Communication optical axis autonomous correction method and system based on tracking point nutation and satellite laser communication terminal

Abstract

The invention discloses a communication optical axis autonomous correction method based on tracking point nutation, which comprises the following steps: controlling a fine-following fast reflector to scan, monitoring the output power of an erbium-doped fiber amplifier (EDFA) within scanning residence time, searching the position of the maximum power by adopting a sliding window average algorithm, and recording the position; and after scanning for one period, returning to the tracking point with the maximum recorded power, thereby realizing rapid and accurate calibration of the tracking optical axis of the laser communication terminal. According to the invention, a closed loop is formed based on tracking point nutation and a pre-amplification output signal, so that high-precision correction of a camera tracking point is realized, the stability of precise tracking of the system can be improved, and the signal-to-noise ratio received by the laser communication system can also be improved; the traditional receiving optical axis calibration convergence speed and precision are improved; higher real-time performance and automation degree are achieved, relevant data can be acquired and processed in real time, and correction of a receiving optical axis is achieved; the method has wide applicability and expandability, and can be applied to other spacecraft systems needing high-precision tracking control.

Description

Technical Field

[0001] The present invention belongs to the technical field of space laser communication, and specifically relates to a method and system for autonomous correction of a communication optical axis based on tracking point nutation, as well as a satellite laser communication terminal, which are applicable to rapid calibration of an in-orbit receiving optical axis of a spaceborne laser communication terminal. By controlling a fine tracking fast steering mirror to perform scanning and combining with a sliding window averaging algorithm to monitor the output power of an erbium-doped fiber amplifier (EDFA) in real time, automatic detection and correction of optical axis deviation are realized, thereby improving the stability, signal-to-noise ratio and communication quality of the laser communication system. Background Art

[0002] With the rapid development of the global satellite Internet, such as the deployment of large-scale low-Earth orbit satellite constellations like SpaceX's Starlink, China's GW constellation, Hongyan constellation, Xingyun project, and Galaxy, space laser communication technology has become an important means for high-speed data transmission between satellites due to its advantages such as high bandwidth and strong anti-interference ability. The rapid increase in the number of satellites in a short period of time has made the traditional manual monitoring and management methods unable to meet the requirements, and at the same time, a large amount of on-board data has also brought unprecedented processing challenges. To address these challenges, automation has become an inevitable trend.

[0003] In a space laser communication system, a small deviation of the optical axis may lead to a significant decrease in signal quality, thereby affecting the stability and accuracy of communication demodulation. This deviation may be caused by various factors, such as the slight movement of equipment caused by environmental factors (such as temperature), or the slight deformation of optical components after long-term use. Therefore, it is particularly important to develop a method that can monitor and compensate these small deviations in real time. For the determination of the optimal tracking point of a space laser communication system, a power feedback method is generally adopted. Using a fine tracking fast steering mirror as the execution mechanism for scanning, the position change of the fast steering mirror is mapped to the position change of the tracking point of the camera through a beam splitter and a nutation algorithm for monitoring; the signal light is coupled into the optical fiber, and the output power of the erbium-doped fiber amplifier (EDFA) is sampled and processed. By comparing the output power at different tracking point positions, the tracking point position that maximizes the output power can be found, that is, the optimal tracking point. After a cycle of scanning by the fast steering mirror, the position of the camera tracking point when returning to the point with the maximum power is obtained, and the optimal tracking point of the camera is finally determined through multiple iterations.

[0004] For the traditional determination of the optimal tracking point of a space laser communication system, it is necessary to control the position of the tracking point of the scanning camera through a large number of instructions and manually interpret the data, which has the characteristics of low timeliness and insufficient judgment accuracy. At the same time, the traditional method also has the characteristic of fixed parameters, which results in slow convergence speed and poor accuracy, and is not conducive to the stability of communication.

[0005] Therefore, there is an urgent need for a method that can correct the optical axis deviation in real time and automatically to improve the reliability and adaptability of the space laser communication system. Summary of the Invention

[0006] In a space laser communication system, a slight deviation of the optical axis will lead to a decrease in signal coupling efficiency, seriously affecting the communication quality. Traditional optical axis calibration methods rely on manual intervention and have problems such as low timeliness, insufficient accuracy, and poor automation, making it difficult to meet the efficient operation and maintenance requirements of large-scale satellite constellations.

[0007] To overcome the deficiencies of the above-mentioned prior art, the present invention provides an autonomous correction method for the communication optical axis based on the nutation of the tracking point. By guiding the light spot to scan through the fine tracking fast steering mirror (FSM), and combining the sliding window averaging algorithm to monitor the output power of the erbium-doped fiber amplifier (EDFA) in real time, fast and high-precision correction of the optical axis is achieved.

[0008] The technical solution of the present invention is as follows:

[0009] An autonomous correction method for the communication optical axis based on the nutation of the tracking point, characterized by comprising the following steps:

[0010] Step 1) Initialize the camera tracking point nutation parameters, including the scanning initial points X center and Y center , the nutation radius r, the nutation step size Δd, the residence time Δt for collecting one point, the number of iterations N, and the number of sampling points n for scanning one week;

[0011] Step 2) Control the fine tracking fast steering mirror (FSM) to drive the light spot to move along a circular trajectory, and the position of the camera tracking point:

[0012] X' = X center + rcos(2πm / (n - 1)) * K x

[0013] Y' = Y center + rsin(2πm / (n - 1)) * K y

[0014] where m = 0, 1,..., n - 2; K x and K y is the conversion coefficient from the fine tracking fast steering mirror to the tracking camera, with the unit of DA / pixel; the position of the first output point is the initial center points X center and Y center ;

[0015] Step 3) Collect the output power of the erbium-doped fiber amplifier (EDFA) at each sampling point, and calculate the average value of the output power of the erbium-doped fiber amplifier (EDFA) using the sliding window averaging algorithm;

[0016] Step 4) Record and compare the output powers of the erbium-doped fiber amplifiers (EDFAs) at each sampling point, and determine the coordinates X of the maximum power point within the current scanning period max and Y max ;

[0017] Step 5) Update the scanning center coordinates:

[0018] X center = X max

[0019] Y center = Y max

[0020] Step 6) Repeat steps S2 - S5 until the termination condition is met.

[0021] Furthermore, the sliding window averaging algorithm adopts a recursive calculation method:

[0022] P a = (m1 + m2 + m3 +... + m a ) / a

[0023] where P a is the recorded average power value; m a is the output power of each sampling; a is the number of samplings at one tracking point.

[0024] Furthermore, it also includes a spot centroid assisted positioning step:

[0025] Extract the spot images for the sampling points with the top 10% power;

[0026] Calculate the centroid position:

[0027]

[0028] where G(x, y) is the gray value at the coordinate (x, y) in the image;

[0029] Perform a weighted average of the centroid position and the point with the maximum power.

[0030] Furthermore, the K x and K y are the conversion coefficients from the fine tracking and fast steering mirror to the tracking camera, which are obtained through ground calibration, and calibrate the pixel position relationship coefficients corresponding to the movement of the fine tracking and fast steering mirror in the x and y directions mapped to the spot position movement on the tracking camera.

[0031] Furthermore, the radius r of the nutation can adopt a method combining coarse and fine. Use a scanning radius of the mrad order in the initial scan, and continuously reduce it to the urad order in subsequent iterations to achieve fast and more accurate locking of the tracking points.

[0032] In addition, the present invention also provides a communication optical axis autonomous correction system based on the nutation of tracking points, which is characterized by comprising:

[0033] An optical receiving component, including a reflecting mirror, a telescope system and a beam splitter;

[0034] A fine tracking fast steering mirror (FSM), whose parameters include: effective aperture φ30mm, deflection range ±5mrad, resolution 0.1μrad;

[0035] A detection unit, including a tracking camera and an erbium-doped fiber amplifier (EDFA);

[0036] A control unit, used to execute the above method.

[0037] Furthermore, the reflecting mirror is used to receive signal light and perform two-dimensional rotational scanning;

[0038] The telescope is composed of a lens group, and the signal light from a distance is effectively guided to the subsequent optical path through the lens group for further observation, analysis or processing.

[0039] The beam splitter can obtain the required reflected light and transmitted light by irradiating the beam onto the beam splitter, which are used as signal light and monitoring light respectively.

[0040] Thirdly, the present invention provides a satellite laser communication terminal, which is characterized by including the above communication optical axis autonomous correction system.

[0041] Compared with the prior art, the technical effects of the present invention are as follows:

[0042] 1) The method of the present invention can combine the coarse and fine composite scanning method. When performing coarse scanning, a large nutation radius is used, which is beneficial to quickly locate near the best tracking point that may contain the target. Due to the large scanning range, the general position of the target can be quickly captured in the coarse scanning stage, providing an effective reference for the subsequent fine scanning stage; when performing fine scanning, a small nutation radius is adopted, which can achieve precise measurement and tracking of the target area. Scanning in a small range near the best tracking point helps to maintain the stability of scanning and reduce errors caused by external interference or target movement.

[0043] 2) The optimized sliding window averaging algorithm can effectively reduce the noise interference in the spot signal and improve the accuracy of centroid calculation. At the same time, the spot centroid algorithm itself also has a high positioning accuracy. The combination of the two can further improve the accuracy of optical axis calibration, and the size of the sliding window and scanning parameters can be adjusted according to the actual situation to adapt to different communication environments and requirements. Since both the optimized sliding window averaging algorithm and the spot centroid algorithm have fast calculation speeds, this combined method can achieve real-time tracking and positioning in practical applications. This is of great significance for communication systems and optical axis calibration tasks that require quick response.

[0044] 3) The present invention realizes the rapid calibration of the on-orbit receiving optical axis by integrating a complex control feedback system. Compared with traditional calibration methods, this method has higher real-time performance and automation. The real-time correction of the receiving optical axis is achieved by tracking the nutation of the tracking point. The improvement of this real-time performance and automation is of great significance for improving the stability and reliability of the space laser communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a block diagram of an embodiment of the communication optical axis self-correction system based on the nutation of the tracking point of the present invention.

[0046] Figure 2 It is a schematic diagram of the tracking point scanning and updating of the communication optical axis self-correction based on the nutation of the tracking point of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will be further described below in conjunction with the embodiments and the drawings, but the protection scope of the present invention should not be limited thereby.

[0048] Please refer to Figure 1 , Figure 1 It is a block diagram of an embodiment of the communication optical axis self-correction system based on the nutation of the tracking point of the present invention. As shown in the figure, a communication optical axis self-correction system based on the nutation of the tracking point includes the following hardware components:

[0049] Mirror 1, which is used to receive the signal light and has the function of two-dimensional rotation, and can flexibly scan in two directions of azimuth angle and elevation angle.

[0050] Telescope 2, which is composed of a lens group. One of its core functions is to effectively guide the distant signal light to the subsequent optical path through the lens group for further observation, analysis or processing.

[0051] Fine tracking and fast steering mirror 3 is an opto-mechatronic precision device that can accurately control the direction of the light beam. By real-time monitoring the position of the camera spot and making adjustments, it can stabilize the pointing of the light beam and reduce the beam jitter caused by external interference.

[0052] Beam splitter 4. By irradiating a light beam onto the beam splitter, the required reflected light and transmitted light can be obtained as signal light and monitoring light respectively. In this embodiment, a dielectric film beam splitter placed at 45° with a transmittance - reflectance ratio of 50:50 and a working wavelength of 1550 nm ± 50 nm is adopted.

[0053] Lens 5, which is used to focus the light beam. 1) The light beam processed by the filter 6 will be guided to the photosensitive element of the tracking camera 7; 2) Before coupling the light beam into the optical fiber 8, it is first necessary to use the lens to focus the light beam onto a point.

[0054] Erbium - doped fiber amplifier (EDFA) 9, as a power monitor, amplifies the optical power under the condition of hardly changing the optical signal - to - noise ratio to reach a power suitable for the communication receiving end. Its output power can reflect the intensity and quality of the optical signal. When the optical axis position is optimal, the output power of the EDFA will reach the maximum value. Therefore, by monitoring the output power of the EDFA, the accuracy of the optical axis position can be indirectly judged.

[0055] Communication receiving end 10, which performs optoelectronic conversion on the optical signal and conducts signal processing to achieve communication demodulation. Its output bit error rate is also an important indicator for measuring the receiving optical axis. When the communication performance is excellent, that is, the bit error rate is better than 1×10 -7 , the nutation radius of the fast steering mirror will be reduced to improve the stability of the communication system.

[0056] A method for autonomous correction of a communication optical axis based on tracking point nutation uses a fine - tracking fast steering mirror to guide the light spot on the focal plane to move in a circular motion along a specific radius. In each complete motion cycle, the system performs power sampling to determine and record the position with the maximum output power. Subsequently, the scanning center point is adjusted by the fine - tracking fast steering mirror to align it with the previously recorded position with the maximum power, and the next round of scanning is started. After continuous multiple scanning iterations, the system can gradually approach and finally lock on the global optimal position, thereby achieving precise positioning of the maximum coupling efficiency. Specifically, it includes the following steps:

[0057] Step 1) Set the camera tracking point nutation parameters:

[0058] The parameter settings of the tracking point nutation mainly include the initial scanning points X center and Y center , the nutation radius r, the nutation step size Δd, the residence time Δt for collecting one point, the number of iterations N, and the number of sampling points n for scanning one week.

[0059] Step 2) Output the camera tracking point position:

[0060] X' = X center + rcos(2πm / (n - 1))*K x

[0061] Y' = Y center + rsin(2πm / (n - 1)) * K y

[0062] where m = 0, 1, …, n - 2; K x and K y is the conversion coefficient from the fine tracking and fast steering mirror to the tracking camera, with the unit of DA / pixel; the position of the first output point is the initial center point X center and Y center .

[0063] Step 3) Record the point X max and Y max with the maximum power by the sliding window average algorithm:

[0064] 3.1 Calculate the output power of the erbium-doped fiber amplifier (EDFA):

[0065] P a = (p1 + p2 + p3 +... + p a ) / a

[0066] where P a is the recorded average power value; p a is the output power of each sampling; a is the number of samplings for one tracking point.

[0067] 3.2 Record the maximum power value and the corresponding tracking point by the sliding window method:

[0068] To accurately find the position of the maximum power, the present invention adopts the sliding window average algorithm. This algorithm determines the position of the maximum power by calculating the average value of the EDFA output power within a certain window and comparing the average values of different windows.

[0069] P a+1 = (p1 + p2 + p3 +... + p a ) / a + (p a+1 - P a )

[0070] The size of the sliding window can be adjusted according to the actual situation to ensure the accuracy and response speed of the algorithm. At the same time, the method of updating the sliding average by adding new data and subtracting the average value can effectively reduce the use of registers and save software resources.

[0071] 3.3 Record the position of the tracking point at the moment of the maximum power during the scanning process, X max and Y max .

[0072] Step 4) After one week of scanning, update the scanning center:

[0073] X center = X max

[0074] Y center = Y max

[0075] Step 5) Repeat Step 2 to Step 4 until the maximum power meets the preset requirements or the number of iterations reaches N.

[0076] In the first embodiment, the acquisition module, the control module and the signal processing module are comprehensively applied. The rapid and accurate calibration of the receiving optical axis is realized by methods such as controlling the scanning fast steering mirror, recording the position of the tracking point of the camera, and sampling the output power of the EDFA. Second, the optimized sliding window averaging algorithm is adopted, which reduces the influence of jitter on the system and reduces the use of registers, saving software resources. Third, it has higher real-time performance and automation level, can acquire and process relevant data in real time, and realize the real-time correction of the tracking point of the receiving optical axis. Fourth, it has wide applicability and scalability, and can be applied to other spacecraft systems that require high-precision pointing control. The present invention provides an efficient and accurate on-orbit optical axis calibration method for spaceborne laser communication terminals, which is of great significance for improving the performance and stability of spaceborne laser communication systems.

Claims

1. A method for autonomous correction of a communication optical axis based on the nutation of a tracking point, characterized in that It includes the following steps: Step 1) Initialize the nutation parameters of the camera tracking point, including the scanning initial points X center and Y center , the nutation radius r, the nutation step size Δd, the residence time Δt for collecting one point, the number of iterations N, and the number of sampling points n for scanning one week; Step 2) Control the fine tracking fast steering mirror (FSM) to drive the light spot to move along a circular trajectory, and the camera tracks the position of the point: X' = X center + r cos(2πm / (n - 1)) * K x Y' = Y center + rsin(2πm / (n - 1)) * K y where m = 0, 1, …, n - 2; K x and K y is the conversion coefficient from the precision tracking and rapid response mirror to the tracking camera, with the unit of DA / pixel; the position of the first output point is the initial center point X center and Y center ; Step 3) Collect the output power of the erbium-doped fiber amplifier (EDFA) at each sampling point, and use the sliding window average algorithm to calculate the average value of the output power of the erbium-doped fiber amplifier (EDFA); Step 4) Record and compare the output powers of the erbium-doped fiber amplifiers (EDFAs) at each sampling point, and determine the coordinates X max and Y max ; Step 5) Update the scanning center coordinates: X center = X max Y center = Y max Step 6) Repeat steps S2 - S5 until the termination condition is met.

2. The communication optical axis autonomous correction method based on the nutation of the tracking point according to claim 1, wherein The sliding window average algorithm adopts a recursive calculation method: P a = (m1 + m2 + m3 + … + m a ) / a where P a is the recorded average power value; m a is the output power of each sampling; a is the number of samplings at one tracking point.

3. The communication optical axis autonomous correction method based on tracking point nutation according to claim 1, wherein It also includes a light spot centroid assisted positioning step: Extract the light spot image for the sampling points with the top 10% of the power; Calculate the centroid position: where G(x, y) is the gray value at the coordinate (x, y) in the image; Perform a weighted average of the centroid position and the point with the maximum power.

4. The communication optical axis autonomous correction method based on tracking point nutation according to claim 1, characterized in that The said K x and K y is the conversion coefficient from the fine tracking and fast steering mirror to the tracking camera, which is obtained by ground calibration. The pixel position relationship coefficient corresponding to the movement of the spot position mapped on the tracking camera caused by the movement of the fine tracking and fast steering mirror in the x and y directions is calibrated.

5. The method for autonomously correcting a communication optical axis based on the nutation of a tracking point according to claim 1, wherein The radius r of the nutation can adopt a method combining coarse and fine. Use a scanning radius of the order of mrad in the initial scan, and continuously reduce it to the order of urad in subsequent iterations to achieve fast and more accurate locking of the tracking point.

6. A communication optical axis autonomous correction system based on the nutation of tracking points, characterized in that It includes: An optical receiving component, including a mirror, a telescope system, and a beam splitter; A fine tracking fast steering mirror (FSM), whose parameters include: effective aperture φ30mm, deflection range ±5mrad, resolution 0.1μrad; A detection unit, including a tracking camera and an erbium-doped fiber amplifier (EDFA); A control unit, used to execute the method described in any one of claims 1 - 5.

7. The communication optical axis autonomous correction system based on the nutation of the tracking point according to claim 6, wherein The mirror is used to receive the signal light and perform two-dimensional rotational scanning; The telescope is composed of a lens group, and the lens group effectively guides the distant signal light to the subsequent optical path for further observation, analysis, or processing. The beam splitter can obtain the required reflected light and transmitted light by irradiating the beam onto the beam splitter, which are used as the signal light and the monitoring light respectively.

8. A satellite laser communication terminal, characterized in that, It includes the communication optical axis autonomous correction system described in claim 6 or 7.

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