Optical clock absolute frequency tracing device and method based on photo-generated microwaves
By directly comparing the frequency with the cesium fountain clock through photogenerated microwave technology, the problem of slow absolute frequency tracing of optical clocks is solved, high-precision optical clock frequency measurement is achieved, and the operating efficiency and availability of optical clocks are improved.
Patent Information
- Application Number
- CN202511056936.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-30
- Publication Date
- 2025-10-03
AI Technical Summary
Existing methods for tracing the absolute frequency of optical clocks are slow and time-consuming, making it difficult to achieve high-precision frequency comparison in a short period of time.
Using photogenerated microwave technology, the repetition frequency of the optical comb is locked to the optical clock. The microwave signal controlled by the optical clock is detected by a photodetector and directly compared with the frequency of the cesium fountain clock. After mixing and filtering, high-precision measurement is performed using a frequency counter.
It improves the short-term stability of the optical clock, shortens the frequency measurement time, and can achieve absolute frequency traceability of the optical clock at the E-16 level within one day, thereby improving the operating efficiency and availability of the optical clock.
Smart Images
Figure CN120742641A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of time and frequency technology, and more specifically, relates to an optical clock absolute frequency tracing device and method based on photogenerated microwaves. Background Art
[0002] Currently, the method for tracing the absolute frequency of optical clocks mainly relies on hydrogen clocks as flywheel clocks. The specific implementation methods are divided into the following three types:
[0003] 1. Trace the absolute frequency of an optical clock to International Atomic Time (TAI) based on the Global Navigation Satellite System (GNSS);
[0004] 2. Using an active hydrogen atomic clock as a flywheel clock to trace the absolute frequency of an optical clock back to a cesium fountain clock;
[0005] 3. Lock the optical comb to the secondary frequency standard, and then beat the optical clock with the optical comb to trace the absolute frequency of the optical clock back to the International Atomic Time.
[0006] Among them, method 1 is suitable for long-distance optical clock comparison, which enables effective frequency comparison between optical clocks in different laboratories or countries and cesium fountain clocks or international atomic time. However, due to the relatively large noise of GNSS links, it usually takes several months to achieve frequency traceability at the E-16 level; method 2 uses active hydrogen atomic clocks as flywheel clocks to provide stable frequency output when the optical clock is not working, so that the time scale can run continuously, avoiding the interruption of frequency traceability due to discontinuous operation of the optical clock, but the short-term stability of active hydrogen atomic clocks is usually in the E-13 level. The comparison time is limited by the short-term stability of the active hydrogen atomic clock. It takes dozens of days to achieve the traceability uncertainty of E-16. Method 3 uses an optical comb as a bridge. The optical comb is locked to the local time of the Universal Coordinated Time (UTC), and the local time is kept in long-term comparison with TAI via a satellite link. Then, a low-frequency signal is generated by beating the frequency of the optical clock with one of the teeth of the optical comb. The frequency measurement result of the optical clock can be directly connected with the international standard. However, the comparison between the local time and TAI is also carried out through a satellite link. Similar to method 1, it also takes a long time. Summary of the Invention
[0007] In response to the above defects or improvement needs of the prior art, the present invention provides an optical clock absolute frequency tracing device and method based on photogenerated microwaves, the purpose of which is to solve the technical problem of slow speed and long time consumption of optical clock absolute frequency tracing in the prior art.
[0008] To achieve the above objectives, according to one aspect of the present invention, there is provided an optical clock absolute frequency tracing device based on optically generated microwaves, comprising:
[0009] The cesium fountain clock module is used to convert the output signal of the local oscillator into a reference microwave signal f under the control of the cesium fountain clock. cs ;
[0010] Optical microwave module, used to convert the optical clock frequency f oc Convert to microwave frequency f OMG ; comprising: an optical clock, a first mixer, an optical comb, a photodetector, a first filter, a second filter and a frequency multiplier; the absolute frequency of the optical clock f oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep The photogenerated microwave signal f is detected by the photodetector and filtered by the second filter, and then multiplied by the frequency multiplier to obtain the photogenerated microwave signal f OMG ;
[0011] The frequency measurement module, together with the cesium fountain clock module and the optical microwave module, is used to measure the reference microwave signal f cs and the optically generated microwave signal f OMG Mixing is performed to obtain a difference frequency signal, and then the difference frequency signal is subjected to frequency counting measurement to obtain a measurement frequency signal f test , to the absolute frequency f of the optical clock oc Conduct traceability.
[0012] In one embodiment, the cesium fountain clock module includes: a local oscillator, a first microwave integrated chain, a power divider, a second microwave integrated chain and the cesium fountain clock;
[0013] The local oscillator is used to generate a local oscillation signal;
[0014] The first microwave synthesis chain is connected to the output end of the local oscillator and the output end of the cesium fountain clock, and is used to convert the local oscillator signal into a reference microwave signal f under the control of the cesium fountain clock. cs ;
[0015] The power divider is connected to the first microwave integrated chain and is used to divide the reference microwave signal f cs Divided into the same first path and second path, the first path serves as the output signal of the cesium fountain clock module;
[0016] The second microwave integrated chain is connected to the second path and is used to convert the reference microwave signal f cs Converting into a frequency signal that meets the input requirements of the cesium fountain clock;
[0017] The cesium fountain clock is connected to the second microwave integrated chain and is used to feed back the difference between the input required frequency signal and its own transition frequency to the first microwave integrated chain to control the reference microwave signal f cs Generation.
[0018] In one embodiment, the reference microwave signal f cs Expressed as:
[0019] f cs =f cs (1±δy cs );
[0020] Among them, δy cs is the relative uncertainty of the cesium fountain clock itself.
[0021] In one embodiment, the relative uncertainty δy of the cesium fountain clock itself cs The expression is:
[0022]
[0023] Among them, δy cs-A Indicates type A uncertainty, which is statistical uncertainty; δy cs-B is the Type B uncertainty, which is the systematic error.
[0024] In one embodiment, the absolute frequency f of the optical clock oc With the optically generated microwave signal f OMG The relational expression is:
[0025] f oc =mf OMG +f ceo +f beat ;
[0026] Among them, f ceo is the bias frequency of the optical comb, and m is a set multiple related to the frequency multiplication factor of the frequency multiplier and the beat frequency comb tooth frequency band of the optical comb.
[0027] In one embodiment, the frequency measurement module includes:
[0028] The second mixer is used to receive the reference microwave signal f cs and the optically generated microwave signal f OMG And perform mixing to obtain difference frequency signal;
[0029] A frequency counter is connected to the second mixer and is used to measure the frequency of the difference frequency signal to obtain a measured frequency signal f test .
[0030] In one embodiment, the measurement frequency signal f test The expression is:
[0031]
[0032] in, To measure the frequency signal f test The mean value of δy test is the relative uncertainty of the frequency counter measurement.
[0033] In one embodiment, the relative uncertainty of the optical clock is expressed as:
[0034]
[0035] Among them, δy cs is the relative uncertainty of the cesium fountain clock itself.
[0036] According to another aspect of the present invention, a method for tracing the absolute frequency of an optical clock based on optically generated microwaves is provided, which is applied to the apparatus for tracing the absolute frequency of an optical clock based on optically generated microwaves, comprising:
[0037] Driven by the cesium fountain clock, the output signal of the local oscillator is converted into a reference microwave signal f cs ;
[0038] The absolute frequency f of the optical clock oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep After filtering by the second filter and then frequency multiplication by the frequency multiplier, the optically generated microwave signal f is obtained. OMG ;
[0039] The reference microwave signal f cs and the optically generated microwave signal f OMG Mixing is performed to obtain a difference frequency signal, and then the difference frequency signal is subjected to frequency counting measurement to obtain a measurement frequency signal f test , to the absolute frequency f of the optical clock oc Conduct traceability.
[0040] According to another aspect of the present invention, a time-frequency calibration method based on optically generated microwaves is provided, comprising: obtaining the measurement frequency signal f using the optical clock absolute frequency tracing method; test ; Using the measured frequency signal f test Perform time tracing and / or frequency tracing.
[0041] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:
[0042] (1) The present invention provides an optical clock absolute frequency tracing device based on photogenerated microwaves. Based on the photogenerated microwaves, the repetition frequency of the optical comb is locked to the optical clock, and then a photodetector is used to detect the microwave signal driven by the optical clock. This signal is then used to directly compare the beat frequency with the local oscillator signal driven by the cesium fountain clock, which can solve the problem of hydrogen clocks as flywheel clocks reducing the traceability accuracy. Compared with the existing technology, the flywheel clock scheme is no longer used. Instead, the optical clock is used to directly compare the frequency with the reference clock cesium fountain clock. The purpose is to improve the short-term stability index of the measurement and reduce the measurement time of the optical clock frequency, so that the optical clock can complete the frequency tracing in a shorter time, improve its operating efficiency and availability, and help to more quickly verify and promote the optical clock as a new second definition device, thereby promoting the development of time and frequency standards.
[0043] (2) The cesium fountain clock module in this solution includes: a local oscillator, a first microwave integrated chain, a power divider, a second microwave integrated chain and the cesium fountain clock; this design takes into account that the oscillator signal can be converted into the 9.192631700GHz local oscillator signal required by the cesium fountain clock while maintaining the high stability of the oscillator signal by using the low-noise microwave integrated chain; at the same time, the error signal of the cesium fountain clock is fed back to the first microwave integrated chain. The advantage is that the output reference microwave signal f cs The excellent short-term stability of the local oscillator is maintained while the long-term stability is ensured by the cesium fountain clock.
[0044] (3) This scheme uses a sapphire oscillator with excellent short-term stability as the local oscillator signal of the cesium fountain clock, which is expected to improve the relative frequency stability of the cesium fountain clock to better than This allows the traceability requirement of the absolute frequency of an optical clock at the E-16 level to be achieved within one day.
[0045] (4) The frequency measurement module described in this solution includes: a second mixer and a frequency counter connected thereto; this design takes into account the problems of high cost and limited bandwidth when using a high-frequency frequency counter to directly measure the optical clock and optically generated microwave signals. Instead, the optical clock signal and optically generated microwave signal are reduced to low-frequency signals after passing through the mixer, thereby reducing the measurement difficulty. This solution will measure the fOMG The microhertz resolution requirement is converted to the measurement requirement of f near the center frequency of megahertz. test The measurement requirements of microhertz measurement resolution are to increase the relative frequency uncertainty from 10 -14 Reduced to 10 -12 In this case, a mature low-frequency counter can be used to achieve high-precision, low-noise frequency measurement. This ensures the frequency accuracy of the optical clock traceable to the cesium fountain clock with low-frequency measurement accuracy. Furthermore, the frequency counter can directly determine the frequency difference between the optical clock and the cesium fountain clock, thus achieving traceability of the optical clock to the cesium fountain clock.
[0046] (5) The relative uncertainty of the absolute frequency traceability of the optical clock described in this scheme is limited by the uncertainty of the comparison link δy test and the uncertainty δy of the reference cesium fountain clock cs The specific expression is: When comparing link δy test is δy test When the Class A uncertainty δ of the cesium fountain clock is cs for Under the premise of the absolute frequency of the optical clock, the absolute frequency can be traced back to 1E-16 (from 8×10 -14 The time required to obtain an absolute frequency of 1E-16 is 64,000 seconds, which can meet the traceability requirements of the absolute frequency of the optical clock at the order of E-16 within one day. BRIEF DESCRIPTION OF THE DRAWINGS
[0047] Figure 1 This is a schematic structural diagram of an optical clock absolute frequency tracing device based on optically generated microwaves provided in Example 1 of the present invention;
[0048] Figure 2 1 is a schematic structural diagram of a cesium fountain clock module provided in Example 1 of the present invention;
[0049] Figure 3 1 is a schematic structural diagram of a photogenerated microwave module provided in Example 1 of the present invention;
[0050] Figure 4 It is a structural diagram of the frequency measurement module provided in Example 1 of the present invention. DETAILED DESCRIPTION
[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
[0052] The present invention provides an optical clock absolute frequency tracing scheme based on photogenerated microwaves that effectively shortens the frequency comparison time. This method no longer uses a flywheel clock scheme, but instead directly compares the frequency of an optical clock with a reference clock, a cesium fountain clock. Its purpose is to improve the short-term stability index of the measurement and reduce the measurement time of the optical clock frequency, so that the optical clock can complete frequency tracing in a shorter time, improve its operating efficiency and availability, and help to more quickly verify and promote optical clocks as new second definition devices, thereby promoting the development of time and frequency standards.
[0053] Example 1
[0054] This embodiment provides an optical clock absolute frequency tracing device based on optically generated microwaves, such as Figure 1 As shown, it includes: a cesium fountain clock module, a photogenerated microwave module and a frequency measurement module. Among them, the cesium fountain clock module is used to convert the output signal of the local oscillator into a reference microwave signal f under the control of the cesium fountain clock. cs The optical microwave module is used to convert the optical clock frequency f oc Convert to microwave frequency f OMG , comprising: an optical clock, a first mixer, an optical comb, a photodetector, a first filter, a second filter and a frequency multiplier; the absolute frequency of the optical clock f oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep The photogenerated microwave signal f is detected by the photodetector and filtered by the second filter, and then frequency multiplied by the frequency multiplier to obtain the photogenerated microwave signal f OMG The frequency measurement module, together with the cesium fountain clock module and the optical microwave module, is used to receive the reference microwave signal f cs and the optically generated microwave signal f OMG The difference frequency signal is mixed and then the frequency counting measurement is performed on the difference frequency signal to obtain the measurement frequency signal f test , to the absolute frequency f of the optical clock oc Conduct traceability.
[0055] Further, if Figure 2As shown, the cesium fountain clock module includes: a local oscillator, a first microwave synthesis chain, a power divider, a second microwave synthesis chain and the cesium fountain clock; the local oscillator is used to generate a local oscillation signal; the first microwave synthesis chain is connected to the output end of the local oscillator and the output end of the cesium fountain clock, and is used to convert the local oscillation signal into a reference microwave signal f under the control of the cesium fountain clock. cs The power divider, connected to the first microwave integrated chain, for the reference microwave signal f cs The first path is used as the output signal of the cesium fountain clock module. The second microwave integrated chain is connected to the second path and is used to convert the reference microwave signal f cs The cesium fountain clock is connected to the second microwave integrated chain and is used to transmit the difference between the input frequency signal and its own transition frequency to the first microwave integrated chain to control the reference microwave signal f cs Generation.
[0056] Specifically, the cesium fountain clock is the clock that reproduces the definition of the second with the highest accuracy and can be used as a traceability benchmark. The working principle of the cesium fountain clock in this patent is as follows: Figure 2 As shown: The performance of the local oscillator of the fountain clock determines the short-term stability of the cesium fountain clock. This solution preferably selects a low-temperature sapphire signal as the local oscillator of the cesium fountain clock. After passing through the first microwave integrated chain, a 9GHz microwave signal is generated, which is then divided into two paths through a power divider. One output (port A) is used as a reference microwave signal output, and the other output (port B) is then passed through the second microwave integrated chain to generate a frequency-modulated 9.192631770GHz signal for the cesium fountain clock to perform frequency discrimination, so that it can feed back the error signal to the first microwave integrated chain. Therefore, the 9GHz signal output by the first microwave integrated chain is a reference microwave signal. The microwave signal of the second microwave integrated chain has a modulation sideband and therefore cannot be directly used for frequency tracing. After using low-temperature sapphire as the local oscillator, the cesium fountain clock is expected to achieve better performance than The absolute accuracy of the 9 GHz signal output by the first microwave synthesis chain can be expressed as:
[0057] f cs =f cs (1±δy cs )
[0058] where δy cs is the relative uncertainty of the cesium fountain clock itself. It includes the type A uncertainty δy cs-A and Type B uncertainty δy cs-BThe Class B uncertainty is obtained in advance through systematic evaluation; the Class A uncertainty is statistical uncertainty, which is related to the measurement time. The Allan deviation of the relative stability is inversely proportional to the square root of the integration time. Under the premise of , its uncertainty can be expressed as:
[0059]
[0060] where δy cs-B is the systematic error of the cesium fountain clock. It can be seen that the accuracy of absolute frequency traceability is related to the measurement time, where τ represents the integration time and s represents the time in seconds.
[0061] Furthermore, the principle diagram of the optical clock converting to 9.01 GHz through photogenerated microwaves is shown in the following figure: Figure 3 Optical clocks typically have an uncertainty of the order of 1E-18, and better than The relative stability of the second. The optical comb is also called the ultrafast femtosecond optical frequency comb. In the time domain, it is a pulse signal with uniform phase lock, and in the frequency domain, it has a series of uniform frequency components, which can be expressed as f comb =Nf rep +f ceo , where N is the number of the comb teeth that beat with the optical clock, f rep is the repetition frequency of the optical comb, and the repetition frequency of different optical combs usually varies from 100MHz to 1 GHz. ceo is the bias frequency of the optical comb. After the optical comb beats with the optical clock, the beat frequency f is obtained after passing through a low-pass filter (the first filter). beat Lock to lock the repetition frequency f rep , thus achieving the locking of the optical comb to the optical clock, and the repetition frequency f after locking rep The relative stability of the second will follow the optical clock and have the order of E-16. The repetition frequency f rep After passing through the bandpass filter (second filter) and the M-th frequency multiplier, a high-frequency optical microwave signal f is obtained. OMG In this embodiment, f rep is 250.139MHz, M is 36, f OMG It is 9.005GHz.
[0062] The absolute frequency of the optical clock can be written as
[0063] f oc =nf rep +f ceo +f beat
[0064] Further written
[0065] f oc =mf OMG+f ceo +f beat
[0066] where n is 10 6 Integers of the order of magnitude can be obtained in advance through other auxiliary means. The absolute frequency of an optical clock is usually in the range of 10 15 Hz level, in order to achieve 10 -16 The measurement accuracy of relative uncertainty requires the absolute frequency to be measured to the sub-Hz level. ceo and f beat , usually in the order of hundreds of megahertz, and can be easily measured to sub-hertz levels using conventional methods. rep , considering that there are 10 6 The coefficient of , so the repetition frequency needs to be measured to hundreds of nanohertz, so the relative measurement accuracy needs to reach 10 -16 After the repetition frequency is doubled, the measurement requirements of the repetition frequency are converted into f OMG Relative measurement accuracy 10 -16 The absolute frequency measurement accuracy is in the microhertz range. Conventional measurement methods are difficult to achieve this accuracy.
[0067] Furthermore, the frequency measurement module includes: a second mixer for receiving the reference microwave signal f cs and the optically generated microwave signal f OMG and mixing to obtain a difference frequency signal; a frequency counter connected to the second mixer for performing frequency counting measurement on the difference frequency signal to obtain a measurement frequency signal f test .
[0068] Furthermore, if Figure 4 As shown in the figure, the 9.005GHz signal of the photogenerated microwave is mixed with the 9.0GHz signal of the cesium fountain clock using a mixer to obtain a 5MHz signal, which is then measured using a frequency counter to obtain f test . OMG The measurement requirements of microhertz are converted to 5MHz f test The measurement requirements of microhertz. The relative frequency uncertainty requirements are from 10 -14 Reduced to 10 -12 This measurement accuracy is easy to achieve. Using a relatively mature commercial frequency comparator, it can be easily achieved. The relative measurement uncertainty of the frequency counter can be expressed as
[0069]
[0070] in Is the average value of the measurement within the measurement time τ. test is the relative uncertainty of the frequency counter measurement.
[0071] It should be noted that f OMG The measurement results can be expressed as:
[0072]
[0073] in is the average value of the measurements, which can be expressed as δy OMG is the relative uncertainty, which can be expressed as:
[0074]
[0075] The final measurement result of the optical clock can be expressed as:
[0076]
[0077] in is the average value of the measurement, which has the following expression:
[0078]
[0079] The relative uncertainty of an optical clock can be approximated by the following expression:
[0080]
[0081] In δy test 2 The limit Frequency comparator and Under the premise of the Class A uncertainty of the cesium fountain clock, the time required to measure the target statistical uncertainty of 1E-16 is 64,000 seconds, thus realizing the traceability requirement of the absolute frequency of the optical clock at the order of E-16 within one day.
[0082] In summary, this invention leverages the power of optical microwaves to lock the repetition frequency of an optical comb to an optical clock. This is then converted into a microwave signal driven by the optical clock. This signal is then directly compared with the local oscillator signal of a cesium fountain clock for beat frequency comparison, thereby addressing the issue of hydrogen clocks acting as flywheel clocks, which reduces traceability accuracy. By preferably using a low-temperature sapphire oscillator with excellent short-term stability as the local oscillator signal of the cesium fountain clock, it is expected that the second stability of the cesium fountain clock can be reduced to 1E-14, thereby achieving traceability requirements of the optical clock's absolute frequency on the order of E-16 within a single day.
[0083] Example 2
[0084] This embodiment provides an optical clock absolute frequency tracing method based on optically generated microwaves, which is applied to the optical clock absolute frequency tracing device based on optically generated microwaves, comprising: converting the output signal of the local oscillator into a reference microwave signal f under the control of a cesium fountain clock. cs ; The absolute frequency f of the optical clock oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep The photogenerated microwave signal f is detected by the photodetector and filtered by the second filter, and then frequency multiplied by the frequency multiplier to obtain the photogenerated microwave signal f OMG ; The reference microwave signal f cs and the optically generated microwave signal f OMG Mixing is performed to obtain a difference frequency signal, and then the difference frequency signal is subjected to frequency counting measurement to obtain a measurement frequency signal f test , to the absolute frequency f of the optical clock oc Conduct traceability.
[0085] Example 3
[0086] This embodiment provides a time-frequency calibration method based on optically generated microwaves, comprising: obtaining the measurement frequency signal f using the optical clock absolute frequency tracing method; test ; Using the measured frequency signal f test Perform time tracing and / or frequency tracing.
[0087] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. An optical clock absolute frequency tracing device based on optically generated microwaves, characterized in that: include: The cesium fountain clock module is used to convert the output signal of the local oscillator into a reference microwave signal f under the control of the cesium fountain clock. cs ; Optical microwave module, used to convert the optical clock frequency f oc Convert to microwave frequency f OMG ; comprising: an optical clock, a first mixer, an optical comb, a photodetector, a first filter, a second filter and a frequency multiplier; the absolute frequency of the optical clock f oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep The photogenerated microwave signal f is detected by the photodetector and filtered by the second filter, and then multiplied by the frequency multiplier to obtain the photogenerated microwave signal f OMG ; The frequency measurement module, together with the cesium fountain clock module and the optical microwave module, is used to measure the reference microwave signal f cs and the optically generated microwave signal f OMG Mixing is performed to obtain a difference frequency signal, and then the difference frequency signal is subjected to frequency counting measurement to obtain a measurement frequency signal f test , to achieve the absolute frequency f of the optical clock oc Conduct traceability.
2. The optical clock absolute frequency tracing device based on optically generated microwaves according to claim 1, characterized in that: The cesium fountain clock module includes: a local oscillator, a first microwave integrated chain, a power divider, a second microwave integrated chain and the cesium fountain clock; The local oscillator is used to generate a local oscillation signal; The first microwave synthesis chain is connected to the output end of the local oscillator and the output end of the cesium fountain clock, and is used to convert the local oscillator signal into a reference microwave signal f under the control of the cesium fountain clock. cs ; The power divider is connected to the first microwave integrated chain and is used to divide the reference microwave signal f cs Divided into the same first path and second path, the first path serves as the output signal of the cesium fountain clock module; The second microwave integrated chain is connected to the second path and is used to convert the reference microwave signal f cs Converting into a frequency signal that meets the input requirements of the cesium fountain clock; The cesium fountain clock is connected to the second microwave integrated chain and is used to feed back the difference frequency between the input required frequency signal and its own transition frequency to the first microwave integrated chain to control the reference microwave signal f cs Generation.
3. The optical clock absolute frequency tracing device based on optically generated microwaves according to claim 2, characterized in that: The reference microwave signal f cs Expressed as: f cs =f cs (1±δy cs ); Among them, δy cs is the relative uncertainty of the cesium fountain clock itself, δy cs-A Indicates type A uncertainty, i.e. statistical uncertainty; δy cs-B is the Type B uncertainty, i.e. the systematic error.
4. The optical clock absolute frequency tracing device based on light-generated microwaves according to claim 3, characterized in that: The local oscillator is a sapphire oscillator.
5. The optical clock absolute frequency tracing device based on optically generated microwaves according to claim 1, characterized in that: The absolute frequency f of the optical clock oc With the optically generated microwave signal f OMG The relational expression is: favorite oc =mf OMG +f ceo +f beat ; Among them, f ceo is the bias frequency of the optical comb, and m is a set multiple related to the frequency multiplication factor of the frequency multiplier and the beat frequency comb tooth frequency band of the optical comb.
6. The optical clock absolute frequency tracing device based on light-generated microwaves according to claim 1, characterized in that: The frequency measurement module includes: The second mixer is used to cs and the optically generated microwave signal f OMG Performing frequency mixing to obtain a difference frequency signal; A frequency counter is connected to the second mixer and is used to measure the frequency of the difference frequency signal to obtain a measured frequency signal f test .
7. The optical clock absolute frequency tracing device based on light-generated microwaves according to claim 6, characterized in that: The measured frequency signal f test The expression is: in, To measure the frequency signal f test The mean value of δy test is the relative uncertainty of the frequency counter measurement.
8. The optical clock absolute frequency tracing device based on light-generated microwaves according to claim 7, characterized in that: The expression of the relative uncertainty of the optical clock is: Among them, δy cs is the relative uncertainty of the cesium fountain clock itself.
9. A method for tracing the absolute frequency of an optical clock based on optically generated microwaves, characterized in that: The optical clock absolute frequency tracing device based on optically generated microwaves as described in any one of claims 1 to 8, wherein the absolute frequency tracing method comprises: Driven by the cesium fountain clock, the output signal of the local oscillator is converted into a reference microwave signal f cs ; The absolute frequency f of the optical clock oc and the comb frequency f of the optical comb comb After the beat frequency is obtained by the first mixer, the beat frequency is filtered by the first filter to obtain the beat frequency f beat , the beat frequency f beat Used to transmit to the optical comb to lock its repetition frequency f rep , the repetition frequency f rep The photogenerated microwave signal f is detected by the photodetector and filtered by the second filter, and then multiplied by the frequency multiplier to obtain the photogenerated microwave signal f OMG ; The reference microwave signal f cs and the optically generated microwave signal f OMG Mixing is performed to obtain a difference frequency signal, and then the difference frequency signal is subjected to frequency counting measurement to obtain a measurement frequency signal f test , to achieve the absolute frequency f of the optical clock oc Conduct traceability.
10. A time-frequency calibration method based on photogenerated microwaves, characterized in that: include: The measured frequency signal f is obtained by using the optical clock absolute frequency tracing method according to claim 9. test ; Using the measured frequency signal f test Perform time tracing and / or frequency tracing.