A femtosecond laser time synchronization system and method

Abstract

This application discloses a femtosecond laser time synchronization system and method, solving the problem of insufficient precision in free-space time transmission. The femtosecond laser time synchronization system includes: a transmitting device that transmits a first pulse carrying time information from a calibrated first atomic clock; and a receiving device that receives the first pulse and compares it with a second pulse carrying time information from an uncalibrated second atomic clock, calibrating the second atomic clock using the clock difference information between the two. This application can rapidly construct a long-distance free-space laser time-frequency synchronization link, maintain link stability over a long period through precise servo control of the laser beam direction, and achieve precise time-frequency synchronization in long-distance free space using femtosecond laser asynchronous optical sampling technology.

Description

Technical Field

[0001] This application relates to the field of femtosecond laser time synchronization technology, and in particular to a femtosecond laser time synchronization system and method. Background Technology

[0002] Fiber-optic laser time-frequency synchronization technology is widely used due to its advantages such as large communication capacity, long relay distance, small size, and light weight. However, in wide-area applications such as space-to-ground and inter-satellite communication, as well as in complex applications such as air and sea where fiber optic cables cannot be laid, more flexible free-space time transfer technology is used to achieve remote synchronization of time and frequency references. Since atmospheric turbulence in free space affects the laser beam direction, causing signal flicker at the receiver, research is needed to develop a free-space femtosecond laser ultra-precise time synchronization system. This system aims to rapidly construct a laser transmission link with precisely controllable and long-term laser beam direction, thereby eliminating the impact of atmospheric turbulence on signal stability. Simultaneously, femtosecond-level clock difference measurement can be achieved using femtosecond laser asynchronous optical sampling technology. Therefore, this is of great significance for the stable transmission and precise comparison of free-space laser time-frequency signals. Summary of the Invention

[0003] This application provides a femtosecond laser time synchronization system and method, which solves the problem of insufficient precision in free space time transfer.

[0004] This application provides a femtosecond laser time synchronization system, including a transmitting device. The transmitting device includes a first atomic clock, a first femtosecond laser, a propagating femtosecond laser, and a first determining module. The repetition frequency of the first femtosecond laser is f1 + Δf. The repetition frequency of the propagating femtosecond laser is f1. The pulses of the two femtosecond lasers scan each other in the time domain, simultaneously locking to the first atomic clock, and establishing a bidirectional transmission link. The pulses of the two femtosecond lasers form a laser interference signal. The first determining module is used to determine the first pulse based on the laser interference signal and by calibrating the first atomic clock.

[0005] This application also provides a femtosecond laser time synchronization system, including a receiving device. The receiving device includes a second atomic clock, a second femtosecond laser, and a second determining module. The repetition frequency of the second femtosecond laser is f1 + Δf, and it is locked to the second atomic clock to determine a second pulse. The second pulse is a femtosecond laser pulse carrying uncalibrated time-frequency information from the second atomic clock. The second determining module is used to determine a first pulse and compare it with the second pulse, adjusting the time of the second atomic clock based on the clock difference information between the two. The first pulse is a femtosecond laser pulse carrying accurate time-frequency information.

[0006] This application also provides a femtosecond laser time synchronization system, comprising one of the aforementioned transmitting devices and at least one of the aforementioned receiving devices. The transmitting device sends a first pulse, which is compared with a second pulse from one of the receiving devices. A second atomic clock is calibrated, and a third pulse carrying the calibrated time-frequency information of the second atomic clock is generated and sent to other receiving devices.

[0007] Furthermore, it also includes a signal transmitting module for connecting the transmitting device and the receiving device, or two receiving devices interconnected, to transmit pulse signals. The signal transmitting module includes a first beam expander telescope, a beam splitter, a pressure-controlled reflector, a PID controller, and a four-quadrant detector. The first pulse is split by the beam splitter; one part enters the first beam expander telescope through the pressure-controlled reflector, and the other part enters the four-quadrant detector. The four-quadrant detector is used to convert the pulse into a two-dimensional directional photocurrent, obtaining the two-dimensional coordinates of the pulse. The PID controller is used to receive the two-dimensional coordinates of the pulse and fine-tune the position of the pressure-controlled reflector.

[0008] More preferably, the signal transmitting module further includes a calibration module and a turntable. The calibration module includes a beacon laser and a control module. The beacon laser is used to emit beacon light into the first beam expander telescope. The control module is used to receive the beacon light fed back from the first beam expander telescope and control the rotation of the turntable. The rotation of the turntable drives the first pulse and the beacon laser to rotate.

[0009] Furthermore, the first determining module is also configured to determine a second pulse. The first determining module determines the clock difference between the first atomic clock and the second atomic clock by comparing the first pulse and the second pulse. The second pulse is a femtosecond laser pulse carrying time-frequency information from an uncalibrated atomic clock. The second determining module is also configured to transmit the second pulse towards the source of the first pulse.

[0010] Furthermore, it also includes a receiving feedback module. The receiving feedback module is disposed between the first beam-expanding telescope and the receiving device. The receiving feedback module includes a second beam-expanding telescope and a fiber optic reflector. The second beam-expanding telescope is used to receive the beacon laser and transmit it to the fiber optic reflector, and also to receive the first pulse and transmit it to the receiving device. The fiber optic reflector is used to reflect the beacon laser back along its original path.

[0011] This application also provides a femtosecond laser time synchronization method, using the femtosecond laser time synchronization system described in any of the above embodiments, comprising the following steps:

[0012] By setting the first femtosecond laser and the propagating femtosecond laser to have a small repetition rate difference, the pulses of the two femtosecond lasers can be mutually scanned in the time domain.

[0013] The first femtosecond laser and the propagating femtosecond laser are simultaneously locked to the first atomic clock through a phase-locked loop. The clock difference of the first atomic clock is set to zero, and the time deviation caused by factors other than the atomic clock is obtained.

[0014] Two femtosecond lasers form a bidirectional transmission link, enabling their pulses to form a laser interference signal;

[0015] The time deviation data obtained from the laser interferometric signal was used to calibrate the first atomic clock;

[0016] The femtosecond laser generates the first pulse carrying the time information of the calibrated first atomic clock.

[0017] A second femtosecond laser with the same repetition frequency as the first femtosecond laser locks onto the second atomic clock and outputs a second pulse carrying the time information of the second atomic clock.

[0018] The clock difference between the first and second atomic clocks is obtained by comparing the first pulse and the second pulse, and the second atomic clock is calibrated.

[0019] Furthermore, it also includes the step of calibrating other signal receiving modules with a third pulse carrying the calibrated time information of the second atomic clock.

[0020] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in any of the above embodiments.

[0021] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects:

[0022] This application enables the rapid construction of a long-distance free-space laser time-frequency synchronization link. The link is maintained in a long-term stable manner through precise servo control of the laser beam pointing, and precise time-frequency synchronization in long-distance free space is achieved by utilizing femtosecond laser asynchronous optical sampling technology. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0024] Figure 1 This is a structural diagram of a femtosecond laser time synchronization system transmitter according to this application;

[0025] Figure 2 This is a schematic diagram of the signal generation module structure in an embodiment of this application;

[0026] Figure 3 This is a structural diagram of the signal transmission module according to an embodiment of this application;

[0027] Figure 4 This is a structural diagram of a receiving device for a femtosecond laser time synchronization system according to this application;

[0028] Figure 5 This is a schematic diagram of the signal receiving module according to an embodiment of this application;

[0029] Figure 6 This is a structural diagram of a femtosecond laser time synchronization system according to an embodiment of this application;

[0030] Figure 7 This is a flowchart of a femtosecond laser time synchronization method according to an embodiment of this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0033] Figure 1 This is a structural diagram of a femtosecond laser time synchronization system transmitter according to this application.

[0034] This application provides a femtosecond laser time synchronization system, including a transmitting device 1.

[0035] The transmitting device includes a first atomic clock 11, a first femtosecond laser 12, a propagating femtosecond laser 13, and a first determining module 14.

[0036] The repetition frequency of the first femtosecond laser is f1 + Δf. The repetition frequency of the propagating femtosecond laser is f1, and the pulses of the two lasers scan each other in the time domain.

[0037] The pulses from the two femtosecond lasers scan each other in the time domain, while simultaneously locking onto the first atomic clock, and establishing a bidirectional transmission link.

[0038] The pulses from two femtosecond lasers form a laser interference signal.

[0039] The first determining module is used to determine the first pulse based on the laser interference signal and the calibration of the first atomic clock.

[0040] The first pulse is a femtosecond laser pulse carrying the time and frequency information of the first atomic clock after calibration.

[0041] For example, a laser interference signal is collected and the first atomic clock is calibrated to generate the first pulse.

[0042] Furthermore, the first determining module is also used to determine the second pulse. The first determining module determines the clock difference between the first atomic clock and the second atomic clock by comparing the first pulse and the second pulse.

[0043] For example, the first determining module receives the second pulse and calculates the clock difference between the first atomic clock and the second atomic clock by comparing the first pulse and the second pulse. The second pulse is a femtosecond laser pulse carrying the time and frequency information of an uncalibrated atomic clock.

[0044] Figure 2 This is a schematic diagram of the signal generation module structure in an embodiment of this application.

[0045] For example, the first atomic clock, the first femtosecond laser, the propagating femtosecond laser, and the first determining module together constitute the signal generation module.

[0046] like Figure 2 As shown, the signal generation module includes two femtosecond lasers. The repetition frequency of the first femtosecond laser is f1 + Δf, and the repetition frequency of the propagating femtosecond laser is f1. The two femtosecond lasers have a small repetition frequency difference Δf, so their pulses can scan each other in the time domain, i.e., femtosecond laser asynchronous optical sampling, thereby achieving femtosecond-level time deviation measurement. The two femtosecond lasers are simultaneously locked to a first atomic clock via a phase-locked loop, thus setting the clock difference of the first atomic clock to zero for simultaneous clock testing, thereby obtaining the time deviation caused by factors other than the atomic clock in the system. The two femtosecond lasers form a bidirectional transmission link through a short optical fiber. The propagating femtosecond laser pulses and the pulses of the first femtosecond laser form a laser interference signal, which is acquired by a balanced photodetector. This signal is then collected using a high-speed acquisition card in the data acquisition system, and finally, the time deviation data is extracted and the atomic clock is calibrated. After the first atomic clock is calibrated, a portion of the pulses from the propagating femtosecond laser carrying the information from the first atomic clock enters the transmitting module via an optical fiber, while the other portion is used as the local oscillator light and undergoes femtosecond laser asynchronous optical sampling with the second pulse subsequently transmitted to the signal generation module. The clock difference between the first and second atomic clocks is obtained through the aforementioned data acquisition and time deviation calculation methods.

[0047] Figure 3 This is a structural diagram of the signal transmission module in an embodiment of this application.

[0048] Furthermore, it also includes a signal transmission module 3.

[0049] The signal transmission module includes a first beam expander telescope 31, a beam splitter 32, a pressure-controlled reflector 33, a PID controller 34, and a four-quadrant detector 35.

[0050] Preferably, in this application, both the light rays entering and exiting the beam expander telescope need to be collimated by a collimator.

[0051] The first pulse is split by a beam splitter; one portion passes through a pressure-controlled mirror and enters the first beam expander telescope, while the other portion enters a four-quadrant detector. The four-quadrant detector converts the pulse into a two-dimensional directional photocurrent, obtaining the pulse's two-dimensional coordinates. The PID controller receives the pulse's two-dimensional coordinates and fine-tunes the position of the pressure-controlled mirror.

[0052] For example, the first pulse, after passing through a reflector, a pressure-controlled reflector, and a thin-film beam splitter, is also transmitted to the signal receiving module via the first beam expander telescope. Simultaneously, the second pulse emitted by the signal receiving module reaches the transmitting module. After reaching the transmitting module, part of the second pulse passes through the thin-film beam splitter, the pressure-controlled reflector, the reflector, and the collimator before reaching the beam expander telescope, while the other part enters the four-quadrant detector. The four-quadrant detector converts the beam energy into a two-dimensional directional photocurrent. Through current-to-voltage conversion in the signal processing unit, the two-dimensional coordinate information of the beam on the detection surface of the four-quadrant detector is obtained. In practical applications, the obtained coordinates are compared with pre-set coordinates. Negative feedback servo control is used to drive the pressure-controlled reflector to adjust in real time, ensuring efficient coupling and detection of the free-space beam.

[0053] Furthermore, the signal transmitting module also includes a calibration module 36 and a turntable 37. The calibration module includes a beacon laser 361 and a control module 362.

[0054] The beacon laser is used to emit beacon light into the first beam expander telescope.

[0055] The control module is used to receive the beacon light fed back from the first beam expander telescope and control the rotation of the turntable.

[0056] The rotation of the turntable drives the first pulse and beacon laser to rotate.

[0057] For example, the signal transmission module includes two parts: beacon light and signal light. The main function of the beacon light is to quickly establish a spatial transmission link between the transmitting and receiving devices. First, the beacon light emitted by the beacon laser is collimated by a collimator and then reflected by two thin-film beam splitters to the beam expander telescope, subsequently reaching the receiving feedback module of the laser terminal in the receiving device. By adjusting the two-axis turntable of the transmitting and receiving devices, the beacon light is directed into the beam expander telescope of the receiving reflection module. The beacon light then travels through an optical fiber coupler to a fiber optic reflector. Under the action of the fiber optic reflector, the beacon light returns along its original path to the signal transmission module emitted by the femtosecond laser. The reflected beacon light is reflected by the thin-film beam splitter and then converged by a lens in front of the CCD, entering the CCD. The CCD and data acquisition card are used to extract the pixel position of the CCD image where the centroid of the reflected beacon light spot is located, and this position is fed back to the two-axis turntable controller. The two-axis turntable maintains precise alignment between the transmitting module and the receiving feedback module.

[0058] Figure 4 This is a structural diagram of a receiving device for a femtosecond laser time synchronization system according to this application.

[0059] A femtosecond laser time synchronization system includes a receiving device 2.

[0060] The receiving device includes a second atomic clock 21, a second femtosecond laser 22, and a second determination module 23.

[0061] The repetition frequency of the second femtosecond laser is f1+Δf, and it is locked to the second atomic clock to determine the second pulse.

[0062] The second pulse is a femtosecond laser pulse carrying the time and frequency information of an uncalibrated second atomic clock.

[0063] The second determining module is used to determine the first pulse and compare it with the second pulse, and adjust the time of the second atomic clock by using the clock difference information between the two.

[0064] The first pulse is a femtosecond laser pulse carrying accurate time and frequency information.

[0065] It should be noted that, in the embodiments of this application, the time and frequency information carried by the calibrated first atomic clock transmitted by the transmitting device is considered to be accurate time and frequency information.

[0066] Furthermore, the second determining module is also used to transmit the second pulse toward the source of the first pulse.

[0067] Figure 5 This is a schematic diagram of the signal receiving module in an embodiment of this application.

[0068] For example, the signal receiving module includes a femtosecond laser, denoted as the second femtosecond laser, whose repetition frequency is the same as that of the first femtosecond laser, f1 + Δf. The second femtosecond laser is locked to a second atomic clock, and its output femtosecond pulses contain the time-frequency information of the second atomic clock, i.e., the second pulse. The first pulse enters the signal receiving module through an optical fiber coupler, and is sampled asynchronously with the second pulse using femtosecond laser technology to obtain the clock difference data between the first and second atomic clocks. The transmitting and receiving devices exchange atomic clock difference information via laser communication to achieve atomic clock calibration synchronization between the systems.

[0069] Furthermore, it also includes a receiving feedback module 24. The receiving feedback module is disposed between the first beam expander telescope and the signal receiving module. The receiving feedback module includes a second beam expander telescope 241 and a fiber optic reflector 242. The second beam expander telescope is used to receive the beacon laser and transmit it to the fiber optic reflector, and also to receive the first pulse and transmit it to the signal receiving module. The fiber optic reflector is used to reflect the beacon laser back along its original path.

[0070] Furthermore, it also includes a signal transmission module. The signal transmission module includes a first beam expander telescope, a beam splitter, a pressure-controlled reflector, a PID controller, and a four-quadrant detector.

[0071] The first pulse is split by a beam splitter, with one part entering the first beam expander telescope through a pressure-controlled mirror and the other part entering the four-quadrant detector.

[0072] The four-quadrant detector is used to convert pulses into two-dimensional directional photocurrents to obtain the two-dimensional coordinates of the pulses.

[0073] The PID controller is used to receive the two-dimensional coordinates of the pulse and fine-tune the position of the pressure-controlled reflector.

[0074] It should be noted that the signal transmitting module connected to the signal receiving module has the same structure as the signal transmitting module connected to the signal generating module.

[0075] The signal transmitting module is used to connect the transmitting device and the receiving device, or two receiving devices interconnected, to transmit pulse signals. The pulse signals include the first pulse, second pulse, and third pulse mentioned above. The structure of the signal transmitting module connected to the transmitting device is basically the same as that of the signal transmitting module of the receiving device. After the third pulse transmitted by the signal receiving module enters the corresponding signal transmitting module through an optical fiber coupler, it transmits the calibrated second atomic clock information and compares it with other receiving devices for calibration, thereby constructing an atomic clock network.

[0076] Furthermore, the signal transmitting module also includes a calibration module. The calibration module includes a beacon laser, a control module, and a turntable.

[0077] The beacon laser is used to emit beacon light into the first beam expander telescope.

[0078] The control module is used to receive the beacon light fed back from the first beam expander telescope and control the rotation of the turntable.

[0079] The rotation of the turntable drives the first pulse and beacon laser to rotate.

[0080] Figure 6 This is a structural diagram of a femtosecond laser time synchronization system according to an embodiment of this application.

[0081] This application also provides a femtosecond laser time synchronization system, which includes the transmitting device 1 described in any of the above embodiments and the receiving device 2 described in any of the above embodiments.

[0082] This application also provides a femtosecond laser time synchronization system, comprising one of the above-described transmitting devices and at least one of the above-described receiving devices.

[0083] The transmitting device sends a first pulse, which is compared with a second pulse from a receiving device. The second atomic clock is then calibrated to generate a third pulse carrying the calibrated time and frequency information of the second atomic clock, which is then sent to other receiving devices.

[0084] Alternatively, the transmitting device can send a first pulse that passes sequentially through multiple receiving devices to calibrate the second atomic clocks among them.

[0085] This application mainly includes a precision two-axis turntable, a CCD camera, a high-speed data acquisition card, a femtosecond laser, a high-speed photodetector, etc., with the aim of providing a highly mobile free-space ultra-precise time and frequency synchronization device that can quickly construct free-space links and realize femtosecond-level time deviation measurement.

[0086] After the signal transmitting module of the transmitting device transmits the first pulse to the signal receiving feedback module, the beacon light direction is adjusted by the two-axis turntable, that is, the laser terminal is coarsely aligned, and the free-space laser link is initially constructed.

[0087] After establishing the link, the atomic clock in the signal generation module locks with the femtosecond laser through a phase-locked loop, loads the atomic clock's time and frequency information onto a femtosecond pulse to generate signal light, and then enters the signal transmission module via optical fiber. The first pulse, after passing through a beam expander telescope and transmitted via a free-space link, reaches the receiving feedback module of the receiving device. There, the clock difference between the atomic clocks of the transmitting and receiving devices is measured using a femtosecond laser asynchronous optical sampling method. Simultaneously, a portion of the femtosecond laser pulse carrying the time information of the second atomic clock, i.e., the second pulse, is transmitted to the transmitting device via the same free-space link, and its clock difference is compared with that of the first atomic clock using the same method. The bidirectional transmission link between the transmitting and receiving devices aims to eliminate one-way time delay variations caused by environmental changes. The clock difference data between the transmitting and receiving devices is exchanged via laser communication, ultimately synchronizing the atomic clocks of both systems. After atomic clock calibration, another portion of the femtosecond pulse carrying the calibrated second atomic clock information, i.e., the third pulse, enters the signal transmission module of the receiving device for clock difference comparison with other receiving devices.

[0088] Figure 7 This is a flowchart of a femtosecond laser time synchronization method according to an embodiment of this application.

[0089] This application also provides a femtosecond laser time synchronization method, using the femtosecond laser time synchronization system described in any of the above embodiments, comprising the following steps:

[0090] Step 101: Set the first femtosecond laser and the propagating femtosecond laser to have a small repetition rate difference, so that the pulses of the two femtosecond lasers can scan each other in the time domain;

[0091] Step 102: Lock the first femtosecond laser and the propagating femtosecond laser to the first atomic clock simultaneously through a phase-locked loop, set the clock difference of the first atomic clock to zero, and obtain the time deviation caused by factors other than the atomic clock.

[0092] Step 103: Two femtosecond lasers establish a bidirectional transmission link, enabling their pulses to form a laser interference signal;

[0093] Step 104: Obtain laser interference signal extraction time deviation data to calibrate the first atomic clock;

[0094] Step 105: The femtosecond laser generates the first pulse carrying the time information of the calibrated first atomic clock;

[0095] Step 106: The second femtosecond laser, which has the same repetition frequency as the first femtosecond laser, locks onto the second atomic clock and outputs a second pulse carrying the time information of the second atomic clock;

[0096] Step 107: Compare the first pulse and the second pulse to obtain the clock difference between the first atomic clock and the second atomic clock, and calibrate the second atomic clock.

[0097] Furthermore, it may also include the following steps:

[0098] Step 108: Use the third pulse carrying the calibrated second atomic clock time information to calibrate other signal receiving modules.

[0099] This application also provides a computer-readable storage medium storing a computer program thereon, characterized in that the program, when executed by a processor, implements the above-described method.

[0100] This application also provides a communication device, including a memory, a processor, and a computer program stored in the memory and executable by the processor, characterized in that the processor implements the above-described method when executing the computer program.

[0101] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0102] Therefore, this application also proposes a computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the methods described in any embodiment of this application.

[0103] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0104] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0105] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0106] Furthermore, this application also proposes a communication device (or computing device) including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method described in any embodiment of this application.

[0107] In a typical configuration, a computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory. Memory may include non-persistent storage in computer-readable media, random access memory (RAM), and / or non-volatile memory such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media. Computer-readable media includes both permanent and non-persistent, removable and non-removable media that can store information by any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transfer medium that can be used to store information that can be accessed by the computing device. As defined in this article, computer-readable media do not include transient media, such as modulated data signals and carrier waves.

[0108] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0109] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A femtosecond laser time synchronization system, characterized in that, Includes a transmitting device and a receiving device; The transmitting device includes a first atomic clock, a first femtosecond laser, a propagating femtosecond laser, and a first determining module; The repetition frequency of the first femtosecond laser is f1 + Δf, where Δf is the difference in repetition rates between the two femtosecond lasers; The repetition frequency of the propagating femtosecond laser is f1; The pulses from the two femtosecond lasers scan each other in the time domain, are locked to the first atomic clock, and establish a bidirectional transmission link; The pulses from two femtosecond lasers form a laser interference signal; The first determining module is used to determine the first pulse based on the laser interference signal and by calibrating the first atomic clock; The receiving device includes a second atomic clock, a second femtosecond laser, and a second determination module; The repetition frequency of the second femtosecond laser is f1+Δf, and it is locked to the second atomic clock to determine the second pulse; The second pulse is a femtosecond laser pulse carrying uncalibrated second atomic clock time and frequency information; The second determining module is used to determine the first pulse and compare it with the second pulse, and adjust the time of the second atomic clock based on the clock difference information between the two. The first pulse is a femtosecond laser pulse carrying accurate time and frequency information; The transmitting device sends a first pulse, which is compared with a second pulse from a receiving device. The second atomic clock is then calibrated to generate a third pulse carrying the calibrated time and frequency information of the second atomic clock, which is then sent to other receiving devices.

2. The femtosecond laser time synchronization system according to claim 1, characterized in that, It also includes a signal transmitting module for connecting the transmitting device and the receiving device or connecting two receiving devices to each other to transmit pulse signals; The signal transmission module includes a first beam expander, a beam splitter, a pressure-controlled mirror, a PID controller, and a four-quadrant detector; The first pulse is split by a beam splitter, with one part entering the first beam expander telescope through a pressure-controlled mirror and the other part entering the four-quadrant detector. The four-quadrant detector is used to convert pulses into two-dimensional directional photocurrents to obtain the two-dimensional coordinates of the pulses; The PID controller is used to receive the two-dimensional coordinates of the pulse and fine-tune the position of the pressure-controlled reflector.

3. The femtosecond laser time synchronization system according to claim 2, characterized in that, The signal transmitting module also includes a calibration module and a turntable; The calibration module includes a beacon laser and a control module; The beacon laser is used to emit beacon light into the first beam expander telescope; The control module is used to receive beacon light fed back from the first beam expander and control the rotation of the turntable; The rotation of the turntable drives the first pulse and beacon laser to rotate.

4. The femtosecond laser time synchronization system according to any one of claims 1 to 3, characterized in that, The first determining module is further configured to determine the second pulse; The first determining module determines the clock difference between the first atomic clock and the second atomic clock by comparing the first pulse and the second pulse; The second determining module is also used to transmit the second pulse toward the source of the first pulse.

5. The femtosecond laser time synchronization system according to claim 3, characterized in that, It also includes a feedback receiving module; The receiving feedback module is located between the first beam expander telescope and the receiving device; The receiving feedback module includes a second beam expander telescope and an optical fiber reflector; The second beam expander telescope is used to receive beacon laser and transmit it to the fiber optic reflector, and also to receive the first pulse and transmit it to the receiving device; The fiber optic reflector is used to reflect the beacon laser back along its original path.

6. A femtosecond laser time synchronization method, characterized in that, Using the femtosecond laser time synchronization system according to any one of claims 1 to 5, the steps include: By setting the first femtosecond laser and the propagating femtosecond laser to have a small repetition rate difference, the pulses of the two femtosecond lasers can be mutually scanned in the time domain. The first femtosecond laser and the propagating femtosecond laser are simultaneously locked to the first atomic clock through a phase-locked loop. The clock difference of the first atomic clock is set to zero, and the time deviation caused by factors other than the atomic clock is obtained. Two femtosecond lasers form a bidirectional transmission link, enabling their pulses to form a laser interference signal; The time deviation data obtained from the laser interferometric signal was used to calibrate the first atomic clock; The femtosecond laser generates the first pulse carrying the time information of the calibrated first atomic clock. A second femtosecond laser with the same repetition frequency as the first femtosecond laser locks onto the second atomic clock and outputs a second pulse carrying the time information of the second atomic clock. The clock difference between the first and second atomic clocks is obtained by comparing the first pulse and the second pulse, and the second atomic clock is calibrated.

7. The femtosecond laser time synchronization method according to claim 6, characterized in that, It also includes the following steps: The other signal receiving modules are calibrated using a third pulse carrying the time information of the calibrated second atomic clock.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in claim 6 or 7.

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