Chip active optical clock based on grating magneto-optical trap cooling and implementation method thereof

Abstract

The application discloses a chip active optical clock based on grating magneto-optical trap cooling and an implementation method thereof. Three saturated absorption spectrum frequency stabilization DBR lasers are used to generate cooling laser, re-pumping laser and pumping laser respectively, wherein the cooling laser and the re-pumping laser cooperate with the grating magneto-optical trap, are used for cooling and confining atoms, and form a cold atom group in an atom chamber; the pumping laser excites the cold atoms, and the generated stimulated radiation signal is directly used as an optical frequency standard signal output, and after frequency beating with a microcavity optical comb, a chip active optical clock is realized. Compared with a traditional cold atom optical clock, the application greatly reduces the volume of the system, can be integrated on a chip, and is suitable for a compact and portable device application scene; compared with a current chip microwave atomic clock, the stability index of the application is higher. The application has important application value, and can provide a long-time and high-precision frequency reference for a movable device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser, and particularly relates to a chip active optical clock based on a grating magneto-optical trap cooling and an implementation method thereof. BACKGROUND

[0002] In the past century, optical atomic (molecular) frequency reference has played an important role in scientific research and engineering, providing a standard for realizing precise measurement. Since the concept of laser was first proposed in 1958, the scientific community has been exploring ways to use lasers to improve the accuracy of time measurement. Currently, the performance of optical frequency atomic clocks (hereinafter referred to as optical clocks) has exceeded that of microwave atomic clocks, and has been widely used in key fields such as basic physics research and optical communication. The frequency stability and frequency uncertainty of the best optical clock have both reached the 10 -19 order of magnitude, and the roadmap for redefining the second using optical clocks in the future is being deployed. Among them, the miniaturized chip optical clock can be integrated into mobile devices, especially in the military field. High-stability chip optical clocks can be used in inertial navigation systems and global positioning navigation systems to provide higher precision navigation and positioning accuracy for unmanned aerial vehicles, military vehicles, handheld military devices, etc. They can also be used for synchronization of mobile communication systems, thereby achieving high-strength communication encryption.

[0003] Traditional optical clocks are passive optical clocks that require an external quantum frequency reference. The frequency of the local oscillator laser is locked to the quantum frequency reference through a servo feedback circuit, thereby stabilizing the frequency of the local oscillator laser. The passive optical clock operates in the good cavity region, and the cavity mode linewidth is much smaller than the gain linewidth. The cavity length thermal noise directly affects the frequency of the output optical frequency standard signal, thereby affecting the short-term frequency stability of the passive optical clock. In contrast, the active optical clock does not require an external frequency reference. The stimulated emission signal of the atom is directly used as the frequency standard, and the active optical clock operates in the bad cavity region. The gain linewidth is much smaller than the cavity mode linewidth. The frequency of the optical frequency standard signal depends on the center frequency of the quantum reference, and the cavity pulling effect is naturally suppressed. The short-term frequency stability is better. In summary, the active optical clock has the advantages of cavity pulling suppression, narrow linewidth, excellent short-term frequency stability, and simple system compared to the passive optical clock, and has wide application prospects. The active optical clock system is simple and easy to miniaturize. However, the current chip active optical clock still mainly uses hot atoms as the gain medium of the resonant cavity. The Brownian thermal motion of hot atoms will cause Doppler effect and collision effect between atoms, causing frequency drift of the optical frequency standard signal generated by stimulated emission, resulting in poor frequency stability of the active optical clock. If the gain medium is replaced by a cold atom group, the velocity of the atom is slowed down, and the Doppler frequency shift and collision frequency shift phenomena can be greatly suppressed, further improving the frequency stability of the chip active optical clock.

[0004] The establishment of Maxwell equations predicts the existence of light pressure, and laser can achieve high energy density, realizing the idea of manipulating micro particles with light. When the frequency of laser is slightly less than the transition frequency of atom (i.e. "red detuning"), due to the Doppler effect, the ground state atoms moving towards the photons with a certain speed will absorb the photons to jump to the excited state, and receive a damping force. When the atom returns to the ground state, the direction of the spontaneously emitted photons is random, and in statistics, the atom is decelerated, achieving the purpose of cooling. The magneto-optical trap is a cold atom device, which first cools the atom by using the red-detuned laser, and then further uses the non-uniform magnetic field and the trap light to capture and confine the atom, forming a cold atom group. The traditional magneto-optical trap needs to manually configure the optical path, and multiple lasers are shot into the magneto-optical trap according to specific positions, directions and polarization rotation directions to form trap light. Such a magneto-optical trap is large in size and complex in optical path, and is not suitable for compact chip-level systems. In recent years, a new type of grating magneto-optical trap has appeared, which etches a diffraction grating structure on the surface of a silicon-based chip to make a grating chip. Only one circularly polarized laser needs to be vertically irradiated on the etching surface of the grating chip to automatically generate another three (or more than three) circularly polarized lights to form trap light together with the incident laser. The invention of the grating magneto-optical trap greatly reduces the complexity, volume and power consumption of the cold atom device, and its performance is comparable to that of the traditional six-beam magneto-optical trap. However, how to integrate the grating magneto-optical trap and related elements on a silicon-based chip to realize a small-size, low-power cold atom chip active optical clock is a problem to be solved at present. SUMMARY

[0005] In view of the technical problems existing in the prior art, the purpose of the present application is to provide a chip active optical clock based on grating magneto-optical trap cooling and an implementation method thereof. The present application combines the grating magneto-optical trap with microcavity optical comb, distributed Bragg reflection (DBR) narrow linewidth laser, chip electro-optical modulator, thin film photodetector and other micro-optoelectronic components to realize a small-size, low-power cold atom chip active optical clock.

[0006] The present application uses three DBR lasers with saturated absorption spectrum frequency stabilization to generate cooling laser, re-pumping laser and pumping laser respectively. The cooling laser and the re-pumping laser cooperate with the grating magneto-optical trap to cool and confine the atoms, forming a cold atom group in the atom chamber. The pumping laser excites the cold atoms, and the generated stimulated radiation signal is directly output as an optical frequency standard signal. After frequency mixing with the microcavity optical comb, the chip active optical clock is realized. Compared with the traditional cold atom optical clock, the present application greatly reduces the size of the system and can be integrated on a chip to adapt to the application scenarios of compact and portable devices. Compared with the current chip microwave atomic clock, the stability index of the present application is higher.

[0007] To solve the above technical problems, the application provides a chip active optical clock based on grating magneto-optical trap cooling, taking cesium atoms as an example, which comprises:

[0008] A first DBR laser 1 with a center wavelength of 852nm is used to generate a narrow-line-width cooling laser corresponding to a cooling pump energy level transition of cesium atoms from 6S 1 / 2 state to 6P 3 / 2 state.

[0009] A first laser controller 2 is used to control the temperature and current of the first DBR laser 1, so as to control the output frequency of the first DBR laser 1 and enable scanning of the output frequency; meanwhile, the first laser controller 2 is used to receive a saturated absorption spectrum electric signal, calculate the frequency error of the first DBR laser 1, so as to lock the output frequency of the first DBR laser 1 on the cooling pump energy level transition frequency of cesium atoms from 6S 1 / 2 -(F=4) to 6P 3 / 2 (F'=5).

[0010] A first beam adjusting device 3 divides the output laser of the first DBR laser 1 into two beams, one of which is used as a cooling laser, and the other of which is used for saturated absorption spectrum frequency stabilization.

[0011] A second DBR laser 4 with a center wavelength of 852nm is used to generate a narrow-line-width repump laser corresponding to a cooling repump energy level transition of cesium atoms from 6S 1 / 2 state to 6P 3 / 2 state.

[0012] A second laser controller 5 is used to control the temperature and current of the second DBR laser 4, so as to control the output frequency of the second DBR laser 4 and enable scanning of the output frequency; meanwhile, the second laser controller 5 is used to receive a saturated absorption spectrum electric signal, calculate the frequency error of the second DBR laser 4, so as to lock the output frequency of the second DBR laser 4 on the cooling repump energy level transition frequency of cesium atoms from 6S 1 / 2 -(F=3) to 6P 3 / 2 (F'=4).

[0013] A second beam adjusting device 6 divides the output laser of the second DBR laser 4 into two beams, one of which is used as a repump laser, and the other of which is used for saturated absorption spectrum frequency stabilization.

[0014] A third DBR laser 7 with a center wavelength of 455nm is used to generate a narrow-line-width pump laser corresponding to a pump energy level transition of cesium atoms from 6S 1 / 2 state to 7P 3 / 2 state.

[0015] A third laser controller 8 is used to control the temperature and current of the third DBR laser 7, so as to control the output frequency of the third DBR laser 7 and enable scanning of the output frequency; meanwhile, the third laser controller 8 is used to receive the saturated absorption spectrum electrical signal, calculate the frequency error of the third DBR laser 7, and thus lock the output frequency of the third DBR laser 7 at the cesium atom 6S 1 / 2 -(F=4)→7P 3 / 2 (F”=3) of the pump energy level transition frequency.

[0016] A third beam adjusting device 9 divides the output laser of the third DBR laser 7 into two beams, one of which is used as the pump laser, and the other of which is used for saturated absorption spectrum frequency stabilization.

[0017] A saturated absorption spectrum device 10 is used to receive the divided light of the first beam adjusting device 3, the second beam adjusting device 6 and the third beam adjusting device 9 respectively, and three beams of laser enter the saturated absorption spectrum device 10 from three different directions (x, y, z). Through the interaction between the atom and the laser, a saturated absorption spectrum light signal is generated, which is converted into an electrical signal by a thin film photodetector and then fed back to the corresponding first laser controller 2, second laser controller 5 and third laser controller 8 as a frequency reference, so as to realize saturated absorption spectrum frequency stabilization.

[0018] A chip electro-optical modulator 11 is used to produce a -10MHz red detuning to the frequency of the cooling laser, so as to realize laser deceleration of the cesium atom in the atomic cell 18.

[0019] A first polarization beam splitter prism 12 is used to combine the cooling laser and the repump laser to generate a cooling and repump mixed laser.

[0020] A beam expander lens 13 and a collimating lens 14 are used to expand the beam diameter of the cooling and repump mixed laser while keeping the beam still parallel light.

[0021] A λ / 4 wave plate 15 is used to adjust the polarization state of the cooling and repump mixed laser to circular polarization.

[0022] A Helmholtz coil magnetic shielding chamber 16 is used to offset the external magnetic field by passing a proper current through the coil, so as to avoid the influence of the interference of the external magnetic field on the non-uniform magnetic field in the grating magneto-optical trap on the cooling effect.

[0023] A counter Helmholtz coil 17 is used to generate a non-uniform magnetic field in the grating magneto-optical trap, so as to cause the Zeeman splitting of the energy level of the cesium atom. The two coils are parallel and coaxial, the current passing through them is of the same size and opposite direction, the magnetic field strength at the midpoint of the axis is zero, the magnetic field strength linearly increases along the axial or radial direction, and the magnetic field directions of the two positions symmetric about the midpoint of the axis are opposite.

[0024] The atomic cell 18 is filled with pure cesium atoms as gain medium. One side window is flat (hereinafter referred to as front window), and the other side window is convex (hereinafter referred to as rear window). The two windows are coated with dielectric films which are highly transmissive to 455 nm wavelength and have certain reflectivity to 1359 nm wavelength, serving as flat and convex cavity mirrors of the resonator. The cooling and repumping mixed laser enters from the side surface parallel to the two windows, and the cesium atoms complete 6S 1 / 2 (F = 4) → 6P 3 / 2 (F' = 5) cooling and pumping energy level transition, and are decelerated; the repumping laser makes the cesium atoms complete 6S 1 / 2 (F = 3) → 6P 3 / 2 (F' = 4) cooling and repumping energy level transition, preventing the cesium atoms from gathering in 6S 1 / 2 (F = 3) state, thereby weakening the action with the cooling laser. In the center of the cell, the strength of the non-uniform magnetic field generated by the anti-Helmholtz coil 17 is zero, which is also the intersection of the trapping light. The decelerated cesium atoms are captured and trapped in the center point by the magneto-optical trap, forming a cold atom group. In the direction perpendicular to the two windows, the 455 nm pumping laser enters from the front window, and the cold atom group undergoes pumping energy level transition from 6S 1 / 2 state to 7P 3 / 2 state under the pumping of the pumping laser. The cesium atoms pumped to 7P 3 / 2 state drop to 7S 1 / 2 state through spontaneous emission, thereby establishing population inversion between the target energy levels of 7S 1 / 2 state and 6P 1 / 2 state of cesium atoms. The cesium atoms undergo target energy level transition from 7S 1 / 2 state to 6P 1 / 2 state due to spontaneous emission, generating 1359 nm fluorescence signal. The resonator continuously amplifies the fluorescence signal generated after pumping the cesium atoms, until the 1359 nm wavelength stimulated radiation signal is formed, which is used as the optical frequency standard signal (hereinafter referred to as optical frequency standard signal) of the active optical clock, and is output through the rear window.

[0025] The grating chip 19 is etched with a diffraction grating structure on the surface. The expanded cooling and repumping mixed laser is vertically incident on the surface, and three beams of cooling and repumping diffraction light are generated by diffraction, the wave vector directions of which are similar to three edges of a regular tetrahedron, and the polarization rotation directions thereof are opposite to that of the incident laser, forming trapping light with the incident laser. The intersection of the trapping light is located in the center of the atomic cell 18, and cooperates with the non-uniform magnetic field generated by the anti-Helmholtz coil 17 to form a cold atom group in the center of the atomic cell 18.

[0026] The microcavity optical comb 20 is used to generate a series of comb tooth optical signals with equal frequency intervals, and to down-convert the optical frequency, so as to realize measurement of the optical frequency standard signal.

[0027] The second polarization beam splitting prism 21 is used for combining the 1359nm light frequency standard signal output by the plano-concave cavity mirror 9 and the comb tooth light signal generated by the microcavity optical comb 20 to generate a beat frequency light signal.

[0028] The thin film photodetector 22 is used for receiving the beat frequency light signal and converting it into an electrical signal.

[0029] The frequency counter 23 is used for receiving and processing the beat frequency electrical signal from the second thin film photodetector 22 and outputting a clock signal to realize the chip active optical clock.

[0030] The selection of the cooling pump energy level transition, the cooling repump energy level transition, the pump energy level transition and the target energy level transition needs to be specifically considered according to the type of alkali metal atom and the target wavelength of the required optical frequency standard signal, and meanwhile, the combination of the cooling pump energy level transition and the cooling repump energy level transition needs to ensure that the atom cannot be accumulated on the same state to realize the overall “cyclic transition” effect; the upper energy level of the cooling pump energy level transition and the cooling repump energy level transition cannot coincide with the lower energy level of the target energy level transition, otherwise it will be difficult to realize the population inversion of the target energy level.

[0031] The atom type contained in the saturated absorption spectrum device 10 is the same as that in the atomic cell 18.

[0032] The resonant cavity parameters composed of the front window and the rear window of the atomic cell 18 are calculated to make the cavity mode line width much larger than the gain line width of the cesium atom in the atomic cell 18, that is, to work in the bad cavity region.

[0033] The cold atom chip active optical clock further comprises a magnetic shielding module and a heating, temperature maintaining and temperature controlling module arranged outside the saturated absorption spectrum device 10, so as to isolate the influence of external magnetic field and temperature fluctuation on the transition frequency of the cesium atom and improve the frequency stabilization performance of the saturated absorption spectrum.

[0034] The cold atom chip active optical clock further comprises that the chip electro-optical modulator 11 is driven by a microwave signal generated by a driving chip.

[0035] The cold atom chip active optical clock further comprises that the Helmholtz coil magnetic shielding chamber 16 and the anti-Helmholtz coil 17 are connected to an adjustable current source circuit, which can control the current through each coil respectively.

[0036] In addition, the application also provides an implementation method of the chip active optical clock based on the grating magnetic optical trap cooling, which specifically comprises the following steps:

[0037] Step S1: The first DBR laser 1 adjusts its frequency to be equal to the 6S 1 / 2 →6P3 / 2 The frequency of the 852 nm cooling laser is locked on the cesium atom 6S 1 / 2 (F = 4) → 6P 3 / 2 (F' = 5) cooling pump energy level transition;

[0038] Step S2: The second DBR laser 4 adjusts its frequency with the cesium atom 6S 1 / 2 → 6P 3 / 2 The frequency of the 852 nm cooling laser is locked on the cesium atom 6S 1 / 2 (F = 3) → 6P 3 / 2 (F' = 4) cooling pump energy level transition;

[0039] Step S3: The third DBR laser 7 adjusts its frequency with the cesium atom 6S 1 / 2 → 7P 3 / 2 The frequency of the 455 nm pump laser is locked on the cesium atom 6S 1 / 2 (F = 4) → 7P 3 / 2 (F" = 3) pump energy level transition;

[0040] Step S4: Adjust the microwave drive signal loaded on the chip electro-optical modulator 11, so that the cooling laser passing through the chip electro-optical modulator 11 produces a constant -10 MHz red detuning;

[0041] Step S5: The frequency-shifted cooling laser and the repump laser are combined on the first polarization beam splitter prism 12 to produce cooling and repump mixed laser;

[0042] Step S6: The cooling and repump mixed laser passes through the beam expander lens 13 and the collimating lens 14 to expand the diameter of the light beam, so that the cross-sectional area of the light beam can roughly cover the entire surface of the grating chip 19, thereby improving the cooling efficiency;

[0043] Step S7: The cooling and repump mixed laser enters the atom cell 18 from the side of the two windows parallel to the atom cell 18. Due to the Doppler effect, the cesium atoms with a certain speed moving towards the red-detuned cooling laser photons will absorb the photons, completing the cooling pump energy level transition from 6S1 / 2 (F=4) state to 6P 3 / 2 (F'=5) state; then drop to 6S by spontaneous emission 1 / 2 (F=4) state and 6S 1 / 2 (F=3) state; according to momentum conservation, the cesium atom absorbing a counter-moving photon will be decelerated, while the direction of the velocity of the spontaneously emitted photon is random, i.e. in statistics, the change of the velocity of the spontaneously emitted photon is zero, thus the overall effect of the deceleration of the cesium atom;

[0044] Step S8: the cesium atom in 6S 1 / 2 (F=3) state is excited by the re-pumping laser, completing the cooling re-pumping energy level transition to 6P 3 / 2 (F'=4) state, and returning to 6S by spontaneous emission 1 / 2 (F=4) state, thus preventing the accumulation of the cesium atom in 6S 1 / 2 (F=3) state, weakening the effect of the cooling laser;

[0045] Step S9: adjust the current through the Helmholtz coil magnetic shielding chamber 16 to make the magnetic field strength inside it zero, avoiding the interference of external magnetic field;

[0046] Step S10: apply appropriate current to the anti-Helmholtz coil 17, and the current directions of the two coils are opposite, thus forming the required non-uniform magnetic field in the atomic gas chamber 18;

[0047] Step S11: the cooling and re-pumping mixed laser transmits through the atomic gas chamber 18, and is vertically incident on the surface of the grating chip 19, generating three beams of positive tetrahedron-shaped cooling and re-pumping diffracted light, which together with the incident laser form the trap light, and the intersection of the trap light is located at the center point of the atomic gas chamber 18;

[0048] Step S12: the cesium atom in the atomic gas chamber 18 is located in the non-uniform magnetic field generated by the anti-Helmholtz coil 17, and for different positions of the atom, the shift amount of the Zeeman sub-energy level is different, and the detuning amount of the cooling laser is also different. At the same time, according to the selection rule, the magnetic quantum number of the excited state Zeeman sub-energy level has a requirement for the spin direction of the absorbed circularly polarized photon. When the cesium atom deviates from the center point of the atomic gas chamber 18, it will selectively absorb more photons moving towards the center point, and continuously receive a force towards the center point, thus achieving the effect of further capturing and trapping the decelerated cesium atom, and finally forming a cold atom group at the center point;

[0049] Step S13: the 455nm pumping laser generated by the third DBR laser 7 vertically transmits through the front window of the atomic gas chamber 18, enters the resonant cavity, and irradiates on the cold atom group, pumping the cesium atom in the cold atom group from 6S 1 / 2 state to 7P 3 / 2state, complete the pump energy level transition; 7P 3 / 2 state, drop to 7S 1 / 2 state by spontaneous emission, and finally establish the population inversion between the target energy levels of cesium atom 7S 1 / 2 state and 6P 1 / 2 state, and complete the target energy level transition by spontaneous emission to generate a 1359nm fluorescence signal;

[0050] Step S14: under the gain of the cold atom group, under the enhancement of the resonant cavity composed of the front window and the rear window of the atomic cell 18, and when the 455nm pump light power reaches a suitable value, the gain of the 1359nm fluorescence signal is greater than the loss, and the 1359nm stimulated radiation signal light is realized;

[0051] Step S15: the 1359nm stimulated radiation signal light is output from the rear window of the atomic cell 18 as the optical frequency standard signal of the active optical clock;

[0052] Step S16: the optical frequency standard signal and the comb tooth optical signal generated by the microcavity optical comb 20 are combined in the second polarization beam splitter prism 21 to generate a beat frequency optical signal;

[0053] Step S17: the beat frequency optical signal enters the second thin film photoelectric detector 22, is converted into a beat frequency electrical signal, is input into the digital frequency counter 23, and after a series of digital operations, outputs a time signal, realizing the chip active optical clock.

[0054] Among them, the method further comprises: the atomic type in the saturable absorption spectrum device 10 and the atomic cell 18 can be changed to rubidium atoms; the frequency shift amount of the chip electro-optical modulator to the cooling laser can be changed to-12MHz; the cooling laser of the first DBR laser 1 can be changed to 780nm and locked to the cooling pump energy level transition frequency of the rubidium atom 5S 1 / 2 (F=2)→5P 3 / 2 (F’=3) of the rubidium atom; the repump laser of the second DBR laser 4 can be changed to 780nm and locked to the cooling repump energy level transition frequency of the rubidium atom 5S 1 / 2 (F=1)→5P 3 / 2 (F’=2) of the rubidium atom; the pump laser of the third DBR laser 7 can be changed to 421nm and locked to the pump energy level transition frequency of the rubidium atom 5S 1 / 2 (F=3)→6P 1 / 2 (F”=2) of the rubidium atom, thereby cooling the rubidium atoms in the atomic cell 18 to form a cold atom group, and establishing the population inversion between the target energy levels of the rubidium atom 6S 1 / 2 state and 5P 1 / 2The population inversion between the two target energy levels is realized, the target energy level transition is completed through spontaneous emission, a light frequency standard signal with a center wavelength of 1324 nm is output, and the steps of the cold atom chip active optical clock are realized.

[0055] Compared with the prior art, the positive effects of the present application are:

[0056] Taking cesium atoms as an example, the present application utilizes 852 nm cooling laser and repump laser, cooperates with grating magneto-optical trap cooling, captures and confines cesium atoms, forms a cold atom group in an atomic cell, and takes the cold atom group as a gain medium, pumps the cesium atoms to 7P 3 / 2 state through 455 nm pump laser, establishes population inversion between cesium atom 7S 1 / 2 state and 6P 1 / 2 state through spontaneous emission, continuously amplifies the spontaneous emission corresponding to the transition of cesium atom 7S 1 / 2 state and 6P 1 / 2 state through cavity feedback of a resonant cavity, outputs 1359 nm stimulated emission signal after reaching a laser threshold, and the output laser is directly used as a light frequency standard signal. Since the active optical clock works in a bad cavity region, the gain line width is much smaller than the cavity mode line width, the influence of cavity dragging effect on short-term frequency stability can be greatly suppressed, compared with the traditional passive optical clock, a complex high-precision servo circuit is not needed to stabilize the resonant cavity length, the volume and power consumption of the system are reduced. At the same time, since the gain medium is a cold atom group, the influence of collision frequency shift and Doppler frequency shift on the light frequency standard signal is suppressed, and the stability of the active optical clock is further improved. Compared with the traditional cold atom optical clock, the present application takes the grating magneto-optical trap with simple optical path, small volume and low power consumption as a core component, cooperates with active optical clock technology and various micro-optoelectronic components, and can integrate the cold atom optical clock system on a chip, which is suitable for portable application scenarios; compared with the existing chip microwave atomic clock, the stability index is higher. The present application has important application value, and can provide a long-time and high-precision frequency reference for mobile devices. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 A structure diagram of the chip active optical clock based on grating magneto-optical trap cooling is shown in the present application.

[0058] Figure 2 An energy level structure diagram of related cesium atoms and rubidium atoms in the implementation process of the present application is shown;

[0059] (a) is an energy level structure diagram of cesium atoms, and (b) is an energy level structure diagram of rubidium atoms. DETAILED DESCRIPTION

[0060] In order to make the purpose, content and advantages of the present application clearer, the specific implementation manner of the present application is described in further detail below in combination with the drawings and examples.

[0061] To solve the problems of the prior art, the application provides a chip active optical clock based on grating magneto-optical trap cooling, as shown in Figure 1 The device comprises:

[0062] A first DBR laser 1 with a center wavelength of 852 nm is used to generate a narrow-line-width cooling laser corresponding to a cooling pump energy level transition of cesium atoms from 6S 1 / 2 to 6P 3 / 2 .

[0063] A first laser controller 2 is used to control the temperature and current of the first DBR laser 1, thereby controlling the output frequency of the first DBR laser 1 and enabling scanning of the output frequency; meanwhile, the first laser controller 2 is used to receive a saturated absorption spectrum electrical signal, calculate the frequency error of the first DBR laser 1, and thereby lock the output frequency of the first DBR laser 1 on the cooling pump energy level transition frequency of cesium atoms from 6S 1 / 2 (F = 4) to 6P 3 / 2 (F' = 5).

[0064] A first beam adjusting device 3 divides the output laser of the first DBR laser 1 into two beams, one of which is used as a cooling laser and the other of which is used for saturated absorption spectrum frequency stabilization.

[0065] A second DBR laser 4 with a center wavelength of 852 nm is used to generate a narrow-line-width repump laser corresponding to a cooling repump energy level transition of cesium atoms from 6S 1 / 2 to 6P 3 / 2 .

[0066] A second laser controller 5 is used to control the temperature and current of the second DBR laser 4, thereby controlling the output frequency of the second DBR laser 4 and enabling scanning of the output frequency; meanwhile, the second laser controller 5 is used to receive a saturated absorption spectrum electrical signal, calculate the frequency error of the second DBR laser 4, and thereby lock the output frequency of the second DBR laser 4 on the cooling repump energy level transition frequency of cesium atoms from 6S 1 / 2 (F = 3) to 6P 3 / 2 (F' = 4).

[0067] A second beam adjusting device 6 divides the output laser of the second DBR laser 4 into two beams, one of which is used as a repump laser and the other of which is used for saturated absorption spectrum frequency stabilization.

[0068] A third DBR laser 7 with a center wavelength of 455 nm is used to generate a narrow-line-width pump laser corresponding to a pump energy level transition of cesium atoms from 6S 1 / 2 to 7P 3 / 2 .

[0069] The third laser controller 8 is used to control the temperature and current of the third DBR laser 7, so as to control the output frequency of the third DBR laser 7 and enable the output frequency to be scanned; meanwhile, the third laser controller 8 is used to receive the saturated absorption spectrum electrical signal, calculate the frequency error of the third DBR laser 7, and thus lock the output frequency of the third DBR laser 7 at the cesium atom 6S 1 / 2 -(F=4)→7P 3 / 2 (F”=3) of the pump energy level transition frequency.

[0070] The third light beam adjusting device 9 divides the output laser of the third DBR laser 7 into two beams, one of which is used as the pump laser, and the other of which is used for saturated absorption spectrum frequency stabilization.

[0071] The saturated absorption spectrum device 10 is used to receive the divided light of the first light beam adjusting device 3, the second light beam adjusting device 6 and the third light beam adjusting device 9 respectively, three beams of laser enter the saturated absorption spectrum device 10 from three different directions (x, y, z), through the interaction between the atom and the laser, the saturated absorption spectrum light signal is generated, and after being converted into an electrical signal by a thin film photodetector, the electrical signal is fed back to the corresponding first laser controller 2, second laser controller 5 and third laser controller 8 as a frequency reference, so as to realize saturated absorption spectrum frequency stabilization.

[0072] The chip electro-optical modulator 11 is used to produce a -10MHz red detuning to the frequency of the cooling laser, so as to realize the laser deceleration of the cesium atom in the atomic cell 18.

[0073] The first polarization beam splitter prism 12 is used to combine the cooling laser and the repump laser to generate a cooling and repump mixed laser.

[0074] The beam expander lens 13 and the collimating lens 14 are used to expand the beam diameter of the cooling and repump mixed laser while keeping the beam still as parallel light.

[0075] The λ / 4 wave plate 15 is used to adjust the polarization state of the cooling and repump mixed laser to be circular polarization.

[0076] The Helmholtz coil magnetic shielding chamber 16 is used to offset the external magnetic field by passing a proper current in the coil, so as to avoid the influence of the interference of the external magnetic field on the non-uniform magnetic field in the grating magneto-optical trap on the cooling effect.

[0077] The anti-Helmholtz coil 17 is used to generate the non-uniform magnetic field in the grating magneto-optical trap, so as to cause the Zeeman splitting of the energy level of the cesium atom. The two coils are parallel and coaxial, the current passing through them is of the same size and opposite direction, the magnetic field intensity at the midpoint of the axis is zero, the magnetic field intensity linearly increases along the axial or radial direction, and the magnetic field directions of the two positions which are symmetric about the midpoint of the axis are opposite.

[0078] The atomic cell 18 is filled with pure cesium atoms as gain medium, one side window is flat (hereinafter referred to as front window), and the other side window is convex (hereinafter referred to as rear window). The two windows are coated with dielectric films which are highly transparent to 455 nm wavelength and have certain reflectivity to 1359 nm wavelength, serving as flat mirror and flat-convex mirror of the resonant cavity. The cooling and repumping mixed laser enters from the side surface parallel to the two windows, and the cesium atoms complete 6S 1 / 2 (F = 4)→6P 3 / 2 (F' = 5) cooling and pumping energy level transition, and are decelerated; the repumping laser makes the cesium atoms complete 6S 1 / 2 (F = 3)→6P 3 / 2 (F' = 4) cooling and repumping energy level transition, preventing the cesium atoms from gathering in 6S 1 / 2 (F = 3) state, thereby weakening the action with the cooling laser. In the center of the cell, the strength of the non-uniform magnetic field generated by the anti-Helmholtz coil 17 is zero, which is also the intersection of the trapping light. The decelerated cesium atoms are captured and trapped in the center point by the magneto-optical trap, forming a cold atom group. In the direction perpendicular to the two windows, the 455 nm pumping laser enters from the front window, and the cold atom group undergoes pumping energy level transition from 6S 1 / 2 state to 7P 3 / 2 state under the pumping of the pumping laser. The cesium atoms pumped to 7P 3 / 2 state fall to 7S 1 / 2 state through spontaneous emission, thereby establishing population inversion between the target energy levels of 7S 1 / 2 state and 6P 1 / 2 state of cesium atoms. The cesium atoms undergo target energy level transition from 7S 1 / 2 state to 6P 1 / 2 state due to spontaneous emission, generating 1359 nm fluorescence signal. The resonant cavity continuously amplifies the fluorescence signal generated after pumping the cesium atoms, until the 1359 nm wavelength stimulated radiation signal is formed, which is used as the optical frequency standard signal (hereinafter referred to as optical frequency standard signal) of the active optical clock, and is output through the rear window.

[0079] The grating chip 19 is etched with a diffraction grating structure on the surface. The expanded cooling and repumping mixed laser is vertically incident on the surface to generate three beams of cooling and repumping diffraction light through diffraction, and the wave vector directions of the three beams are similar to three edges of a regular tetrahedron, and the polarization rotation directions of the three beams are opposite to that of the incident laser, forming trapping light with the incident laser. The intersection of the trapping light is located at the center of the atomic cell 18, and cooperates with the non-uniform magnetic field generated by the anti-Helmholtz coil 17 to form a cold atom group at the center of the atomic cell 18.

[0080] The microcavity optical comb 20 is used to generate a series of comb tooth optical signals with equal frequency intervals, and to down-convert the optical frequency, so as to realize measurement of the optical frequency standard signal.

[0081] The second polarization beam splitting prism 21 is used for combining the 1359nm light frequency standard signal output by the plano-concave cavity mirror 9 and the comb tooth light signal generated by the microcavity optical comb 20 to generate a beat frequency light signal.

[0082] The thin film photodetector 22 is used for receiving the beat frequency light signal and converting it into an electric signal.

[0083] The frequency counter 23 is used for receiving the beat frequency electric signal from the second thin film photodetector 22 and processing it to output a clock signal, so as to realize the chip active optical clock.

[0084] The selection of the cooling pump energy level transition, the cooling repump energy level transition, the pump energy level transition and the target energy level transition needs to be specifically considered according to the type of alkali metal atom and the target wavelength of the required optical frequency standard signal, and meanwhile, the combination of the cooling pump energy level transition and the cooling repump energy level transition needs to ensure that the atom cannot be accumulated in a certain state to realize the overall "cyclic transition" effect; the upper energy level of the cooling pump energy level transition and the cooling repump energy level transition cannot coincide with the lower energy level of the target energy level transition, otherwise it will be difficult to realize the population inversion of the target energy level.

[0085] The atom type contained in the saturated absorption spectrum device 10 is the same as that in the atomic cell 18.

[0086] The front window and the rear window of the atomic cell 18 constitute a resonant cavity, and the parameters of the resonant cavity are calculated to make the cavity mode line width much larger than the gain line width of the cesium atom in the atomic cell 18, that is, working in the bad cavity region.

[0087] The cold atom chip active optical clock further comprises a magnetic shielding module and a heating, temperature maintaining and temperature controlling module arranged outside the saturated absorption spectrum device 10, so as to isolate the influence of external magnetic field and temperature fluctuation on the transition frequency of the cesium atom and improve the frequency stabilization performance of the saturated absorption spectrum.

[0088] The cold atom chip active optical clock further comprises that the chip electro-optical modulator 11 is driven by a microwave signal generated by a driving chip.

[0089] The cold atom chip active optical clock further comprises that the Helmholtz coil magnetic shielding chamber 16 and the anti-Helmholtz coil 17 are connected to an adjustable current source circuit, which can control the current through each coil respectively.

[0090] In addition, the application also provides an implementation method of the chip active optical clock based on the grating magnetic optical trap cooling, which is implemented according to the foregoing device and comprises the following steps:

[0091] Step S1: the first DBR laser 1 adjusts its frequency to be equal to the 6S 1 / 2→ 6P 3 / 2 resonance, and sweep it, adjust the first beam adjusting device 3 to make part of the output laser enter the saturated absorption spectrum device 10, the saturated absorption spectrum electric signal generated is fed back to the first laser controller 2, which is used to lock the frequency of the 852nm cooling laser on the cesium atom 6S 1 / 2 (F=4)→6P 3 / 2 (F'=5) cooling pump energy level transition;

[0092] Step S2: the second DBR laser 4 adjusts its frequency with the cesium atom 6S 1 / 2 → 6P 3 / 2 resonance, and sweep it, adjust the second beam adjusting device 6 to make part of the output laser enter the saturated absorption spectrum device 10, the saturated absorption spectrum electric signal generated is fed back to the second laser controller 5, which is used to lock the frequency of the 852nm re-pumping laser on the cesium atom 6S 1 / 2 (F=3)→6P 3 / 2 (F'=4) cooling re-pumping energy level transition;

[0093] Step S3: the third DBR laser 7 adjusts its frequency with the cesium atom 6S 1 / 2 → 7P 3 / 2 resonance, and sweep it, adjust the third beam adjusting device 9 to make part of the output laser enter the saturated absorption spectrum device 10, the saturated absorption spectrum electric signal generated is fed back to the second laser controller 5, which is used to lock the frequency of the 455nm pump laser on the cesium atom 6S 1 / 2 (F=4)→7P 3 / 2 (F''=3) pump energy level transition;

[0094] Step S4: adjust the microwave drive signal loaded on the chip electro-optic modulator 11, so that the cooling laser passing through the chip electro-optic modulator 11 produces a constant-10MHz red detuning;

[0095] Step S5: the frequency-shifted cooling laser and re-pumping laser are combined on the first polarization beam splitter prism 12 to produce cooling, re-pumping mixed laser;

[0096] Step S6: the cooling, re-pumping mixed laser passes through the beam expander lens 13 and the collimating lens 14 to expand the diameter of the light beam, so that the cross-sectional area of the light beam can roughly cover the entire surface of the grating chip 19, thereby improving the cooling efficiency;

[0097] Step S7: the cooling, re-pumping mixed laser enters the atom cell 18 from the side of the two windows parallel to the atom cell 18, due to the Doppler effect, the cesium atoms with a certain speed moving towards the photons of the red-detuned cooling laser will absorb the photons, completing the cooling pump energy level transition from 6S1 / 2 (F=4) state to 6P 3 / 2 (F'=5) state; then drop to 6S by spontaneous emission 1 / 2 (F=4) state and 6S 1 / 2 (F=3) state; according to momentum conservation, the cesium atom absorbing a counter-moving photon will be decelerated, while the direction of the velocity of the spontaneously emitted photon is random, i.e. in statistics, the change of the velocity of the spontaneously emitted photon is zero, thus the overall effect of the deceleration of the cesium atom;

[0098] Step S8: the cesium atom in 6S 1 / 2 (F=3) state is excited by the re-pumping laser, completing the cooling re-pumping energy level transition to 6P 3 / 2 (F'=4) state, and returning to 6S by spontaneous emission 1 / 2 (F=4) state, thus preventing the accumulation of the cesium atom in 6S 1 / 2 (F=3) state, weakening the effect of the cooling laser;

[0099] Step S9: adjust the current through the Helmholtz coil magnetic shielding chamber 16 to make the magnetic field strength inside it zero, avoiding the interference of external magnetic field;

[0100] Step S10: apply appropriate current to the anti-Helmholtz coil 17, and the current directions of the two coils are opposite, thus forming the required non-uniform magnetic field in the atomic gas chamber 18;

[0101] Step S11: the cooling and re-pumping mixed laser transmits through the atomic gas chamber 18, and is vertically incident on the surface of the grating chip 19, generating three beams of positive tetrahedron-shaped cooling and re-pumping diffracted light, which together with the incident laser form the trap light, and the intersection of the trap light is located at the center point of the atomic gas chamber 18;

[0102] Step S12: the cesium atom in the atomic gas chamber 18 is located in the non-uniform magnetic field generated by the anti-Helmholtz coil 17, and for different positions of the atom, the shift amount of the Zeeman sub-energy level is different, and the detuning amount of the cooling laser is also different. At the same time, according to the selection rule, the magnetic quantum number of the excited state Zeeman sub-energy level has a requirement for the spin direction of the absorbed circularly polarized photon. When the cesium atom deviates from the center point of the atomic gas chamber 18, it will selectively absorb more photons moving towards the center point, and continuously receive a force towards the center point, thus achieving the effect of further capturing and trapping the decelerated cesium atom, and finally forming a cold atom group at the center point;

[0103] Step S13: the 455nm pumping laser generated by the third DBR laser 7 vertically transmits through the front window of the atomic gas chamber 18, enters the resonant cavity, and irradiates on the cold atom group, pumping the cesium atom in the cold atom group from 6S 1 / 2 state to 7P 3 / 2state, complete the pump energy level transition; 7P 3 / 2 state, drop to 7S 1 / 2 state by spontaneous emission, and finally establish the population inversion between the target energy levels of cesium atom 7S 1 / 2 state and 6P 1 / 2 state, and complete the target energy level transition by spontaneous emission to generate a 1359nm fluorescence signal;

[0104] Step S14: under the gain of the cold atom group, under the enhancement of the resonant cavity composed of the front window and the rear window of the atomic cell 18, and when the 455nm pump light power reaches a suitable value, the gain of the 1359nm fluorescence signal is greater than the loss, and the 1359nm stimulated radiation signal light is realized;

[0105] Step S15: the 1359nm stimulated radiation signal light is output from the rear window of the atomic cell 18 as the optical frequency standard signal of the active optical clock;

[0106] Step S16: the optical frequency standard signal is combined with the comb tooth optical signal generated by the microcavity optical comb 20 in the second polarization beam splitter prism 21 to generate a beat frequency optical signal;

[0107] Step S17: the beat frequency optical signal enters the second thin film photoelectric detector 22, is converted into a beat frequency electrical signal, is input into the digital frequency counter 23, and after a series of digital operations, outputs a time signal, realizing the chip active optical clock.

[0108] Among them, the method further comprises: the atomic type in the saturable absorption spectrum device 10 and the atomic cell 18 can be changed to rubidium atoms; the frequency shift amount of the chip electro-optical modulator to the cooling laser can be changed to-12MHz; the cooling laser of the first DBR laser 1 can be changed to 780nm and locked to the 5S 1 / 2 (F=2)→5P 3 / 2 (F’=3) cooling pump energy level transition frequency; the re-pumping laser of the second DBR laser 4 can be changed to 780nm and locked to the 5S 1 / 2 (F=1)→5P 3 / 2 (F’=2) cooling re-pumping energy level transition frequency; the pump laser of the third DBR laser 7 can be changed to 421nm and locked to the 5S 1 / 2 (F=3)→6P 1 / 2 (F”=2) pump energy level transition frequency, so as to cool the rubidium atoms in the atomic cell 18, form a cold atom group, and establish the population inversion between the target energy levels of the rubidium atom 6S 1 / 2 state and 5P 1 / 2The process involves achieving population inversion between the two target energy levels, completing the target energy level transition through spontaneous emission, and outputting an optical frequency standard signal with a center wavelength of 1324nm, thus realizing the active optical clock of the cold atom chip.

[0109] The following is a detailed description with reference to specific embodiments.

[0110] Example

[0111] In this embodiment, as Figure 1 As shown, a quantum thermometer based on active lasing includes: a first DBR laser 1, a second DBR laser 4, a third DBR laser 7, a first laser controller 2, a second laser controller 5, a third laser controller 8, a first beam adjustment device 3, a second beam adjustment device 6, a third beam adjustment device 9, a saturated absorption spectrum device 10, a chip electro-optic modulator 11, a first polarization beam splitter 12, a beam expander lens 13, a collimating lens 14, a λ / 4 waveplate 15, a Helmholtz coil magnetic shielding chamber 16, a Helmholtz coil 17, an atomic gas chamber 18, a grating chip 19, a microcavity optical comb 20, a second polarization beam splitter 21, a thin-film photodetector 22, and a frequency counter 23.

[0112] The first DBR laser 1, the second DBR laser 4, and the third DBR laser 7 are used to generate an 852nm cooling laser, an 852nm re-pumped laser, and a 455nm pump laser, respectively. The first beam adjustment device 3, the second beam adjustment device 6, the third beam adjustment device 9, and the saturable absorption spectrum device 10 are used to generate three saturable absorption spectrum electrical signals, which are fed back to the first laser controller 2, the second laser controller 5, and the third laser controller 8, respectively, to achieve saturable absorption spectrum frequency stabilization. The chip electro-optic modulator 11 is used to generate a -10MHz red detuning for the cooling laser. The first polarization beam splitter prism 12 is used to combine the cooling laser and the re-pumped laser beam. The beam expander lens 13 and the collimating lens 14 are used to expand the cooling... The beam diameter of the re-pumped hybrid laser is adjusted while maintaining the beam as parallel light. The Helmholtz coil magnetic shielding chamber 16 is used to cancel the external environmental magnetic field, the anti-Helmholtz coil 17 is used to generate a non-uniform magnetic field, the atomic gas chamber 18 is used to contain cesium atoms, which form cold atom clusters under the action of the magneto-optical trap, the dielectric films on the front and rear windows form a resonant cavity, amplify the 1359nm fluorescence signal to generate an optical frequency standard signal, the grating chip 19 is used to generate trap light, the microcavity optical comb 20 is used to generate comb tooth signals, the second polarization beam splitter 21 is used to perform beat frequency down-conversion between the optical frequency standard signal and the comb tooth signal, the thin film photodetector 22 is used to detect the beat frequency optical signal, and the digital frequency counter 13 is used to read the beat frequency and process the output clock signal.

[0113] like Figure 2(a) As shown in the energy level diagram of cesium atom, the first DBR laser 1 outputs 852nm red-detuned cooling laser, and the cesium atom with a certain speed in the atom cell 18 is excited from 6S 1 / 2 (F=4) state to 6P 3 / 2 (F'=5) state and decelerated; the second DBR laser 4 outputs 852nm repump laser, and the cesium atom is prevented from gathering in 6S 1 / 2 (F=3) state; under the action of magneto-optical trap, the cold atom group is formed in the center of the atom cell 18, the third DBR laser 7 outputs 455nm pump laser, and the cesium atom in the cold atom group is pumped to 7P 3 / 2 state, and the population inversion is established between 7S 1 / 2 state and 6P 1 / 2 state, the medium film on the front and back windows of the atom cell 18 has optical feedback to 1359nm laser, the power of the pump laser is adjusted, when the gain is greater than the loss, the stimulated radiation is realized, and the optical frequency marker signal corresponding to the 1359nm transition of the cesium atom is output from the back window.

[0114] Another embodiment of the present application is that the saturated absorption spectrum device 10 in the above embodiment and the atom type in the atom cell 18 are replaced by rubidium atom, the red-detuned amount of the cooling laser generated by the chip electro-optical modulator 11 is changed to -12MHz, the cooling laser of the first DBR laser 1 is changed to 780nm and is locked to the 5S 1 / 2 (F=2)→5P 3 / 2 (F'=3) transition of the rubidium atom, the repump laser of the second DBR laser 4 is changed to 780nm and is locked to the 5S 1 / 2 (F=1)→5P 3 / 2 (F'=2) transition of the rubidium atom, the pump laser of the third DBR laser 7 is changed to 421nm and is locked to the 5S 1 / 2 (F=3)→6P 1 / 2 (F''=2) transition of the rubidium atom, and meanwhile, the front and back windows of the atom cell 18 are composed of medium film and have optical feedback ability to 1324nm wavelength. The energy level diagram of the rubidium atom is shown in Figure 2 (b), from the energy level diagram, the red-detuned cooling laser excites the rubidium atom in 5S 1 / 2 (F=2) state to 5P 3 / 2 (F'=3) state and decelerates, the repump laser prevents the rubidium atom from gathering in 5S 1 / 2 (F=1) state, the pump laser pumps the rubidium atom in the cold atom group to 6P 1 / 2 state, and the population inversion is established between 6S 1 / 2 state and 5P 1 / 2The population inversion between the states is established, the resonant cavity provides optical feedback for the 1324nm laser, the power of the pump laser is adjusted, when the gain is greater than the loss, the stimulated radiation is realized, and the optical frequency standard signal corresponding to the 1324nm transition of rubidium atom is output from the rear window. Other techniques and methods are consistent with the embodiment of the cold atom chip active optical clock based on cesium atom 1359nm optical frequency standard.

[0115] The current and temperature of the first DBR laser 1, the second DBR laser 4 and the third DBR laser 7 are adjusted by the first laser controller 2, the second laser controller 5 and the third laser controller 8, so that the output frequency of the first DBR laser 1, the second DBR laser 4 and the third DBR laser 7 is adjusted.

[0116] The power of the pump laser is adjusted by adjusting the angle of the half-wave plate in the third beam adjusting device 9.

[0117] The parameters of the resonant cavity composed of the front and rear window medium films of the atomic cell 18 need to be calculated, so that the cavity mode linewidth is much larger than the gain linewidth of the atoms in the atomic cell 18, that is, the optical clock works in the bad cavity region.

[0118] The Helmholtz coil magnetic shielding chamber 16 and the anti-Helmholtz coil 17 are connected to an adjustable current source circuit, which can adjust the current through each coil, so as to shield the external environment magnetic field in the atomic cell 18, and at the same time generate the non-uniform magnetic field required by the grating magnetic optical trap.

[0119] The above is only the preferred embodiment of the present application, in addition to cesium atom as gain medium, the application of the present application can also be extended to rubidium atom, potassium atom and other alkali metal atoms. For ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can also be made, which should be considered as the protection scope of the present application.

Claims

1. A chip active optical clock based on grating magneto-optical trap cooling, characterized in that, The first laser (1), the second laser (4), the third laser (7), the saturated absorption spectrum device (10), the anti-Helmholtz coil (17), the atomic gas chamber (18), the microcavity optical comb (20), the second polarization beam splitter prism (21), the thin film photodetector (22), the frequency counter (23); The grating chip (19) is arranged in the atomic gas chamber (18); the atomic gas chamber (18) is filled with atoms as a gain medium, the atoms filled in the atomic gas chamber (18) are determined according to a target wavelength of an optical frequency standard signal, and corresponding cooling pump energy level transitions, cooling heavy pump energy level transitions, pump energy level transitions and target energy level transitions are selected; The laser generated by the first laser (1) is divided into two beams by the first beam adjusting device (3), one of which is used as a cooling laser and is incident on the first polarization beam splitter prism (12) through the chip electro-optical modulator (11), and the other of which is used for saturated absorption spectrum frequency stabilization and is input into the saturated absorption spectrum device (10); the frequency of the cooling laser corresponds to the frequency of the cooling pump energy level transition; The laser generated by the second laser (4) is divided into two beams by the second beam adjusting device (6), one of which is used as a heavy pump laser and is incident on the first polarization beam splitter prism (12), and the other of which is used for saturated absorption spectrum frequency stabilization and is input into the saturated absorption spectrum device (10); the frequency of the heavy pump laser corresponds to the frequency of the cooling heavy pump energy level transition; The laser generated by the third laser (7) is divided into two beams by the third beam adjusting device (9), one of which is used as a pump laser and is incident on the atomic gas chamber (18) along a first direction, and the other of which is used for saturated absorption spectrum frequency stabilization and is input into the saturated absorption spectrum device (10); the frequency of the pump laser corresponds to the frequency of the pump energy level transition; The chip electro-optical modulator (11) is used for red detuning of the frequency of the cooling laser; The first polarization beam splitter prism (12) is used for combining the cooling laser and the heavy pump laser, generating cooling and heavy pump mixed laser, and adjusting the cooling and heavy pump mixed laser into circular polarization through the λ / 4 wave plate (15) to be incident on the atomic gas chamber (18) along a second direction; The anti-Helmholtz coil (17) is used for generating a non-uniform magnetic field in the grating magnetic optical trap, so that the energy levels of the gain medium in the atomic gas chamber (18) are subjected to Zeeman splitting; Both windows of the atomic gas chamber (18) along the first direction are coated with a medium film which has high transmittance to the cooling and heavy pump mixed laser and a certain reflectivity to the target wavelength, forming a resonant cavity; the cooling laser and the heavy pump laser cooperate with the grating magnetic optical trap to cool and confine atoms, forming a cold atom group; the pump laser is used for exciting the cold atoms to realize population inversion between target energy levels, so that target energy level transitions occur, and the target wavelength of the stimulated emission signal is output as an optical frequency standard signal; The surface of the grating chip (19) is etched with a diffraction grating structure, which is used for diffracting the incident cooling and heavy pump mixed laser to generate three beams of cooling and heavy pump diffracted light with a positive tetrahedral structure, and the polarization rotation directions of the three beams are opposite to that of the incident laser, and the three beams and the incident laser form a trap light; The microcavity optical comb (20) is used for generating comb tooth optical signals. The second polarization beam splitter prism (21) is used for combining the optical frequency standard signal and the comb optical signal to generate a beat optical signal; The thin film photodetector (22) is used for receiving the beat optical signal and converting it into a beat electrical signal; The frequency counter (23) is used for processing the beat electrical signal and outputting a clock signal to realize a chip active optical clock; The atoms in the saturated absorption spectrum device (10) interact with the incident laser beams of the first light beam adjusting device (3), the second light beam adjusting device (6) and the third light beam adjusting device (9), generate saturated absorption spectrum optical signals, and convert the saturated absorption spectrum optical signals into electrical signals, which are fed back to the first laser controller (2), the second laser controller (5) and the third laser controller (8) as frequency references respectively; The first laser controller (2) is used for controlling the output frequency of the first laser (1) according to the received saturated absorption spectrum electrical signal; the second laser controller (5) is used for controlling the output frequency of the second laser (4) according to the received saturated absorption spectrum electrical signal; and the third laser controller (8) is used for controlling the output frequency of the third laser (7) according to the received saturated absorption spectrum electrical signal.

2. The chip active optical clock according to claim 1, wherein, The gain medium is cesium atoms, the target energy level transition is 7S 1 / 2 state to 6P 1 / 2 state, the pump energy level transition is 6S 1 / 2 state to 7P 3 / 2 state, the cooling heavy pump energy level transition is from 6S 1 / 2 (F=3) to 6P 3 / 2 (F'=4), the cooling pump energy level transition is from 6S 1 / 2 (F=4) to 6P 3 / 2 (F'=5), the first laser controller (2) locks the output frequency of the first laser (1) at the transition frequency of the cesium atom 6S 1 / 2 (F=4) to 6P 3 / 2 (F'=5), the second laser controller (5) locks the output frequency of the second laser (4) at the transition frequency of the cesium atom 6S 1 / 2 (F=3) to 6P 3 / 2 (F'=4), the third laser controller (8) locks the output frequency of the third laser (7) at the transition frequency of the cesium atom 6S 1 / 2 (F=4) to 7P 3 / 2 (F"=3).

3. The chip active optical clock of claim 1, wherein, The resonant cavity works in a bad cavity region.

4. The chip active optical clock according to claim 1 or 2 or 3, characterized in that, The incident laser beams of the first light beam adjusting device (3), the second light beam adjusting device (6) and the third light beam adjusting device (9) enter the saturated absorption spectrum device (10) in three different directions respectively.

5. The chip active optical clock according to claim 1 or 2 or 3, characterized in that, The cooled and repumped mixed laser generated by the first polarization beam splitter prism (12) is expanded by the expansion lens (13) and collimated by the collimation lens (14) and then enters the λ / 4 wave plate (15).

6. The chip active optical clock according to claim 1 or 2 or 3, wherein, The outside of the atomic cell (18) is provided with a Helmholtz coil magnetic shielding chamber (16) for offsetting the magnetic field of the external environment and avoiding the influence of the interference of the external magnetic field on the non-uniform magnetic field in the grating magneto-optical trap on the cooling effect.

7. The chip active optical clock of claim 1, wherein, The first direction is perpendicular to the second direction; the intersection of the trap light is located at the center of the atomic cell (18) and cooperates with the non-uniform magnetic field generated by the anti-Helmholtz coil (17) to form a cold atom group at the center of the atomic cell (18).

8. An implementation method based on the chip active optical clock of claim 1, which comprises the following steps: 1) The laser output by the first laser (1) controlled by the first laser controller (2) is divided into two beams by the first light beam adjusting device (3), one of which is used as a cooling laser and enters the first polarization beam splitter prism (12) through the chip electro-optical modulator (11), and the other of which is used for saturated absorption spectrum frequency stabilization and input into the saturated absorption spectrum device (10); the frequency of the cooling laser corresponds to the frequency of the cooling pump level transition; 2) The laser output by the second laser (4) controlled by the second laser controller (5) is divided into two beams by the second light beam adjusting device (6), one of which is used as a repumping laser and enters the first polarization beam splitter prism (12), and the other of which is used for saturated absorption spectrum frequency stabilization and input into the saturated absorption spectrum device (10); the frequency of the repumping laser corresponds to the frequency of the cooling repumping level transition; 3) The laser output from the third laser (7) is controlled by the third laser controller (8) and split into two beams by the third beam adjustment device (9). One beam is used as a pump laser and incident into the photoatomic gas cell (18) along the first direction. The other beam is used for saturated absorption spectrum frequency stabilization input to the saturated absorption spectrum device (10). The frequency of the pump laser corresponds to the frequency of the pump energy level transition. 4) Adjust the microwave drive signal loaded on the chip electro-optic modulator (11) to cause the cooling laser passing through the chip electro-optic modulator (11) to produce red detuning; 5) The frequency-shifted cooled laser and the re-pumped laser are combined on the first polarization beam splitter (12) to generate a cooled and re-pumped mixed laser, which is then adjusted to circular polarization by the λ / 4 waveplate (15) and incident into the atomic gas cell (18) along the second direction. 6) The cooling laser and the re-pumping laser work together with the grating magneto-optical trap to cool and trap atoms, forming cold atom clusters; the pump laser excites the cold atoms to complete the pump level transition, resulting in population inversion at the target level, causing the target level transition, and generating the stimulated emission signal of the target wavelength as the optical frequency standard signal output. 7) The second polarizing beam splitter (21) combines the optical frequency standard signal with the comb light signal generated by the microcavity optical comb (20) to generate a beat frequency light signal; 8) The thin-film photodetector (22) converts the beat frequency optical signal into a beat frequency electrical signal, inputs it into the digital frequency counter (23) for processing, and outputs a time signal to realize the chip active optical clock.

9. The method of claim 8, wherein, The incident laser beams from the first beam adjustment device (3), the second beam adjustment device (6), and the third beam adjustment device (9) enter the saturated absorption spectrum device (10) from three different directions.

10. The method of claim 8, wherein, The first direction is perpendicular to the second direction; the intersection of the trap light is located at the center of the atomic gas chamber (18), and in conjunction with the non-uniform magnetic field generated by the anti-Helmholtz coil (17), a cold atom cluster is formed at the center of the atomic gas chamber (18).

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