Laser communication terminal device and method for pointing mark calibration and target capture

Abstract

The application discloses a laser communication terminal device and a pointing mark calibration and target capture method based on an infrared star sensor. The infrared star sensor has the advantages of large star library capacity, large field of view, the ability to sense communication wavelength laser, strong anti-sun interference capability and low background noise. The device is designed in an optical-mechanical integrated manner, so that the optical axis of the infrared star sensor is parallel to the optical transmitting and receiving axis of the communication terminal, thereby constructing a unified high-precision space pointing reference. The infrared star sensor can observe a known position star in orbit, so that the initial pointing calibration of the terminal transmitting axis in the inertial coordinate system can be completed, and according to the target orbit prediction, the terminal can realize rapid and accurate scanning and capture on the target in a small uncertain area; or the infrared star sensor can directly realize rapid capture in a large uncertain area by virtue of the advantages of a large field of view and high sensitivity, so that the establishment speed of the space laser link and the integration degree of the system are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of space laser communication technology, specifically relating to a laser communication terminal device and a method for integrating pointing calibration and target acquisition functions. Background Technology

[0002] With the continuous development of satellite communication technology, the application of inter-satellite services is becoming increasingly widespread, showing an exponential growth trend. Free-space optical communication has become the preferred method for long-distance inter-satellite communication due to its advantages such as high communication rate, low power consumption, and good confidentiality. To achieve high-speed and stable laser communication, the terminal is required to have extremely high pointing accuracy and rapid target acquisition capability.

[0003] Traditional laser communication terminals typically employ separate pointing calibration and target acquisition / tracking systems. Pointing calibration often relies on visible light star sensors, making the calibration process complex and highly dependent on lighting conditions. Target acquisition, when scanning large, uncertain areas, is time-consuming, impacting system response speed and link establishment efficiency. Furthermore, these separate systems increase the terminal's size, weight, and complexity.

[0004] With the rise of low-Earth orbit satellite internet, spaceborne laser communication missions are evolving towards multi-target, highly dynamic, complex space environments, and deep space applications. Existing technologies are no longer sufficient to meet the terminal's requirements for autonomy, speed, lightweight design, and high reliability. Therefore, there is an urgent need for an integrated terminal device that can deeply integrate pointing calibration and target acquisition functions to simplify processes and enhance on-orbit autonomous operation capabilities.

[0005] To address the shortcomings of the aforementioned technologies, this invention proposes a laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor. This device leverages the large field of view, high sensitivity, and all-weather operation capabilities of the infrared star sensor, implementing calibration and target acquisition functions based on the same optical reference. This allows for rapid target acquisition within a large uncertainty area with only coarse initial pointing calibration, significantly improving the terminal's overall performance and on-orbit adaptability. It provides a reliable technical solution for shortening the on-orbit calibration cycle and achieving rapid establishment. Summary of the Invention

[0006] This invention discloses a laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor. Through optomechanical integration, a high-performance infrared star sensor is deeply integrated into the terminal's optical transceiver link, ensuring its optical axis is strictly parallel to the transmit and receive optical axes of the communication optical system, thereby constructing a unified, high-precision spatial pointing measurement reference. This infrared star sensor combines the functions of an inertial attitude reference measurement unit and a large field-of-view coarse acquisition sensor, achieving hardware reuse and functional integration.

[0007] The technical solution of this invention is as follows:

[0008] A laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor, characterized in that it includes:

[0009] A common aperture optical front end includes a single pendulum mirror, an optical antenna located after the single pendulum mirror for beam contraction and collimation of the received beam and beam expansion and collimation of the emitted beam, and a first fast reflector located in the subsequent optical path of the optical antenna for fast and precise tracking and fine-tuning of the beam direction.

[0010] A receiving and processing branch for processing the light beam received by the common aperture optical front end, the branch comprising:

[0011] The pointing calibration and coarse acquisition unit includes a first reflector, a second reflector, a first focusing lens, and an infrared star sensor arranged sequentially along a first branch optical path. The first and second reflectors are configured to make the optical axis of the first branch optical path parallel to the main communication optical axis of the optical antenna, thereby enabling the infrared star sensor to directly detect the acquisition beacon light incident along the main communication optical axis and provide an inertial space pointing reference for the main communication optical axis based on the observation of stars.

[0012] The precision tracking and signal detection unit is used to process the second branch optical path after passing through the optical antenna and the first fast reflector. This unit includes a second beam splitter, a CMOS camera, a third focusing lens, a first erbium-doped fiber amplifier, and a signal processing system. The second beam splitter splits the beam to the CMOS camera for precision tracking and to the first erbium-doped fiber amplifier and signal processing system coupled through the third focusing lens for communication signal demodulation. The transmission branch is used to generate and transmit a communication beam, including a laser, an optical modulator, a second erbium-doped fiber amplifier, a fourth focusing lens, and a second fast reflector arranged sequentially along the transmission direction. The light emitted from the second fast reflector is reflected by the first beam splitter and then merges into the common optical path formed by the common aperture optical front end and the first fast reflector.

[0013] The self-calibration component includes a corner bevel mirror disposed on the transmission light path of the first beam splitter and located between the first beam splitter and the second beam splitter. In self-calibration mode, it is used to reflect part of the emitted light back to the receiving and processing branch along the original path. By analyzing the position of the returned light spot on the CMOS camera, the alignment deviation between the transmitting axis and the receiving axis is measured and closed-loop corrected.

[0014] The infrared star sensor serves as both a calibration sensor providing an inertial pointing reference for the main communication optical axis and a coarse acquisition sensor for detecting the incident beacon light during the target acquisition phase, thus integrating pointing calibration and target acquisition functions.

[0015] Furthermore, it also includes a signal source and a signal driving amplifier, the output end of the signal source is connected to the input end of the signal driving amplifier, the output end of the signal driving amplifier is connected to the radio frequency signal input port of the optical modulator; the output end of the laser is connected to the optical input port of the optical modulator through an optical fiber; the optical output port of the optical modulator is connected to the input port of the second erbium-doped fiber amplifier through an optical fiber.

[0016] Furthermore, the first beam splitter is disposed between the first fast reflector and the second beam splitter, and is used to transmit the received beam from the first fast reflector to the second beam splitter, and reflect the emitted beam from the second fast reflector back to the first fast reflector.

[0017] Furthermore, the corner bevel mirror is located in the optical path between the first beam splitter and the second beam splitter, and its retroreflection direction is strictly aligned with the incident direction of the transmitted light from the first beam splitter.

[0018] Furthermore, the infrared star sensor operates in a band that covers the wavelength of communication lasers, has a field of view of not less than 4.2°×5°, and has a built-in large-capacity navigation star library and star map recognition algorithm.

[0019] Furthermore, the pointing calibration and coarse acquisition unit is configured to: observe stars through the infrared star sensor, calculate and obtain the high-precision theoretical pointing of the main communication optical axis in the inertial coordinate system; obtain the system-level pointing deviation by comparing the theoretical pointing with the actual pointing measurement value of the terminal and use it for compensation of subsequent pointing commands; and, when the target is acquired, directly use the large field of view of the infrared star sensor to detect the target beacon light and obtain coarse pointing error information.

[0020] Second, the present invention also provides a pointing calibration method based on the above-mentioned device, characterized by comprising the following steps:

[0021] The infrared star sensor was used to observe multiple stars within its field of view;

[0022] Based on the matching of the observed star map and the navigation star library and attitude calculation, the precise pointing of the optical axis of the infrared star sensor in inertial space is determined;

[0023] Based on the parallel relationship between the optical axis of the infrared star sensor and the optical axis of the main communication, the precise direction of the main communication optical axis in inertial space is directly obtained, which serves as the reference for terminal pointing control.

[0024] Third, the present invention also provides a target acquisition method based on the above-mentioned device, characterized in that it includes the following steps:

[0025] After completing the pointing calibration, based on the target trajectory prediction, the driving terminal is used to make the target fall into the field of view of the infrared star sensor;

[0026] The infrared star sensor is used to directly detect the capture beacon light from the target and obtain the position of its spot on the target surface of the infrared star sensor.

[0027] The coarse pointing error is calculated based on the position of the light spot, and the single pendulum mirror and / or the first fast reflector are driven to guide the target beam into the fine tracking field of view of the CMOS camera, thus completing the transfer from coarse acquisition to fine tracking.

[0028] Furthermore, when the target's angular uncertainty area is smaller than the field of view of the infrared star sensor, a staring wait mode is used for acquisition, eliminating the need for scanning.

[0029] The present invention also provides a spacecraft, characterized in that it is equipped with a laser communication terminal device that integrates pointing calibration and target acquisition based on an infrared star sensor, as described above.

[0030] Compared with the prior art, the technical effects of the present invention are as follows:

[0031] 1) This device uses a high-precision infrared star sensor as a reference unit. While completing the pointing calibration, it directly provides high-precision feedback for the initial pointing of the laser communication terminal and the rapid acquisition and tracking of the target. This significantly simplifies the system architecture, reduces the number of independent sensors and optical channels, and effectively reduces the size, weight and power consumption of the terminal, realizing the miniaturization and lightweighting of the terminal as a whole.

[0032] 2) This device avoids complex calibration processes between subsystems and completes two key tasks using the same set of hardware and data streams, which greatly shortens the calibration preparation cycle for system use in orbit or in the field.

[0033] 3) This device fully utilizes the large field of view of the infrared star sensor, enabling it to directly cover a larger uncertain area during the acquisition and tracking phase. This reduces the time required for large-scale blind scanning by traditional terminals, thus significantly shortening the initial target acquisition time and improving the acquisition success rate and link establishment efficiency. In-orbit verification has shown that the system can achieve initial acquisition within 10 seconds and successfully establish four two-way links with five satellites within seven days, demonstrating excellent rapid response capabilities. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the structure of the laser communication terminal device based on the integrated pointing calibration and target acquisition of an infrared star sensor according to the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to implementation examples and accompanying drawings, so that those skilled in the art can fully understand and implement the present invention. This description is intended to provide specific and operable embodiments, but the scope of protection of the present invention is not limited thereto.

[0036] Please see Figure 1 , Figure 1 The figure shows a schematic diagram of the laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor according to the present invention. The device includes:

[0037] 1. Common Aperture Optical Front End: The single pendulum mirror 1 serves as the unified receiving and transmitting window for the terminal. Its reflective surface can deflect over a large angle range, responsible for receiving external incident beams and reflecting outgoing beams. The optical antenna 6 (usually an off-axis Cassegrain or transmission telescope) is located after the single pendulum mirror 1, used for beam contraction and collimation of the received beam, and beam expansion and collimation of the transmitted beam. The first fast reflector 7 is located in the subsequent optical path of the optical antenna 6. Its reflective surface can deflect at high speed and high precision over a small angle range, used for rapid and precise beam tracking and fine-tuning of the direction.

[0038] 2. Receiving Calibration Branch: In the reflected light path of the single pendulum mirror 1, a portion of the beam is guided to the first reflecting mirror 2 through optical path spatial beam splitting. The first reflecting mirror 2 and the second reflecting mirror 3 are arranged sequentially to form a deflecting optical path, adjusting the optical axis of this beam (i.e., the "calibration beam") to be strictly parallel to the main communication optical axis incident on the optical antenna 6. After deflection, the beam is converged by the first focusing lens 4 and finally imaged on the detector target surface of the infrared star sensor 5. This branch constitutes the "calibration reference optical path" parallel to the communication axis.

[0039] 3. Receiving Communication and Fine Tracking Branch: Most of the light beam reflected from the single pendulum mirror 1 (i.e., the "communication signal light") enters the optical antenna 6, is collimated by its beam-contraction mechanism, is reflected by the first fast-reflecting mirror 7, and then transmitted through the first beam splitter 8. The transmitted light continues to the second beam splitter 10. The second beam splitter 10 splits the beam into two paths according to wavelength or energy ratio: a reflected beam and a transmitted beam.

[0040] - Precision tracking path: The reflected beam passes through the second focusing lens 11 for imaging and the narrowband filter 12 (the center wavelength is consistent with the communication laser wavelength and is used to suppress background stray light) for filtering. After filtering, a clear spot image is formed on the target surface of the CMOS camera 13, which is used to achieve high-precision, high-bandwidth closed-loop tracking control.

[0041] - Signal Detection Path: After being focused by the third focusing lens 14, the transmitted light beam is coupled into a single-mode optical fiber. This fiber is connected to the first erbium-doped fiber amplifier 15, which amplifies the weak communication optical signal with low noise. The amplified optical signal is then sent to the signal processing system 16 to complete photoelectric conversion, demodulation, and data recovery.

[0042] 4. Transmitting Optical Path: Laser 21, in this embodiment, uses a distributed feedback laser with an output wavelength of 1550nm. The generated continuous optical carrier is input to optical modulator 20 (such as a Mach-Zehnder modulator) via optical fiber. The communication baseband signal from signal source 23 is amplified by signal drive amplifier 22 and then drives optical modulator 20 to modulate the signal onto the optical carrier. The modulated signal light enters the second erbium-doped fiber amplifier 19 for power amplification via optical fiber. The amplified transmitted light is collimated into parallel light by the fourth focusing lens 18 and then reflected by the second fast reflector 17. The reflected light is incident on the first beam splitter 8 and reflected by it, thus converging into the aforementioned common optical path: sequentially reflected by the first fast reflector 7, expanded and collimated by the optical antenna 6, reflected by the single pendulum mirror 1, and finally emitted towards the far-field target.

[0043] 5. Self-calibration component: The corner cone reflector 9, as a passive, high-precision optical retroreflector, is fixedly installed in the transmission light path direction of the first beam splitter 8, located between the first beam splitter 8 and the second beam splitter 10.

[0044] The workflow is as follows:

[0045] When acting as a receiver:

[0046] The laser beam (including beacon and signal beams) from the target arrives at the terminal and is reflected into the system by a single pendulum mirror 1. Through a space-division multiplexing optical path design, a calibration optical path parallel to the communication transceiver axis is constructed. Specifically, the beam is deflected and guided by the first reflector 2 and the second reflector 3 to form an optical path parallel to the communication transceiver axis. Finally, it is converged on the target surface of the infrared star sensor 5 by the first focusing lens 4, providing high-precision spot position information for pointing calibration and target acquisition. The remaining beams serve as communication signal beams. After being collimated and emitted by the optical antenna 6, they are reflected sequentially by the first fast reflector 7, transmitted by the first beam splitter 8, and split by the second beam splitter 10 for precise tracking and signal transmission. The beam used for fine tracking passes through the second focusing lens 11 and the narrowband filter 12 in sequence, and is clearly imaged on the target surface of the CMOS camera 13, realizing high-precision closed-loop tracking of the target beam; the beam used for signal processing is focused by the third focusing lens 14 and coupled into the optical fiber, amplified by the first erbium-doped fiber amplifier 15, and then transmitted to the signal processing system 16 to complete the demodulation and recovery of the communication signal.

[0047] When used as a transmitter:

[0048] The output of the laser 21 is connected to the optical input port of the optical modulator 20 via an optical fiber; the output of the signal source 23 is connected to the input port of the signal drive amplifier 22; the output of the signal drive amplifier 22 is connected to the radio frequency signal input port of the optical modulator 20, thereby loading the communication signal onto the optical carrier to generate modulated signal light; the signal light then enters the second erbium-doped fiber amplifier 19 for power amplification, and the amplified light is collimated by the fourth focusing lens 18, and then sequentially reflected by the second fast reflector 17, transmitted by the first beam splitter 8, and emitted by the first fast reflector 7 before entering the optical antenna 6. After being expanded and collimated by the antenna, a parallel beam is formed, and finally reflected by the single pendulum mirror 1 and emitted toward the target.

[0049] The corner bevel mirror 9 is disposed on the transmission light path of the first beam splitter 8 as a built-in passive calibration reference. When the device is in self-calibration mode, part of the emitted light is transmitted by the first beam splitter 8 to the corner bevel mirror 9 and returns to the system along the original path. By analyzing the position of the returned light spot on the CMOS camera 13, the emission optical axis is calibrated and corrected, thereby ensuring that the alignment deviation between the transmitting and receiving axes is stable at the μrad level.

[0050] The device fully leverages the inherent advantages of the infrared star sensor 5: its large-capacity star library ensures rapid star identification and high reliability, its strong resistance to solar interference ensures stable operation under complex light backgrounds, and its low background noise characteristics provide an extremely high detection signal-to-noise ratio. Based on these advantages, the device can stably acquire high-precision inertial attitude references and efficiently calibrate the pointing deviation of the system's optical axis through continuous observation of stars, achieving a pointing error calibration capability superior to mrad at the system level in a more efficient and robust manner.

[0051] The device uses the infrared star sensor 5 to perform pointing error calibration, which includes the following steps:

[0052] 1) Adjust the terminal pointing so that the infrared star sensor's field of view is aligned with the preset target sky area.

[0053] 2) Adjust the exposure time of the infrared star sensor according to the magnitude and background light to ensure that the stars are not overexposed and can be clearly detected, and collect multiple star images.

[0054] 3) Achieve star point extraction and centroid positioning, star map recognition and matching with navigation star catalog, and output the theoretical orientation of the terminal through attitude calculation.

[0055] 4) Compare the theoretical pointing with the actual pointing of the terminal, and use the difference as the system pointing deviation to compensate in subsequent pointing control to achieve high-precision correction.

[0056] The infrared star sensor 5 has a field of view of 4.2°×5° and an aperture of 15mm. Utilizing its large field of view, after a relatively rough initial pointing error calibration, it can directly capture the target communication beam in a large area of ​​angular uncertainty.

[0057] This invention transforms the infrared star sensor 5 from a traditional platform-level attitude sensor into a terminal-level sensor for direct optical axis measurement and calibration. Its integrated design eliminates the need for a separate visible light calibration system. Leveraging the strong anti-interference capabilities of the infrared band and its ability to directly sense communication band lasers, it simplifies the calibration process and enables all-day calibration. Simultaneously, its large field of view allows it to directly handle coarse acquisition, eliminating the need for a traditional coarse tracking camera and independent optical path, significantly reducing terminal size, weight, and power consumption. Ultimately, this device achieves a seamless transition from "inertial calibration" to "target acquisition," integrating the traditional step-by-step, serial working mode into a highly efficient, parallel mode, greatly improving the rapid establishment capability of the space laser link and system reliability.

Claims

1. A laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor, characterized in that, include: The common aperture optical front end includes a single pendulum mirror (1), an optical antenna (6) located after the single pendulum mirror (1), and a first fast reflector (7) located in the subsequent optical path of the optical antenna (6). A receiving and processing branch for processing the light beam received by the common aperture optical front end, the branch comprising: The pointing calibration and coarse acquisition unit includes a first reflector (2), a second reflector (3), a first focusing lens (4), and an infrared star sensor (5) arranged sequentially along the first branch optical path. The first reflector (2) and the second reflector (3) make the optical axis of the first branch optical path parallel to the main communication optical axis of the optical antenna (6). The first branch optical path is guided out from the reflected light of the single pendulum mirror (1) by spatial beam splitting. The fine tracking and signal detection unit is used to process the second branch optical path after the optical antenna (6) and the first fast reflector (7). The unit includes a second beam splitter (10), a CMOS camera (13), a third focusing lens (14), a first erbium-doped fiber amplifier (15), and a signal processing system (16). The second beam splitter (10) splits the beam to the CMOS camera (13) for fine tracking and to the first erbium-doped fiber amplifier (15) and signal processing system (16) coupled through the third focusing lens (14) for communication signal demodulation. The transmission branch is used to generate and transmit a communication beam, including a laser (21), an optical modulator (20), a second erbium-doped fiber amplifier (19), a fourth focusing lens (18), and a second fast reflector (17) arranged sequentially along the transmission direction. The light emitted from the second fast reflector (17) is reflected by the first beam splitter (8) and then merges into the optical path after the first fast reflector (7). The self-calibration component includes a corner bevel mirror (9) disposed on the transmission light path of the first beam splitter (8) and located between the first beam splitter (8) and the second beam splitter (10). In self-calibration mode, it reflects part of the emitted light back to the receiving processing branch along the original path. By analyzing the position of the returned light spot on the CMOS camera (13), it realizes the measurement and closed-loop correction of the alignment deviation between the transmitting axis and the receiving axis. The pointing calibration and coarse acquisition unit is configured to: observe stars through the infrared star sensor (5), calculate and obtain the high-precision theoretical pointing of the main communication optical axis in the inertial coordinate system; obtain the system-level pointing deviation by comparing the theoretical pointing with the actual pointing measurement value of the terminal and use it for compensation of subsequent pointing commands; and directly use the large field of view of the infrared star sensor (5) to detect the target beacon light when the target is acquired to obtain coarse pointing error information.

2. The laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor according to claim 1, characterized in that, It also includes a signal source (23) and a signal driver amplifier (22). The output end of the signal source (23) is connected to the input end of the signal driver amplifier (22), and the output end of the signal driver amplifier (22) is connected to the radio frequency signal input port of the optical modulator (20). The output end of the laser (21) is connected to the optical input port of the optical modulator (20) through an optical fiber. The optical output port of the optical modulator (20) is connected to the input port of the second erbium-doped fiber amplifier (19) through an optical fiber.

3. The laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor according to claim 1, characterized in that, The first beam splitter (8) is disposed between the first fast reflector (7) and the second beam splitter (10) for transmitting the received beam from the first fast reflector (7) to the second beam splitter (10) and reflecting the emitted beam from the second fast reflector (17) back to the first fast reflector (7).

4. The laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor according to claim 1, characterized in that, The corner cone reflector (9) is located in the optical path between the first beam splitter (8) and the second beam splitter (10), and its retroreflection direction is strictly aligned with the incident direction of the transmitted light from the first beam splitter (8).

5. The laser communication terminal device integrating pointing calibration and target acquisition based on an infrared star sensor according to claim 1, characterized in that, The infrared star sensor (5) operates in a band that covers the wavelength of communication lasers, with a field of view of not less than 4.2°×5°, and has a built-in large-capacity navigation star library and star map recognition algorithm.

6. A pointing calibration method based on the device according to any one of claims 1 to 5, characterized in that, Includes the following steps: The infrared star sensor (5) was used to observe multiple stars within its field of view; Based on the matching of the observed star map and the navigation star library and attitude calculation, the precise pointing of the optical axis of the infrared star sensor (5) in inertial space is determined; Based on the parallel relationship between the optical axis of the infrared star sensor (5) and the main communication optical axis, the precise direction of the main communication optical axis in inertial space is directly obtained, which serves as the reference for terminal pointing control.

7. A target acquisition method based on the apparatus according to any one of claims 1 to 5, characterized in that, Includes the following steps: After the pointing calibration is completed, the target trajectory is predicted, and the driving terminal is driven to make the target fall into the field of view of the infrared star sensor (5); The infrared star sensor (5) is used to directly detect the capture beacon light from the target and obtain the position of its spot on the target surface of the infrared star sensor (5); The coarse pointing error is calculated based on the position of the light spot, and the single pendulum mirror (1) and / or the first fast reflector (7) are driven to guide the target beam into the fine tracking field of view of the CMOS camera (13), thus completing the transfer from coarse acquisition to fine tracking.

8. The target acquisition method according to claim 7, characterized in that, When the target's angular uncertainty area is smaller than the field of view of the infrared star sensor (5), a staring wait mode is used for acquisition, without the need for scanning.

9. A spacecraft, characterized in that, A laser communication terminal device equipped with an integrated pointing calibration and target acquisition based on an infrared star sensor as described in any one of claims 1 to 5.

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