Microwave electric field measuring device and method

Abstract

The embodiment of the invention relates to the field of microwave electric field measurement, in particular to a microwave electric field measurement device and method, and the device comprises a laser light source module, a microwave generation module, and a data processing module. The laser light source module is used for exciting Rydberg atoms in the atomic gas chamber and generating an electromagnetic induction transparent spectrum; the microwave generation module is used for generating a microwave signal to be measured, the microwave signal to be measured is radiated to the atomic gas chamber through the horn antenna, and the electromagnetic induction transparent spectrum is split or heterodyne interference occurs due to the microwave signal to be measured; the data processing module is used for collecting electric signals and calculating the microwave electric field intensity by analyzing the splitting frequency spacing of the electromagnetic induction transparent spectrum, and the electric signals are jointly obtained by the laser light source module and the microwave generation module. According to the invention, high-precision measurement of the microwave electric field is realized.

Description

Technical Field

[0001] This application relates to the field of microwave electric field measurement, and more particularly to a microwave electric field measurement method. Background Technology

[0002] In the field of microwave electric field measurement, traditional dipole antenna measurement methods face several technical challenges. First, these methods require calibration and lack traceability to the International System of Units (SI), affecting the standardization and accuracy of the measurements. Second, the metallic materials contained in the dipole antenna can interfere with the measured field, leading to inaccurate measurement results. Furthermore, the antenna size is limited by the Chu limit, restricting its application in high-precision measurements. Finally, sensitivity is limited by factors such as thermal noise, failing to meet the requirements for high-precision, high-sensitivity, and high-bandwidth microwave electric field measurements.

[0003] In contrast, Rydberg atoms, due to their high polarizability and large dipole moments between adjacent energy levels, exhibit high sensitivity to external electric fields, long coherence times, narrow natural linewidths, and a wide transition frequency range (1-500 GHz). These characteristics give Rydberg atoms a significant advantage in microwave electric field measurements. By utilizing the quantum coherence effects of Rydberg atoms (such as electromagnetically induced transparency and the Autler-Townes effect), the measurement of microwave electric field intensity can be transformed into the measurement of optical frequency, realizing microwave electric field amplitude measurement, and this method is traceable to the International System of Units (SI).

[0004] However, to further improve the accuracy of microwave electric field measurements, narrow-linewidth ultra-stable lasers have become key components. Their ultra-narrow linewidth, low noise, good coherence, and high frequency stability are crucial for achieving high-resolution laser spectroscopy, precise optical frequency control, and precision measurement physics. However, the frequency stability of lasers is limited by factors such as ambient temperature, mechanical vibration, and acoustic noise, and is typically improved using passive measures such as ambient temperature control, vibration isolation platforms, and soundproof environments.

[0005] To achieve higher precision microwave electric field measurements, active frequency stabilization is required. Common methods include spectral-referenced and length-referenced frequency stabilization techniques. Among these, high-precision FP reference cavity frequency stabilization combined with Pound-Drever-Hall (PDH) technology is the best-performing method. PDH stabilization generates an error signal, processes it through a proportional-integral-differential circuit, and then feeds it back to the laser to achieve frequency compensation and stabilize the frequency. The integration and application of these technologies will significantly improve the accuracy and stability of microwave electric field measurements. Currently, the aforementioned microwave electric field measurement methods based on the Rydberg atomic quantum coherence effect are mainly still in the laboratory research stage. Summary of the Invention

[0006] One objective of this application is to provide a microwave electric field measurement device and method to address the technical problem that existing microwave electric field measurement methods based on the Rydberg atomic quantum coherence effect remain at the laboratory research stage.

[0007] In a first aspect, a microwave electric field measuring device is provided, comprising: a laser source module, a microwave generating module, and a data processing module; the laser source module is used to excite Rydberg atoms in an atomic gas chamber and generate an electromagnetically induced transparency spectrum; the microwave generating module is used to generate a microwave signal to be measured, which is radiated to the atomic gas chamber through a horn antenna, and the microwave signal to be measured causes the electromagnetically induced transparency spectrum to split or undergo heterodyne interference; the data processing module is used to acquire electrical signals and calculate the microwave electric field strength by analyzing the splitting frequency spacing of the electromagnetically induced transparency spectrum, wherein the electrical signals are jointly obtained by the laser source module and the microwave generating module.

[0008] In conjunction with the first aspect, in one possible implementation, the laser source module includes a first laser frequency stabilization module, a second laser frequency stabilization module, the atomic gas cell, a dichroic beam splitter, a first fiber coupler, and a second fiber coupler; the first laser frequency stabilization module outputs coupled light through the first fiber coupler, and the second laser frequency stabilization module outputs probe light through the second fiber coupler; the coupled light and the probe light are refracted against each other in the atomic gas cell to form the electromagnetically induced transparency spectrum; the dichroic beam splitter separates the probe light carrying the electromagnetically induced transparency spectrum to form the electrical signal, and transmits the electrical signal to the data processing module.

[0009] In conjunction with the first aspect, in one possible implementation, both the first laser frequency stabilization module and the second laser frequency stabilization module are connected to a portable ultra-stable optical reference cavity module; the first laser frequency stabilization module is connected to a first port and a second port of the portable ultra-stable optical reference cavity module, with the first port located opposite the second port; the second laser frequency stabilization module is connected to a third port and a fourth port of the portable ultra-stable optical reference cavity module, with the third port located opposite the fourth port; the portable ultra-stable optical reference cavity module is used for laser frequency stabilization.

[0010] In conjunction with the first aspect, in one possible implementation, the first laser frequency stabilization module includes a single-frequency fiber laser, a seed light, a first fiber acousto-optic modulator, a first fiber beam splitter, a fiber amplifier, a frequency doubling crystal, a second fiber beam splitter, a first fiber electro-optic phase modulator, a first fiber collimator, a first mirror, a first plano-convex lens, a first λ / 2 waveplate, a first polarizing beam splitter, a first λ / 4 waveplate, a second mirror, a third mirror, a first beam splitter, a silicon photodetector, a first charge-coupled device camera, a high-bandwidth silicon photodetector, a first mixer, a first direct digital frequency synthesis signal generator, a first signal generator, and a first proportional-integral-differential circuit.

[0011] In conjunction with the first aspect, in one possible implementation, the second laser frequency stabilization module includes an external cavity semiconductor laser, a third fiber beam splitter, a second fiber electro-optic phase modulator, a second fiber collimator, a fourth mirror, a second plano-convex lens, a second λ / 2 waveplate, a second polarizing beam splitter, a second λ / 4 waveplate, a fifth mirror, a sixth mirror, a second beam splitter, a photodetector, a second charge-coupled device camera, a first high-bandwidth photodetector, a second mixer, a second direct digital frequency synthesis signal generator, a second signal generator, and a second proportional-integral-differential circuit.

[0012] In conjunction with the first aspect, in one possible implementation, the microwave generating module includes a microwave signal source, a power amplifier, and a horn antenna; the microwave signal source is used to transmit the microwave signal to be tested, and the microwave signal to be tested is amplified by the power amplifier and then transmitted to the horn antenna to transmit a microwave electric field.

[0013] In conjunction with the first aspect, in one possible implementation, the data processing module includes a second high-bandwidth photodetector, an oscilloscope, and a computer device; the second high-bandwidth photodetector acquires the electrical signal and transmits the electrical signal to the oscilloscope to display the spectral morphology in real time, and calculates the microwave electric field intensity by analyzing the splitting frequency spacing of the electromagnetically induced transparency spectrum.

[0014] In conjunction with the first aspect, in one possible implementation, the distance between the atomic gas chamber and the horn antenna in the microwave generating module reaches the far-field condition.

[0015] In a second aspect, a microwave electric field measurement method is provided, implemented based on the apparatus described in any one of the first aspects, characterized in that it includes: Acquire the microwave signal to be tested; The microwave signal to be measured is processed to obtain the splitting frequency spacing of the electromagnetically induced transparent spectrum; The microwave electric field strength of the microwave signal under test is calculated based on the splitting frequency spacing of the electromagnetically induced transparent spectrum.

[0016] In conjunction with the second aspect, in one possible implementation, after acquiring the microwave signal to be measured, the method further includes: performing frequency mixing processing on the microwave signal to be measured to generate heterodyne interference and obtain phase information of the microwave signal to be measured; and calculating the microwave electric field strength of the microwave signal to be measured based on the phase information of the microwave signal to be measured.

[0017] In the aforementioned microwave electric field measurement device and method, this scheme, based on the EIT-AT effect and the quantum properties of Rydberg atoms, enables high-precision, wide dynamic range microwave electric field measurement. The measurement accuracy reaches the V / cm level, and the results are traceable to Planck's constant, possessing metrological reference characteristics. By analyzing the splitting spacing and heterodyne interference signal of the electromagnetically induced transparent spectrum, the device can simultaneously acquire multiple parameters such as electric field amplitude, phase, and frequency, with a frequency resolution on the Hz level. Compared to traditional antenna measurement methods, this device employs optical detection, avoiding field disturbances introduced by metal antennas. The atomic gas chamber provides natural shielding against electromagnetic interference, and combined with differential measurement technology, it effectively eliminates the influence of environmental noise. The modular system design (separating the laser source module, microwave generation module, and data processing module) facilitates independent optimization of each component. Fiber optic transmission reduces optical system jitter, and the absence of mechanical scanning components improves system reliability. Furthermore, the device exhibits excellent application scalability. By altering the Rydberg state energy levels, it can be adapted to measurement requirements in different frequency bands. Adjusting the cell-antenna distance supports near-field / far-field measurements, and the movable cell design also accommodates spatial field strength distribution measurements. Example data shows that within the 1-10 GHz frequency band, the relative uncertainty of electric field measurement is less than 0.5% (k=2), verifying the device's high accuracy and reliability. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a microwave electric field measuring device according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a first laser frequency stabilization module in one embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a second laser frequency stabilization module in one embodiment of the present invention; Figure 4aThis is a structural schematic diagram of the optical cavity design and fixing method in a portable ultra-stable optical reference cavity module according to an embodiment of the present invention; Figure 4b This is a schematic diagram of the thermal shielding design in a portable ultra-stable optical reference cavity module according to one embodiment of the present invention; Figure 4c This is a schematic diagram of the vacuum chamber design in a portable ultra-stable optical reference cavity module according to an embodiment of the present invention; Figure 5 This is a schematic flowchart of a microwave electric field measurement method according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0021] It should be noted that, unless there is a conflict, the various features in the embodiments of this application can be combined with each other, all of which are within the protection scope of this application. Furthermore, although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than the module division in the device or the order in the flowchart. Moreover, the terms "first," "second," and "third" used in this application do not limit the data or execution order, but only distinguish identical or similar items with essentially the same function and effect.

[0022] The present invention will now be described in detail through specific embodiments.

[0023] This application proposes a microwave electric field measurement device, which will be described in detail below.

[0024] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of the microwave electric field measuring device provided in an embodiment of the present invention. Figure 1The microwave electric field measurement device includes a laser source module (composed of numbers 55, 57, 63, 59, 58, and 56 in the figure), a microwave generation module 68 (composed of numbers 60-62 in the figure), and a data processing module 69 (composed of numbers 64-66 in the figure). The laser source module is used to excite Rydberg atoms in the atomic gas chamber and generate an electromagnetically induced transparent spectrum. The microwave generation module 68 is used to generate the microwave signal to be measured, which is radiated to the atomic gas chamber through a horn antenna. The microwave signal to be measured causes the electromagnetically induced transparent spectrum to split or undergo heterodyne interference. The data processing module 69 is used to acquire the electrical signal and calculate the microwave electric field strength by analyzing the splitting frequency spacing of the electromagnetically induced transparent spectrum. The electrical signal is obtained jointly by the laser source module and the microwave generation module 68.

[0025] Specifically, the laser source module includes a first laser frequency stabilization module 55, a second laser frequency stabilization module 56, an atomic gas cell 59, a dichroic beam splitter 63, a first fiber coupler 57, and a second fiber coupler 58. The first laser frequency stabilization module 55 outputs coupled light through the first fiber coupler 57, and the second laser frequency stabilization module 56 outputs probe light through the second fiber coupler 58. The coupled light and the probe light are refracted against each other within the atomic gas cell 59 to form the electromagnetically induced transparency spectrum. The dichroic beam splitter 63 separates the probe light carrying the electromagnetically induced transparency spectrum to form an electrical signal, which is then transmitted to the data processing module 69.

[0026] Among them, the atomic gas chamber can be a cesium atomic gas chamber, that is, the alkali metal gas is cesium atoms. Other alkali metal gases can be adapted to this device by replacing the corresponding alkali metal gas chamber and the laser required to excite the energy level transition. For example, when replacing it with a rubidium atomic gas chamber, it is necessary to adapt it to 780nm and 480nm narrow linewidth lasers.

[0027] In this design, the first laser frequency stabilization module 55 can be a 509nm laser frequency stabilization module, and the second laser frequency stabilization module 56 can be an 852nm laser frequency stabilization module. When the first laser frequency stabilization module 55 is a 509nm laser frequency stabilization module, the single-frequency fiber laser 11 can be a 509nm single-frequency fiber laser. When the second laser frequency stabilization module 56 is an 852nm laser frequency stabilization module, the external cavity semiconductor laser 36 can be an 852nm external cavity semiconductor laser. Therefore, in the case of both the 509nm and 852nm laser frequency stabilization modules, the emitted light is 509nm coupled light and 852nm probe light.

[0028] If a rubidium atom gas chamber is used instead, a 780nm probe light and a 480nm coupling light are required.

[0029] Specifically, both the first laser frequency stabilization module 55 and the second laser frequency stabilization module 56 are connected to the portable ultra-stable optical reference cavity module 27; the first laser frequency stabilization module 55 is connected to the first port and the second port of the portable ultra-stable optical reference cavity module 27, with the first port located opposite the second port; the second laser frequency stabilization module is connected to the third port and the fourth port of the portable ultra-stable optical reference cavity module 27, with the third port located opposite the fourth port; the portable ultra-stable optical reference cavity module is used for laser frequency stabilization.

[0030] Among them, the portable ultra-stable optical reference cavity module cavity is Figure 2 and Figure 3 27 in the middle, Figure 2 This is a schematic diagram of the structure of the first laser frequency stabilization module. Figure 3 This is a schematic diagram of the second laser frequency stabilization module.

[0031] Among them, you can refer to Figure 4a -c, Figure 4a -c forms the structural diagram of the portable ultrastable optical reference cavity module, where... Figure 4a A structural diagram showing the optical cavity design and its fixing method. Figure 4b Schematic diagram of the structure designed for heat shielding Figure 4c A schematic diagram of the structure designed for a vacuum chamber.

[0032] Specifically, according to Figure 4a As shown in -c, the portable ultra-stable optical reference cavity module cavity 27 includes an ultra-low expansion glass (ULE) FP reference cavity and cavity fixing structure 1; a multi-layer thermal shielding structure 2; a first thermal shield 3; a second thermal shield 4; a third thermal shield 5; a high vacuum cavity 6; an optical device fixing breadboard 7; a 5L / s ion pump 8; a high vacuum all-metal valve 9; and an aviation plug 10.

[0033] Among them, the portable ultra-stable optical reference cavity module cavity 27 serves as a frequency reference, and its stability is mainly affected by three external environmental factors: (1) the air refractive index in the light transmission direction of the cavity; (2) the length change of the cavity itself; and (3) environmental mechanical vibration. In response to the above three influencing factors, the optimization methods adopted are: (1) providing a high vacuum environment to reduce the influence of air refractive index; (2) using materials with low thermal expansion coefficients for the cavity and implementing temperature control, and designing a thermal shielding layer to reduce the length change caused by thermal expansion; and (3) optimizing the fixing method of the cavity to reduce the influence of external vibration.

[0034] For details, please refer to Figure 4aIn this design, the ultra-low expansion glass (ULE) FP reference cavity and its fixing structure 1 utilize Corning 7973P-grade ultra-low expansion glass (ULE), whose coefficient of thermal expansion at room temperature is close to zero, facilitating better temperature control of the cavity. The cavity employs a dual-channel light transmission design, consisting of two pairs of highly reflective plano-concave mirrors, capable of simultaneously serving as frequency references for two laser beams of different wavelengths. Four fixing grooves are set on each of the four vertical edges of the cavity, each containing a fluororubber ball, for a total of 16 fixing points. Finite element simulation software was used to optimize the position of the grooves within the cavity to obtain the optimal vibration resistance sensitivity. The cavity is fixed by connecting the first layer of gold-plated aluminum alloy heat shielding layer with set screws and pressing the fluororubber balls together.

[0035] For details, please refer to Figure 4b The design of the multi-layer thermal shielding structure 2 is shown. To reduce interlayer thermal radiation and lighten the weight of the module for portability, the first thermal shield 3 and the third thermal shield 5 (inner and outermost layers) are made of gold-plated aluminum alloy, while the second thermal shield 4 (middle layer) is made of gold-plated oxygen-free copper. To reduce interlayer heat conduction, the layers are fixed at four axially symmetrical points using four hollow Torlon cylinders. To minimize the influence of ambient temperature on the cavity, three thermoelectric cooler (TEC) recesses are designed at the bottom of the third thermal shield 5 (outermost layer). The TECs simultaneously cool and heat. The TECs are placed between the third thermal shield 5 (outermost layer) and the base of the high-vacuum cavity 6, and in contact with each other, the temperature of the cavity is controlled through heat conduction.

[0036] For details, please refer to Figure 4c The presentation showcases the appearance of the portable, ultra-stable optical reference cavity module 27. The aforementioned components a and b are housed within the high-vacuum cavity 6, creating an ultra-high vacuum environment to reduce the impact of air refractive index on frequency reference stability. Optical components are fixed to a breadboard 7, integrating the optical path onto the four outer walls of the high-vacuum cavity 6, enabling the reference cavity to be portable. Furthermore, a high vacuum of 10⁻⁶ Pa is achieved through pre-evacuation using an external molecular pump and mechanical pump connected to a high-vacuum all-metal valve 9, followed by long-term vacuum maintenance using a 5 L / s ion pump 8. An aviation connector 10 connects the internal semiconductor cooling chip and thermistor sensor to external temperature control instruments via multiple pins, enabling precise temperature control without affecting the vacuum environment.

[0037] Specifically, the first laser frequency stabilization module 55 includes a single-frequency fiber laser 11, a seed light 12, a first fiber acousto-optic modulator 13, a first fiber beam splitter 14, a fiber amplifier 15, a frequency doubling crystal 16, a second fiber beam splitter 17, a first fiber electro-optic phase modulator 18, a first fiber collimator 19, a first mirror 20, a first plano-convex lens 21, a first λ / 2 waveplate 22, a first polarizing beam splitter prism 23, a first λ / 4 waveplate 24, a second mirror 25, a third mirror 26, a first beam splitter 28, a silicon photodetector 29, a first charge-coupled device camera 30, a high-bandwidth silicon photodetector 31, a first mixer 32, a first direct digital frequency synthesis signal generator 33, a first signal generator 34, and a first proportional-integral-differential circuit 35.

[0038] The components in the first laser frequency stabilization module 55 can be connected in sequence, namely, a single-frequency fiber laser 11, a seed light 12, a first fiber acousto-optic modulator 13, a first fiber beam splitter 14, a fiber amplifier 15, a frequency doubling crystal 16, a second fiber beam splitter 17, a first fiber electro-optic phase modulator 18, a first fiber collimator 19, a first mirror 20, a first plano-convex lens 21, a first λ / 2 waveplate 22, a first polarizing beam splitter prism 23, a first λ / 4 waveplate 24, a second mirror 25, a third mirror 26, a first beam splitter 28, a silicon photodetector 29, a first charge-coupled device camera 30, a high-bandwidth silicon photodetector 31, a first mixer 32, a first direct digital frequency synthesis signal generator 33, a first signal generator 34, and a first proportional-integral-differential circuit 35 are connected in sequence.

[0039] The seed light can be 1018nm seed light, and this is not a unique limitation.

[0040] Specifically, a single-frequency fiber laser 11 is used to generate the 509nm coupling light required for the experiment. The 1018nm seed light 12, before frequency doubling, is used by a first fiber acousto-optic modulator (AOM) 13 for rapid frequency feedback of the laser. The output is then fed into a first fiber beam splitter 14, splitting it into two paths. One path is transmitted through a fiber amplifier 15 to a frequency-doubling crystal 16, where it outputs the 509nm laser for the experiment. The other path is further split into two paths by a second fiber beam splitter 17. One laser path is transmitted to a wavelength meter 67 to monitor its wavelength, while the other path is input to a first fiber electro-optic phase modulator (EOM) 18. A first signal generator 34 generates a frequency of... The sinusoidal signal is split into one path by a power beam splitter and input to the external phase modulation port of the first direct digital frequency synthesizer (DDS) signal generator 33. The first direct digital frequency synthesizer (DDS) signal generator 33 then generates a carrier frequency of... The signal drives the first fiber electro-optic phase modulator (EOM) 18 to perform phase modulation on the laser, and after optimizing the modulation depth, it is output to free space through the first fiber collimator 19.

[0041] After being reflected by the first mirror 20 in free space, the laser beam passes through the first plano-convex lens 21 for mode matching, and then the beam power entering the cavity is adjusted by a combination of the first λ / 2 waveplate 22 and the first polarizing beam splitter (PBS) 23. The first λ / 4 waveplate 24 is used for subsequent extraction of the reflected light signal. The angle and position of the laser entering the portable ultra-stable optical reference cavity module cavity 27 are then adjusted by the second mirror 25 and the third mirror 26. The first beam splitter (BS) 28 splits the laser beam transmitted through the cavity into two paths, which are received by the silicon photodetector 29 and the first charge-coupled device (CCD) camera 30, respectively, to obtain the transmitted light signal and beam pattern information, and to monitor the laser locking status in real time. The reflected light signal extracted by the first λ / 4 waveplate 24 is reflected by the first polarizing beam splitter (PBS) 23 to the high-bandwidth silicon photodetector 31, obtaining the carrier and sideband signals of the reflected light. This signal is then modulated with the phase generated by the first signal generator 34 at a frequency of... The sinusoidal signal is input to the first mixer 32 along with another channel, thereby demodulating the error signal with the frequency discrimination characteristic curve.

[0042] Furthermore, the error signal is processed by the first proportional-integral-differential circuit (PID) 35 and divided into fast and slow feedback. The fast feedback is sent to the first fiber acousto-optic modulator (AOM) 13, and the slow feedback is sent to the 1018nm seed light 12 piezoelectric ceramic (PZT) module inside the single-frequency fiber laser 11 to achieve frequency compensation and obtain a frequency stabilization effect. In the experiment, by adjusting the parameters in the first proportional-integral-differential circuit (PID) 35, the laser frequency can be better locked at the resonant frequency of the ultra-stable cavity. The above parts constitute the first laser frequency stabilization module 55 located on the optical device fixing breadboard 7.

[0043] Specifically, the second laser frequency stabilization module 56 includes an external cavity semiconductor laser 36, a third fiber beam splitter 37, a second fiber electro-optic phase modulator 38, a second fiber collimator 39, a fourth mirror 40, a second plano-convex lens 41, a second λ / 2 waveplate 42, a second polarizing beam splitter 43, a second λ / 4 waveplate 44, a fifth mirror 45, a sixth mirror 46, a second beam splitter 47, a photodetector 48, a second charge-coupled device camera 49, a first high-bandwidth photodetector 50, a second mixer 51, a second direct digital frequency synthesis signal generator 52, a second signal generator 53, and a second proportional-integral-differential circuit 54.

[0044] The components in the second laser frequency stabilization module 56 can be connected in sequence, namely, the external cavity semiconductor laser 36, the third fiber beam splitter 37, the second fiber electro-optic phase modulator 38, the second fiber collimator 39, the fourth mirror 40, the second plano-convex lens 41, the second λ / 2 waveplate 42, the second polarizing beam splitter 43, the second λ / 4 waveplate 44, the fifth mirror 45, the sixth mirror 46, the second beam splitter 47, the photodetector 48, the second charge-coupled device camera 49, the first high-bandwidth photodetector 50, the second mixer 51, the second direct digital frequency synthesis signal generator 52, the second signal generator 53, and the second proportional-integral-differential circuit 54 are connected in sequence.

[0045] Specifically, the external cavity semiconductor laser 36 is used to generate the 852nm probe light required for the experiment. After laser output, it is fed into a third fiber beam splitter 37 to split into two paths. One path is used for the experiment, and the other path is input into a second fiber electro-optic phase modulator (EOM) 38. The second signal generator 53 first generates a phase modulation frequency of... The sinusoidal signal is split into two paths by a power beam splitter. One path is input to the external phase modulation port of the second direct digital frequency synthesizer (DDS) signal generator 52, which then generates a carrier frequency of... The laser beam is phase-modulated by a second fiber electro-optic phase modulator (EOM) 38, and after the modulation depth is optimized, it is output to free space via a second fiber collimator 39. In free space, the laser beam is reflected by a fourth mirror 40 and passes through a second plano-convex lens 41 for mode matching. The beam power entering the cavity is then adjusted by a combination of a second λ / 2 waveplate 42 and a second polarizing beam splitter (PBS) 43, with a second λ / 4 waveplate 44 used for subsequent extraction of the reflected light signal. The angle and position of the laser beam entering the portable ultra-stable optical reference cavity module 27 are then adjusted by a fifth mirror 45 and a sixth mirror 46. A second beam splitter (BS) 47 splits the laser beam transmitted through the cavity into two paths, which are received by a high-bandwidth photodetector 48 and a second charge-coupled device (CCD) camera 49, respectively, to obtain the transmitted light signal and beam pattern information, and to monitor the laser locking status in real time. The second λ / 4 waveplate 44 extracts the reflected light signal, which is reflected by the second polarizing beam splitter (PBS) 43 and output to a first high-bandwidth photodetector 50, obtaining the carrier and sideband signals of the reflected light. The frequency of this signal is modulated by another phase generated by the second signal generator 53. The sinusoidal signal is input into the second mixer 51 to demodulate an error signal with frequency discrimination characteristics. After processing by the proportional-integral-differential (PID) circuit 54, the error signal is directly fed back to the piezoelectric ceramic (PZT) module and current modulation port inside the external cavity semiconductor laser 36 to achieve frequency compensation and obtain a frequency stabilization effect. In the experiment, adjusting the parameters in the second PID circuit 54 can better lock the laser frequency to the transmission peak of the ultra-stable cavity. The above parts constitute the second laser frequency stabilization module 56 located on the optical device fixing breadboard 7.

[0046] Specifically, such as Figure 1 As shown, the microwave generating module 68 includes a microwave signal source 62, a power amplifier 61, and a horn antenna 60; the microwave signal source 62 is used to transmit the microwave signal to be tested, and the microwave signal to be tested is amplified by the power amplifier 61 and then transmitted to the horn antenna 60 to transmit a microwave electric field.

[0047] Specifically, such as Figure 1 As shown, the data processing module 69 includes a second high-bandwidth photodetector 64, an oscilloscope 65, and a computer device 66; the second high-bandwidth photodetector 64 collects the electrical signal and transmits the electrical signal to the oscilloscope 65 to display the spectral morphology in real time, and calculates the microwave electric field intensity by analyzing the splitting frequency spacing of the electromagnetically induced transparent spectrum.

[0048] In this process, the 852nm probe light passes through the atomic gas cell 59, is reflected by the dichroic beam splitter 63, and is converted into an electrical signal by the high-bandwidth photodetector 64. This signal is then transmitted to the oscilloscope 65 to observe the experimental results. The computer device 66 is used to record and store the signal obtained by the oscilloscope 65.

[0049] Specifically, the distance between the atomic gas chamber 59 and the horn antenna 60 in the microwave generating module 68 reaches the far-field condition.

[0050] Specifically, the far-field condition must be met: (1) Among them is The dimensions of the microwave horn antenna 60 to be calibrated It is the wavelength of microwaves.

[0051] Under far-field conditions, the atomic gas cell 59 can be a cesium atomic gas cell. The cesium atomic gas cell senses the plane electromagnetic wave emitted by the standard gain horn antenna. The amplitude of the microwave field emitted by the standard gain horn antenna can be calculated from the far-field equation: (2) It is the gain of the horn antenna. It is the net input power of the antenna. It is free space impedance.

[0052] The gain of the calibrated microwave horn antenna 60 is the measurement to be performed in the experiment. The relative distance between the horn and the atomic gas chamber 59 can be measured. Therefore, for a measured electric field amplitude, the output power of the horn antenna can be calculated using a formula. The microwave generating module 68 can be controlled by the control software in the microwave signal source 62. After inputting the desired measured microwave field amplitude and microwave frequency, the theoretical output power of the horn antenna can be calculated. The microwave power meter will detect the actual output power of the power amplifier 61 and compare it with the theoretical value. The PID module will adjust the actual microwave output power until it matches the theoretical value.

[0053] In the specific implementation, the 509nm coupled light after frequency doubling is output from the single-mode fiber of the single-frequency fiber laser 11 and enters free space through the first coupler 57. The 852nm probe light is output through one of the third fiber beam splitters 37 and enters free space through the second fiber coupler 58. The two beams are refracted against each other in the atomic gas cell 59. The frequency of the 852nm probe light is the same as the resonance frequency of the two energy level transition of the D2 line of the atom, so that the probe light resonates with the two energy levels of the alkali metal atom. Then, the frequency of the 509nm coupled light is scanned to obtain the EIT-AT spectral signal.

[0054] For example, when the first laser frequency stabilization module 55 can be a 509nm laser frequency stabilization module and the second laser frequency stabilization module 56 can be an 852nm laser frequency stabilization module, a 509nm coupling light and an 852nm probe light are generated in the laser source module. The 509nm coupling light is generated by the single-frequency fiber laser 11 and enters free space through the first fiber coupler 57. This beam is used to excite atoms in the atomic chamber to the Rydberg state, and its frequency is scanned to achieve the observation of the EIT-AT spectrum. The 852nm probe light is split into one path by the third fiber beam splitter 37 and enters free space through the second fiber coupler 58. This beam resonates with the D2 line of cesium atoms and is used to detect changes in atomic energy levels. The two beams are directed towards each other (propagating in opposite directions) in the cesium atom gas chamber, and the EIT-AT split spectral signal can be observed by adjusting the frequency scan of the 509nm coupling light. Furthermore, a microwave signal of a specified frequency is emitted, then amplified to the required power, and the amplified microwave signal is emitted as a plane electromagnetic wave, satisfying the far-field condition (Formula 1) to ensure that the cesium atom gas cell receives the standard plane wave. The microwave field amplitude is then calculated using Formula 2, and the output power of the power amplifier 61 is adjusted to match the actual power with the theoretical value (PID control). In the data processing module 69, the optical signal after the 852nm probe light passes through the cesium atom gas cell is converted into an electrical signal, and the signal output by the photodetector 64 (such as an EIT-AT spectrum or heterodyne signal) is displayed in real time. The data from the oscilloscope 65 is recorded and stored for subsequent analysis.

[0055] Based on the EIT-AT effect and the quantum properties of Rydberg atoms, this device enables high-precision, wide dynamic range microwave electric field measurement, achieving a measurement accuracy on the order of V / cm. The measurement results are traceable to Planck's constant, providing metrological reference characteristics. By analyzing the splitting spacing and heterodyne interference signal of the electromagnetically induced transparent spectrum, the device can simultaneously acquire multiple parameters such as electric field amplitude, phase, and frequency, with a frequency resolution on the order of Hz. Compared to traditional antenna measurement methods, this device employs optical detection, avoiding field disturbances introduced by metal antennas. The atomic gas chamber provides natural shielding against electromagnetic interference, and combined with differential measurement technology, it effectively eliminates the influence of environmental noise. The modular system design (separate laser source module, microwave generation module, and data processing module) facilitates independent optimization of each component. Fiber optic transmission reduces optical system jitter, and the absence of mechanical scanning components improves system reliability. Furthermore, the device exhibits excellent application scalability. By altering the Rydberg state energy levels, it can be adapted to measurement requirements in different frequency bands. Adjusting the cell-antenna distance supports near-field / far-field measurements, and the movable cell design also accommodates spatial field strength distribution measurements. Example data shows that within the 1-10 GHz frequency band, the relative uncertainty of electric field measurement is less than 0.5% (k=2), verifying the device's high accuracy and reliability.

[0056] It should be noted that in the above embodiments, there is no necessarily a certain order between the steps. Those skilled in the art can understand from the description of the embodiments of this application that the above steps may have different execution orders in different embodiments, that is, they may be executed in parallel or in turn, etc.

[0057] Figure 2 A flowchart illustrating a microwave electric field measurement method provided in an embodiment of the present invention is shown, characterized in that the method includes the following steps: S10. Acquire the microwave signal to be tested.

[0058] Typically, microwaves are radiated into the atomic gas cell via a horn antenna. The frequency and amplitude of the microwave signal must cover the measurement range (e.g., 1-10 GHz), and signal stability must be ensured. The microwave signal to be measured must resonate with the Rydberg states in the atomic gas cell to trigger the EIT-AT effect. The distance between the antenna and the gas cell must satisfy the far-field condition (L≥2D). 2 / λ, where D is the antenna aperture and λ is the microwave wavelength.

[0059] S20. The microwave signal to be measured is processed to obtain the splitting frequency spacing of the electromagnetically induced transparent spectrum.

[0060] The measurement and processing process involves simultaneously incident a probe light (e.g., 852 nm probe light) and a coupling light (e.g., 509 nm coupling light) onto a cesium atom gas cell. The probe light frequency is locked at the D2 transition, and the coupling light frequency is scanned to obtain the EIT-AT spectrum. The transmission light intensity is recorded as a function of the coupling light frequency using a photodetector to obtain the spectral splitting characteristics. The splitting frequency interval fMW (i.e., the frequency difference between two peaks) is then extracted.

[0061] Therefore, the splitting frequency spacing is obtained by locking the frequency of one laser beam and scanning the frequency of another laser beam. In cesium atomic vapor, one can choose to lock the 852 nm probe frequency and scan the 509 nm coupling frequency, or vice versa.

[0062] S30. The microwave electric field strength of the microwave signal to be measured is calculated based on the splitting frequency spacing of the electromagnetically induced transparent spectrum.

[0063] For example, when using 852nm probe light and 509nm coupling light, the S10-S30 process can be represented by the following formula for the microwave electric field intensity when the microwave frequency resonates with two adjacent Rydberg states: (3) in The EIT-AT spectral splitting frequency spacing, To reduce Planck's constant, The transition dipole moments of the two Rydberg states are given. In microwave electric field amplitude metrology experiments, the EIT-AT spectral splitting frequency spacing is obtained by locking the frequency of one laser beam and scanning the frequency of the other laser beam. The microwave electric field intensity is obtained by combining the traceability formula (3). For cesium atomic vapor, the EIT-AT spectrum can be obtained by locking the 852nm probe light frequency and scanning the 509nm coupling light frequency, or by locking the 509nm coupling light frequency and scanning the 852nm probe light frequency. Among them, when locking the 509nm coupling light frequency and scanning the 852nm probe light frequency, due to the Doppler mismatch effect, the Rydberg state AT splitting interval caused by the microwave is increased. It is not equal to the EIT-AT spectral splitting frequency spacing. The two differ by a wavelength scaling factor. The relationship between the two at this point: (4) Therefore, when the laser system locks the coupling light frequency and scans the probe light frequency, formula (3) needs to be modified as follows: (5) in To detect the wavelength of light, The wavelength of the coupled light.

[0064] In addition, if a rubidium atom gas chamber is used instead, this device needs to be compatible with 780nm and 480nm narrow linewidth lasers.

[0065] As can be seen, in this embodiment, the microwave electric field is converted into spectral parameters through atomic quantum effects, and then inverted through physical formulas to achieve high-precision electric field measurement with a wide dynamic range.

[0066] This approach first provides high-precision microwave electric field measurements, relying on detailed spectral analysis to ensure accuracy. Second, it employs a non-invasive measurement method, preventing interference with the microwave signal and maintaining signal integrity. Furthermore, the high sensitivity of Rydberg atoms enables the detection of subtle changes in the microwave electric field, making it suitable for applications requiring high sensitivity. This method has broad applicability, covering multiple fields such as communications and radar. Further, an automated data processing module makes the measurement process efficient and resource-saving. Finally, the method is scalable and can be adjusted according to experimental conditions and requirements, such as by replacing different atomic gas cells or lasers to adapt to different measurement needs.

[0067] In one possible example, after acquiring the microwave signal to be measured, the method further includes: performing frequency mixing processing on the microwave signal to be measured to generate heterodyne interference and obtain phase information of the microwave signal to be measured; and calculating the microwave electric field strength of the microwave signal to be measured based on the phase information of the microwave signal to be measured.

[0068] The process involves mixing the microwave signal under test with a local oscillator (LO) signal of known frequency. Mixing produces sum and difference frequency components, with the difference frequency component forming a heterodyne interference signal. The principle of heterodyne interference utilizes the beat frequency phenomenon generated when two electromagnetic waves with similar frequencies are superimposed; the envelope or phase change of the interference signal directly reflects the phase difference between the signal under test and the local oscillator signal.

[0069] By detecting the phase change of the heterodyne interference signal (e.g., using a high-sensitivity phase demodulation circuit or digital signal processing techniques), the phase information of the microwave signal under test relative to the local oscillator signal can be accurately obtained. Since the phase of the local oscillator signal is known, the absolute phase or phase change of the signal under test can be determined.

[0070] According to electromagnetic principles, the microwave electric field strength (E) is directly related to the rate of phase change or amplitude of the signal. In specific calculations, the instantaneous frequency or amplitude of the signal can be derived using phase information. Then, combined with known free-space impedance (Z0≈377Ω) or power relationships, the phase information can be converted into an electric field strength value using formulas or phase-sensitive calibration factors. Furthermore, by incorporating the EIT-AT effect, phase information can also be used to calibrate the relationship between atomic level splitting and electric field strength, thereby achieving higher precision measurements.

[0071] The principle of a traditional heterodyne receiver is as follows: the microwave signal field to be measured is output through a horn antenna, amplified by a microwave low-noise amplifier, and then mixed with the intrinsic signal field in a mixer. The output is a sum frequency and a difference frequency signal. The difference frequency signal is also called the intermediate frequency signal. The intermediate frequency signal is filtered by a narrow-band bandpass filter to remove the high-frequency signal, and then amplified by an intermediate frequency signal amplifier. Finally, it is detected by the measurement circuit to complete the measurement of the microwave signal.

[0072] For example, when using 852nm probe light and 509nm coupling light, in a four-level Rydberg atom EIT system, the Rydberg atom heterodyne receiver is equivalent to replacing the mixer with a Rydberg atom gas cell. After locking the frequencies of the 852nm probe light and 509nm coupling light at the resonant frequencies of the prepared Rydberg state, EIT-AT splitting is generated by coupling the Rydberg atom energy levels through a local oscillator microwave field. Then, a signal microwave field slightly detuned from the local oscillator microwave field is added to perform heterodyne interference in the Rydberg atom vapor cell. The intermediate frequency signal is obtained by detecting the transmitted probe light signal through a photodetector, where the probe light transmittance changes with time as follows: (6) in It is the average transmitted light intensity of the probe light. It is the total intrinsic gain coefficient of the atomic superheterodyne system. It is a frequency detuning of the signal microwave field relative to the intrinsic microwave field. This refers to the relative phase between the signal microwave field and the intrinsic microwave field. Therefore, we can measure the phase information of the microwave field of the signal under test using the probe light. Furthermore, the minimum measurable microwave electric field value using the heterodyne measurement method is much smaller than the minimum measurable microwave electric field value using the EIT-AT splitting effect, thus it can be used to measure weak microwave signals.

[0073] It is evident that heterodyne interferometry in this implementation can significantly improve the sensitivity of phase measurement, avoid the difficulties of directly measuring high-frequency signals, and expand the dynamic range by combining it with mixing technology, making it suitable for wide-bandwidth, high-precision microwave electric field measurement scenarios.

[0074] It should be noted that in the above embodiments, there is no necessarily a certain order between the steps. Those skilled in the art can understand from the description of the embodiments of this application that the above steps may have different execution orders in different embodiments, that is, they may be executed in parallel or in turn, etc.

[0075] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0076] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with the claims of this application shall still fall within the scope of this application.

Claims

1. A microwave electric field measuring device, characterized in that, include: The system comprises a laser source module, a microwave generator module, and a data processing module. The laser source module excites Rydberg atoms in the atomic gas chamber and generates an electromagnetically induced transparency spectrum. The microwave generator module generates a microwave signal to be measured, which is radiated to the atomic gas chamber via a horn antenna. The microwave signal to be measured causes the electromagnetically induced transparency spectrum to split or undergo heterodyne interference. The data processing module acquires an electrical signal and calculates the microwave electric field strength by analyzing the splitting frequency spacing of the electromagnetically induced transparency spectrum. The electrical signal is obtained jointly by the laser source module and the microwave generator module.

2. The microwave electric field measuring device according to claim 1, characterized in that, The laser source module includes a first laser frequency stabilization module, a second laser frequency stabilization module, the atomic gas cell, a dichroic beam splitter, a first fiber coupler, and a second fiber coupler. The first laser frequency stabilization module outputs coupled light through the first fiber coupler, and the second laser frequency stabilization module outputs probe light through the second fiber coupler. The coupled light and the probe light are refracted against each other in the atomic gas cell to form the electromagnetically induced transparency spectrum. The dichroic beam splitter separates the probe light carrying the electromagnetically induced transparency spectrum to form the electrical signal, which is then transmitted to the data processing module.

3. The microwave electric field measuring device according to claim 2, characterized in that, Both the first laser frequency stabilization module and the second laser frequency stabilization module are connected to the portable ultra-stable optical reference cavity module; the first laser frequency stabilization module is connected to the first port and the second port of the portable ultra-stable optical reference cavity module, and the first port is located opposite the second port; The second laser frequency stabilization module is connected to the third and fourth ports of the portable ultra-stable optical reference cavity module, with the third port located opposite the fourth port; the portable ultra-stable optical reference cavity module is used for laser frequency stabilization.

4. The microwave electric field measuring device according to claim 3, characterized in that, The first laser frequency stabilization module includes a single-frequency fiber laser, a seed light, a first fiber acousto-optic modulator, a first fiber beam splitter, a fiber amplifier, a frequency doubling crystal, a second fiber beam splitter, a first fiber electro-optic phase modulator, a first fiber collimator, a first mirror, a first plano-convex lens, a first λ / 2 waveplate, a first polarizing beam splitter, a first λ / 4 waveplate, a second mirror, a third mirror, a first beam splitter, a silicon photodetector, a first charge-coupled device camera, a high-bandwidth silicon photodetector, a first mixer, a first direct digital frequency synthesis signal generator, a first signal generator, and a first proportional-integral-differential circuit.

5. The microwave electric field measuring device according to claim 3, characterized in that, The second laser frequency stabilization module includes an external cavity semiconductor laser, a third fiber beam splitter, a second fiber electro-optic phase modulator, a second fiber collimator, a fourth mirror, a second plano-convex lens, a second λ / 2 waveplate, a second polarizing beam splitter, a second λ / 4 waveplate, a fifth mirror, a sixth mirror, a second beam splitter, a photodetector, a second charge-coupled device camera, a first high-bandwidth photodetector, a second mixer, a second direct digital frequency synthesis signal generator, a second signal generator, and a second proportional-integral-differential circuit.

6. The microwave electric field measuring device according to claim 1, characterized in that, The microwave generating module includes a microwave signal source, a power amplifier, and a horn antenna; the microwave signal source is used to transmit the microwave signal to be tested, and the microwave signal to be tested is amplified by the power amplifier and transmitted to the horn antenna to transmit the microwave electric field.

7. The microwave electric field measuring device according to claim 1, characterized in that, The data processing module includes a second high-bandwidth photodetector, an oscilloscope, and a computer. The second high-bandwidth photodetector collects the electrical signal and transmits the electrical signal to the oscilloscope to display the spectral morphology in real time. The microwave electric field intensity is calculated by analyzing the splitting frequency spacing of the electromagnetically induced transparency spectrum.

8. The microwave electric field measuring device according to claim 1, characterized in that, The distance between the atomic gas chamber and the horn antenna in the microwave generator module reaches the far-field condition.

9. A microwave electric field measurement method, implemented based on the apparatus according to any one of claims 1 to 8, characterized in that, include: Acquire the microwave signal to be tested; The microwave signal to be measured is processed to obtain the splitting frequency spacing of the electromagnetically induced transparent spectrum; The microwave electric field strength of the microwave signal under test is calculated based on the splitting frequency spacing of the electromagnetically induced transparent spectrum.

10. The method according to claim 9, characterized in that, After acquiring the microwave signal to be measured, the method further includes: The microwave signal under test is mixed to generate heterodyne interference, thereby obtaining the phase information of the microwave signal under test. The microwave electric field strength of the microwave signal under test is calculated based on the phase information of the microwave signal under test.

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