阅读说明：本技术 基于微波-光频调制转移技术的铯微波原子钟及实现方法 (Cesium microwave atomic clock based on microwave-optical frequency modulation transfer technology and implementation method ) 是由 陈景标 潘多 刘天宇 于 2019-10-11 设计创作，主要内容包括：本发明公布了一种基于微波-光频调制转移技术的铯微波原子钟及实现方法,包括：铯原子真空系统、激光系统、光电信号探测系统、微波频率源、相位调制器和综合电路系统；微波频率源与相位调制器相连接；相位调制器与电路综合系统和铯原子真空系统相连接；光电信号探测系统连接电路综合系统,再连接微波频率源；应用原子介质钟微波与光频之间调制转移探测得到误差信号,得到用于晶体振荡器频率锁定的色散型误差信号。本发明具有钟跃迁谱线信噪比高的优势,直接获得色散型误差信号,无需外部锁相放大器调制解调,有效减小系统体积及复杂度,减小噪声干扰,实现钟激光频率的高精度锁定,极大提高原子钟的信噪比和稳定度。(The invention discloses a cesium microwave atomic clock based on a microwave-optical frequency modulation transfer technology and an implementation method, wherein the cesium microwave atomic clock comprises the following steps: the system comprises a cesium atom vacuum system, a laser system, a photoelectric signal detection system, a microwave frequency source, a phase modulator and a comprehensive circuit system; the microwave frequency source is connected with the phase modulator; the phase modulator is connected with the circuit integrated system and the cesium atom vacuum system; the photoelectric signal detection system is connected with the circuit integrated system and then connected with the microwave frequency source; and modulating, transferring and detecting between the microwave and the optical frequency of the atomic medium clock to obtain an error signal, and obtaining a dispersion type error signal for locking the frequency of the crystal oscillator. The invention has the advantage of high signal-to-noise ratio of the clock transition spectral line, directly obtains the dispersion type error signal, does not need modulation and demodulation of an external phase-locked amplifier, effectively reduces the volume and the complexity of a system, reduces noise interference, realizes high-precision locking of clock laser frequency, and greatly improves the signal-to-noise ratio and the stability of an atomic clock.)

1. A cesium microwave atomic clock based on a microwave-optical frequency modulation transfer technology comprises: a cesium atom vacuum system, a laser system for providing pumping and detecting laser, a photoelectric signal detection system, a microwave frequency source, a phase modulator and a comprehensive circuit system;

the cesium atom vacuum system comprises a cesium atom oven and a microwave resonant cavity;

the laser system comprises a laser frequency stabilization system;

the photoelectric signal detection system is used for detecting a laser signal to obtain a microwave resonance spectral line;

the microwave frequency source comprises a voltage-controlled oscillator and a frequency synthesizer and is used for generating a microwave signal with microwave frequency which is in transition resonance with the cesium atom ground state hyperfine energy level;

the phase modulator is used for carrying out phase modulation on the microwave frequency, carrying out phase modulation on the microwave frequency by adopting a sine wave, and increasing the modulation frequency;

the integrated circuit system comprises a scanning signal module for generating a scanning signal of microwave frequency and an error signal module for providing an error signal by a phase demodulation and PID (proportion integration differentiation) regulation method; the servo feedback module controls the frequency of the voltage-controlled oscillator through the high-speed servo feedback circuit to enable the microwave frequency source to be always in a resonance state with atoms;

the microwave frequency source is connected with the phase modulator; the phase modulator is connected with the circuit integrated system and the cesium atom vacuum system; pumping light and detection light generated by a laser system act on cesium atoms emitted from front and rear windows of a cesium atom vacuum system, and then a resonance spectrum line signal is detected by a photoelectric signal detection system; the photoelectric signal detection system is connected with the circuit integrated system and then connected with the microwave frequency source;

the cesium microwave atomic clock obtains an error signal by applying modulation transfer detection between atomic medium clock microwaves and optical frequencies, and obtains a dispersion type error signal for frequency locking of a crystal oscillator.

2. Cesium microwave atomic clock according to claim 1, characterized in that said laser system is a 852nm laser system.

3. Cesium microwave atomic clock according to claim 1, characterized in that the modulation frequency and the clock transition line width are of the same order of magnitude when phase modulating a microwave frequency source.

4. A preparation method of a cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection comprises the following steps:

1) outputting a microwave signal through a microwave frequency source, performing frequency scanning on the microwave signal by using a scanning signal generated by the integrated circuit system, filling the microwave signal into a microwave resonant cavity in the cesium atom vacuum system, and interacting with cesium atoms in the cesium atom vacuum system;

2) outputting frequency-stabilized pumping light and detection light by using a laser system, and pumping and detecting cesium atoms at front and rear windows of a cavity of a cesium atom vacuum system respectively; detecting the resonance spectral line signal after the interaction by a photoelectric signal detection system to be a Ramsey spectral line signal;

3) phase modulation is carried out on a microwave signal generated by a microwave frequency source by adopting a phase modulator, after the modulated microwave signal interacts with cesium atoms, the cesium atoms transfer modulation information to detection laser through a hole burning effect and are detected by a photoelectric signal detection system;

4) inputting the signal detected by the photoelectric detection system into the integrated circuit system for modulation and demodulation, and simultaneously inputting the driving signal of the phase modulator to the integrated circuit system in the process to obtain a dispersion type modulation transfer spectrum signal; the modulation transfer spectrum signal generates a servo signal through a high-speed servo feedback module in the integrated circuit system, the servo signal is fed back to a voltage-controlled oscillator in a microwave frequency source, the frequency of a clock microwave is controlled, and the locking of the microwave frequency is realized;

through the steps, the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection is prepared.

5. The method for preparing cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection according to claim 4, wherein step 1) outputs 9.192GHz microwave signal by microwave frequency source.

6. The method for preparing the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection according to claim 4, wherein step 2) adopts a 852nm laser system to output stabilized 852nm pump light and probe light.

7. The method for preparing cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection according to claim 4, wherein the frequency of phase modulation in step 3) is 0.5-1.0 times the line width of resonance line signal in step 2).

Technical Field

The invention belongs to the technical field of time frequency standard, and relates to a method for realizing a high-performance cesium atomic microwave clock by using a microwave-optical frequency modulation transfer technology and the cesium microwave atomic clock.

Background

An atomic clock is a system that outputs a standard frequency signal by locking a crystal oscillator or a laser frequency to an atomic transition frequency with a quantum transition frequency between atomic internal energy levels as a reference, and has very high frequency accuracy. As a primary time frequency standard, the cesium atomic clock is widely used for ground time keeping, time service, time frequency measurement, telecommunication network clock synchronization, satellite navigation and positioning and the like, and is a core device of an independent time frequency system. The application of the high-quality cesium atomic clock relates to a plurality of fields or industries, such as military affairs, scientific research, metering, aviation, aerospace, communication, meteorology, resources, environment, geodetic survey and the like.

In order to realize a high-stability cesium atomic clock, the signal-to-noise ratio of the cesium atomic clock needs to be further improved on the basis of ensuring the line width of the microwave transition spectral line. At present, the existing scheme for realizing the cesium atomic clock mainly comprises three types, namely magnetic separation state optical detection, magnetic separation state optical detection and optical pumping optical detection, wherein optical detection is based on a detection mode of a Rabi (Rabi) or a ramssey (Ramsey) to obtain a clock transition spectral line signal. However, the signal-to-noise ratio of the clock transition spectral line of the existing adopted cesium atomic clock is relatively low, and the locking precision of the feedback loop is not high, which are not favorable for further improving the stability index of the cesium atomic clock.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a cesium microwave atomic clock generation device based on a microwave-optical frequency modulation transfer technology, which is used for further improving the signal-to-noise ratio of clock transition spectral line signals based on cesium microwave-optical frequency modulation transfer detection, so that the signal-to-noise ratio of the cesium atomic clock is improved, and the stability index of the cesium atomic clock is further improved.

The invention applies modulation transfer spectrum to a microwave cesium atomic clock, combines a light frequency lamb plug detection scheme to perform phase modulation on microwave signals, transfers modulation information to 852nm detection laser through the interaction of microwaves and light frequencies with atoms respectively, obtains a dispersion type error signal with high signal-to-noise ratio through the characteristic of low noise floor under high modulation frequency, is directly used for servo feedback of the frequency of a crystal oscillator, greatly improves the signal-to-noise ratio and stability of the atomic clock, and thus realizes a brand new cesium atomic clock based on the microwave-light frequency modulation transfer technology and a preparation method thereof.

The technical scheme of the invention is as follows:

a cesium microwave atomic clock based on a microwave-optical frequency modulation transfer technology comprises:

1. a cesium atom vacuum system comprises a cesium atom oven and a microwave resonant cavity.

2.852nm laser system including a laser frequency stabilization system to provide pumping and probe lasers.

3. And the photoelectric signal detection system is used for detecting the laser signal to obtain a microwave resonance spectral line.

4. And the microwave frequency source comprises a voltage-controlled oscillator and a frequency synthesizer and is used for generating a microwave signal with a microwave frequency which is in resonance with the transition of the cesium atom ground state hyperfine energy level.

5. The phase modulator is used for phase modulating the microwave frequency, and is different from the traditional modulation in that the sine wave is used for phase modulating the microwave frequency instead of the square wave in the traditional device, and meanwhile, the modulation frequency is greatly increased compared with the traditional device.

6. The integrated circuit system comprises a scanning signal module, an error signal module and a servo feedback module and is used for generating a scanning signal of microwave frequency; an error signal module, which provides an error signal through phase demodulation, PID (Proportional-Integral-Differential) regulation and other means; and the servo feedback module controls the frequency of the voltage-controlled oscillator through a high-speed servo feedback circuit, so that the microwave frequency source is always kept in an atomic resonance state.

In the cesium microwave atomic clock device based on microwave-optical frequency modulation transfer detection, a microwave frequency source is connected with a phase modulator, then the phase modulator is connected with a circuit integrated system and a cesium atomic vacuum system, pumping light and detection light generated by a 852nm laser system act on cesium atoms emitted from front and rear windows of the cesium atomic vacuum system, and then a photoelectric signal detection system detects resonance line signals. The photoelectric signal detection system is connected with the circuit synthesis system and then connected with the microwave frequency source.

According to the cesium microwave atomic clock based on the microwave-optical frequency modulation transfer technology, the error signal is obtained by applying a modulation transfer detection scheme between the microwave and the optical frequency of an atomic medium clock, so that a dispersion type error signal for locking the frequency of a crystal oscillator can be directly obtained, and a complex modulation and demodulation circuit such as an external phase-locked amplifier is not needed. In specific implementation, when the phase modulation is performed on the microwave frequency source, the modulation frequency and the line width of the clock transition spectral line are in the same order of magnitude.

The invention also aims to provide a preparation method of the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection, which comprises the following steps:

1) outputting 9.192GHz microwave signals by the microwave frequency source, performing frequency scanning on the microwave signals by using scanning signals generated by the integrated circuit system, filling the microwave signals into a microwave resonant cavity in the cesium atom vacuum system, and interacting with cesium atoms in the cesium atom vacuum system;

2) outputting frequency-stabilized 852nm pumping light and detection light by a 852nm laser system, and pumping and detecting cesium atoms at front and rear windows of a cavity of a cesium atom vacuum system respectively. And detecting the resonance spectral line signal after the interaction by a photoelectric signal detection system, wherein the spectral line signal is a Ramsey spectral line signal.

3) The microwave signal generated by the microwave frequency source is subjected to phase modulation by adopting a phase modulator, and after the modulated microwave signal interacts with cesium atoms, the cesium atoms transfer modulation information to the detection laser through a hole burning effect and are detected by a photoelectric signal detection system.

4) The signal detected by the photoelectric detection system is input into the integrated circuit system for modulation and demodulation, in the process, the driving signal of the phase modulator is simultaneously input into the integrated circuit system to obtain a dispersion type modulation transfer spectrum signal, the modulation transfer spectrum signal generates a servo signal through a high-speed servo feedback module in the integrated circuit system, and the servo signal is fed back to a voltage-controlled oscillator in a microwave frequency source to control the frequency of the clock microwave so as to realize the locking of the microwave frequency.

Through the steps, the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection is prepared.

In each step of the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection, the frequency of phase modulation in the step 3) is 0.5-1.0 time of the line width of the resonance spectrum line signal in the step 2).

Compared with the prior art, the invention has the beneficial effects that:

compared with the common laser, the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection has the main characteristics that:

the invention innovatively provides a modulation transfer detection scheme between microwave and optical frequency applied to cesium atom beams, and the signal-to-noise ratio and clock stability of clock transition spectral lines are improved by using smaller noise floor characteristics under high modulation frequency, so that a high-stability cesium atom microwave clock is realized. The scheme thoroughly changes the implementation path of the cesium microwave atomic clock in principle, realizes high-precision clock transition modulation transfer spectrum by greatly improving the signal-to-noise ratio, and is expected to improve the stability of the cesium atomic clock by one order of magnitude on the existing basis. The technical advantages of the invention mainly include:

1) the modulation transfer detection scheme applied to the cesium atom beam between the microwave and the optical frequency is innovatively provided, and the signal-to-noise ratio and the clock stability of a clock transition spectral line are improved through the characteristic of a low noise background under high modulation frequency, so that the high-stability cesium atom microwave clock is realized;

2) the invention can directly obtain the dispersion type error signal for locking the frequency of the crystal oscillator, does not need complex modulation and demodulation circuits such as an external phase-locked amplifier and the like, can effectively reduce the volume and the complexity of a system and reduce the interference introduced by the noise of the system circuit to a certain extent;

3) the invention is not limited to the modulation transfer detection of cesium atoms, and can also be applied to other microwave atomic clocks, such as rubidium atomic clocks and the like.

Therefore, the cesium microwave atomic clock for microwave-optical frequency modulation transfer detection provided by the invention has the advantage of high signal-to-noise ratio of clock transition spectral line, can directly obtain dispersion type error signals, does not need complex modulation and demodulation circuits such as an external phase-locked amplifier and the like, effectively reduces the volume and complexity of the system, reduces noise interference introduced by the system circuit, obtains high-precision locking of clock laser frequency, and greatly improves the signal-to-noise ratio and stability of the atomic clock.

Drawings

FIG. 1 is a schematic structural diagram of a cesium microwave atomic clock generating device based on microwave-optical frequency modulation transfer detection in an embodiment of the present invention;

wherein: the system comprises a 1-cesium atom vacuum system, a 2-852 nm laser system, a 3-photoelectric detection system, a 4-microwave frequency source, a 5-phase modulator and a 6-comprehensive circuit system.

The dotted line is the optical path portion and the solid line is the circuit connection portion.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention are described in detail below by way of the embodiments and with reference to the accompanying drawings.

The structure of the cesium microwave atomic clock generating device based on microwave-optical frequency modulation transfer detection is shown in fig. 1, and the preparation of the cesium microwave atomic clock based on microwave-optical frequency modulation transfer detection mainly comprises the following steps:

1) 9.192GHz microwave signals output by a microwave frequency source 4 and subjected to transition resonance with two ground state hyperfine structures of cesium atoms are subjected to frequency scanning on microwave frequency by utilizing scanning signals generated by an integrated circuit system, and are injected into a microwave resonant cavity in a cesium atom vacuum system to interact with the cesium atoms twice to form Ramsey spectral lines;

2) locking 852nm laser frequency to cesium atom 6S _1/2-6P _3/2And (4) making 852nm laser system 2. The emergent laser is divided into two beams by a spectroscope, atoms are pumped and detected at the front window and the rear window of the cesium atom beam tube respectively, and a photoelectric signal detection system 3 detects Ramsey spectral line signals after interaction;

3) and a phase modulator 5 is adopted to perform phase modulation on the microwave signal generated by the microwave frequency source 4, and the modulation frequency is 0.5-1.0 time of the line width of the spectral line detected in the previous step. After the modulated microwave signal interacts with atoms, the atoms transfer the modulation information to the detection laser through a hole burning effect and are detected by the photoelectric signal detection system 3;

4) the signal detected by the photodetection system 3 and the drive signal of the phase modulator 5 are demodulated by using a demodulation circuit part in the integrated circuit system 6 to obtain a dispersion type demodulated signal, and then the signal is adjusted by a PID control circuit in the integrated circuit system 6 to obtain an error signal.

5) And applying an error signal to a voltage-controlled oscillator in the microwave frequency source 4 to control the output frequency of the controller, so that the output frequency of the microwave frequency source 4 is strictly equal to the transition frequency between the two hyperfine energy levels of the cesium atom ground state, namely, the transition frequency is locked on the cesium atom transition frequency. And then, evaluating the stability and accuracy of the cesium atomic clock through an external frequency comparison system.

The scheme for detecting modulation transfer between microwaves and optical frequencies of cesium atom beams in the embodiment of the invention is characterized in that a microwave frequency source is subjected to phase modulation, the modulation frequency is transferred to optical frequency transition through a hole burning effect, a dispersion type clock transition spectral line is generated, and the signal-to-noise ratio and the clock stability of the clock transition spectral line are improved through the characteristic of low noise background under high modulation frequency, so that the high-stability cesium atom microwave clock is realized. The invention is distinguished in this case from the conventional cesium atomic microwave clock which modulates the microwave frequency source with a lower frequency and detects the Ramsay clock transition spectrum line due to the change in the number of atomic layouts by the probe light. In addition, the invention is not limited to the modulation transfer detection of cesium atoms, and can also be applied to other microwave atomic clocks, such as rubidium atomic clocks and the like.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the invention without departing from the spirit and scope of the invention.