An atomic frequency discriminator, and a method for implementing the same and a frequency discrimination method

Abstract

This invention relates to the field of laser frequency discrimination, specifically to an atomic frequency discriminator and its implementation method. In this invention, asynchronous sampling using dual optical combs directly obtains the real-time amplitude and phase response of the atomic medium across the entire comb bandwidth, achieving scan-free, broadband, absolute frequency-scaled rotational spectral measurements. Traditional frequency discrimination schemes typically operate only within a narrow frequency range near atomic transitions, while this invention can simultaneously obtain optical rotation information over a wide spectral range, significantly expanding the frequency domain coverage of the atomic frequency discriminator. Simultaneously, this system coherently converts the Faraday rotation effect into a measurable phase difference. Combined with the high-resolution phase reconstruction capability of dual optical combs, subtle changes in the rotational spectral line shape can be obtained, constructing a frequency discrimination function with a large slope and a wide linear range, providing a foundation for high-sensitivity frequency measurements.

Description

Technical Field

[0001] This invention relates to the field of laser frequency discrimination, specifically to an atomic frequency discriminator and its implementation method and frequency discrimination method. Background Technology

[0002] Precise measurement and stable control of laser frequency are fundamental to modern optics and quantum technology, playing a crucial role in applications such as atomic clocks, cold atom physics, quantum communication, high-precision spectral measurement, lidar, inter-satellite optical communication, and space environment monitoring. To obtain the frequency deviation of the laser relative to atomic transitions and generate a stable and reliable error signal, an atomic frequency discriminator (AFD) is typically used. As a core module in the laser stabilization chain, the performance of the atomic frequency discriminator directly determines the robustness and measurement sensitivity of the frequency reference system.

[0003] Currently, the most widely used atomic frequency discrimination techniques internationally mainly include two categories: continuous-wave scanning spectral frequency discrimination methods and polarization frequency discrimination methods based on the Faraday effect. Continuous-wave scanning methods involve scanning the laser near atomic absorption or dispersive spectral lines and constructing error signals using saturated absorption spectra, frequency modulation spectroscopy (FM spectroscopy), or lock-in amplifier outputs. However, these methods require mechanical or electro-optical scanning to obtain the frequency discrimination signal, resulting in limited dynamic response speed; furthermore, the signal acquisition range is limited to the vicinity of specific atomic transitions, making it difficult to meet the needs of broadband, multi-channel, or rapidly changing laser systems.

[0004] Another typical approach is the Faraday atom filter and polarization splitting frequency discrimination technique. This technique relies on the differential refractive index generated by the Zeeman splitting of atoms induced by an external magnetic field. The polarization angle of the transmitted light changes with frequency, forming a steep frequency discrimination curve. Faraday discriminators do not require modulation, have fast response speeds, and simple structures, but their operating bandwidth is typically only a few hundred MHz to several GHz, strictly limited to the vicinity of specific atomic transitions. In addition, their center frequency and slope are sensitive to temperature and magnetic field fluctuations, resulting in limited long-term stability and making them difficult to adapt to complex environments and broadband frequency measurement requirements. Summary of the Invention

[0005] In view of this, the present invention provides an atomic frequency discriminator and its implementation method and frequency discrimination method, so as to solve the technical problem that the atomic frequency discriminator in the prior art cannot quickly achieve wideband frequency discrimination.

[0006] The technical solution provided by this invention is as follows:

[0007] In a first aspect, the present invention provides an atomic frequency discriminator, comprising: The light source module is used to generate two coherently locked optical frequency comb signals and combine the two optical signals into a first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference. The atomic interaction module is used to modulate the optical signal in the first polarization state using the Faraday optical rotation effect; A polarization detection module is used to convert and detect modulated optical signals. After asynchronous optical sampling, the optical signal is down-converted to radio frequency through interference on the detector surface to obtain a multi-heterodyne interference electrical signal. The polarization detection module includes a detector. The processing module is used to perform a fast Fourier transform on the electrical signal, reconstruct the optical rotation spectrum from the transformed signal, and generate a frequency discrimination function based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

[0008] This invention utilizes asynchronous sampling with dual optical combs to directly obtain the real-time amplitude and phase response of the atomic medium across the entire comb bandwidth, achieving scan-free, broadband, and absolute frequency-calibrated rotational spectral measurements. Traditional frequency discrimination schemes typically operate only within a narrow frequency range near atomic transitions, while this invention can simultaneously acquire optical rotation information over a wide spectral range, significantly expanding the frequency domain coverage of the atomic frequency discriminator. Simultaneously, this system coherently converts the Faraday rotation effect into a measurable phase difference. Combined with the high-resolution phase reconstruction capability of the dual optical combs, it can obtain subtle changes in the rotational spectral line shape, constructing a frequency discrimination function with a large slope and a wide linear range, providing a foundation for high-sensitivity frequency measurements.

[0009] In one optional implementation, the light source module includes: A first optical frequency comb is used to generate a first optical frequency comb signal, wherein the repetition frequency of the first optical frequency comb signal is locked to the carrier envelope offset frequency to a radio frequency reference source. The second optical frequency comb is used to generate a second optical frequency combed optical signal; A coherent controller is used to perform optical frequency coherent locking between the second optical frequency comb signal and the first optical frequency comb signal, so that the repetition frequency of the two optical frequency comb signals has a preset difference. The polarization generation module is used to combine two coherently locked optical signals and convert them into a first polarization state.

[0010] In this invention, by introducing a dual optical frequency comb and a coherent controller, precise coherent locking and preset difference frequency control of the two optical comb signals are achieved. Combined with a polarization generation module for beam combining conversion, the frequency stability and coherence of the dual optical comb system are significantly improved. The preset difference frequency mechanism forms asynchronous sampling conditions, providing a basis for broadband measurement.

[0011] In one optional embodiment, the atomic interaction module includes an atomic chamber, a magnet, and a temperature control module. The magnet and the temperature control module are disposed outside the atomic chamber and are used to provide a magnetic field to the atomic chamber and adjust the temperature of the atomic chamber.

[0012] In one optional implementation, the polarization detection module further includes: a polarization analyzer; The analyzer is used to convert the polarization state information of the modulated optical signal into light intensity information; The detector is used to detect light intensity information to obtain radio frequency electrical signals.

[0013] In one optional implementation, the polarization detection module further includes a quarter-wave plate and a polarizer; The quarter-wave plate is used to separate the optical components in the modulated optical signal; The analyzer is used to convert the polarization state information of the separated light components into light intensity information; The detector is used to detect light intensity information to obtain radio frequency electrical signals.

[0014] In this invention, by setting different structures in the polarization detection module, the atomic frequency discriminator can operate in either Faraday atomic frequency discriminator mode or Zeeman atomic frequency discriminator mode to meet the needs of different application scenarios.

[0015] In one optional implementation, the processing module is specifically used to: perform a fast Fourier transform on the electrical signal to obtain a frequency domain signal; map the frequency coordinates of the frequency domain signal to absolute optical frequency coordinates based on the repetition frequency and frequency difference parameter of the two optical frequency comb signals, and reconstruct the optical rotation spectrum; and perform frequency differentiation on the optical rotation spectrum to obtain a frequency discrimination function.

[0016] In a second aspect, the present invention provides a method for implementing an atomic frequency discriminator, applied to the atomic frequency discriminator described in the first aspect and any one of the first aspects of the present invention, the method comprising: Two coherently locked optical frequency comb signals are generated, and the two optical signals are combined and converted into the first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference. The optical signal in the first polarization state is modulated using the Faraday rotation effect; The modulated optical signal is converted, analyzed, and detected to obtain an electrical signal; The electrical signal is subjected to asynchronous optical sampling and fast Fourier transform. The transformed signal is reconstructed to obtain the optical rotation spectrum. A frequency discrimination function is generated based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

[0017] In an optional implementation, the method further includes: Determine whether the optical rotation spectrum meets the requirements of the preset application scenario; If the requirements are not met, adjust the magnetic field strength generated by the magnet in the atomic chamber / or change the temperature in the atomic chamber to change the optical response function of the atomic frequency discriminator until the obtained optical rotation spectrum meets the requirements of the preset application scenario.

[0018] This invention utilizes the millisecond-level real-time capability of dual-comb spectroscopy to achieve rapid scanning and optimization of the atomic chamber temperature. This allows for the determination of the operating temperature point with the highest optical transmittance in a short time, thereby obtaining a rotational spectrum with high signal intensity and low noise. Through dual optimization of magnetic field and temperature, the parameters of the atomic frequency discriminator can be calibrated quickly.

[0019] Thirdly, the present invention provides a frequency discrimination method using the atomic frequency discriminator described in the first aspect and any one of the first aspects of the present invention, the method comprising: The laser to be discriminated is input into the atomic frequency discriminator to obtain the rotation angle of the laser to be discriminated; Based on the frequency discrimination function, the deviation between the rotation angle and the target optical rotation angle is determined; The error signal is determined based on the slope value of the frequency discrimination function corresponding to the deviation and the target frequency; The laser frequency of the laser to be discriminated is adjusted based on the error signal, so that the laser frequency is adjusted to the target frequency.

[0020] This invention employs a frequency discrimination function based on the frequency derivative of the cyclotron spectrum, combined with an absolute optical frequency scale using a dual-comb, to achieve real-time frequency deviation measurement and closed-loop control of incoming laser light. This characteristic makes this invention suitable not only for precision frequency measurement in laboratories but also for applications such as solar activity monitoring, space physics exploration, inter-satellite laser links, and quantum sensing, which require broadband, fast, and highly stable frequency standards. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a structural block diagram of the atomic frequency discriminator in an embodiment of the present invention; Figure 2 This is a structural block diagram of an atomic frequency discriminator in another embodiment of the present invention; Figure 3This is a schematic diagram of the red and blue wings of the Zeeman atom frequency discriminator in an embodiment of the present invention; Figure 4 This is the absorption spectrum of potassium atoms transmitted through the dual-comb spectrum in an embodiment of the present invention; Figure 5 This is a schematic diagram showing the shape of the Zeeman peak transmitted by the Faraday potassium atom frequency discriminator in an embodiment of the present invention and its comparison with the shape of the solar spectrum; Figure 6 This is a flowchart illustrating a method for implementing an atomic frequency discriminator in an embodiment of the present invention; Figure 7 This is a flowchart illustrating a frequency discrimination method for an atomic frequency discriminator according to an embodiment of the present invention. Detailed Implementation

[0023] As described in the background section, atomic frequency discriminators in related technologies cannot meet the requirements for rapid broadband frequency measurements. However, the demand for rapid broadband frequency measurements is currently increasing. For example, in addition to ground-based optics and quantum applications, atomic frequency discriminators also play a crucial role in solar activity research and space physics. Solar activities (such as coronal mass ejections, solar flares, and solar wind variations) significantly disturb the structure of the Earth's ionosphere and space communication links. To conduct high-precision solar spectral monitoring, solar atmospheric magnetic field inversion, Lyman-α remote sensing, coronal temperature and velocity diagnostics, and solar wind plasma parameter measurements, it is necessary to precisely lock the probe laser near the resonance spectral lines of target atoms or ions to achieve the inversion of Doppler shifts and plasma physical quantities. In these tasks, atomic frequency discriminators perform key functions such as laser frequency reference, drift compensation, and frequency scale calibration.

[0024] In space physics and space situational awareness, laser frequency stability plays a fundamental role in deep space communication, inter-satellite laser links, satellite-borne spectrometers, and the detection of space environment disturbances. The time-frequency disturbances of the space environment on laser links change rapidly with solar wind activity; therefore, space payloads often require highly stable, drift-resistant laser frequency reference modules. The limitations of traditional scanning and Faraday discriminators in terms of bandwidth, dynamic response, long-term stability, and environmental adaptability make them unsuitable for meeting the ever-increasing frequency stability requirements of solar and space physics exploration missions.

[0025] In summary, both widely used continuous-wave scanning methods and Faraday polarization discrimination techniques generally suffer from common problems such as limited bandwidth, insufficient dynamic response speed, sensitivity to temperature and magnetic field drift, operation only near a single spectral line, and difficulty in achieving multi-channel or wideband discrimination. Furthermore, with the rapid development of applications such as solar physics observation, space environment monitoring, and high-speed inter-satellite communication, higher demands are placed on the real-time performance, robustness, and wideband absolute frequency calibration of laser frequency stabilization links. Existing atomic discrimination techniques have gradually revealed their limitations in these emerging application contexts, necessitating new technological means to achieve higher-performance atomic discrimination functions.

[0026] Therefore, existing atomic frequency discrimination techniques, such as continuous-wave scanning spectral frequency discrimination methods and Faraday effect-based polarization frequency discrimination methods, suffer from limitations including limited frequency response bandwidth, operation only near specific atomic transitions, insufficient dynamic response speed, sensitivity to temperature and magnetic field drift, inability to directly provide an absolute frequency scale, and difficulty in simultaneously identifying multiple laser frequencies. With the increasing demands of quantum measurement, solar activity monitoring, space physics exploration, inter-satellite laser communication, and optical frequency stabilization systems in complex environments, traditional frequency discriminators are no longer sufficient to meet the comprehensive performance requirements of broadband, high speed, disturbance resistance, and multi-channel operation.

[0027] In this invention, the absolute frequency scale capability of a dual-comb spectrometer is combined with the high-sensitivity dispersion response of the atomic Faraday effect to construct an atomic frequency discriminator with broadband coverage, fast response, high sensitivity, anti-drift, and multi-channel compatibility, thereby overcoming the limitations of existing swept-frequency spectroscopy techniques in frequency measurement.

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] This invention provides an atomic frequency discriminator, such as... Figure 1 As shown, it includes: The light source module 100 is used to generate two coherently locked optical frequency comb signals and combine the two optical signals into a first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference. Atomic interaction module 200 is used to modulate the optical signal of the first polarization state using the Faraday optical rotation effect; The polarization detection module 300 is used to convert and detect the modulated optical signal. After asynchronous optical sampling, the optical signal is down-converted to radio frequency through interference on the detector surface to obtain a multi-heterodyne interference electrical signal. The polarization detection module includes a detector. The processing module 400 is used to perform a fast Fourier transform on the electrical signal, reconstruct the optical rotation spectrum from the transformed signal, and generate a frequency discrimination function based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

[0033] Specifically, an optical frequency comb can be understood as a special type of laser source whose spectrum consists of a series of uniformly spaced frequency components with coherent and stable phase relationships. In other words, an optical frequency comb includes a series of equally spaced, known-frequency comb teeth. The number of comb teeth is determined by the frequency width of the optical frequency comb, which in turn determines the range of frequencies that the atomic frequency discriminator can rapidly discriminate. Therefore, the frequency width of the optical frequency comb can be set based on the frequency discrimination range requirements of the atomic frequency discriminator for different application scenarios.

[0034] In an optical frequency comb, the frequency of each comb tooth can be expressed as: f n =f ceo +n f rep ,in,f ceo This indicates the repetition frequency, i.e., the comb tooth spacing. f rep The carrier envelope frequency is represented by this value. Therefore, once the repetition frequency and carrier envelope frequency in each comb tooth are determined, the optical frequency comb is also determined, thus giving it absolute scaling capability. In this embodiment, two coherently locked optical frequency comb signals are generated, and the repetition frequencies of the two locked signals have a preset difference, which can be a small, fixed difference. Thus, when the two beams with the frequency difference are combined and detected, optical heterodyne occurs, generating a slow-paced beat frequency signal in the time domain. Processing this signal yields the corresponding spectrum.

[0035] Specifically, the atomic frequency discriminator in this embodiment employs the Faraday effect. During operation, a beam of linearly polarized light passes through an atomic chamber situated in a strong axial magnetic field. Under the influence of the applied magnetic field, the energy levels of the atoms split (Zeeman effect). For atoms with a specific angular momentum, their absorption spectrum splits into components that respond differently to different circularly polarized light (left-handed and right-handed). Since left-handed and right-handed circularly polarized light have different refractive indices in the medium, their propagation speeds after passing through the medium also differ. When these two beams of light recombine into linearly polarized light, their polarization direction rotates relative to the incident light. This rotation angle is a function of the light frequency and varies drastically near the atomic resonance frequency, forming a steep dispersive curve.

[0036] Simultaneously, a polarization detection module is also incorporated into this atomic frequency discriminator, which converts the rotation of the polarization direction into a change in light intensity for detection. Specifically, during detection, the detector cannot respond to the oscillation of the light frequency, but it can respond to the change in light intensity. Because the comb teeth of the two optical combs are very dense and close in frequency, each pair of comb teeth with similar frequencies will generate a difference frequency signal on the detector. That is, the process of detecting two optical frequency comb signals that are coherently locked and have a preset difference in repetition frequency can be called an asynchronous optical sampling process.

[0037] The detected electrical signals (including time-varying interference waveforms) are input to the processing module for processing. The processing module performs a Fast Fourier Transform (FFT) on the electrical signals, converting the time-domain interference signal to the frequency domain. In the frequency domain, a series of discrete spectral peaks appear. Each spectral peak corresponds to a specific radio frequency (RF) frequency. This RF frequency value has a one-to-one linear mapping relationship with the original optical frequency. Based on this mapping relationship, each frequency point in the spectrum is mapped to the optical frequency, thus achieving spectral reconstruction and obtaining the optical rotation spectrum. Frequency differentiation processing of the optical rotation spectrum generates a frequency discrimination function. This frequency discrimination function can map the laser frequency deviation into an error signal when using this atomic frequency discriminator for laser frequency discrimination.

[0038] In one optional implementation, the light source module includes: A first optical frequency comb is used to generate a first optical frequency comb signal, wherein the repetition frequency of the first optical frequency comb signal is locked to the carrier envelope offset frequency to a radio frequency reference source. The second optical frequency comb is used to generate a second optical frequency combed optical signal; A coherent controller is used to perform optical frequency coherent locking between the second optical frequency comb signal and the first optical frequency comb signal, so that the repetition frequency of the two optical frequency comb signals has a preset difference. The polarization generation module is used to combine two coherently locked optical signals and convert them into a first polarization state.

[0039] Specifically, the radio frequency reference source refers to a highly stable radio frequency source, which can be understood as a radio frequency atomic clock. In this embodiment, the repetition frequency and carrier envelope offset frequency of the first optical frequency comb signal are locked to a radio frequency reference. Specifically, the optical frequency comb signal can be regarded as the optical signal output by the laser. When achieving repetition frequency locking, the frequency interval of the laser's longitudinal modes can be locked; when achieving carrier envelope offset frequency locking, the position of the first longitudinal mode comb tooth of the laser can be locked. Thus, the repetition frequency and carrier envelope offset frequency of the optical frequency comb signal output by the laser are locked, and the first optical frequency comb signal has an absolute frequency scale function.

[0040] When coherently locking two optical signals, the coherent controller can use a narrow-linewidth, highly stable continuous-wave laser as a common reference. First, the frequency of this continuous-wave laser is locked to a specific tooth of the first optical frequency comb signal. In this way, the continuous-wave laser inherits the frequency stability and accuracy of the first optical frequency comb signal and establishes a fixed phase relationship with that tooth. Then, the light from this same continuous-wave laser is beat-matched with a tooth of the second optical frequency comb signal. Similarly, the resulting beat-match signal is used as an error signal to feed back and control the second optical frequency comb signal, locking that tooth of the second optical frequency comb signal to the continuous-wave laser as well.

[0041] Since both optical frequency combs are locked to the same continuous laser, a definite and stable phase relationship is established between them through this common reference. This means that the relative phase difference between each tooth of the two optical combs is fixed, or in other words, their optical frequency scales are synchronously characterized. This achieves coherent locking, also known as phase locking. Regarding the preset difference between repetition frequencies, since the repetition frequency of optical frequency combs is typically around 100MHz, in this embodiment, the preset difference can be 100Hz, i.e., the frequency down-conversion factor is 1,000,000.

[0042] To achieve beam combining and polarization conversion functions, a beam combiner and a polarizer are set in the polarization generation module. The beam combiner combines two optical signals with a preset difference in repetition frequency and transmits them to the polarizer. The polarizer converts the combined optical signal into linearly polarized light so that it can interact with atoms to produce the Faraday effect.

[0043] In one optional embodiment, the atomic interaction module includes an atomic chamber, a magnet, and a temperature control module. The magnet and temperature control module are disposed outside the atomic chamber to provide a magnetic field and adjust the temperature of the atomic chamber. The atomic chamber is filled with alkali metal atomic vapor, such as rubidium, potassium, cesium, and sodium. In this embodiment, a neodymium magnet is used as the magnetic field source to obtain significant Zeeman splitting. Neodymium magnets have high remanence and high coercivity, enabling them to provide a stable longitudinal magnetic field at the center of the chamber, resulting in an observable refractive index difference between left- and right-polarized light in the atomic medium, thus inducing significant Faraday rotation. The rotation effect manifests as a characteristic double-peak structure in the atomic resonance region, with the peak spacing varying with the magnetic field strength. Furthermore, by placing a temperature control module outside the atomic chamber, which includes a controller and a heater, the controller adjusts the temperature of the heater, ensuring that the atomic density within the atomic chamber remains stable within a set range.

[0044] In one optional implementation, the polarization detection module further includes: a polarizer; the polarizer is used to convert the polarization state information of the modulated optical signal into light intensity information; and the detector is used to detect the light intensity information to obtain a radio frequency electrical signal. Specifically, the polarizer can measure the rotation angle of the polarization plane of linearly polarized light resulting from the synthesis of left-handed and right-handed circularly polarized light caused by the Faraday effect. The function of the polarizer is to convert this rotation of the polarization plane into a change in light intensity. The detector can be a photodetector.

[0045] The light incident on the photodetector is the combined beam of two optical frequency combs. Each optical frequency comb consists of tens of thousands of comb teeth with optical frequencies (e.g., frequencies on the order of hundreds of THz, or 10^14 Hz). The photodetector responds to the change in light intensity (i.e., the square of the light field amplitude) over time. When two beams of light with similar frequencies (here referring to pairs of comb teeth with similar frequencies in two optical frequency combs) meet on the photosensitive surface of the detector, they interfere, and their combined light intensity changes periodically with the frequency difference between the two beams (i.e., the beat frequency). Because the spacing between the comb teeth of the two optical frequency combs differs by a tiny value (typically on the order of tens of Hz to hundreds of kHz), and they are coherently locked as a whole, the beat frequencies of most pairs of comb teeth fall within the radio frequency range (typically the frequency range of kHz to GHz). Based on this, the photodetector directly converts the rapidly changing light intensity signal into a voltage signal proportional to it. This voltage signal contains the superposition of the beat frequency components generated by all pairs of comb teeth, and its frequency components are mainly distributed in the radio frequency band. Therefore, the detector's output is also known as a radio frequency signal.

[0046] The atomic frequency discriminator described above, which consists of an analyzer and a photodetector in the polarization detection module, can be understood as a direct application of the Faraday effect. This atomic frequency discriminator can be called a Faraday atomic frequency discriminator. Furthermore, the left-handed and right-handed circularly polarized light generated by Zeeman splitting in the atomic chamber can be separated into optical components by setting a quarter-wave plate in the polarization detection module.

[0047] In one optional embodiment, the polarization detection module further includes: a quarter-wave plate and an analyzer; the quarter-wave plate is used to separate the optical components in the modulated optical signal; the analyzer is used to convert the polarization state information of the separated optical components into light intensity information; and the detector is used to detect the light intensity information to obtain a radio frequency electrical signal.

[0048] Specifically, when linearly polarized light enters the atomic chamber, under the influence of Zeeman splitting and the Faraday effect, the outgoing light becomes a combination of two circularly polarized components, one left-handed and one right-handed. A quarter-wave plate (whose fast / slow axis direction needs to be precisely set, usually at a 45-degree angle to the incident polarization direction) converts these two orthogonal circularly polarized components into two orthogonal linearly polarized components. Specifically, one circularly polarized component becomes linearly polarized light vibrating in a certain direction, and the other becomes linearly polarized light vibrating in the perpendicular direction. The analyzer then spatially separates these two orthogonal linearly polarized lights and detects them separately using two photodetectors. In this way, the intensity spectra corresponding to the left-handed and right-handed circularly polarized light components are obtained. These two spectral lines are a direct manifestation of Zeeman splitting; the difference in their center frequencies is proportional to the magnetic field strength, and their line shapes contain information about atomic absorption and dispersion.

[0049] In one optional implementation, the processing module is specifically used to: perform a fast Fourier transform on the electrical signal to obtain a frequency domain signal; map the frequency coordinates of the frequency domain signal to absolute optical frequency coordinates based on the repetition frequency and frequency difference parameter of the two optical frequency comb signals, and reconstruct the optical rotation spectrum; and perform frequency differentiation on the optical rotation spectrum to obtain a frequency discrimination function.

[0050] Specifically, the photodetector converts the interference light signals from two atomically modulated optical frequency combs into time-domain radio frequency analog electrical signals. This signal is then acquired by the processing module and converted into a digital signal. The processing module performs a Fast Fourier Transform (FFT) on the acquired digital time-domain signal. The result of the FFT is a series of discrete frequency-domain data points, each corresponding to a radio frequency (RF) frequency and containing complex information (i.e., amplitude and phase) of that frequency component. Due to the asynchronous sampling characteristics of the dual optical combs, a definite proportional relationship exists between the RF frequency and the original optical frequency. Using known, locked repetition frequencies and preset difference parameters, the processing unit maps each RF frequency point obtained from the FFT and its corresponding amplitude / phase data to an absolute optical frequency through this relationship. Finally, all the mapped data points are arranged and displayed in frequency order to obtain the reconstructed optical spectrum, i.e., the optical rotation spectrum. Differentiating the optical rotation spectrum yields the frequency discrimination function.

[0051] As one or more specific application embodiments of the present invention, such as Figure 2As shown, the atomic frequency discriminator includes a first optical frequency comb 1, a second optical frequency comb 2, a phase lock 3, a beam combiner 4, a polarizer 5, a first permanent magnet 6, an atomic cell 8, a first heater 9, a second heater 10, a second permanent magnet 11, a quarter-wave plate 12, an analyzer 13, a photodetector 14, a high-speed data acquisition unit 15, and a dual-comb spectrum 16. The first optical frequency comb 1 (referred to as the first optical frequency comb) and the second optical frequency comb 2 (referred to as the second optical frequency comb) are used to output optical frequency comb signals. The phase lock 3 coherently locks the two optical signals. The beam combiner 4 combines the coherently locked optical signals. The polarizer 5 converts the combined optical signals into linearly polarized light. The first permanent magnet 6 and the second permanent magnet 11 provide a magnetic field for the atomic cell 8 (i.e., the atomic chamber). The first heater 9 and the second heater 10 provide the corresponding temperature for the atomic cell 8. A quarter-wave plate 12 separates the optical components in the optical signal modulated by the atomic chamber, and an analyzer 13 converts the polarization state information of the separated optical components into light intensity information. A photodetector 14 is used to detect the light intensity information to obtain the radio frequency electrical signal. High-speed data acquisition 15 uses a data acquisition card to acquire the radio frequency electrical signal. The dual-comb spectroscopy 16 includes a dual-comb asynchronous sampling and discriminant function processing unit. This unit performs a fast Fourier transform on the electrical signal, reconstructs the optical rotation spectrum from the transformed signal, and generates a frequency discriminant function based on the optical rotation spectrum.

[0052] Specifically, the first optical frequency comb outputs a broadband comb spectrum, and its repetition frequency is locked to the carrier envelope offset frequency using an RF reference, giving it an absolute frequency scale. The second optical frequency comb is locked to the first optical frequency comb via a coherent controller. The repetition frequency of the second optical frequency comb has a slight difference from that of the first optical frequency comb to form an asynchronous sampling condition, generating an RF beat frequency signal in the time domain. The dual-comb spectrum is obtained through Fourier transform.

[0053] Two optical frequency combs are first combined. Before the beam enters the atomic medium, a polarizer (polarizer) is placed to give the light field a definite linear polarization direction, providing a uniform polarization reference substrate for optical rotation measurements. The comb-shaped light field then enters the atomic chamber. The atomic chamber is made of glass or quartz and filled with alkali metal atomic vapor. The atomic density is stabilized within a set range by a temperature control module. Directly passing through an analyzer results in a Faraday atom frequency discriminator. If a quarter-wave plate is placed after passing through the atomic chamber, converting circularly polarized light into linearly polarized light to separate different optical rotations, it becomes a Zeeman atom frequency discriminator. Figure 3As shown, the horizontal axis represents frequency, and the vertical axis represents intensity. To obtain a significant Zeeman splitting, this invention uses neodymium magnets as the magnetic field source. Neodymium magnets possess high remanence and high coercivity, enabling them to provide a stable longitudinal magnetic field at the center of the atomic chamber. This results in an observable refractive index difference between left- and right-polarized light in the atomic medium, thereby inducing significant Faraday rotation. The rotation effect manifests as a characteristic double-peak structure in the atomic resonance region, with the peak spacing varying with the magnetic field strength.

[0054] After the light field passes through the atomic chamber, an analyzer (a polarizer or analyzer before the PBS) is set up to project the polarization direction after Faraday rotation onto a specified polarization direction, converting the optical rotation information into a measurable quantity of light intensity. This is then converted into an radio frequency (RF) signal by a high-speed photodetector. A dual-comb asynchronous sampling processing unit performs a fast Fourier transform and spectral reconstruction on the RF signal, obtaining the spectral signals corresponding to the two polarization channels, such as... Figure 4 As shown, the horizontal axis represents wavelength, and the vertical axis represents intensity.

[0055] Leveraging the millisecond-level or even faster real-time performance of a dual-comb optical system, this invention enables rapid scanning of the atomic chamber temperature and neodymium magnet position within a short time. By adjusting the magnetic field distribution, the frequency interval between the two peaks of the cyclotron spectrum is made comparable to the effective width of the solar spectrum, thus meeting the requirements for broadband spectral response in scenarios such as solar activity monitoring and space plasma diagnostics. After magnetic field optimization, the atomic density is changed by adjusting the atomic chamber temperature, thereby adjusting the overall transmittance of the cyclotron spectrum. The dual-comb optical system measures the transmission peaks under different temperature conditions in real time, quickly identifying the operating temperature point that maximizes the intensity of the cyclotron light. After magnetic field and temperature optimization, the optimal cyclotron spectrum is obtained. ,like Figure 5 As shown, the horizontal axis represents frequency, and the vertical axis represents intensity. Differentiating the intensity by frequency yields the frequency discrimination function. It is used to map the laser frequency deviation into an error signal, and finally complete the calibration and fabrication of the atomic frequency discriminator.

[0056] Compared with existing continuous optical scanning atomic frequency discriminators and traditional frequency discrimination techniques based on Faraday filtering, the Faraday atomic frequency discrimination scheme based on dual optical comb spectroscopy of the present invention has the following significant advantages.

[0057] First, this invention utilizes asynchronous sampling with dual optical combs to directly obtain the real-time amplitude and phase response of the atomic medium across the entire optical comb bandwidth, achieving scan-free, broadband, absolute frequency-scaled rotational spectral measurements. Traditional frequency discrimination schemes typically operate only within a narrow frequency range near atomic transitions, while this invention can simultaneously obtain optical rotation information over a wide spectral range, thus significantly expanding the frequency domain coverage of the atomic frequency discriminator.

[0058] Secondly, this invention uses a polarization link consisting of a polarizer, an atomic medium, an analyzer, and a polarization beam splitter to completely convert the Faraday rotation effect into a measurable phase difference in a coherent manner. Combined with the high-resolution phase reconstruction capability of the dual optical comb, it can obtain subtle changes in the spectral shape and construct a frequency discrimination function with a large slope and a wide linear range, providing a foundation for high-sensitivity frequency measurement.

[0059] Third, this invention utilizes the millisecond-level real-time capability of dual-comb spectroscopy to achieve rapid scanning and optimization of the atomic chamber temperature. It can determine the operating temperature point with the highest optical rotation transmittance in a short time, thereby obtaining a rotation spectrum with high signal intensity and low noise level. Through dual optimization of magnetic field and temperature, the parameters of the atomic frequency discriminator can be calibrated quickly.

[0060] Fourth, this solution does not rely on mechanical scanning or modulation structures, and has the advantages of simple structure and high stability. The dual optical combs rely on a unified RF reference for coherent locking, which greatly reduces the sensitivity of the entire system to disturbances such as external temperature and magnetic field drift, and the long-term operating stability is significantly better than that of traditional Faraday discriminators.

[0061] Finally, this invention can directly output a frequency discrimination function based on the frequency derivative of the cyclotron spectrum. Combined with the absolute optical frequency scale of the dual optical comb, it can realize real-time frequency deviation measurement and closed-loop control of incoming lasers. This feature makes this invention not only suitable for precision frequency measurement in the laboratory, but also able to meet the needs of applications such as solar activity monitoring, space physics exploration, inter-satellite laser links, and quantum sensing for broadband, fast, and highly stable frequency standards.

[0062] Specifically, this invention is the first to apply dual-comb spectroscopy to Faraday rotation measurement, achieving a broadband, scan-free atomic frequency discriminator with an absolute frequency scale. Compared to traditional continuous-scan or single-point Faraday discriminators, this invention directly measures the optical rotation phase spectrum through asynchronous sampling with dual optical combs, enabling the entire atomic frequency response to be reconstructed in a single, full-bandwidth operation, fundamentally overcoming the limitations of narrowband discriminators. Simultaneously, a coherent polarization link—polarizer—atomic medium—analyzer—polarization beam splitter—is proposed, achieving high-precision reconstruction of the optical rotation phase. This polarization structure allows the Faraday rotation angle to be extracted as a coherent phase difference, rather than through traditional intensity difference measurement, fundamentally improving the discriminator's sensitivity and stability.

[0063] Furthermore, leveraging the real-time nature of dual-comb phase reconstruction, rapid bidirectional optimization of temperature and magnetic field parameters is achieved. Rotational spectra can be reconstructed in milliseconds without scanning. By comparing the rotational intensity and linearity under different conditions in real time, the optimal operating temperature and magnetic field combination can be quickly identified, which is crucial for the long-term stability of the atomic frequency discriminator. A frequency discrimination function based on the phase derivative of the rotational spectrum is constructed, and full bandwidth availability is achieved through absolute frequency scaling using dual-combs. Compared to traditional frequency discriminators that only provide a narrow linear region, this invention offers broadband linear discrimination capabilities scalable to the THz level, which can be directly used for real-time frequency deviation feedback of external lasers. In addition, a dual-parameter collaborative optimization mechanism is proposed, utilizing magnetic field control to regulate the rotational peak structure and temperature control to enhance rotational transmittance. This enables dual customization of the rotational spectral structure and signal intensity, allowing the performance of the atomic frequency discriminator to be adjusted as needed and exhibiting high repeatability. Therefore, this invention presents for the first time a complete and quantifiable atomic frequency discriminator fabrication chain, possessing standardization and engineering potential, facilitating its application in aerospace, solar physics, quantum sensing, and other fields.

[0064] This embodiment also provides a method for implementing an atomic frequency discriminator, applied to the atomic frequency discriminator described in the above embodiments, such as... Figure 6 As shown, the method includes the following steps: Step S101: Two coherently locked optical frequency comb signals are generated, and the two optical signals are combined to convert them into a first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference.

[0065] Step S102: The optical signal of the first polarization state is modulated using the Faraday rotation effect.

[0066] Step S103 involves converting, polarizing, and probing the modulated optical signal to obtain an electrical signal.

[0067] Step S104: Asynchronous optical sampling and fast Fourier transform are performed on the electrical signal, the transformed signal is reconstructed to obtain the optical rotation spectrum, and a frequency discrimination function is generated based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

[0068] The implementation method of the atomic frequency discriminator provided in the embodiments of the present invention can be implemented by the atomic frequency discriminator provided in any of the above embodiments of the present invention, and has the corresponding beneficial effects of the atomic frequency discriminator. Further functional descriptions of the above steps are the same as the functional modules in the corresponding embodiments above, and will not be repeated here.

[0069] In an optional embodiment, the method further includes: determining whether the optical rotation spectrum meets the requirements of a preset application scenario; if not, adjusting the magnetic field strength generated by the magnet in the atomic chamber / or changing the temperature in the atomic chamber to change the optical response function of the atomic frequency discriminator until the obtained optical rotation spectrum meets the requirements of the preset application scenario.

[0070] Specifically, to achieve optimal performance of the atomic frequency discriminator in different application scenarios, it is necessary to find the operating point that maximizes the optical rotation signal and yields the most ideal frequency response curve (i.e., the rotation spectrum). Based on this, two key adjustable parameters are the magnetic field strength and the atomic chamber temperature. The magnetic field strength directly affects the size of the Zeeman split, thus determining the spacing and slope of the characteristic double peaks (or the zero-crossing point of the dispersion curve) in the rotation spectrum. The atomic chamber temperature primarily affects the density of the atomic vapor, thereby influencing the intensity and signal-to-noise ratio of the optical rotation signal.

[0071] In this embodiment, a scanning adjustment method is used to determine the ideal operating point. Magnetic field adjustment can be achieved through a magnet adjustment mechanism (e.g., a power supply controlling the electromagnet current, or a precision displacement stage adjusting the position of the permanent magnet); temperature adjustment is achieved through a temperature control module. During magnetic field adjustment using the magnet adjustment mechanism, a cyclotron spectrum is obtained after each adjustment. The spacing between the two Zeeman splitting peaks in the cyclotron spectrum is then analyzed to determine if it meets the target value (based on the application scenario, e.g., matching the width of the solar spectrum being measured), and if the slope of the zero-crossing point is maximized (a larger slope results in higher frequency discrimination sensitivity), to obtain the optimal magnetic field. During temperature adjustment, the atomic density is changed by adjusting the temperature of the atomic chamber, thereby adjusting the overall transmittance of the cyclotron spectrum. Real-time measurement of the transmission peaks of the cyclotron spectrum under different temperature conditions allows for rapid identification of the operating temperature point that maximizes the intensity of the cyclotron light.

[0072] This embodiment also provides a frequency discrimination method using the atomic frequency discriminator described in the above embodiments, such as... Figure 7 As shown, the method includes the following steps: Step S201 involves inputting the laser to be frequency-discriminated into an atomic frequency discriminator to obtain its rotation angle. Specifically, after obtaining the frequency discrimination function of the atomic frequency discriminator, the discriminator can use this function to generate an error signal. During the frequency discrimination process, the dual optical comb can be turned off or removed from the optical path. Then, the laser to be frequency-discriminated is first converted into linearly polarized light by a polarizer, and then input into the atomic interaction module to achieve modulation by the Faraday rotation effect. After modulation, the polarization plane rotates, and the polarization detection module converts the polarization rotation information into light intensity information. Based on the relationship between the light intensity information and the rotation angle, the rotation angle can be deduced.

[0073] Step S202: Based on the frequency discrimination function, determine the laser frequency corresponding to the rotation angle; specifically, after obtaining the rotation angle, compare it with the inverse function of the frequency discrimination function. Since the frequency discrimination function is a monotonic function with a large slope near the atomic resonance frequency, the current laser frequency can be uniquely solved.

[0074] Step S203: Determine the error signal based on the deviation between the laser frequency and the target frequency; compare the laser frequency and the target frequency (e.g., the center of the atomic resonance peak), and determine the error signal based on the difference between the two and a certain scaling factor.

[0075] Step S204 involves adjusting the laser frequency of the laser to be discriminated against based on the error signal, thereby adjusting the laser frequency to the target frequency. Specifically, after obtaining the error signal, it is fed back to the frequency tuning mechanism of the laser emitting the laser to be discriminated against (e.g., changing the cavity length of a piezoelectric ceramic or changing the injection current of a diode laser). This feedback drives the laser frequency to change in the direction of reducing the error signal. Steps S201 to S204 are repeated until the final laser frequency emitted by the laser is adjusted to the target frequency, thus locking the laser frequency.

[0076] While exemplary embodiments and their advantages have been described in detail, those skilled in the art can make various changes, substitutions, and modifications to these embodiments without departing from the spirit of the invention and the scope of protection defined by the appended claims. Such modifications and variations all fall within the scope defined by the appended claims. For other examples, those skilled in the art should readily understand that the order of process steps can be changed while remaining within the scope of the invention.

[0077] Furthermore, the scope of this invention is not limited to the processes, mechanisms, manufacturing methods, material compositions, means, methods, and steps of the specific embodiments described in the specification. From the disclosure of this invention, those skilled in the art will readily understand that any existing or future processes, mechanisms, manufacturing methods, material compositions, means, methods, or steps that perform substantially the same function or obtain substantially the same results as the corresponding embodiments described in this invention can be applied according to this invention. Therefore, the appended claims are intended to include these processes, mechanisms, manufacturing methods, material compositions, means, methods, or steps within their scope of protection.

Claims

1. An atomic frequency discriminator, characterized in that, include: The light source module is used to generate two coherently locked optical frequency comb signals and combine the two optical signals into a first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference. The atomic interaction module is used to modulate the optical signal in the first polarization state using the Faraday optical rotation effect; A polarization detection module is used to convert and detect modulated optical signals. After asynchronous optical sampling, the optical signal is down-converted to radio frequency through interference on the detector surface to obtain a multi-heterodyne interference electrical signal. The polarization detection module includes a detector. The processing module is used to perform a fast Fourier transform on the electrical signal, reconstruct the optical rotation spectrum from the transformed signal, and generate a frequency discrimination function based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

2. The atomic frequency discriminator according to claim 1, characterized in that, The light source module includes: A first optical frequency comb is used to generate a first optical frequency comb signal, wherein the repetition frequency of the first optical frequency comb signal is locked to the carrier envelope offset frequency to a radio frequency reference source. The second optical frequency comb is used to generate a second optical frequency combed optical signal; A coherent controller is used to perform optical frequency coherent locking between the second optical frequency comb signal and the first optical frequency comb signal, so that the repetition frequency of the two optical frequency comb signals has a preset difference. The polarization generation module is used to combine two coherently locked optical signals and convert them into a first polarization state.

3. The atomic frequency discriminator according to claim 1, characterized in that, The atomic interaction module includes an atomic chamber, a magnet, and a temperature control module. The magnet and the temperature control module are located outside the atomic chamber and are used to provide a magnetic field to the atomic chamber and adjust the temperature of the atomic chamber.

4. The atomic frequency discriminator according to claim 1, characterized in that, The polarization detection module further includes: a polarization analyzer; The analyzer is used to convert the polarization state information of the modulated optical signal into light intensity information; The detector is used to detect light intensity information to obtain radio frequency electrical signals.

5. The atomic frequency discriminator according to claim 1, characterized in that, The polarization detection module also includes: a quarter-wave plate and a polarizer; The quarter-wave plate is used to separate the optical components in the modulated optical signal; The analyzer is used to convert the polarization state information of the separated light components into light intensity information; The detector is used to detect light intensity information to obtain radio frequency electrical signals.

6. The atomic frequency discriminator according to claim 1, characterized in that, The processing module is specifically used for: performing a fast Fourier transform on the electrical signal to obtain a frequency domain signal; mapping the frequency coordinates of the frequency domain signal to absolute optical frequency coordinates based on the repetition frequency and frequency difference parameter of the two optical frequency comb signals to reconstruct the optical rotation spectrum; and performing frequency differentiation on the optical rotation spectrum to obtain a frequency discrimination function.

7. A method for implementing an atomic frequency discriminator, characterized in that, The method, applied to the atomic frequency discriminator according to any one of claims 1-6, comprises: Two coherently locked optical frequency comb signals are generated, and the two optical signals are combined and converted into the first polarization state. The repetition frequencies of the two optical frequency comb signals have a preset difference. The optical signal in the first polarization state is modulated using the Faraday rotation effect; The modulated optical signal is converted, analyzed, and detected to obtain an electrical signal; The electrical signal is subjected to asynchronous optical sampling and fast Fourier transform. The transformed signal is reconstructed to obtain the optical rotation spectrum. A frequency discrimination function is generated based on the optical rotation spectrum. The frequency discrimination function is used to map the laser frequency deviation into an error signal.

8. The method according to claim 7, characterized in that, The method further includes: Determine whether the optical rotation spectrum meets the requirements of the preset application scenario; If the requirements are not met, adjust the magnetic field strength generated by the magnet in the atomic chamber / or change the temperature in the atomic chamber to change the optical response function of the atomic frequency discriminator until the obtained optical rotation spectrum meets the requirements of the preset application scenario.

9. A frequency discrimination method using the atomic frequency discriminator according to any one of claims 1-6, characterized in that, The method includes: The laser to be discriminated is input into the atomic frequency discriminator to obtain the rotation angle of the laser to be discriminated; Based on the frequency discrimination function, the deviation between the rotation angle and the target optical rotation angle is determined; The error signal is determined based on the slope value of the frequency discrimination function corresponding to the deviation and the target frequency; The laser frequency of the laser to be discriminated is adjusted based on the error signal, so that the laser frequency is adjusted to the target frequency.

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