Relay node download method and device based on optical frequency comb

Abstract

The present invention discloses a relay node download method and device based on an optical frequency comb. The present invention is used to address the problem of difficulty for nodes in obtaining frequency information transmitted in a link in a time-frequency information transmission system. The present invention is characterized in that an optical comb signal transmitted and a return optical comb signal in the optical comb-based time-frequency transmission system link are obtained through an optical coupling module. The transmitted optical comb signal is converted into an electrical signal through a photoelectric detection module, and then two electrical signals are obtained through a power distribution module. The center frequencies of the electrical bandpass filters connected to the two electrical signals are then adjusted to obtain low-order harmonic components and high-order harmonic components with a frequency doubled. The return optical comb signal is mirrored, and the two low-order harmonic components are connected to a phase detection module to obtain relative delay information. Based on this delay information, the high-order harmonic components are directly phase-shifted through a phase shift module to restore the original signal. Compared with the prior art, the present invention fully utilizes the characteristic of optical comb signals containing multiple frequency components, avoids the use of complex electrical components such as frequency dividers and multipliers, reduces costs, significantly reduces electrical noise at the download node, and improves the stability of node frequency extraction.

Description

Technical Field

[0001] The present invention relates to the field of time frequency transmission and measurement in information science, and in particular to a multi-point downloading method based on optical frequency comb. Background Art

[0002] Time, as a fundamental unit of measurement and one of the seven fundamental physical quantities, is deeply embedded in every aspect of life. The precision and accuracy of time measurement are increasingly valued. With the advancement of existing technologies, the accuracy of atomic optical clocks has continued to improve, reaching levels of 1E-18. However, existing telemetry transmission technologies are currently unable to meet the rapidly growing demand for high-precision optical clock remote comparisons. Accurately transmitting the time and frequency information of atomic clocks has become a crucial research topic. Optical fiber, currently the most effective medium for light wave propagation, offers advantages such as long transmission distances, high speeds, low loss, and strong anti-interference capabilities. Fiber-based time and frequency transmission has become the preferred solution for future ground-based clock comparison networks.

[0003] There are three main high-precision, long-distance fiber-optic time-frequency transfer technologies: radio frequency modulation, direct optical frequency transmission, and optical frequency comb transmission. Optical frequency combs are frequency- and phase-stable mode-locked lasers. Compared to other methods, optical frequency combs, due to their ability to produce a large number of equally spaced coherent spectral lines, can simply and accurately link optical frequencies to cesium atomic microwave frequency standards. They have broad applications and promising prospects in optical precision measurement.

[0004] Most current time-frequency transmission systems are based on point-to-point transmission. If more than two nodes attempt to use the transmitted frequency information, the point-to-point structure will not function properly. To obtain transmitted frequency information at any node in a fiber optic link, numerous schemes and structures have been proposed. However, most rely on radio frequency modulation and direct optical transmission, and their structures are generally complex and exhibit poor frequency extraction stability. Optical frequency combs present significant gaps in this area. By leveraging the multiple frequency components and high signal-to-noise ratio of optical frequency combs, it is theoretically possible to optimize the node structure for extracting frequency information, reduce costs, and improve frequency extraction stability. Summary of the Invention

[0005] To fill this gap in optical frequency combs and fully utilize the characteristics of optical frequency combs, the present invention provides a multi-point download method based on optical frequency combs. This method can be used in most complete time-frequency transmission systems based on optical frequency combs. It uses a fiber coupling module at any node on the transmission link to extract the optical comb signal traveling back and forth on the link. A photoelectric detection module and a bandpass filter corresponding to the center frequency are used to obtain the N-fold frequency signal and the 2N-fold frequency signal of the traveling optical comb signal. A phase detection module is used to obtain the phase difference between the N-fold frequency signals of the traveling optical comb signal. This phase difference is twice the link phase delay that needs to be compensated for the N-fold frequency signal at the node. Based on the characteristics of the optical frequency comb, the aforementioned phase difference is equal to the link phase delay that needs to be compensated for the 2N-fold frequency signal at the node. This phase information is used to control the phase shift module to compensate for the 2N-fold frequency signal at the node.

[0006] The technical solution of the present invention is:

[0007] A multi-point download method based on optical frequency comb, comprising the following steps:

[0008] 1) Select a node in a complete optical frequency comb-based time-frequency transfer system and use a fiber coupling module to obtain the transmitted optical comb signal 1 and the returned optical comb signal 2 at the node without affecting the normal transmission of the link signal.

[0009] 2) using a photoelectric detection module to convert the optical comb signal 1 and the optical comb signal 2 into the electrical signal 1 and the electrical signal 2;

[0010] 3) dividing electrical signal 1 into electrical signal 3 and electrical signal 4 through a power distribution module, wherein electrical signal 3 passes through a bandpass filter module having a center frequency of N times the repetition rate of the optical comb, and electrical signal 4 passes through a bandpass filter module having a center frequency of 2N times the repetition rate of the optical comb. Electrical signal 3 is converted into a sinusoidal signal with a frequency of N times the repetition rate, and electrical signal 4 is converted into a sinusoidal signal with a frequency of 2N times the repetition rate;

[0011] 4) Electrical signal 2 is the same as above, wherein the sinusoidal signal with a frequency of N times the repetition rate is electrical signal 5, and the sinusoidal signal with a frequency of 2N times the repetition rate is electrical signal 6;

[0012] 5) Pass the electrical signal 3 and the electrical signal 5 into the phase detection module to obtain the difference in phase information carried by the two signals

[0013] 6) Use the phase shift module to change the phase information of electrical signal 4 and electrical signal 6, and the phase of electrical signal 4 is shifted Phase shift of electrical signal 6 That is, the signal compensation is completed and the original signal of the time-frequency transmission system is restored.

[0014] Furthermore, a complete time-frequency transfer system based on an optical frequency comb includes a source end, a transmission link, and a remote end, and has a compensation structure that can pre-compensate for the phase delay generated by the entire link, so that the signal transmitted in the link has already compensated for the phase delay of the entire link.

[0015] Furthermore, the repetition rate of the optical comb is determined by the optical frequency comb itself used in the time-frequency transfer system.

[0016] Furthermore, the power distribution module can be replaced by adding an optical fiber coupling module in front of the photoelectric detection module, that is, the optical fiber coupling module is used to divide the optical comb signal 1 into optical comb signal 3 and optical comb signal 4, and the optical comb signal 2 is divided into optical comb signal 5 and optical comb signal 6, and then converted into electrical signal 3, electrical signal 4, electrical signal 5, and electrical signal 6 through the photoelectric detection module, and the subsequent steps are the same as above.

[0017] Furthermore, the value of N should be determined based on whether the center frequency of the bandpass filter and the power of the N-fold repetition frequency component meet the experimental requirements.

[0018] Further, Theoretically, it is twice the phase delay of the N-fold repetition frequency component in the optical comb signal after the optical comb signal is transmitted from the node to the remote end of the system.

[0019] Further, Theoretically, it is equal to the phase delay of the 2N-fold repetition frequency component in the optical comb signal after it is transmitted from the node to the far end of the system.

[0020] The fiber coupling module is used to split the optical comb signals transmitted back and forth in the optical fiber link into two paths: one path continues to participate in the overall system signal transmission, and the other participates in the multi-point download method. The splitting ratio is determined by the actual situation and needs to be split while minimizing the impact on the overall system's time-frequency information transmission.

[0021] The bandpass filter module is used to extract a sinusoidal signal corresponding to the center frequency from electrical signals 3 and 4. This sinusoidal signal is generated based on the characteristics of an optical frequency comb, with its frequency being an integer multiple of the comb's repetition rate. This characteristic allows sine waves of different frequencies to be generated by adjusting the center frequency of the bandpass filter module, eliminating the need for additional components such as frequency multipliers and dividers to adjust the frequency multiples of the obtained signal.

[0022] The phase shift module is used to perform phase shift on the electrical signal 4 and the electrical signal 6. It can perform forward phase shift or reverse phase shift on the reference signal according to the input phase information.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) By performing photoelectric detection, filtering, and phase detection on the extracted round-trip optical comb signal, the phase delay that needs to be compensated for the node-end signal can be obtained, thus avoiding the need to modify the structure of the time-frequency transmission system and the use of complex devices at the node end.

[0025] (2) Using an optical frequency comb as the light source for a time-frequency transmission system using multi-point downloading technology, and taking advantage of the fact that the optical frequency comb can generate a large number of equally spaced coherent spectral lines, the center frequency of the bandpass filter module after photoelectric detection can be adjusted to obtain sine waves with different multiple repetition frequencies, thus avoiding the use of electrical devices such as frequency multipliers and frequency dividers, significantly reducing the electrical noise of the downloading node, and thus improving the stability of the node frequency extraction;

[0026] (3) The phase shift module is used to phase shift the signal obtained at the node end. By adjusting the center frequency of the bandpass filter module to change the frequency of the reference signal connected to the phase shift module, the phase information obtained in (1) can be directly used for phase shifting without the need for additional operations. Therefore, the present invention fully utilizes the characteristics of the optical frequency comb, optimizes the existing multi-point download structure, reduces the error introduced by the electrical components, reduces the cost, and improves the accuracy of recovering the original signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a system structure diagram of the multi-point download method based on optical frequency comb in the present invention.

[0028] Figure 2 This is a system structure diagram of the multi-point download method based on optical frequency comb after adding a fiber coupling module in the present invention.

[0029] Figure 3 Schematic diagram of the structure of an embodiment of the multi-point download method based on optical frequency comb in the present invention. DETAILED DESCRIPTION

[0030] In order to make the above features and advantages of the present invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings.

[0031] See attached Figure 1 The present invention includes an optical comb signal 1, an optical comb signal 2, an optical fiber coupling module, two photoelectric detection modules, two power distribution modules, four bandpass filtering modules, a phase detection module, and a phase shift module.

[0032] The optical comb signal 1 is the optical comb signal sent by the source end, and the optical comb signal 2 is the optical comb signal transmitted back from the remote end. It is required that the time-frequency transmission system has already delayed the phase of the entire link. Pre-compensation is performed. Optical comb signal 1 and optical comb signal 2 enter the fiber coupling module and are divided into optical comb signals 3, 4 and optical comb signals 5, 6 respectively. Optical comb signal 3 and optical comb signal 5 re-enter the link to participate in time-frequency transmission. Optical comb signal 4 and optical comb signal 6 pass into the photoelectric detection module to obtain electrical signal 1 and electrical signal 2. Electrical signal 1 is divided into electrical signal 3 and electrical signal 4 after passing through the power distribution module. Electrical signal 2 is divided into electrical signal 5 and electrical signal 6 after passing through the power distribution module. Electrical signal 3 and electrical signal 5 pass through the bandpass filtering module with a center frequency of N times the optical comb repetition frequency and become sinusoidal signals with a frequency of N times the repetition frequency. The phase information is respectively and Afterwards, electrical signal 3 and electrical signal 5 enter the phase detection module to obtain the phase difference between the two The electrical signals 4 and 6 pass through a bandpass filter module with a center frequency of 2N times the repetition rate of the optical comb, and are converted into sinusoidal signals with a frequency of 2N times the repetition rate. The phase information is and The phase information obtained by the phase detection module is used to control the phase shift module to perform positive and negative phase shifts on the electrical signals 4 and 6, thereby compensating for the phase delay at the node and restoring the original signal.

[0033] The above power distribution modules can be replaced by more fiber coupling modules, see the attached Figure 2 The above-mentioned optical comb signal 4 and optical comb signal 6 are first divided into optical comb signals 7, 8 and optical comb signals 9, 10 through a fiber coupling module, and then converted into electrical signals 3, 4, 5, and 6 through a photoelectric detection module. The subsequent steps are the same as the above scheme.

[0034] The present invention will be further described below by taking an optical frequency comb with a repetition frequency of 100 MHz and a bandpass filter module with a value of N being 1 as an example.

[0035] Example:

[0036] See attached Figure 3 , the method comprises the following steps:

[0037] 1) The transmitted optical comb signals 1 and 2 are passed into the fiber coupling module and are divided into optical comb signals 3 and 4 and optical comb signals 5 and 6. Optical comb signals 3 and 5 then re-enter the link to participate in time-frequency transmission.

[0038] 2) Optical comb signal 4 and optical comb signal 6 are converted into electrical signal 1 and electrical signal 2 through a photoelectric detection module;

[0039] 3) Electrical signal 1 and electrical signal 2 are respectively divided into electrical signal 3, electrical signal 4, electrical signal 5, and electrical signal 6 through the power distribution module;

[0040] 4) After the electrical signals 3 and 5 pass through the bandpass filter module with a center frequency of 100 MHz, ignoring the amplitude effect of the sinusoidal signal, they are recorded as:

[0041]

[0042]

[0043] Where ω1 = 100 MHz. The overall phase delay of the transmission link is The phase delay of the link from the node to the source is The phase delay from the node to the remote link is So Because the system has a phase delay on the entire link Pre-compensation is performed, then

[0044] 5) Then pass the above electrical signal 3 and electrical signal 5 into the phase detection module to obtain the phase difference between the two

[0045] 6) After the electrical signals 4 and 6 pass through the bandpass filter module with a center frequency of 200 MHz, ignoring the amplitude effect of the sinusoidal signal, they are recorded as:

[0046]

[0047]

[0048] Where ω2 = 200 MHz.

[0049] 7) The phase difference obtained by the above phase detection module Phase shift is performed on electrical signal 4 and electrical signal 6, and the phase of electrical signal 4 is Electrical signal 6 phases Therefore, the phase-shifted signal F4′(t)=F6′(t)=sin(ω2t), the phase delay in the signal has been compensated, and the original signal has been restored.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The scope of protection of the present invention shall be based on the claims.

Claims

1. A multi-point download method based on optical frequency comb, comprising the following steps: 1) using an optical coupling module at a node end of a complete frequency transmission system to obtain a first optical frequency comb signal and a second optical frequency comb signal traveling back and forth in a link; 2) converting the first optical frequency comb signal and the second optical frequency comb signal into a first electrical signal and a second electrical signal respectively through a photoelectric detection module, and then using a power distribution module to divide the first electrical signal into a third electrical signal and a fourth electrical signal, and the second electrical signal into a fifth electrical signal and a sixth electrical signal; 3) connecting the third electrical signal, the fourth electrical signal, the fifth electrical signal, and the sixth electrical signal to a bandpass filter to convert them into a seventh electrical signal, an eighth electrical signal, a ninth electrical signal, and a tenth electrical signal; 4) Connecting the seventh electrical signal and the ninth electrical signal to a phase detection module to obtain a phase difference between the two; 5) Using the phase difference to control the phase shift module to phase shift the eighth electrical signal and the tenth electrical signal respectively, to compensate for the phase drift introduced by the optical fiber transmission.

2. The method according to claim 1, characterized in that The complete frequency transmission system refers to a system with a source end, a remote end, a transmission link, and a structure capable of compensating for drift of the entire transmission link; the light source at the source end of the system is an optical comb light source with a certain fundamental frequency, and the addition of a node end in the transmission link will not affect the frequency information transmission of the entire system.

3. The method according to claim 1, characterized in that The first electrical signal, the second electrical signal, the third electrical signal, the fourth electrical signal, the fifth electrical signal, and the sixth electrical signal contain a large number of frequency components, and the frequency of each frequency component is a positive integer multiple of the fundamental frequency of the optical comb.

4. The method according to claim 1, wherein The center frequency of the bandpass filter connected before the seventh and ninth electrical signals is N times the optical comb fundamental frequency, where N is a positive integer. The center frequency of the bandpass filter connected before the eighth and tenth electrical signals is 2N times the optical comb fundamental frequency.

5. The method according to claim 1, characterized in that The seventh electrical signal, the eighth electrical signal, the ninth electrical signal, and the tenth electrical signal contain only one frequency component, wherein the frequencies of the seventh electrical signal and the ninth electrical signal are N times the optical comb fundamental frequency, where N is a positive integer, and the frequencies of the eighth electrical signal and the tenth electrical signal are 2N times the optical comb fundamental frequency.

6. The method according to claim 1 or 2, characterized in that The phase difference obtained by the phase detection module is twice the phase delay of the N-fold frequency component in the optical comb signal after it is transmitted from the node end to the remote end, where N is a positive integer and is equal to the phase delay of the 2N-fold frequency component.

7. The method according to claim 1, 2 or 6, characterized in that: The phase shift module uses the eighth electrical signal and the tenth electrical signal as reference signals. The value of the phase delay to be compensated is equal to the phase difference value obtained after the seventh electrical signal and the ninth electrical signal are connected to the phase detection module. The phase shift module whose reference signal is the eighth electrical signal needs to perform positive phase shift on the signal, and the phase shift module whose reference signal is the tenth electrical signal needs to perform negative phase shift on the signal.

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