A method and apparatus for optical fiber direct atomic spectroscopy frequency locking

Abstract

The application discloses an optical fiber direct connection atomic spectrum frequency locking device, which comprises an atomic cell, an error signal acquisition device, a locking device and a coupling light generation and modulation device connected by an optical fiber. The coupling light generation and modulation device generates coupling laser with a wavelength of 509 nm containing a radio frequency modulation signal. The atomic cell receives the coupling laser and probe laser with a wavelength of 852 nm. In the atomic cell, the probe laser is divided into reference light and signal light. The signal light is transmitted in the opposite direction of the coupling light in the atomic cell to generate Rydberg atomic spectrum. The error signal acquisition device detects the signal light and the reference light to generate an error signal. The locking device generates the radio frequency modulation signal and locks the coupling light output frequency according to the error signal. The application also discloses a method using the device. The device and the method solve the problems of complexity and poor effect of the all-fiber laser frequency locking device for preparing Rydberg atoms.

Description

Technical Field

[0001] This application relates to the field of atomic spectroscopy, and to a method for stabilizing the frequency of atomic spectroscopy lasers, particularly to the application of frequency locking in the coupling light of Rydberg atomic preparation lasers. Background Technology

[0002] Laser frequency locking is a crucial step in single-frequency laser development, as its performance directly determines the laser's frequency stability, especially in applications related to atomic spectroscopy, such as magnetometers, electric field meters, optical clocks, ion clocks, and atomic quantum computers. Atomic spectral frequency locking is an absolute physical parameter-based laser frequency locking method, particularly useful for high-sensitivity electric field measurements using Rydberg atoms, where frequency locking of the coupling light is required. In Rydberg electric field measurement applications, existing coupled laser frequency locking methods require either frequency shifting of the laser to lock onto an optical reference cavity, or frequency modulation of the probe light followed by frequency modulation transfer to the Rydberg resonant excitation spectrum to obtain an error signal. The former method cannot achieve frequency locking at atomic transition energy levels, requiring additional frequency shifting to the resonant mode of the reference cavity, while the latter method, which modulates the probe light, has a low modulation transfer rate, particularly at high Rydberg principal quantum number levels, resulting in poor modulation performance. Summary of the Invention

[0003] This application proposes a fiber-optic direct-connection atomic spectral frequency locking method and apparatus, which solves the problems of complex apparatus and poor performance in frequency locking of all-fiber laser light sources used in Rydberg atom preparation.

[0004] This application provides a fiber-optic direct-connect atomic spectral frequency locking method. It utilizes electro-optic modulation of an integrated fiber waveguide to create a radio frequency modulator for the coupled light. After fiber amplification and a single-pass fiber frequency multiplier, a 509nm coupled light with doubled frequency is obtained. This laser, together with an 852nm probe light, excites cesium atoms to obtain a modulated Rydberg excitation spectral signal. The spectral signal and the radio frequency signal are mixed to obtain an error signal for the laser frequency. This error signal is then fed back to the piezoelectric ceramic port of the coupled light seed source via a PID feedback circuit, enabling high-speed laser frequency locking.

[0005] This application also provides an optical fiber-connected atomic spectral frequency locking device, including an atomic gas cell, an error signal acquisition device, a locking device, and a coupling light generation and modulation device connected by optical fiber.

[0006] The coupled light generating and modulation device is used to generate coupled laser light with a wavelength of 509 nm that includes a radio frequency modulation signal.

[0007] The atomic gas chamber is used to receive the coupling laser and the probe laser with a wavelength of 852nm. In the atomic gas chamber, the probe laser is divided into a reference light and a signal light. The signal light is transmitted in opposite directions through the atomic gas chamber to generate a Rydberg atomic spectrum.

[0008] The error signal acquisition device is used to detect the signal light and the reference light and generate an error signal.

[0009] The locking device is used to generate a radio frequency modulation signal and lock the output frequency of the coupled light according to the error signal.

[0010] In one embodiment of this application, in the coupled light generation and modulation device, the seed source of the coupled light is a 1018nm single-frequency laser, which is radio frequency modulated by an electro-optic phase modulator, and then injected sequentially into an optical fiber amplifier and an optical fiber frequency multiplier to output a modulated 509nm laser.

[0011] In one embodiment of this application, the atomic gas chamber uses optical fiber coupling for laser transmission via optical fiber counter-transmission; the probe light and coupling light are transmitted to the atomic gas chamber via optical fiber connectors connecting the input and output optical fibers, and the laser transmission optical fiber is a polarization-maintaining fiber.

[0012] In one embodiment of this application, an 852nm probe laser and a 509nm coupling laser enter the atomic gas chamber from opposite ends. The 852nm probe laser is split into two equal-power parts by a beam splitter. The first laser beam is transmitted and undergoes total internal reflection on the second surface, while the other beam is directly reflected and transmitted parallel to the first laser beam into the atomic gas chamber. The 509nm laser beam is reflected by a dichroic beam splitter and enters the atomic gas chamber, coinciding with the first 852nm laser beam and transmitted in opposite directions to the left end face. The two 852nm probe laser beams exit from the right end face and are reflected by the two inclined surfaces of the prism, respectively. Finally, they are converged by a focusing lens, and atomic spectral signals are collected using fiber optic coupling.

[0013] Among them, the first of the two 852nm probe beams serves as a reference laser, providing the absorption background of the atoms, while the other beam, as a Rydberg EIT spectrum, generates a transmission peak on the atomic absorption background. The position of the transmission peak corresponds to the resonance point of the atomic energy level.

[0014] In one embodiment of this application, the error signal acquisition device includes a balanced photodetector, a mixer, and a low-pass filter. Reference light and signal light output from the atomic gas cell are respectively input into the balanced photodetector, which outputs a spectral detection electrical signal. The error signal acquisition involves mixing the spectral detection electrical signal and using a low-pass filter. The mixing signals are the spectral detection electrical signal and the radio frequency drive signal of the electro-optic phase modulator.

[0015] In one embodiment of this application, the locking device includes a radio frequency (RF) source, a phase shifter, and a PID control circuit. The RF signal participating in the mixing passes through the phase shifter, which is used to adjust the relative phase of the spectral detection electrical signal and the RF signal to achieve demodulation of the error signal. The error signal passes through the PID control circuit and is finally connected to the laser frequency control port of the fiber optic seed source.

[0016] In one embodiment of this application, the bandwidth of the low-pass filter is lower than the frequency of the radio frequency signal to ensure that the high-frequency components of the mixing are blocked, while the difference frequency portion of the two signals passes through.

[0017] This application also proposes an atomic spectral frequency locking method for direct fiber connection, using the apparatus described in any embodiment of this application, comprising the following steps: The 509nm laser is generated and a modulation signal is applied. The generated 509nm laser carries a frequency-doubled radio frequency modulation, which is reflected in the atomic spectrum after entering the atomic gas cell. Adjusting the frequency parameters of the radio frequency signal, and achieving radio frequency doubling synchronously by using a seed laser to multiply the frequency through a frequency multiplier; Atomic spectral signals from Rydberg and Doppler background spectral signals of the ground state background were obtained using an optical fiber atomic gas cell. Adjusting the dual-probe differential device, DC background elimination is achieved by passing the spectral signals of the two probes through the differential detection circuit; The phase shift of the RF signal at the mixer input is adjusted, and then a low-pass filter is used to generate an error signal. The seed source optical frequency is adjusted until the slope of the error signal is greater than a set reference. The error signal is made as steep as possible within the range under investigation to achieve high-sensitivity frequency locking.

[0018] In one embodiment, the optimal radio frequency parameters are found for the frequency-locked loop to obtain the optimal frequency-locked spectral signal.

[0019] Preferably, the cutoff wavelength of the probe laser guiding fiber connected to the atomic gas cell is higher than the coupling laser wavelength.

[0020] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects: This scheme employs direct modulation of the seed source frequency of the coupled laser, resulting in second-harmonic modulation of the coupled light. This solves the problem of the lack of fiber-optic modulation schemes for 509nm lasers. Since the coupled light is the decisive light source for preparing Rydberg atoms, the modulation information of the coupled light is transferred to the acquired Rydberg atom spectrum. Furthermore, the use of an all-fiber link eliminates the need to consider RF modulation impedance matching compared to block phase modulation methods, achieving efficient spectral modulation results with low modulation voltage. The direct fiber-optic connection structure of the atomic spectrum offers advantages such as strong vibration resistance and absence of interference light, allowing for flexible plug-and-play connection with compatible light sources and circuits.

[0021] This invention allows for the use of low-voltage, low-power radio frequency sources to achieve radio frequency modulation of the light source frequency, while also reducing electromagnetic interference to the frequency locking system and solving the problem of the lack of effective electro-optic modulation devices in the 509nm band.

[0022] Direct fiber optic frequency-locking paths are no longer limited to laboratory environments. Utilizing the plug-and-play nature of fiber optic links and the low-loss characteristics of optical connections, they can be used in remote scenarios as well as industrial applications involving vibration. This avoids the problems of reduced laser polarization purity and power fluctuations caused by multiple free-space optical components when the fiber optic light source passes through the free-space optical path. It also reduces the complexity of the device.

[0023] Fiber optic spectral detection features high integration, structural stability, and mass production without the need for manual correction. Furthermore, fiber optic transmission reduces the impact of stray light on spectral quality, resulting in excellent signal quality. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 Schematic diagram of a 509nm coupled-optical laser frequency locking scheme; Figure 2 A diagram of an atomic spectral frequency-locking device directly connected to an optical fiber; Figure 3 The waveforms of the frequency-locked spectrum and error signal are shown below; Figure 4 This is a flowchart of an embodiment of the optical fiber direct-connected atomic spectral frequency locking method of this application.

[0025] In the diagram, 1. 1018nm seed source, 2. Electro-optic phase modulator (EOM), 3. 1018nm amplifier, 4. Frequency multiplier, 5. Coupled laser fiber, 6. 852nm probe laser, 7. Probe fiber, 8. Cemented beam splitter, 9. Atomic gas cell, 10. Two-color beam splitter, 11. Signal output fiber, 12. Reference output fiber, 13. Balanced photodetector, 14. Radio frequency signal source, 15. Phase shifter, 16. Mixer, 17. Low-pass filter, 18. PID circuit. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] This application discloses a fiber-optic direct-connected atomic spectrum frequency locking method and apparatus, comprising a laser source and fiber optic transmission, fiber-optic atomic gas cell spectrum acquisition, and spectrum error signal acquisition. The source includes a frequency resonant probe light source and a fiber-optic electro-optic modulated coupling light laser source. The optical paths are sequentially connected through a direct fiber-optic connection to acquire the fiber-optic structure frequency-locked spectrum. Then, the error signal is acquired through modulation and demodulation to complete the frequency closed-loop control of the coupling light seed, thereby locking the frequency of the coupling light to the atomic transition line. This indirect method of locking the coupling light laser frequency can be extended to laser frequency locking of non-resonant atomic transition lines.

[0028] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0029] This embodiment provides a method for frequency locking of atomic spectroscopy via direct fiber optic connection. For example... Figure 1 As shown, by injecting 852nm and 509nm lasers into the fiber atomic gas cell in reverse transmission, a Rydberg atomic spectrum is generated. The transmission spectrum signal of the 852nm laser is collected, and after being mixed and low-pass processed, it is fed back to the 509nm light source through a PID circuit. Closed-loop feedback is performed to address the frequency drift of the 509nm laser, thereby achieving stable frequency control of the 509nm light source.

[0030] Figure 2 This diagram illustrates a fiber-optic direct-connected atomic spectral frequency-locking device. The fiber-optic direct-connected atomic spectral frequency-locking device proposed in this application utilizes atomic spectroscopy to achieve frequency transfer between two wavelengths, locking the frequency of a 509nm laser by detecting an 852nm laser. The fiber-optic direct-connected atomic spectral frequency-locking device includes an atomic gas cell, an error signal acquisition device, a locking device, and a coupling light generation and modulation device connected via optical fiber.

[0031] The coupled light generation and modulation device is used to generate a coupled laser with a wavelength of 509 nm containing a radio frequency (RF) modulation signal. Preferably, the coupled light is generated using an all-fiber seed laser, a fiber electro-optic phase modulator, a fiber amplifier, and a fiber frequency doubler. The seed source is a 1018 nm single-frequency laser, and the RF modulation is achieved with high efficiency using the RF modulator. Injecting the modulated seed laser sequentially into the fiber amplifier and fiber frequency doubler outputs a modulated 509 nm laser. When an RF signal is applied to the RF modulator, the generated 509 nm laser exhibits second-harmonic modulation. The RF signal doubles the frequency synchronously with the light wave as a carrier. The typical frequency range of the RF signal is 500 kHz to 6 MHz, and the bandwidth of the photodetector is similarly high.

[0032] The laser transmission path of the fiber-optic direct-connected atomic spectroscopy frequency-locking device is entirely fiber-optic. The atomic gas cell receives the coupled laser and the 852nm wavelength probe laser. Within the atomic gas cell, the probe laser is split into a reference beam and a signal beam. The signal beam is transmitted in opposite directions through the atomic gas cell to generate a Rydberg atomic spectrum. The atomic gas cell also employs fiber-optic coupling for laser transmission, which improves laser transmission efficiency, eliminates laser pointing jitter, reduces stray light entering the fiber optic detection system, improves the atomic spectral signal quality, and facilitates the acquisition of a high-quality frequency-locking error signal.

[0033] Coupled optical modulation uses a 1018nm laser modulator with a longer wavelength, which has high phase modulation efficiency for fiber waveguide structures. It can achieve a greater modulation depth with a low half-wave voltage, and the coupling efficiency of long-wavelength fiber waveguides is relatively high.

[0034] The probe light and coupling light are transmitted to the atomic gas cell via fiber optic connectors to connect the input and output optical fibers, and the laser transmission fiber is a single-mode polarization-maintaining fiber (PM fiber).

[0035] A preferred structure is as follows: an 852nm probe laser and a 509nm coupling laser enter the atomic gas chamber from opposite ends. The 852nm probe laser is split into two equal-power beams by a cemented beam-splitting prism. One beam is transmitted and undergoes total internal reflection on a second surface, while the other is directly reflected and propagates parallel to the first beam into the atomic gas chamber. The 509nm laser, after being reflected by a dichroic beam-splitting prism, enters the atomic gas chamber and coincides with the first 852nm laser beam, propagating in opposite directions to the left end face. The two 852nm probe laser beams exit from the right end face and are reflected by the two inclined surfaces of the prism. Finally, the probe lasers are converged by a focusing lens, and the atomic spectral signals are collected using fiber optic coupling.

[0036] Two 852nm probe beams are used. The first beam serves as a reference laser, providing the atomic absorption background. The second beam, representing the Rydberg EIT spectrum, generates a transmission peak against the atomic absorption background. The position of the transmission peak corresponds to the resonance point of the atomic energy level. The frequency locking device is used to lock onto this resonance point. Typically, the probe laser is a frequency-stable laser beam, while the coupling beam needs to be locked using this EIT spectrum.

[0037] It should be noted that the 509nm coupled laser transmitted in reverse is output from the left end face of the atomic gas cell and then irradiates the end face of the 852nm optical fiber. Due to the large difference in wavelength between the two sides, the optical path focusing parameters are also very different. Furthermore, the cutoff wavelength of the probe laser transmission fiber is higher than that of 509nm, which prevents the 509nm laser from entering the 852nm optical fiber. This can form good laser isolation and prevent the reverse 509nm laser from affecting the normal operation of the 852nm laser source.

[0038] In one embodiment of this application, the error signal acquisition device includes a balanced photodetector, a mixer, and a low-pass filter. The error signal acquisition device is used to detect the signal light and the reference light, and generate an error signal. The two probe beams, including the reference light and the signal light, are respectively output to the balanced photodetector. Because their power is equal, the DC information of the light can be canceled, the AC atomic spectral signal can be acquired, the Rydberg atomic spectral signal background ratio can be enhanced, and the fluctuations in DC background voltage caused by fiber optic splicing, disturbances, and front-end power fluctuations can be offset.

[0039] The output electrical signal of the balanced photodetector is a spectral detection signal. The error signal is obtained by mixing the spectral detection electrical signal and then passing it through a low-pass filter. The signals involved in the mixing are the spectral detection electrical signal and the radio frequency signal driving the electro-optic phase modulator.

[0040] The radio frequency (RF) signal involved in the mixing needs to pass through a phase shifter to adjust the relative phase of the spectral detection electrical signal and the RF signal, thereby demodulating the error signal. The bandwidth of the low-pass filter is required to be lower than the RF signal frequency to ensure that the high-frequency components of the mixing are blocked, while the difference frequency portion of the two signals passes through.

[0041] In one embodiment of this application, the locking device includes a radio frequency (RF) source, a phase shifter, and a PID control circuit. The locking device is used to generate an RF modulation signal and lock the output frequency of the coupled light based on an error signal. The error signal then passes through the PID control circuit and is finally connected to the laser frequency control port of the optical fiber seed source.

[0042] It should be noted that the error signal reflects the stability of the laser frequency. The error signal is a zero-crossing ramp signal, obtained after mixing and low-pass filtering. The steepness of the ramp signal indicates how quickly the laser frequency deviates from its target frequency, and the range of variation in the ramp signal is proportional to the deviation of the laser frequency from the atomic resonance transition line. At the atomic resonance transition point, the frequency misharmonicity is zero, and the spectral signal received by the detector corresponds to a peak value, which contains high-speed radio frequency modulation. The peak position is the zero-crossing voltage of the error signal corresponding to the resonance transition point. The waveforms of the frequency-locked spectrum and the error signal are shown below. Figure 3 As shown.

[0043] It is also necessary to explain how the modulated radio frequency (RF) signal works, and how the RF signal, after frequency doubling, affects the output signal of the atomic gas cell L1. The RF-modulated laser has an RF modulation signal added at its optical center frequency. The modulated 509nm laser, acting as a coupling beam, passes through the atomic gas cell together with the probe laser propagating in the opposite direction, generating Rydberg atoms. Since the probe and coupling beams only resonate at the energy difference between the ground state and the Rydberg excited state when their energies are added together, a Rydberg EIT resonance peak (h) will occur. f c +h f p = E l - E0, h is Planck's constant. f p To detect the frequency of light, f c E is the frequency of the coupled light. l E0 is the Rydberg state energy, and E0 is the ground state energy. Due to the four-wave mixing effect, the modulation information of the coupled light is transmitted to the probe laser after atomic transmission. By collecting the absorption spectrum signal of the probe light, the signal output by the atomic gas cell L1 carries the radio frequency modulation signal and the frequency drift information of the coupled light.

[0044] The specific frequency relationships are as follows: output terminals 11 and 12 of the atomic gas chamber, output terminal 13 of the balanced detector, input and output terminals of mixer 16, and input and output terminals of low-pass filter 17. Output terminal L1 of the atomic gas chamber is a probe light carrying a radio frequency modulated signal. f p +2 f m ,in, f p To detect the frequency of light, f m The frequency of the modulation signal is used. The output terminal L2 of the atomic gas chamber only contains the detection laser. f pWithout the coupling light having the effect of radio frequency transmission, the two probes at the balanced detector L3 respectively receive the absorption spectrum of the probe light carrying the radio frequency modulation signal and the absorption spectrum of the probe light without the modulation signal. The left side of the two input ports of mixer 16 receives the radio frequency signal carrying 2 f m Frequency, the right side is the input EIT spectrum, and there exists Δ f +2 f m Frequency information, where Δ f This is due to the frequency drift of the coupled light. After mixing, there exists a Δ... f +4 f m and Δ f The information, after being low-pass filtered, yields Δ. f Frequency components. Figure 4 This is a flowchart of an embodiment of the optical fiber direct-connected atomic spectral frequency locking method of this application.

[0045] Step 10: 509nm laser generation and modulation signal loading.

[0046] The generated 509nm laser carries a frequency-doubled radio frequency modulation, which is reflected in the atomic spectrum after entering the atomic gas cell.

[0047] To further illustrate the embodiments of this application, the 509nm laser generation is achieved using a 1018nm fiber seed source, a 1018nm fiber amplifier, and a fiber frequency multiplier. For example... Figure 2 As shown, an electro-optic phase modulator is inserted between the 1018nm seed source and the 1018nm amplifier. This electro-optic phase modulator is a fiber optic waveguide modulator, capable of achieving low half-wave voltage and utilizing low-power radio frequency (RF) for phase modulation. By applying RF modulation, the frequency of the seed source is modulated; the larger the amplitude of the modulation signal, the greater the modulation depth of the laser frequency. After passing through a laser frequency multiplier, the generated 509nm laser carries a second-harmonic modulation. Since the 509nm laser does not carry modulation information when the applied RF signal amplitude is zero, a smaller modulation amplitude results in less interference to the light source, facilitating subsequent coupling of the light source to other application scenarios.

[0048] Preferably, the 1018nm seed source is a single-frequency narrow-linewidth laser source, the 1018nm amplifier is a narrow-linewidth amplifier, and the fiber frequency multiplier is a single-frequency single-pass PPLN crystal frequency multiplier. The matching temperature is controlled to achieve the optimal matching temperature and achieve high frequency multiplication efficiency. Since the frequency variation range of the light source generated by phase modulation is relatively small compared to the laser wavelength, it has a negligible impact on the frequency multiplication efficiency and the influence of the modulator can be ignored.

[0049] Step 20: Adjust the frequency parameters of the radio frequency signal and achieve radio frequency doubling by using a seed laser to multiply the frequency synchronously.

[0050] The laser frequency doubling and the RF modulation frequency doubling of the seed source are adjusted synchronously. Preferably, the laser frequency doubling and the RF modulation frequency doubling of the seed source are synchronized. After passing through the electro-optic modulator, the seed source generates a modulation sideband on the optical frequency. The modulation sideband's distance from the laser center frequency corresponds to the RF frequency. When the wavelength of the seed source is changed, the temperature of the frequency multiplier needs to be changed accordingly. The frequency doubling using a single-pass structure does not require a resonant cavity locking stage; the output of 509nm laser can be achieved simply by adjusting the temperature, facilitating subsequent 509nm laser frequency locking and avoiding the dual locking problem of the seed source and the frequency multiplier. The optimal RF frequency parameters are found for the frequency locking loop to obtain the optimal frequency locking spectral signal.

[0051] Step 30: Obtain the atomic spectral signal of Rydberg and the Doppler background spectral signal of the ground state background using an optical fiber atomic gas cell.

[0052] The aforementioned fiber optic atomic gas cell is a four-port fiber optic input-output structure atomic gas cell. A spectral scheme for closely packed optical elements was designed, and high-transmittance, high-thermal-stability optical adhesive was used for the installation and bonding of the optical elements.

[0053] The aforementioned fiber optic atomic gas cell includes two input ports and two output ports. The two input ports are an 852nm single-mode polarization-maintaining fiber input and a 509nm single-mode polarization-maintaining fiber input. Both fiber output ports are 852nm laser fiber outputs, where L1 is the Rydberg atomic spectrum signal, output through the signal light output fiber, and L2 is the Doppler background signal of the ground state spectrum, output through the reference light output fiber.

[0054] Step 40: Adjust the dual-probe differential device to eliminate DC background by passing the spectral signals of the two probes through the differential detection circuit.

[0055] The signal light output fiber and reference light output fiber of the optical fiber atomic gas cell are connected to two photoelectric sensors of a balanced photodetector, which is a photodetector with a fiber optic flange interface. After connection, the photodetector only receives the laser output from the fiber, with no stray background light entering the detector. Combined with the dual-probe differential detection method, the DC background signal of the Rydberg atomic spectrum is eliminated, resulting in a higher quality spectral signal. The differential detection involves converting the optical signals from the two probes into voltages and then subtracting them to eliminate the DC background.

[0056] Step 50: Adjust the phase shift of the RF signal on the input side of the mixer, then generate an error signal through low-pass filtering, and adjust the seed source optical frequency until the slope of the error signal is greater than the reference.

[0057] It should be noted that, based on the error signal distribution, in the optimal state, the slope of the error signal should be as steep as possible to achieve high-sensitivity frequency locking. A reference value can be set based on the change in the slope of the error signal; when the slope of the error signal within the range of the observed conditions exceeds the set reference value, frequency locking is achieved.

[0058] The electrical signal output from the photodetector passes sequentially through a mixer and a low-pass filter. Simultaneously, a radio frequency (RF) signal of the same frequency is also phase-shifted and fed into the mixer. After mixing, the phase-shifted RF signal and the detector's spectral electrical signal produce a high-frequency component and a difference-frequency component. This difference-frequency component, obtained after passing through a low-pass filter, becomes the error signal. Finally, this error signal is input to the piezoelectric ceramic of the seed source via a PID circuit, achieving closed-loop control and frequency stabilization of the laser.

[0059] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when an element is “connected” or “coupled” to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein may include wireless connections or wireless coupling. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0061] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical, technical, and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0062] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A fiber-optic direct-connect atomic spectral frequency-locking device, characterized in that, This includes an atomic gas cell, an error signal acquisition device, a locking device, and a coupling light generation and modulation device connected by optical fiber; The coupled light generation and modulation device specifically includes: a 1018nm seed source, an electro-optic phase modulator, a 1018nm fiber amplifier, and a fiber frequency multiplier. The laser output from the 1018nm seed source is subjected to radio frequency modulation by the electro-optic phase modulator and then sequentially injected into the 1018nm fiber amplifier and the fiber frequency multiplier to output a coupled laser with a wavelength of 509nm containing a second-harmonic radio frequency modulation signal. The 1018nm seed source is a single-frequency narrow-linewidth laser source, the 1018nm fiber amplifier is a narrow-linewidth amplifier, and the fiber frequency multiplier is a single-frequency single-pass PPLN crystal frequency multiplier. The atomic gas cell is used to receive the coupled laser and the probe laser with a wavelength of 852 nm. In the atomic gas cell, the probe laser is divided into a reference light and a signal light. The signal light is transmitted in opposite directions through the atomic gas cell to generate a Rydberg atomic spectrum. The error signal acquisition device is used to detect the signal light and the reference light and generate an error signal; The locking device is used to generate a radio frequency modulation signal and lock the output frequency of the coupled light according to the error signal.

2. The optical fiber direct-connected atomic spectral frequency-locking device as described in claim 1, characterized in that, The atomic gas chamber uses fiber optic coupling for laser transmission via optical fiber in opposite directions; the probe light and coupling light are transmitted to the atomic gas chamber via fiber optic connectors connecting the input and output optical fibers, and the laser transmission fiber is a polarization-maintaining fiber.

3. The optical fiber direct-connected atomic spectral frequency-locking device as described in claim 1, characterized in that, An 852nm probe laser and a 509nm coupling laser enter the atomic gas chamber from opposite ends, respectively. The 852nm probe laser is split into two equal parts by a beam splitter. The first laser beam is transmitted and then totally reflected on the second surface. The other beam is directly reflected and transmitted parallel to the first laser beam into the atomic gas chamber. After being reflected by the two-color beam splitter, the 509nm laser enters the atomic gas chamber and is transmitted to the left end face in opposite directions, coinciding with the first 852nm laser beam. Two 852nm probe beams are emitted from the right end face and reflected by the two inclined surfaces of the prism. Finally, the probe lasers are converged by the focusing lens and the atomic spectral signals are collected by fiber optic coupling. Two 852nm probe beams are used. The first beam serves as a reference laser, providing the atomic absorption background, while the other beam, as a Rydberg EIT spectrum, generates a transmission peak on the atomic absorption background. The position of the transmission peak corresponds to the resonance point of the atomic energy level.

4. The optical fiber direct-connected atomic spectral frequency-locking device as described in claim 1, characterized in that, The error signal acquisition device includes a balanced photodetector, a mixer, and a low-pass filter; The reference light and signal light output from the atomic gas cell are respectively input into the balanced photodetector to output a spectral detection electrical signal. The error signal is obtained by mixing the spectral detection electrical signal with a low-pass filter. The mixing signals are the spectral detection electrical signal and the radio frequency drive signal of the electro-optic phase modulator.

5. The optical fiber direct-connected atomic spectral frequency-locking device as described in claim 4, characterized in that, The locking device includes a radio frequency source, a phase shifter, and a PID control circuit; The radio frequency signal involved in the mixing passes through a phase shifter, which is used to adjust the relative phase of the spectral detection electrical signal and the radio frequency signal to achieve demodulation of the error signal; The error signal is passed through a PID control circuit and finally connected to the laser frequency control port of the optical fiber seed source.

6. The optical fiber direct-connected atomic spectral frequency-locking device as described in claim 4, characterized in that, The bandwidth of the low-pass filter is lower than the frequency of the radio frequency signal to ensure that the high-frequency components of the mixing are blocked, while the difference frequency of the two signals passes through.

7. A fiber-optic direct-connect atomic spectral frequency locking method, using the apparatus described in any one of claims 1 to 6, characterized in that, Includes the following steps: The 509nm laser is generated and a modulation signal is applied. The generated 509nm laser carries a second-harmonic radio frequency modulation, which is reflected in the atomic spectrum after entering the atomic gas cell. Adjusting the frequency parameters of the radio frequency signal, and achieving radio frequency doubling through frequency doubling and synchronization using a seed laser via a frequency multiplier; Atomic spectral signals from Rydberg and Doppler background spectral signals of the ground state background were obtained using an optical fiber atomic gas cell. Adjusting the dual-probe differential device, DC background elimination is achieved by passing the spectral signals of the two probes through the differential detection circuit; Adjust the phase shift of the RF signal on the input side of the mixer, then pass it through a low-pass filter to generate an error signal. Adjust the seed source optical frequency until the slope of the error signal is greater than the set reference.

8. The optical fiber direct-connected atomic spectral frequency locking method as described in claim 7, characterized in that, Find the optimal RF frequency parameters for the frequency-locked loop and obtain the optimal frequency-locked spectral signal.

9. The optical fiber direct-connected atomic spectral frequency locking method as described in claim 7, characterized in that, The cutoff wavelength of the probe laser fiber connected to the atomic gas chamber is higher than the coupling laser wavelength.

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