Non-paper-surface high-precision real-time time physical signal generation system and method based on light clock

Abstract

The invention particularly relates to a non-paper real-time time physical signal generation system and method based on an optical clock. The system comprises the optical clock, a microwave clock, an optical frequency comb, a counter, a phase fine tuning instrument and a PC terminal. The method comprises the following steps: recording and storing frequency difference data of an optical clock and a microwave clock in real time through a counter; establishing communication with a storage device of the PC end, reading the frequency difference data in real time, and filtering the frequency difference data to remove abnormal values; a linear quadratic Gaussian optimal control algorithm combined with Kalman filtering is adopted, and the control adjustment amount of the microwave clock is obtained through real-time calculation according to the filtered frequency difference data flow; and establishing communication with the phase fine tuning instrument, inputting the control adjustment quantity to the phase fine tuning instrument, performing real-time control adjustment on the microwave signal, and outputting a frequency domain or time domain signal by the phase fine tuning instrument, namely a real-time time physical signal after the light clock is controlled. According to the invention, real-time non-paper-surface high-precision time physical signals are generated, and the method can be widely applied to the field of optical frequency standards.

Description

Technical Field

[0001] The present invention relates to the technical field of optical frequency standards, and in particular to a non-paper-based high-precision time generation system and method based on an optical clock. Background Art

[0002] Time is one of the seven fundamental physical quantities in the International System of Units (SI) and is currently the most precisely measured and reproduced physical quantity. Currently, aerospace, communications, navigation and positioning, deep space exploration, geodesy, astronomical observation, and fundamental physics research all rely on high-precision time and frequency standards.

[0003] Currently, the global time standard, Coordinated Universal Time (UTC), is published monthly in the form of a time bulletin (Circular T) based on a comprehensive calculation of approximately 500 microwave atomic clocks around the world. As a time scale determined based on post-calculation, UTC is essentially a non-real-time, non-physical "paper" time, making it difficult to use directly for time services. For this reason, time laboratories in various countries around the world independently maintain their own local Coordinated Universal Time standard, UTC(k). The current excellent performance of UTC(k) is that its 30-day time deviation is in the nanosecond range, and its frequency stability reaches 10 -16 The generation of UTC(k) mainly relies on the cesium atomic fountain clock as the reference clock, and its frequency uncertainty is 1×10 -16 , which has approached the technical limit and has become a key factor restricting the further improvement of UTC(k) performance.

[0004] In the past two decades, optical frequency standards have developed rapidly. Currently, the stability and accuracy of neutral atom and single ion optical clocks have reached 10 -18 The optical clock based on optical frequency transitions has become a strong candidate for the definition of the next-generation second. A recognized requirement for redefining the second is to incorporate the optical frequency standard into the existing time scale. Many international research teams have carried out theoretical and experimental research on the time scale output based on optical clocks. At present, most of the research is still in the post-processing of frequency difference data, that is, to achieve the time scale output of the optical clock on paper. This paper time is a non-real-time time signal and it is difficult to meet the actual application needs. In the future, with optical clocks as the new generation of time standards, it is imperative to generate non-paper real-time time physical signals based on optical clocks. Therefore, it is urgent to establish a set of optical time scale generation systems and methods based on optical clocks, so as to fully utilize the excellent performance of optical clocks, generate real-time non-paper high-precision time physical signals, and effectively improve the performance of UTC(k).

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0006] The present invention provides a non-paper-based high-precision time generation system and method based on an optical clock, which can realize the real-time physical signal output driven by the optical clock, thereby overcoming the defects existing in the prior art to a certain extent.

[0007] Other features and advantages of the present invention will become apparent from the following detailed description, or may be learned in part by practice of the present invention.

[0008] According to a first aspect of the present invention, a non-paper-based high-precision time generation system based on an optical clock is provided, comprising: an optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for connecting optical and microwave signals to achieve frequency difference measurement, a counter for data acquisition, a phase trimmer for controlling the microwave clock, and a PC for data calculation. The outputs of the optical clock and the microwave clock are connected to the optical frequency comb; The output of the optical frequency comb is connected to the counter; The output of the counter is connected to the PC terminal; The outputs of the microwave clock and the PC are connected to the phase fine tuner, and the phase fine tuner outputs a time physics signal.

[0009] According to a first aspect of the present invention, there is provided a non-paper-based high-precision time generation method based on an optical clock, comprising: The frequency difference data between the optical clock and the microwave clock is recorded and stored in real time through a counter. Communication is established with the storage device on the PC to read the frequency difference data in real time and filter the frequency difference data to remove abnormal values. The linear quadratic Gaussian optimal steering algorithm (LQG) combined with Kalman filtering is used to calculate the steering adjustment of the microwave clock in real time based on the filtered frequency difference data stream. Establish communication with the phase fine tuner, input the control adjustment amount to the phase fine tuner, and perform real-time control adjustment on the microwave signal. The phase fine tuner outputs a frequency domain or time domain signal, which is the real-time time physical signal after the optical clock control.

[0010] In some exemplary embodiments, the filtering process uses the 3σ criterion to perform gross error elimination and difference, specifically: Calculate the standard deviation σ and mean value of the frequency difference data over a period of time. If the absolute value of the difference between a certain data and the mean value exceeds 3σ, it will be regarded as an outlier and removed.

[0011] In some exemplary embodiments, the linear quadratic Gaussian optimal steering algorithm combined with Kalman filtering is used to calculate the steering adjustment value for the microwave clock in real time based on the filtered frequency difference data stream, specifically: The Kalman filter estimates the state of the atomic clock based on the state equation and the measurement equation. The state equation is:

[0012] in, , 、 They are The frequency offset and frequency drift rate of the hydrogen clock relative to the optical clock; Transfer Matrix , It is k +1 and k The interval between measurements, i.e. ; Process noise , and are the noise terms of the fractional frequency difference and its drift rate, which obey the Gaussian distribution with mean zero and covariance Q; The measurement equation is:

[0013] in, It is k +1 frequency difference measurement value, , the observation noise is , with a mean of 0 and a standard deviation of R Gaussian distribution; Initial values ​​are set by prior conditions , initial covariance matrix 、 Q and R , combined with the measured values According to the Kalman filter theory, the estimated value is obtained by the following formula :

[0014]

[0015]

[0016]

[0017]

[0018] in, I is the identity matrix; After the microwave clock is driven, the control quantity must be added to the clock model ,in is the frequency correction control value, is the propagation quantity, and the state equation of the microwave clock under free operation is rewritten as:

[0019] Use the LQG optimal control algorithm to calculate the frequency correction control value in the above formula , by selecting the frequency correction control value Make the cost function J Minimum, the cost function is:

[0020] in, and There are two 2x2 diagonal matrices with variable non-zero parameters and a variable parameter value, which are adjusted by and The proportional relationship between the parameters realizes the frequency correction control value The best choice; The linear quadratic regulator is obtained by solving the Kalman filter steady-state Ricatti equation :

[0021] Let gain , by the linear quadratic regulator Calculate the gain , predicted by the Kalman filter Time estimate and gain , calculate the frequency correction control value :

[0022] The frequency correction control value This is the frequency control adjustment amount of the microwave clock, which is used to compensate for the frequency deviation of the microwave clock and realize the time scale output based on the optical clock.

[0023] In some exemplary embodiments, the inputting of the steering adjustment amount to the phase fine tuner to perform real-time steering adjustment on the microwave signal is specifically as follows: Correct the obtained frequency control value The signal is encoded according to the input rules of the phase fine tuner and sent to the phase fine tuner. The phase fine tuner adjusts the frequency of the input microwave clock signal 10MHz, that is, it adds the frequency correction control value to the 10MHz signal. The corrected signal is output from the output end of the phase fine-tuner in the form of frequency domain or time domain. The output signal is the real-time time physical signal after the optical clock is controlled.

[0024] In some exemplary embodiments, the phase trimmer output terminal outputs 10 MHz in frequency domain form.

[0025] In some exemplary embodiments, the phase trimmer output terminal outputs 1 pps in time domain format.

[0026] Embodiments of the present invention provide a non-paper, high-precision time generation system and method based on an optical clock. The system includes an optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for linking optical and microwave signals to measure frequency differences, a counter for data acquisition, and a phase trimmer for steering the microwave clock. The method includes a module for reading and filtering frequency difference data in real time, an LQG steering algorithm module combined with a Kalman filter, and a frequency steering module for communication and control between hardware systems, as well as calculation and adjustment of steering variables. Through the integration of the system and method, real-time physical signal output for optical clock steering is achieved. The present invention establishes a system and method based on optical time scale generation, fully leveraging the exceptional performance of optical clocks to generate real-time, non-paper, high-precision time physical signals. It can be widely used in the field of optical frequency standards, providing high-precision, real-time physical signals for applications such as aerospace, navigation and positioning, and geodesy. Furthermore, this invention represents a key step in addressing changes to the international definition of the second.

[0027] Compared with the existing technology, it has at least the following advantages: (1) Real-time physical time output: Based on this system and method, communication and control between hardware systems, real-time calculation and adjustment of driving quantities are completed, and non-paper physical time signals are output.

[0028] (2) Improved accuracy: The intermittent operation of the optical clock can improve the system time accuracy to the order of e-17, and the time difference with UTC is less than 1ns.

[0029] (4) Reduced cost and complexity: A single optical clock drives a microwave clock, replacing the traditional multi-clock weighted mode, reducing system complexity by more than 50%.

[0030] (5) High robustness: The LQG algorithm combined with Kalman filtering can effectively reduce the impact of various types of noise on the system, eliminate the impact of outliers on frequency control in the shortest time, and improve the stability of the signal after frequency control and the reliability of the system when the optical clock is interrupted or data is unavailable.

[0031] (6) At the same time, this system is a key step in redefining the international unit of second based on optical clocks in the future.

[0032] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are incorporated into and constitute a part of this specification, illustrate embodiments consistent with the present invention, and together with the description, serve to explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and it is clear that those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0034] Figure 1 Schematic diagram of the non-paper high-precision real-time time physical signal generation system based on an optical clock of the present invention; Figure 2 Schematic diagram of the non-paper high-precision real-time time physical signal generation method based on an optical clock of the present invention; Figure 3 This is a flow chart for establishing an LQG steering algorithm combined with Kalman filtering according to embodiment 1 of the present invention. DETAILED DESCRIPTION

[0035] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0036] In addition, the accompanying drawings are merely schematic illustrations of the present invention and are not necessarily drawn to scale. Identical reference numerals in the figures denote identical or similar parts, and thus repetitive descriptions thereof will be omitted. Some of the blocks shown in the accompanying drawings are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0037] Prior art has disclosed a method for intermittently operating an optical clock to control a microwave clock to produce high-precision time. This method includes three steps: frequency downconversion of the optical clock and determination of the frequency difference with the microwave clock, establishment of a frequency difference model, optical clock control, and output of optical-frequency atomic time. By intermittently operating the optical clock to control the microwave clock, continuous high-precision timescale output is achieved. This method uses a linear fitting method to calculate the control adjustment of the microwave clock relative to the optical clock. However, this method requires a certain amount of historical data accumulation because it is based on historical data forecasts and cannot detect anomalies in real time. The frequency correction results will be affected by outliers throughout the forecast period, ultimately affecting the short-term and long-term stability of the output signal. Furthermore, this method does not involve the processing of real-time frequency difference data streams or the real-time calculation and control of control values. Therefore, it is a paper time signal achieved through post-processing of frequency difference data.

[0038] In response to the shortcomings and deficiencies of the existing technology, this exemplary embodiment provides a non-paper-based high-precision time generation system based on an optical clock, which is used to complete the real-time filtering processing of frequency difference data, the real-time calculation and control of the steering adjustment amount, and the final physical signal output based on the optical clock. Figure 1 As shown, it includes an optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for connecting optical signals and microwave signals to complete frequency difference measurement, a counter for data acquisition, a phase trimmer for driving and controlling the microwave clock, and a PC for data processing.

[0039] The connection relationship between the various components: the output of the optical clock and microwave clock is connected to the optical frequency comb; the output of the optical frequency comb is connected to the counter; the output of the counter is connected to the PC end; the output of the microwave clock and PC end is connected to the phase fine tuner, and the phase fine tuner outputs the time physics signal.

[0040] Based on the aforementioned optical clock-based, non-paper-based, high-precision time generation system, this example embodiment also provides an optical clock-based, non-paper-based, high-precision time generation method. This method is used to implement communication and control between hardware systems, as well as calculation and adjustment of steering variables. The method includes a frequency difference data reading and real-time filtering processing module, an LQG steering algorithm module combined with a Kalman filter, and a frequency steering module. This method achieves real-time physical signal output for optical clock steering.

[0041] refer to Figure 1 As shown, the non-paper high-precision time generation method based on an optical clock may specifically include the following steps: Step S11, recording and storing the frequency difference data between the optical clock and the microwave clock in real time through a counter; establishing communication with a storage device, reading the frequency difference data in real time, and filtering the frequency difference data to remove abnormal values; Step S12, using the LQG steering algorithm combined with Kalman filtering to obtain a steering adjustment value for the microwave clock through real-time calculation based on the frequency difference data stream; Step S13: establish communication with the phase fine tuner, input the control adjustment amount to the phase fine tuner, perform real-time control adjustment on the microwave signal, and the phase fine tuner outputs a 1pps or 10MHz signal.

[0042] Below, each step in this exemplary implementation will be described in more detail with reference to the accompanying drawings and embodiments.

[0043] Example 1 In step S11, the frequency difference data reading and real-time filtering processing module establishes communication with the frequency difference data storage device, reads the frequency difference data in real time, and performs filtering processing on the frequency difference data.

[0044] Because optical clocks operate intermittently and may experience lock-out or noise during measurement, frequency difference data anomalies can occur. Therefore, filtering the real-time frequency difference data is necessary to eliminate outliers. This filtering primarily utilizes the 3σ criterion for gross error removal and interpolation. First, the standard deviation σ and average value of the frequency difference data over a period of time are calculated. If the absolute value of a data point differs from the average by more than 3σ, it is considered an outlier and removed. The average of the preceding and following data is then calculated as the interpolated value to obtain valid measurement data.

[0045] In step S12, by combining the LQG steering algorithm with Kalman filtering, the LQG algorithm is used to continuously approximate the optimal control by minimizing the quadratic cost function, and then combined with the Kalman filtering method, a recursive formula for the gain matrix is ​​constructed, and the control value and the filter are continuously iterated until convergence to obtain the optimal filter. The LQG algorithm combined with Kalman filtering does not require the accumulation of historical data and has higher real-time performance in detecting anomalies. This algorithm can effectively reduce the impact of various types of noise on the system, eliminate the impact of outliers on frequency steering in the shortest time, and improve the stability of the signal after frequency steering and the reliability of the system when the optical clock is interrupted or data is unavailable. This method further improves the short-term stability of the final result by considering the short-term stability of atomic time. Compared with the linear fitting method used in the existing patent "Method for Driving Microwave Clocks to Produce High-Precision Time by Intermittent Operation of Optical Clocks," it can effectively improve the time scale performance after steering.

[0046] Specifically, the detection mode may include pre-configured: long-range detection mode, short-range detection mode.

[0047] The steering adjustment for the microwave clock is calculated by combining the LQG steering algorithm module with the Kalman filter. The Kalman filter mainly estimates the state of the atomic clock based on the state equation and measurement equation. The state equation is: (1) in, , 、 They are The frequency offset and frequency drift rate of the hydrogen clock relative to the optical clock; Transfer Matrix , is the interval between the k+1th and kth measurements, that is, ; Process noise , and are the noise terms of the fractional frequency difference and its drift rate, respectively. Assuming they obey zero mean, the covariance is Q Gaussian distribution, and Mainly comes from the noise of the free running of the hydrogen clock and the time interval Regarding, different time intervals, Q There are different values.

[0048] The measurement equation is: (2) in, It is k +1 frequency difference measurement value, , the observation noise is , assuming that its mean is 0 and its standard deviation is R Gaussian distribution.

[0049] Initial values ​​are set by prior conditions , initial covariance matrix 、 Q and R , combined with the measured values According to the Kalman filter theory, the estimated value is obtained by the following formula .

[0050] (3) (4) (5) (6) (7) in, I is the identity matrix.

[0051] After the microwave clock is driven, the control quantity must be added to the clock model ,in is the frequency correction control value, is the propagation quantity, and the state equation (1) under free operation is rewritten as: (8) Use the LQG optimal control algorithm to calculate the frequency correction control value in equation (8): , by selecting the frequency correction control value Minimize the cost function J, the cost function is: (9) in, and There are two 2x2 diagonal matrices with variable non-zero parameters and a variable parameter value, which are adjusted by and The proportional relationship between the parameters realizes the frequency correction control value The linear quadratic regulator is obtained by solving the Kalman filter steady-state Ricatti equation. : (10) Let gain , by the linear quadratic regulator Calculate the gain , predicted by the Kalman filter Time estimate and gain , the frequency correction control value can be calculated : (11) The frequency correction control value This is the frequency control adjustment amount of the microwave clock, which is used to compensate for the frequency deviation of the microwave clock and realize the time scale output based on the strontium atomic optical clock.

[0052] The specific establishment process of the LQG steering algorithm combined with Kalman filtering is as follows Figure 3 shown.

[0053] Step 1. According to the prior conditions, set the initial values ​​X(0) and P(0), set k=1, and estimate the covariance matrices R and Q; Step 2. In the gain calculation loop, solve based on the values ​​of R and Q. and ; Step 3. In the filter calculation loop, calculate X(k+1) by combining the frequency difference measurement value Z(k) at time k. Step 4. Calculate the minimum cost function J , get the optimal frequency correction control value , to compensate for the frequency deviation of the hydrogen clock; let k=k+1 and return to Step 2.

[0054] In step S13, the output signal of the free-running microwave clock is controlled by a phase fine-tuner, and the frequency difference predicted in step S12 is input into the phase fine-jumper as the frequency control variable, thereby correcting the phase fine-tuner in real time and finally outputting a real-time, high-precision time physics signal driven by the optical clock.

[0055] Specifically, after establishing communication with the phase fine-tuning instrument, the frequency correction control value obtained above is The signal is encoded according to the input rules of the phase fine tuner and sent to the phase fine tuner. The phase fine tuner adjusts the frequency of the input microwave clock 10MHz signal, that is, it adds the frequency correction control value to the 10MHz signal. The corrected signal is output from the output end of the phase fine-tuner in the form of frequency domain (10MHz) and time domain (1pps). The output signal is the real-time time physical signal after the optical clock is controlled.

[0056] Furthermore, the above-described figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention and are not intended to be limiting. It is readily understood that the processes illustrated in the above-described figures do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0057] Other embodiments of the present invention will readily occur to those skilled in the art after considering the specification and practicing the invention herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the claims.

[0058] It should be understood that the present invention is not limited to the exact construction described above and shown in the drawings and that various modifications and variations can be made without departing from the scope thereof, which is limited only by the appended claims.

Claims

1. A non-paper real-time time physical signal generation system based on an optical clock, characterized in that: include: An optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for connecting optical and microwave signals to measure frequency differences, a counter for data acquisition, a phase trimmer for controlling the microwave clock, and a PC for data calculations. The outputs of the optical clock and the microwave clock are connected to the optical frequency comb; The output of the optical frequency comb is connected to the counter; The output of the counter is connected to the PC terminal; The outputs of the microwave clock and the PC are connected to the phase fine tuner, and the phase fine tuner outputs a time physics signal.

2. A method for generating a non-paper real-time physical time signal based on an optical clock, based on the non-paper real-time physical time signal generation system based on an optical clock according to claim 1, characterized in that: include: The frequency difference data between the optical clock and the microwave clock is recorded and stored in real time through a counter; Establish communication with the storage device on the PC side, read the frequency difference data in real time, and filter the frequency difference data to remove abnormal values; The linear quadratic Gaussian optimal steering algorithm (LQG) combined with Kalman filtering is used to calculate the steering adjustment of the microwave clock in real time based on the filtered frequency difference data stream. Establish communication with the phase fine tuner, input the control adjustment amount to the phase fine tuner, and perform real-time control adjustment on the microwave signal. The phase fine tuner outputs a frequency domain or time domain signal, which is the real-time time physical signal after the optical clock control.

3. The method according to claim 2, characterized in that The filtering process uses the 3σ criterion to remove gross errors and perform difference, specifically: Calculate the standard deviation σ and mean value of the frequency difference data over a period of time. If the absolute value of the difference between a certain data and the mean value exceeds 3σ, it will be regarded as an outlier and removed.

4. The method according to claim 2, characterized in that The linear quadratic Gaussian optimal steering algorithm combined with Kalman filtering is used to calculate the steering adjustment of the microwave clock in real time based on the filtered frequency difference data stream, specifically: The Kalman filter estimates the state of the atomic clock based on the state equation and the measurement equation. The state equation is: in, , 、 They are The frequency offset and frequency drift rate of the hydrogen clock relative to the optical clock; Transfer Matrix , It is k +1 and k The interval between measurements, i.e. ; Process noise , and are the noise terms of the fractional frequency difference and its drift rate, which obey the Gaussian distribution with mean zero and covariance Q; The measurement equation is: in, It is k +1 frequency difference measurement value, , the observation noise is , with a mean of 0 and a standard deviation of R Gaussian distribution; Initial values ​​are set by prior conditions , initial covariance matrix 、 Q and R , combined with the measured values According to the Kalman filter theory, the estimated value is obtained by the following formula : in, I is the identity matrix; After the microwave clock is driven, the control quantity must be added to the clock model ,in is the frequency correction control value, is the propagation quantity, and the state equation of the microwave clock under free operation is rewritten as: Use the LQG optimal control algorithm to calculate the frequency correction control value in the above formula , by selecting the frequency correction control value Make the cost function J Minimum, the cost function is: in, and There are two 2x2 diagonal matrices with variable non-zero parameters and a variable parameter value, which are adjusted by and The proportional relationship between the parameters realizes the frequency correction control value The best choice; The linear quadratic regulator is obtained by solving the Kalman filter steady-state Ricatti equation : Let gain , by the linear quadratic regulator Calculate the gain , predicted by the Kalman filter Time estimate and gain , calculate the frequency correction control value : The frequency correction control value This is the frequency control adjustment amount of the microwave clock, which is used to compensate for the frequency deviation of the microwave clock and realize the time scale output based on the optical clock.

5. The method according to claim 4, characterized in that The control adjustment amount is input to the phase fine tuner to perform real-time control adjustment on the microwave signal, specifically: Correct the obtained frequency control value The signal is encoded according to the input rules of the phase fine tuner and sent to the phase fine tuner. The phase fine tuner adjusts the frequency of the input microwave clock signal 10MHz, that is, it adds the frequency correction control value to the 10MHz signal. The corrected signal is output from the output end of the phase fine-tuner in the form of frequency domain or time domain. The output signal is the real-time time physical signal after the optical clock is controlled.

6. The method according to claim 5, characterized in that The output of the phase fine tuner is 10 MHz in the frequency domain.

7. The method according to claim 5, characterized in that The output of the phase trimmer is 1 pps in the time domain.

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