Optical fiber frequency synchronization device

Abstract

The embodiment of the invention discloses an optical fiber frequency synchronization device which comprises the following steps: a frequency synchronization main end modulates a reference frequency signal to obtain a first carrier optical signal, transmits part of the optical signal through a first optical fiber link and a second optical fiber link, and sends part of the optical signal through the first optical fiber link; detecting part of the optical signal to obtain a first microwave signal, and comparing the first microwave signal with a reference frequency signal to obtain a first signal comprising first phase jitter; the first signal performs phase modulation on the reference frequency signal to obtain a second microwave signal including second phase jitter, modulates the second microwave signal to obtain a second carrier optical signal, transmits part of the optical signal through a second optical fiber link and a first optical fiber link, and sends part of the optical signal through a second optical fiber link; and detecting the optical signal of the part to obtain a third microwave signal comprising the first sub-phase jitter, detecting the optical signal of the part to obtain a fourth microwave signal comprising the second sub-phase jitter, and processing the third microwave signal and the fourth microwave signal to output a synchronous frequency signal.

Description

Technical Field

[0001] This invention relates to the field of high-precision time and frequency network technology. More specifically, it relates to an optical fiber frequency synchronization device. Background Technology

[0002] Currently, with the continuous development of atomic frequency standard technology, its performance is constantly improving, and correspondingly, the requirements for transmission and synchronization are becoming increasingly stringent. Radio astronomy observation, high-precision time and frequency networks, navigation and positioning, and many other fields all require time and frequency synchronization. Time and frequency synchronization methods include shortwave time and frequency synchronization, longwave time and frequency synchronization, satellite time and frequency synchronization, and fiber optic time and frequency synchronization. Considering synchronization performance, high-precision time and frequency synchronization is typically achieved using fiber optic time and frequency synchronization, free-space laser time and frequency synchronization, or microwave time and frequency synchronization. With the development of fiber optic frequency synchronization technology, synchronization performance is constantly improving, and its application is becoming increasingly widespread; however, the security of synchronization is not guaranteed. If there is a malicious disruptor in the link, the frequency synchronization result will be affected. Summary of the Invention

[0003] The purpose of this invention is to provide an optical fiber frequency synchronization device to solve at least one of the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides an optical fiber frequency synchronization device, the device comprising: a frequency synchronization master end, a frequency download end, a first optical fiber link, and a second optical fiber link; The frequency synchronization master terminal is used to output a reference frequency signal, modulate the reference frequency signal to obtain a first carrier optical signal, transmit the first carrier optical signal through the first optical fiber link and split it into two beams through the frequency download terminal, wherein the first part of the optical signal enters the second optical fiber link and is transmitted back to the frequency synchronization master terminal, and the second part of the optical signal is used for photoelectric detection at the frequency download terminal; the first part of the first carrier optical signal is detected to obtain a first microwave signal; the reference frequency signal and the first microwave signal are compared to obtain a first signal, the first signal including a first phase jitter introduced by transmission through the first optical fiber link and the second optical fiber link, the first phase jitter including a first sub-phase jitter and a second sub-phase jitter; the reference frequency signal is phase-modulated according to the first signal to obtain a second microwave signal, the second microwave signal including a second phase jitter opposite to the first phase jitter; the second microwave signal is modulated onto a laser signal to obtain a second carrier optical signal, the second carrier optical signal is transmitted through the second optical fiber link and split into two beams through the frequency download terminal, wherein the first part of the optical signal enters the first optical fiber link and is transmitted back to the frequency synchronization master terminal, and the second part of the optical signal is used for photoelectric detection at the frequency download terminal; The frequency download terminal is used to detect the second part of the optical signal of the first carrier optical signal to obtain a third microwave signal including the first sub-phase jitter, detect the second part of the optical signal of the second carrier optical signal to obtain a fourth microwave signal including the second sub-phase jitter, and perform upmixing, frequency locking, and frequency multiplication processing on the third microwave signal and the fourth microwave signal to output a synchronized frequency signal.

[0005] Optionally, the frequency synchronization master is connected to the first optical fiber link, the first optical fiber link is connected to the frequency download end, the frequency download end is connected to the second optical fiber link, and the second optical fiber link is connected to the frequency synchronization master.

[0006] Optionally, the frequency synchronization master terminal includes: a reference frequency source, a frequency processing unit, a power divider, a first laser, a first fiber optic circulator, a second fiber optic circulator, a first detector, a phase comparison unit, a phase control unit, and a second laser; The reference frequency source is connected to the frequency processing unit, the frequency processing unit is connected to the power divider, the power divider is connected to the first laser, the phase comparison unit, and the phase control unit, the first laser is connected to the first fiber optic circulator, the first fiber optic circulator is connected to the first fiber optic link, the phase comparison unit is connected to the phase control unit and the first detector, the phase control unit is connected to the second laser, and the second fiber optic circulator is connected to the first detector, the second laser, and the second fiber optic link.

[0007] Optionally, the phase comparison unit includes: a frequency doubler and a mixer; The frequency doubler and the power divider are connected, and the mixer is connected to the frequency doubler, the mixer, and the first detector, respectively.

[0008] Optionally, the frequency download end includes: an optical fiber coupler, a second detector, a third detector, and a radio frequency processing unit; The fiber optic coupler is connected to the first fiber optic link, the second fiber optic link, the second detector, and the third detector, respectively, and the radio frequency processing unit is connected to the second detector and the third detector, respectively.

[0009] Optionally, the number of frequency download terminals is greater than or equal to 1.

[0010] Optionally, the first signal may also include frequency variations introduced by transmission through the first optical fiber link and the second optical fiber link.

[0011] Optionally, the device also includes a monitoring unit; The monitoring unit is used to determine whether the frequency change is equal to 0; If not, an alarm signal will be issued.

[0012] Optionally, the splitting ratio of the fiber coupler is in the range of 50:50 to 99:1.

[0013] Optionally, the output wavelength of the first laser is in the range of 1540nm~1565nm; The output wavelength of the second laser ranges from 1540nm to 1565nm.

[0014] The beneficial effects of this invention are as follows: The technical solution described in this invention provides a high-security fiber optic frequency synchronization device. The main end of this device simultaneously possesses functions for transmitting, receiving, comparing phases, and controlling optical radio frequency signals. A frequency synchronization system is constructed using a ring fiber optic link. A 2×2 fiber optic coupler is connected at any point in the fiber optic link where frequency synchronization is required, coupling out a portion of the optical radio frequency signal transmitted back and forth in the fiber optic link. After processing such as detection, high-precision frequency synchronization is achieved. The main end can obtain real-time data on the phase difference and frequency difference of the radio frequency signal before and after transmission through the fiber optic link. While achieving high-precision phase control, it can also monitor the frequency difference data of the radio frequency signal before and after transmission through the fiber optic link, thereby reporting frequency difference changes caused by anomalies in the fiber optic link. This device, while achieving high-precision frequency synchronization, can also report frequency difference changes caused by anomalies in the fiber optic link, offering the advantage of high security. Attached Figure Description

[0015] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0016] Figure 1 This diagram illustrates an optical fiber frequency synchronization device provided in an embodiment of the present invention.

[0017] Figure 2 This diagram illustrates another schematic of the fiber optic frequency synchronization device provided in an embodiment of the present invention. Detailed Implementation

[0018] To more clearly illustrate the present invention, the following description, in conjunction with embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0019] Currently, with the continuous development of atomic frequency standard technology, its performance is constantly improving, and correspondingly, the requirements for transmission and synchronization are becoming increasingly stringent. Radio astronomy observation, high-precision time and frequency networks, navigation and positioning, and many other fields all require time and frequency synchronization. Time and frequency synchronization methods include shortwave time and frequency synchronization, longwave time and frequency synchronization, satellite time and frequency synchronization, and fiber optic time and frequency synchronization. Considering synchronization performance, high-precision time and frequency synchronization is typically achieved using fiber optic time and frequency synchronization, free-space laser time and frequency synchronization, or microwave time and frequency synchronization. With the development of fiber optic frequency synchronization technology, synchronization performance is constantly improving, and its application is becoming increasingly widespread; however, the security of synchronization is not guaranteed. If there is a malicious disruptor in the link, the frequency synchronization result will be affected.

[0020] In view of this, one embodiment of the present invention provides an optical fiber frequency synchronization device, which includes: a frequency synchronization master end, a frequency download end, a first optical fiber link, and a second optical fiber link; the frequency synchronization master end is used to output a reference frequency signal, modulate the reference frequency signal to obtain a first carrier optical signal, transmit the first carrier optical signal through the first optical fiber link and split it into two beams through the frequency download end, wherein a first part of the optical signal enters the second optical fiber link and is transmitted back to the frequency synchronization master end, and the second part of the optical signal is used for photoelectric detection at the frequency download end, the first part of the first carrier optical signal is detected to obtain a first microwave signal, and the reference frequency signal and the first microwave signal are compared to obtain... A first signal is obtained, the first signal including a first phase jitter introduced by transmission through the first optical fiber link and the second optical fiber link, the first phase jitter including a first sub-phase jitter and a second sub-phase jitter. The reference frequency signal is phase-modulated according to the first signal to obtain a second microwave signal, the second microwave signal including a second phase jitter opposite to the first phase jitter. The second microwave signal is modulated onto a laser signal to obtain a second carrier optical signal. The second carrier optical signal is transmitted through the second optical fiber link and split into two beams through the frequency download end, wherein the first part of the optical signal enters the first optical fiber link and is transmitted back to the frequency synchronization master end, and the second part of the optical signal is used for photoelectric detection at the frequency download end. The frequency download terminal is used to detect the second part of the optical signal of the first carrier optical signal to obtain a third microwave signal including the first sub-phase jitter, detect the second part of the optical signal of the second carrier optical signal to obtain a fourth microwave signal including the second sub-phase jitter, and perform upmixing, frequency locking, and frequency multiplication processing on the third microwave signal and the fourth microwave signal to output a synchronized frequency signal.

[0021] In a specific example, the modulated carrier optical signal is transmitted from fiber optic link a to fiber optic link b, enters the first detector through the fiber optic circulator, and is demodulated to produce a microwave signal. This signal enters the phase comparison unit and is compared with the reference microwave signal output by the power divider to obtain the phase jitter introduced by the fiber optic link transmission. and frequency changes .

[0022] Furthermore, regarding the phase jitter obtained from the phase comparison unit... The signal is input to the phase control unit, which performs phase modulation processing on the reference frequency signal, so that the microwave signal input to the second laser contains... The phase information of the signal is used to modulate the second laser.

[0023] Furthermore, the modulated carrier optical signal enters the optical fiber link for transmission via the optical fiber circulator, and the signal is transmitted to optical fiber link a through optical fiber link b.

[0024] Furthermore, the fiber optic coupler at the download end couples out a portion of the carrier optical signal transmitted from fiber optic link a to fiber optic link b in the fiber optic link. After passing through the second detector, this portion contains the phase jitter introduced by the fiber optic transmission. The microwave signal. Simultaneously, the fiber optic coupler also couples out a portion of the carrier optical signal transmitted from fiber optic link b to fiber optic link a, which, after passing through the third detector, yields a signal containing... Phase jitter introduced by fiber optic transmission microwave signals.

[0025] Furthermore, due to By upmixing the two microwave signals at the download end, a microwave signal that does not include noise introduced by the fiber optic link can be obtained, that is, its phase is locked to the master end reference signal.

[0026] The technical solution described in this invention provides a high-security fiber optic frequency synchronization device. The main end of this device simultaneously possesses functions for transmitting, receiving, comparing phases, and controlling optical radio frequency signals. A frequency synchronization system is constructed using a ring fiber optic link. A 2×2 fiber optic coupler is connected at any point in the fiber optic link where frequency synchronization is required, coupling out a portion of the optical radio frequency signal transmitted back and forth in the fiber optic link. After processing such as detection, high-precision frequency synchronization is achieved. The main end can obtain real-time data on the phase difference and frequency difference of the radio frequency signal before and after transmission through the fiber optic link. While achieving high-precision phase control, it can also monitor the frequency difference data of the radio frequency signal before and after transmission through the fiber optic link, thereby reporting frequency difference changes caused by anomalies in the fiber optic link. This device, while achieving high-precision frequency synchronization, can also report frequency difference changes caused by anomalies in the fiber optic link, offering the advantage of high security.

[0027] In one possible implementation, the frequency synchronization master is connected to the first optical fiber link, the first optical fiber link is connected to the frequency downloader, the frequency downloader is connected to the second optical fiber link, and the second optical fiber link is connected to the frequency synchronization master.

[0028] In a specific example, the connection of the reference frequency source, optical components, fiber optic link, and microwave devices is completed. A hydrogen atomic clock is selected as the reference frequency source, with an output frequency of 100MHz as the reference frequency signal.

[0029] In a specific example, the frequency processing unit uses a frequency multiplier to multiply a 100MHz reference frequency signal to 2GHz.

[0030] In a specific example, a 2 GHz frequency signal modulates an optical signal using an electroabsorption modulator.

[0031] In a specific example, the phase comparison unit uses a frequency doubler and a mixer to obtain the difference frequency signal between the microwave signal output by the first detector and the reference frequency signal. This signal is input to the phase control unit for measurement to obtain the phase difference. and frequency difference The data is then used to control the phase of the reference frequency signal, ensuring that it contains... . The data is then used for system monitoring.

[0032] In a specific example, the radio frequency processing unit includes 2GHz signal power amplification, mixing, filtering, and phase-locked loop functions. The specific implementation process is to amplify the two 2GHz signals obtained by photoelectric conversion to make the power greater than 8dBm, then perform up-mixing, and obtain a 4GHz signal after bandpass filtering. The phase of a 100MHz voltage-controlled crystal oscillator is locked to the 2GHz signal, and the output signal of the 100MHz voltage-controlled crystal oscillator is the synchronized 100MHz frequency output.

[0033] In a specific example, the output signal of the 100MHz voltage-controlled crystal oscillator was compared with the reference frequency signal, and the relative frequency stability index was 2E-14 / second, which means that the 100MHz frequency signal was synchronized between the master end and the download end.

[0034] In one possible implementation, the frequency synchronization master includes: a reference frequency source, a frequency processing unit, a power divider, a first laser, a first fiber optic circulator, a second fiber optic circulator, a first detector, a phase comparison unit, a phase control unit, and a second laser; the reference frequency source is connected to the frequency processing unit, the frequency processing unit is connected to the power divider, the power divider is connected to the first laser, the phase comparison unit, and the phase control unit, the first laser is connected to the first fiber optic circulator, the first fiber optic circulator is connected to the first fiber optic link, the phase comparison unit is connected to the phase control unit and the first detector, the phase control unit is connected to the second laser, and the second fiber optic circulator is connected to the first detector, the second laser, and the second fiber optic link.

[0035] In a specific example, the frequency synchronization master includes: a reference frequency source, a frequency processing unit, a power divider, a first laser, a first fiber optic circulator, a second fiber optic circulator, a first detector, a phase comparison unit, a phase control unit, and a second laser.

[0036] In a specific example, the reference frequency source is connected to the frequency processing unit, which is used to perform frequency conversion. The frequency processing unit is also connected to the power divider, which divides the reference frequency signal output from the reference frequency source into three paths, which are respectively connected to the first laser, the phase comparison unit, and the phase control unit. The first laser is connected to port 1 of the first fiber optic circulator, port 2 of the first fiber optic circulator is connected to one end of the fiber optic link, a fiber optic coupler is connected between the two fiber optic links, and the other end of the fiber optic link is connected to port 2 of the second fiber optic circulator. Port 3 of the second fiber optic circulator is connected to the first detector, the first detector is connected to the phase comparison unit, the phase comparison unit is connected to the phase control unit, the phase control unit is connected to the second laser, and the second laser is connected to port 1 of the second fiber optic circulator.

[0037] In a specific example, the frequency processing unit includes, but is not limited to, a frequency multiplier, a PDRO phase-locked loop, etc., which can perform frequency conversion processing on the frequency signal output from the reference frequency source.

[0038] In a specific example, the power divider can also be replaced with devices such as an isolation amplifier to divide the reference frequency signal output from the reference frequency source into at least three channels.

[0039] In a specific example, the first laser has radio frequency modulation capabilities, and the modulation methods include, but are not limited to, direct current modulation or intensity modulation of the laser signal, or modulation of the laser using a modulator such as MZM, and the output wavelength includes, but is not limited to, the 1550nm band and the 1310nm band.

[0040] In a specific example, the second laser has radio frequency modulation capabilities, and the modulation methods include, but are not limited to, direct current modulation or intensity modulation of the laser signal, or modulation of the laser using a modulator such as MZM, and the output wavelength includes, but is not limited to, the 1550nm band and the 1310nm band.

[0041] In a specific example, the phase comparison unit includes, but is not limited to, using methods such as mixing and phase comparators to obtain the phase difference and frequency difference between two input signals.

[0042] In a specific example, the functions of the radio frequency processing unit include, but are not limited to, upmixing, frequency locking, and frequency multiplication of microwave signals, with the final output being a synchronized frequency signal.

[0043] In a specific example, such as Figure 1 As shown, the frequency synchronization master includes: a reference frequency source 1, a frequency processing unit 2, a power divider 3, a first laser 4, a first fiber optic circulator 5, a second fiber optic circulator 11, a first detector 7, a phase comparison unit 8, a phase adjustment unit (phase control unit) 9, and a second laser 10.

[0044] In a specific example, the frequency download end includes: fiber optic coupler 12, second detector 13, third detector 14, and radio frequency processing unit 15.

[0045] In a specific example, fiber optic link 6 includes two optical fibers (fiber a between the first fiber circulator and the fiber coupler, and fiber b between the second fiber circulator and the fiber coupler) for connecting the frequency synchronization master and the frequency download end.

[0046] In one possible implementation, the phase comparison unit includes a frequency doubler and a mixer; the frequency doubler is connected to the power divider, and the mixer is connected to the frequency doubler, the mixer, and the first detector, respectively.

[0047] In a specific example, such as Figure 2 As shown, the frequency synchronization master includes: a reference frequency source 1, a frequency processing unit 2, a power divider 3, a first laser 4, a first fiber optic circulator 5, a second fiber optic circulator 11, a first detector 7, a phase comparison unit 8, a phase modulation unit 9, and a second laser 10. The phase comparison unit 8 includes a frequency doubler and a mixer.

[0048] In a specific example, the frequency download end includes: fiber optic coupler 12, second detector 13, third detector 14, and radio frequency processing unit 15.

[0049] In a specific example, fiber optic link 6 includes two optical fibers used to connect the frequency synchronization master and the frequency downloader.

[0050] In one possible implementation, the frequency download end includes: an optical fiber coupler, a second detector, a third detector, and a radio frequency processing unit; the optical fiber coupler is connected to the first optical fiber link, the second optical fiber link, the second detector, and the third detector, respectively, and the radio frequency processing unit is connected to the second detector and the third detector, respectively.

[0051] In a specific example, the frequency download end includes: an optical fiber coupler, a second detector, a third detector, and an RF processing unit. The two ports of the optical fiber coupler are connected to the second and third detectors respectively. The second and third detectors are connected to the RF processing unit to perform RF signal amplification, mixing, phase-locked looping, and other processing to achieve frequency synchronization signal output.

[0052] In one possible implementation, the number of frequency downloaders is greater than or equal to 1.

[0053] In a specific example, the frequency synchronization master and the frequency downloader are connected via two fiber optic links. The number of downloaders can be expanded; the fiber optic links can be disconnected and frequency downloaders connected at the locations where frequency synchronization is required.

[0054] In one possible implementation, the first signal further includes frequency variations introduced by transmission through the first optical fiber link and the second optical fiber link.

[0055] In a specific example, the optical fiber is manually pulled, causing the frequency difference measured by the phase unit to change. The system alarmed, verifying the safety of the synchronization device.

[0056] In one possible implementation, the device further includes a monitoring unit; the monitoring unit is used to determine whether the frequency change is equal to 0; if not, it issues an alarm signal.

[0057] In a specific example, when there is no malicious frequency disturbance in the environment where the fiber optic link is located, If there is malicious interference, The system can perform operations such as issuing warnings.

[0058] In one possible implementation, the splitting ratio of the fiber coupler ranges from 50:50 to 99:1.

[0059] In a specific example, the optical fiber coupler has a splitting ratio of 90:10, where 90% of the optical signal is transmitted through the next optical fiber link and 10% of the optical signal is coupled to the second detector 14 and the third detector 15.

[0060] In one possible implementation, the output wavelength of the first laser is in the range of 1540nm to 1565nm; the output wavelength of the second laser is in the range of 1540nm to 1565nm.

[0061] In a specific example, the first laser outputs a wavelength of 1547.72 nm, and the second laser outputs a wavelength of 1548.53 nm. The optical components, including fiber optic circulators, fiber optic couplers, and photodetectors, all cover the 1550 nm band.

[0062] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0063] It should also be noted that in the description of this invention, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0064] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A fiber optic frequency synchronization device, characterized in that, The device includes: a frequency synchronization master terminal, a frequency download terminal, a first optical fiber link, and a second optical fiber link; The frequency synchronization master terminal is used to output a reference frequency signal, modulate the reference frequency signal to obtain a first carrier optical signal, transmit the first carrier optical signal through the first optical fiber link and split it into two beams through the frequency download terminal, wherein the first part of the optical signal enters the second optical fiber link and is transmitted back to the frequency synchronization master terminal, and the second part of the optical signal is used for photoelectric detection at the frequency download terminal; the first part of the first carrier optical signal is detected to obtain a first microwave signal; the reference frequency signal and the first microwave signal are compared to obtain a first signal, the first signal including a first phase jitter introduced by transmission through the first optical fiber link and the second optical fiber link, the first phase jitter including a first sub-phase jitter and a second sub-phase jitter; the reference frequency signal is phase-modulated according to the first signal to obtain a second microwave signal, the second microwave signal including a second phase jitter opposite to the first phase jitter; the second microwave signal is modulated onto a laser signal to obtain a second carrier optical signal, the second carrier optical signal is transmitted through the second optical fiber link and split into two beams through the frequency download terminal, wherein the first part of the optical signal enters the first optical fiber link and is transmitted back to the frequency synchronization master terminal, and the second part of the optical signal is used for photoelectric detection at the frequency download terminal; The frequency download terminal is used to detect the second part of the optical signal of the first carrier optical signal to obtain a third microwave signal including the first sub-phase jitter, detect the second part of the optical signal of the second carrier optical signal to obtain a fourth microwave signal including the second sub-phase jitter, and perform upmixing, frequency locking, and frequency multiplication processing on the third microwave signal and the fourth microwave signal to output a synchronized frequency signal.

2. The fiber optic frequency synchronization device according to claim 1, characterized in that, The frequency synchronization master is connected to the first optical fiber link, the first optical fiber link is connected to the frequency download end, the frequency download end is connected to the second optical fiber link, and the second optical fiber link is connected to the frequency synchronization master.

3. The fiber optic frequency synchronization device according to claim 2, characterized in that, The frequency synchronization master terminal includes: a reference frequency source, a frequency processing unit, a power divider, a first laser, a first fiber optic circulator, a second fiber optic circulator, a first detector, a phase comparison unit, a phase control unit, and a second laser; The reference frequency source is connected to the frequency processing unit, the frequency processing unit is connected to the power divider, the power divider is connected to the first laser, the phase comparison unit, and the phase control unit, the first laser is connected to the first fiber optic circulator, the first fiber optic circulator is connected to the first fiber optic link, the phase comparison unit is connected to the phase control unit and the first detector, the phase control unit is connected to the second laser, and the second fiber optic circulator is connected to the first detector, the second laser, and the second fiber optic link.

4. The fiber optic frequency synchronization device according to claim 3, characterized in that, The phase comparison unit includes: a frequency doubler and a mixer; The frequency doubler and the power divider are connected, and the mixer is connected to the frequency doubler, the mixer, and the first detector, respectively.

5. The fiber optic frequency synchronization device according to claim 4, characterized in that, The frequency download terminal includes: an optical fiber coupler, a second detector, a third detector, and a radio frequency processing unit; The fiber optic coupler is connected to the first fiber optic link, the second fiber optic link, the second detector, and the third detector, respectively, and the radio frequency processing unit is connected to the second detector and the third detector, respectively.

6. The fiber optic frequency synchronization device according to claim 5, characterized in that, The number of frequency download terminals is greater than or equal to 1.

7. The fiber optic frequency synchronization device according to claim 6, characterized in that, The first signal also includes frequency variations introduced by transmission through the first optical fiber link and the second optical fiber link.

8. The fiber optic frequency synchronization device according to claim 7, characterized in that, The device also includes a monitoring unit; The monitoring unit is used to determine whether the frequency change is equal to 0; If not, an alarm signal will be issued.

9. The fiber optic frequency synchronization device according to claim 8, characterized in that, The splitting ratio of the fiber optic coupler ranges from 50:50 to 99:

1.

10. The fiber optic frequency synchronization device according to claim 9, characterized in that, The output wavelength of the first laser ranges from 1540nm to 1565nm; The output wavelength of the second laser ranges from 1540nm to 1565nm.

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