CN112187363A - High-precision optical fiber time frequency transmission system and method compatible with Ethernet - Google Patents
High-precision optical fiber time frequency transmission system and method compatible with Ethernet Download PDFInfo
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Abstract
A high-precision optical fiber time frequency transmission system compatible with Ethernet and a method thereof are provided, wherein the system comprises a time/frequency source, a first terminal machine, an optical fiber link, a second terminal machine and a time/frequency output; the time/frequency source is connected with a first terminal machine, the first terminal machine is connected with a second terminal machine through an optical fiber link, and the second terminal machine is connected with the time/frequency output. The invention takes the Ethernet digital signal as the carrier wave and takes the high-precision frequency signal as the modulation signal to mix the digital signal, improves the frequency transmission performance, does not destroy the original Ethernet data and network topological structure, greatly improves the compatibility of the high-precision time frequency transmission system, has the characteristics of simple structure and low cost, and widens the application field.
Description
Technical Field
The invention relates to the technical field of optical fiber time frequency transmission and measurement and control, in particular to a high-precision optical fiber time frequency transmission system and method based on fusion of time transmission of Ethernet digital coding and high-precision analog frequency transmission.
Background
The time frequency is a bearing base stone for human activities and information interaction, is the only physical quantity with highest measurement precision among all physical quantities and capable of being remotely transmitted and calibrated in the global range, and the high-precision time frequency transmission comprehensively supports aspects of modern society such as social and economic activities, frontier scientific research, national defense and military operations and the like. The laser is used as a carrier wave of a time frequency signal, the optical fiber is used as a transmission medium, the remote transmission with the highest precision can be realized, and the optical fiber has the advantages of high reliability and high safety, is considered as a main means of the next generation of precision time frequency transmission, and is a key field of international time frequency information science and technology competition.
The special optical fiber link can realize high-precision time frequency transmission and synchronization, but the cost of laying or leasing the special optical fiber link is very high, and the large-scale and large-range high-precision time frequency transmission and application are seriously limited. The cost can be greatly saved by carrying out optical fiber time frequency transmission through the existing widely distributed optical fiber communication network, and the method is an ideal choice for realizing high-precision large-range time frequency transmission. WR (WhiterRabbit White Rabbit) clock synchronization technology is a typical time and Frequency transfer technology based on Ethernet and optical fiber communication, which integrates a synchronous Ethernet (SyncE), a precision timing protocol (IEEE1588 v2) and a distributed synchronous timing technology developed by a digital double mixing measurement technology (DDMTD), and can realize multi-node sub-nanosecond precision clock distribution in a range of thousands of meters [ reference 1: Rizzi, M., et al. "IEEE Rabbit clock synchronization: ultra ports on phase in phase noise and port-term stability to FPGA amplification." IEEE Transactions on ultrasound, Ferrooectrics, and Frequency Control (2018):1-1 ]. The technology is compatible with a standard Ethernet protocol, has the advantages of no occupation of extra network bandwidth, direct integration with a data link, simple structure, low cost and the like, can directly run in the existing optical fiber communication network, can well meet the requirements of multiple long-distance multi-node high-precision time service, and is increasingly widely applied.
The time frequency transmission technology based on the Ethernet is realized by using an Ethernet physical layer, and frequency source broadcasting is realized by utilizing clock data embedding and clock recovery technology, wherein key devices are a high-speed serial transceiver or a serial-parallel conversion chip and an FPGA (Field Programmable Gate Array). due to the influences of clock recovery noise of the high-speed serial transceiver or the serial-parallel conversion chip, clock tree noise in the FPGA, DDMTD measurement noise and the like, under the existing system, the frequency transmission performance is difficult to break through the 7E-13@1s limitation, and the requirement for high-precision frequency transmission in practical application is difficult to meet.
Disclosure of Invention
In order to overcome the defects of the prior art, aiming at the problem of poor frequency transmission stability caused by the influences of clock recovery noise of a high-speed serial transceiver or a serial-parallel conversion chip, clock tree noise in an FPGA, DDMTD measurement noise and the like in the time frequency transmission technology of the Ethernet, the invention provides a high-precision optical fiber time frequency transmission system and a method compatible with the Ethernet.
A high-precision optical fiber time frequency transmission system compatible with Ethernet is characterized by comprising a time/frequency source, a first terminal, an optical fiber link, a second terminal and a time/frequency output; the time/frequency source is connected with a first terminal machine, the first terminal machine is connected with a second terminal machine through an optical fiber link, and the second terminal machine is connected with the time/frequency output.
The first terminal machine comprises a first Ethernet time synchronization unit, a first frequency synchronization unit and a first mixing/separating unit, and the second terminal machine comprises a second Ethernet time synchronization unit, a second frequency synchronization unit and a second mixing/separating unit;
the first Ethernet time synchronization unit is used for time signal synchronization of a time/frequency source, time signal encoding and decoding, measuring the time difference between the second Ethernet time synchronization unit and the first Ethernet time synchronization unit and sending the time difference to the second terminal machine, and data communication between the first terminal machine and the second terminal machine;
the first frequency synchronization unit is used for synchronizing frequency signals of a time/frequency source, measuring the phase difference between the second frequency synchronization unit and the first frequency synchronization unit and sending frequency phase difference data to the second frequency synchronization unit;
the first mixing/separating unit is used for pulse amplitude modulation of the analog frequency signal of the first frequency synchronizing unit and the digital coding signal of the first Ethernet time synchronizing unit, sending the pulse amplitude modulation to the optical fiber link, receiving the mixed signal of the second terminal machine, carrying out synchronization and threshold demodulation, recovering the digital coding signal and the analog frequency signal, and sending the digital coding signal and the analog frequency signal to the first Ethernet time synchronizing unit and the first frequency synchronizing unit respectively;
the second Ethernet time synchronization unit is used for coding and decoding time signals, data communication between the first terminal and the second terminal, receiving time coding signals of the first terminal and unidirectional link compensation time delay data, adjusting local time according to unidirectional link compensation time delay, outputting time signals synchronized with the first terminal, simultaneously sending local time codes, receiving frequency phase difference data of the first terminal and the second terminal and forwarding the data to the second frequency synchronization unit;
the second frequency synchronization unit is used for receiving the frequency signal and the frequency phase difference data sent by the first terminal, adjusting the received frequency signal according to the frequency phase difference data and outputting a frequency signal synchronized with the first terminal;
the second mixing/separating unit is used for pulse amplitude modulation of the analog frequency signal of the second frequency synchronizing unit and the digital coding signal of the second Ethernet time synchronizing unit, sending the pulse amplitude modulation to the optical fiber link, receiving the mixed signal of the first terminal unit, carrying out synchronization and threshold demodulation, recovering the digital coding signal and the analog frequency signal, and sending the digital coding signal and the analog frequency signal to the second Ethernet time synchronizing unit and the second frequency synchronizing unit respectively.
Preferably, the first mixing/separating unit and the second mixing/separating unit comprise an SFP optical module, a Q-point controller, an electro-optical modulator, a first circulator, a splitter, a photodetector, and a band-pass filter;
the SFP optical module receives a digital coding signal from the Ethernet time synchronization unit and carries out electro-optical conversion, an output optical signal enters an electro-optical modulator as a carrier signal, the other end of the electro-optical modulator is connected to the frequency synchronization unit, an analog frequency signal is used as a modulation signal and carries out pulse amplitude modulation in the electro-optical modulator, and the modulated optical signal enters an optical fiber link through the circulator. The modulation signal returned by the other end machine is separated by the circulator, enters the splitter and then is divided into two paths, one path enters the receiving end of the SFP optical module, the other path enters the photoelectric detector, the digital coding signal received by the SFP optical module enters the Ethernet time synchronization unit, the signal received by the photoelectric detector is restored into an analog frequency signal through the band-pass filter, and the signal enters the frequency synchronization unit.
Preferably, the first mixing/separating unit and the second mixing/separating unit comprise a level conversion driver, a laser, an electroabsorption modulator, a circulator, a photoelectric detector and a band-pass filter;
the level conversion driver receives a digital coding signal from the Ethernet time synchronization unit and drives the laser to perform electro-optical conversion, an output optical signal of the laser enters the electric absorption modulator as a carrier signal, the other end of the electric absorption modulator is connected to an analog frequency signal of the frequency synchronization unit, the signal serves as a modulation signal, pulse amplitude modulation is performed in the electric absorption modulator, and the modulated optical signal enters the optical fiber link through the circulator. The modulation signal returned by the other end machine enters the photoelectric detector after being separated by the circulator, the output signal of the photoelectric detector is divided into two paths, one path is connected to the level conversion driver, the other path is connected to the band-pass filter, the digital coding signal received by the level conversion driver enters the Ethernet time synchronization unit, and the analog frequency signal demodulated by the band-pass filter is transmitted to the frequency synchronization unit for processing.
The invention relates to a high-precision optical fiber time frequency transmission method compatible with Ethernet, which comprises the following steps:
after the first Ethernet time synchronization unit in the first terminal synchronizes to the time/frequency source time signal, the coded local time information and the measured round trip link compensation time delay information are sent to the second Ethernet time synchronization unit in the second terminal. The second Ethernet time synchronization unit returns the received time coding information to the first Ethernet time synchronization unit, carries out delay compensation on the second Ethernet time synchronization unit according to the round-trip link compensation delay information, and outputs the time information synchronized with the first Ethernet time synchronization unit.
When the first frequency synchronization unit in the first terminal is synchronized to the time/frequency source frequency signal, the frequency signal is sent to the second frequency synchronization unit, and the phase difference information of the frequency signals of the first frequency unit and the second frequency unit which are coded is sent. The second frequency synchronization unit divides the received frequency into two paths, one path returns to the first frequency synchronization unit, and the other path controls the frequency output of the second frequency synchronization unit according to the frequency phase difference information in a compensation mode, so that the frequency of the second frequency synchronization unit is synchronized with the frequency of the first frequency synchronization unit.
The Ethernet time synchronization unit processes digital code signals, the frequency synchronization unit processes analog frequency signals, and the digital code signals and the analog frequency signals are modulated and demodulated in the mixing/demodulating unit.
The modulation method comprises the following steps: the digital coding signal and the analog frequency signal respectively enter a carrier end and a modulation end of the mixing/separating unit, and are modulated by using a pulse amplitude modulation mode to generate an analog-digital mixed signal, wherein the mixing formula is as follows:
ms(t) is the analog-to-digital mixed signal, V0For simulating the bias voltage of the frequency signal, maIn order to modulate the depth of the light,
for the initial phase of the frequency signal, dτ(T) is a digitally encoded signal of width τ, TsIs a digitally encoded signal period, where 0.1 < ma＜0.5,V0In order to operate at the point Q,
the separation method comprises the following steps: the analog-digital mixed signal is an optical signal, enters a demodulation end of the mixing/separating unit, the optical signal is equally divided into two parts in the mixing/separating unit and converted into an electric signal, one part uses a narrow-band filter to synchronously demodulate an analog frequency signal, and the other part uses a window comparator to compare a threshold value and restore a digital coding signal.
Compared with the prior art, the invention has the following beneficial effects:
1. by transmitting high-precision frequency signals, the stability of frequency transmission is superior to 1e-13@1s, the frequency transmission performance is improved, the high-precision frequency transmission requirements represented by hydrogen clocks, distributed equipment and the like can be met, and the application field is widened;
2. the Ethernet digital coding signal is mixed with the high-precision analog frequency signal, so that the time frequency transmission channel is reduced, the time frequency signal homology is improved, meanwhile, the Ethernet data stream is reserved, and the compatibility of time frequency transmission is greatly improved;
3. the system is compatible with standard Ethernet protocol, occupies no extra network bandwidth, is directly integrated with a data link, and has simple structure and low cost.
Drawings
Fig. 1 is a block diagram of an embodiment of an ethernet-compatible high-precision fiber time-frequency transfer system.
FIG. 2 is a schematic diagram of signal conversion of the mixing/separating unit
FIG. 3 is a block diagram of one embodiment of a mixing unit
FIG. 4 is a block diagram of another embodiment of a mixing unit
Detailed Description
The following examples illustrate the invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation process are given. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
FIG. 1 is a structural view of example 1. As shown in the figure, the system comprises a time/frequency source (1), a first end machine (2), an optical fiber link (3), a second end machine (4) and a time/frequency output (5), wherein the first end machine (2) consists of a first Ethernet time synchronization unit (2-2), a first frequency synchronization unit (2-3) and a first mixing/separating unit (2-4), the second end machine (4) consists of a second Ethernet time synchronization unit (4-2), a second frequency synchronization unit (4-3) and a second mixing/separating unit (4-4), and the first optical fiber time-frequency synchronization unit is connected with the second optical fiber time-frequency synchronization unit through the optical fiber link (3).
The time synchronization process is as follows: when the first end machine (2) detects a time/frequency source (1)1PPS time pulse signal, the first Ethernet time synchronization unit (2-2) synchronizes the time to the time/frequency source (1), the first Ethernet time synchronization unit (2-2) encodes the synchronized time signal to generate timestamp data 1, the timestamp data 1 is encoded and then packaged into 1.25Gbps Ethernet data, and the Ethernet data is sent to the second end machine (4);
the second Ethernet time synchronization unit (4-2) generates initial time as the time of the second end machine (4), when the second end machine (4) detects the time stamp data 1, the second Ethernet time synchronization unit (4-2) is controlled to record the time of the second end machine (4) and generate the time stamp data 2, the second Ethernet time synchronization unit (4-2) encodes the current time of the second end machine (4) to generate the time stamp data 3, the time stamp data 2 and the time stamp data 3 are encoded and then packaged into 1.25Gbps Ethernet data, and the Ethernet data are sent to the first end machine (2);
the first end machine (2) detects the timestamp data 3, the first Ethernet time synchronization unit (2-2) records the current time of the first end machine (2) to generate timestamp data 4, the first Ethernet time synchronization unit (2-2) calculates a round-trip time difference according to the timestamp data 1, the timestamp data 2, the timestamp data 3, the timestamp data 4 and an asymmetric model of an optical fiber link, sends the round-trip time difference to the second Ethernet time synchronization unit (4-2), the second Ethernet time synchronization unit (4-2) corrects the time of the second end machine (4) according to the round-trip time difference, and outputs a time signal synchronized with the first end machine (1) to a time/frequency output (5);
frequency ofThe synchronization process is as follows: when the first terminal machine (2) detects a 100MHz frequency signal of the time/frequency source (1), the first frequency synchronization unit (2-3) is controlled to synchronize the frequency to the frequency of the time/frequency source (1) with the phase of
The first frequency synchronization unit (2-3) sends the synchronized frequency to the second terminal (4), the second terminal (4) takes the received frequency signal as a reference frequency signal and returns the reference frequency signal to the first terminal (2), and the first terminal (2) detects the return frequency signal, wherein the phase of the return frequency signal is
First frequency synchronization unit (2-3) measurement
And
the phase difference is obtained and the data are sent to a second end machine, the second end machine (4) corrects the frequency of the second end machine (4) according to the reference frequency signal, the frequency phase difference data and the optical fiber link asymmetric model, and outputs a frequency signal synchronous with the first end machine (2) to a time/frequency output (5);
the first end machine (2) has the following mixing process: the digital coding signal output by the first Ethernet time synchronization unit (2-2) and the analog frequency signal output by the first frequency synchronization unit (2-3) enter the carrier end and the modulation end of the first mixing/separating unit (2-4), pulse amplitude modulation is carried out in the first mixing/separating unit (2-4) to generate an analog-digital mixed signal, the digital coding signal is 1.25Gbps, the analog frequency signal is 100MHz, and the modulation depth is ma＝0.4,V0Operating at point Q.
The mixing process of the second end machine (4) is as follows: the digital coding signal output by the second Ethernet time synchronization unit (4-2) and the analog frequency signal output by the second frequency synchronization unit (4-3) enter the carrier end and the modulation end of the second mixing/separating unit (4-4), pulse amplitude modulation is carried out in the second mixing/separating unit (4-4), an analog-digital mixed signal is generated, and the digital coding signal is 1.25Gbps, 100MHz analog frequency signal and m modulation deptha＝0.4,V0Operating at point Q.
The separation process of the first end machine (2) is as follows: the analog-digital mixed signal sent by the second terminal machine (4) enters a demodulation end in the first mixing/separating unit (2-4), an optical signal is divided into two parts in the first mixing/separating unit (2-4) and converted into an electric signal, one part uses synchronous demodulation to recover an analog frequency signal, and the other part uses threshold comparison to recover a digital coding signal.
The separation process of the second end machine (4) is as follows: the analog-digital mixed signal sent by the first terminal (2) enters a demodulation end in the second mixing/separating unit (4-4), the optical signal is divided into two parts in the second mixing/separating unit (4-4) and converted into an electric signal, one part uses synchronous demodulation to recover an analog frequency signal, and the other part uses threshold comparison to recover a digital coding signal.
FIG. 3 is a block diagram of one embodiment of a mixing unit. The first mixing/separating unit (2-4) and the second mixing/separating unit (4-4) comprise an SFP optical module (6), a Q point controller (7), an electro-optical modulator (8), a first circulator (9), a splitter (10), a photoelectric detector (11) and a band-pass filter (12);
the SFP optical module (6) receives digital coding signals from the Ethernet time synchronization unit, performs electro-optical conversion, outputs optical signals to enter an electro-optical modulator (8) as carrier signals, the other end of the electro-optical modulator (8) is connected to analog frequency signals of the frequency synchronization unit, the digital coding signals and the analog frequency signals are modulated in the electro-optical modulator (8), and the modulated optical signals enter an optical fiber link (3) through a circulator (9); a modulation signal transmitted by the other end machine through the optical fiber link (3) is separated through the circulator (9), the modulation signal enters the splitter (10) and then is divided into two paths, one path enters the receiving end of the SFP optical module (6), the other path enters the photoelectric detector (11), Ethernet data received by the SFP optical module (6) enters the Ethernet time synchronization unit, a signal received by the photoelectric detector (11) restores a frequency signal through the band-pass filter (12), and the frequency signal is connected to the frequency synchronization unit.
The SFP optical module (6) adopts commercial modules, including BIDI SFP, DWDM SFP, CWDM SFP modules and the like, and the first terminal machine (2) and the second terminal machine (4) adopt optical modules with different wavelengths to reduce back scattering. The electro-optical modulator (8) can adopt a modulator made of the electro-optical effect of lithium niobate crystal (LiNb03), gallium arsenide crystal (GaAs) and lithium tantalate crystal (LiTa03), the electro-optical modulator works at a Q point so as to obtain a better linear interval, and the power of the splitter (10) is distributed in a ratio of 1: 1.
FIG. 4 is a block diagram of another embodiment of a mixing unit; the first mixing/separating unit (2-4) and the second mixing/separating unit (4-4) comprise a level conversion driver (13), a laser (14), an electro-absorption modulator (15), a second circulator (16), a photoelectric detector (17) and a band-pass filter (18);
the level conversion driver (13) receives Ethernet data from the Ethernet time synchronization unit and drives the laser (14) to perform electro-optical conversion, an output signal of the laser (14) enters the electric absorption modulator (15) as a carrier signal, the other end of the electric absorption modulator (15) is connected to a frequency signal of the frequency synchronization unit, the frequency signal serves as a modulation signal, a digital coding signal and an analog frequency signal are modulated in the electric absorption modulator, and a modulated optical signal enters the optical fiber link through the circulator (16). The modulation signal transmitted by the other end machine through the optical fiber link (3) is separated through the circulator (16) and enters the photoelectric detector (17), the output signal of the photoelectric detector (17) is divided into two paths, one path is connected to the level conversion driver (13), the other path is connected to the band-pass filter (18), the Ethernet data received by the level conversion driver (13) enters the Ethernet time synchronization unit, and the frequency signal demodulated by the band-pass filter (18) is transmitted to the frequency synchronization unit for processing.
The electro-absorption modulator (15) can adopt a transmission type and a reflection type, the laser (14) is an internal modulation DFB laser, the temperature and the flow are controlled through the electro-optical conversion driver (13), the output wavelengths of the first end machine (2) and the second end machine (4) are inconsistent, the back scattering is reduced, the wavelength is compatible with CWDM and DWDM, and DFB-EAM can be adopted by the laser (14) and the electro-absorption modulator (15).
Claims (6)
1. A high-precision optical fiber time frequency transmission system compatible with Ethernet is characterized by comprising a time/frequency source (1), a first end machine (2), an optical fiber link (3), a second end machine (4) and a time/frequency output (5); the time/frequency source (1) is connected with a first terminal machine (2), the first terminal machine (2) is connected with a second terminal machine (4) through an optical fiber link (3), and the second terminal machine (4) is connected with a time/frequency output (5).
2. An ethernet-compatible high-precision fiber time-frequency delivery system according to claim 1, wherein said first end-unit (2) comprises a first ethernet time synchronization unit (2-2), a first frequency synchronization unit (2-3) and a first mixing/splitting unit (2-4), and said second end-unit (4) comprises a second ethernet time synchronization unit (4-2), a second frequency synchronization unit (4-3) and a second mixing/splitting unit (4-4);
the first Ethernet time synchronization unit (2-2) is used for time pulse signal synchronization of the time/frequency source (1), time pulse signal encoding and decoding, digital encoding signals are generated by using time encoding data and Ethernet data, time difference between the second Ethernet time synchronization unit (4-4) and the first Ethernet time synchronization unit (2-2) is measured and sent to the second terminal, and Ethernet data communication between the first terminal (2) and the second terminal (4) is carried out;
the first frequency synchronization unit (2-3) is used for synchronizing frequency signals of the time/frequency source (1), measuring the phase difference between the second frequency synchronization unit (4-3) and the first frequency synchronization unit (2-3), and sending frequency phase difference data to the second frequency synchronization unit (4-3);
the first mixing/separating unit (2-4) is used for pulse amplitude modulation of an analog frequency signal of the first frequency synchronizing unit (2-3) and a digital coding signal of the first Ethernet time synchronizing unit (2-2), sending the pulse amplitude modulation to the optical fiber link (3), receiving a mixed signal of the second terminal (4), performing synchronization and threshold demodulation, recovering the digital coding signal and the analog frequency signal, and sending the recovered digital coding signal and the recovered analog frequency signal to the first Ethernet time synchronizing unit (2-2) and the first frequency synchronizing unit (2-3) respectively;
the second Ethernet time synchronization unit (4-2) is used for coding and decoding time signals, generating digital coding signals by using time coding data and Ethernet data, is used for Ethernet data communication between the first terminal (2) and the second terminal (4), receiving the time coding signals of the first terminal (2) and unidirectional link compensation time delay, adjusting local time according to the unidirectional link compensation time delay, outputting time signals synchronized with the first terminal (2), simultaneously sending local time codes, receiving frequency phase difference data of the first terminal (2) and the second terminal (4) and forwarding the frequency phase difference data to the second frequency synchronization unit (4-3);
the second frequency synchronization unit (4-3) is used for receiving the frequency signal and the frequency phase difference data sent by the first terminal (2), adjusting the received frequency signal according to the frequency phase difference data, and outputting a frequency signal synchronized with the first terminal (2);
the second mixing/separating unit (4-4) is used for pulse amplitude modulation of the analog frequency signal of the second frequency synchronizing unit (4-3) and the digital coding signal of the second Ethernet time synchronizing unit (4-2), sending the pulse amplitude modulation to the optical fiber link, receiving the mixed signal of the first terminal (2), synchronizing the pulse amplitude modulation with a threshold value, recovering the digital coding signal and the analog frequency signal, and sending the digital coding signal and the analog frequency signal to the second Ethernet time synchronizing unit (4-2) and the second frequency synchronizing unit (4-3) respectively.
3. The ethernet-compatible high-precision fiber time-frequency transfer system according to claim 2, wherein the first mixing/splitting unit (2-4) and the second mixing/splitting unit (4-4) comprise an SFP optical module (6), a Q-point controller (7), an electro-optical modulator (8), a circulator (9), a splitter (10), a photodetector (11) and a band-pass filter (12);
the SFP optical module (6) receives digital coding signals from the Ethernet time synchronization unit, performs electro-optical conversion, outputs optical signals to enter an electro-optical modulator (8) as carrier signals, the other end of the electro-optical modulator (8) is connected to analog frequency signals of the frequency synchronization unit, the digital coding signals and the analog frequency signals are modulated in the electro-optical modulator (8), and the modulated optical signals enter an optical fiber link (3) through a circulator (9); a modulation signal transmitted by the other end machine through the optical fiber link (3) is separated through the circulator (9), the modulation signal enters the splitter (10) and then is divided into two paths, one path enters the receiving end of the SFP optical module (6), the other path enters the photoelectric detector (11), Ethernet data received by the SFP optical module (6) enters the Ethernet time synchronization unit, a signal received by the photoelectric detector (11) restores a frequency signal through the band-pass filter (12), and the frequency signal is connected to the frequency synchronization unit.
4. An ethernet-compatible high-precision fiber time-frequency transfer system according to claim 2, characterized in that the first hybrid/splitting unit (2-4) and the second hybrid/splitting unit (4-4) comprise a level shift driver (13), a laser (14), an electro-absorption modulator (15), a circulator (16), a photodetector (17) and a band-pass filter (18);
the level conversion driver (13) receives digital coding signals from the Ethernet time synchronization unit and drives the laser (14) to perform electro-optical conversion, output signals of the laser (14) enter the electric absorption modulator (15) as carrier signals, the other end of the electric absorption modulator (15) is connected to frequency signals of the frequency synchronization unit, the frequency signals serve as modulation signals, the digital coding signals and analog frequency signals are modulated in the electric absorption modulator, and the modulated optical signals enter the optical fiber link (3) through the circulator (16). The modulation signal transmitted by the other end machine through the optical fiber link (3) is separated through the circulator (16) and enters the photoelectric detector (17), the output signal of the photoelectric detector (17) is divided into two paths, one path is connected to the level conversion driver (13), the other path is connected to the band-pass filter (18), the Ethernet data received by the level conversion driver (13) enters the Ethernet time synchronization unit, and the frequency signal demodulated by the band-pass filter (18) is transmitted to the frequency synchronization unit for processing.
5. A method for time-frequency transfer using the ethernet-compatible high-precision fiber-optic time-frequency transfer system according to any one of claims 1 to 4, comprising a time synchronization process and a frequency synchronization process, specifically as follows:
the time synchronization process comprises the following steps:
when the first end machine (2) detects a time pulse signal of the time/frequency source (1), the first Ethernet time synchronization unit (2-2) synchronizes the time to the time of the time/frequency source (1), the first Ethernet time synchronization unit (2-2) encodes the synchronized time signal to generate timestamp data 1, the timestamp data 1 is encoded and then packaged into Ethernet data, and the Ethernet data is sent to the second end machine (4);
the second Ethernet time synchronization unit (4-2) generates initial time as the time of the second terminal (4), when the second terminal (4) detects the timestamp data 1, the second Ethernet time synchronization unit (4-2) is controlled to record the time of the second terminal (4) to generate the timestamp data 2, the second Ethernet time synchronization unit (4-2) encodes the current time of the second terminal (4) to generate the timestamp data 3, the timestamp data 2 and the timestamp data 3 are encoded and then packaged into Ethernet data, and the Ethernet data are sent to the first terminal (2);
the first end machine (2) detects the timestamp data 3, the first Ethernet time synchronization unit (2-2) records the current time to generate timestamp data 4, calculates the round-trip time difference according to the timestamp data 1, the timestamp data 2, the timestamp data 3, the timestamp data 4 and an optical fiber link asymmetric model, sends the round-trip time difference to the second Ethernet time synchronization unit (4-2), and the second Ethernet time synchronization unit (4-2) corrects the time of the second end machine (4) according to the round-trip time difference and outputs a time signal synchronized with the first end machine (1) to a time/frequency output (5);
the frequency synchronization process comprises the following steps:
when the first terminal machine (2) detects the frequency signal of the time/frequency source (1), the first frequency synchronization unit (2-3) is controlled to synchronize the frequency to the frequency of the time/frequency source (1) with the phase of
The first frequency synchronization unit (2-3) sends the synchronized frequency to the second terminal (4), the second terminal (4) takes the received frequency signal as a reference frequency signal and returns the reference frequency signal to the first terminal (2), and the first terminal (2) detects the return frequency signal, wherein the phase of the return frequency signal is
First frequency synchronization unit (2-3) measurement
And
the phase difference is obtained and the data are sent to a second terminal (4), the second terminal (4) corrects the frequency of the second terminal (4) according to the reference frequency signal and the frequency phase difference data, and outputs a synchronous frequency signal with the first terminal (2) to a time/frequency output (5);
the first Ethernet time synchronization unit (2-2) and the second Ethernet time synchronization unit (4-2) generate digital coding signals, the digital coding signals transmit Ethernet data packets such as time stamps and frequency differences, the first frequency synchronization unit (2-3) and the second frequency synchronization unit (4-3) generate frequency signals, and the digital coding signals and the analog frequency signals are mixed and separated in the first mixing/separating unit (2-4) and the second mixing/separating unit (4-4).
6. The ethernet-compatible high-precision fiber time-frequency transfer method according to claim 5, wherein the mixing and the separation, including the mixing process and the separation process, are as follows:
the mixing process comprises the following steps: the digital coding signal and the analog frequency signal respectively enter a carrier end and a modulation end of the mixing/separating unit, and an analog-digital mixed signal is generated by using a pulse amplitude modulation mode, wherein the mixing formula is as follows:
ms(t) is the analog-to-digital mixed signal, V0For simulating the bias voltage of the frequency signal, maIn order to modulate the depth of the light,
for the initial phase of the frequency signal, dτ(T) is a digitally encoded signal of width τ, TsFor digitally encoding messagesNumber period, wherein 0.1 < ma＜0.5,V0In order to operate at the point Q,
the separation process comprises the following steps: the analog-digital mixed signal is an optical signal, enters a demodulation end of the mixing/separating unit, the optical signal is equally divided into two parts in the mixing/separating unit and converted into an electric signal, one part uses a narrow-band filter to synchronously demodulate an analog frequency signal, and the other part uses a window comparator to compare a threshold value and restore a digital coding signal.
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