Inter-satellite time and frequency communication transfer system based on femtosecond optical comb

Abstract

The present application relates to the technical field of inter-satellite time-frequency communication transmission, and proposes an inter-satellite time-frequency communication transmission system based on femtosecond optical comb. The system comprises: a first transmitting or receiving system configured to transmit or receive signal light and exchange the signal light with a laser module and an optical comb module, wherein the signal light comprises laser signal light and first optical comb pulse light; the laser module configured to generate or process the laser signal light and exchange the laser signal light with the transmitting or receiving system, wherein the laser signal light is configured to carry communication information; and the first optical comb module configured to generate or process the first optical comb pulse light and exchange the first optical comb pulse light with the first transmitting or receiving system, wherein the first optical comb pulse light is configured to carry time-frequency information.

Description

Technical Field

[0001] This invention generally relates to the field of inter-satellite time-frequency communication transmission technology. Specifically, this invention relates to an inter-satellite time-frequency communication transmission system based on a femtosecond optical comb. Background Technology

[0002] With the rapid development of optical communication technology, the potential applications of femtosecond optical frequency combs (femtosecond optical combs) in various fields have attracted widespread attention. In 2013, NIST (National Institute of Standards and Technology) achieved a 1fs time-to-analysis accuracy and 10 Hz accuracy over a distance of 2km using linear optical sampling technology based on femtosecond optical frequency combs (femtosecond optical combs). -1 Stability of 8 @ 1000 s. In 2015, NIST improved the experimental protocol and conducted a time synchronization experiment at a distance of 4 km, with a time synchronization accuracy of 4 fs @ 1 min and 50 fs @ 40 h. By 2016, NIST had increased the experimental distance to 12 km, further improving the stability to 10. -19 @10000s.

[0003] The principle of time-frequency transmission in space using femtosecond optical combs is to lock the clock information of two locations to the comb frequency of the local femtosecond optical comb and transmit it to the other party through a link similar to laser communication. Since there is a small difference in the repetition frequency of the comb pulses of the two local femtosecond optical combs, it can be considered that the local optical comb pulses "sample" and interfere with the received remote optical comb pulses, thereby obtaining ultra-high precision time measurement. By comparing the interference signals of the local and received femtosecond optical combs, the clock difference between the two locations can be obtained. Therefore, femtosecond optical combs can effectively improve the accuracy of spatial time-frequency transmission. However, current technologies based on femtosecond optical combs for time-frequency transmission are still in the experimental stage, and research on the integration of laser communication and optical comb time-frequency transmission is still lacking. Summary of the Invention

[0004] To at least partially solve the aforementioned problems in the prior art, this invention proposes an integrated time-frequency transfer and communication system based on a femtosecond optical comb, comprising:

[0005] A first transmitting or receiving system is configured to transmit or receive signal light via an inter-satellite link and exchange the signal light with a laser module and a first optical comb module, wherein the signal light includes laser signal light and first optical comb pulse light.

[0006] A laser module configured to generate or process the laser signal light and exchange the laser signal light with the first transmitting or receiving system, wherein the laser signal light is configured to carry communication information;

[0007] A first optical comb module is configured to generate or process first optical comb pulses and exchange first optical comb pulses with the first transmitting or receiving system, wherein the first optical comb pulses are configured to carry time-frequency information; and

[0008] A beacon light module, wherein the signal light further includes beacon light, the beacon light module being configured to generate or process beacon light and exchange beacon light with the first transmitting or receiving system;

[0009] The first transmitting or receiving system includes:

[0010] An optical antenna configured to transmit or receive beacon light, laser signal light, and first optical comb pulse light;

[0011] A transceiver splitter configured to combine or separate the transmitting or receiving optical paths of the beacon light, laser signal light, and first optical comb pulse light;

[0012] A turntable on which the optical antenna is mounted, wherein rotation of the turntable allows for adjustment of the optical antenna's line-of-sight pointing within a coarse tracking accuracy range of less than 50 μrad; and

[0013] A fast reflector is configured to adjust the line-of-sight pointing of the optical antenna within a fine tracking accuracy range, wherein the fine tracking accuracy range is smaller than the coarse tracking accuracy range, the fine tracking accuracy range being less than 5 μrad.

[0014] In one embodiment of the present invention, the beacon light module includes a beacon light generator and a beacon light detector. The beacon light generator generates beacon light and transmits it to the first transmitting or receiving system, which then transmits the beacon light to other terminals. The beacon light detector detects the beacon light emitted by other terminals received by the first transmitting or receiving system to obtain the alignment error of the optical antenna's line of sight. The detector then corrects the line of sight of the optical antenna by rotating the turntable and the fast reflector, thereby ensuring precise alignment between the two inter-satellite terminals and establishing a stable laser link.

[0015] In one embodiment of the present invention, the laser module includes a laser communication control module, an electro-optic modulator, a communication detector, and a demodulator. The communication process includes the following steps: after a stable laser link is established, the laser communication control module uses the electro-optic modulator to modulate the data to be transmitted onto the laser signal light, amplifies the optical power, and finally emits it. Simultaneously, the laser module receives the laser signal light emitted by the target terminal, uses the communication detector to convert the optical signal into an electrical signal, and performs data demodulation and calculation through the demodulator to achieve communication. This invention is based on the inventor's insight that optical comb time-frequency transfer, as a free-space optical transfer method, shares many similarities with free-space laser communication. For example, it also requires optical transmitters and receivers, and it also needs to capture, track, and align the target terminal to establish a stable laser link. Therefore, this invention proposes an integrated solution for laser communication and optical comb time-frequency transfer, including integrated laser communication and optical comb structure multiplexing, integrated laser communication and optical comb time-division multiplexing, and integrated laser communication and optical comb amplitude modulation.

[0016] The present invention has at least the following beneficial effects: by creatively integrating laser communication with optical comb time and frequency transmission into a single design, the onboard load can be effectively reduced, and the onboard resource consumption during satellite communication and time and frequency transmission can be effectively reduced. Attached Figure Description

[0017] To further illustrate the advantages and other features of the various embodiments of the present invention, a more specific description of the embodiments of the present invention will be presented with reference to the accompanying drawings. It is understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by the same or similar reference numerals for clarity.

[0018] Figure 1 and Figure 2 The diagrams show a schematic of an integrated time-frequency transmission and communication system based on a femtosecond optical comb, according to one embodiment of the present invention.

[0019] Figure 3 A schematic diagram of an optical comb pulse light for time-division multiplexing of time-frequency information and communication information is shown in one embodiment of the present invention.

[0020] Figure 4 A schematic diagram of an optical comb pulse light that simultaneously transmits time-frequency information and communication information is shown in one embodiment of the present invention. Detailed Implementation

[0021] It should be noted that the components in the various figures may be shown exaggeratedly for illustrative purposes and are not necessarily to scale. In each figure, the same reference numerals are used for components that are identical or have the same function.

[0022] In this invention, unless otherwise specified, "arranged on," "arranged above," and "arranged on" do not exclude the possibility of an intermediate element between them. Furthermore, "arranged on or above" merely indicates the relative positional relationship between two components, and in certain cases, such as when the product orientation is reversed, it can also be converted to "arranged below or under," and vice versa.

[0023] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0024] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0025] It should also be noted that, in the embodiments of the present invention, only a portion of the components or parts may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, necessary components or parts can be added as needed for specific scenarios. Furthermore, unless otherwise stated, features in different embodiments of the present invention can be combined with each other. For example, a feature in the second embodiment can replace a corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment will also fall within the scope of disclosure or description of this application.

[0026] It should also be noted that, within the scope of this invention, the terms "same," "equal," and "equal to" do not imply that the two values ​​are absolutely equal, but rather allow for a certain reasonable margin of error. In other words, the terms also encompass "substantially the same," "substantially equal," and "substantially equal to." Similarly, in this invention, the directional terms "perpendicular to," "parallel to," etc., also encompass the meanings of "substantially perpendicular to" and "substantially parallel to."

[0027] Furthermore, the numbering of the steps in the methods of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps may be executed in different orders.

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Option 1: Integrated Solution of Laser Communication and Optical Comb Structure

[0030] Figure 1The diagram illustrates an integrated time-frequency transmission and communication system based on a femtosecond optical comb, according to one embodiment of the present invention. This integrated system may include a transmitting or receiving system, a laser module, an optical comb module, and a beacon optical module. The optical comb module is added to the traditional laser communication system structure, and by enabling the optical comb time-frequency transmission of the optical comb module and the laser communication of the laser module to share a common transmitting or receiving optical path, system integration is achieved.

[0031] The transmitting or receiving system can transmit or receive beacon light, laser signal light, and optical comb pulse light. The transmitting or receiving system may include an optical antenna, a transceiver splitter, a two-dimensional servo turntable, a fast tilt mirror, a pre-aiming mirror, and a beacon light detector.

[0032] Optical antennas can emit or receive beacon light, laser communication signal light, and time-frequency transmission optical comb pulse light. These three types of light are set at different wavelengths, and dichroic mirrors are used to separate the optical paths.

[0033] Transceiver splitters can be used to separate the transmitting optical path of composite beacon light, laser communication signal light, and time-frequency transmission optical comb pulse light, and their receiving optical path.

[0034] The optical antenna can be arranged on a two-dimensional servo turntable. By controlling the two-dimensional servo turntable, the coarse tracking accuracy range of the optical antenna's line of sight can be adjusted, wherein the coarse tracking accuracy range can be less than 50 μ rad.

[0035] The fast tilting mirror and the pre-aiming mirror can be fast reflecting mirrors, which can rapidly adjust the line-of-sight of the optical antenna within a fine tracking accuracy range. This fine tracking accuracy range is smaller than the coarse tracking accuracy range, for example, less than 5 μrad. However, those skilled in the art should understand that the above coarse or fine tracking accuracy ranges are merely examples, and they can select appropriate values ​​based on the actual system.

[0036] The beacon optical module can generate or process beacon light and exchange the beacon light with the transmitting or receiving system. Here, the term "exchange" means that the beacon optical module transmits its generated beacon light to the transmitting or receiving system, or that the transmitting or receiving system transmits beacon light received from other terminals to the beacon optical module.

[0037] The beacon light module may include a beacon light generator and a beacon light detector. The beacon light generator generates beacon light and transmits it to the transmitting or receiving system, which then transmits it to other terminals. The beacon light detector detects the beacon light emitted by other terminals received by the transmitting or receiving system to obtain the alignment error of the optical antenna's line of sight. It then corrects the line of sight of the optical antenna by rotating the two-dimensional servo turntable, the fast tilt mirror, and the pre-aiming mirror, ensuring precise alignment between the two inter-satellite terminals and establishing a stable laser link.

[0038] The laser module can generate or process the laser signal light and exchange the laser signal light with the transmitting or receiving system, wherein the laser signal light is configured to carry communication information. The laser module may include a laser communication control module, an electro-optic modulator, a communication detector, and a demodulator. The communication process may include the following steps: after a stable laser link is established, the laser communication control module uses the electro-optic modulator to modulate the data to be transmitted onto the laser signal light, amplifies the optical power, and finally transmits it. Simultaneously, the laser module can receive the laser signal light emitted by the target terminal, use the communication detector to convert the optical signal into an electrical signal, and use the demodulator to demodulate and calculate the data to achieve communication.

[0039] The optical comb module can generate or process the optical comb pulses and exchange them with the transmitting or receiving system, wherein the optical comb pulses are configured to carry time and frequency information. The optical comb module can transmit an optical comb signal locked to a local terminal time and frequency standard through the transmitting or receiving system, and receive optical comb pulses from a remote location, comparing them with the local optical comb signal to calculate the local time difference. By comparing this with the remote time difference transmitted via laser communication, clock difference data between the two locations is obtained.

[0040] In one embodiment of the present invention, a method of utilizing... Figure 1 The method for time-frequency transmission and communication in the system shown, wherein the first system and the second system perform time-frequency transmission and communication, may include the following steps:

[0041] The first transmitting or receiving system of the first system receives the beacon light emitted by the second system;

[0042] The beacon light module of the first system obtains the alignment error of the line-of-sight pointing between the optical antennas of the first and second systems based on the beacon light, and corrects the line-of-sight pointing through the two-dimensional servo turntable and / or fast reflector of the first system to establish an inter-satellite link between the first and second systems.

[0043] The first transmitting or receiving system of the first system receives the laser signal light and the first optical comb pulse light emitted by the second system;

[0044] The laser module of the first system generates and emits laser signal light, and processes the laser signal light emitted by the second system to enable communication between the first and second systems; and

[0045] The optical comb module of the first system generates and emits optical comb pulses, and processes the first optical comb pulses emitted by the second system to perform time-frequency transfer between the first and second systems.

[0046] Option 2: Integrated Time Division Multiplexing Solution for Laser Communication and Optical Comb Structure

[0047] Figure 2 This diagram illustrates a time-frequency transfer and communication integrated system based on a femtosecond optical comb, according to another embodiment of the present invention. Figure 2 The system shown is in Figure 1 Based on the system shown, the laser module has been removed, and a femtosecond optical comb is used to simultaneously transmit time-frequency signals and communication signals to maximize resource utilization. Time-division communication is employed, transmitting communication signals in a time-division manner while ensuring time-frequency calibration requirements are met. The communication information can be modulated onto the amplitude of the optical comb pulses.

[0048] like Figure 2 As shown, optical combs A and B are located at positions A and B, respectively, with a repetition frequency interval of approximately several kilohertz. Optical comb A is locked to the local clock and is used to emit optical comb pulses, including time-division multiplexing of time-frequency signals and communication signals amplitude-modulated via acousto-optic or amplitude modulators. A schematic diagram of the transmitted signals can be seen as follows. Figure 3 As shown. After signal light A travels through free space, it first passes through a first 50 / 50 coupler at position B, causing part of the signal light to mix with the local light and enter the balanced detector. Further analysis of time-frequency information can be performed using linear optical sampling. The other part of the signal light is then split by the coupler and enters the photodetector. The amplitude of the detected light pulse is processed, and the detected electrical pulse is used to determine whether it is an amplitude-modulated signal. If the received optical comb pulse light triggers a low threshold electrical pulse from the standard signal, it indicates that a modulated pulse is being transmitted, i.e., a communication signal is being transmitted. The electrical pulse is then further demodulated, and the time-frequency information is discarded. If the light pulse is an unmodulated signal, it indicates that a time-frequency signal is being transmitted, and the communication information can be discarded.

[0049] In one embodiment of the present invention, a method of utilizing... Figure 2The method for time-division multiplexing and communication of the system shown, wherein time-division multiplexing and communication are performed between the third system and the fourth system, may include the following steps:

[0050] The second optical comb module of the third system generates second optical comb pulse light carrying time-frequency information or communication information in a time-division manner;

[0051] The second optical comb pulse light is transmitted from the third system to the fourth system;

[0052] The second optical comb pulse light is split by the coupler of the fourth system and sent to the balanced detector and photodetector of the fourth system;

[0053] The time-frequency information of the second optical comb pulse light is detected and processed by the balanced detector of the fourth system; and

[0054] The amplitude of the second optical comb pulse light is detected by the balanced detector of the fourth system, and it is determined whether the second optical comb pulse light carries communication information based on the amplitude. If it carries communication information, the time and frequency information is discarded and the communication information is processed.

[0055] Option 3: Integrated Solution of Laser Communication and Optical Comb Amplitude Modulation

[0056] Scheme 2 employs a time-division multiplexing approach, loading time-frequency information and communication information onto femtosecond optical comb pulses at different times. This means the receiver extracts only one type of information at a time, discarding the other, which still results in some resource waste. To further improve communication efficiency, one embodiment of this invention proposes loading both types of signals simultaneously onto the femtosecond optical comb pulse. The receiver can then use a limiting filter to obtain both communication and time-frequency information. A schematic diagram of the optical comb pulse in this case is shown below. Figure 4 As shown.

[0057] In this scheme, the optical comb pulse transmits time-frequency information while simultaneously modulating optical communication information onto the pulse amplitude. During amplitude modulation, modulation techniques that preserve the original pulse phase information are employed as much as possible. The hardware structure of the receiving end is the same as in Scheme Two, divided into two parts based on time-frequency information analysis and communication information analysis, which simultaneously receive time-frequency information and communication information respectively.

[0058] Considering that amplitude modulation inevitably affects the analysis of time-frequency information by linear optical sampling, specifically because linear optical sampling has a threshold for triggering the acquisition card, limiting the lower limit of optical power, and because the calculated phase becomes more dispersed when the optical power decreases, resulting in poorer linearity and affecting the clock error value obtained after linear fitting, it is necessary to post-process the phase information at the receiving end while maintaining the modulation of phase information as much as possible at the transmitting end. By using the pre-calculated relationship between amplitude and phase, the amplitude modulation situation can be obtained using the demodulated optical communication information, and the phase alteration caused by modulation can be inverted and compensated for to compensate for the resulting errors.

[0059] In one embodiment of the present invention, a method of utilizing... Figure 2 The system shown simultaneously performs time-frequency transmission and communication, wherein the time-frequency transmission and communication are performed by the fifth system and the sixth system, and the method includes the following steps:

[0060] The third optical comb pulse light is generated by the third optical comb module of the fifth system;

[0061] The third optical comb pulse light is transmitted from the fifth system to the sixth system;

[0062] The third optical comb pulse light is split by the second coupler of the sixth system and sent to the second balanced detector and the second photodetector of the sixth system;

[0063] The second balanced detector of the sixth system detects and processes the time-frequency information of the third optical comb pulse light; and

[0064] The communication information of the pulsed light from the third optical comb is detected and processed by the second photodetector of the sixth system.

[0065] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. An inter-satellite time-frequency communication transmission system based on a femtosecond optical comb, characterized in that, include: A first transmitting or receiving system is configured to transmit or receive signal light via an inter-satellite link and exchange the signal light with a laser module and a first optical comb module, wherein the signal light includes laser signal light and first optical comb pulse light. A laser module configured to generate or process the laser signal light and exchange the laser signal light with the first transmitting or receiving system, wherein the laser signal light is configured to carry communication information; A first optical comb module is configured to generate or process first optical comb pulse light and exchange first optical comb pulse light with the first transmitting or receiving system, wherein the first optical comb pulse light is configured to carry time-frequency information. as well as A beacon light module, wherein the signal light further includes beacon light, the beacon light module being configured to generate or process beacon light and exchange beacon light with the first transmitting or receiving system; The first transmitting or receiving system includes: An optical antenna configured to transmit or receive beacon light, laser signal light, and first optical comb pulse light; A transceiver splitter configured to combine or separate the transmitting or receiving optical paths of the beacon light, laser signal light, and first optical comb pulse light; A turntable on which the optical antenna is mounted, wherein rotation of the turntable allows for adjustment of the optical antenna's line-of-sight pointing within a coarse tracking accuracy range of less than 50 μrad; and A fast reflector is configured to adjust the line-of-sight pointing of the optical antenna within a fine tracking accuracy range, wherein the fine tracking accuracy range is smaller than the coarse tracking accuracy range, the fine tracking accuracy range being less than 5 μrad.

2. The inter-satellite time-frequency communication transmission system based on a femtosecond optical comb according to claim 1, characterized in that, The beacon light module includes a beacon light generator and a beacon light detector. The beacon light generator generates beacon light and transmits it to the first transmitting or receiving system, which then transmits the beacon light to other terminals. The beacon light detector detects the beacon light emitted by other terminals received by the first transmitting or receiving system to obtain the alignment error of the optical antenna's line of sight. The turntable and fast reflector are rotated to correct the line of sight of the optical antenna, ensuring precise alignment between the two inter-satellite terminals and establishing a stable laser link.

3. The inter-satellite time-frequency communication transmission system based on a femtosecond optical comb according to claim 2, characterized in that, The laser module includes a laser communication control module, an electro-optic modulator, a communication detector, and a demodulator. The communication process includes the following steps: After a stable laser link is established, the laser communication control module uses the electro-optic modulator to modulate the data to be transmitted onto the laser signal light, amplifies the optical power, and finally emits it. At the same time, the laser module receives the laser signal light emitted by the target terminal, uses the communication detector to convert the optical signal into an electrical signal, and uses the demodulator to demodulate and calculate the data to achieve communication.

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