Short-distance distributed high-precision fiber optic time synchronization system and method

Abstract

A short-distance distributed high-precision optical fiber time synchronization system and method are disclosed. The system consists of a master time unit, several slave time units, and several optical fiber links. In this method, the time signal of the master time unit is looped back and transmitted between the master and slave time synchronization units using an optical carrier of the same wavelength. The master time synchronization unit uses the loopback method to measure the transmission delay of the optical fiber links and adjusts the delay of the transmitted time signal, so that each slave time synchronization unit receives a time signal synchronized with the master time synchronization unit, thereby realizing the distributed transmission of the time signal.

Description

Technical Field

[0001] This invention relates to distributed time synchronization, and in particular to a short-distance distributed time synchronization system and method. Background Technology

[0002] With the development of 5G communication and navigation positioning, the demand for time and frequency allocation for multiple users in a region is becoming increasingly common. However, traditional point-to-point fiber optic time and frequency transmission methods are no longer adequate for time and frequency allocation in multi-terminal user networks. For example, when there are N terminal stations in the network, the central station needs to be equipped with N sets of measurement and compensation equipment. Since each set of equipment can only transmit time and frequency to one terminal station, the system complexity increases with the number of terminal stations. Therefore, in the research of networked time and frequency allocation, it is particularly important to distribute the high-precision time and frequency signal from the time and frequency center to multiple terminal users in the network. To this end, many scholars at home and abroad have proposed many distributed high-precision fiber optic time synchronization systems.

[0003] For distributed fiber optic time transfer, AGH University of Technology in Poland [see P. Krehlik, L. Sliwczynski, L. Buczek, and M. Lipinski, "Multipoint dissemination of RF frequency in fiberoptic link with stabilized propagation delay," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 60, pp. 1804-1810, 2013.] proposed inserting a 2×2 optical coupler in the main link to couple out a portion of the forward and backward propagated optical signals for distributed time transfer. However, this reduces the power of the optical signals transmitted in the main link and also degrades the stability of the main link time transfer. The prior art invention, entitled "A Distributed Time Transfer Method for Multi-Point Access on a Single Optical Fiber Link" [see Wu Guiling; Zhang Hao; Chen Jianping, "High-Precision Long-Distance Distributed Optical Fiber Time Transfer Method and System," application number: CN201610781482.8, 2016.8], can achieve high-precision long-distance distributed optical fiber time transfer. However, this linear distributed system cannot achieve point-to-multipoint optical fiber time synchronization across multiple optical fiber links. The prior art invention, entitled "A Distributed Optical Fiber Time and Frequency Joint Transfer System and Method" [see Wu Guiling; Zuo Faxing; Hu Liang; Chen Jianping, "Distributed Optical Fiber Time and Frequency Joint Transfer System and Method," application number: CN201910215814.X, 2019.3], suffers from the problem that fiber dispersion affects the accuracy of system time transfer due to wavelength asymmetry in the forward and backward directions. Furthermore, the forward and backward asymmetry introduced by dispersion is inconsistent with different optical fiber link lengths. Therefore, this scheme requires complex link calibration when the optical fiber link changes. In addition, the above-mentioned distributed time synchronization solutions are all designed for long-distance application scenarios, and the system structure is relatively complex. The cost of the components required to build the system is difficult to control, so they are not suitable for short-distance distributed time synchronization scenarios. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-cost, sub-nanosecond-level short-range distributed time synchronization system and method.

[0005] The technical solution of the present invention is as follows:

[0006] A distributed optical fiber time synchronization system, characterized in that it includes a master time synchronization unit, N slave time synchronization units, and N optical fiber links, wherein N is a positive integer greater than or equal to 1.

[0007] The master time synchronization unit generates a time signal and broadcasts it, which reaches each slave time synchronization unit along the optical fiber link.

[0008] Each slave time synchronization unit receives the time signal sent by the master time synchronization unit and directly loops back the received time signal to the same optical fiber link.

[0009] The master time synchronization unit receives the time signal directly looped back from the time synchronization unit and measures the time interval between the time signal looped back from the time synchronization unit and the time signal directly sent by the master time synchronization unit.

[0010] The master time synchronization unit uses the measured time interval information and the local frequency signal as a reference to adjust the delay of the time signal directly sent by the master time synchronization unit to the slave time synchronization unit, so that the slave time synchronization unit obtains a time signal synchronized with the master time synchronization unit.

[0011] The main time synchronization unit includes a main time signal splitter module, a main time delay module, a main time interval measurement module, a main time optical transceiver module, and a main optical splitter module; the main time optical transceiver module includes N time optical transmission modules, the main optical splitter module includes N optical splitters, the main time interval measurement module includes N time interval measurement modules, and the main time delay module includes N time delay modules.

[0012] The time synchronization unit includes a light semi-transparent and semi-reflective module and a time-based light receiving module.

[0013] The N output terminals of the main time signal splitter module are respectively connected to the first input ports of the N time delay modules of the main time delay module. The output port of the Nth time interval measurement module is respectively connected to the second input port of the Nth time delay module. The output port of the Nth time delay module is respectively connected to the first input port of the Nth time interval measurement module and the first input port of the Nth time optical transceiver module. The second input port of the Nth time optical transceiver module is connected to the third port of the Nth optical splitter module. The second output terminal of the Nth time optical transceiver module is connected to the second input terminal of the Nth time interval measurement module. The first output terminal of the Nth time optical transceiver module is connected to the first port of the Nth optical splitter module.

[0014] The output port of the optical semi-transparent and semi-reflective module of the time synchronization module is connected to the input port of the time light receiving module, and the output port of the time light receiving module is the output terminal of the time signal.

[0015] The time synchronization method of the short-distance distributed high-precision optical fiber time synchronization system includes the following steps:

[0016] The main time synchronization unit generates a time signal, which is then split into a first time signal by a main time signal splitter module. Each first time signal is then processed by a main time delay module to obtain a second time signal. The second time signal is split into two paths and input to the main time interval measurement module and the main time optical transceiver module, respectively. The main time optical transceiver module loads each time signal onto a wavelength... The optical time signal is obtained from the main optical splitter module and then input into the optical fiber link, and sent along the optical fiber link to each slave time synchronization unit.

[0017] Each time synchronization unit transmits wavelength through a semi-transparent, semi-reflective optical module. The optical signal returns and is input in reverse into the same optical fiber in the optical fiber link, and is sent to the master time synchronization unit along the optical fiber link;

[0018] The main time synchronization unit uses the main optical splitter to receive the wavelength returned from the time synchronization unit. The optical signal is input to the main time optical transceiver module, where it is converted into a third time signal. This third time signal is then input to the main time interval measurement module, which measures the time interval between the received second and third time signals. ;

[0019] The master time synchronization unit synchronizes the time according to the measured time interval. The first time signal is time-delayed by the main time delay module with reference to the local frequency signal.

[0020] The time signal delayed by the main time delay module becomes the second time signal; the main time optical transceiver module loads the second time signal onto its respective wavelength. The optical time signal is obtained from the main optical splitter module and then input into the optical fiber link, and sent along the optical fiber link to each slave time synchronization unit.

[0021] Each time synchronization unit transmits wavelength through a semi-transparent, semi-reflective optical module. The optical signal is input to the time optical receiving mode, and the synchronized time signal is output to achieve short-distance distributed optical fiber time synchronization.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] A loopback method is used to obtain and compensate for the clock difference in time signal transmission. For low-cost distributed time synchronization over short distances, the impact of backscattering Rayleigh scattering on the signal-to-noise ratio is limited due to the short distance. To reduce complexity, only co-fiber / co-wavelength technology is used to ensure link symmetry. After obtaining the clock difference, an active compensation scheme is employed to achieve time synchronization. This scheme is suitable for point-to-multipoint short-distance distributed time synchronization requirements, with synchronization accuracy in the sub-nanosecond range. Furthermore, low-cost programmable devices are used instead of dedicated time interval counting chips and dedicated delay chips, and semi-transparent / semi-reflective devices are used instead of light sources at the slave end, further reducing costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the short-distance distributed high-precision optical fiber time synchronization system of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the main time synchronization unit in embodiment 1 of the short-distance distributed high-precision optical fiber time synchronization system of the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of the time synchronization unit in embodiment 2 of the short-distance distributed high-precision optical fiber time synchronization system of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. These embodiments provide detailed implementation methods and specific workflows of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0028] In this embodiment, a short-distance distributed high-precision fiber optic time synchronization system (such as...) Figure 1 As shown, the system includes: a master time synchronization unit 1, several slave time synchronization units 2, and several fiber optic links 3. The master time synchronization unit 1 and each slave time synchronization unit 2 are connected via multiple fiber optic links 3. The master time synchronization unit 1 broadcasts the generated time signal, which reaches each slave time synchronization unit 2 along the fiber optic links 3. Each slave time synchronization unit 2 receives the time signal sent by the master time synchronization unit 1 and directly loops back the received time signal to the same fiber optic link 3. The master time synchronization unit 1 receives the time signal looped back directly from the slave time synchronization units 2 and measures the time interval between the time signal looped back by the slave time synchronization units 2 and the time signal directly sent by the master time synchronization unit 1. Using the measured time interval information and referencing its local frequency, the master time synchronization unit 1 adjusts the delay of the time signal directly sent by itself, so that the slave time synchronization units receive a time signal synchronized with the time signal generated by the master time synchronization unit. In this embodiment, the transmitted time signal is a 1PPS signal (timing interval of 1s), and the local frequency signal is a 10MHz frequency signal.

[0029] Master time synchronization unit (e.g.) Figure 2 (As shown) includes a main time signal splitter module 1-1, several main time delay modules 1-2, several main time interval measurement modules 1-3, several main time optical transceiver modules 1-4, and several main optical splitter modules 1-5. The main time signal splitter module 1-1 splits the generated time signal to obtain a first time signal. Each first time signal is then processed by the main time delay module 1-2 to obtain a second time signal. The second time signal is split into two paths and input to the main time interval measurement module 1-3 and the main time optical transceiver module 1-4, respectively. The main time optical transceiver module 1-4 loads the time signal onto a wavelength of 1310nm to obtain an optical time signal, which is then input to the optical fiber link 4 via the main optical splitter module 1-5 and transmitted along the optical fiber link 3 to each slave time synchronization unit 2. Each slave time synchronization unit 2 returns a 1310nm wavelength optical signal via a semi-transparent, semi-reflective optical module 2-1, and inputs it in reverse to the same optical fiber in the optical fiber link 3, sending it along the optical fiber link 3 to the master time synchronization unit 1. The master time synchronization unit 1 receives the 1310nm wavelength optical signal returned from the slave end using the master optical splitter module 1-5, inputs it to the master time optical transceiver module 1-4 to convert it into a third time signal, and then inputs the third time signal to the master time interval measurement module 1-3. The master time interval measurement module 1-3 measures the time interval between the received second time signal and the third time signal. Based on the measured time interval, the master time synchronization unit 1 uses the local frequency signal as a reference to delay the first time signal via the master time delay module 1-2, obtaining the second time signal. The master time optical transceiver module 1-4 loads the second time signal onto each 1310nm wavelength to obtain an optical time signal, and then inputs it to the optical fiber link 3 via the master optical splitter module 1-5, sending it along the optical fiber link 3 to each slave time synchronization unit 2. In this embodiment, the master time optical transceiver module 1-4 adopts an SFP (Small Fiber Optic Processing Unit)... The form-factor pluggable is used to generate and receive optical signals. The main time interval measurement modules 1-3 can use the same frequency phase-divided clock interpolation method to improve the resolution.

[0030] Each time synchronization unit 2 inputs a 1310nm wavelength optical signal to the time optical receiving module 2-2 via the optical semi-transparent and semi-reflective module 2-1, and outputs the synchronized time signal to achieve short-distance distributed optical fiber time synchronization. In this embodiment, the time optical receiving module 2-2 uses an SFP (Small Form-factor Pluggable) for optical signal reception.

[0031] In this embodiment, the time synchronization method of the short-distance distributed optical fiber time synchronization system operates as follows:

[0032] (1) The main time synchronization unit 1 generates a time signal and splits it through the main time signal splitter module 1-1 to obtain a first time signal. Each first time signal is then processed by the main time delay module 1-2 to obtain a second time signal. The second time signal is split into two paths and input to the main time interval measurement module 1-3 and the main time optical transceiver module 1-4, respectively. The main time optical transceiver module 1-4 loads the time signal onto a wavelength of 1310nm to obtain an optical time signal, which is then input to the optical fiber link 3 through the main optical splitter module 1-5 and sent to each slave time synchronization unit 2 along the optical fiber link 3.

[0033] (2) Each time synchronization unit 2 transmits the wavelength through the optical semi-transparent and semi-reflective module 2-1. The optical signal returns and is input in reverse to the same optical fiber in optical fiber link 3, and is sent to the main time synchronization unit 1 along optical fiber link 3;

[0034] (3) The main time synchronization unit 1 receives the 1310nm wavelength optical signal returned from the slave end using the main optical splitter module 1-5, inputs it to the main time optical transceiver module 1-4 to convert it into a third time signal, and then inputs the third time signal to the main time interval measurement module 1-3. The main time interval measurement module 1-3 measures the time interval between the received second time signal and the third time signal. ;

[0035] (4) The main time synchronization unit 1 synchronizes the measured time intervals. The local 10MHz frequency signal is phase-locked to 500MHz using an FPGA phase-locked loop. The first time signal is then time-delayed by the main time delay module (1-2) using the 500MHz frequency signal to obtain the second time signal.

[0036] (5) The main time optical transceiver module 1-4 loads the second time signal onto the wavelength 1310nm to obtain the optical time signal, and then uses the main optical splitter module 1-5 to input it into the optical fiber link 3, and sends it to each slave time synchronization unit 3 along the optical fiber link 4.

[0037] (6) Each time synchronization unit 2 inputs a 1310nm wavelength optical signal to the time optical receiving module 2-2 through the optical semi-transparent and semi-reflective module 2-1, and outputs the time signal synchronized with the master, thereby realizing short-distance distributed optical fiber time synchronization.

Claims

1. A short-distance distributed high-precision fiber optic time synchronization system, characterized in that, It includes a master time synchronization unit (1), N slave time synchronization units (2) and N optical fiber links (3). The master time synchronization unit (1) is connected to the N slave time synchronization units (2) through the N optical fiber links (3), where N is a positive integer greater than or equal to 1. The master time synchronization unit (1) broadcasts the generated time signal, which reaches the N slave time synchronization units (2) along the N optical fiber links (3); each slave time synchronization unit (2) loops back the received time signal and sends it in reverse, so that the time signal returns along the original path along the N optical fiber links (3); The main time synchronization unit (1) receives the time signal looped back from the secondary time synchronization unit (2) and measures the time interval between the time signal looped back from the secondary time synchronization unit (2) and the time signal directly sent by the main time synchronization unit (1). Based on this time interval, with the local frequency as a reference, the time signal directly sent by the main time synchronization unit (1) is delayed and adjusted so that the secondary time synchronization unit (2) receives a time signal synchronized with the time signal generated by the main time synchronization unit (1). The main time synchronization unit (1) includes a main time signal splitter module (1-1), N main time delay modules (1-2), N main time interval measurement modules (1-3), N main time optical transceiver modules (1-4), and N main optical splitter modules (1-5); The N output terminals of the main time signal splitter module (1-1) are respectively connected to the first input terminals of the N main time delay modules (1-2). The output terminal of each main time interval measurement module (1-3) is respectively connected to the second input terminal of each main time delay module (1-2). The output terminal of each main time delay module (1-2) is respectively connected to the first input terminal of each main time optical transceiver module (1-4) and the first input terminal of each main time interval measurement module (1-3). The first output terminal of each main time optical transceiver module (1-4) is connected to port 1 of each main optical splitter module (1-5). The second port of each main optical splitter module (1-5) is the output terminal of the delayed time optical signal. The third port of each main optical splitter module (1-5) is connected to the second input terminal of each main time optical transceiver module (1-4). The second output terminal of each main time optical transceiver module (1-4) is connected to the second input terminal of each main time interval measurement module (1-3). The main time signal splitter module (1-1) divides the generated time signal into N first time signals. Each first time signal is split into two by each main time delay module (1-2). One path is input to each main time interval measurement module (1-3), and the other path is modulated on the light wave generated by each main time optical transceiver module (1-4) to obtain an optical time signal. This signal is then input to each optical fiber link (3) via each optical splitter module (1-5) and sent to each slave time synchronization unit (2) along each optical fiber link (3). The optical signals looped back from each time synchronization unit (2) are sent to each main optical splitter module (1-5) along the same optical fiber link (3), and after being converted by each main time optical transceiver module (1-4), they are input to each main time interval measurement module (1-3). Each main time interval measurement module (1-3) transmits the time interval information between the time signal received at the first input terminal and the time signal received at the second input terminal to the second input terminal of each main time delay module (1-2); Each master time delay module (1-2) delays the first time signal based on the input time interval information and with the local frequency signal as a reference. After delay, a second time signal is obtained and loaded onto the light wave generated by each master time optical transceiver module (1-4). After modulation, an optical time signal is obtained and then input to the optical fiber link 3 through the master optical splitter module 1-5. The signal is then sent to each slave time synchronization unit (2) along the optical fiber link 3.

2. The short-distance distributed high-precision fiber optic time synchronization system according to claim 1, characterized in that, The time synchronization unit (2) includes a semi-transparent and semi-reflective optical module (2-1) and a time-light receiving module (2-2); the output port of the semi-transparent and semi-reflective optical module (2-1) is connected to the input port of the time-light receiving module (2-2), and the output port of the time-light receiving module (2-2) is the output end of the time signal.

3. The short-distance distributed high-precision fiber optic time synchronization system according to claim 2, characterized in that: The optical semi-transparent and semi-reflective module (2-1) can adjust the ratio of reflected light to transmitted light power as needed to optimize the performance of this short-distance distributed high-precision fiber optic time synchronization system.

4. A method for achieving fiber optic time synchronization using the short-distance distributed high-precision fiber optic time synchronization system described in any one of claims 1-3, characterized in that, The method includes the following steps: 1) The main time synchronization unit (1) splits the generated time signal through the main time signal splitter module (1-1) to obtain the first time signal. Each first time signal passes through the main time delay module (1-2) to obtain the second time signal. The second time signal is divided into two paths and input to the main time interval measurement module (1-3) and the main time optical transceiver module (1-4) respectively. The main time optical transceiver module (1-4) loads the time signal onto the wavelength. The optical time signal is obtained and then input to the optical fiber link (3) through the main optical splitter module (1-5), and sent to each slave time synchronization unit (2) along the optical fiber link (3); 2) Each time synchronization unit (2) returns the optical signal of wavelength λ through the optical semi-transparent and semi-reflective module (2-1), inputs it in reverse to the same optical fiber in the optical fiber link (3), and sends it to the master time synchronization unit (1) along the optical fiber link (3); 3) The main time synchronization unit (1) receives the wavelength returned by each slave time synchronization module using the main optical splitter module (1-5). The optical signal is input to the main time optical transceiver module (1-4) to be converted into a third time signal. Then, the third time signal is input to the main time interval measurement module (1-3), which measures the time interval between the received second and third time signals. ; 4) Master time synchronization unit (1) Based on the measured time interval The first time signal is delayed by the main time delay module (1-2) with the local frequency signal as a reference to obtain the second time signal; 5) The main time transceiver module (1-4) loads the second time signal onto the respective wavelength. The optical time signal is obtained and then input to the optical fiber link (3) through the main optical splitter module (1-5), and sent to each slave time synchronization unit (2) along the optical fiber link (3); 6) Each time synchronization unit (2) transmits the wavelength through the optical semi-transparent and semi-reflective module (2-1). The optical signal is input to the time optical receiving module (2-2), and the synchronized time signal is output to realize short-distance distributed optical fiber time synchronization.

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