Optical fiber direct connection atomic spectrum frequency locking method and device

Abstract

The invention discloses an optical fiber direct connection atomic spectrum frequency locking device. The device comprises an atomic gas chamber, an error signal acquisition device, a locking device and a coupling light generation and modulation device which are connected through an optical fiber. The coupled light generation and modulation device generates coupled laser which contains a radio frequency modulation signal and has a wavelength of 509 nm. The atomic gas chamber receives the coupling laser and the detection laser with the wavelength of 852 nm, in the atomic gas chamber, the detection laser is divided into reference light and signal light, and the signal light and the coupling light are oppositely transmitted through the atomic gas chamber to generate a Rydberg atomic spectrum. The error signal acquisition device detects the signal light and the reference light and generates an error signal. And the locking device generates a radio frequency modulation signal and locks the coupling light output frequency according to the error signal. The invention also comprises a method for using the device. According to the device and the method, the problems that an all-fiber laser light source frequency locking device for Rydberg atom preparation is complex and poor in effect are solved.

Description

Technical Field

[0001] The present application relates to the field of atomic spectroscopy, to a method for stabilizing the frequency of atomic spectroscopy lasers, and in particular to an application in coupling optical frequency locking of Rydberg atom preparation lasers. Background Art

[0002] Laser frequency locking of single-frequency lasers is an important link, and its frequency locking performance directly determines the frequency stability of single-frequency lasers, especially in application scenarios related to atomic spectroscopy, such as magnetic field meters, electric field meters, optical clocks, ion clocks, atomic quantum computers and other cutting-edge fields. Atomic spectrum frequency locking is a laser frequency locking method for absolute physical parameters, especially when high-sensitivity electric field measurements are performed on Rydberg atoms, the coupled light needs to be frequency locked. In the application of Rydberg electric field measurement, the existing coupled laser frequency locking method requires the laser to be frequency-shifted and locked to an optical reference cavity, or by modulating the frequency of the probe light, and then frequency-modulating and transferring it to the Rydberg resonance excitation spectrum to obtain an error signal. The former method cannot achieve frequency locking located at the atomic transition energy level, and requires additional frequency shifting to the resonant mode of the reference cavity. The latter method of modulating the probe light has a low modulation transfer rate, especially when the Rydberg principal quantum number energy level is high, the modulation effect is very poor. Summary of the invention

[0003] The present application proposes a method and device for frequency locking of atomic spectrum with direct optical fiber connection, which solves the problem that the frequency locking of all-fiber laser light source used for Rydberg atom preparation has a complex device and poor effect.

[0004] The embodiment of the present application provides an atomic spectrum frequency locking method with direct fiber connection, which utilizes electro-optical modulation of a fiber integrated waveguide to realize a radio frequency modulator of coupled light. After fiber amplification and a single-pass fiber frequency doubler, a doubled 509nm coupled light can be obtained. The laser and 852nm detection light jointly excite cesium atoms to obtain a modulated Rydberg excitation spectrum signal. The spectrum signal and the radio frequency signal are mixed to obtain an error signal of the laser frequency, which is then fed back to the piezoelectric ceramic port of the coupled light seed source through a PID feedback circuit to achieve high-speed laser frequency locking.

[0005] The embodiment of the present application also provides an atomic spectrum frequency locking device directly connected to an optical fiber, including an atomic gas chamber, an error signal acquisition device, a locking device, and a coupled light generation and modulation device connected via an optical fiber.

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

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

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

[0010] In one embodiment of the present application, in the coupled light generation and modulation device, the seed source of the coupled light is a 1018nm single-frequency laser, an electro-optical phase modulator is used to achieve radio frequency modulation, and then the modulated 509nm laser is injected into the fiber amplifier and the fiber doubler output in sequence.

[0011] In one embodiment of the present application, the atomic gas chamber uses fiber coupling for counter-transmission of optical fibers for laser conduction; the detection light and coupling light are transmitted to the atomic gas chamber using an optical fiber connector to connect the input and output optical fibers, and the laser conduction optical fiber is a polarization-maintaining optical fiber.

[0012] In one embodiment of the present application, the 852nm detection laser and the 509nm coupling laser enter the atomic gas chamber from both ends of the atomic gas chamber respectively; the 852nm detection laser is evenly divided into two parts of equal power by a beam splitter prism, the first beam of laser is transmitted and fully reflected on the second surface, and the other beam is directly reflected and transmitted parallel to the first beam of laser into the atomic gas chamber. The 509nm laser enters the atomic gas chamber after being reflected by a two-color beam splitter prism, and overlaps with the first beam of 852nm laser and is transmitted to the left end face in an opposite direction. After the two beams of 852nm detection light are emitted through the right end face, they are respectively reflected and output by the two inclined surfaces of the prism, and finally the detection laser is converged by a focusing lens, and the atomic spectrum signal is collected by optical fiber coupling.

[0013] Among them, the first of the two 852nm detection lights is used as a reference laser to provide the atomic absorption background, and the other is used as a Rydberg EIT spectrum to produce 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 the present application, the error signal acquisition device includes a balanced photodetector, a mixer and a low-pass filter. The reference light and the signal light output from the atomic gas chamber are respectively input into the balanced photodetector to output a spectrum detection electrical signal, and the error signal acquisition is to obtain the spectrum signal by mixing the spectrum signal with a low-pass filter, and the signals involved in the mixing are respectively the spectrum detection electrical signal and the radio frequency signal of the electro-optic phase modulator.

[0015] In one embodiment of the present application, the locking device comprises a radio frequency source, a phase shifter and a PID control circuit. The radio frequency signal involved in the mixing passes through the phase shifter, and the phase shifter is used to adjust the relative phase of the radio frequency signal of the detected spectrum signal to achieve the 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 optical fiber seed source.

[0016] In one embodiment of the present application, the bandwidth of the low-pass is lower than the frequency of the radio frequency signal to ensure that the high-frequency components of the mixing are blocked and the difference frequency parts of the two signals are passed.

[0017] The present application also proposes an atomic spectrum frequency locking method for direct optical fiber connection, using the device described in any embodiment of the present application, comprising the following steps:

[0018] 509nm laser generation and modulation signal loading, the generated 509nm laser carries double frequency RF modulation, which is reflected in the atomic spectrum after entering the atomic gas chamber;

[0019] Adjust the frequency parameters of the RF signal, and achieve RF frequency doubling by frequency doubling the seed laser through the frequency doubling device;

[0020] Use fiber optic atomic gas cell to obtain Rydberg atomic spectrum signal and Doppler background spectrum signal of ground state background;

[0021] Adjust the dual-probe differential device to achieve DC background elimination by passing the spectral signals of the two probes through the differential detection circuit;

[0022] Adjust the phase shift of the RF signal on the mixer input side, generate an error signal through low-pass filtering, and adjust the seed source light frequency until the error signal slope is greater than the set reference. The error signal is as steep as possible within the investigation range, thus achieving high-sensitivity frequency locking.

[0023] In one embodiment, an optimal radio frequency parameter is found for a frequency-locked loop to obtain an optimal frequency-locked spectrum signal.

[0024] Preferably, the cutoff wavelength of the detection laser transmission optical fiber connected to the atomic gas cell is higher than the coupling laser wavelength.

[0025] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0026] This scheme uses direct modulation of the seed source frequency of the coupled laser to produce double frequency modulation of the coupled light, solving the problem of 509nm laser modulation scheme without fiber. Since the coupled light is the decisive light source for preparing Rydberg atoms, the coupled light modulation information is transferred to the acquired Rydberg atomic spectrum. In addition, the all-fiber link is used. Compared with the block phase modulation method, there is no need to consider the factor of RF modulation impedance matching, and a low modulation voltage can achieve efficient spectral modulation results. The atomic spectrum of the fiber direct connection structure has the advantages of strong vibration resistance and no interference light influence, and can be flexibly connected with the matching light source and circuit for plug-and-play.

[0027] The present invention can use a low-voltage, low-power radio frequency source to complete radio frequency modulation of the light source frequency, and can also reduce electromagnetic interference to the frequency locking system, while solving the problem of no effective electro-optical modulation device in the 509nm band.

[0028] The frequency-locked optical path of direct fiber connection is no longer limited to the laboratory environment. The plug-and-play and optical connection loss-free features of the fiber link can be used to achieve remote scenes, and can also achieve frequency locking of light sources in industrial application scenarios such as vibration. This avoids problems such as reduced laser polarization purity and power fluctuations caused by the fiber light source passing through multiple free-space optical components when transmitting to the free-space optical path. This reduces the complexity of the device.

[0029] The optical fiber structure of the spectrum detection has the advantages of high integration and stable structure. Once produced, it can be applied in batches without the need for manual correction. At the same time, optical fiber transmission reduces the impact of invalid stray light on the spectrum quality, and the signal quality is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0031] Figure 1 This is the principle diagram of the 509nm coupled light laser frequency locking scheme;

[0032] Figure 2 This is a diagram of an atomic spectrum frequency locking device directly connected to an optical fiber;

[0033] Figure 3 It is the frequency-locking spectrum and error signal waveform diagram;

[0034] Figure 4 This is a flow chart of an embodiment of the atomic spectrum frequency locking method for direct optical fiber connection of the present application.

[0035] In the figure, 1. 1018nm seed source, 2. electro-optic phase modulator (EOM for short), 3. 1018nm amplifier, 4. frequency doubler, 5. coupled laser fiber, 6. 852nm detection laser, 7. detection light fiber, 8. glued beam splitter prism, 9. atomic gas chamber, 10. two-color beam splitter prism, 11. signal light output fiber, 12. reference light output fiber, 13 balanced photodetector, 14. RF signal source, 15. phase shifter, 16. mixer, 17. low-pass filter, 18. PID circuit. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0037] The present application discloses a method and device for locking the atomic spectrum with direct optical fiber connection, which includes a laser light source and optical fiber transmission, optical fiber atomic gas chamber spectrum acquisition, and spectrum error signal acquisition. The light source includes a frequency-resonant detection light source and a coupling light laser light source modulated by optical fiber electro-optical modulation. The optical paths are connected in sequence by an all-optical direct connection to achieve the acquisition of the optical fiber structure locked spectrum, and then the error signal is acquired by modulation and demodulation to complete the frequency closed-loop control of the coupled light seed, thereby achieving the frequency locking of the coupled light to the atomic transition line. This method of indirectly locking the coupled light laser frequency can be extended to the laser frequency locking of non-resonant atomic transition lines.

[0038] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0039] This embodiment provides an atomic spectrum frequency locking method with direct optical fiber connection. Figure 1 As shown, the Rydberg atomic spectrum is generated by reversely transmitting the 852nm laser and the 509nm laser into the optical fiber atomic gas chamber, collecting the transmission spectrum signal of the 852nm laser, and feeding it back to the 509nm light source through the PID circuit after mixing and low-pass processing, and performing closed-loop feedback on the frequency drift of the 509nm laser to achieve frequency stability control of the 509nm light source.

[0040] Figure 2Figure 1 is a diagram of an atomic spectrum frequency locking device directly connected to an optical fiber. The atomic spectrum frequency locking device directly connected to an optical fiber proposed in the embodiment of the present application uses atomic spectrum to achieve frequency transfer of two wavelengths, and achieves frequency locking of 509nm laser by detecting 852nm laser. The atomic spectrum frequency locking device directly connected to an optical fiber includes an atomic gas chamber connected by an optical fiber, an error signal acquisition device, a locking device, and a coupled light generation and modulation device.

[0041] The coupling light generating and modulating device is used to generate a coupling laser with a wavelength of 509nm containing a radio frequency modulated signal. Preferably, the coupling light is generated by an all-fiber seed laser, a fiber electro-optic phase modulator, a fiber amplifier and a fiber frequency doubler. The seed source is a 1018nm single-frequency laser, and an electro-optic phase modulator is used to achieve efficient seed light plus radio frequency modulation. The modulated seed laser is injected into the fiber amplifier and the fiber frequency doubler in sequence to output a modulated 509nm laser. When an RF signal is applied to the electro-optic phase modulator, the generated 509nm laser has double frequency modulation. The RF follows the light wave as a carrier to achieve frequency doubling. The typical frequency range of the RF signal is 500kHz to 6MHz, and the bandwidth of the photodetector is also at the same level.

[0042] The laser transmission optical path of the atomic spectrum frequency locking device directly connected to the optical fiber is all optical fiber transmission. The atomic gas chamber is used to receive the coupling laser and the detection laser with a wavelength of 852nm. In the atomic gas chamber, the detection laser is divided into reference light and signal light. The signal light is transmitted in opposite directions through the atomic gas chamber and the coupling light to generate the Rydberg atomic spectrum. The atomic gas chamber also uses optical fiber coupling with opposite optical fiber transmission for laser transmission. This structure improves the laser transmission efficiency, eliminates the pointing jitter of the laser, reduces the stray light entering the optical fiber detection system, improves the quality of the atomic spectrum signal, and facilitates the acquisition of high-quality frequency locking error signals.

[0043] The coupled light modulation uses a 1018nm laser modulator with a longer wavelength, which has high phase modulation efficiency for the fiber waveguide structure and can achieve a larger modulation depth with a low half-wave voltage. At the same time, the coupling efficiency of the long-wavelength fiber waveguide is relatively high.

[0044] The detection light and coupling light are transmitted to the atomic gas chamber by connecting the input and output optical fibers using optical fiber connectors, and the laser transmission fiber is a single-mode polarization-maintaining fiber (PM fiber).

[0045] A preferred structure is: the 852nm detection laser and the 509nm coupling laser enter the atomic gas chamber from both ends of the atomic gas chamber respectively. The 852nm detection laser is evenly divided into two parts of equal power by a glued beam splitter prism. One beam of laser is transmitted and fully reflected on the second surface, and the other beam is directly reflected and transmitted parallel to the first beam of laser into the atomic gas chamber. The 509nm laser enters the atomic gas chamber after being reflected by a two-color beam splitter prism, and overlaps with the first beam of 852nm laser and is transmitted to the left end face in an opposite direction. After the two beams of 852nm detection light are emitted from the right end face, they are respectively reflected and output by the two inclined surfaces of the prism. Finally, the detection laser is converged by a focusing lens, and the atomic spectrum signal is collected by optical fiber coupling.

[0046] The first of the two 852nm probe beams is used as a reference laser to provide the atomic absorption background, and the other is used as the Rydberg EIT spectrum to produce a transmission peak on 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 the resonance point. Usually, the lower probe laser is a frequency-stable laser, and the coupling light needs to be locked using the EIT spectrum.

[0047] It should be noted that the reverse-transmitted 509nm coupling laser is output from the left end face of the atomic gas chamber and irradiates the end face of the 852nm optical fiber. Due to the large difference in the two wavelengths, the optical path focusing parameters are also different, and the cutoff wavelength of the detection laser transmission fiber is higher than 509nm, which results in the 509nm laser being unable to enter 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 light source.

[0048] In one embodiment of the present 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 to generate an error signal. The two beams of detection light include a reference light and a signal light, which are respectively output to a balanced photodetector. Since the power is equal, the DC information of the light can be offset, the AC atomic spectrum signal can be acquired, the Rydberg atomic spectrum signal background ratio can be enhanced, and the fluctuation of the DC background voltage caused by the fiber docking, disturbance and front-end power fluctuation can be offset.

[0049] The electrical signal output by the balanced photodetector is a spectrum detection signal, and the error signal is obtained by mixing the spectrum detection signal and then low-pass filtering. The signals involved in the mixing are the spectrum detection electrical signal and the radio frequency signal that drives the electro-optic phase modulator.

[0050] The RF signal involved in the mixing needs to pass through a phase shifter to adjust the relative phase of the detected spectrum signal and the RF signal to achieve demodulation of the error signal. The bandwidth of the low-pass is required to be lower than the RF signal frequency to ensure that the high-frequency components of the mixing are blocked and the difference frequency of the two signals pass.

[0051] In one embodiment of the present application, the locking device comprises a radio frequency source, a phase shifter and a PID control circuit. The locking device is used to generate a radio frequency modulation signal and lock the coupled light output frequency according to 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.

[0052] It should be noted that the error signal reflects the stability of the laser frequency. The error signal is a zero-crossing ramp signal. The error signal is obtained after mixing and low-pass. The steepness of the slope of the ramp signal indicates how fast the laser frequency deviates. The range of change of the ramp signal is proportional to the deviation of the laser frequency from the atomic resonance transition line. The frequency dissonance at the atomic resonance transition point is zero, and the spectral signal received by the detector corresponds to a peak value, in which there is high-speed RF modulation. The peak position is the zero-crossing voltage of the error signal corresponding to the resonance transition point. The waveform diagram of the frequency-locked spectrum and the error signal is shown in the figure. Figure 3 shown.

[0053] It is also necessary to explain how the modulated RF signal works, how the RF signal enters the atomic gas chamber after frequency doubling, and how it affects the output signal of the atomic gas chamber L1. The RF modulated laser is added with an RF modulation signal at the optical center frequency. The modulated 509nm laser is used as coupling light, and passes through the atomic gas chamber together with the reverse colinearly transmitted detection laser to generate Rydberg atoms. Since the detection light and the coupling light have to add their energies and resonate at the energy difference from the ground state to the Rydberg excited state, there will be a Rydberg EIT resonance peak, that is, hf c +hf p =E l -E0, h is Planck's constant, f p is the frequency of the detected light, f c is the coupled optical frequency, E l 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 detection laser through the atom transmission, and by collecting the absorption spectrum signal of the detection light, the signal output by the atomic gas chamber L1 will carry the RF modulation signal and the frequency drift information of the coupled light.

[0054] The specific frequency relationship between the output terminals 11 and 12 of the atomic gas chamber, the output terminal of the balanced detector 13, the input and output terminals of the mixer 16, and the input and output terminals of the low-pass filter 17. The output terminal L1 of the atomic gas chamber is the detection light f carrying the RF modulated signal. p+2f m , where f p is the frequency of the detected light, f m is the modulation signal frequency. At the output end L2 of the atomic gas chamber, only the detection laser f p , there is no effect of RF transmission without coupling light, the two probes at the balanced detector L3 receive the detection light absorption spectrum carrying RF modulated signal and the detection light absorption spectrum without modulation signal respectively, and the left side of the two ports at the input of the mixer 16 is the RF signal carrying 2f m frequency. The right side is the input EIT spectrum, where Δf+2f m The frequency information, where Δf is the frequency drift of the coupled light. After mixing the two, there is Δf+4f m After low-pass filtering, the Δf frequency component is obtained. Figure 4 This is a flow chart of an embodiment of the atomic spectrum frequency locking method for direct optical fiber connection of the present application.

[0055] Step 10: 509 nm laser generation and modulation signal loading.

[0056] The generated 509nm laser carries double frequency RF modulation, which is reflected in the atomic spectrum after entering the atomic gas chamber.

[0057] To further illustrate the embodiment of the present application, the 509nm laser generation is achieved by a 1018nm fiber seed source, a 1018nm fiber amplifier, and a fiber frequency doubler. Figure 2 As shown, an electro-optic phase modulator is inserted between the 1018nm seed source and the 1018nm amplifier. The electro-optic phase modulator is a modulator of the optical fiber waveguide, which can achieve a low half-wave voltage and realize phase modulation using low-power radio frequency. By applying radio frequency modulation, the frequency of the seed source is modulated. The greater the amplitude of the modulation signal, the greater the modulation depth of the laser frequency. After passing through the laser frequency doubler, the generated 509nm laser carries double frequency modulation. Since the 509nm laser does not carry modulation information when the amplitude of the radio frequency signal applied by the electro-optic modulator is zero, the smaller the modulation amplitude, the smaller the interference to the light source, which is convenient for other application scenarios of subsequent coupling light sources.

[0058] Preferably, the 1018nm seed source is a single-frequency narrow-linewidth laser source, the 1018nm amplifier is a narrow-linewidth amplifier, the fiber frequency doubler is a single-frequency single-pass PPLN crystal frequency doubler, and the matching temperature is controlled to achieve the best matching temperature to achieve high frequency doubling efficiency. Since the frequency variation range of the light source generated by phase modulation is very small relative to the laser wavelength, the effect on the frequency doubling efficiency is extremely small, and the influence of the modulator can be ignored.

[0059] Step 20, adjust the frequency parameters of the radio frequency signal, and achieve radio frequency doubling by frequency doubling the seed laser through a frequency multiplier.

[0060] Synchronously adjust the laser frequency doubling and the RF modulation frequency doubling of the seed source. Preferably, the laser frequency doubling is synchronized with the RF modulation frequency doubling of the seed source. After the seed source passes through the electro-optic modulator, a modulation sideband is generated on the optical frequency. The modulation sideband corresponds to the RF frequency at the distance from the laser center frequency. After changing the wavelength of the seed source, the temperature of the frequency doubler needs to be changed accordingly. The frequency doubling using a single-pass structure does not require a resonant optical cavity locking link. The output of the 509nm laser can be achieved only by tuning the temperature, which is convenient for the subsequent 509nm laser frequency locking and avoids the problem of double locking of the seed source and the frequency doubler. Find the optimal RF frequency parameters for the frequency locking loop and obtain the optimal frequency locking spectrum signal.

[0061] Step 30: Use the optical fiber atomic gas cell to obtain the Rydberg atomic spectrum signal and the Doppler background spectrum signal of the ground state background.

[0062] The optical fiber atomic gas chamber is an atomic gas chamber with a four-port optical fiber input and output structure. A spectrum scheme of closely packed optical elements is designed, and optical glue with high light transmittance and high thermal stability is used to install and bond the optical elements.

[0063] The fiber atomic gas chamber comprises two input ports and two output ports, wherein the two input ports are 852nm single-mode polarization-maintaining fiber input and 509nm single-mode polarization-maintaining fiber input respectively. Both fiber output ports are 852nm laser fiber outputs, wherein L1 is the Rydberg atomic spectrum signal, which is output through the signal light output fiber, and L2 is the Doppler background signal of the ground state spectrum, which is output through the reference light output fiber.

[0064] Step 40: Adjust the dual-probe differential device to eliminate the DC background by passing the spectral signals of the two probes through the differential detection circuit.

[0065] The signal light output fiber and the reference light output fiber of the fiber atomic gas chamber are connected to two photoelectric sensors of a balanced photodetector, which is a photodetector with a fiber flange interface. After the connection, the photodetector only receives the laser output by the fiber, and no stray background light enters the detector. In addition, the dual-probe differential detection method eliminates the DC background signal of the Rydberg atomic spectrum, so there will be a better quality spectral signal. The differential detection is to convert the optical signals of the two probes into voltages and then perform subtraction to eliminate the DC background.

[0066] Step 50: Adjust the phase shift of the RF signal at the mixer input side, 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.

[0067] It should be noted that, according to the distribution of the error signal, in the optimal state, the slope of the error signal is as steep as possible, thereby achieving high-sensitivity frequency locking. According to the change in the slope of the error signal, a reference value can be set. When the slope value of the error signal within the range of the inspection conditions is greater than the set reference, the frequency locking is satisfied.

[0068] The electrical signal output by the photodetector passes through the mixer and low-pass filter in turn, and the RF signal of the same frequency is also connected to the mixer after phase shifting. After mixing, the phase-shifted RF signal and the spectral electrical signal of the detector have a high-frequency part and a difference frequency part. After passing through the low-pass filter, the difference frequency part is obtained, and the error signal can be obtained. Finally, it is input into the piezoelectric ceramic of the seed source through the PID circuit to achieve the frequency stability of the closed-loop control laser.

[0069] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, the elements defined by the sentence "comprises..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0070] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the 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. In addition, the "connection" or "coupling" used herein may include wireless connection or wireless coupling. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0071] Those skilled in the art will understand that unless otherwise defined, all terms (including technical, technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0072] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. An atomic spectrum frequency locking device directly connected to an optical fiber, characterized in that: It includes an atomic gas chamber, an error signal acquisition device, a locking device, and a coupled light generation and modulation device connected by optical fibers; The coupling light generating and modulating device is used to generate a coupling laser with a wavelength of 509 nm containing a radio frequency modulation signal; The atomic gas chamber is used to receive the coupling laser and the detection laser with a wavelength of 852nm. In the atomic gas chamber, the detection laser is divided into reference light and signal light. The signal light is transmitted in opposite directions with the coupling light through the atomic gas chamber to generate a Rydberg atomic spectrum. The error signal acquisition device is used to detect the signal light and the reference light to generate an error signal; The locking device is used to generate a radio frequency modulation signal and lock the coupled light output frequency according to the error signal.

2. The optical fiber directly connected atomic spectrum frequency locking device according to claim 1, wherein the coupled light generating and modulating device is characterized in that: The seed source of the coupling light is a 1018nm single-frequency laser, which is modulated by an electro-optical phase modulator and then injected into a fiber amplifier and a fiber frequency doubler to output modulated 509nm laser.

3. The optical fiber directly connected atomic spectrum frequency locking device according to claim 1, characterized in that: The atomic gas chamber uses optical fiber coupling for optical fiber counter-transmission to conduct laser transmission; the detection light and the coupling light are transmitted to the atomic gas chamber using an optical fiber connector to connect the input and output optical fibers, and the laser transmission optical fiber is a polarization-maintaining optical fiber.

4. The optical fiber directly connected atomic spectrum frequency locking device according to claim 1, characterized in that: The 852nm detection laser and the 509nm coupling laser enter the atomic gas cell from both ends of the atomic gas cell respectively; The 852nm detection laser is evenly divided into two parts of equal power by a beam splitter prism. The first laser beam is totally reflected on the second surface after transmission, and the other beam is directly reflected and transmitted parallel to the first laser beam into the atomic gas chamber. The 509nm laser is reflected by the two-color beam splitter prism and enters the atomic gas chamber, where it overlaps with the first 852nm laser beam and is transmitted to the left end face in opposite directions. After two beams of 852nm detection light are emitted from the right end face, they are reflected and output by the two inclined surfaces of the prism respectively, and finally converge the detection laser through the focusing lens, and the atomic spectrum signal is collected by optical fiber coupling; The first of the two 852nm detection lights is used as a reference laser to provide the atomic absorption background, and the other is used as a Rydberg EIT spectrum to produce a transmission peak on the atomic absorption background. The position of the transmission peak corresponds to the resonance point of the atomic energy level.

5. The optical fiber directly connected atomic spectrum frequency locking device according to 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 chamber are respectively input into a balanced photodetector to output a spectral detection electrical signal. The error signal is obtained by mixing the spectral signal with a low pass, and the participating signals in the mixing are the spectral detection electrical signal and the radio frequency drive signal of the electro-optical phase modulator.

6. The optical fiber directly connected atomic spectrum frequency locking device according to claim 1, characterized in that: The locking device comprises 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, and the phase shifter is used to adjust the relative phase of the radio frequency signal of the detected spectrum signal to achieve demodulation of the error signal; The error signal passes through a PID control circuit and is finally connected to a laser frequency control port of an optical fiber seed source.

7. The optical fiber directly connected atomic spectrum frequency locking device according to claim 1, characterized in that: The bandwidth of the low-pass is lower than the frequency of the radio frequency signal to ensure that the high-frequency components of the mixing are blocked and the difference frequency parts of the two signals pass through.

8. A method for frequency locking an atomic spectrum by direct optical fiber connection, using the device according to any one of claims 1 to 7, characterized in that: The following steps are involved: 509nm laser generation and modulation signal loading, the generated 509nm laser carries double frequency RF modulation, which is reflected in the atomic spectrum after entering the atomic gas chamber; Adjust the frequency parameters of the RF signal, and achieve RF frequency doubling by frequency doubling the seed laser through the frequency doubling device; Use fiber optic atomic gas cell to obtain Rydberg atomic spectrum signal and Doppler background spectrum signal of ground state background; Adjust the dual-probe differential device to achieve DC background elimination by passing the spectral signals of the two probes through the differential detection circuit; Adjust the phase shift of the RF signal on the mixer input side, generate an error signal through low-pass filtering, and adjust the seed source light frequency until the error signal slope is greater than the set reference.

9. The method for frequency locking an atomic spectrum by direct optical fiber connection according to claim 8, characterized in that: Find the best RF frequency parameters for the frequency-locked loop and obtain the optimal frequency-locked spectrum signal.

10. The method for frequency locking an atomic spectrum by direct optical fiber connection according to claim 8, characterized in that: The cutoff wavelength of the detection laser transmission fiber connected to the atomic gas cell is higher than the coupling laser wavelength.

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