A time-frequency signal phase-locked transmission system

Abstract

The present invention relates to the field of distributed radar technology, and specifically to a time-frequency signal phase-locked transmission system, comprising a phase-locked transmission front-end unit, a long transmission optical fiber, and a phase-locked transmission back-end unit; the long transmission optical fiber is connected to the phase-locked transmission front-end unit, and the phase-locked transmission back-end unit is connected to the long transmission optical fiber; the time-frequency signal enters the phase-locked transmission front-end unit, and the two functions of time-frequency transmission and link phase-locked control are completed through the long transmission optical fiber and the phase-locked transmission back-end unit. When the present invention is in operation, the two functions operate simultaneously, the time-frequency transmission function ensures the purity of the transmitted time-frequency signal, and the link phase-locked control ensures the backtracking and stability of the time-frequency transmission phase. There is no need to multiplex the delay measurement light wavelength and the phase measurement light in the transmission optical fiber channel, so the problem of stable phase transmission of the time-frequency signal of the distributed radar array is efficiently solved. Moreover, after the system is restarted, the delay and phase of the link can be locked to the stable state before the system restart.

Description

Technical Field

[0001] The present invention relates to the field of distributed radar technology, and in particular to a time-frequency signal phase-locked transmission system. Background Art

[0002] Distributed radar arrays require phase synchronization of the time-frequency references within each subarray. Therefore, the control center must transmit the same time-frequency signal to each subarray. However, optical fiber is often used as the transmission medium for long-distance time-frequency transmission. The temperature drift of single-mode fiber is approximately 40 ps / km / °C. Over long transmission distances and in environments with drastic temperature fluctuations, the optical link transmission delay is unstable. This unstable delay can lead to phase fluctuations in the transmitted time-frequency signal, disrupting the timing of each subarray and reducing the detection capability of the distributed radar system.

[0003] Therefore, it is necessary to introduce a phase-stabilization mechanism for long-distance optical transmission of time-frequency signals. Currently, the most common phase-stabilization scheme in engineering applications uses two optical wavelengths, digital pulse coarse delay measurement light and microwave standard frequency fine phase measurement light, to measure link delay changes within the transmission optical chain. The variable delay line is then adjusted to offset the phase drift of the transmission signal caused by temperature drift of the transmission fiber. However, given the fixed relative frequency characteristics of the time-frequency signals required to be transmitted by distributed radar arrays, the original phase-stabilization scheme is relatively complex and has a high implementation cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a time-frequency signal phase-locked transmission system that does not require multiplexing of delay measurement light wavelength and phase measurement light in the transmission optical fiber channel, thereby solving the problem of stable phase transmission of time-frequency signals in distributed radar arrays.

[0005] To achieve the above-mentioned object, the present invention provides a time-frequency signal phase-locked transmission system, comprising a phase-locked transmission front-end unit, a long transmission optical fiber, and a phase-locked transmission back-end unit;

[0006] The long transmission optical fiber is connected to the phase-locked transmission front-end unit, and the phase-locked transmission back-end unit is connected to the long transmission optical fiber.

[0007] The phase-locked transmission front-end unit includes a first time-frequency bandpass filter, a combiner, an electro-optical conversion module, a first optical circulator, an adjustable optical delay line, a measurement and control processing module, a variable standard frequency source, a power divider, a first optoelectronic conversion module, a time-frequency bandstop filter and a phase detector module;

[0008] The combiner is connected to the first time-frequency bandpass filter, the electro-optical conversion module is connected to the combiner, the first optical circulator is connected to the electro-optical conversion module, the adjustable optical delay line is connected to the first optical circulator and the long transmission optical fiber, the measurement and control processing module is connected to the adjustable optical delay line, the variable standard frequency source is connected to the measurement and control processing module, the power splitter is connected to the variable standard frequency source and the combiner, the first optoelectronic conversion module is connected to the first optical circulator, the time-frequency bandstop filter is connected to the first optoelectronic conversion module, and the phase detection module is connected to the power splitter, the time-frequency bandstop filter, and the measurement and control processing module.

[0009] Wherein, the phase-locked transmission back-end unit includes a second optical circulator, an optical splitter, a second optoelectronic conversion module and a second time-frequency bandpass filter;

[0010] The second optical circulator is connected to the long transmission optical fiber, the optical splitter is connected to the second optical circulator, the second optoelectronic conversion module is connected to the optical splitter, and the second time-frequency bandpass filter is connected to the second optoelectronic conversion module.

[0011] The present invention provides a time-frequency signal phase-locked transmission system, in which the time-frequency signal enters the phase-locked transmission front-end unit, and completes the two functions of time-frequency transmission and link phase-locked control through the long transmission optical fiber and the phase-locked transmission back-end unit. When the system of the present invention is in operation, the two functions operate simultaneously. The time-frequency transmission function ensures the purity of the transmitted time-frequency signal, and the link phase-locked control ensures the backtracking and stability of the time-frequency transmission phase. There is no need to multiplex the delay measurement light wavelength and the phase measurement light in the transmission optical fiber channel, which effectively solves the problem of stable phase transmission of time-frequency signals in distributed radar arrays. Moreover, after the system is restarted, the link delay and phase can be locked to the stable state before the system restart. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 It is a structural schematic diagram of a time-frequency signal phase-locked transmission system provided by the present invention.

[0014] Figure 2 This is a schematic diagram of the phase calibration process.

[0015] Figure 3 This is a schematic diagram of the link phase-locked control process.

[0016] Figure 4 It is a detailed flow chart of phase detection.

[0017] Figure 5 It is a schematic diagram of the phase-comparison linear phase interval.

[0018] 1-phase-locked transmission front-end unit, 2-long transmission optical fiber, 3-phase-locked transmission back-end unit, 4-first time-frequency bandpass filter, 5-combiner, 6-electro-optical conversion module, 7-first optical circulator, 8-adjustable optical delay line, 9-measurement and control processing module, 10-variable standard frequency source, 11-power divider, 12-first optoelectronic conversion module, 13-time-frequency bandstop filter, 14-phase detection module, 15-second optical circulator, 16-optical splitter, 17-second optoelectronic conversion module, 18-second time-frequency bandpass filter. DETAILED DESCRIPTION

[0019] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0020] See also Figures 1 to 5 The present invention provides a time-frequency signal phase-locked transmission system: comprising a phase-locked transmission front-end unit 1, a long transmission optical fiber 2 and a phase-locked transmission back-end unit 3;

[0021] The long transmission optical fiber 2 is connected to the phase-locked transmission front-end unit 1 , and the phase-locked transmission back-end unit 3 is connected to the long transmission optical fiber 2 .

[0022] In this embodiment, the time-frequency signal enters the phase-locked transmission front-end unit 1, and the time-frequency transmission and link phase-locked control functions are completed through the long transmission optical fiber 2 and the phase-locked transmission back-end unit 3. When the system of the present invention is running, the two functions run simultaneously. The time-frequency transmission function ensures the purity of the transmitted time-frequency signal, and the link phase-locked control ensures the traceback and stability of the time-frequency transmission phase. There is no need to multiplex the delay measurement light wavelength and the phase measurement light in the transmission optical fiber channel, which effectively solves the problem of stable phase transmission of time-frequency signals in distributed radar arrays. Moreover, after the system is restarted, the delay and phase of the link can be locked in the stable state before the system restart.

[0023] Furthermore, the phase-locked transmission front-end unit 1 includes a first time-frequency bandpass filter 4, a combiner 5, an electro-optical conversion module 6, a first optical circulator 7, an adjustable optical delay line 8, a measurement and control processing module 9, a variable standard frequency source 10, a power divider 11, a first optoelectronic conversion module 12, a time-frequency bandstop filter 13 and a phase detector module 14;

[0024] The combiner 5 is connected to the first time-frequency bandpass filter 4, the electro-optical conversion module 6 is connected to the combiner 5, the first optical circulator 7 is connected to the electro-optical conversion module 6, the adjustable optical delay line 8 is connected to the first optical circulator 7 and the long transmission optical fiber 2, the measurement and control processing module 9 is connected to the adjustable optical delay line 8, the variable standard frequency source 10 is connected to the measurement and control processing module 9, the power splitter 11 is connected to the variable standard frequency source 10 and the combiner 5, the first optoelectronic conversion module 12 is connected to the first optical circulator 7, the time-frequency bandstop filter 13 is connected to the first optoelectronic conversion module 12, and the phase detection module 14 is connected to the power splitter 11, the time-frequency bandstop filter 13, and the measurement and control processing module 9.

[0025] In this embodiment, the first time-frequency bandpass filter 4 is mainly used to filter out the out-of-band interference signal and harmonic component signal of the input time-frequency signal;

[0026] The combiner 5 combines the input time-frequency signal and the standard frequency signal output by the measurement and control processing module 9 and outputs the combined signal to the electro-optical conversion module 6;

[0027] The electro-optical conversion module 6 performs electro-optical conversion on the radio frequency signal mixed with the time frequency and the standard frequency, and outputs optical power.

[0028] The first optical circulator 7 sends the forward light output by the electro-optical conversion module 6 to the adjustable optical delay line 8, and sends the looped light on the link to the measurement and control processing module 9;

[0029] The adjustable optical delay line 8 adjusts its delay according to the control information of the measurement and control processing module 9. When the system is initialized, the adjustable optical delay line 8 returns to the midpoint of its adjustable delay range. Its adjustment accuracy is designed to be better than the system steady-state accuracy. The adjustable optical delay line 8 can be composed of a temperature-controlled optical fiber and a motor-driven spatial optical delay line. The adjustable range is designed to be twice the delay variation range caused by changes in ambient temperature of the optical fiber link.

[0030] The measurement and control processing module 9 is used to store and read the locked link delay phase information, control the frequency of the output variable standard frequency source 10, analyze the phase detection information of the phase detection module 14, and control the delay of the adjustable optical delay line 8 according to the phase detection information. It is the intelligent control center of the entire system.

[0031] The variable standard frequency source 10 is used to accept the control of the measurement and control processing module 9 and emit standard frequency signals of different frequencies as needed to obtain time delay phase information of different accuracy. The standard frequency signal should be selected to avoid at least three orders of intermodulation signals with the transmission time frequency signal and not fall within the transmission signal bandwidth. The output frequency range of the variable standard frequency is 10MHz to f max(the highest frequency supported by the phase detector module 14), during the entire link delay phase measurement locking process, the variable standard frequency source 10 will output three standard frequency signals, namely, low-precision standard frequency f L , medium precision standard frequency f M , high-precision standard frequency f H , corresponding to high, medium and low precision phase / delay difference measurement respectively. The system uses high precision standard frequency f H Calibrate the highest precision vector phase difference change and the medium and low precision frequency f M 、f L Calibrate the time delay difference to prevent high-precision phase measurement from crossing the cycle. H Equal to f max (the highest frequency supported by the phase detector module 14), intermediate frequency standard frequency f M The recommended value range is f H / 5~f H / 10, low frequency standard frequency f L The recommended value range is f H / 5~f H / 10. ;

[0032] The power divider 11 divides the input variable frequency signal into two, one of which is output to the combiner 5 of the phase-locked transmission front-end unit 1 and the other is output to the phase detection module 14;

[0033] The first photoelectric conversion module 12 performs photoelectric conversion on the input loopback light, and appropriately amplifies the converted radio frequency signal before outputting it to the time-frequency band-stop filter 13;

[0034] The function of the time-frequency band-stop filter 13 is to filter out the time-frequency signal transmitted in the input radio frequency signal, leaving only the frequency component of the loopback standard frequency signal;

[0035] The phase detection module 14 performs phase detection on the original standard frequency signal input by the power divider 11 and the loopback standard frequency signal component to obtain phase detection information of the vector phase difference between the two, and sends the vector phase difference information to the measurement and control processing module 9.

[0036] Furthermore, the phase-locked transmission back-end unit 3 includes a second optical circulator 15, an optical splitter 16, a second optoelectronic conversion module 17 and a second time-frequency bandpass filter 18;

[0037] The second optical circulator 15 is connected to the long transmission optical fiber 2 , the optical splitter 16 is connected to the second optical circulator 15 , the second optoelectronic conversion module 17 is connected to the optical splitter 16 , and the second time-frequency bandpass filter 18 is connected to the second optoelectronic conversion module 17 .

[0038] In this embodiment, the second optical circulator 15 transmits the optical signal transmitted to the phase-locked transmission back-end unit 3 through the long transmission optical fiber 2 to the optical splitter 16, and transmits the coupled light from the optical splitter 16 back to the phase-locked transmission front-end unit 1 through the original optical path. The optical splitter 16 couples 10% of the optical signal output by the second optical circulator 15 and transmits it to the second optical circulator 15, and 90% of the optical power is transmitted to the second optoelectronic conversion module 17. The second optoelectronic conversion module 17 performs optoelectronic conversion on the input optical signal, amplifies it, and then transmits it to the second time-frequency bandpass filter 18. The second time-frequency bandpass filter 18 filters out signals outside the time-frequency signal band and outputs a clean time-frequency signal.

[0039] A time-frequency signal phase-locked transmission system of the present invention includes two functions: time-frequency transmission and link phase-locked control. When the system of the present invention is running, the two functions run simultaneously. The time-frequency transmission function ensures the purity of the time-frequency signal, and the link phase-locked control ensures the calibration, backtracking and stability of the link phase.

[0040] The following is a description of the implementation of the time-frequency transmission function. For example, the transmission time-frequency signal frequency is f0. The time-frequency signal f0 is input to the phase-locked transmission front-end unit 1 and first passes through the first time-frequency bandpass filter 4. The 3dB bandwidth of the filter can be designed to be the transmission time-frequency signal passband. The use of the first time-frequency bandpass filter 4 can effectively filter out the harmonics and out-of-band spurious of the input time-frequency signal f0, and effectively suppress the time-frequency signal and its harmonics from the standard frequency (f i) of the mixing and intermodulation products, which ensures the purity of the transmitted time-frequency signal spectrum to a certain extent; the filtered time-frequency signal is synthesized into a mixed radio frequency signal with the standard frequency signal in the combiner 5 and output to the electro-optical conversion module 6. The working bandwidth of the electro-optical conversion module 6 needs to completely cover the frequency range of the time-frequency signal and the standard frequency signal. The electro-optical conversion module 6 performs electro-optical conversion on the mixed radio frequency signal and outputs the optical power to the No. 1 input port of the first optical circulator 7, and then outputs it to the adjustable optical delay line 8 through the No. 3 port, and is connected to the external transmission long optical fiber 2 after phase adjustment through the adjustable optical delay line 8. The optical signal is transmitted to the phase-locked transmission back-end unit 3 through the long transmission optical fiber 2. In the phase-locked transmission back-end unit 3, the input light first passes through port 3 of the second optical circulator 15, and is output to the optical splitter 16 through port 2 of the second optical circulator 15. The main signal passing through the optical splitter 16 is output to the second optoelectronic conversion module 17. In the second optoelectronic conversion module 17, the optical signal is converted into a radio frequency signal, which is then amplified and output to the second time-frequency bandpass filter 18. The radio frequency signal input to the second time-frequency bandpass filter 18 includes a time-frequency signal, a standard frequency signal, and a mixed signal of the time-frequency and standard frequency signals derived from the nonlinearity of the electro-optical / optoelectronic conversion module. The second time-frequency bandpass filter 18 filters out other out-of-band signals and retains the pure time-frequency signal for output.

[0041] The link phase-lock control function is implemented in two operating scenarios: during system initialization and during system restart. Initialization includes calibration of link phase information, link phase retracing, and real-time locking. System restart involves retracing and real-time locking. System initialization is triggered by two conditions: the measurement and control processing module 9 triggers system initialization, and the adjustable optical delay line 8 reaches its adjustment limit.

[0042] The phase calibration process is to clear the original clear stored standard frequency / phase information, and return the optical delay line to the midpoint, and then adjust the standard frequency (f i ) frequency, the vector phase difference measurement (phase detection) between the reference standard frequency and the loopback standard frequency is performed at high, medium and low precision and the vector phase difference value is ensured to be in the linear phase region of the phase detection module 14, and the standard frequency (f i ) should be selected so that the frequency of the intermodulation signal within the third order of the transmission time-frequency signal (f0) falls within the 10dB bandwidth of the first time-frequency bandpass filter 4; the phase calibration process is as follows Figure 2As shown in the figure, in the calibration process, the measurement, determination, storage, and clearing of the vector phase difference; the adjustment, determination, storage, and clearing of the standard frequency; and the adjustment of the adjustable optical delay line 8 are all controlled by the measurement and control processing module 9. After starting the phase calibration process, the original stored standard frequency / phase information is first cleared, and then the optical delay line is returned to the midpoint, and the highest standard frequency (f max ), if the measurement and control processing module 9 determines that the currently measured high-precision measurement vector phase difference value is in the nonlinear phase region, the adjustable optical delay line 8 is adjusted until it is in the linear phase region; if the currently measured high-precision measurement vector phase difference value is in the linear phase region, the delay of the adjustable optical delay line 8 is slightly increased or decreased at this point, and after determining whether the linear phase region is in the rising region or the falling region, the delay is returned to the position before the delay fine-tuning, and the high-precision vector phase difference information λ is stored. H Then enter the medium precision vector phase difference measurement λ M ; The standard frequency is selected from f when measuring the medium-precision vector phase difference (medium-precision phase discrimination) max / 10 starts to measure the medium-precision vector phase difference value. If the current medium-precision vector phase difference value is in the nonlinear phase region of the phase detector module 14, gradually increase the standard frequency until the medium-precision vector phase difference value is in the linear phase region of the phase detector module 14. The medium-precision standard frequency at this time is stored as f m If the current medium-precision vector phase difference value is in the linear phase region of the phase detector module 14, slightly increase or decrease the delay of the adjustable optical delay line 8, determine whether the linear phase region is in the rising region or the falling region, and then return to the position before the delay fine-tuning, and store the medium-precision vector phase difference information λ M Then enter the low-precision vector phase difference measurement λ L ; When measuring low-precision vector phase difference, the standard frequency is selected from f m / 10 starts to measure the low-precision vector phase difference value. If the current low-precision vector phase difference value is in the nonlinear phase region of the phase detector module 14, gradually increase the standard frequency until the medium-precision vector phase difference value is in the linear phase region of the phase detector module 14. The low-precision standard frequency at this time is stored as f L If the current low-precision vector phase difference value is in the linear phase region of the phase detector module 14, increase or decrease the delay of the adjustable optical delay line 8, determine whether the linear phase region is in the rising region or the falling region, and then return to the position before the delay fine-tuning, and store the medium-precision vector phase difference information λ L The high, medium and low precision vector phase difference information λ stored in the measurement and control processing module 9 H ,λ M ,λ L As the initial phase of the link.

[0043] The link phase backtracking and real-time locking process refers to reading the high, medium and low precision standard frequency information f stored in the measurement and control processing module 9. max 、f m 、f L And high, medium and low precision vector phase difference information λ H ,λ M ,λ L Then, through low, medium and high precision frequency calibration and loopback frequency calibration phase detection, and according to the phase difference of phase detection, the adjustable optical delay line 8 is adjusted to reach the initial phase state of the original phase calibration of the link. Then, through high precision phase difference measurement and real-time adjustment of the adjustable optical delay line 8, the real-time locking of the link phase is achieved. When the delay line reaches the limit range, the initialization program is started. Since the adjustable range of the adjustable optical delay line 8 is designed to be twice the delay variation range caused by the ambient temperature change of the optical fiber link, the delay line will not reach the limit range under normal circumstances. The link phase tracing and real-time locking flow chart is as follows. Figure 3 shown.

[0044] Phase detection refers to the measurement of the vector phase difference between the reference standard frequency and the looped standard frequency. The detailed process is as follows: the measurement and control processing module 9 controls the standard frequency source to output the standard frequency signal. The standard frequency signal is split into two by the power splitter 11. One path is input to the reference end of the phase detection module 14 and the other path is input to the combiner 5. After being converted into an optical signal by the electro-optical conversion module 6, it is input through one port of the first optical circulator 7 and output through three ports to the adjustable optical delay line 8. The optical signal then passes through the adjustable optical delay line 8 and the long transmission fiber 2 and is connected to the three ports of the second optical circulator 15. After the second port of the second optical circulator 15 outputs light to the optical splitter 16, the optical splitter 16 splits out 10% of the light. The signal is input through one port of the second optical circulator 15, and returns to the three ports of the first optical circulator 7 through the transmission long optical fiber 2 and the adjustable optical delay line 8 along the original path. The signal is then input to the first optical-to-electrical conversion module 12 through the second port of the first optical circulator 7 for optical-to-electrical conversion and radio frequency signal amplification, and then output to the time-frequency band-stop filter 13. The transmitted time-frequency signal is filtered out and the looped-back standard frequency signal is retained. The signal is then input to the loopback end of the phase detection module 14. The phase detection module 14 performs phase detection on the two input same-frequency signals and feeds back the phase difference information to the measurement and control processing module 9. The detailed phase detection process is as follows: Figure 4 As shown, the process is executed by steps 1 to 17.

[0045] The phase detection linear phase interval means that the phase detection results of the two same-frequency signals input to the phase detection module 14 are relatively accurate within a certain phase difference range, such as Figure 5As shown, for example, the phase detection module 14 with AD8302 as the core is taken as an example. The AD8302 phase detector has a phase detection linear phase rising area (-150° to -30°) and a phase detection linear phase falling area (+150° to +30°). In these two phase difference intervals, the phase detection error is less than 1°, and in other phase difference intervals, the phase detection error is larger.

[0046] The present invention does not require multiplexing the delay measurement light wavelength and the phase measurement light in the transmission optical fiber channel, and effectively solves the problem of stable phase transmission of time-frequency signals of distributed radar arrays. Moreover, after the system is restarted, the delay and phase of the link can be locked in the stable state before the system restart.

[0047] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of the rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A time-frequency signal phase-locked transmission system, characterized in that: It includes a phase-locked transmission front-end unit, a long transmission optical fiber and a phase-locked transmission back-end unit; The long transmission optical fiber is connected to the phase-locked transmission front-end unit, and the phase-locked transmission back-end unit is connected to the long transmission optical fiber; the phase-locked transmission front-end unit includes a first time-frequency bandpass filter, a combiner, an electro-optical conversion module, a first optical circulator, an adjustable optical delay line, a measurement and control processing module, a variable standard frequency source, a power splitter, a first optoelectronic conversion module, a time-frequency bandstop filter and a phase detection module; the combiner is connected to the first time-frequency bandpass filter, the electro-optical conversion module is connected to the combiner, the first optical circulator is connected to the electro-optical conversion module, and the The adjustable optical delay line is connected to the first optical circulator and the long transmission optical fiber, the measurement and control processing module is connected to the adjustable optical delay line, the variable standard frequency source is connected to the measurement and control processing module, the power splitter is connected to the variable standard frequency source and the combiner, the first photoelectric conversion module is connected to the first optical circulator, the time-frequency band stop filter is connected to the first photoelectric conversion module, the phase detection module is connected to the power splitter, the time-frequency band stop filter, and the measurement and control processing module; the phase-locked transmission back-end unit includes a second optical circulator, a splitter The optical circulator is connected to the long transmission fiber, the optical splitter is connected to the second optical circulator, the second optical splitter is connected to the optical splitter, and the second time-frequency bandpass filter is connected to the second optical-electrical conversion module; the first time-frequency bandpass filter filters out-of-band interference signals and harmonic component signals of the input time-frequency signal; the adjustable optical delay line adjusts the delay amount according to the control information of the measurement and control processing module, and the adjustable optical delay line returns to its adjustable delay range when the system is initialized. The midpoint of the circle, the adjustable optical delay line is composed of a temperature-controlled optical fiber and a motor-driven spatial optical delay line; the measurement and control processing module is used to store and read the locked link delay phase information, control the frequency of the variable standard frequency source, analyze the phase detection information of the phase detection module, and control the delay of the adjustable optical delay line according to the phase detection information. The variable standard frequency source is used to accept the control of the measurement and control processing module and send standard frequency signals of different frequencies as needed to obtain delay phase information of different precisions. The variable standard frequency source outputs three standard frequency signals, namely, low-precision standard frequency f L , medium precision standard frequency f M , high-precision standard frequency f H , corresponding to high, medium and low precision phase / delay difference measurement respectively. The system uses high precision standard frequency f H Calibrate the highest precision vector phase difference change and the medium and low precision frequency f M 、f L Calibration delay difference, where f H Equal to f max , f max The highest frequency supported by the phase detector module, the intermediate frequency standard frequency f M The recommended value range is f H / 5~f H / 10, low frequency standard frequency f L The recommended value range is f H / 5~f H / 10.

2. A time-frequency signal phase-locked transmission system according to claim 1, characterized in that: The time-frequency signal enters the phase-locked transmission front-end unit, and the long transmission optical fiber and the phase-locked transmission back-end unit complete the two functions of time-frequency transmission and link phase-locked control. The time-frequency transmission function ensures the purity of the transmitted time-frequency signal, and the link phase-locked control ensures the traceability and stability of the time-frequency transmission phase.

3. A time-frequency signal phase-locked transmission system as claimed in claim 2, characterized in that: The time-frequency signal is input into the phase-locked transmission front-end unit, and first passes through the first time-frequency bandpass filter. The filtered time-frequency signal is synthesized with the standard frequency signal in the combiner to form a mixed radio frequency signal and output to the electro-optical conversion module. The electro-optical conversion module performs electro-optical conversion on the mixed radio frequency signal and outputs the optical power to the No. 1 input port of the first optical circulator, and then outputs it to the adjustable optical delay line through the No. 3 port. After the phase is adjusted by the adjustable optical delay line, it is connected to the long transmission optical fiber; the optical signal is transmitted to the phase-locked transmission back-end unit through the long transmission optical fiber. In the phase-locked transmission back-end unit, the input Light first passes through port 3 of the second optical circulator and is output to the optical splitter through port 2 of the second optical circulator. The main signal passing through the optical splitter is output to the second optoelectronic conversion module. In the second optoelectronic conversion module, the optical signal is converted into a radio frequency signal, which is then amplified and output to the second time-frequency bandpass filter. The radio frequency signal input to the second time-frequency bandpass filter includes a time-frequency signal, a standard frequency signal, and a mixed signal of the time-frequency and standard frequency signals derived from the nonlinearity of the electro-optical / optoelectronic conversion module. The second time-frequency bandpass filter filters out other out-of-band signals and retains the pure time-frequency signal for output.

4. A time-frequency signal phase-locked transmission system as claimed in claim 3, characterized in that: The link phase-locked control function includes implementation in two working scenarios, namely, implementation during system initialization and implementation during system restart; the implementation of the link phase-locked control function during system initialization includes calibration of link phase information, link phase backtracking and real-time locking; link phase backtracking and real-time locking are performed during system restart; system initialization has two triggering conditions, one is triggering system initialization through the measurement and control processing module, and the other is when the adjustable optical delay line reaches the adjustment limit range.

5. A time-frequency signal phase-locked transmission system as claimed in claim 4, characterized in that: When the phase calibration process starts, the original stored standard frequency / phase information is cleared and the optical delay line returns to the midpoint. The measurement and control processing module controls and adjusts the standard frequency (f i ) frequency, the vector phase difference between the reference standard frequency and the loopback standard frequency is measured at high, medium and low precision and the vector phase difference value is ensured to be in the linear phase region of the phase detector module; the adjustment of the adjustable optical delay line is controlled by the measurement and control processing module. After starting the phase calibration process, the original stored standard frequency / phase information is first cleared, and then the optical delay line is returned to the midpoint, and the highest standard frequency (f max ), if the measurement and control processing module determines that the currently measured high-precision measurement vector phase difference value is in the nonlinear phase region, the adjustable optical delay line is adjusted until it is in the linear phase region; if the currently measured high-precision measurement vector phase difference value is in the linear phase region, the delay of the adjustable optical delay line is slightly increased or decreased, and after determining whether the linear phase region is in the rising region or the falling region, the delay is returned to the position before the delay fine-tuning, and the high-precision vector phase difference information λ is stored. H Then enter the medium-precision vector phase difference measurement λ M ; The standard frequency is selected from f when measuring the medium precision vector phase difference max / 10 starts to measure the medium-precision vector phase difference. If the current medium-precision vector phase difference is in the nonlinear phase area of ​​the phase detector module, gradually increase the standard frequency until the medium-precision vector phase difference is in the linear phase area of ​​the phase detector module. The medium-precision standard frequency at this time is stored as f m If the current medium-precision vector phase difference value is in the linear phase region of the phase detector module, increase or decrease the delay of the adjustable optical delay line, determine whether the linear phase region is in the rising or falling region, and then return to the position before the delay fine-tuning, and store the medium-precision vector phase difference information λ M Then enter the low-precision vector phase difference measurement λ L ; When measuring low-precision vector phase difference, the standard frequency is selected from f m / 10 starts to measure the low-precision vector phase difference value. If the current low-precision vector phase difference value is in the nonlinear phase area of ​​the phase detector module, gradually increase the standard frequency until the medium-precision vector phase difference value is in the linear phase area of ​​the phase detector module. The low-precision standard frequency at this time is stored as f L If the current low-precision vector phase difference value is in the linear phase region of the phase detector module, increase or decrease the delay of the adjustable optical delay line, determine whether the linear phase region is in the rising or falling region, and then return to the position before the delay fine-tuning, and store the medium-precision vector phase difference information λ L ; High, medium and low precision vector phase difference information λ stored in the measurement and control processing module H ,λ M ,λ L As the initial phase of the link.

6. A time-frequency signal phase-locked transmission system according to claim 5, characterized in that: The link phase tracing and real-time locking will first read the high, medium and low precision frequency standard information f stored in the measurement and control processing module. max 、f m 、f L And high, medium and low precision vector phase difference information λ H ,λ M ,λ L Then, through low, medium and high precision frequency calibration and loopback frequency calibration phase detection and adjustment of the adjustable optical delay line according to the phase difference of the phase detection, the initial phase state of the original phase calibration of the link is reached.

7. A time-frequency signal phase-locked transmission system according to claim 6, characterized in that: The phase detection refers to the measurement of the vector phase difference between the reference standard frequency and the looped standard frequency. The detailed process is that the measurement and control processing module controls the variable standard frequency source to output the standard frequency signal. The standard frequency signal is divided into two by the power splitter, one of which is input to the reference end of the phase detection module and the other is input to the combiner. After being converted into an optical signal by the electro-optical conversion module, it is input through one port of the first optical circulator and output to the adjustable optical delay line through the third port. After that, the optical signal is respectively input through the adjustable optical delay line and the long transmission optical fiber to the three ports of the second optical circulator. The second port of the second optical circulator outputs light to the optical splitter. Afterwards, the optical splitter splits out 10% of the light, which is input through one port of the second optical circulator, and then returns to the three ports of the first optical circulator through the three ports of the transmission long optical fiber and the adjustable optical delay line along the original path. The light is then input through the second port of the first optical circulator to the first optoelectronic conversion module for optoelectronic conversion and radio frequency signal amplification, and then output to the time-frequency band-stop filter. The transmitted time-frequency signal is filtered out, and the looped-back standard frequency signal is retained. The signal is then input to the loopback end of the phase detector module. The phase detector module performs phase detection on the two input co-frequency signals and feeds back phase difference information to the measurement and control processing module.

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