ⑦ is located on the focal plane), containing four independent photosensitive units, each corresponding to one of the four focusing channels. The photodetector array 5 is sequentially connected to a TIA transimpedance amplifier, a LIA lock-in amplifier, and a PC (TIA, LIA, and PC constitute a signal processing system 6). The LIA lock-in amplifier is connected to a coil in the magnetic probe assembly 3. The alkali metal gas cell probe light incident side in the magnetic probe assembly is connected to a laser source assembly 1 via a collimation and polarization state preparation lens group 2.

[0052] A four-channel polarization decoupling detection method and device based on metasurface optical atomic magnetometers is proposed to address the problems of large probe size and susceptibility to pump light ellipticity fluctuations in single-beam atomic magnetometers. The technical solution of this invention is as follows: A four-channel focusing metasurface device integrating a sub-aperture pseudo-random spatial multiplexing nanopillar array is used to replace discrete components in the traditional probe optical path. This directly separates and simultaneously focuses the single-beam probe light carrying magnetic field information into four independent spots: left-handed, right-handed, 45-degree, and 135-degree. Pseudo-random arrangement achieves uniform sampling of the Gaussian beam cross-section with a common aperture. The signal processing system uses the circular polarization channel to invert the pump light ellipticity in real time, uses the linear polarization channel to extract the magnetic field signal, and performs dynamic correction through a full polarization state decoupling algorithm. This invention facilitates chip-level integration of the magnetometer and achieves high-sensitivity, high-stability, and interference-resistant measurements.

[0053] A four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces, the method being based on a single-beam elliptical polarization optical atomic magnetic sensor architecture, includes the following steps:

[0054] Step S1: Metasurface Four-Channel Beam Splitting and Focusing. A four-channel focusing metasurface device is placed on the light-emitting side of the atomic gas cell of the magnetometer. The anisotropic nanopillar array distributed on the surface of the device is used to perform wavefront modulation on the transmitted light carrying magnetic field information, directly separating it in space and simultaneously focusing it into four independent detection spots: a left-handed circularly polarized spot (L), a right-handed circularly polarized spot (R), a 45-degree linearly polarized spot (45°), and a 135-degree linearly polarized spot (135°).

[0055] Step S2: Four-parameter light intensity acquisition. A photodetector array is set on the rear focal plane of the metasurface device to acquire the focused light intensity values ​​of the four light spots mentioned above, and denoted as follows: , , , .

[0056] Step S3: Construct an ellipticity monitoring channel. Based on the principle of light polarization, a circular polarization component is used to construct a channel characterizing the real-time ellipticity of the pump light. monitoring signals :

[0057]

[0058] Step S4: Construct the original magnetic field signal channel. The original signal characterizing the magnetic field information is constructed using linear polarization components. ,in The Faraday rotation angle is proportional to the strength of the magnetic field being measured.

[0059]

[0060] Step S5: Decoupling correction and magnetic field inversion. Utilizing monitoring signals... For the original signal Make corrections to eliminate the ellipticity term. The modulation effect is used to obtain the precise magnetic field rotation angle. :

[0061]

[0062] The four-channel focusing metasurface device employs a "sub-aperture pseudo-random spatial multiplexing" design method: To address the uneven spatial intensity distribution caused by the incident Gaussian beam, the metasurface aperture is logically divided into several tiny sub-aperture units. Within each sub-aperture unit, nanopillar focusing units, responding to left-handed circular polarization, right-handed circular polarization, and linear polarization respectively, are strictly included in a preset ratio. The positions of the nanopillars within each sub-aperture unit are determined by a pseudo-random algorithm. This design ensures a uniform mixed distribution of the three functional nanopillars across the macroscopic aperture, achieving uniform sampling of the same Gaussian beam cross-section with a common aperture, and effectively suppressing high-order diffraction noise that may be generated by periodic arrangement.

[0063] The nanopillar focusing unit responding to linear polarization is a dual-function multiplexed unit: by jointly controlling the length and width dimensions of the rectangular nanopillar (introducing propagation phase) and the rotation angle (introducing geometric phase), specific structural parameters are selected to simultaneously satisfy two phase-matching conditions: generating a focusing phase pointing to the 45° channel focus for incident 45° linearly polarized light, and generating a focusing phase pointing to the 135° channel focus for incident 135° linearly polarized light. Thus, a single nanopillar can simultaneously detect two orthogonally linearly polarized channels, improving light energy utilization.

[0064] Example 1: Overall Hardware Architecture and Signal Flow of the Detection Device

[0065] like Figure 1As shown, this invention discloses a four-channel polarization decoupling detection device for an optical atomic magnetic sensor based on a metasurface. Along the propagation direction of the probe beam, the device comprises: a laser source assembly 1, a collimation and polarization state preparation lens group 2, a magnetic shielding and coil system (i.e., a magnetic probe assembly 3), a four-channel focusing metasurface device 4, and a photodetector array 5 located on the focal plane of the metasurface device. The output of the photodetector array 5 is electrically connected to a signal processing system 6. The laser source assembly 1 preferably employs a distributed feedback (DFB) semiconductor laser, whose center wavelength is locked to the D1 transition line of alkali metal atoms (e.g., 795 nm for Rb atoms). The collimation and polarization state preparation lens group 2 is used to adjust the laser to elliptically polarized light, so as to simultaneously achieve spin polarization (pumping effect) and optical rotation detection (probing effect) of atoms. An alkali metal atom gas cell is fixed at the center of the magnetic probe assembly 3. When the probe beam passes through the gas cell, it is affected by the Faraday effect caused by the external magnetic field (the signal to be measured), causing the major axis of its elliptically polarized state to deflect. The four-channel focusing metasurface device 4 is the core beam-splitting element of this system, located on the light-emitting side of the alkali metal atom gas cell. This device is based on all-dielectric metasurface technology, using silicon dioxide (SiO2) as the substrate material and high-refractive-index amorphous silicon (a-Si) nanopillars as the surface microstructure. The device's design wavelength matches the laser wavelength, and the focal length is determined according to the actual optical path requirements. The photodetector array 5 is a four-quadrant photodetector, corresponding to the four focal coordinates of the metasurface design: channels L and R receive left-handed and right-handed circularly polarized components, respectively, for real-time calculation of the beam ellipticity; channels 45° and 135° receive linearly polarized projection components in the 45° and 135° directions, respectively, for calculating the principal axis deflection angle. The signal processing system 6 receives the four photocurrent signals output from the photodetector array 5, amplifies and digitizes them; then, using a built-in polarization decoupling algorithm, it corrects the linearly polarized channel data in real-time based on the circularly polarized channel data, thereby outputting accurate magnetic field information after eliminating the real-time pump light ellipticity.

[0066] Example 2: Design Method of Four-Channel Focusing Metasurface Devices

[0067] 1. Sub-aperture pseudo-random spatial multiplexing arrangement (e.g.) Figure 2 (As shown)

[0068] To achieve uniform sampling across the same aperture, the metasurface array arrangement follows these rules: Logical partitioning: The metasurface aperture is divided into several 3×3 sub-aperture units. Local equalization: Within each 3×3 sub-aperture, the ratio of the three functional units is strictly configured to 1:1:1, namely: 3 left-handed circular polarization focusing units, 3 right-handed circular polarization focusing units, and 3 linear polarization dual-function focusing units. Pseudo-random shuffling: A pseudo-random algorithm is used to shuffle the spatial positions of the 9 units within each sub-aperture. For example... Figure 2As shown in (b), this design breaks the periodic grating structure and ensures that the light intensity acquired by the four channels truly reflects the average state of the same beam cross section.

[0069] 2. Unit structure and parameters (e.g.) Figure 3 (As shown)

[0070] For any nanopillar unit on the metasurface array, its physical center coordinates are: In order to focus the incident light onto a specific target focal point on the focal plane. (in To design the focal length, this infinitesimal element must incorporate a phase compensation. To compensate for the optical path difference. This phase distribution follows the phase formula for a non-paraxial hyperbolic lens:

[0071]

[0072] in, The operating wavelength is 795nm in this embodiment.

[0073] Different control mechanisms are employed for different channels. For the circular polarization channel, the Pancharatnam-Berry (PB) phase principle is utilized. First, the nanopillar size is selected to be a half-wave plate condition to maximize polarization conversion efficiency, and then the phase difference between the orthogonal linear polarization components is chosen to achieve this. And it is the geometric dimension with the highest transmittance. Then, according to the PB phase theory, when circularly polarized light passes through a rotation angle of... When nanopillars are used, the additional phase of the emitted light is obtained. Determined solely by the rotation angle, and satisfying a linear relationship:

[0074]

[0075] For LCP, For RCP, .

[0076] For a left-handed focusing element, calculate the coordinates. To the focal point of the left-hand channel Required phase Set the rotation angle of the nanopillar at this location. for:

[0077]

[0078] For right-handed focusing elements, calculate coordinates. To the focal point of the right-hand channel Required phase Since the geometric phase introduced by RCP has an opposite sign, the rotation angle of the nanopillar at this location is set. for:

[0079]

[0080] For a linearly polarized channel, a single nanopillar needs to simultaneously respond to two orthogonal polarization components, 45° and 135°. A library of nanopillar geometric parameters (length L, width W) is established, and a cost function is defined:

[0081]

[0082] in and The actual phase is from the parameter library. and For the target phase, , where is the weighting coefficient (preferably 3.0), and T is the transmittance. For the position of each nanopillar, the database is traversed to select the geometric parameters that minimize Cost(L, W). During arrangement, the nanopillar of the preferred size is rotated 45° in the plane. Since the two principal axes (fast axis and slow axis) of the rotated nanopillar are aligned with the 45° and 135° directions in the global coordinate system, this structure can apply a phase pointing towards the 45° channel focus to the 45° linearly polarized component of the incident light and a phase pointing towards the 135° channel focus to the 135° linearly polarized component, respectively, using the selected length and width dimensions. This achieves independent decoupling and focusing of two orthogonal diagonal linearly polarized states on a single unit.

[0083] This invention successfully integrates four independent wavefront modulation functions on a monolithic metasurface device. The circularly polarized channel utilizes the broadband characteristics of geometric phase to ensure a high signal-to-noise ratio for ellipticity monitoring, while the linearly polarized channel achieves crosstalk-free focusing of orthogonal components through multi-objective optimization of birefringence phase. Combined with a pseudo-random sub-aperture arrangement strategy, this device not only overcomes the inherent defects of uneven beam spatial sampling but also effectively suppresses high-order diffraction sidelobes, providing high-fidelity light intensity input for subsequent signal processing systems and forming the hardware foundation for high-precision magnetic field inversion.

[0084] Example 3: Polarization Decoupling Detection Method and Signal Processing Flow

[0085] This embodiment combines Figure 1 The signal processing system 6 and its mathematical derivation principles are explained in detail, along with the specific measurement steps for using the aforementioned device to resist ellipticity fluctuation interference.

[0086] Step S1: Establishing a single-beam elliptically polarized physical model. In a single-beam magnetometer, the incident probe light is prepared as elliptically polarized light, and its Jones vector... In the principal axis coordinate system, it can be represented as:

[0087]

[0088] in, Let be the ellipticity angle of the beam.

[0089] When the light beam passes through the atomic gas cell, it is affected by the Faraday effect caused by the magnetic field, causing the principal axis of the elliptically polarized light to rotate by an angle of θ. (Magnetic field signal to be measured). The emitted light field at this time... Elliptically polarized light deflected along its principal axis:

[0090]

[0091] Step S2: Acquire magnetic field signal

[0092] The wobble of the elliptical principal axis is detected using 45° and 135° linearly polarized channels separated by a metasurface. The light intensities received by the photodetector are as follows:

[0093]

[0094]

[0095] Signal processing system 6 calculates normalized differential signals :

[0096]

[0097] The formula indicates the detected magnetic field signal The amplitude is directly affected by the ellipticity of the beam. Modulation. In actual operation, due to temperature drift or fiber disturbance, the ellipticity of the incident light... Random fluctuations can occur, causing instability in the magnetometer's sensitivity coefficient and generating noise.

[0098] Step S3: Acquire ellipticity monitoring signals. The ellipticity of the beam is monitored in real time using left-handed and right-handed circular polarization channels separated from the metasurface. Their light intensities are:

[0099]

[0100]

[0101] Signal processing system 6 calculates and monitors signals. :

[0102]

[0103] Formula surface Only with the current ellipticity of the beam Related to the rotation of the principal axis caused by the magnetic field It is irrelevant. Therefore, this channel can calculate the ellipticity in real time, eliminating the need to measure the ellipticity of the probe light.

[0104] Step S4: Four-polarization state decoupling and magnetic field inversion. Signal processing system 6 performs real-time decoupling operations to extract pure magnetic field information from the elliptical light with principal axis oscillation. First, the current modulation factor is calculated:

[0105]

[0106] Secondly, this factor is used to analyze the original signal. Make corrections:

[0107]

[0108] Finally, the precise magnetic field rotation angle is obtained through inversion. :

[0109]

[0110] Through the aforementioned signal processing flow, this invention achieves real-time tracking and dynamic compensation for fluctuations in the ellipticity of the probe light. This method overcomes the limitation of traditional single-beam magnetometers that rely on a constant polarization state of the light source. By utilizing an independent monitoring benchmark constructed using a circular polarization channel, it mathematically eliminates common-mode noise introduced by ellipticity variations. This not only significantly suppresses scaling factor instability caused by fiber disturbances or temperature drift but also greatly improves the low-frequency sensitivity and measurement accuracy of the magnetometer, providing a highly interference-resistant signal demodulation scheme for high-sensitivity weak magnetic field detection.

[0111] A four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces is proposed. This method is applied to the detection end of a single-beam elliptical polarization optical atomic magnetic sensor, aiming to achieve miniaturized integration of the detection optical path and anti-interference measurement. The method includes the following steps: Step S1: Place a four-channel focusing metasurface device on the light output path of the atomic gas cell of the magnetometer, replacing the traditional quarter-wave plate, polarization beam splitter, and lens group; Step S2: Use the metasurface device to directly separate and simultaneously focus the single beam of transmitted light carrying magnetic field information into four independent light spots: left-handed circularly polarized, right-handed circularly polarized, 45-degree linearly polarized, and 135-degree linearly polarized; Step S3: Use a photoelectric detection array to synchronously collect the light intensity of the four light spots. , , , Step S4: Based on the principle of light polarization, calculate the monitoring signal characterizing the real-time ellipticity of the pump light. and the original signal characterizing magnetic field information. Step S5: Utilize monitoring signals For the original signal Decoupling corrections are performed to eliminate ellipticity interference, and the accurate magnetic field rotation angle is obtained through inversion. .

[0112] The four-channel focusing metasurface device employs a "sub-aperture pseudo-random spatial multiplexing" design method to ensure uniform sampling of the Gaussian beam cross-section. Specifically, this includes: logically dividing the metasurface aperture into several tiny sub-aperture units; within each sub-aperture unit, nanopillar focusing units that respond to left-handed circular polarization, right-handed circular polarization, and linear polarization are set according to a preset ratio; the positions of the nanopillars within the sub-aperture units are determined by a pseudo-random algorithm, resulting in a uniform mixed distribution of each functional unit on the macroscopic aperture.

[0113] The preset ratio is 1:1:1, meaning that within each sub-aperture unit, the number of nanopillars responding to left-handed circular polarization, right-handed circular polarization, and linear polarization is equal.

[0114] The nanopillar focusing unit, responding to both left-handed and right-handed circular polarization, performs wavefront modulation based on the Pancharatnam-Berry phase principle. The nanopillars have fixed length and width dimensions and are configured as a half-wave plate structure at the operating wavelength to maximize polarization conversion efficiency. The polarization conversion efficiency is maximized by changing the rotation angle of the nanopillars within the plane. To introduce the required focusing phase And satisfy (in (as a sign factor related to rotation), thereby enabling independent focusing of left-handed and right-handed circularly polarized light respectively.

[0115] The nanopillar focusing unit with linear polarization response is a dual-function multiplexing unit; the unit is configured to have a dual phase response: when the incident light is linearly polarized at 45 degrees, it generates a focusing phase pointing to the 45° channel focus; when the incident light is linearly polarized at 135 degrees, it generates a focusing phase pointing to the 135° channel focus; thus, a single nanopillar can be used to simultaneously detect two orthogonally linearly polarized channels.

[0116] 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 four-channel polarization decoupling detection method based on a metasurface-based optical atomic magnetic sensor, characterized in that, Includes the following steps: Step 1: Set up a four-channel focusing metasurface device between the alkali metal gas cell detector light output side in the photoelectric detection array and the magnetic probe assembly; Step 2: Using the four-channel focusing metasurface device, the light emitting side probe carrying magnetic field information is directly separated in space and simultaneously focused into the following four independent light spots: left-hand circularly polarized focusing light spot, right-hand circularly polarized focusing light spot, 45-degree linearly polarized focusing light spot, and 135-degree linearly polarized focusing light spot. Step 3: Simultaneously collect the following four parameters using the photoelectric detection array: , , , , It is the light intensity of the left-handed circularly polarized focused spot. It is the light intensity of the right-hand circularly polarized focused spot. It is the light intensity of the 45-degree linearly polarized focused spot. It is the light intensity of the 135-degree linearly polarized focused spot; Step 4, based on the principle of light polarization, using , , ,and Calculate respectively and , It is a monitoring signal characterizing the real-time ellipticity of the pump light. It is the original signal that characterizes magnetic field information; Step 5, using right Decoupling corrections are performed to eliminate ellipticity interference, and the inversion is obtained. , It is the rotation angle of the magnetic field.

2. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 1, characterized in that, Step 4 includes the following expression: in It is the pump light ellipticity.

3. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 1, characterized in that, Step 5 includes the following expression: The above expression eliminates the ellipticity term. The modulation effect can be accurately obtained. value, It is proportional to the strength of the magnetic field being measured.

4. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 1, characterized in that, In step 1, the four-channel focusing metasurface device adopts a "sub-aperture pseudo-random spatial multiplexing" design method to ensure uniform sampling of the Gaussian beam cross section. Specifically, this includes: dividing the metasurface aperture logic into several tiny sub-aperture units; within each sub-aperture unit, nanopillar focusing units that respond to left-hand circular polarization, right-hand circular polarization, and linear polarization are set according to a preset ratio; the positions of the nanopillars within the sub-aperture units are determined by a pseudo-random algorithm, so that each functional unit presents a uniform mixed distribution on the macroscopic aperture.

5. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 4, characterized in that, The preset ratio is 1:1:1, meaning that within each sub-aperture unit, the number of nanopillars responding to left-handed circular polarization, right-handed circular polarization, and linear polarization is equal.

6. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 4, characterized in that, The nanopillar focusing unit, responding to left-handed and right-handed circular polarization, performs wavefront modulation based on the geometric phase principle. The nanopillar has fixed length and width dimensions and is configured as a half-wave plate structure at the operating wavelength to maximize polarization conversion efficiency. The polarization conversion efficiency is maximized by changing the rotation angle of the nanopillar in the plane. To introduce the required focusing phase And satisfy , (as a sign factor related to rotation), thereby enabling independent focusing of left-handed and right-handed circularly polarized light respectively.

7. The four-channel polarization decoupling detection method for an optical atomic magnetic sensor based on metasurfaces according to claim 4, characterized in that, The nanopillar focusing unit that responds to linear polarization is a dual-function multiplexing unit, which is configured to have a dual phase response: when the incident light is linearly polarized at 45 degrees, it generates a focusing phase pointing to the 45° channel focus; when the incident light is linearly polarized at 135 degrees, it generates a focusing phase pointing to the 135° channel focus. This allows for the simultaneous detection of two orthogonal linear polarization channels using a single nanopillar.

8. A four-channel polarization decoupling detection device for an optical atomic magnetic sensor based on a metasurface, characterized in that, The four-channel polarization decoupling detection method based on a metasurface optical atomic magnetic sensor according to any one of claims 1-7 is adopted.

9. The four-channel polarization decoupling detection device for an optical atomic magnetic sensor based on metasurfaces according to claim 8, characterized in that, The device includes a four-channel focusing metasurface device with an anisotropic nanopillar array integrated on its surface. The photodetector array is located on the focal plane of the four-channel focusing metasurface device and contains four independent photosensitive units, each corresponding to one of the four focusing channels. The photodetector array is sequentially connected to a TIA transimpedance amplifier, a LIA lock-in amplifier, and a PC. The LIA lock-in amplifier is connected to a coil in a magnetic probe assembly. The alkali metal gas cell in the magnetic probe assembly is connected to a laser source assembly via a collimation and polarization state preparation lens group.

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