A fiber optic time synchronization system based on gain-switched laser control

Abstract

This invention discloses an optical fiber time synchronization system based on gain-switched laser modulation in the field of optical fiber time synchronization technology, comprising a central station, an optical fiber link, and a terminal station. The central station uses a clock source signal to generate a coded pulse train of a defined duration to modulate a gain-switched laser, generating a laser pulse train which is then injected into the optical fiber. The terminal station splits the received laser pulse in two: one part is delayed and amplified before being injected into the terminal station's gain-switched laser, locking its operating wavelength with that of the central station's laser; the other part is used to extract the second pulse generated by the central station, completing the time interval measurement between the terminal station's second pulse and the second pulse generated by the central station. The terminal station generates a time-frequency and information-coded pulse train, modulates its own gain-switched laser to generate a laser pulse train, injects it into the optical fiber, and transmits it back to the central station. The central station and the terminal station use single-fiber, single-wavelength bidirectional time transmission to compare and obtain the clock difference between the two stations, and the terminal station completes the servo regeneration of the time-frequency signal.

Description

Technical Field

[0001] This invention belongs to the field of high-precision time and frequency synchronization technology, specifically relating to an optical fiber time synchronization system based on gain-switched laser control and its implementation method. Background Technology

[0002] Currently, high-precision fiber optic time transfer systems typically employ either wavelength division multiplexing (WDM) bidirectional transmission or time division multiplexing (TDM) transmission. WDM transmission utilizes two different standard wavelengths to achieve bidirectional transmission of time and frequency signals within a single fiber. However, optical fibers exhibit different dispersion coefficients for different wavelengths of light, resulting in varying group velocities. Consequently, the transmission delays of different wavelengths of light on the round-trip link cannot be identical. As the operating wavelength interval increases, the accuracy of time transfer cannot be guaranteed due to this asymmetry in transmission delay.

[0003] Taking a distance of 100 km as an example, when using commercial G.652 fiber for time transmission, since the dispersion coefficient D at 1550 nm is approximately 17 ps / (nm·km), a laser wavelength drift of ±0.1 nm will result in a timing error of approximately 340 ps. Although theoretical corrections can be made by estimating the dispersion value of standard single-mode fiber for a given synchronization distance, in practical applications, the center wavelength of the laser fluctuates randomly during use (generally, the specification for commercial lasers is ±0.1 nm), and the dispersion value of commercial fiber itself also fluctuates between different batches and under different environments. Therefore, as long as the timing system uses two different wavelengths for time transmission, fiber dispersion and dispersion fluctuations, as well as the random drift of the two laser wavelengths, will lead to asymmetric timing deviations and deviation fluctuations, with timing errors reaching hundreds of picoseconds over distances of hundreds of kilometers.

[0004] Time-division multiplexing (TDM) transmission operates with the optical transmitters of both the timing center and terminal stations in half-duplex mode, where each station transmits signals but does not receive laser signals simultaneously. The advantage of this mode is that the lasers at both the center and terminal stations can theoretically operate at the same wavelength, and the half-duplex mode avoids interference from backscattered light of the transmitted laser signal in the optical fiber. However, existing systems typically require complex switching mechanisms to ensure optical isolation during same-wavelength transmission. More importantly, the lasers at the center and terminal stations still operate independently, making it difficult to avoid wavelength deviations due to temperature drift and aging, which can still lead to dispersion asymmetry issues. Summary of the Invention

[0005] The purpose of this invention is to provide a fiber optic time synchronization system based on gain-switched laser control, which features high time synchronization accuracy, low cost, and easy compatibility with fiber optic links.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides an optical fiber time synchronization system based on gain-switched laser control, comprising a central station and a terminal station connected by optical fibers;

[0008] The central station is equipped with a central control module and a central gain-switching laser; the terminal station is equipped with a delay amplification device, a terminal control module, and a terminal gain-switching laser.

[0009] The information transmission and reception process from the central station to the terminal station includes:

[0010] The central control module controls the central gain-switching laser to send a central laser pulse to the terminal station. The central laser pulse includes a clock source second pulse, a frequency signal, time information, and a second time interval between the clock source second pulse and the second pulse sent by the terminal station. The terminal station splits the central laser pulse sent by the central station into two parts. One part of the central laser pulse is sent to the terminal gain switch laser after being delayed and amplified by a delay amplification device. The operating wavelength of the terminal gain switch laser is locked to the operating wavelength of the central gain switch laser. The other part of the central laser pulse is sent directly to the terminal control module.

[0011] The information transmission and reception process from the terminal station to the central station includes:

[0012] The terminal control module controls the terminal gain-switching laser to send terminal laser pulses to the central station. The terminal laser pulses include the terminal station's second pulse, frequency signal, time information, and a first time interval between the terminal station's second pulse and the clock source's second pulse. ;

[0013] The clock difference is calculated by the interaction information between the central station and the terminal station, and the time of the servo clock in the terminal station is corrected according to the clock difference to achieve time synchronization with the clock source.

[0014] Furthermore, the central control module includes a central time measurement unit, a central control unit, and a central optical receiver;

[0015] The central optical receiver is used to receive terminal laser pulses, convert the terminal laser pulses into photoelectric signals, and then send them to the central control unit.

[0016] The central time measurement unit is used to measure the second time interval between the second pulse sent by the terminal station and the second pulse from the clock source. And send it to the central control unit;

[0017] The central control unit is used to extract the second pulse sent by the terminal station from the terminal laser pulse and send the second pulse sent by the terminal station to the central time measurement unit; the central control unit is used to measure the time signal, frequency signal, time information and second time interval of the central station. A center-coded pulse train is generated and sent to the center gain-switched laser.

[0018] Furthermore, the terminal control module includes a servo clock, a terminal time measurement unit, a terminal control unit, and a terminal optical receiver;

[0019] The terminal optical receiver is used to receive the central laser pulse, convert the central laser pulse into a photoelectric signal, and then send it to the terminal control unit.

[0020] The terminal control unit is used to extract the clock source second pulse from the central laser pulse and send the clock source second pulse to the terminal time measurement unit; the terminal control unit is used to calculate the second pulse, frequency signal, time information and first time interval from the terminal station. Generate a terminal encoded pulse train; extract information from the central laser pulse to obtain the second time interval. According to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and send the clock difference to the terminal station's servo clock;

[0021] The terminal time measurement unit measures the first time interval between the second pulse within the terminal station and the second pulse from the clock source. , the first time interval Send to the terminal control unit;

[0022] The servo clock is used to send the second pulse of the terminal station to the terminal time measurement unit, and to send the second pulse, frequency signal and time information of the terminal station to the terminal control unit; the servo clock is used to receive the clock difference sent by the terminal control unit, and to correct its own time according to the clock difference to achieve time synchronization with the clock source.

[0023] Furthermore, the central station is equipped with a central looper; the central looper is connected to a central optical receiver and a central gain-switching laser via optical fiber; the terminal station is equipped with a terminal looper; the terminal looper is connected to a delay amplifier, a terminal optical receiver, and a terminal gain-switching laser via optical fiber; the central looper and the terminal looper are connected via optical fiber.

[0024] Furthermore, an injection control signal is provided at the end of the central laser pulse. The duration of the central laser pulse is adjusted by the injection control signal, and the duration of the central laser pulse is less than the total round-trip time delay from the central station to the terminal station. When the terminal encoded pulse train modulates the terminal gain switch laser, the terminal gain switch laser is in the position of receiving the injection control signal in the central laser pulse sent by the central station.

[0025] Furthermore, during pulse train modulation, the bias current of the center gain-switched laser and the terminal gain-switched laser is higher than the gain-switched laser threshold; during the absence of pulse train modulation, the bias current of the center gain-switched laser and the terminal gain-switched laser is lower than the gain-switched laser threshold; during laser pulse reception, the backscattered light power of the transmitted optical signal at the center station and the terminal station is at least 20 dB lower than the received optical power of the optical receiver.

[0026] In a second aspect, the present invention provides an optical fiber time synchronization method based on gain-switched laser modulation, comprising:

[0027] The central station receives laser pulses from the terminal and measures the second time interval between the second pulse within the terminal station and the second pulse from the clock source based on the terminal laser pulses. The first transmission of the center-coded pulse train is generated based on the clock source second pulse, frequency signal, and time information; the time information in the center-coded pulse train includes a second time interval. The second time interval during the first transmission of the center-coded pulse train Set to discard mask; send the center encoded pulse train to the center gain-switched laser, convert the center encoded pulse train into a center laser pulse and send it to the terminal station;

[0028] The terminal station receives the central laser pulse and splits it into two. One portion of the central laser pulse, after delay and amplification, is sent to the terminal gain-switching laser, whose operating wavelength is locked to that of the central gain-switching laser. The other portion of the central laser pulse is sent to the terminal control module. The first time interval is obtained by measuring the second pulse within the terminal station and the second pulse from the clock source based on the central laser pulse. Based on the terminal station's second pulse, frequency signal, time information, and first time interval A terminal encoded pulse train is generated, and a terminal gain-switching laser is modulated to convert the terminal encoded pulse train into a terminal laser pulse.

[0029] The second time interval in the center-coded pulse train received by the terminal station To discard the mask, the time of the current calibration terminal station is prohibited; otherwise, information is extracted from the central laser pulse to obtain the second time interval. According to the second time interval and the first time interval Calculate the clock difference between the central station and the terminal station, and correct the time of the terminal station based on the clock difference.

[0030] Furthermore, based on the first time interval between the second pulse within the terminal station and the second pulse from the clock source measured at the terminal station... Specifically, it includes:

[0031]

[0032] In the formula, The time of the second pulse from the central station clock source; The time of the second pulse of the servo clock at the terminal station; The optical fiber transmission delay is from the central station to the terminal station.

[0033] Furthermore, based on the second time interval between the second pulse within the central station's measurement terminal and the second pulse from the clock source... The specific process includes:

[0034]

[0035] In the formula, The time of the second pulse from the central station clock source; The time of the second pulse of the servo clock at the terminal station; This refers to the fiber optic transmission delay from the terminal station to the central station.

[0036] Furthermore, the terminal station, based on the second time interval... and the first time interval The calculation of the clock difference between the central station and the terminal station includes the following steps:

[0037]

[0038] In the formula, The clock difference between the central station and the terminal station, The asymmetric residuals between the central station and the terminal station.

[0039] Furthermore, the terminal station servo clock utilizes clock bias. The servo control algorithm calibrates its own time in real time, thereby achieving time synchronization with the clock source.

[0040] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0041] This invention utilizes single-fiber single-wavelength bidirectional transmission technology based on gain switch control to ensure the symmetry of transmission delay in bidirectional channels. Furthermore, due to the wavelength tracking characteristics of the terminal gain switch laser in the terminal station, even when the wavelength of the central station laser drifts due to temperature and aging, the symmetry of bidirectional transmission delay can still be guaranteed. This invention can achieve high-precision time transmission within existing fiber optic repeater segments, and has the advantages of high timing accuracy, low cost, and easy compatibility with existing fiber optic links. Attached Figure Description

[0042] Figure 1 This is a structural diagram of the fiber optic time synchronization system provided in this embodiment. Detailed Implementation

[0043] The following is in conjunction with the appendix Figure 1 The present invention will be further described below. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be used to limit the scope of protection of the present invention.

[0044] It should be noted that in the description of this invention, the terms "front," "rear," "left," "right," "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "front," "rear," "left," "right," "upper," and "lower" used in the description of this invention refer to the directions shown in the accompanying drawings, while the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0045] like Figure 1 As shown, this embodiment provides a fiber optic time synchronization system based on gain-switched laser control, including a central station and a terminal station connected by optical fibers. The central station is equipped with a central time measurement unit, a central control unit, a central optical receiver, and the central gain-switched laser; the terminal station is equipped with a delay amplification device, a servo clock, a terminal time measurement unit, a terminal control unit, a terminal optical receiver, and a terminal gain-switched laser.

[0046] The working process of the fiber optic time synchronization system is as follows:

[0047] (1) Time and frequency information transmission from the time service center station:

[0048] The clock source second pulse signal, 10MHz frequency signal, and time information (e.g., in this embodiment, the time information includes year, month, day, hour, minute, and second) are sent to the central control unit to generate a center-coded pulse train TIM-S of a certain length. The center-coded pulse train TIM-S contains the second pulse and its header indication, frequency signal, time information encoding, and an injection modulation signal used to keep the terminal station gain-switched laser locked during signal transmission. The total length of the center-coded pulse train TIM-S should be sufficient to ensure complete transmission of time and frequency information and support terminal station detection and wavelength injection locking; the total length of the center-coded pulse train TIM-S should be less than the total round-trip delay of the fiber optic link. The center-coded pulse train TIM-S modulates the center gain-switched laser operating at a stable wavelength (such as the standard wavelength of a wavelength division multiplexing system) to generate the center laser pulse train, and injects the center laser pulse into the fiber optic channel through a center optical circulator. During the modulation of the center gain-switched laser by the center-coded pulse train TIM-S, the bias current I of the gain-switched laser is... B Above the threshold. During the pulse-free modulation period, the bias current I of the center gain-switched laser is... B Below the threshold, the central gain-switched laser is not in stimulated emission state, ensuring that during the optical pulse sent by the receiving terminal station, the backscattered light power of the optical signal sent by the central station is at least 20dB lower than the optical power of the terminal laser pulse reaching the central optical receiver.

[0049] (2) Terminal station wavelength locking and time measurement:

[0050] After the laser pulse train sent by the central station arrives at the terminal station, the central laser pulse is split into two. One portion of the central laser pulse is delayed and amplified before being injected into the terminal gain-switching laser. The delay ensures that the operating wavelength of the terminal gain-switching laser is locked to that of the central station's gain-switching laser, while also ensuring that the terminal gain-switching laser's signal transmission does not interfere with the normal reception of the time-frequency information in the central laser pulse sent by the central station. The terminal gain-switching laser uses a low-isolation package, and its lasing wavelength is close to that of the central gain-switching laser. Under the locking effect of the central station's optical pulse injection, the wavelengths of the terminal gain-switching laser and the central gain-switching laser are equal. The other portion of the central laser pulse undergoes photoelectric conversion to obtain the central coded pulse train TI. M-S , center-coded pulse train TI M-S The terminal control unit at the terminal station restores the second pulse, frequency, and time information from the central station. The terminal control unit will restore 1 PPS of second pulses. M-S The data is sent to the terminal time measurement module, which measures the 1PPS of the second pulse within the terminal station and the 1PPS of the second pulse from the clock source. M-S The time difference (TIV) between them is fed back to the terminal control unit, and the formula is as follows:

[0051]

[0052] In the formula, The time of the second pulse from the central station clock source; The time of the second pulse of the terminal station servo clock; The fiber optic transmission delay from the central station to the terminal station; The time interval between the second pulse within the terminal station and the second pulse from the clock source is denoted as the first time interval. .

[0053] (3) Terminal station time and frequency information transmission:

[0054] After the central laser pulse sent by the central station is fully received, the terminal control unit of the terminal station uses the second pulse signal, frequency signal, time information, and the first time interval measured by the station's servo clock. Generate terminal encoded pulse train TI S-M At the same time, increase the bias current I of the injection gain switching laser. B Greater than the threshold. Terminal encoded pulse train TI S-M The duration of the pulse train should ideally be sufficient to meet the minimum requirements for stable operation of the terminal gain-switched laser and the transmission of second pulses, time difference data, and management information. Terminal Encoded Pulse Train (TI) S-M When modulating the terminal gain-switched laser, the laser receives the injection modulation signal at the end of the central laser pulse transmitted from the central station, where the signal level is relatively stable. This ensures wavelength locking and avoids the injection signal affecting the modulated transmission signal. The modulated terminal laser pulse is injected into the fiber optic channel through a terminal optical circulator. During the pulse-free modulation period, the bias current I of the terminal gain-switched laser... B Below the threshold, ensure that during the reception of the central laser pulse sent by the central station, the optical power of the backscattered light signal of the terminal laser pulse sent by the terminal station is more than 20dB lower than the optical power of the central laser pulse reaching the terminal optical receiver.

[0055] (4) Time difference measurement and transmission from the central station:

[0056] After receiving the terminal laser pulse train from the terminal station, the central station injects it into the optical receiver via the central optical circulator to complete the photoelectric conversion and recover the terminal encoded pulse train TI. S-M The signal is sent to the central control unit. The central control unit extracts the 1PPS second pulse signal transmitted from the terminal station to the central station. S-M The central time measurement unit completes the time difference measurement with the second pulse of the central station clock source, expressed by the formula:

[0057]

[0058] In the formula, The time of the second pulse from the central station clock source; The time of the second pulse of the servo clock at the terminal station; The fiber optic transmission delay from the terminal station to the central station; The time interval between the second pulse within the terminal station and the second pulse from the clock source is denoted as the second time interval. .

[0059] The second time interval Included in the center-coded pulse train TI sent to the terminal station M-S Content. The central station utilizes information including a second time interval. Center-coded pulse train TI M-S A center gain-switched laser is modulated to generate a center laser pulse of a defined duration, and the center laser pulse is injected into the fiber optic channel through a center optical looper.

[0060] (5) Terminal station time-frequency servo regeneration:

[0061] The terminal station receiving center station includes a second time interval. The central laser pulse is converted into photoelectric signals by the terminal optical circulator and the terminal optical receiver, and then sent to the terminal control unit. The terminal control unit extracts the second time interval sent by the central station. The first time interval measured by the terminal station Furthermore, since the terminal gain-switched laser operates in the injection-locked state, the wavelengths of the light transmitted in both directions are the same, thus the transmission delay from the central station to the terminal station is... Fiber optic transmission delay from terminal station to central station Equal, that is, The terminal control unit can then calculate the clock difference between the terminal station servo clock and the central station clock source using a two-way time comparison method, expressed by the following formula: ;In the formula, The clock difference between the central station and the terminal station, This addresses the asymmetric residuals between the central station and the terminal station. The terminal station servo clock performs time calibration based on the clock difference and the corresponding clock servo algorithm, achieving high-precision time and frequency synchronization with the clock source.

[0062] In this embodiment, the single-fiber single-wavelength bidirectional transmission technology based on gain switch control is used to ensure the complete symmetry of the bidirectional transmission channel. Furthermore, due to the wavelength tracking characteristics of the terminal gain switch laser in the terminal station, the drift and aging of the central station laser have no impact on the timing accuracy. High-precision time transmission can be achieved within the existing fiber optic repeater segment. It has the advantages of high timing accuracy, low cost, and easy compatibility with existing fiber optic links.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fiber optic time synchronization system based on gain-switched laser modulation, characterized in that, This includes central stations and terminal stations connected by optical fibers; The central station is equipped with a central control module and a central gain-switching laser. The terminal station is equipped with a delay amplification device, a terminal control module, and a terminal gain switching laser; The information transmission and reception process from the central station to the terminal station includes: The central control module controls the central gain-switching laser to send a central laser pulse to the terminal station. The central laser pulse includes a clock source second pulse, a frequency signal, time information, and the time interval between the clock source second pulse measured by the central control module and the second pulse sent by the terminal station. The terminal station splits the central laser pulse sent by the central station into two parts. One part of the central laser pulse is sent to the terminal gain switch laser after being delayed and amplified, so that the operating wavelength of the terminal gain switch laser is locked to the operating wavelength of the central gain switch laser. The other part of the central laser pulse is sent directly to the terminal control module. The information transmission and reception process from the terminal station to the central station includes: The terminal control module controls the terminal gain-switching laser to send terminal laser pulses to the central station. The terminal laser pulses contain the terminal station's second pulse, frequency signal, time information, and time interval. The laser pulses from the terminal are received and processed by the central control module within the central station; time interval The time interval between the terminal station's internal second pulse and the clock source's second pulse, as measured by the terminal control module; The central station and the terminal station exchange information to calculate the clock difference. The terminal station corrects the time of the servo clock in the station according to the clock difference, thereby achieving time synchronization with the clock source. The central station is equipped with a central looper; the central looper is connected to a central optical receiver and a central gain-switching laser via optical fiber; the terminal station is equipped with a terminal looper; the terminal looper is connected to a delay amplifier, a terminal optical receiver, and a terminal gain-switching laser via optical fiber; the central looper and the terminal looper are connected via optical fiber.

2. The fiber optic time synchronization system according to claim 1, characterized in that, The central control module includes a central time measurement unit, a central control unit, and a central optical receiver; The central optical receiver is used to receive terminal laser pulses, convert the terminal laser pulses into photoelectric signals, and then send them to the central control unit. The central control unit is used to extract the second pulse sent by the terminal station from the terminal laser pulse and send the second pulse sent by the terminal station to the central time measurement unit; the central control unit is used to calculate the second pulse from the clock source, the frequency signal, the time information, and the time interval. A central encoded pulse train is generated and sent to a central gain-switched laser to generate a central laser pulse. The central time measurement unit is used to measure the time interval between the second pulse sent by the terminal station and the second pulse from the clock source. , the time interval It is sent to the central control unit.

3. The fiber optic time synchronization system according to claim 2, characterized in that, The terminal control module includes a servo clock, a terminal time measurement unit, a terminal control unit, and a terminal optical receiver; The terminal optical receiver is used to receive the central laser pulse, convert the central laser pulse into a photoelectric signal, and then send it to the terminal control unit. The terminal control unit is used to extract the clock source second pulse from the central laser pulse and send the clock source second pulse to the terminal time measurement unit; the terminal control unit is used to calculate the second pulse, frequency signal, time information and time interval from the terminal station. The terminal encoded pulse train is generated and sent to the terminal gain-switching laser to generate the terminal laser pulse; the terminal control unit is used to extract information from the center laser pulse to obtain the time interval. According to the time interval and time interval Calculate the clock difference between the central station and the terminal station, and send the clock difference to the terminal station's servo clock; The terminal time measurement unit is used to measure the time interval between the second pulse within the terminal station and the second pulse from the clock source. , the time interval Send to the terminal control unit; The servo clock is used to send the terminal station's second pulse to the terminal time measurement unit, and to send the terminal station's second pulse, frequency signal, and time information to the terminal control unit; the servo clock is used to receive the clock difference sent by the terminal control unit, and to correct its own time according to the clock difference to achieve time synchronization with the clock source.

4. The fiber optic time synchronization system according to claim 1, characterized in that, The central laser pulse is provided with an injection control signal at the end. The duration of the central laser pulse is adjusted by the injection control signal, and the duration of the central laser pulse is less than the total round-trip time delay from the central station to the terminal station. When the terminal encoded pulse train modulates the terminal gain-switched laser, the terminal gain-switched laser receives the injection modulation signal from the central laser pulse sent by the central station.

5. The fiber optic time synchronization system according to claim 1, characterized in that, During pulse train modulation, the bias current of the center gain-switched laser and the terminal gain-switched laser is higher than the gain-switched laser threshold; during the absence of pulse train modulation, the bias current of the center gain-switched laser and the terminal gain-switched laser is lower than the gain-switched laser threshold; during laser pulse reception, the backscattered power of the transmitted optical signal at the center station and the terminal station is at least 20 dB lower than the received optical power of the optical receiver.

6. The time synchronization execution method of the fiber optic time synchronization system according to any one of claims 1 to 5, characterized in that, include: The central station receives laser pulses from the terminal and measures the time interval between the second pulse within the terminal station and the second pulse from the clock source based on the terminal laser pulses. Based on the second pulse, frequency signal, time information, and time interval of the clock source Generate a center-coded pulse train; send the center-coded pulse train to the center gain-switching laser, which converts the center-coded pulse train into a center laser pulse and sends it to the terminal station; The terminal station receives the central laser pulse and splits it into two. One portion of the central laser pulse, after delay and amplification, is sent to the terminal gain-switching laser, causing the operating wavelength of the terminal gain-switching laser to lock onto the operating wavelength of the central gain-switching laser. The other portion of the central laser pulse is sent to the terminal control unit to measure the time interval between the second pulse within the terminal station and the second pulse from the clock source. Based on the terminal station's second pulse, frequency signal, time information, and time interval... Generate a terminal encoded pulse train; convert the terminal encoded pulse train into a terminal laser pulse; the terminal station extracts information from the central laser pulse to obtain the time interval. According to the time interval and time interval The clock difference between the central station and the terminal station is calculated, and the time of the servo clock of the terminal station is corrected according to the clock difference, so as to achieve time synchronization with the clock source.

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