An optical frequency comb time-frequency transfer device based on the white rabbit protocol

Abstract

The present invention discloses an optical frequency comb time-frequency transfer device based on the White Rabbit protocol, belonging to the field of time synchronization detection, comprising: two symmetric dense wavelength division multiplexers form a transmission link through an optical fiber link; after locking the frequency according to the time-frequency reference, the heterodyne signals S1 of the third and the first optical frequency comb pulse sequences are respectively calculated, and the detection results S3 of the second and the third optical frequency comb pulse sequences are sent to the first time-frequency transfer module; at the same time, the detection result S2 of the third and the second optical frequency comb pulse sequences is calculated and sent to the second time-frequency transfer module; the first time-frequency transfer module is connected in series with the second time-frequency transfer module through the transmission link to establish a White Rabbit connection; the detection results S1 and S3 are transmitted to the second time-frequency transfer module; according to the fixed delay and the transmission link delay, combining S1, S2 and S3, the phase offset of the second and the first optical frequency comb output pulse sequences is calculated, and the phases of the two optical frequency combs are adjusted to be consistent to complete time synchronization; the time synchronization accuracy of the present invention is improved to the femtosecond level.

Description

Technical Field

[0001] The present invention belongs to the field of detection of time synchronization accuracy, and specifically relates to an optical frequency comb time-frequency transfer device based on the White Rabbit protocol. Background Art

[0002] Currently, the standard connection in the White Rabbit protocol is formed by connecting two time-frequency transfer modules that support the White Rabbit protocol in series through an optical fiber link. As Figure 1 shown, each time-frequency transfer module has a clock circuit, a control module, and an optical module that support the White Rabbit protocol. According to the time synchronization mode, the nodes where these two modules are located can be divided into a master node and a slave node. At the master node, a high-precision time-frequency signal provided by a time-frequency reference can be accessed as a reference. The clock circuit generates a clock signal according to the White Rabbit protocol, combines it with a communication signal through the control module, and the optical module generates an optical signal carrying the White Rabbit clock signal, which enters the optical fiber link and is transmitted to a remote node, where the remote time-frequency transfer module processes the signal accordingly.

[0003] In terms of frequency transfer, the time-frequency transfer module at the master node generates a data stream at a fixed rate based on the reference frequency and modulates the signal light. After being transmitted to the slave node, the frequency signal is restored according to the rate of the data stream, thereby achieving frequency transfer;

[0004] In terms of time synchronization, the clock signal is transmitted bidirectionally between the master and slave nodes. By recording the time points of receiving and sending the clock signal, the transmission delay and clock deviation between the two nodes are calculated, and time synchronization is performed at the slave node.

[0005] In the White Rabbit protocol, the input clock signal generates an output clock signal with unchanged phase and lower frequency through digital mixing, thereby improving the accuracy of time-domain signal detection. Combining the above content, the uncertainty of time synchronization of the standard White Rabbit connection device is at the sub-nanosecond level.

[0006] Since the usual pulse sequence detection will introduce an uncertainty of picosecond level, it is very difficult to further improve the time synchronization performance of the standard White Rabbit connection.

[0007] Similar prior arts:

[0008] 1. Standard white rabbit connection, compared with previous network time synchronization connections, achieves sub-nanosecond instability. By digitally mixing and detecting clock signals, the detection accuracy is picosecond level; as described in Document 1: P. Moreira, J. Serrano, T. Wlostowski, et al., “White rabbit: Sub-nanosecond timing distribution over ethernet,” in 2009 International Symposium on Precision Clock Synchronization for Measurement, Control and Communication (2009), 1-5.

[0009] 2. RF modulation enhanced white rabbit connection. Through a technology based on RF modulation, the frequency transfer performance of the white rabbit connection is enhanced.

[0010] As described in Document 2: Z, Lu, Y. Gui, J. Wang, et al, “Fiber-optic time-frequency transfer in gigabit ethernet networks over urban fiber links,” Opt. Express 29(8), 11693-11701(2021), the RF signal is modulated onto the optical carrier modulated with the white rabbit signal and restored to the RF signal and the white rabbit signal at the receiving end. Time-frequency transfer is performed through the restored RF signal and white rabbit signal, mainly enhancing the frequency transfer performance. Summary of the Invention

[0011] The present invention proposes an optical frequency comb time-frequency transfer device based on the white rabbit protocol. Using the time synchronization technology based on the white rabbit protocol, it performs wide-scale detection required in the detection of optical frequency comb pulses. At the same time, it transmits the heterodyne signal required in the detection of optical frequency comb pulses through the communication function of the white rabbit connection, achieving femtosecond-level time synchronization and improving the time synchronization accuracy of the white rabbit connection.

[0012] The optical frequency comb time-frequency transfer device based on the white rabbit protocol specifically includes: a transmission link in which two symmetric dense wavelength division multiplexers are connected by an optical fiber link; the dense wavelength division multiplexer includes a first dense wavelength division multiplexer and a second dense wavelength division multiplexer.

[0013] Among them, the master node includes a time-frequency reference (microwave atomic clock, optical clock, etc.), a first time-frequency transfer module, a phase discriminator, a first controller, a first optical frequency comb, a third optical frequency comb, a first heterodyne detection module, a third heterodyne detection module, and a first dense wavelength division multiplexer.

[0014] The slave node includes: a second time-frequency transfer module, a second controller, a second optical frequency comb, a second heterodyne detection module and a second dense wavelength division multiplexer;

[0015] The first time-frequency transfer module is connected to the time-frequency reference, the first heterodyne detection module and the third heterodyne detection module at the same time; the time-frequency reference and the first optical frequency comb are connected to the phase detector, and the phase detector is connected to the controller; the controller is connected to the first optical frequency comb; the first optical frequency comb and the third optical frequency comb are connected to the first heterodyne detection module, and the third optical frequency comb and the first dense wavelength division multiplexer are connected to the third heterodyne detection module; the first time-frequency transfer module and the third optical frequency comb are connected to the first dense wavelength division multiplexer;

[0016] The first dense wavelength division multiplexer is connected to the optical fiber link, and the other end of the optical fiber link is connected to the second dense wavelength division multiplexer;

[0017] The second dense wavelength division multiplexer and the second heterodyne detection module are connected to the second time-frequency transfer module; the second time-frequency transfer module is connected to the second controller; the second controller is connected to the second optical frequency comb; the second optical frequency comb and the second dense wavelength division multiplexer are connected to the second heterodyne detection module; the second optical frequency comb is connected to the second dense wavelength division multiplexer;

[0018] The advantages of the present invention are:

[0019] 1. An optical frequency comb time-frequency transfer device based on the White Rabbit protocol realizes optical frequency comb pulse detection and synchronization using standard White Rabbit connection, and improves the time synchronization accuracy to the femtosecond level through digital mixing.

[0020] 2. An optical frequency comb time-frequency transfer device based on the White Rabbit protocol improves the accuracy of time synchronization by detecting optical frequency comb pulses. The detection of optical frequency comb pulses requires combining the heterodyne information and link delay of three optical frequency combs, and uses the inherent delay of the White Rabbit connection calibration device to measure the link delay and transfer the heterodyne information, completing the optical frequency comb pulse detection. The second optical frequency comb is controlled by the second controller to achieve time synchronization with the first optical frequency comb.

[0021] 3. An optical frequency comb time-frequency transmission device based on the White Rabbit protocol. Compared with the existing technology of enhancing the White Rabbit connection with RF modulation, the RF signal is modulated onto the signal light modulated with the White Rabbit clock signal through phase amplitude modulation. The modulation depth will affect the stability of the RF signal transmission and the bit error rate of the White Rabbit clock signal. The light transmitted by the optical frequency comb pulse of the present invention is different from the optical carrier wavelength used in the White Rabbit connection, and is transmitted in parallel through dense wavelength division multiplexing technology without interfering with each other.

[0022] 4. An optical frequency comb time-frequency transfer device based on the White Rabbit protocol mainly detects the pulse sequence of the optical frequency comb, enhancing the time synchronization performance compared to detecting the clock signal inside the White Rabbit connection. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of a standard White Rabbit connection device in the prior art.

[0024] Figure 2 It is a schematic diagram of the optical frequency comb time-frequency transfer device based on the White Rabbit protocol of the present invention. Detailed Embodiments

[0025] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0026] The present invention proposes an optical frequency comb time-frequency transfer device based on the White Rabbit protocol. On the basis of the standard White Rabbit connection device, an optical frequency comb is added, and fine synchronization is performed by detecting the ultrashort pulses of the optical frequency comb, so that the time synchronization performance of the enhanced White Rabbit connection device reaches the femtosecond level.

[0027] The described optical frequency comb time-frequency transfer device based on the White Rabbit protocol, as Figure 2 shown, in order to combine time-frequency transfer based on the White Rabbit protocol and time synchronization based on the optical frequency comb, a first dense wavelength division multiplexer 160, an optical fiber link, and a second dense wavelength division multiplexer 161 are used as the transmission link. First, this device uses a time-frequency reference 120 to provide a reference signal and provides a frequency reference signal for the first time-frequency transfer module 110. The first time-frequency transfer module 110 based on the White Rabbit protocol is connected in series with the second time-frequency transfer module 170 through the transmission link to establish a White Rabbit connection.

[0028] The first time-frequency transfer module 110 is simultaneously connected to the time-frequency reference 120, the first heterodyne detection module 150, and the third heterodyne detection module 151; the time-frequency reference 120 and the first optical frequency comb 130 are connected to a phase discriminator 131, and the phase discriminator 131 is connected to a first controller 132; the first controller 132 is connected to the first optical frequency comb 130; the first optical frequency comb 130 and the third optical frequency comb 140 are connected to the first heterodyne detection module 150, and the third optical frequency comb 140 and the first dense wavelength division multiplexer 160 are connected to the third heterodyne detection module 151; the first time-frequency transfer module 110 and the third optical frequency comb 140 are connected to the first dense wavelength division multiplexer 160;

[0029] The first dense wavelength division multiplexer 160 is connected to the optical fiber link, and the other end of the optical fiber link is connected to the second dense wavelength division multiplexer 161;

[0030] The second dense wavelength division multiplexer 161 and the second heterodyne detection module 190 are connected to the second time-frequency transfer module 170; the second time-frequency transfer module 170 is connected to the second controller 181; the second controller 181 is connected to the second optical frequency comb 180; the second optical frequency comb 180 and the second dense wavelength division multiplexer 161 are connected to the second heterodyne detection module 190; the second optical frequency comb 180 is connected to the second dense wavelength division multiplexer 161;

[0031] The process of the optical frequency comb time-frequency transfer device based on the White Rabbit protocol to achieve time synchronization is as follows:

[0032] Step 1: The time-frequency reference provides a frequency reference signal for the first time-frequency transfer module. The first time-frequency transfer module is connected in series with the second time-frequency transfer module through a transmission link to establish a White Rabbit connection, and the rough time difference τ of the device and the transmission delay T of the transmission link are measured. link ;

[0033] Step 2: The output of the first optical frequency comb and the reference frequency signal given by the time-frequency reference pass through a phase discriminator for phase discrimination together, and the output phase difference signal drives the first controller to adjust the first optical frequency comb to complete the locking of the first optical frequency comb to the optical clock, and the repetition frequency is f. r 。

[0034] Step 3: There is a deviation Δf between the repetition frequencies of the third optical frequency comb and the first optical frequency comb. r The output pulse sequences of the two are detected in the first heterodyne detection module. The time information of the peak is extracted from the interference pattern of the cross-correlation of the pulse sequences of the two optical frequency combs. After scaling, the obtained heterodyne signal S1 is sent to the first time-frequency transfer module.

[0035]

[0036] where n is an integer related to the number of peaks of the interference pattern, and τ I 、τ III are the time delays of the pulse sequences of the first and third optical frequency combs respectively.

[0037] Step 4: The output pulse sequence of the third optical frequency comb is transmitted to the slave node through the transmission link and detected in the second heterodyne detection module together with the output pulse sequence of the second optical frequency comb. The peak position is extracted from the interference pattern of the cross-correlation of the pulse sequences of the two optical frequency combs. After scaling, the detection result S2 is sent to the second time-frequency transfer module.

[0038]

[0039] τ II is the time delay of the pulse sequence of the second optical frequency comb.

[0040] The repetition frequency of the second optical frequency comb of the slave node is basically the same as that of the first optical frequency comb.

[0041] Step 5: The pulse sequence of the second optical frequency comb is transmitted to the master node through the transmission link and detected in the third heterodyne detection module with the pulse sequence output by the third optical frequency comb. The peak position of the interference pattern of the cross-correlation of the two optical frequency comb pulse sequences is extracted. After scaling, the detection result S3 is sent to the first time-frequency transfer module.

[0042]

[0043] Step 6: The first time-frequency transfer module uses the communication function of the White Rabbit connection to transfer the detection results S1 and S3 from the first heterodyne detection module and the third heterodyne detection module to the second time-frequency transfer module.

[0044] Step 7: The second time-frequency transfer module combines the received three-party heterodyne detection results S1, S2, and S3 to calculate the time deviation between the output pulse sequences of the second optical frequency comb and the first optical frequency comb.

[0045]

[0046] where Δn is an integer related to the pulse sequence.

[0047] Step 8: Adjust the second optical frequency comb through the second controller according to the phase offset so that the phase of its output pulse sequence is consistent with the phase of the output pulse sequence of the first optical frequency comb, completing high-precision time synchronization.

Claims

1. An optical frequency comb time-frequency transfer device based on the white rabbit protocol, characterized in that Specifically include: A transmission link in which two symmetric dense wavelength division multiplexers are connected by an optical fiber link; the dense wavelength division multiplexer includes a first dense wavelength division multiplexer and a second dense wavelength division multiplexer; Among them, the master node includes a time-frequency reference, a first time-frequency transfer module, a phase discriminator, a first controller, a first optical frequency comb, a third optical frequency comb, a first heterodyne detection module, a third heterodyne detection module and a first dense wavelength division multiplexer; The slave node includes: a second time-frequency transfer module, a second controller, a second optical frequency comb, a second heterodyne detection module and a second dense wavelength division multiplexer; The first time-frequency transfer module is simultaneously connected to the time-frequency reference, the first heterodyne detection module and the third heterodyne detection module; the time-frequency reference and the first optical frequency comb are connected to the phase discriminator, and the phase discriminator is connected to the first controller; the first controller is connected to the first optical frequency comb; the first optical frequency comb and the third optical frequency comb are connected to the first heterodyne detection module, the third optical frequency comb and the first dense wavelength division multiplexer are connected to the third heterodyne detection module; the first time-frequency transfer module and the third optical frequency comb are connected to the first dense wavelength division multiplexer; The first dense wavelength division multiplexer is connected to the optical fiber link, and the other end of the optical fiber link is connected to the second dense wavelength division multiplexer; The second dense wavelength division multiplexer and the second heterodyne detection module are connected to the second time-frequency transfer module; the second time-frequency transfer module is connected to the second controller; the second controller is connected to the second optical frequency comb; the second optical frequency comb and the second dense wavelength division multiplexer are connected to the second heterodyne detection module; the second optical frequency comb is connected to the second dense wavelength division multiplexer; First, the first time-frequency transfer module based on the White Rabbit protocol accesses the reference signal from the time-frequency reference, is connected in series with the second time-frequency transfer module through the transmission link, and establishes a White Rabbit connection; Then, the output of the first optical frequency comb passes through the reference frequency signal given by the time-frequency reference, and after being adjusted by the phase discriminator and the first controller, the locking of the time-frequency reference is completed; The output pulse sequences of the third optical frequency comb and the first optical frequency comb are heterodyned by the first heterodyne detection to obtain a heterodyne signal S1 and sent to the first time-frequency transfer module; The output pulse sequence of the third optical frequency comb is transmitted to the slave node through the transmission link, and is detected by the second heterodyne detection with the output pulse sequence of the second optical frequency comb, and the detection result S2 is sent to the second time-frequency transfer module; The pulse sequence of the second optical frequency comb is transmitted to the master node through the transmission link, and is detected by the third heterodyne detection with the output pulse sequence of the third optical frequency comb, and the detection result S3 is sent to the first time-frequency transfer module; The first time-frequency transfer module uses the communication function of the White Rabbit connection to transfer the detection results S1 and S3 from the first heterodyne detection and the third heterodyne detection to the second time-frequency transfer module; The second time-frequency transfer module calculates the fixed delay of the device and the transmission delay of the transmission link according to the White Rabbit connection, combines the received three-way heterodyne detection results S1, S2, and S3, calculates the phase offset between the output pulse sequences of the second optical frequency comb and the first optical frequency comb, and adjusts the second optical frequency comb through the second controller according to the phase offset to make the phase of its output pulse sequence consistent with the phase of the output pulse sequence of the first optical frequency comb, completing high-precision time synchronization.

2. The optical frequency comb time-frequency transfer device based on the white rabbit protocol according to claim 1, wherein, The process of the optical frequency comb time-frequency transfer device based on the White Rabbit protocol to achieve time synchronization is as follows: Step 1: The time-frequency reference provides a frequency reference signal for the first time-frequency transfer module. The first time-frequency transfer module establishes a White Rabbit connection with the second time-frequency transfer module through a transmission link, and measures the coarse time difference τ of the device and the transmission delay T of the transmission link. link ; Step 2: The output of the first optical frequency comb and the reference frequency signal given by the time-frequency reference pass through the phase discriminator for phase discrimination together, and the output phase difference signal drives the first controller to adjust the first optical frequency comb to complete the locking of the first optical frequency comb to the time-frequency reference. Step 3: There is a deviation Δf between the repetition frequency of the third optical frequency comb and that of the first optical frequency comb. r After being detected by the first heterodyne detection module, the time information of the peak value of the interference pattern of the cross-correlation of the two optical frequency comb pulse sequences is extracted, scaled, and then the heterodyne signal S1 is sent to the first time-frequency transfer module. where n is an integer related to the number of interference pattern peaks, f r is the repetition frequency of the first optical frequency comb, τ I , τ III are the time delays of the pulse trains of the first and third optical frequency combs, respectively; Step 3: The second heterodyne detection module extracts the peak position of the interference pattern of the cross-correlation of the pulse sequences of the third and second optical frequency combs, scales it, and sends the detection result S2 to the second time-frequency transfer module. τ II is the time delay of the second optical frequency comb pulse train; The repetition frequency of the second optical frequency comb of the slave node is basically the same as that of the first optical frequency comb. Step 5: The third heterodyne detection module extracts the peak position of the interference pattern of the cross-correlation of the pulse sequences of the second and third optical frequency combs, scales it, and sends the detection result S3 to the first time-frequency transfer module. Step 6: The first time-frequency transfer module transfers the detection results S1 and S3 to the second time-frequency transfer module. Step 7: The second time-frequency transfer module combines the three-way heterodyne detection results S1, S2, and S3, calculates the time deviation between the output pulse sequences of the second optical frequency comb and the first optical frequency comb, and uses the time deviation to make the phases of the output pulse sequences of the second and first optical frequency combs consistent, completing high-precision time synchronization. The calculation formula for the time deviation ΔT is as follows: where Δn is an integer related to the pulse sequence.

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