Airborne optical fiber time-frequency transmission system and method

Abstract

The present invention discloses an airborne optical fiber time-frequency transmission system and method. The system includes: a master node for distributing time-frequency information to slave nodes, and multiple slave nodes for receiving time-frequency information, achieving signal phase stabilization, and time synchronization. The master node includes: a first B-code generation module, a first time interval counter, a digital logic module, a first electro-optical conversion module, and a first photoelectric conversion module; and the slave nodes include: a second photoelectric conversion module, a second electro-optical conversion module, a delay adjustment module, a second time interval counter, a carrier recovery and phase-locking module, and a second B-code generation module. The present invention directly recovers frequency information from the B-code transmitted by the master node, rather than transmitting a reference clock separately. This system achieves both frequency transmission and bidirectional time comparison between the master and slave nodes on the same optical fiber link. This reduces system complexity, volume, and weight.

Description

Technical Field

[0001] The present invention relates to the technical field of time synchronization, and in particular to an airborne optical fiber time and frequency transmission system and method. Background Art

[0002] Radar, communications, navigation, and electronic warfare systems require the transmission of synchronized time information between nodes. Time and frequency transmission, as a crucial component of the time and frequency system, determines the highest precision of time and frequency applications. Fiber-optic clock time and frequency transmission is a major research area for high-precision time and frequency transmission and currently offers one of the highest-precision timing methods. Airborne platforms have strict restrictions on equipment size and weight. Using signal transmission cables between nodes as the medium for transmitting time information would significantly impact the aircraft's internal space, payload, and energy consumption. Optical fiber, due to its small size and light weight, is highly suitable as a transmission medium for aircraft platforms. Furthermore, optical fiber is immune to electromagnetic interference. Therefore, switching from cable-based transmission systems to fiber-optic transmission significantly reduces the cost and weight of avionics systems while also improving their resistance to electromagnetic interference.

[0003] For airborne platforms, optical fiber time and frequency transmission has the following characteristics:

[0004] It is necessary to accurately transmit frequency signals from the master node to the slave node, and perform time comparison and synchronization between the master and the slave nodes; it is necessary to realize time and frequency transmission between a single master node and dozens of slave nodes.

[0005] Traditional time-frequency transmission systems implement all compensation and synchronization functions in the master node, making it bulky and bloated, and not meeting the size requirements of airborne equipment. Furthermore, since all synchronization equipment is centralized in the master node, a failure of the master node will affect the time synchronization of all slave nodes, reducing the reliability of the entire system. Summary of the Invention

[0006] The purpose of the present invention is to provide an airborne optical fiber time-frequency transmission system and method to further improve the reliability of the system.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] An airborne optical fiber time-frequency transmission system, comprising:

[0009] A master node for distributing time-frequency information to slave nodes, and multiple slave nodes for receiving time-frequency information, achieving signal phase stabilization and time synchronization, wherein:

[0010] The master node includes:

[0011] A first B code generating module, configured to generate a B code signal;

[0012] A first time interval counter is used to measure the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node;

[0013] Digital logic module, used to turn on or off the code stream superposition function of the master node;

[0014] a first electro-optical conversion module, configured to modulate the code stream of the B code signal onto an optical carrier, thereby converting the electrical signal into an optical signal;

[0015] a first photoelectric conversion module, configured to convert the optical signal sent from the second electro-optical conversion module of the slave node into an electrical signal, and send the electrical signal to the digital logic module;

[0016] The slave node includes:

[0017] a second photoelectric conversion module, configured to convert the optical signal output by the first electro-optical conversion module into an electrical signal and send the electrical signal to the delay adjustment module;

[0018] A second electro-optical conversion module, configured to convert the B code signal output by the second B code generation module into an optical signal;

[0019] A delay adjustment module, used for delaying the electrical signal output by the second photoelectric conversion module;

[0020] The second time interval counter is used to measure the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node;

[0021] Carrier recovery and phase locking module, used to recover the carrier and lock the slave node crystal oscillator to the carrier;

[0022] The second B code generating module is used to generate a B code signal; wherein the B code signal uses the recovered carrier as a clock reference.

[0023] Furthermore, the airborne optical fiber time-frequency transmission system provides time-frequency information to multiple slave nodes through a master node.

[0024] Furthermore, when the system is running, a time-division multiplexing method is used to perform two-way time comparison and frequency transfer respectively.

[0025] Furthermore, a polling method is used to implement a time comparison function between a single master node and multiple slave nodes.

[0026] An airborne optical fiber time-frequency transmission method, comprising:

[0027] Step 1: In the initial stage, the B code signals generated by the first and second B code generation modules are input into the first and second electro-optical conversion modules, respectively, and converted into optical signals, which are then sent to the first and second optoelectronic conversion modules at the opposite end. After the first and second optoelectronic conversion modules at the opposite end modulate the code stream of the B code signal onto an optical carrier and convert it into an electrical signal, the first and second optoelectronic conversion modules at the opposite end use the second pulse of the local node as the start and the second pulse transmitted by the opposite end as the stop, respectively, and use the first and second time interval counters to measure their time intervals T1 and T2, and calculate the clock difference (T1-T2) / 2 between the two nodes. Based on the clock difference between the two nodes, the slave node adjusts the adjustable delay line in the delay adjustment module to change the delay of the output electrical signal to compensate for the clock difference between the two nodes, thereby achieving the purpose of clock synchronization between the two nodes.

[0028] Step 2: After bidirectional time comparison and synchronization, the master node uses the first time interval counter to measure the time interval between the local second pulse and the second pulse from the slave node, inputs the time interval into the first electro-optical conversion module, and then sends it to the slave node. At this time, the code stream superposition function is disabled by the digital logic module, that is, the B code stream generated by the master node through the first B code generation module and the code stream generated by the slave node through the second B code generation module after conversion by the second photoelectric conversion module are not performed bit by bit. The B code stream generated by the first B code generation module and the B code stream generated by the second B code generation module are denoted as code 1 and code 2, respectively.

[0029] Step 3: After receiving the time interval through the second photoelectric conversion module, the slave node sends the code to the master node through the second electro-optical conversion module. After the code is converted into an electrical signal by the first photoelectric conversion module at the master node, it is input into the digital logic module.

[0030] Step 4: Adjust the master node's digital logic module and enable the master node's code stream superposition function. This involves performing a logical OR operation on code 1 and code 2. The new code stream output by the digital logic module is then input into the first electro-optical conversion module, converted into an optical signal, and sent to the slave node. The optical signal is then input into the second photoelectric conversion module, converted into an electrical signal, and then input into the delay adjustment module. The delay adjustment module has both pulse width testing and delay adjustment functions. The slave node obtains information about link delay changes based on changes in code stream pulse width.

[0031] Step 5: After measuring the link delay variation, adjust the electrically adjustable delay line in the delay adjustment module to compensate for the link delay variation;

[0032] Step 6: Input the delay-compensated electrical signal into the carrier recovery and phase-locking module, demodulate the carrier of the electrical signal in the carrier recovery and phase-locking module, and use the demodulated carrier signal as a reference to build a phase-locked loop to phase-lock the slave node crystal oscillator to the carrier, thereby realizing the frequency transmission from the master node to the slave node.

[0033] Furthermore, the delay adjustment module is adjusted so that when code 1 and code 2 are superimposed by opening the code stream superposition function at the master node digital logic module, the rising edges of the first flag bits of code 1 and code 2 can be close to each other, and the time interval between their falling edges can also be controlled within 10ns.

[0034] Furthermore, the pulse width test function of the delay adjustment module can be implemented by TDC measurement or charge pump phase detection circuit.

[0035] Furthermore, if the pulse width is measured through TDC, the rising edge of the first flag bit Pr is used as the opening signal of TDC, and the falling edge of Pr is used as the closing signal of TDC, a time interval value can be measured. The time interval value is obtained by taking the average value of multiple measurements, and the difference between the current time interval value and the initial time interval value is compared to obtain the link delay change that needs to be compensated.

[0036] Furthermore, if a charge pump phase-locked circuit is used, its output voltage is proportional to the pulse width and is continuously variable. This method can obtain a continuously adjustable control voltage, and when this control voltage acts on an analog electrically variable delay line, a fine compensation effect without stepping can be obtained.

[0037] Compared with the prior art, the present invention has the following technical features:

[0038] The present invention utilizes delay measurement and compensation technology based on B-code pulse width variation, time division multiplexing, polling, and other technologies to achieve time and frequency transmission between a single master node and multiple slave nodes, and is suitable for airborne environments. The present invention can achieve the following effects:

[0039] 1. The slave node realizes the master-slave time pairing and synchronization function, reducing the weight and volume of the master node.

[0040] 2. Since the time-frequency transmission function is decentralized to each slave station, the master-slave transmission links do not affect each other. When a link fails, it is usually only necessary to replace the transmission function module of the slave node on the link, so the reliability and maintainability of the entire system are improved.

[0041] 3. Frequency information is directly recovered from the B code transmitted by the master node, rather than transmitting a separate reference clock. This enables both frequency transmission and bidirectional time comparison between the master and slave nodes over the same fiber link, reducing system complexity, size, and weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the basic principle of the airborne optical fiber time-frequency transmission system;

[0043] Figure 2 It is a flowchart of the master-slave time synchronization execution link;

[0044] Figure 3 This is a schematic diagram of the principle of measuring link delay changes based on pulse width changes;

[0045] Figure 4 This is a schematic diagram of the principle of master-slave link delay compensation technology.

[0046] Explanation of the numbers in the figure: 1 first B code generation module, 2 first time interval counter, 3 digital logic module, 4 first electro-optical conversion module, 5 first photoelectric conversion module, 6 second photoelectric conversion module, 7 second electro-optical conversion module, 8 delay adjustment module, 9 second time interval counter, 10 carrier recovery and phase-locked module, 11 second B code generation module. DETAILED DESCRIPTION

[0047] This invention proposes a novel airborne optical fiber time-frequency transmission system and method. This system offloads the comparison and synchronization functions between the master node and each slave node to the slave nodes, significantly reducing the size of the master node. Furthermore, since the transmission functions are distributed among the slave nodes, the master-slave transmission links are independent of each other. Furthermore, if a link fails, typically only the transmission module of the slave node on that link needs to be replaced, thereby improving the reliability and maintainability of the entire system.

[0048] Referring to the accompanying drawings, the technical solutions of the present invention are as follows:

[0049] An airborne optical fiber time-frequency transmission system comprises: a master node for distributing time-frequency information to slave nodes, and a plurality of slave nodes for receiving time-frequency information and achieving signal phase stabilization and time synchronization, wherein:

[0050] The master node includes:

[0051] The first B code generating module 1 is used to generate an IRIG-B code signal (hereinafter referred to as the B code signal);

[0052] The first time interval counter 2 is used to measure the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node;

[0053] Digital logic module 3, used to turn on or off the code stream superposition function of the master node;

[0054] A first electro-optical conversion module 4 is configured to modulate the code stream of the B code signal onto an optical carrier, thereby converting the electrical signal into an optical signal;

[0055] The first photoelectric conversion module 5 is used to convert the optical signal sent from the second electro-optical conversion module of the slave node into an electrical signal and send it to the digital logic module;

[0056] The slave node includes:

[0057] A second photoelectric conversion module 6 is used to convert the optical signal output by the first electro-optical conversion module into an electrical signal and send it to the delay adjustment module;

[0058] A second electro-optical conversion module 7, configured to convert the B code signal output by the second B code generation module into an optical signal;

[0059] The delay adjustment module 8 is used to delay the electrical signal output by the second photoelectric conversion module 7;

[0060] The second time interval counter 9 is used to measure the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node;

[0061] The carrier recovery and phase locking module 10 is used to recover the carrier and lock the slave node crystal oscillator to the carrier;

[0062] The second B code generating module 11 is configured to generate a B code signal; wherein the B code signal uses the recovered carrier as a clock reference.

[0063] Furthermore, the airborne optical fiber time-frequency transmission system provides time-frequency information to multiple slave nodes through a master node.

[0064] Furthermore, in order to obtain a smoother control process, this system tends to use analog electrically adjustable delay lines to compensate for link delays. Because its control quantity is continuous, it avoids the step-like control process caused by the delay step (about 10ps) of the digitally controlled electrically adjustable delay line.

[0065] The airborne optical fiber time-frequency transfer method applicable to the aforementioned airborne optical fiber time-frequency transfer system comprises the following steps:

[0066] Step 1: In the initial stage after power-on, the B code signals generated by the first and second B code generation modules 1 and 11 are input into the first and second electro-optical conversion modules 4 and 7 respectively, converted into optical signals, and sent to the first and second optoelectronic conversion modules 5 and 6 of the opposite end (i.e., the master node sends it to the slave node, and the slave node sends it to the master node); after the first and second optoelectronic conversion modules 5 and 6 of the opposite end modulate the code stream of the B code signal on the optical carrier and convert it into an electrical signal, they use the second pulse of the local node as the start and the second pulse transmitted by the opposite end as the stop, use the first and second time interval counters 2 and 9 to measure their time intervals T1 and T2, and calculate the clock difference (T1-T2) / 2 between the two nodes; at the slave node, based on the clock difference between the two nodes, by adjusting the adjustable delay line in the delay adjustment module 8, change the delay of the output electrical signal (time pulse signal) to compensate for the clock difference between the two nodes, so as to achieve the purpose of clock synchronization between the two nodes.

[0067] Step 2: After two-way time comparison and synchronization, the master node uses the first time interval counter 2 to measure the time interval between the local second pulse and the second pulse from the slave node, inputs it into the first electro-optical conversion module 4 and sends it to the slave node. At this time, the code stream superposition function is turned off through the digital logic module 3, that is, the B code stream (referred to as code 1) generated by the master node through the first B code generation module 1 and the code stream (referred to as code 2) generated by the slave node through the second B code generation module 11 are not converted by the second photoelectric conversion module and then the logical OR operation is performed bit by bit, that is, the overlapping operation of the two columns of code streams is not performed.

[0068] Step 3: After receiving the time interval through the second photoelectric conversion module 6, the slave node sends the code 2 to the master node through the second electro-optical conversion module 7. After the code 2 is converted into an electrical signal through the first photoelectric conversion module 5 at the master node, it is input into the digital logic module 3.

[0069] Step 4, adjust the digital logic module 3 of the master node, turn on the code stream superposition function of the master node, that is, perform a logical OR operation on code 1 and code 2, and input the new code stream (electrical signal) output by the digital logic module 3 into the first electro-optical conversion module 4 to convert it into an optical signal, and send it to the slave node; the optical signal is input into the second photoelectric conversion module 6 to convert it into an electrical signal and then input into the delay adjustment module 8. The delay adjustment module 8 has a pulse width test function and a delay adjustment function. The pulse width test function can be implemented by TDC measurement or a charge pump phase detection circuit; the slave node obtains information on the delay change of the master-slave node link based on the change in the code stream pulse width.

[0070] If the pulse width is measured by TDC, the rising edge of the first flag bit Pr can be used as the opening signal of TDC, and the falling edge of Pr can be used as the closing signal of TDC. A time interval value can be measured. In order to reduce the influence of signal edge jitter on the measurement results, the method of taking the average value of multiple measurements is usually adopted to obtain the time interval value. By comparing the difference between the current time interval value and the initial time interval value, the link delay change that needs to be compensated can be obtained; if a charge pump phase detection circuit is used, its output voltage is proportional to the pulse width, and the output voltage is continuously variable. Although this method cannot obtain a specific pulse width value, it can obtain a continuously adjustable control voltage. When the control voltage acts on an analog electrical variable delay line, a fine compensation effect without stepping can be obtained. The principle of measuring link delay changes based on pulse width changes is as follows Figure 3 shown.

[0071] The delay adjustment module 8 is adjusted so that when code 1 and code 2 are superimposed by opening the code stream superposition function at the master node digital logic module 3, the rising edges of the first flag bits of code 1 and code 2 can be close to each other, and the time interval between their falling edges can also be controlled within 10ns. This is conducive to the pulse width measurement of the new code stream after the two columns of code streams are superimposed. The change in the pulse width can naturally reflect the change in the one-way delay of the link from the node to the master node.

[0072] Step 5: After measuring the link delay variation, the electrically adjustable delay line in the delay adjustment module 8 is adjusted to compensate for the link delay variation.

[0073] In step 6, the delay-compensated electrical signal is input into the carrier recovery and phase-locking module 10. The carrier recovery and phase-locking module 10 demodulates the electrical signal's carrier wave. Using the demodulated carrier wave as a reference, a phase-locked loop (PLL) is constructed to phase-lock the slave node's crystal oscillator to the carrier wave, thereby achieving frequency transfer from the master node to the slave node. This PLL achieves a loose phase lock, meaning the locking process is relatively slow. This allows for appropriate shielding of the delay adjustment transition process, thereby preventing the delay compensation process from affecting the short-term stability of the crystal oscillator signal.

[0074] Furthermore, when the system is running, considering the possible conflict between time comparison and frequency transfer, a time-division multiplexing method is used to perform two-way time comparison and frequency transfer respectively.

[0075] Furthermore, considering the resource usage problem when performing time comparison between the master node and many slave nodes, a polling method is used to implement the time comparison function between a single master node and multiple slave nodes. In this way, only one time interval measurement unit is used, which greatly saves hardware resources and makes the device smaller.

[0076] Example:

[0077] The present invention can be applied to an airborne environment, where a master node transmits time-frequency information to multiple sub-nodes.

[0078] Since all slave nodes have the same structure, only one slave node is described below. The method is also applicable to other slave nodes, such as Figure 1 As shown, the system includes: a master node for distributing time-frequency information to slave nodes, and multiple slave nodes for receiving time-frequency information and achieving signal phase stabilization and time synchronization.

[0079] The master node includes: B code generation module 1, time interval counter 2, digital logic module 3, electro-optical conversion module 4, photoelectric conversion module 5. The slave node includes: photoelectric conversion module 6, electro-optical conversion module 7, delay adjustment module 8, time interval counter 9, carrier recovery and phase locking module 10, and B code generation module 11.

[0080] An airborne optical fiber time-frequency transmission method of an airborne optical fiber time-frequency transmission system of the present invention comprises the following steps:

[0081] Step 1: In the initial stage after power-on, the B code signal generated by the B code generation module 1 / 11 of the master / slave node is input into the electro-optical conversion module 4, 7 to be converted into an optical signal and sent to the other end. After the opto-electrical conversion module 5, 6 of the other end converts the optical signal into an electrical signal, the two nodes use the second pulse of the local node as the start and the second pulse transmitted by the other end as the stop, and use the time interval counter 2, 9 to measure the time intervals T1 and T2, and calculate the clock difference (T1-T2) / 2 of the two nodes. Then the slave node compensates for the clock difference of the two nodes by adjusting the delay adjustment module 8 to achieve the purpose of clock synchronization of the two nodes. The synchronization execution link is as follows: Figure 2 For clock errors within 10ns, an electrically adjustable delay line is used to generate the required delay for clock error compensation. For clock errors greater than 10ns, a delay equal to an integer multiple of the carrier period (100MHz, 10ns) is generated by directly intervening in the time code encoding process. Any remaining clock error is compensated by the electrical delay adjustment module.

[0082] Step 2: After two-way time comparison and synchronization, the master node uses the time interval counter 2 to measure the time interval between the local second pulse and the second pulse from the slave node, and then inputs the time interval value into the electro-optical conversion module 4 to convert it into an optical signal, and then sends it to the slave node. At this time, the code stream sent by the master node (referred to as code 1) and the code stream sent and returned by the slave node (referred to as code 2) are not logically ORed bit by bit, that is, the overlapping operation of the two columns of code streams is not performed.

[0083] Step 3: After the slave node receives the time interval value and inputs it into the optoelectronic conversion module 6 to convert it into an electrical signal, it changes the delay of the code 2 output by adjusting the delay adjustment module 8. Then, the code 2 is input into the electro-optical conversion module 7 to convert it into an optical signal and then sent to the master node. The optical signal is converted into an electrical signal through the optoelectronic conversion module 5 of the master node and then input into the digital logic module 3.

[0084] Step 4: Regulate the master node's digital logic module 3, enabling the master node's code stream superposition function (i.e., performing a logical OR operation). The electrical signal output by digital logic module 3 is then fed into electro-optical conversion module 4, converted into an optical signal, and sent to the slave node. The optical signal is then fed into photoelectric conversion module 6, converted into an electrical signal, and then fed into delay adjustment module 8. Delay adjustment module 8 has both pulse width measurement and delay adjustment functions. The pulse width measurement function can be implemented using a TDC or charge pump phase detector circuit.

[0085] By adjusting the delay adjustment module 8, when the two code streams are superimposed at the master node, the rising edge of the first flag bit Pr can be close, and the time interval between the falling edges of the two can be controlled within 10ns. This is conducive to the measurement of the Pr pulse width of the new code stream after the two code streams are superimposed. The change in the pulse width can naturally reflect the change in the one-way delay of the link from the node to the master node.

[0086] Step 5: After measuring the link one-way delay variation, the link delay variation can be compensated using the adjustable delay line in the delay adjustment module 8. To obtain a smoother control process, this solution tends to use an analog electrically adjustable delay line. Because its control quantity is continuous, it avoids the step-like control process caused by the delay step (about 10ps) of the digitally controlled electrically adjustable delay line. To ensure that the delay variation can be accurately measured, it is necessary to add an electrical delay line of the same type to the slave node, place it above the backward path, and subject it to the same control voltage as the electrical delay line of the forward path, such as Figure 3 As shown. Then, when the delay compensation values ​​of the forward and backward paths are very close, the delay compensation effect of the forward path can be accurately reflected in the Pr pulse width, and subsequent measurements can be accurate. The principle of delay compensation technology is as follows: Figure 4 shown.

[0087] In step 6, the signal after delay compensation is input into the carrier recovery and phase-locking module 10. Using the carrier signal demodulated from the slave node as a reference, a phase-locked loop is constructed to phase-lock the slave node crystal oscillator to it, thereby achieving frequency transmission. This phase-locked loop achieves loose phase lock, that is, the locking process is relatively slow, and the transition process of delay adjustment can be properly shielded, thereby avoiding the impact of the delay compensation process on the short-term stability of the crystal oscillator signal. The frequency signal output by the carrier recovery and phase-locking module 10 can be used as the reference clock of the B code generation module 11, which is used to generate a B code signal synchronized with the master node at the slave node.

[0088] When executing the phase stabilization function, Code 1 and Code 2 overlap, making it impossible for the master node to send time interval information to the slave node. Therefore, time comparison and delay compensation must be performed in a time-sharing manner. The slave node checks whether the device address in the code stream matches its own address. If the addresses match, the received code stream is used for two-way time comparison; otherwise, it is used for frequency transfer. Because time comparison is performed infrequently, typically every tens of minutes and typically takes less than a second, the link delay changes very little (sub-picoseconds) within such a short period of time, exceeding the error range of delay compensation. Therefore, this time-sharing method of executing time comparison does not significantly affect the frequency transfer function.

[0089] Furthermore, since the master node needs to perform bidirectional time comparisons with dozens of slave nodes, to save space, it can alternately measure the time interval between its local pulse-second signal and that of a particular slave node. This allows the use of a single time interval measurement unit, significantly saving hardware resources and making the device smaller. To implement this round-robin time comparison method, a unique device address must be defined for each node. Since the number of nodes typically does not exceed 100, a single-byte address length is sufficient. The master node maintains a list of slave node addresses. When a new slave node is added to the system, it sends its device address to the master node. The master node then extracts the address from the bitstream, stores it in the address list, and associates it with the bitstream receiving port. During the comparison process, the master node receives the bitstream signal from a slave node, generates a demodulated second, and measures the time interval between the demodulated second and the current second. When the master node generates the B code, it appends this time interval data to the time information field and then appends the device address of the slave node. This code stream signal is sent to all slave nodes. When a slave node with a mismatched address receives the B code, it does not extract the comparison data generated by the master node from the code stream. However, when a slave node with a matching address receives the B code, it extracts the comparison data generated by the master node from the code stream to calculate the clock difference between the slave node and the master node, which is used for clock synchronization. During the process of sending the comparison data from the slave node to the master node, since the communication link between the master node and the slave node is one-to-one, the master node can distinguish which slave node the code stream originated from. Therefore, after a stable communication link is established, the slave node does not need to add the device address when encoding.

[0090] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. An airborne optical fiber time-frequency transmission system, characterized in that: include: A master node for distributing time-frequency information to slave nodes, and multiple slave nodes for receiving time-frequency information, achieving signal phase stabilization and time synchronization, wherein: The master node includes: A first B code generating module (1) is used to generate a B code signal; A first time interval counter (2) is used to measure the time interval between the local second pulse of the master node and the second pulse transmitted from the slave node; A digital logic module (3) is used to turn on or off the code stream superposition function of the master node; A first electro-optical conversion module (4) is used for modulating the code stream of the B code signal on an optical carrier, thereby converting the electrical signal into an optical signal; A first photoelectric conversion module (5) is used to convert the optical signal sent from the second electro-optical conversion module of the slave node into an electrical signal and send the electrical signal to the digital logic module; The slave node includes: A second photoelectric conversion module (6) is used to convert the optical signal output by the first electro-optical conversion module (4) into an electrical signal and send the electrical signal to the delay adjustment module (8); A second electro-optical conversion module (7) is used to convert the B code signal output by the second B code generation module into an optical signal; A delay adjustment module (8) is used to time delay the electrical signal output by the second photoelectric conversion module (6); A second time interval counter (9) is used to measure the time interval between the local second pulse of the slave node and the second pulse transmitted from the master node; A carrier recovery and phase locking module (10) is used to recover the carrier and lock the slave node crystal oscillator to the carrier; The second B code generating module (11) is used to generate a B code signal; wherein the B code signal uses the recovered carrier as a clock reference.

2. The airborne optical fiber time-frequency transmission system according to claim 1, characterized in that: The airborne optical fiber time-frequency transmission system provides time-frequency information to multiple slave nodes through a master node.

3. The airborne optical fiber time-frequency transmission system according to claim 1, characterized in that: When the system is running, time-division multiplexing is used to perform two-way time comparison and frequency transfer.

4. The airborne optical fiber time-frequency transmission system according to claim 1, characterized in that: The polling method is used to realize the time comparison function between a single master node and multiple slave nodes.

5. An airborne optical fiber time-frequency transmission method, characterized in that: include: Step 1: In the initial stage, the B code signals generated by the first B code generation module (1) and the second B code generation module (11) are respectively input into the first electro-optical conversion module (4) and the second electro-optical conversion module (7) to be converted into optical signals, and then sent to the first photoelectric conversion module (5) and the second photoelectric conversion module (6) at the opposite end; after the first photoelectric conversion module (5) and the second photoelectric conversion module (6) at the opposite end modulate the code stream of the B code signal on the optical carrier and convert it into an electrical signal, the first time interval counter (2) and the second time interval counter (9) are used to measure the time intervals T1 and T2 respectively, with the second pulse of the local node as the start and the second pulse transmitted by the opposite end as the stop, and the clock difference (T1-T2) / 2 between the two nodes is calculated; at the slave node, according to the clock difference between the two nodes, the adjustable delay line in the delay adjustment module (8) is adjusted to change the delay of the output electrical signal to compensate for the clock difference between the two nodes, so as to achieve the purpose of clock synchronization between the two nodes; Step 2: After bidirectional time comparison and synchronization, the master node uses the first time interval counter (2) to measure the time interval between the local second pulse and the second pulse from the slave node, inputs the time interval into the first electro-optical conversion module (4) and sends it to the slave node. At this time, the code stream superposition function is turned off through the digital logic module (3), that is, the B code stream generated by the master node through the first B code generation module (1) and the code stream generated by the slave node through the second B code generation module (11) are not converted by the second photoelectric conversion module and the logic OR operation is not performed bit by bit; the B code stream generated by the first B code generation module (1) and the B code stream generated by the second B code generation module (11) are recorded as code 1 and code 2 respectively. Step 3, after receiving the time interval through the second photoelectric conversion module (6), the slave node sends the code 2 to the master node through the second electro-optical conversion module (7), and the code 2 is converted into an electrical signal by the first photoelectric conversion module (5) at the master node and then input into the digital logic module (3); Step 4: Adjust the master node digital logic module (3) and enable the code stream superposition function of the master node, that is, perform a logical OR operation on code 1 and code 2, and input the new code stream output by the digital logic module (3) into the first electro-optical conversion module (4) to convert it into an optical signal, which is then sent to the slave node; the optical signal is input into the second photoelectric conversion module (6) to convert it into an electrical signal and then input into the delay adjustment module (8), which has a pulse width test function and a delay adjustment function; the slave node obtains information on link delay changes based on the code stream pulse width change; Step 5, after measuring the link delay variation, adjusting the electrically adjustable delay line in the delay adjustment module (8) to compensate for the link delay variation; Step 6: Input the delay-compensated electrical signal into the carrier recovery and phase-locking module (10), demodulate the carrier of the electrical signal in the carrier recovery and phase-locking module (10), and use the demodulated carrier signal as a reference to construct a phase-locked loop to phase-lock the slave node crystal oscillator to the carrier, thereby realizing the frequency transmission from the master node to the slave node.

6. The airborne optical fiber time-frequency transfer method according to claim 5, characterized in that: The delay adjustment module (8) is adjusted so that when code 1 and code 2 are superimposed by opening the code stream superposition function at the master node digital logic module (3), the rising edges of the first flag bits of code 1 and code 2 can be close to each other, and the time interval between their falling edges can also be controlled within 10ns.

7. The airborne optical fiber time-frequency transfer method according to claim 5, characterized in that: The pulse width test function of the delay adjustment module (8) can be realized by TDC measurement or charge pump phase detection circuit.

8. The airborne optical fiber time-frequency transfer method according to claim 5, characterized in that: If the pulse width is measured through TDC, the rising edge of the first flag bit Pr is used as the TDC opening signal, and the falling edge of Pr is used as the TDC closing signal. A time interval value can be measured. The time interval value is obtained by taking the average value of multiple measurements. The difference between the current time interval value and the initial time interval value is compared to obtain the link delay change that needs to be compensated.

9. The airborne optical fiber time-frequency transfer method according to claim 5, characterized in that: If a charge pump phase detector circuit is used, its output voltage is proportional to the pulse width and the output voltage is continuously variable. This method can obtain a continuously adjustable control voltage. When this control voltage acts on an analog electrical variable delay line, a fine compensation effect without stepping can be obtained.

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