CN113162621A - Precise frequency spectrum reference output method and atomic clock - Google Patents
Precise frequency spectrum reference output method and atomic clock Download PDFInfo
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/26—Automatic control of frequency or phase; Synchronisation using energy levels of molecules, atoms, or subatomic particles as a frequency reference
Abstract
The invention provides an atomic clock for precise frequency spectrum reference output, which comprises: a spectral lamp having an active metal gas therein for generating an excitation light signal; the optical filter is arranged at one end of the spectrum lamp and can adjust the light intensity of the exciting light signal; the high-frequency oscillator is used for generating oscillation excitation frequency and providing pumping energy for the spectrum lamp; the filter resonance bulb is filled with active metal gas which is the same as that of the spectrum lamp and provides a microwave magnetic field for the spectrum lamp, so that the active metal gas in the filter resonance bulb and an excitation light signal generated by the spectrum lamp are subjected to resonance amplification to generate a resonance transition frequency light signal and are converted into an electric signal; and the microprocessor is used for detecting and acquiring the electric signal and outputting a reference frequency.
Description
Technical Field
The invention relates to an atomic clock and frequency standard technology, in particular to a precision frequency spectrum reference output method and an atomic clock.
Background
The precision time is a basic physical parameter in aspects of scientific research, scientific experiments and engineering technology, and has important functions in the field of basic research, such as earth dynamics research such as earth rotation change, relativity theory research, pulsar period research, artificial satellite dynamics geodesic research and the like; but also has common application in application research, national defense and national economy construction, such as aerospace, deep space communication, satellite launching and monitoring, information highway, geological mapping, navigation communication, power transmission, scientific measurement and the like; even the method has gone deep into the social life of people, and is almost not good.
Since 1963, the time reference name was replaced by PRIMARY CLOCK, which refers to a laboratory cesium CLOCK. In view of published data, federal "federal technical materialThe accuracy of PTB-CsI of the research institute ", NBS-6 of the national Bureau of standards and NRC-CsV of the national institute of Canada has reached 10-14Magnitude. CsII and CsIII of China metering institute also reach 10-13Magnitude. It can be seen that the accuracy of the PRIMARY CLOCK is at least an order of magnitude higher than the commercial cesium CLOCK. For the first-class time standard of the cesium clock, only a few countries of the world have time-frequency laboratories, and some of the time-frequency laboratories cannot work reliably for a long time. However, most laboratories around the world that do not have a large cesium clock may also have their own timescale. The method comprises the following steps: using a plurality of commercial cesium clocks (the accuracy of the current 5071A small cesium clock is 1 multiplied by 10-12) Constituting an average time scale. The more small cesium clocks a laboratory has, the better the stability of the time scale. The time scale with high stability is provided, so that the requirements of national defense, scientific research, aerospace and other aspects can be met, and along with the high-speed development of atomic time and frequency ratio on precision, relativity to clock correction has theoretical significance, and correction must be carried out in actual comparison.
Disclosure of Invention
The invention provides an atomic clock for precise frequency spectrum reference output.A magnetic hyperfine component optical filter is arranged at one end of a spectrum lamp, so that the light intensity of the spectrum lamp can be controlled, the spectral line shape of pumping light is improved, the spectral line shape of the pumping light is completely symmetrical around the central frequency, and the generation of light frequency shift can be further reduced.
It is still another object of the present invention to provide a method for outputting a precision frequency spectrum reference, in which a phase adjustment module is added to perform phase adjustment to improve the precision of the output reference frequency.
The technical scheme provided by the invention is as follows:
an atomic clock for a precision spectral reference output, comprising:
a spectral lamp having an active metal gas therein for generating an excitation light signal;
the optical filter is arranged at one end of the spectrum lamp and can adjust the light intensity of the exciting light signal;
the high-frequency oscillator is used for generating oscillation excitation frequency and providing pumping energy for the spectrum lamp;
the filter resonance bulb is filled with active metal gas which is the same as that of the spectrum lamp and provides a microwave magnetic field for the spectrum lamp, so that the active metal gas in the filter resonance bulb and an excitation light signal generated by the spectrum lamp are subjected to resonance amplification to generate a resonance transition frequency light signal and are converted into an electric signal;
and the microprocessor is used for detecting and acquiring the electric signal and outputting a reference frequency.
Preferably, the spectrum lamp also comprises inert gas which is mixed with the active metal gas;
wherein the active metal gas is rubidium gas.
Preferably, the inert gas is krypton and/or argon.
Preferably, the optical filter is a magnetic hyperfine component optical filter, and the optical filter has an optical transmittance of 70%.
Preferably, the high frequency oscillator employs a square wave excitation oscillator circuit.
Preferably, the filter resonance bubble includes:
a resonant cavity for providing a microwave magnetic field;
a photocell for converting an optical signal carrying resonance transition information into an electrical signal;
and the temperature control component is arranged on the resonant cavity and can control the temperature of the resonant cavity.
Preferably, the method further comprises the following steps:
a DDS module which is connected with the microprocessor in a serial communication mode, can receive a frequency synthesis instruction sent by the video microprocessor and generates a direct digital frequency synthesis modulation signal by taking an external clock as a reference source;
the synchronous phase demodulation module is used for acquiring difference information between the frequency of the microwave interrogation signal and the quantum reference frequency, returning the difference information to the microprocessor and outputting a reference frequency signal;
a phase adjustment module capable of phase adjusting the microwave interrogation signal frequency and the quantum reference frequency to improve the accuracy of the reference frequency signal.
A method of fine spectral reference output, comprising:
placing the spectrum lamp in an oscillating circuit of a high-frequency oscillator;
setting the oscillation frequency and power of the high-frequency oscillator to ionize inert gas and active metal gas in the spectrum lamp, enabling metal atoms to absorb energy to generate energy level transition by collision of inert gas molecules and the metal atoms, radiating photons and further generating an excitation light signal;
setting the filtering resonance bubble to be at a constant temperature, enabling two coherent microwave pulses with a certain time interval to act on the filtering resonance bubble so as to enable active metal gas in the filtering resonance bubble to resonate and amplify with an excitation light signal generated by the spectrum lamp to generate a resonance transition frequency light signal, and converting the resonance transition frequency light signal into an electric signal through a photocell;
the microprocessor transmits a 79Hz key control frequency modulation signal to the DDS module;
the DDS module receives the 79Hz keying frequency modulation signal of the microprocessor, generates an 5.3125MHz +/-Delta f comprehensive modulation signal synthesized by direct digital frequency by taking an external clock as a reference source, outputs a 5.3125MHz + Delta f and 5.3125 MHz-Delta f comprehensive modulation signal after frequency synthesis by taking 79Hz as a frequency period keying output, wherein the size of Delta f is determined by the specific line width of an atomic frequency standard physical system;
the comprehensive modulation signal is subjected to microwave multiplication and frequency mixing to generate a microwave interrogation signal of 6834.6875MHz + delta f to act on a physical system, and a physical system frequency discrimination signal is generated after the quantum frequency discrimination of the physical system;
the physical system phase frequency discrimination signal and the comprehensive modulation signal are subjected to phase adjustment through the phase adjustment module and then sent to the synchronous phase discrimination module to be subjected to synchronous phase discrimination to generate a synchronous phase discrimination signal, and a reference frequency signal is output.
Preferably, the oscillation frequency of the oscillation circuit is set to 100MHz, and the power is set to 1-5W.
Preferably, the method further comprises the following steps: and setting a sampling area for the synchronous phase discrimination signal, and carrying out N times of sampling averaging to reduce the influence of level jitter on the synchronous phase discrimination.
Advantageous effects
The invention provides an atomic clock for precise frequency spectrum reference output.A magnetic hyperfine component optical filter is arranged at one end of a spectrum lamp, so that the light intensity of the spectrum lamp can be controlled, the spectral line shape of pumping light is improved, the spectral line shape of the pumping light is completely symmetrical around the central frequency, and the generation of light frequency shift can be further reduced.
The invention also provides a precision frequency spectrum reference output method, and a phase adjustment module is added for phase adjustment so as to improve the precision of the output reference frequency.
Drawings
Fig. 1 is a schematic structural diagram of an atomic clock for precision spectrum reference output according to the present invention.
Fig. 2 is a schematic diagram of a high frequency oscillator according to the present invention.
Fig. 3 is an equivalent schematic diagram of the high-frequency oscillator according to the present invention.
FIG. 4 shows a transistor threshold level V according to the present inventionBEOGraph with temperature T.
FIG. 5 is an experimental graph of temperature versus light intensity for an integrated filter resonance bulb according to the present invention.
FIG. 6 shows a schematic view of the present invention87Rb atomic energy level transition diagram.
Figure 7 is a schematic diagram of optical pumping according to the present invention.
Fig. 8 is a schematic circuit diagram of the pulsed pumping light generation according to the present invention.
FIG. 9 is a schematic diagram of an integrated servo module according to the present invention.
Fig. 10 is a waveform diagram of a frequency discriminated output lock signal of a physical system according to the present invention.
Fig. 11 is a schematic diagram of a synchronous phase detection according to the present invention.
Fig. 12 is a schematic diagram of the phase-adjusted synchronous phase detection according to the present invention.
Detailed Description
The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that in the description of the present invention, the terms "in", "upper", "lower", "lateral", "inner", etc. indicate directions or positional relationships based on those shown in the drawings, which are merely for convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Furthermore, it should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; may be a mechanical connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
As shown in fig. 1, based on the technical problem of the background art, the present invention provides an atomic clock for precision spectrum reference output, including: spectrum lamp, optical filter, high frequency oscillator, filter resonance bubble and microprocessor.
The spectrum lamp is internally provided with active metal gas for generating an exciting light signal; preferably, the active metal gas is metal rubidium or metal cesium;
the light source bulb is commonly provided with a spherical glass bulb, and the diameter of the spherical glass bulb is about 10-15 mm. Besides rubidium metal, the bulb is also filled with a starting gas with low excitation potential and inactive chemical properties. Kr or Ar is usually used, and the gas pressure is 1-2 Torr.
As shown in fig. 2-3, a high frequency oscillator for generating an oscillation excitation frequency to provide pumping energy for the spectrum lamp; as shown in FIG. 2, the spectrum lamp exciting circuit is a Krarson oscillating circuit, and its AC equivalent circuit is shown in FIG. 3, where L3I.e. the driver coil inductance, and Cec is the inter-electrode capacitance between the transistors c, e. The oscillation frequency can be calculated:
wherein the content of the first and second substances,
the circuit feedback coefficient is:
the luminous intensity of the spectrum lamp is determined by the excitation power, so that the spectrum lamp light intensity has a direct relation with the excitation current, and the oscillating excitation current is directly influenced by the parameters beta and I of the power tubeCBO、VBEOEtc. The theory and experiment prove that the transistor parameters beta and ICBO、VBEOHas close relation with the ambient temperature T. Wherein, ICBOFor reverse penetration current
The rate of change of β with temperature is: Δ β/Δ T ═ (1+ β)2×2×10-4/° c; transistor threshold level VBEOThe temperature-dependent change was: dVBEO/dT＝-2.5mv/℃。
As can be seen from FIG. 4, the transistor threshold level VBEOIn relation to the temperature T, as the temperature rises, at VBEOUnder the condition of smaller static operating point current IBQ. The three factors are combinedIt can be seen that as the ambient temperature increases, the excitation tube current ICCThe increase results in the increase of the excitation power and the increase of the light intensity; conversely, the light intensity decreases, and the higher the oscillation frequency, the smaller the required excitation power, and the lower the oscillation frequency, the larger the required excitation power. A lamp is easily ignited when the excitation power is large, but the larger the excitation power, the shorter the lamp life. In addition, the excitation power is too high, the generated heat is too much, and the temperature of the lamp chamber is not easy to control. The excitation power is large, the high-frequency interference to other lines in the frequency scale is also large, and the high-frequency interference is not easy to eliminate. Therefore, in general, the lamp is operated with as little excitation power as possible under conditions that ensure stable operation of the lamp, in the present embodiment the lamp bulb is placed in an oscillating coil of a high-frequency oscillator, the oscillating frequency being selected to be 100MHz and the power being 1-5W.
The high-frequency electric field accelerates a small amount of ions and electrons originally existing in the starting gas to increase kinetic energy, so that the ions and the electrons collide with the starting gas molecules to generate more ions and electrons, and the ions or the electrons with higher kinetic energy collide with the starting gas molecules to excite the starting gas molecules to an excited state. The glow-initiating gas molecules are seen to emit light when it returns to the ground state. However, if the excited starting gas molecules collide with rubidium atom molecules, the excited energy can be transferred to the rubidium atoms, and the rubidium atoms return to the ground state without radiation, so that the rubidium atoms are excited to the excited state. The rubidium atoms are seen to emit light when they return from an excited state to a ground state. When the temperature of the bulb is extremely low and the density of rubidium atoms is low, only the glow-starting gas molecules are often seen to emit light. Under the conditions of high temperature of the bulb and high density of rubidium atoms, the rubidium atoms have absolute advantages in light emission, and at the moment, only the rubidium atoms are seen to emit light, but the starting gas molecules cannot be seen to emit light. In the case of transitions of the two light-emitting processes, it is often observed that the two light-emitting processes occur alternately: the light-emitting material mainly starts to emit light by gas molecules after a while, and mainly emits light by rubidium atoms after a while. This phenomenon is called relaxation oscillation, and oscillation frequencies from a few tenths of hertz to several kilohertz are possible. In order to obtain stable pumping light, the entire lamp chamber, including the lamp bulb and the oscillator circuit, should be thermostatted to control the temperature at which the rubidium atoms stably emit light.
The optical filter is arranged at one end of the spectrum lamp and can adjust the light intensity of the exciting light signal;
the spectral lamp has long-term operation, and due to the change of the operating state, the interior of the bulb87Factors such as Rb consumption and the like, and the light intensity changes, influence the stability index of the system.
As shown in fig. 5, through experiments, it can find out the parameters of the complete machine output frequency insensitive to the light intensity, and consider the selection of the light intensity and the temperature selection of the integrated filter resonance bubble together, and select the proper bubble temperature to minimize the light frequency shift. During the experiment, the required zero-light-intensity frequency shift bubble temperature is obtained by changing the temperature of the integrated filtering resonance bubble and measuring the output of the whole machine frequency under different light intensities.
The frequency curve of the whole machine measured by changing the light intensity cannot be completely intersected at one point, often in a small triangular area, so that the influence of the light frequency shift on the stability cannot be completely eliminated. Under the condition of selecting the optimal temperature of the integrated filter resonance bubble, the influence of the light intensity on the frequency can be 1 multiplied by 10–121%, i.e. a 1% change in light intensity, causes a 1 × 10 change in frequency–12. Of course, the degree of influence of the light intensity on the frequency varies from system to system, and also varies for the same system operating in different states. Because of pumping light with different sizes and the same spectral line type, the difference frequency value change caused by the cavity temperature change is different, the slope of the 70% light intensity curve in the analysis and selection graph is smaller than that of the 100% light intensity curve, namely the 70% light intensity is used as better slope light intensity,
in this embodiment, a magnetic hyperfine component filter is added at the rear stage of the emission light path of the spectral lamp, and different filters are selected, so that the light intensity of the spectral lamp required in the above theory can be controlled, and more importantly, the spectral line shape of the pumping light can be improved, so that the spectral line shape of the pumping light is completely symmetrical around the center frequency, and the generation of light frequency shift can be further reduced.
The filtering resonance bubble comprises a photocell, a temperature control component and a photocell, wherein the filtering resonance bubble is filled with active metal gas which is the same as that of the spectrum lamp, and provides a microwave magnetic field for the spectrum lamp, so that the active metal gas in the filtering resonance bubble and an excitation light signal generated by the spectrum lamp are subjected to resonance amplification to generate a resonance transition frequency light signal, and the resonance transition frequency light signal is converted into an electric signal;
a resonant cavity for providing a microwave magnetic field; a photocell for converting an optical signal carrying resonance transition information into an electrical signal; and the temperature control component is arranged on the resonant cavity and can control the temperature of the resonant cavity.
As shown in figure 6 of the drawings,87the transition frequencies of two hyperfine energy levels in the ground state of Rb atomic energy level are about 6835MHz, and the first excited state has two fine structure energy levels 52P3/2And 52P1/2The hyperfine splitting of these two levels is smaller than the ground state, 840MHz (F3 and F0) and 430MHz (F2 and F1), respectively. Because the doppler spread is almost the same as this split value, the hyperfine structure of the excited state cannot be resolved. Thus, it is possible to provide87The transition line between the first excited and ground state of the Rb atom comprising only D1And D2Line two hyperfine structure components a line and b line. In the ground state, | F ═ 2, mF＝0>And | F ═ 1, mF＝0>The exact value of the transition frequency between these two energy levels is 6834.68XXXX MHz (external magnetic field H ═ 0), the last four digits being determined by the perturbations of the magnetic field and the buffer gas in the filter resonance module. This is the quantum discriminator reference frequency value.
As shown in fig. 7, the simplest87The Rb system is to be charged with87Rb glass bubble is placed in a microwave resonant cavity with magnetic field to adjust the resonant frequency of the cavity at87At the jump frequency of two hyperfine energy levels of the Rb ground state, when a microwave signal with the frequency of 6834.6875MHz is input, the microwave signal is obtained by a microwave detection device87Absorption line of Rb. The spectral line can be used as a frequency discrimination spectral line. But due to the gaseous state87Low Rb particle number density, | F ═ 2, mF＝0>And | F ═ 1, mF＝1>The distance between the two energy levels is small, and the difference between the numbers of particles at the two energy levels is very small at normal temperature, so that the absorption spectral line obtained by the device is very weak finally. And in the air bubble87Spectra due to movement and collision of Rb atomsThe line broadening is also large, which greatly affects the frequency stability of the frequency scale
Therefore, in the present embodiment, the filling of the filter resonance module with the buffer gas can greatly reduce the doppler broadening. The buffer gas to be introduced is generally an inert gas or87Rb atoms are used as non-inert gas for elastic collision. After the filtering resonance module is filled with buffer gas, the rubidium atoms have large chance of elastic collision with buffer gas molecules, the original movement direction and speed can be changed every time of collision, and the Doppler frequency shift can also be changed. The greater the number of collisions of each atom with a gas molecule over an observation period, the smaller the average frequency shift. Meanwhile, the buffer gas also prolongs the diffusion time of atoms to the bubble wall, and greatly reduces the effect of wall relaxation on line width.
Pumped to a base emission state by b-component pumping light87The Rb atom, which can return to the ground state by spontaneous emission, emits a photon during spontaneous emission, i.e., "resonance fluorescence". If the atoms return to the energy level of 1 in the ground state F during spontaneous emission, a photon of b-line frequency is emitted, which is not detrimental to the optical pumping effect. However, if the atom returns to an energy level of 2, the ground state F, upon spontaneous emission, radiates an a-line photon. It is clear that the presence of such a photon causes an atom in the ground state F-2 level to be excited into an excited state, thereby destroying the optical pumping effect. But due to the presence of the buffer gas, the molecules of the buffer gas and87rb atoms collide to be in excited state87The Rb atoms transfer energy to the buffer gas molecules, thereby exciting the buffer gas molecules87The Rb atom returns to the ground state by itself without radiation. This process is "quenching of fluorescence". When the buffer gas molecules spontaneously radiate back to the ground state, the radiated photons are no longer at the frequency of the a-line, and thus the optical pumping effect is not damaged. So-called "excited state energy level intermixing", i.e. the buffer gas molecules are in an excited state with87Frequent collisions of Rb atoms so that87The probability that the Rb atom is at each energy level of the excited state is equal. Thus, when87When the Rb atom returns to the ground state, the probability of falling on each energy level of the ground stateAre equal.
And the microprocessor is used for detecting and acquiring the electric signal and outputting a reference frequency.
A DDS module which is connected with the microprocessor in a serial communication mode, can receive a frequency synthesis instruction sent by the video microprocessor and generates a direct digital frequency synthesis modulation signal by taking an external clock as a reference source;
the synchronous phase demodulation module is used for acquiring difference information between the frequency of the microwave interrogation signal and the quantum reference frequency, returning the difference information to the microprocessor and outputting a reference frequency signal;
a phase adjustment module capable of phase adjusting the microwave interrogation signal frequency and the quantum reference frequency to improve the accuracy of the reference frequency signal.
Pumping light pair87Energy level shift formula of Rb atom ground state:
wherein P is the electric dipole moment operator, E is the complex amplitude of the optical electric field, 1/gamma is | α > the lifetime of the excited state, EαAnd EiThe energies of the excited and ground states, respectively.
The optical frequency shift and the energy level shift have the following relationships:
from the above equation, the optical frequency shift is proportional to the optical intensity and related to the spectral profile. : if it is
The pumping light is monochromatic and just omega ═ omegaaiNo optical frequency shift is caused; if ω > ωaiIf yes, then a negative frequency shift is caused; if omega is less than omegaaiThen cause it to be positiveFrequency shifting; if ω and ωaiIf the difference is far away, the absolute value of the frequency shift amount is caused to be equal to | omega-omegaaiI is inversely proportional, the pump light is not monochromatic but a superposition of multiple spectral lines with certain line width and line type function. A part of frequency components in the linear function range of the pumping light spectrum generate positive optical frequency shift, and the other part of frequency components generate negative optical frequency shift. This non-monochromatic light-induced shift of the 0-0 transition is a superposition of the shifts induced by a number of monochromatic lights. Therefore, it is important to keep the spectral linetype and intensity of the pump light constant to reduce the effect of optical frequency shift on the aging drift of the frequency scale.
The invention also provides a precision frequency spectrum reference output method, which comprises the following steps:
placing the spectrum lamp in an oscillating circuit of a high-frequency oscillator;
setting the oscillation frequency and power of a high-frequency oscillator to ionize inert gas and active metal gas in the spectrum lamp, enabling metal atoms to absorb energy to generate energy level transition by collision of inert gas molecules and the metal atoms, radiating photons and further generating an excitation light signal;
setting the filtering resonance bubble to be at a constant temperature, enabling two coherent microwave pulses with a certain time interval to act on the filtering resonance bubble so as to enable active metal gas in the filtering resonance bubble to resonate and amplify with an excitation light signal generated by the spectrum lamp to generate a resonance transition frequency light signal, and converting the resonance transition frequency light signal into an electric signal through a photocell;
as shown in fig. 8, the time sequence of the whole process is sampled and detected by the microprocessor, after the light detection is completed, the microwave pulse and the spectrum lamp are turned off, and the quantum deviation correction information is transmitted to the microwave interrogation signal generating circuit to complete the servo of the whole machine, and the steps are repeated. When a pumping light pulse passes through the rubidium atom frequency standard integrated filtering resonance bubble in the whole process, rubidium atoms in the absorption bubble are concentrated on five sub-energy levels of F2, then two coherent microwave pulses with certain time intervals are used for acting on the rubidium atoms, the microwave frequency is just equal to the transition frequency of the rubidium atom ground state 0-0, and the microwave pulse action is kept. The spectral lamp is simultaneously lit while the second microwave pulse is applied.
As shown in fig. 9, the core components of the entire photodetection loop are composed of a physical system, synthesis, and servo. The microprocessor sends a frequency synthesis instruction to the DDS module in a serial communication mode, and simultaneously, the microprocessor directly sends a 79Hz keying frequency modulation signal to a keying frequency modulation pin (namely FSK) of the DDS module.
The DDS module receives a frequency synthesis instruction sent by the microprocessor and generates an 5.3125MHz +/-Deltaf comprehensive modulation signal of direct digital frequency synthesis by taking an external clock as a reference source, wherein the size of Deltaf is determined by the specific line width of an atomic frequency standard physical system. Meanwhile, 79Hz keying frequency modulation signals of the microprocessor are received to control the DDS module to key and output 5.3125MHz + delta f and 5.3125 MHz-delta f comprehensive modulation signals by taking 79Hz as a frequency period.
The comprehensive modulation signal is subjected to microwave multiplication and frequency mixing to generate a microwave interrogation signal of 6834.6875MHz + delta f to act on a physical system, a quantum frequency discrimination effect of the physical system is performed to generate a physical system frequency discrimination signal and send the physical system frequency discrimination signal to a synchronous phase discrimination module, and meanwhile, a 79Hz phase discrimination signal which is generated by a microprocessor and has the same phase with the 79Hz key control frequency modulation signal sent to the DDS module is also sent to the synchronous phase discrimination module. The frequency discrimination signal of the physical system and the 79Hz phase discrimination signal are subjected to synchronous phase discrimination in the synchronous phase discrimination module, and the result is sent to the microprocessor for generating a corresponding synchronous phase discrimination voltage control signal to act on the VCXO. It should be noted that, theoretically, two paths of 79Hz keying frequency modulation signals and 79Hz synchronous phase discrimination signals with the same phase are generated by a microprocessor, but because the whole atomic frequency standard system has phase noise on the circuit and the voltage difference acquisition is performed for the synchronous phase discrimination, the phase adjustment of the 79Hz keying frequency modulation signals and the 79Hz synchronous phase discrimination signals needs to be performed in different systems.
Therefore, the phase adjustment module is introduced in the present application, and the adjustment mechanism thereof is as follows:
assume that the integrated modulation signal is:
S＝Asin(2πft)；
the photo-detection fundamental wave output of the physical system photocell is as follows:
S1＝ABsin(2πft+φ+φ1)；
wherein φ is equal to 0 or 180 degrees, φ1Is the phase shift introduced by the phase and frequency doubling circuits. After frequency-selective amplification, the signal expression is as follows:
S2＝KαABsin(2πft+φ+φ1+φ2)；
wherein phi is2Is the phase shift of the frequency selective amplifier in the atomic frequency standard circuit.
Since the mathematical expression of phase-sensitive detection is a multiplier, after passing through a phase-sensitive amplifier, the signal is
Through the filtering action of the integrator, the alternating current component in the output of the phase sensitive amplifier is filtered, and the voltage-controlled voltage output finally is as follows:
caused by any cause (phi)1+φ2) Will cause the gain of the system to change, thereby causing frequency drift. In order for the system to operate properly and have maximum gain, a phase shifter must be added to the system to cancel out (phi)1+φ2) The phase shift of (2).
In the existing digitization technology, because a digitization component with high signal-to-noise ratio is adopted, the value is reduced to a certain extent (phi)1+φ2) The phase shift of (2) still exists, how the influence is necessarily reflected in the final servo synchronous phase detection of the whole system, and the core technology of the phase shift is to acquire the voltage difference of the locking signal output by the physical system.
The frequency of the 79Hz square-wave fm signal applied to the synthesizer to achieve the key modulation as shown in fig. 10-11 determines how fast the frequency signal around the center frequency of the alignment quantum is switched, and due to the relaxation time of the atomic spins, the key modulation microwave signal applied to the physical system will generate a lock signal waveform after the frequency discrimination of the physical system: in the locking signal waveform of fig. 10, in addition to the relaxation time C region of the atomic spins, the circuit design should be focused on A, B in the figure, because the region A, B is the region where the servo module performs the phase-detecting signal voltage difference acquisition. In the DDS link, 79Hz square wave signals for key frequency modulation are generated by a microprocessor, so that the timing sequence of 79Hz synchronous phase discrimination for acquisition of a servo system is also generated by the microprocessor, and the phases of the two paths of signals are the same. Because the external clock of the microprocessor still adopts a high frequency stabilizing source which is the same as the DDS part, the phase difference of the two paths of signals is considered to be constant within an allowable range as long as the phase difference is set at the beginning, and the point ensures that the position A, B of each sampling is constant when the servo system samples the synchronous phase discrimination signal voltage difference.
Taking the locking state in fig. 11 as an example, the synchronous phase detection processing diagram of the servo module is as follows: although two sampling points determined by the synchronous phase detection signal are not suitable in the upper diagram, in a certain actual system, the waveform of the synchronous phase detection signal generated by the microprocessor can be output by observing the corresponding physical system phase detection signal, as shown in fig. 12, the phase adjustment module enables the microprocessor to change the phase of the synchronous phase detection signal in fig. 12, and in order to further improve the precision of the synchronous phase detection of the servo loop, a method of sampling average for N times is set in a sampling area of A, B to reduce the influence of the level jitter of a locking signal A, B area on the synchronous phase detection.
In addition, the digital modulation mode is utilized, which is beneficial to conveniently changing the phase difference, because for each actual system, the physical part is different and the circuit constitution is inconsistent, the quantum frequency discrimination output links are different inevitably, and then the phase difference between the sampling time sequence and the modulation time sequence of the servo system is different
The invention also provides a precision frequency spectrum reference output method, which adds a phase adjustment module to carry out phase adjustment so as to improve the precision of the output reference frequency.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.
Claims (10)
1. An atomic clock for outputting a precision spectrum reference, comprising:
a spectral lamp having an active metal gas therein for generating an excitation light signal;
the optical filter is arranged at one end of the spectrum lamp and can adjust the light intensity of the exciting light signal;
the high-frequency oscillator is used for generating oscillation excitation frequency and providing pumping energy for the spectrum lamp;
the filter resonance bulb is filled with active metal gas which is the same as that of the spectrum lamp and provides a microwave magnetic field for the spectrum lamp, so that the active metal gas in the filter resonance bulb and an excitation light signal generated by the spectrum lamp are subjected to resonance amplification to generate a resonance transition frequency light signal and are converted into an electric signal;
and the microprocessor is used for detecting and acquiring the electric signal and outputting a reference frequency.
2. The atomic clock for precision spectral reference output according to claim 1, further comprising an inert gas mixed with the active metal gas in the spectral lamp;
wherein the active metal gas is rubidium gas.
3. The atomic clock for precision spectral reference output according to claim 2, wherein the inert gas is krypton and/or argon.
4. The atomic clock for precision spectral reference output according to claim 2 or 3, wherein the optical filter is a magnetic hyperfine component filter, and the optical transmittance of the optical filter is 70%.
5. The atomic clock for precise frequency spectrum reference output according to claim 4, wherein the high frequency oscillator employs a square wave to excite the oscillator circuit.
6. The atomic clock for fine spectrum reference output according to claim 4, wherein the filtering resonance bubble comprises:
a resonant cavity for providing a microwave magnetic field;
a photocell for converting an optical signal carrying resonance transition information into an electrical signal;
and the temperature control component is arranged on the resonant cavity and can control the temperature of the resonant cavity.
7. The atomic clock for precision spectral reference output according to claim 6, further comprising:
a DDS module which is connected with the microprocessor in a serial communication mode, can receive a frequency synthesis instruction sent by the video microprocessor and generates a direct digital frequency synthesis modulation signal by taking an external clock as a reference source;
the synchronous phase demodulation module is used for acquiring difference information between the frequency of the microwave interrogation signal and the quantum reference frequency, returning the difference information to the microprocessor and outputting a reference frequency signal;
a phase adjustment module capable of phase adjusting the microwave interrogation signal frequency and the quantum reference frequency to improve the accuracy of the reference frequency signal.
8. A method of fine spectral reference output using the method of any of claims 1-7, comprising:
placing the spectrum lamp in an oscillating circuit of a high-frequency oscillator;
setting the oscillation frequency and power of the high-frequency oscillator to ionize inert gas and active metal gas in the spectrum lamp, enabling metal atoms to absorb energy to generate energy level transition by collision of inert gas molecules and the metal atoms, radiating photons and further generating an excitation light signal;
setting the filtering resonance bubble to be at a constant temperature, enabling two coherent microwave pulses with a certain time interval to act on the filtering resonance bubble so as to enable active metal gas in the filtering resonance bubble to resonate and amplify with an excitation light signal generated by the spectrum lamp to generate a resonance transition frequency light signal, and converting the resonance transition frequency light signal into an electric signal through a photocell;
the microprocessor transmits a 79Hz key control frequency modulation signal to the DDS module;
the DDS module receives the 79Hz keying frequency modulation signal of the microprocessor, generates an 5.3125MHz +/-Delta f comprehensive modulation signal synthesized by direct digital frequency by taking an external clock as a reference source, outputs a 5.3125MHz + Delta f and 5.3125 MHz-Delta f comprehensive modulation signal after frequency synthesis by taking 79Hz as a frequency period keying output, wherein the size of Delta f is determined by the specific line width of an atomic frequency standard physical system;
the comprehensive modulation signal is subjected to microwave multiplication and frequency mixing to generate a microwave interrogation signal of 6834.6875MHz + delta f to act on a physical system, and a physical system frequency discrimination signal is generated after the quantum frequency discrimination of the physical system;
the physical system phase frequency discrimination signal and the comprehensive modulation signal are subjected to phase adjustment through the phase adjustment module and then sent to the synchronous phase discrimination module to be subjected to synchronous phase discrimination to generate a synchronous phase discrimination signal, and a reference frequency signal is output.
9. The method as claimed in claim 8, wherein the oscillating frequency of the oscillating circuit is set to 100MHz, and the power is set to 1-5W.
10. The precision spectral reference output method according to claim 9, further comprising: and setting a sampling area for the synchronous phase discrimination signal, and carrying out N times of sampling averaging to reduce the influence of level jitter on the synchronous phase discrimination.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2024035621A1 (en) * | 2022-08-08 | 2024-02-15 | Northrop Grumman Systems Corporation | Atomic clock system |
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Application publication date: 20210723 |