A fully automatic acquisition and tracking system based on a quadrant detector

Abstract

A fully automatic acquisition and tracking system based on a quadrant detector belongs to the technical field of space laser communication servo tracking. It solves the problems that in the case of radio frequency interference in the existing space laser communication system, acquisition failure and tracking non-convergence are likely to occur without auxiliary guidance. The system includes a master communication terminal and a slave communication terminal. The structures of the master communication terminal and the slave communication terminal are the same. The master communication terminal and the slave communication terminal cooperate with each other to complete full-automatic acquisition. After completing full-automatic acquisition, the master communication terminal and the slave communication terminal perform corresponding data transmission, that is, enter the tracking mode. The master communication terminal includes a mirror system, a beacon transmitting antenna, a transmissive optical antenna, a beacon laser, a signal processing board, a fine tracking servo controller, a fine tracking fast steering mirror, a first mirror, a coarse / fine tracking camera, a first converging lens, an energy beam splitter, a quadrant detector, a second converging lens, and a first wavelength beam splitter.

Description

Technical Field

[0001] The present invention belongs to the technical field of space laser communication servo tracking, and particularly relates to a full-automatic acquisition and tracking system based on a quadrant detector. Background Art

[0002] Space laser communication has gradually become the core means to solve the problem of "the last mile of optical fiber" due to its characteristics such as high bandwidth, low latency, and strong anti-interference ability. However, due to the small beam divergence angle and difficult acquisition and alignment in space laser communication, especially in the case of radio frequency silence and electromagnetic interference, it seriously affects the acquisition and link establishment of the space laser communication system. At the same time, in the existing space laser communication system, a low-bandwidth radio frequency service is usually used as an auxiliary command transmission link for double-end acquisition and convergent tracking. In the real battlefield and in the case of radio frequency interference, the phenomenon of acquisition failure and tracking non-convergence is likely to occur without auxiliary guidance. Summary of the Invention

[0003] In order to solve the problem that the existing space laser communication system is prone to acquisition failure and tracking non-convergence without auxiliary guidance in the case of radio frequency interference, the present invention provides a full-automatic acquisition and tracking system based on a quadrant detector.

[0004] The system includes a master communication terminal and a slave communication terminal. The structures of the master communication terminal and the slave communication terminal are the same. The master communication terminal and the slave communication terminal cooperate with each other to complete full-automatic acquisition. After completing full-automatic acquisition, the master communication terminal and the slave communication terminal perform corresponding data transmission, that is, enter the tracking mode. The master communication terminal includes a mirror system, a beacon transmitting antenna, a transmissive optical antenna, a beacon laser, a signal processing board, a fine tracking servo controller, a fine tracking fast steering mirror, a first mirror, a coarse / fine tracking camera, a first converging lens, an energy beam splitter, a quadrant detector, a second converging lens, and a first wavelength beam splitter;

[0005] The incident light passes through the mirror system and then enters the transmissive optical antenna for beam reduction, and then enters the fine tracking fast steering mirror through the first mirror. The fine tracking fast steering mirror reflects the light beam to the energy beam splitter. The energy beam splitter divides the light beam into two beams in proportion. One beam passes through the first converging lens and enters the coarse / fine tracking camera, and the other beam enters the first wavelength beam splitter. The first wavelength beam splitter reflects part of the light beam into the second converging lens, and after being emitted, enters the quadrant detector. Both the coarse / fine tracking camera and the quadrant detector are connected to the signal processing board. The signal processing board is also respectively connected to the beacon laser, the fine tracking servo controller, and the mirror system. The fine tracking servo controller controls the movement of the fine tracking fast steering mirror.

[0006] Further, the mirror system includes a first mirror and a second mirror. The pitch motor drives the first mirror and the second mirror to rotate simultaneously, and the azimuth motor drives the first mirror to rotate.

[0007] Further, the main communication terminal further includes a second wavelength beam splitter, a third focusing lens, a pre - optical amplifier, and an avalanche photodetector. The beam transmitted through the first wavelength beam splitter is incident on the second wavelength beam splitter, then reflected and enters the third focusing lens and exits. After passing through the pre - optical amplifier, it enters the avalanche photodetector.

[0008] Further, the main communication terminal further includes a pre - aiming fast steering mirror, a fourth focusing lens, an erbium - doped fiber amplifier, and a semiconductor laser. The beam emitted by the semiconductor laser enters the fourth focusing lens after passing through the erbium - doped fiber amplifier, exits and enters the pre - aiming fast steering mirror, and then is transmitted through the second wavelength beam splitter and output along the optical path.

[0009] Further, when using the full - automatic acquisition and tracking system for automatic acquisition, the system works through three stages in sequence, namely the acquisition stage, the convergence tracking stage, and the communication fine - tuning stage.

[0010] Further, the specific workflow of the acquisition stage is as follows:

[0011] S61. Main communication terminal: Calculate the position and pointing angle of the slave communication terminal through the ephemeris table, and at the same time control the mirror system for initial pointing.

[0012] S62. Main communication terminal: After completing the initial pointing, the signal processing board receives the feedback that the mirror system has reached the specified position. The signal processing board controls the beacon laser to send an acquisition modulation signal. The pulse width of the acquisition modulation signal is 1 μs, and the pulse interval is 5 μs. The signal processing board simultaneously controls the mirror system to start spiral scanning synchronously.

[0013] S63. Slave communication terminal: The signal processing board controls the mirror system to start spiral scanning. After the coarse / fine tracking camera receives the acquisition modulation signal sent by the main communication terminal, it sends the information to the signal processing board, and the signal processing board continues to control the mirror system for spiral scanning.

[0014] Further, the specific workflow of the convergence tracking stage is as follows:

[0015] S71. Main communication terminal: When the coarse / fine tracking camera detects the light spot and the quadrant detector synchronously detects the energy, after the signal processing board receives the above information, the signal processing board controls the beacon laser to send a convergence tracking modulation signal. The pulse width of the convergence tracking modulation signal is 1 μs, and the pulse interval is 10 μs.

[0016] S72, Master Communication Terminal: The off-target amount output by the coarse / fine tracking camera is sent to the signal processing board, and the signal processing board controls the mirror system to reduce the spiral scanning amplitude;

[0017] S73, Slave Communication Terminal: The coarse / fine tracking camera receives the convergence tracking modulation signal sent by the master communication terminal, sends the information to the signal processing board, and the signal processing board simultaneously controls the mirror system to start reducing the spiral scanning amplitude synchronously;

[0018] S74, Master Communication Terminal: When the coarse / fine tracking camera detects that the light spot converges to the center area of the camera, the coarse / fine tracking camera switches to a small window for fine tracking convergence;

[0019] S75, Slave Communication Terminal: When the coarse / fine tracking camera detects that the light spot converges to the center area, the coarse / fine tracking camera switches to a small window for fine tracking convergence;

[0020] S76, Master Communication Terminal: After the fine tracking convergence is completed, the quadrant detector performs light spot center detection. At this time, the signal processing board receives the signals output by the four quadrants of the quadrant detector, and the signals are the amplitude and information of the opposite-side convergence tracking signal.

[0021] Furthermore, the specific working process of the communication fine-tuning stage is as follows:

[0022] S81, Master Communication Terminal: When it is detected that the signal amplitudes output by the four quadrants of the quadrant detector are the same, the signal processing board controls the beacon laser to send a communication fine-tuning modulation signal. The pulse width of the communication fine-tuning modulation signal is 1 μs, and the pulse interval is 15 μs;

[0023] S82, Master Communication Terminal: When the signal received by the avalanche photodetector gradually increases, the fine tracking servo controller controls the fine tracking fast steering mirror to perform fine adjustment, and the signal processing board continues to control the beacon laser to send a communication fine-tuning modulation signal;

[0024] S83, Slave Communication Terminal: After receiving the communication fine-tuning modulation signal, the fine tracking servo controller controls the fine tracking fast steering mirror to perform fine adjustment;

[0025] S84, Master Communication Terminal: When the signal received by the avalanche photodetector decreases, the signal processing board controls the beacon laser to send a continuous "1" signal and stops the fine adjustment of the fine tracking fast steering mirror;

[0026] S85, Slave Communication Terminal: After receiving the continuous "1" signal, it stops the fine adjustment of the fine tracking fast steering mirror, and the master communication terminal and the slave communication terminal complete automatic acquisition.

[0027] The beneficial effects of the system of the present invention are as follows: By modulating the beacon light, command information such as capture, tracking, and communication is modulated in the beacon light. Using a quadrant detector as the detector for optical command information for capture and convergence tracking, and coordinating with the coarse servo motor control and fine servo control controller to achieve full-automatic capture and tracking, effectively avoiding the difficult situation of capture and link establishment of the space laser communication system under radio frequency silence and electromagnetic interference. At the same time, the traditional coarse capture and fine capture processes are adjusted and refined, split into a capture stage, a convergence tracking stage, and a communication fine-tuning stage, making the terminal alignment more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural diagram of the master communication terminal and the slave communication terminal in the full-automatic capture and tracking system based on a quadrant detector according to an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of modulation signals in different stages of the full-automatic capture and tracking system based on a quadrant detector according to an embodiment of the present invention;

[0030] Figure 3 It is a working flow chart of the full-automatic capture and tracking system based on a quadrant detector according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Embodiment 1

[0033] This embodiment provides a full-automatic capture and tracking system based on a quadrant detector. The structural diagram of the master communication terminal and the slave communication terminal in the system is as shown in Figure 1 The system includes a master communication terminal and a slave communication terminal. The structures of the master communication terminal and the slave communication terminal are the same. The master communication terminal and the slave communication terminal cooperate with each other to complete full-automatic capture. After completing full-automatic capture, the master communication terminal and the slave communication terminal perform corresponding data transmission, that is, enter the tracking mode. The system includes a mirror system 0, a beacon transmitting antenna 3, a transmissive optical antenna 4, a beacon laser 5, a signal processing board 6, a fine tracking servo controller 7, a fine tracking fast steering mirror 8, a first mirror 9, a coarse / fine tracking camera 10, a first converging lens 11, an energy beam splitter 12, a quadrant detector 13, a second converging lens 14, and a first wavelength beam splitter 15;

[0034] The incident light passes through the mirror system 0 and then enters the transmissive optical antenna 4 for beam reduction. Then it enters the fine tracking fast steering mirror 8 through the first mirror 9. The fine tracking fast steering mirror 8 reflects the light beam to the energy beam splitter 12. The energy beam splitter 12 divides the light beam into two beams in proportion. One beam passes through the first focusing lens 11 and enters the coarse / fine tracking camera 10, and the other beam enters the first wavelength beam splitter 15. The first wavelength beam splitter 15 reflects part of the light beam into the second focusing lens 14, and after being emitted, it enters the quadrant detector 13. Both the coarse / fine tracking camera 10 and the quadrant detector 13 are connected to the signal processing board 6. The signal processing board 6 is also respectively connected to the beacon laser 5, the fine tracking servo controller 7, and the mirror system 0. The fine tracking servo controller 7 controls the movement of the fine tracking fast steering mirror 8.

[0035] The mirror system 0 includes a first mirror 1 and a second mirror 2. The first mirror 1 and the second mirror 2 are simultaneously driven by a pitch motor to rotate, and the first mirror 1 is driven by an azimuth motor to rotate.

[0036] Embodiment 2

[0037] This embodiment is a further limitation of Embodiment 1. The main communication terminal further includes a second wavelength beam splitter 16, a third focusing lens 17, a pre - optical amplifier 22, and an avalanche photodetector 24. The light beam transmitted through the first wavelength beam splitter 15 enters the second wavelength beam splitter 16 and is then reflected into the third focusing lens 17 and emitted. After passing through the pre - optical amplifier 22, it enters the avalanche photodetector 24. The main communication terminal further includes a pre - aiming fast steering mirror 18, a fourth focusing lens 19, an erbium - doped fiber amplifier 23, and a semiconductor laser 25. The light beam emitted by the semiconductor laser 25 passes through the erbium - doped fiber amplifier 23 and then enters the fourth focusing lens 19. After being emitted, it enters the pre - aiming fast steering mirror 18, and then is transmitted through the second wavelength beam splitter 16 and output along the optical path. The above devices are mainly used to complete the corresponding data transmission between the main communication terminal and the slave communication terminal after full - automatic acquisition. In addition, it also includes a communication receiving optical fiber fixing bracket 20 and a communication transmitting optical fiber fixing bracket 21 for fixing optical fibers.

[0038] Embodiment 3

[0039] This embodiment is a further limitation of Embodiment 1. When using the full - automatic acquisition and tracking system for automatic acquisition, the system works through three stages in sequence, namely the acquisition stage, the convergence tracking stage, and the communication fine - tuning stage. When in different stages, the main communication terminal will emit different modulation signals, and the slave communication terminal will make corresponding adjustments according to different modulation signals. The specific modulation signals in different stages are as Figure 2 shown.

[0040] such as Figure 3This is the working flowchart of the full-automatic acquisition and tracking system of the present invention, where QD represents the quadrant detector 13, and APD represents the avalanche photodetector 24. The entire working process can be automatically completed without human judgment.

[0041] The specific working process of the acquisition stage is as follows:

[0042] S1. Master communication terminal: Calculate the position and pointing angle of the slave communication terminal through the ephemeris table, and at the same time control the mirror system 0 for initial pointing.

[0043] S2. Master communication terminal: After completing the initial pointing, the signal processing board 6 receives the feedback that the mirror system 0 has reached the specified position. At this time, neither the coarse / fine tracking camera 10 nor the quadrant detector 13 has received the optical signal. The signal processing board 6 controls the beacon laser 5 to send an acquisition modulation signal. The pulse width of the acquisition modulation signal is 1 μs, and the pulse interval is 5 μs. The signal processing board 6 simultaneously controls the mirror system 0 to start spiral scanning synchronously.

[0044] S3. Slave communication terminal: The signal processing board 6 controls the mirror system 0 to start spiral scanning. After the coarse / fine tracking camera 10 receives the acquisition modulation signal sent by the master communication terminal, it sends the information to the signal processing board 6, and the signal processing board 6 continues to control the mirror system 0 for spiral scanning. Thus, both ends perform spiral scanning within the acquisition uncertainty region.

[0045] The specific working process of the convergence tracking stage is as follows:

[0046] S1. Master communication terminal: When the coarse / fine tracking camera 10 detects the light spot and the quadrant detector 13 synchronously detects the energy, at this time the light spot is at the edge of the target surface of the coarse / fine tracking camera 10 or in one quadrant of the quadrant detector 13. After the signal processing board 6 receives the above information, the signal processing board 6 controls the beacon laser 5 to send a convergence tracking modulation signal. The pulse width of the convergence tracking modulation signal is 1 μs, and the pulse interval is 10 μs.

[0047] S2. Master communication terminal: The coarse / fine tracking camera 10 outputs the off-target amount to the signal processing board 6, and the signal processing board 6 controls the mirror system 0 to reduce the spiral scanning amplitude.

[0048] S3. Slave communication terminal: The coarse / fine tracking camera 10 receives the convergence tracking modulation signal sent by the master communication terminal, sends the information to the signal processing board 6, and the signal processing board 6 simultaneously controls the mirror system 0 to start reducing the spiral scanning amplitude synchronously.

[0049] S4. Master communication terminal: When the coarse / fine tracking camera 10 detects that the light spot converges to the center area of the camera, the coarse / fine tracking camera 10 switches to a small window for fine tracking convergence.

[0050] S5. Slave communication terminal: When the coarse / fine tracking camera 10 detects that the light spot converges to the central area, the coarse / fine tracking camera 10 switches to a small window for fine tracking convergence.

[0051] S6. Master communication terminal: After the fine tracking convergence is completed, the quadrant detector 13 performs light spot center detection. At this time, the signal processing board 6 receives the signals output from the four quadrants of the quadrant detector 13, and the signals are the amplitudes and information of the opposite-side convergence tracking signals.

[0052] The specific workflow of the communication fine-tuning stage is as follows:

[0053] S1. Master communication terminal: When it is detected that the signal amplitudes output from the four quadrants of the quadrant detector 13 are the same, the signal processing board 6 controls the beacon laser 5 to send a communication fine-tuning modulation signal. The pulse width of the communication fine-tuning modulation signal is 1 μs, and the pulse interval is 15 μs.

[0054] S2. Master communication terminal: When the signal received by the avalanche photodetector 24 gradually increases, the fine tracking servo controller 7 controls the fine tracking fast steering mirror 8 to perform fine adjustment, and the signal processing board 6 continues to control the beacon laser 5 to send a communication fine-tuning modulation signal.

[0055] S3. Slave communication terminal: After receiving the communication fine-tuning modulation signal, the fine tracking servo controller 7 controls the fine tracking fast steering mirror 8 to perform fine adjustment.

[0056] S4. Master communication terminal: When the signal received by the avalanche photodetector 24 decreases, the signal processing board 6 controls the beacon laser 5 to send a continuous "1" signal and stops the fine adjustment of the fine tracking fast steering mirror 8.

[0057] S5. Slave communication terminal: After receiving the continuous "1" signal, it stops the fine adjustment of the fine tracking fast steering mirror 8, and the master communication terminal and the slave communication terminal complete automatic acquisition.

[0058] The misalignment between tracking and communication causes the communication received energy not to reach the peak after tracking to the light spot center from the image. Therefore, it is necessary to scan the peak of the received energy, enter the communication fine-tuning stage, and use the energy received by the avalanche photodetector 24 as the feedback quantity to fine-tune the fine tracking fast steering mirror to maximize the communication energy.

[0059] Embodiment 4

[0060] This embodiment further limits Embodiment 1. After the full-automatic capture is completed, corresponding data transmission is carried out between the master communication terminal and the slave communication terminal. At this time, the communication receiving link of the master communication terminal is the link composed of the second wavelength beam splitter 16, the third converging lens 17, the preamplifier 22 and the avalanche photodetector 24; at this time, the communication transmitting link of the master communication terminal is the link composed of the erbium-doped fiber amplifier 23, the fourth converging lens 19, the pre-aiming fast steering mirror 18 and the second wavelength beam splitter 16.

Claims

1. A fully automatic capture and tracking system based on a four-quadrant detector, the system comprising a master communication terminal and a slave communication terminal, the master communication terminal and the slave communication terminal having the same structure, the master communication terminal and the slave communication terminal cooperate to complete fully automatic capture, after completing fully automatic capture, the master communication terminal and the slave communication terminal perform corresponding data transmission, i.e. enter a tracking mode, characterized in that: The main communication terminal comprises a reflector system (0), a beacon transmitting antenna (3), a transmissive optical antenna (4), a beacon laser (5), a signal processing board (6), a fine tracking servo controller (7), a fine tracking fast reflection mirror (8), a first reflector (9), a coarse / fine tracking camera (10), a first converging lens (11), an energy spectroscope (12), a four-quadrant detector (13), a second converging lens (14) and a first wavelength spectroscope (15); After passing through the reflector system (0), the incident light enters the transmission optical antenna (4) for beam contraction, and then enters the fine tracking fast reflection mirror (8) through the first reflector (9). The fine tracking fast reflection mirror (8) reflects the light beam to the energy beam splitter (12). The energy beam splitter (12) divides the light beam into two beams in proportion. One beam passes through the first converging lens (11) and enters the coarse / fine tracking camera (10), and the other beam enters the first wavelength beam splitter (15). The first wavelength beam splitter (15) reflects part of the light beam and enters the second converging lens (14). After exiting, the light beam enters the four-quadrant detector (13). The coarse / fine tracking camera (10) and the four-quadrant detector (13) are both connected to the signal processing board (6). The signal processing board (6) is also connected to the beacon laser (5), the fine tracking servo controller (7) and the reflector system (0) respectively. The fine tracking servo controller (7) controls the movement of the fine tracking fast reflection mirror (8).

2. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 1 is characterized in that: The reflector system (0) comprises a first reflector (1) and a second reflector (2), wherein the first reflector (1) and the second reflector (2) are driven to rotate by a pitch motor at the same time, and the first reflector (1) is driven to rotate by an azimuth motor.

3. The fully automatic capture and tracking system based on the four-quadrant detector according to claim 2 is characterized in that: The main communication terminal further comprises a second wavelength spectroscope (16), a third converging lens (17), a pre-optical amplifier (22) and an avalanche photodetector (24); the light beam transmitted by the first wavelength spectroscope (15) is incident on the second wavelength spectroscope (16), reflected into the third converging lens (17), and then emitted, passing through the pre-optical amplifier (22) and then entering the avalanche photodetector (24).

4. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 3 is characterized in that: The main communication terminal further comprises a pre-aiming quick-reflection mirror (18), a fourth focusing lens (19), an erbium-doped fiber amplifier (23) and a semiconductor laser (25); a light beam emitted by the semiconductor laser (25) passes through the erbium-doped fiber amplifier (23) and then enters the fourth focusing lens (19), and then enters the pre-aiming quick-reflection mirror (18) and then is transmitted through the second wavelength splitter (16) and output along the optical path.

5. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 4 is characterized in that: When the fully automatic capture and tracking system is used for automatic capture, the system works in three stages, namely, the capture stage, the convergence and tracking stage, and the communication fine-tuning stage.

6. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 5, characterized in that: The specific workflow of the capture phase is as follows: S61, the master communication terminal: calculates the position and pointing angle of the slave communication terminal through the ephemeris table, and controls the reflector system (0) to perform initial pointing; S62, main communication terminal: after completing the initial pointing, the signal processing board (6) receives feedback that the reflector system (0) has reached the designated position, and the signal processing board (6) controls the beacon laser (5) to send a capture modulation signal, wherein the capture modulation signal has a pulse width of 1 μs and a pulse interval of 5 μs, and the signal processing board (6) simultaneously controls the reflector system (0) to synchronously start spiral scanning; S63, from the communication terminal: the signal processing board (6) controls the reflector system (0) to start spiral scanning, and after the coarse / fine tracking camera (10) receives the capture modulation signal sent by the main communication terminal, it sends the information to the signal processing board (6), and the signal processing board (6) continues to control the reflector system (0) to perform spiral scanning.

7. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 6, characterized in that: The specific workflow of the convergence tracking stage is as follows: S71, main communication terminal: when the coarse / fine tracking camera (10) detects a light spot and the four-quadrant detector (13) synchronously detects energy, after the signal processing board (6) receives the above information, the signal processing board (6) controls the beacon laser (5) to send a convergence tracking modulation signal, wherein the pulse width of the convergence tracking modulation signal is 1 μs and the pulse interval is 10 μs; S72, main communication terminal: the coarse / fine tracking camera (10) outputs the miss amount to the signal processing board (6), and the signal processing board (6) controls the reflector system (0) to reduce the spiral scanning amplitude; S73, from the communication terminal: the coarse / fine tracking camera (10) receives the convergence tracking modulation signal sent by the main communication terminal, and sends the information to the signal processing board (6), and the signal processing board (6) simultaneously controls the reflector system (0) to synchronously start reducing the spiral scanning amplitude; S74, main communication terminal: when the coarse / fine tracking camera (10) detects that the light spot converges to the center area of ​​the camera, the coarse / fine tracking camera (10) switches to a small window for fine tracking convergence; S75, from the communication terminal: when the coarse / fine tracking camera (10) detects that the light spot converges to the central area, the coarse / fine tracking camera (10) switches to a small window for fine tracking convergence; S76, main communication terminal: When the fine tracking convergence is completed, the four-quadrant detector (13) performs spot center detection. At this time, the signal processing board (6) receives the signals output by the four quadrants of the four-quadrant detector (13), and the signals are the amplitude and information of the opposite side convergence tracking signal.

8. The fully automatic capture and tracking system based on a four-quadrant detector according to claim 7, characterized in that: The specific workflow of the communication fine-tuning stage is as follows: S81, main communication terminal: when it is detected that the signal amplitudes outputted by the four quadrants of the four-quadrant detector (13) are the same, the signal processing board (6) controls the beacon laser (5) to send a communication fine-tuning modulation signal, wherein the pulse width of the communication fine-tuning modulation signal is 1 μs and the pulse interval is 15 μs; S82, main communication terminal: when the signal received by the avalanche photodetector (24) gradually increases, the fine tracking servo controller (7) controls the fine tracking fast reflection mirror (8) to perform fine adjustment, and the signal processing board (6) continues to control the beacon laser (5) to send a communication fine adjustment modulation signal; S83, from the communication terminal: after receiving the communication fine-tuning modulation signal, the fine tracking servo controller (7) controls the fine tracking fast reflection mirror (8) to perform fine-tuning; S84, main communication terminal: when the signal received by the avalanche photodetector (24) decreases, the signal processing board (6) controls the beacon laser (5) to send a continuous "1" signal and stops the fine tracking fast reflection mirror (8) from fine-tuning; S85, slave communication terminal: after receiving continuous "1" signals, stop fine tracking and fine adjustment of the fast-reflection mirror (8), and the master communication terminal and the slave communication terminal complete automatic capture.

Images