Elliptically polarized optomagnetic signal detection system and method based on cascade metasurface

Abstract

The invention discloses an elliptically polarized optomagnetic signal detection system and method based on a cascade metasurface, and the system employs a cascade metasurface polarization conversion device to emit elliptically polarized light with a specific ellipticity, and guides the elliptically polarized light into an atomic gas chamber, and the elliptically polarized light interacts with alkali metal atoms to achieve the measurement of a magnetic field. The Jones matrix of the cascade metasurface is designed according to the needed ovality, the material, the structure and the period of the metasurface are designed, light emitted by the laser is converted into elliptically polarized light with the preset ovality, and after the elliptically polarized light enters the atom air chamber, an optical rotation effect is generated while alkali metal atoms are polarized, so that the metal atoms are polarized. And the information of the magnetic field to be detected is obtained by using a differential detection technology and a phase-locked amplification technology. Compared with a conventional magnetic signal detection system, the magnetic signal detection system constructed by using the cascaded metasurface polarization conversion device has the advantages of small size and easiness in integration due to a compact structure and a miniaturized design concept.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum precision magnetic field measurement, and relates to an ellipsometric photomagnetic signal detection system and method based on a cascaded metasurface. Background Art

[0002] Magnetic phenomena are one of the earliest physical phenomena known to humans. The compass invented in ancient China is a classic example of using the earth's magnetic field. With the advancement of science and technology, the detection technology of weak magnetic fields has received increasing attention and has played a vital role in many fields such as geological exploration, military protection, earthquake early warning, industrial production and archaeological exploration.

[0003] The core sensor of magnetic field measurement technology is the magnetometer. Commonly used high-performance magnetometers for measuring the geomagnetic field can be divided into fluxgate magnetometers, superconducting quantum interferometer magnetometers, proton magnetometers, induction magnetometers, fiber optic magnetometers and optically pumped atomic magnetometers according to different measurement principles. Among them, the optically pumped atomic magnetometer based on the optical magnetic resonance effect shows significant advantages such as fast response speed, wide measurement range, and no need for ultra-low temperature refrigeration.

[0004] However, in practical applications, especially for wearable devices such as portable heart and brain magnetic detection, the bulky structure of existing optically pumped atomic magnetometers greatly limits their application scope. In the process of polarization conversion, most of the laser light sources commonly used in optically pumped atomic magnetometers still need to pass through large optical devices such as collimating lenses, polarizers and quarter-wave plates to produce elliptically polarized light with a specific ellipticity. This traditional large optical component is not only large in size and bulky in structure, but also has insufficient polarization conversion accuracy, which is not conducive to the miniaturization and integration of the system.

[0005] As an artificial electromagnetic material composed of micro-nano structures, metasurfaces can arbitrarily control the polarization, phase, and amplitude dimensions of light fields, and exhibit excellent optical performance on a subwavelength scale. Compared with traditional wave plates, metasurfaces are more flexible, smaller, and lighter, and are simple to process, thin, easy to integrate, and have low losses. Therefore, by utilizing the revolutionary technology of metasurfaces, polarization devices based on wave plate cascades can be greatly miniaturized.

[0006] Therefore, based on the above technical problems, the development of a new type of optically pumped magnetometer with small size and high sensitivity is crucial for its promotion in outdoor applications. Summary of the invention

[0007] (I) Purpose of the invention

[0008] The purpose of the present invention is to provide an elliptically polarized optical magnetic signal detection system and method based on a cascaded metasurface, construct a cascaded metasurface polarization conversion device, change the polarization state and ellipticity of the output light by adjusting the angle between the light transmission axis of the metal grating structure and the fast axis of the quarter-wave plate metaatom, and collimate the light beam by adjusting the arrangement of the quarter-wave plate metaatom, and introduce the collimated elliptically polarized light into the atomic gas chamber as a pumping laser, avoiding the use of traditional large-volume optical devices for polarization state conversion, thereby reducing the volume of the system's optical components, and improving the polarization conversion accuracy, thereby improving the sensitivity of the magnetic signal detection system.

[0009] (II) Technical solution

[0010] In order to solve the above technical problems, the present invention provides an elliptically polarized optical magnetic signal detection system based on a cascaded metasurface, which includes: a laser unit 1, a cascaded metasurface polarization conversion device 2, a magnetic probe unit 3 and a signal processing unit 4; the cascaded metasurface polarization conversion device 2 is arranged at the light output end of the laser unit 1, the magnetic probe unit 3 is arranged at the output end of the cascaded metasurface polarization conversion device 2, and the signal processing unit 4 is located at the output end of the magnetic probe unit 3 and receives the optical signal output by the magnetic probe unit 3; the laser unit 1 emits a linearly polarized laser beam with a fixed wavelength and set power, and emits it to the cascaded metasurface polarization conversion device 2, the elliptically polarized light converted by the cascaded metasurface polarization conversion device 2 enters the atomic gas chamber 10 heated by the magnetic probe unit 3, polarizes the atomic gas inside the atomic gas chamber 10, and at the same time, the elliptically polarized light passing through the atomic gas chamber 10 enters the signal processing unit 4 as a detection light, and the magnetic field information to be measured is obtained through differential detection and phase-locked amplification.

[0011] The laser unit 1 includes a laser 5 and a controller 6 , and the controller 6 controls the laser 5 to emit a linearly polarized laser beam with a fixed wavelength and set power; the laser beam with a fixed wavelength emitted by the laser 5 enters the cascaded metasurface polarization conversion device 2 .

[0012] Among them, the cascaded metasurface polarization conversion device 2 includes a silicon substrate 9, a metal grating structure 7 formed on the front surface of the silicon substrate 9 and a quarter-wave plate metaatom 8 formed on the rear surface of the silicon substrate 9. The metal grating structure 7 is used to convert the laser light source into linearly polarized light with a clear direction, and the quarter-wave plate metaatom 8 is used to convert the linearly polarized light into elliptically polarized light; by adjusting the angle between the transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate metaatom 8, elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit 3.

[0013] The metal grating structure 7 and the quarter wave plate super atom 8 are cascaded by being respectively etched on both sides of the silicon substrate 9, and the metal grating structure 7 and the quarter wave plate super atom 8 have different materials, structures and periods.

[0014] Among them, the magnetic probe unit 3 includes: an atomic gas chamber 10, an oven 11 located outside the atomic gas chamber 10, and a temperature control system 12 for controlling the temperature of the oven 11; under the control of the temperature control system 12, the temperature of the oven 11 is adjusted to heat the atomic gas chamber 10, and the elliptically polarized light beam enters the heated atomic gas chamber 10 to polarize the internal atomic gas and enters the signal processing unit 4 as a detection light.

[0015] The atomic gas chamber 10 is filled with alkali metal atoms and inert buffer gas. After heating, the number density of alkali metal vapor atoms in the atomic gas chamber 10 reaches 10 13 ~10 14 Pieces / cm 3 .

[0016] Among them, the signal processing unit 4 includes: a polarization beam splitter 14, a balanced photodetector 15 located on the rear side of the polarization beam splitter 14, a phase-locked amplifier 16 connected to the balanced photodetector 15, and a data processing system 17 connected to the phase-locked amplifier 16 and used to calculate the magnetic field value to be measured; after the detection light is incident on the polarization beam splitter 14, it is divided into two beams of linearly polarized light, and after being introduced into the balanced photodetector 15, it is converted into a photocurrent signal processed by differential amplification. The phase-locked amplifier 16 uses a demodulation signal to demodulate the photocurrent signal to obtain a phase-locked amplified signal, and finally the magnetic field value to be measured is calculated by the data processing system 17.

[0017] 8. The ellipsoidal polarization optical magnetic signal detection system based on the cascaded metasurface as described in claim 7 is characterized in that the magnetic probe unit 3 also includes a radio frequency coil 13 arranged at both ends of the oven 11, and the radio frequency coil 13 is connected to a phase-locked amplifier 16. The phase-locked amplifier 16 sweeps the radio frequency magnetic field of the radio frequency coil 13. When the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the signal measured by the balanced photodetector 15 reaches a maximum. After this signal passes through the data processing system 17, the magnetic field value to be measured is obtained.

[0018] The present invention also provides an ellipsometric optical magnetic signal detection method, comprising the following steps:

[0019] S1, using the controller 6 to adjust the frequency of the laser light source generated by the laser 5 to the alkali metal D1 line resonance frequency, the polarization state is linearly polarized light, and at the same time adjust the intensity of the laser light source to the set power;

[0020] S2, adjusting the cascaded metasurface polarization conversion device 2 so that the light transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate metaatom 8 form a set angle;

[0021] S3, injecting the laser light source generated in step S1 into the cascade metasurface polarization conversion device 2 modulated in step S2, converting it into collimated elliptically polarized light with a set ellipticity, using the elliptically polarized light as both pump light and probe light to illuminate the atomic gas chamber 10, realizing polarization of alkali metal atoms and generating optical rotation angle for magnetic field detection;

[0022] S4, direct current heating is performed on the atomic gas chamber 10 through the heating film on the oven 11, so that the atoms in the atomic gas chamber 10 reach a vaporized state to increase the atomic polarizability in the atomic gas chamber 10, the temperature of the atomic gas chamber 10 is monitored in real time by a thermistor, and the temperature of the atomic gas chamber 10 is stabilized by PID control of the temperature control system 12;

[0023] S5. Place the magnetic signal detection system under the geomagnetic field or simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas chamber 10 through differential detection technology, connect the differential amplified signal obtained after differential amplification to the phase-locked amplifier, use the demodulation signal to demodulate the differential amplified signal using the phase-locked amplification technology to obtain the phase-locked amplified signal, and finally calculate the magnetic field value to be measured through the data processing system 17.

[0024] In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is expressed as:

[0025]

[0026] The Jones matrix of the quarter-wave plate superatomic structure with an angle β between the fast axis and the horizontal direction is G2, which is expressed as:

[0027]

[0028] The difference between α and β is the angle between the light transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate metaatom 8;

[0029] In step S3, the linearly polarized light component of the elliptically polarized light undergoes magneto-optical effect in the polarized atomic gas chamber, generating an optical rotation angle θ, which is expressed as:

[0030]

[0031] Where v′ is the optical frequency, v0′ is the resonant frequency of the alkali metal D1 transition, and r e is the classical electron radius, c is the speed of light in a vacuum, f osc is the oscillator strength, is the alkali metal atom density, d is the length of the interaction between light and polarized atoms, V is the Voigt function, P z represents the spin polarization, which is a function of the transverse external magnetic field and is defined as P z =2〈Sz 〉, where 〈S z 〉 is the average atomic spin value along the z direction; the optical rotation angle θ is monitored and detected by a balanced photodetector consisting of a linear polarization beam splitter and two photodetectors, and outputs a differential amplification signal to the phase-locked amplifier 16.

[0032] (III) Beneficial effects

[0033] The ellipsometric photomagnetic signal detection system and method based on cascaded metasurface provided by the above technical solution have the following beneficial effects:

[0034] (1) The detection system of the present invention utilizes a cascaded metasurface polarization conversion device to change the polarization state of the incident laser, emits elliptically polarized light with a set ellipticity, and introduces the light beam into the atomic gas chamber so that it interacts with alkali metal atoms to achieve magnetic field measurement.

[0035] (2) The detection system of the present invention calculates the Jones matrix of the cascaded metasurface polarization conversion device according to the set ellipticity, and selects the structure, material, period and arrangement of the metasurface accordingly, so that the cascaded metasurface polarization conversion device emits elliptically polarized light with the set ellipticity, and introduces the elliptically polarized light into the atomic gas chamber to polarize the alkali metal atoms. At the same time, a modulated magnetic field is applied in a direction perpendicular to the light beam, and the information of the magnetic field to be measured is obtained by using differential detection technology and phase-locked amplification technology.

[0036] (3) Compared with conventional atomic magnetometers, the present invention adopts a cascaded metasurface polarization conversion device to replace the traditional large-volume collimating lens, polarizer and quarter-wave plate, making the magnetic signal detection system more compact, smaller in size, more portable, and conducive to outdoor working environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of an ellipsometric optical magnetic signal detection system based on a cascaded metasurface disclosed in an embodiment of the present invention;

[0038] Figure 2 yes Figure 1 Schematic diagram of the working principle of the mid-cascade metasurface polarization conversion device.

[0039] Figures 3 to 5 They are Figure 2 Left, top, and right views of the cascaded metasurface polarization conversion device.

[0040] The following are the descriptions of the reference numerals:

[0041] 1. Laser unit; 2. Cascaded metasurface polarization conversion device; 3. Magnetic probe unit; 4. Signal processing unit; 5. Laser; 6. Controller; 7. Metal grating; 8. Quarter wave plate metaatom; 9. Silicon substrate; 10. Atomic gas chamber; 11. Oven; 12. Temperature control system; 13. RF coil; 14. Polarization beam splitter; 15. Balanced photodetector; 16. Phase-locked amplifier; 17. Data processing system. DETAILED DESCRIPTION

[0042] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0043] The present embodiment is based on the cascaded metasurface elliptically polarized optical magnetic signal detection system and method, which uses the cascaded metasurface polarization conversion device to emit elliptically polarized light with a specific ellipticity, and introduces it into the atomic gas chamber to interact with the alkali metal atoms to achieve magnetic field measurement. The core of the present embodiment is to design the Jones matrix of the cascaded metasurface according to the required ellipticity, accurately design the material, structure, and period of the metasurface, and convert the light emitted by the laser into elliptically polarized light with a predetermined ellipticity. After this elliptically polarized light enters the atomic gas chamber, it can produce an optical rotation effect while polarizing the alkali metal atoms, and use differential detection technology and phase-locked amplification technology to obtain the magnetic field information to be measured.

[0044] Reference Figures 1 to 5 As shown, the elliptical polarization optical magnetic signal detection system based on the cascaded metasurface of this embodiment includes a laser unit 1, a cascaded metasurface polarization conversion device 2, a magnetic probe unit 3 and a signal processing unit 4; the cascaded metasurface polarization conversion device 2 is arranged at the light output end of the laser unit 1, the magnetic probe unit 3 is arranged at the output end of the cascaded metasurface polarization conversion device 2, and the signal processing unit 4 is located at the output end of the magnetic probe unit 3 and receives the optical signal output by the magnetic probe unit 3; the laser unit 1 emits a linearly polarized laser beam with a fixed wavelength and set power, and emits it to the cascaded metasurface polarization conversion device 2, the elliptically polarized light converted by the cascaded metasurface polarization conversion device 2 enters the atomic gas chamber 10 heated by the magnetic probe unit 3 to polarize the atomic gas inside the atomic gas chamber 10, and the elliptically polarized light passing through the atomic gas chamber 10 enters the signal processing unit 4 as the detection light, and the magnetic field information to be measured is obtained through differential detection and phase-locked amplification.

[0045] The laser unit 1 includes a laser 5 and a controller 6 , and the controller 6 controls the laser 5 to emit a linearly polarized laser beam with a fixed wavelength and set power; the laser beam with a fixed wavelength emitted by the laser 5 enters the cascaded metasurface polarization conversion device 2 .

[0046] The cascaded metasurface polarization conversion device 2 includes a silicon substrate 9 and two metasurface structures formed on the two side surfaces thereof, the two metasurface structures being a metal grating structure 7 for generating linearly polarized light and a quarter-wave plate meta-atom 8 with a beam collimation function. The metal grating structure 7 and the quarter-wave plate meta-atom 8 are cascaded by etching them on both sides of the silicon substrate 9, respectively. The front half of the silicon substrate 9 is a metal grating 7 structure for converting a laser light source into linearly polarized light with a clear direction, and the rear half of the silicon substrate 9 is a quarter-wave plate meta-atom 8 structure with a beam collimation function, which can convert linearly polarized light into elliptically polarized light; the metal grating structure 7 and the quarter-wave plate meta-atom 8 are different in material, structure and period; by adjusting the angle between the light transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate meta-atom 8, elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit 3.

[0047] The magnetic probe unit 3 includes: an atomic gas chamber 10, an oven 11 located outside the atomic gas chamber 10, a temperature control system 12 for controlling the temperature of the oven 11, and a radio frequency coil 13 arranged at both ends of the oven 11; an elliptically polarized light beam enters the heated atomic gas chamber 10 to polarize the internal atomic gas and enters the signal processing unit 4 as a detection light.

[0048] The atomic gas chamber 10 is filled with alkali metal atoms and inert buffer gas. The temperature of the oven 11 is adjusted under the control of the temperature control system 12 to heat the atomic gas chamber 10 so that the number density of alkali metal vapor atoms in the atomic gas chamber 10 reaches 10 13 ~10 14 Pieces / cm 3 .

[0049] The signal processing unit 4 includes: a polarization beam splitter 14, a balanced photodetector 15 located at the rear side of the polarization beam splitter 14, a phase-locked amplifier 16 connected to the balanced photodetector 15 and the radio frequency coil 13, and a data processing system 17 connected to the phase-locked amplifier 16 and used to calculate the magnetic field value to be measured; after the detection light is incident on the polarization beam splitter 14, it is divided into two beams of linear polarized light, and after being introduced into the balanced photodetector 15, it is converted into a photocurrent signal processed by differential amplification. The phase-locked amplifier 16 uses a demodulation signal to demodulate the photocurrent signal to obtain a phase-locked amplified signal, and finally calculates the magnetic field value to be measured through the data processing system 17; wherein, the phase-locked amplifier 16 sweeps the radio frequency magnetic field of the radio frequency coil 13, and when the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the signal measured by the balanced photodetector 15 reaches a maximum, and this signal is passed through the data processing system 17 to obtain the magnetic field value to be measured.

[0050] The working principle of the elliptically polarized photomagnetic signal detection system based on the cascaded metasurface in this embodiment is: the controller 6 is used to adjust the laser 5 to emit a linearly polarized laser beam of set wavelength and power, the laser beam is incident on the incident surface of the cascaded metasurface polarization conversion device 2 and converted into a collimated elliptically polarized light of set ellipticity, the elliptically polarized light enters the heated atomic gas chamber 10 as pump light, so that the alkali metal gas inside the atomic gas chamber 10 is polarized, and at the same time, it is incident on the polarization beam splitter 14 as detection light and then split into two beams of linearly polarized light, which are then introduced into the balanced photodetector 15 and converted into a photocurrent signal, and the photocurrent signal is demodulated by using the demodulation signal using the phase-locked amplifier 16 to obtain a phase-locked amplified signal, and finally the magnetic field value to be measured is calculated by the data processing system 17.

[0051] Based on the aforementioned ellipsometric optical magnetic signal detection system, the ellipsometric optical magnetic signal detection method of this embodiment includes the following steps:

[0052] S1. Use controller 6 to adjust the frequency of the light source generated by laser 5 to the alkali metal D1 line resonance frequency, strengthen the interaction between light and atomic spin, and make the polarization state linearly polarized light. At the same time, adjust the intensity of the laser light source to the set power.

[0053] S2, adjusting the cascaded metasurface polarization conversion device 2 so that the light transmission axis of the metal grating structure 7 and the fast axis of the quarter-wave plate metaatom 8 form a set angle;

[0054] S3, injecting the laser light source generated in step S1 into the cascade metasurface polarization conversion device 2 modulated in step S2, converting it into collimated elliptically polarized light with a set ellipticity, using the elliptically polarized light as both pump light and probe light to illuminate the atomic gas chamber 10, realizing polarization of alkali metal atoms and generating optical rotation angle for magnetic field detection;

[0055] S4, direct current heating is performed on the atomic gas chamber 10 through the heating film on the oven 11, so that the atoms in the atomic gas chamber 10 reach a vaporized state to increase the atomic polarizability in the atomic gas chamber 10, the temperature of the atomic gas chamber 10 is monitored in real time by a thermistor, and the temperature of the atomic gas chamber 10 is stabilized by PID control of the temperature control system 12;

[0056] S5. Place the magnetic signal detection system under the geomagnetic field or simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas chamber 10 through differential detection technology, connect the differential amplified signal obtained after differential amplification to the phase-locked amplifier, use the demodulation signal to demodulate the differential amplified signal using the phase-locked amplification technology to obtain the phase-locked amplified signal, and finally calculate the magnetic field value to be measured through the data processing system 17.

[0057] In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is expressed as:

[0058]

[0059] The Jones matrix of the quarter-wave plate superatomic structure with an angle β between the fast axis and the horizontal direction is G2, which is expressed as:

[0060]

[0061] The difference between α and β is the angle between the metal grating transmission axis and one quarter of the superatom fast axis.

[0062] In step S3, the linearly polarized light component of the elliptically polarized light undergoes magneto-optical effect in the polarized atomic gas chamber, generating an optical rotation angle θ, which is expressed as:

[0063]

[0064] Where v′ is the optical frequency, ν0′ is the resonant frequency of the alkali metal D1 transition, and r e is the classical electron radius, c is the speed of light in a vacuum, f osc is the oscillator strength, is the alkali metal atom density, d is the length of the interaction between light and polarized atoms, and V is the Voigt function. z represents the spin polarization, which is a function of the transverse external magnetic field and is defined as P z =2〈S z 〉, where 〈S z 〉 is the average atomic spin value along the z direction.

[0065] The optical rotation angle θ is accurately monitored and detected by a balanced photodetector composed of a linear polarization beam splitter and two photodetectors, and a differential amplification signal is output to a phase-locked amplifier; the phase-locked amplifier demodulates the differential amplification signal using a phase-locked amplification technique through a demodulation signal to obtain an output signal of an atomic magnetometer, and enters the data processing system to calculate the magnetic field value to be measured.

[0066] It can be seen from the above technical scheme that the present invention uses a magnetic signal detection system built with cascaded metasurface polarization conversion devices, which replaces the traditional large-volume cascaded metasurface polarization conversion devices of collimating lenses, polarizers and quarter-wave plates. The cascaded metasurface polarization conversion devices perform high-precision light field manipulation on the incident linear polarization laser, and emit collimated elliptically polarized light with a set ellipticity, which reduces the volume of the magnetometer while increasing the polarization conversion accuracy.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An ellipsometric optical magnetic signal detection system based on cascaded metasurfaces, characterized in that: include: A laser unit (1), a cascaded metasurface polarization conversion device (2), a magnetic probe unit (3) and a signal processing unit (4); the cascaded metasurface polarization conversion device (2) is arranged at the light output end of the laser unit (1), the magnetic probe unit (3) is arranged at the output end of the cascaded metasurface polarization conversion device (2), and the signal processing unit (4) is located at the output end of the magnetic probe unit (3) and receives the optical signal output by the magnetic probe unit (3); the laser unit (1) emits a linearly polarized laser beam with a fixed wavelength and set power, and emits it to the cascaded metasurface polarization conversion device (2); the elliptically polarized light converted by the cascaded metasurface polarization conversion device (2) enters the heated atomic gas chamber (10) of the magnetic probe unit (3), polarizing the atomic gas inside the atomic gas chamber (10); and the elliptically polarized light passing through the atomic gas chamber (10) enters the signal processing unit (4) as detection light, and obtains the magnetic field information to be measured through differential detection and phase-locked amplification.

2. The ellipsometry optical magnetic signal detection system based on cascaded metasurface according to claim 1, characterized in that: The laser unit (1) comprises a laser (5) and a controller (6), wherein the controller (6) controls the laser (5) to emit a linearly polarized laser beam with a fixed wavelength and a set power; the laser beam with a fixed wavelength emitted by the laser (5) enters the cascaded metasurface polarization conversion device (2).

3. The ellipsometry optical magnetic signal detection system based on cascaded metasurface according to claim 2, characterized in that: The cascaded metasurface polarization conversion device (2) comprises a silicon substrate (9), a metal grating structure (7) formed on the front surface of the silicon substrate (9), and a quarter-wave plate metaatom (8) formed on the rear surface of the silicon substrate (9); the metal grating structure (7) is used to convert a laser light source into linearly polarized light with a clear direction, and the quarter-wave plate metaatom (8) is used to convert the linearly polarized light into elliptically polarized light; by adjusting the angle between the light transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate metaatom (8), elliptically polarized light with a set ellipticity is obtained and emitted to the magnetic probe unit (3).

4. The ellipsometry optical magnetic signal detection system based on cascaded metasurface according to claim 3, characterized in that: The metal grating structure (7) and the quarter-wave plate superatom (8) are cascaded by being respectively etched on both sides of a silicon substrate (9); the metal grating structure (7) and the quarter-wave plate superatom (8) are different in material, structure and period.

5. The ellipsometry optical magnetic signal detection system based on cascaded metasurface according to claim 3, characterized in that: The magnetic probe unit (3) comprises: an atomic gas chamber (10), an oven (11) located outside the atomic gas chamber (10), and a temperature control system (12) for controlling the temperature of the oven (11); the temperature of the oven (11) is adjusted under the control of the temperature control system (12) to heat the atomic gas chamber (10), and an elliptically polarized light beam enters the heated atomic gas chamber (10) to polarize the internal atomic gas and enters the signal processing unit (4) as detection light.

6. The ellipsometry optical magnetic signal detection system based on cascaded metasurface according to claim 5, characterized in that: The atomic gas chamber (10) is filled with alkali metal atoms and inert buffer gas. After heating, the number density of alkali metal vapor atoms in the atomic gas chamber (10) reaches 10 13 ~10 14 Pieces / cm 3 .

7. The ellipsometry optical magnetic signal detection system based on cascaded metasurfaces according to claim 6, characterized in that: The signal processing unit (4) comprises: a polarization beam splitter (14), a balanced photodetector (15) located at the rear side of the polarization beam splitter (14), a phase-locked amplifier (16) connected to the balanced photodetector (15), and a data processing system (17) connected to the phase-locked amplifier (16) and used to calculate the magnetic field value to be measured; after the detection light is incident on the polarization beam splitter (14), it is split into two beams of linearly polarized light, which are introduced into the balanced photodetector (15) and converted into a photocurrent signal that has been subjected to differential amplification processing; the phase-locked amplifier (16) demodulates the photocurrent signal using a demodulation signal to obtain a phase-locked amplified signal, and finally the magnetic field value to be measured is calculated by the data processing system (17).

8. The ellipsometry optical magnetic signal detection system based on cascaded metasurfaces according to claim 7, characterized in that: The magnetic probe unit (3) further comprises a radio frequency coil (13) arranged at both ends of the oven (11); the radio frequency coil (13) is connected to a phase-locked amplifier (16); the phase-locked amplifier (16) sweeps the radio frequency magnetic field of the radio frequency coil (13); when the radio frequency magnetic field signal is consistent with the magnetic field signal to be measured, the signal measured by the balanced photodetector (15) reaches a maximum value; and after the signal passes through a data processing system (17), the magnetic field value to be measured is obtained.

9. A method for detecting ellipsometric optical magnetic signals based on the detection system of claim 8, characterized in that: The following steps are involved: S1, using a controller (6) to adjust the frequency of the laser light source generated by the laser (5) to the alkali metal D1 line resonance frequency, the polarization state is linearly polarized light, and at the same time adjust the intensity of the laser light source to a set power; S2, adjusting the cascaded metasurface polarization conversion device (2) so that the light transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate metaatom (8) form a set angle; S3, injecting the laser light source generated in step S1 into the cascaded metasurface polarization conversion device (2) modulated in step S2, converting it into collimated elliptically polarized light with a set ellipticity, using the elliptically polarized light as both pump light and probe light to illuminate the atomic gas chamber (10), realizing polarization of alkali metal atoms and generating an optical rotation angle for magnetic field detection; S4, direct current heating is performed on the atomic gas chamber (10) through the heating film on the oven (11), so that the atoms in the atomic gas chamber (10) reach a vaporized state to increase the atomic polarizability in the atomic gas chamber (10), the temperature of the atomic gas chamber (10) is monitored in real time through a thermistor, and the temperature of the atomic gas chamber (10) is stabilized through PID control of the temperature control system (12); S5. Place the magnetic signal detection system under the geomagnetic field or simulated geomagnetic field, detect the elliptically polarized light passing through the atomic gas chamber (10) by differential detection technology, connect the differential amplified signal obtained after differential amplification to the phase-locked amplifier, use the demodulation signal to demodulate the differential amplified signal using the phase-locked amplification technology to obtain the phase-locked amplified signal, and finally calculate the magnetic field value to be measured by the data processing system (17).

10. The method for detecting ellipsometric optical magnetic signals according to claim 9, characterized in that: In step S2, the Jones matrix of the metal grating structure when the angle between the light transmission axis and the horizontal direction is α is G1, which is expressed as: The Jones matrix of the quarter-wave plate superatomic structure with an angle β between the fast axis and the horizontal direction is G2, which is expressed as: The difference between α and β is the angle between the light transmission axis of the metal grating structure (7) and the fast axis of the quarter-wave plate metaatom (8); In step S3, the linearly polarized light component of the elliptically polarized light undergoes magneto-optical effect in the polarized atomic gas chamber, generating an optical rotation angle θ, which is expressed as: Where v′ is the optical frequency, ν0′ is the resonant frequency of the alkali metal D1 transition, and r e is the classical electron radius, c is the speed of light in a vacuum, f osc is the oscillator strength, is the alkali metal atom density, d is the length of the interaction between light and polarized atoms, V is the Voigt function, P z represents the spin polarization, which is a function of the transverse external magnetic field and is defined as P z =2〈S z 〉, where 〈S z 〉 is the average atomic spin value along the z direction; the optical rotation angle θ is monitored and detected by a balanced photodetector composed of a linear polarization beam splitter and two photodetectors, and outputs a differential amplification signal to a phase-locked amplifier (16).

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