A Non-Paper-Based High-Precision Real-Time Physical Signal Generation System and Method Based on Optical Clock

Abstract

This invention specifically relates to a non-paper-based real-time time physical signal generation system and method based on an optical clock. The system includes: an optical clock, a microwave clock, an optical frequency comb, a counter, a phase fine-tuning instrument, and a PC. The method includes: recording and storing the frequency difference data of the optical clock and the microwave clock in real time through the counter; establishing communication with the storage device on the PC to read the frequency difference data in real time and filtering the frequency difference data to remove outliers; employing a linear quadratic Gaussian optimal driving algorithm combined with Kalman filtering to calculate the driving adjustment amount for the microwave clock in real time based on the filtered frequency difference data stream; establishing communication with the phase fine-tuning instrument, inputting the driving adjustment amount to the phase fine-tuning instrument, and performing real-time driving adjustment of the microwave signal; the phase fine-tuning instrument outputs a frequency domain or time domain signal, which is the real-time time physical signal after optical clock driving. This invention generates a real-time, non-paper-based, high-precision time physical signal, which can be widely used in the field of optical frequency standards.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical frequency standard, and in particular to a non-paper high-precision time generation system and method based on optical clock. BACKGROUND

[0002] Time is one of the seven basic physical quantities in the International System of Units, and is also the physical quantity with the highest measurement and reproduction precision. Currently, aerospace, communication, navigation and positioning, deep space exploration, geodesy, astronomical observation, and fundamental physics research all rely on high-precision time and frequency references.

[0003] Currently, the global time standard, Coordinated Universal Time (UTC), is calculated based on the comparison of about 500 microwave atomic clocks around the world and is published in the form of a time bulletin (Circular T) every month. As a time scale determined based on post-processing, UTC is essentially a non-real-time and non-physical "paper" time, which is difficult to be directly used for time service. Therefore, time laboratories around the world independently maintain their own local Coordinated Universal Time reference UTC(k). The current excellent UTC(k) has a 30-day time deviation of nanoseconds and a frequency stability of 10 -16 orders of magnitude. The generation of UTC(k) mainly relies on cesium fountain clocks as reference clocks, and the frequency uncertainty of cesium fountain clocks is 1×10 -16 , which has approached the technical limit and has become a key factor restricting the further improvement of the performance of UTC(k).

[0004] In the past two decades, optical frequency standards have developed rapidly. Currently, the stability and accuracy of optical frequency standards based on neutral atoms and single-ion optical clocks have reached 10 -18 orders of magnitude, which is more than two orders of magnitude higher than that of the existing reference clock, cesium fountain clock. Optical clocks based on optical frequency transitions have become strong candidates for the new generation of second definition, and a widely recognized requirement for redefining the second is to incorporate optical frequency standards into the existing time scale. Many research teams around the world have carried out theoretical and experimental research on time scale output based on optical clocks. Most of the current research is still in the post-processing of frequency difference data, i.e., realizing the paper-based time scale output of optical clock control. This paper-based time is a non-real-time time signal, which is difficult to meet the real application requirements. In the future, it is imperative to use optical clocks as the new generation of time reference to generate a real-time non-paper physical time signal based on optical clocks. Therefore, it is urgent to establish an optical time scale generation system and method based on optical clocks, so as to fully utilize the excellent performance of optical clocks and generate a real-time non-paper high-precision time physical signal to effectively improve the performance of UTC(k).

[0005] It is to be understood that the information disclosed in the Background section is only for the purpose of enhancing the understanding of the background of the present application, and thus can include information that does not constitute prior art that is already known to those of ordinary skill in the art. SUMMARY

[0006] The present application provides a non-paper high-precision time generation system and method based on an optical clock, which can realize real-time physical signal output under the control of the optical clock, and can overcome the defects in the prior art to some extent.

[0007] Other characteristics and advantages of the present application will become apparent from the following detailed description, or will be learned by practice of the present application.

[0008] According to a first aspect of the present application, a non-paper 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 the optical signal and the microwave signal to complete frequency difference measurement, a counter for data acquisition, a phase trimmer for controlling the microwave clock, and a PC terminal for data calculation.

[0009] The output of the optical clock and the microwave clock is connected to the optical frequency comb;

[0010] The output of the optical frequency comb is connected to the counter;

[0011] The output of the counter is connected to the PC terminal;

[0012] The output of the microwave clock and the PC terminal is connected to the phase trimmer, and the phase trimmer outputs a time physical signal.

[0013] According to a first aspect of the present application, a non-paper high-precision time generation method based on an optical clock is provided, comprising:

[0014] The frequency difference data of the optical clock and the microwave clock are recorded and stored in real time by the counter; communication is established with the storage device of the PC terminal, the frequency difference data is read in real time, and the frequency difference data is filtered to remove outliers;

[0015] A linear quadratic Gaussian optimal control algorithm combined with Kalman filtering, i.e. LQG control algorithm, is used to calculate the control adjustment amount of the microwave clock in real time according to the filtered frequency difference data stream;

[0016] Communication is established with the phase trimmer, the control adjustment amount is input to the phase trimmer, the microwave signal is adjusted in real time, and the phase trimmer outputs a frequency domain or time domain signal, which is the real-time time physical signal after the optical clock control.

[0017] In some exemplary embodiments, the filtering process uses the 3σ criterion for outlier rejection and difference, specifically:

[0018] Calculate the standard deviation σ and mean of frequency data over a period of time. If the absolute value of the difference between a certain data point and the mean exceeds 3σ, it is considered an outlier and removed.

[0019] In some exemplary embodiments, the linear quadratic Gaussian optimal driving algorithm combined with Kalman filtering is used to calculate the driving adjustment amount of the microwave clock in real time based on the filtered frequency difference data stream, specifically as follows:

[0020] Kalman filtering estimates the state of an atomic clock based on a state equation and a measurement equation. The state equation is:

[0021]

[0022] in, , , They are The frequency offset and frequency drift rate of the hydrogen clock relative to the optical clock;

[0023] Transition matrix , It is the first k +1 and the k The interval between measurements, i.e. ;

[0024] Process noise , and These are the noise terms, namely the fractional frequency difference and its drift rate, which follow a Gaussian distribution with zero mean and covariance Q.

[0025] The measurement equation is:

[0026]

[0027] in, It is the first k +1st frequency difference measurement value, The observation noise is The mean is 0 and the standard deviation is . R Gaussian distribution;

[0028] Initial values ​​are set by prior conditions. Initial covariance matrix , Q and R Combined with measured values According to Kalman filtering theory, the estimated value is obtained from the following formula. :

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] in, I It is the identity matrix;

[0035] Once a microwave clock is controlled, control parameters must be added to the clock model. ,in It is the frequency correction control value. It is the propagation quantity. The state equation of the microwave clock under free operation is rewritten as:

[0036]

[0037] The frequency correction control value in the above formula is calculated using the LQG optimal control algorithm. By selecting the frequency correction control value Make the cost function J Minimize, the cost function is:

[0038]

[0039] in, and These are a 2x2 diagonal matrix with two variable non-zero parameters and a variable parameter value, which are adjusted by... and The proportional relationship between parameters enables the control of frequency correction values. The optimal choice;

[0040] The linear quadratic regulator is obtained by solving the steady-state Ricatti equation of the Kalman filter. :

[0041]

[0042] Let gain By a linear quadratic regulator Calculate the gain Predicted using a Kalman filter Time estimate and gain Calculate the frequency correction control value :

[0043]

[0044] The frequency correction control value That is, the frequency control adjustment amount of the microwave clock, so as to compensate for the frequency deviation of the microwave clock, and realize the output of the time scale based on the optical clock.

[0045] In some example embodiments, the control adjustment amount is input to the phase trimmer, and the microwave signal is adjusted in real time, specifically:

[0046] The obtained frequency correction control value According to the input rule of the phase trimmer, the frequency correction control value is encoded and sent to the phase trimmer, and the phase trimmer adjusts the frequency of the input 10MHz microwave clock signal, that is, adds the frequency correction control value to the 10MHz signal The corrected signal is output from the output end of the phase trimmer in frequency domain or time domain, and the output signal is the real-time time physical signal after the optical clock is controlled.

[0047] In some example embodiments, the phase trimmer output end outputs in frequency domain as 10MHz.

[0048] In some example embodiments, the phase trimmer output end outputs in time domain as 1pps.

[0049] The embodiment of the application provides a non-paper high-precision time generation system and method based on an optical clock, wherein the system comprises an optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for connecting an optical signal and a microwave signal to complete frequency difference measurement, a counter for data acquisition, and a phase trimmer for controlling the microwave clock. The method comprises a frequency difference data reading and real-time filtering processing module, a LQG control algorithm module combined with Kalman filtering, and a frequency control module for completing communication and control between hardware systems, control amount calculation and adjustment. Through the integration of the system and the method, the real-time physical signal output after the optical clock control is completed. The application establishes a system and method based on optical time scale generation, fully utilizes the excellent performance of the optical clock, and generates a real-time non-paper high-precision time physical signal. It can be widely used in the field of optical frequency standard, and provides high-precision real-time physical signals for aviation, navigation, positioning, geodetic surveying, etc. At the same time, the application is a key step to cope with the change of international second definition.

[0050] Compared with the prior art, the application has at least the following advantages:

[0051] (1) Real-time physical time output: based on the system and method, the communication and control between hardware systems, the real-time calculation and adjustment of the control amount, and the output of the non-paper physical time signal are completed.

[0052] (2) Precision improvement: the intermittent operation of the optical clock can improve the system time precision to the e-17 order of magnitude, and the time difference with UTC is less than 1ns.

[0053] (4) Cost and complexity reduction: single optical clock governs microwave clock, instead of traditional multi-clock weighted mode, system complexity is reduced by more than 50%.

[0054] (5) High robustness: LQG algorithm combined with Kalman filter can well reduce the influence of various types of noise on the system, eliminate the influence of abnormal values on frequency governance in the shortest time, and improve the stability of the signal after frequency governance and the reliability of the system in the case of optical clock interruption or data unavailability.

[0055] (6) At the same time, the system is a key step for redefining the international unit second based on optical clock in the future.

[0056] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0057] The drawings herein are incorporated into the specification and form a part of the specification, show embodiments consistent with the present application, and together with the specification serve to explain the principles of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0058] Figure 1 is a schematic diagram of the non-paper high-precision real-time time physical signal generation system based on optical clock of the present application;

[0059] Figure 2 is a schematic diagram of the non-paper high-precision real-time time physical signal generation method based on optical clock of the present application;

[0060] Figure 3 is a flowchart of the establishment of the LQG governance algorithm combined with Kalman filter of embodiment 1 of the present application. DETAILED DESCRIPTION

[0061] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations may, however, be implemented in many different forms and should not be construed as limited to the examples set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the gist of the example implementations to those skilled in the art. The features, structures, or characteristics described in connection with the examples can be combined in any suitable manner in one or more implementations.

[0062] Furthermore, the accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which like numerals refer to like elements.

[0063] In the prior art, a method for generating high-precision time by intermittently operating an optical clock to control a microwave clock has been disclosed, which includes three steps of optical clock frequency down-conversion and frequency difference measurement with the microwave clock, frequency difference model establishment, optical clock control, and optical frequency atomic time output. The method realizes continuous high-precision time scale output by intermittently operating the optical clock to control the microwave clock. The method uses linear fitting to calculate the control adjustment amount of the microwave clock relative to the optical clock, but the method needs to accumulate a certain amount of historical data. Because it is based on historical data prediction, it cannot find abnormalities in real time, and the frequency correction result will be affected by abnormal values during the entire prediction period, ultimately affecting the short-term and long-term stability of the output signal. At the same time, the method does not involve processing of real-time frequency difference data stream, real-time calculation and control of the control value, and therefore is a paper time signal based on post-processing of frequency difference data.

[0064] In view of the shortcomings and deficiencies of the prior art, the present example embodiment provides a non-paper high-precision time generation system based on an optical clock, which is used to complete real-time filtering processing of frequency difference data, real-time calculation and control of control adjustment amount, and finally output of a physical signal based on the optical clock. Referring to 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 the optical signal and the microwave signal to complete frequency difference measurement, a counter for data acquisition, a phase trimmer for controlling the microwave clock, and a PC terminal for data processing.

[0065] The connection relationship between the various components is as follows: 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 terminal are connected to the phase trimmer, and the phase trimmer outputs a time physical signal.

[0066] Based on the above-mentioned non-paper high-precision time generation system based on an optical clock, the present example embodiment also provides a non-paper high-precision time generation method based on an optical clock, which is used to complete communication and control between hardware systems, calculation and adjustment of control amount, and contains a frequency difference data reading and real-time filtering processing module, a LQG control algorithm module combined with Kalman filtering, and a frequency control module. The method completes real-time physical signal output of optical clock control.

[0067] Reference Figure 1 As shown, the non-paper-based high-precision time generation method based on the optical clock can specifically include the following steps:

[0068] In step S11, the frequency difference data of the optical clock and the microwave clock is recorded and stored in real time by a counter; a communication is established with a storage device, the frequency difference data is read in real time, and the frequency difference data is filtered to remove abnormal values.

[0069] In step S12, an LQG control algorithm combined with Kalman filtering is used to calculate the control adjustment of the microwave clock in real time according to the frequency difference data stream.

[0070] In step S13, a communication is established with a phase trimmer, the control adjustment is input to the phase trimmer, the microwave signal is adjusted in real time, and the phase trimmer outputs a 1pps or 10MHz signal.

[0071] In the following, each step in the example embodiment will be described in more detail with reference to the accompanying drawings and examples.

[0072] Example 1

[0073] In step S11, a communication is established with a frequency difference data storage device through a frequency difference data reading and real-time filtering module, the frequency difference data is read in real time, and the frequency difference data is filtered.

[0074] Since the optical clock is intermittently operated, and there may be a loss of lock state during operation, or noise during measurement, resulting in abnormal frequency difference data. Therefore, the real-time collected frequency difference data needs to be filtered to eliminate abnormal values. The filtering mainly uses the 3σ criterion for gross error rejection and difference. First, calculate the standard deviation σ and the average value of the frequency difference data in a period of time. If the absolute value of the difference between a certain data and the average value exceeds 3σ, it is considered as an abnormal value, which is removed. After that, the average value of the data before and after the calculation is taken as the interpolated data to obtain the effective measurement data.

[0075] In step S12, the LQG algorithm is used to minimize the quadratic cost function to continuously approach the optimal control, and the Kalman filtering method is combined to construct the recursive formula of the gain matrix, and the control value and the filter are iterated until convergence to obtain the optimal filter. The LQG algorithm combined with Kalman filtering does not need to accumulate historical data, and has higher real-time performance in discovering abnormalities. This algorithm can well reduce the influence of various types of noise on the system, eliminate the influence of abnormal values on frequency control in the shortest time, and improve the stability of the frequency control signal and the reliability of the system in the case of optical clock interruption or unavailable data. It can be used in the fields of time and frequency measurement, satellite navigation, etc.

[0076] Based on the short-term stability of atomic time, the short-term stability of the final result is further improved. Compared with the linear fitting method used in the existing patent "Method for Generating High-Precision Time by Driving Microwave Clocks through Intermittent Operation of Optical Clocks", it can effectively improve the timescale performance after driving.

[0077] Specifically, the detection modes can include pre-configured: long-range detection mode and short-range detection mode.

[0078] The driving adjustment for the microwave clock is calculated by combining the LQG driving algorithm module with Kalman filtering. Kalman filtering primarily estimates the state of the atomic clock based on the state equation and measurement equation. The state equation is:

[0079] (1)

[0080] in, , , They are The frequency offset and frequency drift rate of the hydrogen clock relative to the optical clock;

[0081] Transition matrix , It is the interval between the (k+1)th and the kth measurements, i.e. ;

[0082] Process noise , and These are the noise terms representing the fractional frequency difference and its drift rate, respectively, assumed to have a mean of zero and a covariance of... Q Gaussian distribution, and The noise primarily originates from the free-running of the hydrogen clock, and the time interval... Regarding different time intervals Q It can take different values.

[0083] The measurement equation is:

[0084] (2)

[0085] in, It is the first k +1st frequency difference measurement value, The observation noise is Assume it follows a mean of 0 and a standard deviation of . R The Gaussian distribution.

[0086] Initial values ​​are set by prior conditions. Initial covariance matrix , Q and R Combined with measured values According to Kalman filtering theory, the estimated value is obtained from the following formula .

[0087] (3)

[0088] (4)

[0089] (5)

[0090] (6)

[0091] (7)

[0092] wherein, I is a unit matrix.

[0093] After the microwave clock is controlled, the control quantity must be added to the clock model wherein, is the frequency correction control value, is the propagation quantity, and the state equation (1) under free operation is rewritten as:

[0094] (8)

[0095] The LQG optimal control algorithm is used to calculate the frequency correction control value in equation (8), and the cost function J is minimized by selecting the frequency correction control value The cost function is:

[0096] (9)

[0097] wherein, and are a 2x2 diagonal matrix with two variable non-zero parameters and a variable parameter value, respectively, and the optimal selection of the frequency correction control value is achieved by adjusting the proportional relationship between the parameters The linear quadratic regulator is obtained by solving the Kalman filter steady-state Ricatti equation:

[0098] (10)

[0099] Let the gain be calculated by the linear quadratic regulator , the gain is calculated by the gain , and the estimated value at time ​The frequency correction control value :

[0100] (11)

[0101] The frequency correction control value is the frequency steering adjustment amount of the microwave clock, which compensates for the frequency deviation of the microwave clock, and realizes the time scale output based on the strontium atomic optical clock.

[0102] The specific establishment process of the LQG steering algorithm combined with Kalman filtering is shown in Figure 3 .

[0103] Step 1. According to the prior condition, set the initial value X(0) and P(0), let k=1, estimate the covariance matrix R, Q;

[0104] Step 2. In the gain calculation loop, solve and according to the values of R and Q;

[0105] Step 3. In the filtering calculation loop, calculate X(k+1) combined with the frequency difference measurement value Z(k) at time k;

[0106] 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, return to Step 2.

[0107] In step S13, the control of the free-running microwave clock output signal is realized by the phase trimmer, and the frequency difference predicted in step S12 is input into the phase trimmer as the frequency control amount, so as to real-time correct the phase trimmer, and finally output the real-time high-precision time physical signal of the optical clock steering.

[0108] Specifically, after establishing communication with the phase trimmer, the frequency correction control value obtained above is encoded and sent to the phase trimmer according to the input rules of the phase trimmer, and the phase trimmer adjusts the frequency of the input microwave clock 10MHz signal, that is, adds the frequency correction control value to the 10MHz signal, and the corrected signal is output from the output end of the phase trimmer in the form of frequency domain (10MHz) and time domain (1pps), and the output signal is the real-time time physical signal after the optical clock steering.

[0109] Moreover, the above-described figures are only a schematic representation of the processes comprised in the method according to the exemplary embodiments of the present application, and are not intended to limit purposes. It is readily understood that the processes shown in the above-described figures do not indicate or limit the chronological order of these processes. In addition, it is readily understood that these processes can be executed, for example, synchronously or asynchronously in a plurality of modules.

[0110] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0111] It is to be understood that the application is not limited to the precise details of design and construction set forth above and illustrated in the drawings, but that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is indicated by the appended claims, rather than by the foregoing description.

Claims

1. A non-paper-based real-time time physical signal generation method based on an optical clock, characterized by, The application relates to a non-paper real-time time physical signal generation system based on an optical clock, which comprises an optical clock as a frequency reference, a microwave clock as a flywheel, an optical frequency comb for connecting the optical signal and the microwave signal to complete frequency difference measurement, a counter for data acquisition, a phase trimmer for controlling the microwave clock, and a PC terminal for data calculation; the output of the optical clock and the output of 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 output of the microwave clock and the output of the PC terminal are connected to the phase trimmer, and the phase trimmer outputs a time physical signal; frequency difference data of the optical clock and the microwave clock are recorded and stored in real time through the counter; communication is established with a storage device of the PC terminal, frequency difference data are read in real time, and filtering treatment is conducted on the frequency difference data to remove abnormal values; a linear quadratic Gaussian optimal control algorithm (LQG) combined with Kalman filtering is adopted to obtain a control adjustment amount of the microwave clock in real time according to the filtered frequency difference data stream; communication is established with the phase trimmer, the control adjustment amount is input into the phase trimmer, real-time control adjustment is conducted on the microwave signal, and the phase trimmer outputs a frequency domain or time domain signal, that is, a real-time time physical signal after the optical clock is controlled; the filtering treatment utilizes a 3sigma criterion to remove gross errors and interpolation, and the specific process is as follows: the standard deviation sigma and the average value of a period of frequency difference data are calculated, if the absolute value of the difference between a certain data and the average value exceeds 3sigma, the certain data is regarded as an abnormal value and is removed; the linear quadratic Gaussian optimal control algorithm (LQG) combined with Kalman filtering is adopted to obtain a control adjustment amount of the microwave clock in real time according to the filtered frequency difference data stream, and the specific process is as follows: Kalman filtering estimates the state of the microwave clock according to a state equation and a measurement equation, the state equation is as follows: the measurement equation is as follows: wherein, , , are respectively the frequency difference offset and the frequency difference drift rate of the hydrogen clock relative to the optical clock; transition matrix , is the first k +1 and the second k measurement interval, i.e. ; process noise , and are noise terms for the fractional frequency difference and its drift rate, respectively, following a Gaussian distribution with zero mean and covariance Q; the control adjustment amount is input into the phase trimmer to conduct real-time control adjustment on the microwave signal, and the specific process is as follows: wherein is the first k +1 frequency difference measurement, , the observation noise is , which is subject to a Gaussian distribution with mean 0 and standard deviation R . Setting initial values from prior conditions , initial covariance matrix , Q and R , in combination with measurement values , according to Kalman filter theory, the estimated values are obtained from the following formula: wherein I is the identity matrix; The controlled microwave clock, the clock model must add control quantity wherein is a frequency correction control value, is a propagation quantity, the state equation of the microwave clock under free operation is rewritten as: The frequency correction control value in the above equation is calculated using an LQG optimal control algorithm , by selecting a frequency correction control value that minimizes a cost function J , the cost function being: wherein, and are 2x2 diagonal matrices with two variable non-zero parameters and one variable parameter value, respectively, by adjusting and the ratio between the parameters, an optimal selection of the frequency correction control value is achieved. A linear quadratic regulator is obtained by solving a Kalman filter steady-state Ricatti equation : Let gain , by a linear quadratic regulator Calculate gain , predicted by a Kalman filter Time estimate And gain , Calculate frequency correction control value : The frequency correction control value That is, the frequency steering adjustment amount of the microwave clock, so as to compensate the frequency deviation of the microwave clock, and realize the time scale output based on the optical clock. ​ The obtained frequency correction control value The encoded value is sent to the phase modulator according to the input rule of the phase modulator, and the phase modulator adjusts the frequency of the input microwave clock signal 10MHz, that is, adds the frequency correction control value to the 10MHz signal The corrected signal is output from the output end of the phase modulator in frequency domain or time domain, and the output signal is the real-time time physical signal after the optical clock is controlled; the output end of the phase modulator outputs 10MHz in frequency domain or 1pps in time domain.

Images