Device and method for realizing optically pumped rubidium atomic beam clock

Abstract

The present application belongs to the field of atomic clock technology, and relates to a device and method for realizing an optically pumped rubidium atomic beam clock, wherein the device comprises: a waveguide chip integrated semiconductor laser for outputting fundamental frequency laser; a frequency converter for receiving fundamental frequency laser and converting it into frequency-doubled pumping light; a rubidium atomic beam clock physical module for generating a rubidium atomic beam perpendicular to the direction of the frequency-doubled pumping light; a second photodetector for outputting an absorption spectrum signal of microwave and atomic resonance; a microwave resonance signal demodulation module for receiving the absorption spectrum signal and demodulating it to generate a tuning signal; a microwave frequency synthesizer for receiving the tuning signal, outputting a microwave signal that generates resonance in the rubidium atomic beam clock physical module, locking the frequency to the transition frequency of the ground state sub-energy level of the rubidium atom, and outputting a standard frequency signal. The present application can significantly improve the performance of laser-pumped rubidium atomic beam clocks.

Description

Technical Field

[0001] The present application relates to the technical field of atomic clocks, and in particular to a device and method for realizing an optically pumped rubidium atomic beam clock. Background Art

[0002] As the most accurate time frequency generating device at present, the atomic clock has made the human time measurement standard enter the atomic time era from the astronomical time era. As an important resource, atomic clocks are widely used in military and civilian fields such as satellite navigation positioning, timekeeping, communication, and electricity. Among them, the rubidium atomic clock, as the most widely used atomic clock at present, has the advantages of small size, low power consumption, high reliability, and low price. Traditional, highly mature and practical rubidium atomic clocks all use rubidium 87 spectrum lamps as pumping light sources, and use rubidium 85 atomic gas chambers for filtering. However, the spectrum density of the spectrum lamp is low, the pumping efficiency is greatly limited, and the atomic utilization rate is only a few thousandths, which limits the further improvement of the stability of the rubidium atomic clock; in addition, the traditional spectrum lamp pumped rubidium atomic clock has to use a dual atomic gas chamber, and the size and power consumption are relatively large, making it difficult to miniaturize and integrate.

[0003] The maturity of laser technology has made laser a new type of pumping light source for rubidium atomic clocks, and laser-pumped rubidium atomic clocks have been developed. The main difference between laser-pumped rubidium atomic clocks and spectrum-lamp-pumped rubidium atomic clocks is that semiconductor lasers are used instead of spectrum lamps as pumping light sources. Since semiconductor lasers have the characteristics of high brightness, good monochromaticity and narrow line width, higher pumping efficiency, higher atomic utilization and lower transmission background can be obtained, so stronger microwave resonance signals and lower optical noise can be obtained, which greatly improves the signal-to-noise ratio and has higher frequency stability.

[0004] At present, commonly used semiconductor lasers include vertical cavity surface emitting (VCSEL) lasers, distributed feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers and external cavity semiconductor (ECDL) lasers, etc.

[0005] However, although the vertical cavity surface emitting (VCSEL) laser has the advantages of integration, small size and low price, its light intensity is unstable, the frequency noise is high and the line width is large, reaching the order of hundreds of MHz, due to its small intrinsic cavity length and multiple modes. As the pumping light source of the rubidium atomic clock, its stability performance has not been improved. For distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers, the intensity noise and frequency noise are greatly improved compared with the vertical cavity surface emitting (VCSEL) laser, but the line width has also reached the order of MHz. For the external cavity semiconductor (ECDL) laser, compared with the other three types of lasers, it has the best noise performance, and the line width is usually at the level of hundreds of kHz. However, this laser is composed of a semiconductor laser tube with a longer cavity length and higher precision. Therefore, precise alignment and mode matching are required, the system structure is more complex, discrete components are not easy to integrate, and the stability and continuous operation reliability are low. These shortcomings limit the widespread application of external cavity semiconductor lasers in laser pumped rubidium atomic clocks. Summary of the invention

[0006] Based on this, it is necessary to provide a device and method for realizing a light-pumped rubidium atomic beam clock in response to the above-mentioned technical problems, which can significantly improve the performance of the laser-pumped rubidium atomic beam clock.

[0007] A device for realizing an optically pumped rubidium atomic beam clock, comprising:

[0008] The waveguide chip integrates a semiconductor laser for outputting fundamental frequency laser;

[0009] A frequency converter, used for receiving the fundamental frequency laser and converting it into frequency-doubled pumping light;

[0010] A rubidium atomic beam clock physics module is used to generate a rubidium atomic beam perpendicular to the direction of the frequency-doubled pumping light, absorb the frequency-doubled pumping light, and prepare rubidium atomic states;

[0011] The second photoelectric detector is used to detect the intensity change of the frequency-doubled pump light passing through the rubidium atomic beam clock physics module that has completed the preparation of the rubidium atomic state, and output the absorption spectrum signal of the microwave and atomic resonance;

[0012] A microwave resonance signal demodulation module, used for receiving the absorption spectrum signal and demodulating it to generate a tuning signal;

[0013] The microwave frequency synthesizer is used to receive the tuning signal, output a microwave signal that generates resonance in the rubidium atomic beam clock physical module, lock the microwave frequency to the transition frequency of the ground state sub-energy level of the rubidium atom, and output a standard frequency signal.

[0014] In one embodiment, the rubidium atomic beam clock physics module includes:

[0015] A rubidium atomic beam collimating gun is used to generate a sequential rubidium atomic beam perpendicular to the direction of the frequency-doubled pumping light and interact with the frequency-doubled pumping light;

[0016] A microwave feeding antenna, used for receiving the microwave signal generated by the microwave frequency synthesizer and feeding it into the microwave resonant cavity;

[0017] A microwave resonant cavity is used to resonate the microwave signal input by the microwave feeding antenna and resonate and interact with the rubidium atomic beam generated by the rubidium atomic beam collimating gun, so that the rubidium atomic beam absorbs the doubled frequency pumping light, changes the intensity of the doubled frequency pumping light, and realizes the preparation of rubidium atomic state;

[0018] A rubidium atom recovery box is used to absorb the remaining rubidium atoms of the rubidium atom beam after the resonance interaction occurs;

[0019] The magnetic field coil is used to generate a uniform external magnetic field parallel to the direction of the frequency-doubled pumping light, and the magnetic field provides a quantization axis direction for the rubidium atomic beam.

[0020] In one embodiment, the rubidium atomic beam clock physics module further includes: a magnetic shielding cylinder;

[0021] The magnetic shielding tube is arranged outside the rubidium atomic beam collimating gun, the microwave feeding antenna, the microwave resonant cavity, the rubidium atom recovery box and the magnetic field coil, and is used to shield the earth's magnetic field and stray magnetic field, and reduce the unstable influence of the residual magnetic field on the atomic hyperfine energy level structure.

[0022] In one embodiment, the frequency converter comprises:

[0023] An optical power amplifier, used for receiving the fundamental frequency laser and performing power amplification to obtain a high-power fundamental frequency laser;

[0024] An optical frequency doubler, used for receiving the high-power fundamental frequency laser and performing frequency doubling processing to obtain a mixed light including fundamental frequency light and frequency doubling light;

[0025] A bandpass filter, used for receiving the mixed light and filtering out the fundamental frequency light to obtain spectrally pure double frequency light;

[0026] A spectrometer, used for receiving the frequency-doubled light and dividing it into transmitted light and reflected light;

[0027] A rubidium atomic spectrum frequency stabilization module, used for receiving the reflected light and generating a first driving signal;

[0028] A laser drive control module, configured to receive the first drive signal and perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the frequency-doubled light at a transition frequency between the ground state energy level of the rubidium atom and the first excited state energy level;

[0029] The beam reducer is used to receive the transmitted light and reduce the beam diameter to obtain frequency-doubled pumping light.

[0030] In one embodiment, the beam diameter of the doubled frequency pumping light is smaller than the diameter of the rubidium atomic beam generated by the rubidium atomic beam clock physics module, so that the doubled frequency pumping light within the beam diameter area interacts with the rubidium atomic beam, thereby reducing the background light intensity of the second photodetector.

[0031] In one embodiment, the frequency converter further comprises:

[0032] an acousto-optic modulator, used for converting the frequency-doubled light into zero-order light and frequency-shifted light, and outputting the zero-order light to the spectrometer;

[0033] A first photodetector, configured to receive the frequency-shifted light and convert the frequency-shifted light signal into an electrical signal;

[0034] The optical power stabilization module is used to receive the electrical signal and control and stabilize the driving power of the acousto-optic modulator.

[0035] In one embodiment, a waveguide chip integrated semiconductor laser comprises: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity;

[0036] The semiconductor gain chip and the silicon-based photonic waveguide chip external cavity are efficiently coupled through an optical field mode converter to achieve chip integration.

[0037] A method for realizing an optically pumped rubidium atomic beam clock, using the aforementioned device for realizing an optically pumped rubidium atomic beam clock, comprising:

[0038] Obtaining incident fundamental frequency laser light, and converting the fundamental frequency laser light into frequency-doubled pumping light;

[0039] Prepare rubidium atomic state according to the frequency-doubled pumping light;

[0040] According to the intensity change of the doubled frequency pump light of the rubidium atomic beam clock physical module that has completed the preparation of the rubidium atomic state, the absorption spectrum signal of the microwave and atomic resonance is output, and the absorption spectrum is demodulated to generate a tuning signal;

[0041] According to the tuning signal, the microwave frequency is locked to the transition frequency of the ground state sub-energy level of the rubidium atom, closed-loop locking is achieved and a standard frequency signal is output.

[0042] In one embodiment, converting the fundamental frequency laser into frequency-doubled pumping light comprises:

[0043] According to the fundamental frequency laser, power amplification, frequency doubling processing and light filtering processing are performed in sequence to obtain frequency doubling light;

[0044] Obtaining transmitted light and reflected light according to the frequency-doubled light;

[0045] Generate a first driving signal according to the reflected light, and perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the frequency-doubled light at the transition frequency between the ground state energy level and the first excited state energy level;

[0046] The beam diameter is reduced according to the transmitted light to obtain frequency-doubled pumping light.

[0047] In one embodiment, the waveguide chip integrated semiconductor laser comprises: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity;

[0048] The wavelength tuning of the waveguide chip integrated semiconductor laser includes: adjusting the pump current of the semiconductor gain chip, and / or controlling the temperature of the external cavity of the silicon-based photonic waveguide chip by using the thermo-optic effect.

[0049] The above-mentioned device and method for realizing the optically pumped rubidium atomic beam clock designs a rubidium atomic beam clock based on a waveguide chip integrated semiconductor laser, which has the following beneficial effects:

[0050] 1. The use of waveguide chip integrated semiconductor lasers with extremely narrow line width and extremely low frequency noise can greatly improve the pumping efficiency and atomic utilization rate, and enhance the short-term frequency stability of the optically pumped rubidium atomic beam clock;

[0051] 2. The use of waveguide chip integrated semiconductor lasers can be integrated and chip-based, with high reliability and low power consumption characteristics, which can greatly reduce the volume and power consumption of optically pumped rubidium atomic beam clocks;

[0052] 3. Compared with the traditional optically pumped rubidium atomic clock which uses an atomic gas chamber (i.e., the working substance rubidium atomic vapor is filled in a transparent glass bulb, and the rubidium atomic gases collide with each other due to violent thermal motion), the present application uses a rubidium atomic beam, which greatly reduces the collision frequency shift caused by thermal motion between rubidium atoms, improves the frequency accuracy and frequency stability, and achieves long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a structural diagram of a device for implementing an optically pumped rubidium atomic beam clock in one embodiment;

[0054] Figure 2 is a structural diagram of a device for realizing an optically pumped rubidium atomic beam clock in another embodiment;

[0055] Figure 3 It is a structural diagram of a device for realizing an optically pumped rubidium atomic beam clock in yet another embodiment;

[0056] Figure 4It is a structural diagram of a device for realizing an optically pumped rubidium atomic beam clock in a specific embodiment;

[0057] Figure 5 A schematic flow chart of a method for realizing an optically pumped rubidium atomic beam clock in one embodiment;

[0058] Figure 6 The figure is a flow chart of a method for converting fundamental frequency laser into frequency-doubled pumping light in another embodiment. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0060] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0061] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "multiple groups" means at least two groups, such as two groups, three groups, etc., unless otherwise clearly and specifically defined.

[0062] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0063] In addition, the technical solutions between the various embodiments of the present application can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0064] The present application provides a device for realizing an optically pumped rubidium atomic beam clock, such as Figure 1 As shown, in one embodiment, it includes: a waveguide chip integrated semiconductor laser, a frequency converter, a rubidium atomic beam clock physics module, a second photodetector, a microwave resonance signal demodulation module and a microwave frequency synthesizer. Among them:

[0065] The waveguide chip integrated semiconductor laser is used to output a fundamental frequency laser with a wavelength of 1560nm or 1590nm (the wavelength λ corresponds to the frequency ν one-to-one, satisfying the relationship c=λν, which is not strictly distinguished in this application). The waveguide chip integrated semiconductor laser includes: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity; the semiconductor gain chip and the silicon-based photonic waveguide chip external cavity are efficiently coupled through an optical field mode converter to achieve chip integration; the silicon-based photonic waveguide chip external cavity can be a high-Q microring resonator. As a key part of wavelength selection, the microring resonator can be but is not limited to a single ring, a double ring, a multi-ring, and a composite ring combined with a Mach Zehnder interferometer.

[0066] The frequency converter is used to receive the fundamental frequency laser and convert it into the doubled frequency pump light.

[0067] The rubidium atomic beam clock physics module is used to generate a rubidium atomic beam perpendicular to the direction of the frequency-doubled pump light, absorb the frequency-doubled pump light, and prepare the rubidium atomic state.

[0068] The second photodetector is used to receive the pumping laser that completes the preparation of the rubidium atomic state in the rubidium atomic beam clock physics module based on the absorption detection principle, detect the intensity change of the doubled frequency pumping light in the rubidium atomic beam clock physics module, and output the absorption spectrum signal of microwave and atomic resonance.

[0069] The microwave resonance signal demodulation module is used to receive the absorption spectrum signal, demodulate and generate a discrimination curve, and generate a tuning signal to tune the built-in voltage-controlled crystal oscillator of the microwave frequency synthesizer to achieve closed-loop locking.

[0070] The microwave frequency synthesizer is used to receive the tuning signal and output the microwave signal that generates resonance in the rubidium atomic beam clock physical module, locking the microwave frequency of the built-in voltage-controlled crystal oscillator to the transition frequency of the rubidium atomic ground state sub-energy level (i.e., locking the microwave frequency to the rubidium atomic ground state sub-energy level 5 2 S 1 / 2 The two fine sublevels of |F=2,m F =0> and |F=1,mF =0>'s transition frequency is 6.834682614GHz), which acts on the rubidium atomic beam clock physics module and outputs a standard frequency signal (10MHz) after closed-loop locking.

[0071] In this embodiment, the rubidium atomic beam clock physics module, the second photodetector, the microwave resonance demodulation module and the microwave frequency synthesizer constitute a rubidium atomic ground state sub-level microwave resonance locked loop to lock the frequency of the voltage-controlled crystal oscillator at the rubidium atomic ground state energy level 5 2 S 1 / 2 The two fine sublevels of |F=2,m F =0> and |F=1,m F =0>'s transition frequency is 6.834682614GHz.

[0072] In one embodiment, the rubidium atomic beam clock physics module includes: a rubidium atomic beam collimating gun, a microwave feeding antenna, a microwave resonant cavity, a rubidium atom recovery box, a magnetic field coil, and a magnetic shielding cylinder. Among them:

[0073] The rubidium atomic beam collimating gun is used to generate a sequential rubidium atomic beam that is perpendicular to the direction of the frequency-doubled pump light and interacts with the frequency-doubled pump light. The rubidium atomic beams are sequentially emitted in the same direction, which greatly reduces the probability of mutual collision and greatly reduces the collision frequency shift.

[0074] The microwave feeding antenna is used to receive the 6.834 GHz microwave signal generated by the microwave frequency synthesizer and feed it into the microwave resonant cavity.

[0075] The microwave resonant cavity is used to resonate the microwave signal input by the microwave feeding antenna and resonate with the rubidium atomic beam generated by the rubidium atomic beam collimating gun, so that the rubidium atomic beam absorbs the doubled frequency pumping light, changes the intensity of the doubled frequency pumping light, and realizes the preparation of rubidium atomic state.

[0076] The rubidium atom recovery box is arranged in parallel with the rubidium atom beam collimating gun, and its opening width is larger than the diameter of the rubidium atom beam. It is used to absorb the remaining rubidium atoms of the rubidium atom beam after the resonance interaction occurs to prevent the remaining rubidium atoms from diffusing everywhere.

[0077] The rubidium atom beam collimating gun and the rubidium atom recovery box constitute a rubidium atom beam generating device, which prepares a rubidium atom beam perpendicular to the direction of the frequency-doubled pumping light.

[0078] The magnetic field coil (for example, C field coil) is used to generate a high-precision uniform external magnetic field parallel to the direction of the frequency-doubled pump light. The external magnetic field provides the quantization axis direction for the rubidium atomic beam, which is the direction necessary for the interaction between atoms and light.

[0079] The magnetic shielding tube is installed on the outside of the rubidium atomic beam collimation gun, microwave feeding antenna, microwave resonant cavity, rubidium atom recovery box and magnetic field coil. It is used to shield the earth's magnetic field and stray magnetic field, and reduce the unstable influence of the residual magnetic field on the atomic hyperfine energy level structure.

[0080] like Figure 2 As shown, in one embodiment, the frequency converter includes: an optical power amplifier, an optical frequency multiplier, a bandpass filter, a spectrometer, a rubidium atomic spectrum frequency stabilization module, a laser drive control module, and a beam reducer. Among them:

[0081] The optical power amplifier is used to receive the fundamental frequency laser and amplify the power according to a certain power gain to obtain a high-power fundamental frequency laser. The optical power amplifier can be, but is not limited to, a semiconductor tapered amplifier (TA), an erbium-doped fiber amplifier (EDFA), and the like.

[0082] The optical frequency doubler is used to receive high-power fundamental frequency laser and perform frequency doubling to obtain mixed light containing fundamental frequency light and frequency doubling light. Since frequency doubling has conversion efficiency limitations, it is difficult to convert all high-power lasers into doubled frequency lasers. Therefore, the mixed light includes fundamental frequency light and frequency doubling light.

[0083] The bandpass filter is used to receive the mixed light and filter out the fundamental frequency light to obtain the double frequency light with pure spectrum.

[0084] The optical frequency doubler and the bandpass filter are combined to filter out the fundamental frequency light of the waveguide chip integrated semiconductor laser and obtain the doubled frequency light with pure spectrum. That is to say, the waveguide chip integrated semiconductor laser outputs the laser signal with wavelength of 1560nm or 1590nm, and the optical frequency doubler and the bandpass filter are combined to output the doubled frequency light of the waveguide chip integrated semiconductor laser, that is, the laser signal with wavelength of 780nm or 795nm. Among them, the laser signal with wavelength of 780nm corresponds to 87 The ground state energy level of Rb atom 5 2 S 1 / 2 With the first excited state energy level 5 2 P 3 / 2 The energy level transition wavelength of the laser signal with a wavelength of 795nm corresponds to 87 The ground state energy level of Rb atom 5 2 S 1 / 2 With the first excited state energy level 5 2 P 1 / 2 The wavelength of energy level transition.

[0085] The beam splitter is used to receive the frequency-doubled light and divide it into transmitted light and reflected light.

[0086] The rubidium atomic spectrum frequency stabilization module is used to receive the reflected light, process the reflected light spectrum, and generate a first frequency-stabilized driving signal to control the laser drive control module. The rubidium atomic spectrum frequency stabilization module can be implemented based on, but not limited to, the saturated absorption spectrum frequency stabilization principle or the modulation transfer spectrum frequency stabilization principle.

[0087] The laser drive control module is used to receive the first drive signal and output a control signal to perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the doubled frequency light at the transition frequency between the ground state energy level of the rubidium atom and the first excited state energy level.

[0088] The beam reducer is used to receive the transmitted light and reduce the beam diameter of the transmitted light according to a certain ratio to obtain a reduced beam of light, that is, a frequency-doubled pump light, so that it enters the rubidium atomic beam clock physics module with a smaller beam diameter. The beam diameter of the frequency-doubled pump light is smaller than the diameter of the rubidium atom (Rb atom) beam, so that the frequency-doubled pump light in the beam diameter area interacts with the rubidium atom beam, so that the light intensity detected by the second photodetector is all the light after the interaction with the rubidium atom beam, reducing the background light intensity of the second photodetector. The beam reducer can be, but is not limited to, an anti-Kepler beam expander or an anti-Galilean beam expander.

[0089] In this embodiment, the spectrometer, the rubidium atomic spectrum frequency stabilization module, the laser drive control module, the waveguide chip integrated semiconductor laser, the optical power amplifier, the optical frequency doubler, and the bandpass filter constitute the spectrum frequency stabilization locking loop of the rubidium atomic beam clock pumped laser, which accurately locks the frequency of the doubled laser at 87 The ground state sublevel of Rb atom 5 2 S 1 / 2 , |F=2> and the fine structure level of the first excited state 5 2 P 3 / 2 The energy level transition wavelength is 780nm, or the doubled laser frequency is precisely locked at 87 The ground state sublevel of Rb atom 5 2 S 1 / 2 , |F=2> and the first excited state energy level 5 2 P 1 / 2The energy level transition wavelength is 795nm, that is, the frequency of the frequency-doubled light is locked on the ground state sub-energy level (that is, locked on the atomic spectrum transition spectrum line), and after reaching the locked state, the state output will be maintained to serve as the pumping laser of the rubidium atomic beam clock. Due to the limitation of the material of the waveguide chip integrated semiconductor laser itself, it is generally used in optical modules or optical communications, and the present application designs an optical power amplifier, an optical frequency doubler, and a bandpass filter. The optical power amplifier amplifies the power of the fundamental frequency laser to meet the threshold conditions for generating nonlinear frequency doubling effects. The optical frequency doubler is a carrier for generating nonlinear frequency doubling effects. When the phase matching conditions are met, the fundamental frequency light is partially converted into frequency-doubled light, and the bandpass filter filters out the fundamental frequency light, and outputs spectrally pure frequency-doubled light. The combination of the three can expand the output spectrum range (that is, a fixed band) of the waveguide chip integrated semiconductor laser, and then use the waveguide chip integrated semiconductor laser to generate pumping light that meets the frequency requirements for application in the rubidium atomic beam clock physics module.

[0090] like Figure 3 As shown, in one embodiment, the converter further includes: an acousto-optic modulator, a first photodetector, and an optical power stabilization module.

[0091] The acousto-optic modulator is used to convert the frequency-doubled light into zero-order light (light without frequency shift) and frequency-shifted light (frequency-shifted light, including +1 or -1 order light, etc. At this time, the acousto-optic modulator changes the frequency of the frequency-doubled light, which is equivalent to a frequency shifter), and outputs the zero-order light to the spectrometer, which divides the zero-order light into transmitted light and reflected light.

[0092] The first photoelectric detector is used to receive the frequency-shifted light and perform photoelectric conversion using the photoelectric effect to convert the frequency-shifted light signal into an electrical signal.

[0093] The optical power stabilization module is used to receive an electrical signal and generate a control signal to control and stabilize the driving power of the acousto-optic modulator.

[0094] In the present embodiment, a power stabilization real-time feedback control loop of the rubidium atomic beam clock pumping laser composed of an acousto-optic modulator, a first photodetector and an optical power stabilization module is provided to stabilize the optical power, which can effectively reduce the relative intensity noise of the pumping laser, thereby greatly reducing the intensity light frequency shift caused by the laser frequency noise and amplitude noise, which helps to improve the medium- and long-term frequency stability of the optically pumped rubidium atomic beam clock, while reducing the volume and power consumption of the rubidium atomic beam clock.

[0095] The above-mentioned device and method for realizing the optically pumped rubidium atomic beam clock is a rubidium atomic beam clock based on a waveguide chip integrated semiconductor laser, which has the following beneficial effects:

[0096] 1. The use of waveguide chip integrated semiconductor lasers with extremely narrow line width and extremely low frequency noise can greatly improve the pumping efficiency and atomic utilization rate, and enhance the short-term frequency stability of the optically pumped rubidium atomic beam clock;

[0097] 2. The use of waveguide chip integrated semiconductor lasers can be integrated and chip-based, with high reliability and low power consumption characteristics, which can greatly reduce the volume and power consumption of optically pumped rubidium atomic beam clocks;

[0098] 3. Compared with the traditional optically pumped rubidium atomic clock which uses an atomic gas chamber (i.e., the working substance rubidium atomic vapor is filled in a transparent glass bulb, and the rubidium atomic gases collide with each other due to violent thermal motion), the present application uses a rubidium atomic beam, which greatly reduces the collision frequency shift caused by thermal motion between rubidium atoms, improves the frequency accuracy and frequency stability, and achieves long-term stability.

[0099] like Figure 4 As shown, in a specific embodiment, a device for realizing an optically pumped rubidium atomic beam clock includes: a waveguide chip integrated semiconductor laser 1, an optical power amplifier 2, an optical frequency multiplier 3, a bandpass filter 4, an acousto-optic modulator 5, a spectrometer 6, a rubidium atomic spectrum frequency stabilization module 7, a laser drive control module 8, a first photodetector 9, an optical power stabilization module 10, a beam reducer 11, a rubidium atomic beam clock physical module 12, a second photodetector 13, a microwave resonance signal demodulation module 14 and a microwave frequency synthesizer 15. The rubidium atomic beam clock physical module 12 includes: a magnetic shielding tube 1201, a rubidium atomic beam collimating gun 1202, a magnetic field coil 1203, a microwave resonant cavity 1204, a microwave feeding antenna 1205 and a rubidium atomic absorption box 1206.

[0100] The connection relationship between the various components is as follows: the waveguide chip integrated semiconductor laser 1, the optical power amplifier 2, the optical frequency multiplier 3, the bandpass filter 4, the acousto-optic modulator 5, the spectrometer 6, the beam reducer 11, the rubidium atomic beam clock physics module 12, the second photodetector 13, the microwave resonance signal demodulation module 14 and the microwave frequency synthesizer 15 are connected in sequence, and the acousto-optic modulator 5 is also connected to one end of the optical power stabilization module 10 through the first photodetector 9, and the other end of the optical power stabilization module 10 is connected to the acousto-optic modulator 5, the spectrometer 6 is also connected to the waveguide chip integrated semiconductor laser 1 through the rubidium atomic spectrum frequency stabilization module 7 and the laser drive control module 8, and the microwave frequency synthesizer 15 is also connected to the rubidium atomic beam clock physics module 12.

[0101] In this embodiment, the waveguide chip integrated semiconductor laser 1 includes a semiconductor gain chip 101 and a silicon-based photonic waveguide chip external cavity 102, and a gain medium J is provided in the waveguide chip integrated semiconductor laser 1. The microring resonator in the waveguide chip integrated semiconductor laser 1 adopts a single ring resonance, the optical power amplifier 2 adopts a tapered amplifier (TA), the optical frequency multiplier 3 adopts a periodic lithium niobate (PPLN) crystal, and the bandpass filter 4 adopts an interference filter neutral filter with a central wavelength of 780 nm and a bandwidth of 3 nm.

[0102] The specific working process of this embodiment is as follows:

[0103] 1) The waveguide chip integrated semiconductor laser 1 outputs a narrow linewidth laser of 1560nm, which enters the tapered amplifier (TA) 2 for power amplification, and the optical power is amplified from tens of mW to the W level. The high-power 1560nm laser enters the periodic lithium niobate (PPLN) crystal 3. When the phase matching condition is met, the frequency doubling effect occurs, generating a frequency-doubled light of 780nm at 1560nm. The fundamental frequency light of 1560nm is filtered out by the bandpass filter 4, leaving only the frequency-doubled light of 780nm. The laser passes through the acousto-optic modulator 5 to generate zero-order light and +1 (or -1)-order light.

[0104] 2) The zero-order light generated by the AOM 5 is divided into two paths, namely, the transmitted light and the reflected light, by the beam splitter 6.

[0105] 3) The transmitted light is used as the pumping laser, and the light beam is reduced by the anti-Galilean beam expander 11 and enters the rubidium atomic beam clock physics module 12.

[0106] 4) The reflected light passes through the rubidium atomic spectrum frequency stabilization module 7, and the laser drive control module 8 generates a control signal to adjust the pump current control port of the waveguide chip integrated semiconductor laser 1 to achieve accurate locking of the doubled frequency light frequency at 87 The ground state sublevel of Rb atom 5 2 S 1 / 2 , |F=2> and the fine structure level of the first excited state 5 2 P 3 / 2 The energy level transition frequency (corresponding to a wavelength of 780 nm) is obtained. The 780 nm laser after spectrum stabilization is used as a pump laser, and the beam is reduced by an anti-Galilean beam expander 11 and enters the rubidium atomic beam clock physics module 12.

[0107] 5) The +1 (or -1) level light generated by the AOM 5 passes through the first photodetector 9 and the optical power stabilization module 10 to generate a signal for controlling the power of the driving frequency of the AOM 5, thereby achieving optical power stabilization of the 780nm laser.

[0108] 6) The rubidium atom beam generated by the rubidium atom collimator in the rubidium atom beam clock physics module 12 interacts with the pump laser, absorbs the pump light, and raises the ground state energy level 5 2 S 1 / 2 , the atoms on |F=2> are prepared to the ground state energy level 5 2 S 1 / 2 , |F=1>, the state preparation is completed, and the pump light is no longer absorbed at this time, and the light intensity received by the second photodetector 13 does not change. When the microwave frequency synthesizer 15 generates a microwave signal of 6.834GHz, it resonates with the prepared rubidium atomic beam through the microwave feeding antenna, and the ground state energy level 5 2 S 1 / 2 , the atoms on |F=1> absorb microwave energy and re-transition to the ground state energy level 5 2 S 1 / 2 , |F=2>, the rubidium atomic beam absorbs the pumping laser again and performs state preparation. At this time, the light intensity received by the second photodetector 13 will show a concave change related to the microwave frequency, that is, the frequency discrimination curve, and the lowest point of the concave represents the ground state energy level 5 of the rubidium atom. 2 S 1 / 2 The two fine sublevels of |F=2,m F =0>and|F=1,m F =0>, the spectrum signal is used as an error signal, and the microwave resonance signal demodulation module generates a control voltage to control the voltage-controlled crystal oscillator in the microwave frequency synthesizer, and then fine-tune 6.834GHz, and finally achieve closed-loop locking of the rubidium atomic beam clock. The microwave signal is locked at the ground state energy level of the rubidium atom 5 2 S 1 / 2 The two fine sublevels of |F=2,m F =0> and |F=1,m F =0>, and outputs a standard frequency signal of 10MHz.

[0109] The present application also provides a method for realizing an optically pumped rubidium atomic beam clock, using an implementation device for an optically pumped rubidium atomic beam clock, such as Figure 5 As shown, in one embodiment, the following steps are included:

[0110] Step 501: Obtain incident fundamental frequency laser light, and convert the fundamental frequency laser light into frequency-doubled pumping light.

[0111] Step 502: Prepare rubidium atomic states according to the frequency-doubled pumping light.

[0112] Step 503: output an absorption spectrum signal of microwave and atomic resonance according to the intensity change of the doubled frequency pumping light passing through the rubidium atomic beam clock physical module that has completed the preparation of the rubidium atomic state, and demodulate the absorption spectrum to generate a tuning signal.

[0113] Step 504: According to the tuning signal, the microwave frequency is locked to the transition frequency of the ground state sub-energy level of the rubidium atom, so as to achieve closed-loop locking and output a standard frequency signal.

[0114] like Figure 6 As shown, in one embodiment, in step 501, converting the fundamental frequency laser into the doubled frequency pumping light comprises the following steps:

[0115] Step 5011: Based on the fundamental frequency laser, power amplification, frequency doubling processing and light filtering processing are performed in sequence to obtain frequency doubling light.

[0116] Step 5012: Obtain transmitted light and reflected light based on the frequency-doubled light.

[0117] Step 5013: Generate a first driving signal according to the reflected light, and perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the doubled frequency light at the transition frequency between the ground state energy level and the first excited state energy level.

[0118] Step 5014: According to the transmitted light, the beam diameter is reduced to obtain frequency-doubled pumping light.

[0119] In one embodiment, a waveguide chip integrated semiconductor laser comprises: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity.

[0120] In step 5013, wavelength tuning of the waveguide chip integrated semiconductor laser includes: adjusting the pump current of the semiconductor gain chip, and / or controlling the temperature of the external cavity of the silicon-based photonic waveguide chip by using the thermo-optic effect.

[0121] In one embodiment, between step 5011 and step 5012, the following steps are also included:

[0122] Step A: Obtain frequency-shifted light based on the frequency-doubled light.

[0123] Step B: Perform photoelectric conversion based on the frequency-shifted light to obtain an electrical signal corresponding to the frequency-shifted light signal.

[0124] Step C: According to the electrical signal, the driving power of the AOM is controlled and stabilized by the control circuit.

[0125] It should be understood that although Figure 5 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 5At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0126] The specific definition of the implementation method of an optically pumped rubidium atomic beam clock can be found in the above definition of the implementation device of an optically pumped rubidium atomic beam clock, which will not be repeated here.

[0127] It should be noted that matters not covered in the present invention are all known technologies.

[0128] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0129] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A device for realizing an optically pumped rubidium atomic beam clock, characterized in that: include: The waveguide chip integrates a semiconductor laser for outputting fundamental frequency laser; A frequency converter, used for receiving the fundamental frequency laser and converting it into frequency-doubled pumping light; A rubidium atomic beam clock physics module is used to generate a rubidium atomic beam perpendicular to the direction of the frequency-doubled pumping light, absorb the frequency-doubled pumping light, and prepare rubidium atomic states; The second photoelectric detector is used to detect the intensity change of the frequency-doubled pump light passing through the rubidium atomic beam clock physics module that has completed the preparation of the rubidium atomic state, and output the absorption spectrum signal of the microwave and atomic resonance; A microwave resonance signal demodulation module, used for receiving the absorption spectrum signal and demodulating it to generate a tuning signal; A microwave frequency synthesizer, for receiving the tuning signal, outputting a microwave signal that generates resonance in the rubidium atomic beam clock physical module, locking the microwave frequency to the transition frequency of the ground state sub-energy level of the rubidium atom, and outputting a standard frequency signal; The waveguide chip integrated semiconductor laser comprises: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity; the semiconductor gain chip and the silicon-based photonic waveguide chip external cavity are efficiently coupled through an optical field mode converter to achieve chip integration; the rubidium atomic beam clock physics module comprises: A rubidium atomic beam collimating gun is used to generate a sequential rubidium atomic beam perpendicular to the direction of the frequency-doubled pumping light and interact with the frequency-doubled pumping light; A microwave feeding antenna, used for receiving the microwave signal generated by the microwave frequency synthesizer and feeding it into the microwave resonant cavity; A microwave resonant cavity is used to resonate the microwave signal input by the microwave feeding antenna and resonate and interact with the rubidium atomic beam generated by the rubidium atomic beam collimating gun, so that the rubidium atomic beam absorbs the doubled frequency pumping light, changes the intensity of the doubled frequency pumping light, and realizes the preparation of rubidium atomic state; A rubidium atom recovery box is used to absorb the remaining rubidium atoms of the rubidium atom beam after the resonance interaction occurs; The magnetic field coil is used to generate a uniform external magnetic field parallel to the direction of the frequency-doubled pumping light, and the magnetic field provides a quantization axis direction for the rubidium atomic beam.

2. The device for realizing an optically pumped rubidium atomic beam clock according to claim 1, characterized in that: The rubidium atomic beam clock physics module also includes: a magnetic shielding cylinder; The magnetic shielding tube is arranged outside the rubidium atomic beam collimating gun, the microwave feeding antenna, the microwave resonant cavity, the rubidium atom recovery box and the magnetic field coil, and is used to shield the earth's magnetic field and stray magnetic field, and reduce the unstable influence of the residual magnetic field on the atomic hyperfine energy level structure.

3. The device for realizing an optically pumped rubidium atomic beam clock according to claim 1 or 2, characterized in that: The frequency converter comprises: An optical power amplifier, used for receiving the fundamental frequency laser and performing power amplification to obtain a high-power fundamental frequency laser; An optical frequency doubler, used for receiving the high-power fundamental frequency laser and performing frequency doubling processing to obtain a mixed light including fundamental frequency light and frequency doubling light; A bandpass filter, used for receiving the mixed light and filtering out the fundamental frequency light to obtain spectrally pure double frequency light; A spectrometer, used for receiving the frequency-doubled light and dividing it into transmitted light and reflected light; A rubidium atomic spectrum frequency stabilization module, used for receiving the reflected light and generating a first driving signal; A laser drive control module, configured to receive the first drive signal and perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the frequency-doubled light at a transition frequency between the ground state energy level of the rubidium atom and the first excited state energy level; The beam reducer is used to receive the transmitted light and reduce the beam diameter to obtain frequency-doubled pumping light.

4. The device for realizing an optically pumped rubidium atomic beam clock according to claim 3, characterized in that: The beam diameter of the doubled frequency pumping light is smaller than the diameter of the rubidium atomic beam generated by the rubidium atomic beam clock physics module, so that the doubled frequency pumping light in the beam diameter area interacts with the rubidium atomic beam, thereby reducing the background light intensity of the second photodetector.

5. The device for realizing an optically pumped rubidium atomic beam clock according to claim 4, characterized in that: The frequency converter further comprises: an acousto-optic modulator, used for converting the frequency-doubled light into zero-order light and frequency-shifted light, and outputting the zero-order light to the spectrometer; A first photodetector, configured to receive the frequency-shifted light and convert the frequency-shifted light signal into an electrical signal; The optical power stabilization module is used to receive the electrical signal and control and stabilize the driving power of the acousto-optic modulator.

6. A method for realizing an optically pumped rubidium atomic beam clock, characterized in that: A device for realizing an optically pumped rubidium atomic beam clock according to any one of claims 1 to 5, comprising: Obtaining incident fundamental frequency laser light, and converting the fundamental frequency laser light into frequency-doubled pumping light; Prepare rubidium atomic state according to the frequency-doubled pumping light; According to the intensity change of the frequency-doubled pump light of the rubidium atomic beam clock physical module that has completed the preparation of the rubidium atomic state, the absorption spectrum signal of the microwave and atomic resonance is output, and the absorption spectrum is demodulated to generate a tuning signal; According to the tuning signal, the microwave frequency is locked to the transition frequency of the ground state sub-energy level of the rubidium atom, closed-loop locking is achieved and a standard frequency signal is output.

7. The method for realizing an optically pumped rubidium atomic beam clock according to claim 6, characterized in that: Converting the fundamental frequency laser into frequency-doubled pumping light comprises: According to the fundamental frequency laser, power amplification, frequency doubling processing and light filtering processing are performed in sequence to obtain frequency doubling light; Obtaining transmitted light and reflected light according to the frequency-doubled light; Generate a first driving signal according to the reflected light, and perform frequency tuning on the waveguide chip integrated semiconductor laser to lock the frequency of the frequency-doubled light at the transition frequency between the ground state energy level and the first excited state energy level; The beam diameter is reduced according to the transmitted light to obtain frequency-doubled pumping light.

8. The method for realizing an optically pumped rubidium atomic beam clock according to claim 7, characterized in that: The waveguide chip integrated semiconductor laser comprises: a semiconductor gain chip and a silicon-based photonic waveguide chip external cavity; The wavelength tuning of the waveguide chip integrated semiconductor laser includes: adjusting the pump current of the semiconductor gain chip, and / or controlling the temperature of the external cavity of the silicon-based photonic waveguide chip by using the thermo-optic effect.

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