A method and device for measuring the polarization direction of a microwave electric field based on Rydberg atoms

Abstract

The present invention relates to a method and device for measuring the polarization direction of a microwave electric field based on Rydberg atoms. The method includes: generating two sets of orthogonally polarized lasers, where the probe light and coupling light with the same polarization direction are correspondingly combined and transmitted through two sets of optical fibers respectively to excite the atoms in the alkali metal atomic cell from the ground state to the Rydberg state; based on the interaction between the probe light, coupling light and alkali metal atoms, forming the electromagnetically induced transparency (EIT) effect of a three-level system to obtain an EIT signal. Among them, a specified microwave frequency is selected, and the microwave electric field generated by a microwave source is applied to the alkali metal atomic cell to cause the EIT signal to split and obtain an EIT-AT splitting signal; observing the two sets of EIT-AT splitting signals through an oscilloscope, and determining the angular range between the polarization direction of the microwave electric field and the polarization direction of the laser according to the left and right peak value ratios of the splitting peaks of the two sets of splitting signals. The technical solution provided by the present invention can improve the accuracy of microwave electric field measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and in particular, to a method and device for measuring the polarization direction of a microwave electric field based on Rydberg atoms. Background Art

[0002] In 2012, the related technology first utilized Rydberg atom EIT and AT splitting to convert the measurement of microwave electric field strength into optical frequency measurement, and experimentally realized microwave electric field measurement. The following year, based on microwave measurement, this technology carried out the measurement of microwave polarization direction. In 2021, the related technology realized the vector measurement of the near-field scattering field of radio frequency identification tags based on Rydberg atoms. Through the analysis of the three-peak spectral characteristics, the effective resolution of the complementary angle of the tag can be achieved, and at the same time, the identification of the angle of the radio frequency identification tag is realized, with an angle resolution of 1.64°.

[0003] However, the above method measures the polarization direction of microwaves through a group of lasers (considering the probe light and the coupling light as a group of light), and cannot completely and effectively identify any polarization direction. Moreover, the experimental operation is carried out in free space, and its operability, anti-interference ability, and test accuracy are not very ideal. Therefore, it is necessary to propose a technical method to improve the accuracy of microwave electric field measurement. Summary of the Invention

[0004] In view of this, it is necessary to address the above problems and provide a method and device for measuring the polarization direction of a microwave electric field based on Rydberg atoms, which can reduce the influence of the transmitted peak signal by measuring the specific direction of microwave polarization, thereby improving the accuracy of microwave electric field measurement.

[0005] To achieve the above object, on the one hand, the present invention provides a device for measuring the polarization direction of a microwave electric field based on Rydberg atoms, and the device includes:

[0006] Frequency-doubling laser (301), semiconductor laser (302), dual-path atomic receiving antenna (303), silicon avalanche photodetector (304), oscilloscope (305), computer control terminal (306). The frequency-doubling laser (301) and the semiconductor laser (302) are respectively connected to both sides of the dual-path atomic receiving antenna (303). The silicon avalanche photodetector (304) is used to detect the output signal of the dual-path atomic receiving antenna (303) and input the output signal into the oscilloscope (305). The dual-path atomic receiving antenna (303) includes an alkali metal atomic gas cell (401), a fiber (402) of a detection light pigtail ferrule, a detection light gradient index lens (403), a detection light collimation sleeve (404), a detection light protection sleeve (405), a fiber (406) of a coupling light pigtail ferrule, a coupling light gradient index lens (407), a coupling light collimation sleeve (408), a coupling light protection sleeve (409), where:

[0007] The fiber (402) of the detection light pigtail ferrule and the detection light gradient index lens (403) are jointly cemented in the detection light collimation sleeve (404), the detection light collimation sleeve (404) is cemented in the detection light protection sleeve (405), the fiber (406) of the coupling light pigtail ferrule and the coupling light gradient index lens (407) are jointly cemented in the coupling light collimation sleeve (408), the coupling light collimation sleeve (408) is cemented in the coupling light protection sleeve (409), and the detection light protection sleeve (405) and the coupling light protection sleeve (409) are respectively cemented on both sides of the alkali metal atomic gas cell (401).

[0008] In one embodiment, the alkali metal atomic gas cell (401) is a closed glass bulb filled with an alkali metal elemental gas.

[0009] In one embodiment, the fiber (402) of the detection light pigtail ferrule is a single-mode polarization-maintaining fiber.

[0010] In one embodiment, the fiber (406) of the coupling light pigtail ferrule is a single-mode fiber.

[0011] In one embodiment, the detection light is a laser of 852 nm, and the coupling light is a laser of 509 nm.

[0012] On the other hand, the present invention also provides a method for measuring the polarization direction of a microwave electric field based on Rydberg atoms. The method includes:

[0013] Generating two sets of orthogonally polarized lasers, where the detection light and the coupling light with the same polarization direction are correspondingly combined and transmitted through two sets of optical fibers respectively to excite the atoms in the alkali metal atomic gas cell from the ground state to the Rydberg state;

[0014] Based on the interaction between the probe light, the coupling light and the alkali metal atoms, the electromagnetically induced transparency (EIT) effect of a three-level system is formed to obtain an EIT signal. Among them, a specified microwave frequency is selected, and the microwave electric field generated by the microwave source is applied to the alkali metal atom gas chamber so that the EIT signal is split to obtain an EIT-AT splitting signal;

[0015] The two groups of EIT-AT splitting signals are observed by an oscilloscope, and the included angle range between the polarization direction of the microwave electric field and the polarization direction of the laser is determined according to the ratio of the peak values of the left and right peaks of the splitting peaks of the two groups of splitting signals.

[0016] In one embodiment, the polarization direction of the microwave electric field is calculated according to the following formula:

[0017]

[0018]

[0019] Substituting θ and θ′ into the spherical coordinate system gives:

[0020]

[0021] The unique value of the polarization direction of the microwave electric field is finally determined as That is

[0022] where T and T′ are the amplitude ratio of the transmission peaks of the two groups of splitting signals, and θ and θ′ are the included angles between the polarization directions of the first group of laser and the second group of laser and the polarization direction of the microwave electric field, is the azimuth angle.

[0023] In summary, when measuring, the advantage of the dual-path atomic receiving antenna in the present invention is that it has little interference on the electric field to be measured, high sensitivity, and two measurement dimensions, effectively solving the problem of complementary angles, thereby improving the accuracy of polarization characteristic measurement. Brief Description of the Drawings

[0024] Figure 1 Shows a schematic diagram of the steps of a method for measuring the polarization direction of a microwave electric field based on Rydberg atoms in one embodiment of the present invention;

[0025] Figure 2 Shows a schematic diagram of the microwave polarization and laser polarization directions in the atomic gas chamber in one embodiment of the present invention;

[0026] Figure 3 Shows a schematic diagram of the structure of a device for measuring the polarization direction of a microwave electric field based on Rydberg atoms in one embodiment of the present invention;

[0027] Figure 4The structural schematic diagram of a dual - optical - path atomic receiving antenna in an embodiment of the present invention is shown. Specific embodiments

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described clearly and completely below in conjunction with the embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0029] Please refer to Figure 3 and Figure 4 , the present invention provides a device for measuring the polarization direction of a microwave electric field based on Rydberg atoms. The device includes:

[0030] A frequency - doubling laser 301, a semiconductor laser 302, a dual - optical - path atomic receiving antenna 303, a silicon avalanche photodetector 304, an oscilloscope 305, and a computer control terminal 306. The frequency - doubling laser 301 and the semiconductor laser 302 are respectively connected to both sides of the dual - optical - path atomic receiving antenna 303. The silicon avalanche photodetector 304 is used to detect the output signal of the dual - optical - path atomic receiving antenna 303 and input the output signal into the oscilloscope 305. The dual - optical - path atomic receiving antenna 303 includes an alkali - metal atomic gas cell 401, an optical fiber 402 with a probe - light tail - fiber ferrule, a probe - light gradient - index lens 403, a probe - light collimating sleeve 404, a probe - light protective sleeve 405, an optical fiber 406 with a coupling - light tail - fiber ferrule, a coupling - light gradient - index lens 407, a coupling - light collimating sleeve 408, and a coupling - light protective sleeve 409, where:

[0031] The optical fiber 402 with the probe - light tail - fiber ferrule and the probe - light gradient - index lens 403 are jointly cemented in the probe - light collimating sleeve 404, the probe - light collimating sleeve 404 is cemented in the probe - light protective sleeve 405, the optical fiber 406 with the coupling - light tail - fiber ferrule and the coupling - light gradient - index lens 407 are jointly cemented in the coupling - light collimating sleeve 408, the coupling - light collimating sleeve 408 is cemented in the coupling - light protective sleeve 409, and the probe - light protective sleeve 405 and the coupling - light protective sleeve 409 are respectively cemented on both sides of the alkali - metal atomic gas cell 401.

[0032] In one embodiment, the alkali - metal atomic gas cell 401 is a closed glass bulb filled with an alkali - metal elemental gas.

[0033] In one embodiment, the optical fiber 402 with the probe - light tail - fiber ferrule is a single - mode polarization - maintaining fiber.

[0034] In one embodiment, the optical fiber 406 of the coupled optical pigtail ferrule is a single-mode optical fiber.

[0035] In one embodiment, the probe light is a laser with a wavelength of 852 nm, and the coupled light is a laser with a wavelength of 509 nm.

[0036] In a specific application example, taking cesium atoms as an example, the frequency-doubling laser generates coupled light with a wavelength of 509 nm, and the semiconductor laser generates probe light with a wavelength of 852 nm. The silicon avalanche photodetector is a detector with high sensitivity and low noise, and is very suitable for detecting weak optical signals. The oscilloscope is small in size, strong in performance, and can be connected to the computer port for use, and its sampling is accurate and convenient. The computer control terminal is a control software developed based on EIT spectrum fitting and can be connected to the oscilloscope for use. The dual-path atomic receiving antenna is an integrated receiving antenna with high sensitivity and non-metallic interference-free. In addition, in the actual system structure, a microwave source and a microwave antenna horn can also be included. Among them, the microwave source is used to generate a microwave electric field with a specific frequency, and the microwave antenna horn emits the generated microwave electric field as a plane wave in the far-field region.

[0037] Two sets of lasers with orthogonal polarizations, where the probe light and the coupled light with the same polarization direction are correspondingly combined and transmitted through two sets of optical fibers respectively (one set is horizontally polarized laser, and the other set is vertically polarized light), exciting cesium atoms from the ground state to the Rydberg state. Due to the interaction between the probe light, the coupled light and the cesium atoms, the EIT effect of the three-level system is formed, and then the EIT signal is obtained. Applying the microwave electric field to be measured on the atomic gas cell, the EIT signal is split to obtain the EIT-AT split signal.

[0038] For example, in Figure 2 , 201 represents the first set of probe light and coupled light, 202 represents the Y-axis direction, 203 represents the linearly polarized light in the horizontal direction, 204 represents the microwave polarization in any direction, 205 represents the second set of probe light and coupled light, 206 represents the X-axis direction, 207 represents the linearly polarized light in the vertical direction, and 208 represents the microwave antenna horn.

[0039] The two sets of lasers act simultaneously in the cesium atomic gas cell. Two sets of EIT-AT signals can be observed through the oscilloscope. Under the action of the microwave electric field at any polarization angle, the split signal obtained is a state where the EIT and AT signals coexist. According to the formula of the transmission peak amplitude ratio (T and T′) at ΔC = 0, expressing the polarization angle in terms of the transmission peak amplitude ratio and substituting it into the spherical coordinate system, four value ranges of the microwave electric field polarization angle are obtained. Finally, observe the right peak and the left peak of the two split peaks, and compare their amplitude ratios with "1" to determine the polarization direction of the microwave in the spherical coordinate as

[0040] Among them, the calculation formula for the polarization direction of the microwave electric field to be measured is as follows:

[0041] Assume that the probe light is transmitted along the Z-axis direction, the coupling light and the probe light are transmitted in opposite directions collinearly, and the included angles between the microwave to be measured and the two sets of orthogonally polarized lasers are θ and θ′ respectively. Then, the electric field component in the same direction as the laser polarization is:

[0042]

[0043]

[0044] When there is an arbitrary angle between the laser polarization direction and the linearly polarized microwave electric field polarization direction, the AT effect and the EIT effect coexist, and there is a probe light transmission peak signal at ΔC = 0. Then: the amplitude ratio of the probe light transmission peak at ΔC = 0:

[0045]

[0046]

[0047] Since the two sets of lasers act simultaneously in the atomic gas cell, the following formula can be obtained:

[0048] T = 1 - cos 2 θ

[0049] T′ = 1 - cos 2 θ′

[0050] θ and θ′ can be expressed in terms of T and T′ as:

[0051]

[0052]

[0053] Substituting θ and θ′ into the spherical coordinate system, we can obtain:

[0054]

[0055] Under the action of the same microwave electric field, θ can be expressed by By observing the collected EIT-AT splitting signal and comparing the amplitude ratio of the right split peak to the left split peak with "1", the unique value of the microwave electric field polarization direction can be determined, and finally it is determined as That is

[0056] where T and T′ are the amplitude ratios of the transmission peaks of the two sets of splitting signals respectively, θ and θ′ are the included angles between the polarization directions of the first set of laser and the second set of laser and the microwave electric field polarization direction respectively, is the azimuth angle.

[0057] It can be seen that the method for measuring the polarization direction of a microwave electric field based on Rydberg atoms provided by the present invention may include Figure 1 the multiple steps shown below.

[0058] S1: Generate two groups of orthogonally polarized lasers. Among them, the probe light and the coupling light with the same polarization direction are correspondingly combined and transmitted through two groups of optical fibers respectively, so as to excite the atoms in the alkali metal atomic cell from the ground state to the Rydberg state;

[0059] S2: Based on the interaction between the probe light, the coupling light and the alkali metal atoms, form the electromagnetically induced transparency (EIT) effect of a three-level system to obtain an EIT signal. Among them, select a specified microwave frequency, apply the microwave electric field generated by a microwave source to the alkali metal atomic cell, so that the EIT signal is split to obtain an EIT-AT splitting signal;

[0060] S3: Observe the two groups of EIT-AT splitting signals through an oscilloscope, and determine the included angle range between the polarization direction of the microwave electric field and the polarization direction of the laser according to the left and right peak value ratios of the splitting peaks of the two groups of splitting signals.

[0061] Among them, the polarization direction of the microwave electric field is calculated according to the following formula:

[0062]

[0063]

[0064] Substitute θ and θ′ into the spherical coordinate system to obtain:

[0065]

[0066] The unique value of the polarization direction of the microwave electric field is finally determined as That is

[0067] Among them, T and T′ are respectively the amplitude ratio of the transmission peaks of the two groups of splitting signals, θ and θ′ are respectively the included angles between the polarization directions of the first group of laser and the second group of laser and the polarization direction of the microwave electric field, is the azimuth angle.

[0068] In practical applications, the optical fiber 402 of the probe light tail fiber ferrule and the probe light graded index lens 403 are jointly cemented in the probe light collimating sleeve 404. The probe light collimating sleeve is cemented in the probe light protection sleeve 405. The optical fiber 406 of the coupling light tail fiber ferrule and the coupling light graded index lens 407 are jointly cemented in the coupling light collimating sleeve 408. The coupling light collimating sleeve is cemented in the coupling light protection sleeve 409. The probe light protection sleeve 405 and the coupling light protection sleeve 409 are respectively cemented on both sides of the alkali metal atomic cell 401.

[0069] Taking cesium atoms as an example, the alkali metal atomic gas cell 401 is an ultra-high vacuum atomic gas cell made of quartz material, and the alkali metal atoms are cesium atoms. The probe light is transmitted through the optical fiber 402 of the pigtail ferrule and then focused by the probe light gradient index lens 403 and then enters the alkali metal atomic gas cell 401. At the same time, the coupling light is transmitted through the optical fiber 406 of the pigtail ferrule and then focused by the coupling light gradient index lens 407 and directly enters the alkali metal atomic gas cell 401. The two beams of light coincide and propagate in opposite directions in the alkali metal atomic gas cell 401. The role of the probe light is to excite the atoms from the ground state to the excited state, and the two-level absorption effect will occur; the coupling light is to excite the atoms in the excited state to the Rydberg state, thereby generating an electromagnetically induced transparency window, and then generating an EIT signal. After the probe light exits from the alkali metal atomic gas cell 401, it is coupled into the optical fiber of the coupling light and finally exits and then enters the silicon avalanche photodetector 304.

[0070] In summary, when the present invention is in measurement, the advantage of the dual-path atomic receiving antenna is that it has little interference with the electric field to be measured, high sensitivity, and two measurement dimensions, effectively solving the problem of complementary angles, thereby improving the accuracy of polarization characteristic measurement.

[0071] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A microwave electric field polarization direction measuring device based on Rydberg atoms, characterized in that The device includes: a frequency-doubled laser (301), a semiconductor laser (302), a dual-path atomic receiving antenna (303), a silicon avalanche photodetector (304), an oscilloscope (305), and a computer control terminal (306). The frequency-doubled laser (301) and the semiconductor laser (302) are respectively connected to both sides of the dual-path atomic receiving antenna (303). The silicon avalanche photodetector (304) is used to detect the output signal of the dual-path atomic receiving antenna (303) and input the output signal into the oscilloscope (305). The dual-path atomic receiving antenna (303) includes an alkali metal atomic gas cell (401), a fiber (402) with a detection light tail fiber ferrule, a detection light gradient index lens (403), a detection light collimation sleeve (404), a detection light protection sleeve (405), a fiber (406) with a coupling light tail fiber ferrule, a coupling light gradient index lens (407), a coupling light collimation sleeve (408), and a coupling light protection sleeve (409). Among them: The fiber (402) with the detection light tail fiber ferrule and the detection light gradient index lens (403) are jointly cemented in the detection light collimation sleeve (404), and the detection light collimation sleeve (404) is cemented in the detection light protection sleeve (405). The fiber (406) with the coupling light tail fiber ferrule and the coupling light gradient index lens (407) are jointly cemented in the coupling light collimation sleeve (408), and the coupling light collimation sleeve (408) is cemented in the coupling light protection sleeve (409). The detection light protection sleeve (405) and the coupling light protection sleeve (409) are respectively cemented on both sides of the alkali metal atomic gas cell (401).

2. The microwave electric field polarization direction measuring device based on Rydberg atoms according to claim 1, wherein, The alkali metal atomic gas cell (401) is a closed glass bulb filled with an alkali metal elemental gas.

3. The microwave electric field polarization direction measuring device based on Rydberg atoms according to claim 1, wherein The fiber (402) with the detection light tail fiber ferrule is a single-mode polarization-maintaining fiber.

4. The microwave electric field polarization direction measuring device based on Rydberg atoms according to claim 1, characterized in that The fiber (406) with the coupling light tail fiber ferrule is a single-mode fiber.

5. The microwave electric field polarization direction measuring device based on Rydberg atoms according to claim 1, characterized in that, The detection light is a laser with a wavelength of 852 nm, and the coupling light is a laser with a wavelength of 509 nm.

6. A measurement method applied to the measurement device for measuring the polarization direction of microwave electric field based on Rydberg atoms according to any one of claims 1 to 5, characterized in that, The method includes: generating two sets of orthogonally polarized lasers. Among them, the detection light and the coupling light with the same polarization direction are correspondingly combined and transmitted through two sets of optical fibers respectively to excite the atoms in the alkali metal atomic gas cell from the ground state to the Rydberg state; forming the EIT effect of a three-level system based on the interaction between the detection light, the coupling light and the alkali metal atoms to obtain an EIT signal. Among them, a specified microwave frequency is selected, and the microwave electric field generated by a microwave source is applied to the alkali metal atomic gas cell so that the EIT signal is split to obtain an EIT-AT splitting signal; observing the two sets of EIT-AT splitting signals through an oscilloscope, and determining the included angle range between the polarization direction of the microwave electric field and the polarization direction of the laser according to the left and right peak value ratios of the splitting peaks of the two sets of splitting signals.

7. The measuring method according to claim 6, wherein The polarization direction of the microwave electric field is calculated according to the following formula: Substituting θ and θ′ into the spherical coordinate system, we get: The only value of the polarization direction of the microwave electric field is finally determined as That is where T and T′ are respectively the amplitude ratio of the transmission peaks of the two sets of split signals, and θ and θ′ are respectively the angles between the polarization directions of the first set of laser and the second set of laser and the polarization direction of the microwave electric field, which is the azimuth angle.

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