Space laser communication fine tracking assembly

Abstract

The invention provides a space laser communication fine tracking assembly, which adopts a two-stage closed-loop control system to realize high-precision tracking, the first stage adopts a light spot centroid tracking technology and adjusts a light beam direction in real time through elements such as an FSM fast reflector and a CMOS camera to compensate miss distance, and the second stage adopts an optical fiber nutation coherent tracking technology to compensate miss distance. According to the system, the micro-electromechanical system (MEMS) mirror, the nutation device, photoelectric detection and the like are combined, the tracking precision is further improved through optical fiber coupling and frequency mixing processing, the FPGA programmable processor serves as a core to process images and signals and generate control signals to drive the reflector and the nutation device, accurate alignment of receiving and transmitting optical axes is ensured, and efficient and stable space laser communication is achieved. According to the invention, through combination of the first-stage light spot positioning tracking technology and the second-stage space nutation coherent tracking technology, precise control and tracking of the light spot position in space laser communication are realized, and the suppression bandwidth and precision of precise tracking are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of space laser communication technology, and specifically to a space laser communication precision tracking component. Background Technology

[0002] Space laser communication, which uses laser light as a carrier to carry the information to be transmitted, is an important component of building an integrated space-air information network. Establishing and maintaining a stable laser communication link is a prerequisite for realizing high-speed space laser communication, which requires an acquisition, aiming, and tracking (APT) system to align the transmitter with the receiver and achieve high-precision tracking during the communication time.

[0003] The composite axis tracking system resolves the contradiction between large-angle and high-accuracy tracking in space laser communication by combining fine and coarse tracking. It is currently a commonly used tracking system in space laser communication APT systems. The coarse tracking system, with its low accuracy, low tracking bandwidth, large rotation angle, and large field of view, is used to quickly capture the laser spot and stably guide it into the fine tracking field of view. The fine tracking system, with its high tracking bandwidth, small dynamic range, and high accuracy, compensates for the tracking residuals of coarse tracking, ensuring high-speed, high-precision aiming and tracking of the laser spot. The performance of the fine tracking system determines the performance of the composite axis control system.

[0004] The main factors affecting the performance of the precision tracking system are spot positioning error and satellite platform vibration interference. Detector noise, background light, and star interference can all degrade spot quality, thereby increasing spot positioning error and reducing the overall performance of the precision tracking system. There are two main sources of vibration on the satellite platform: one is vibration caused by the rigid motion of the satellite platform itself, and the other is vibration generated by the external space environment. Generally, these vibrations are characterized by low frequency and high amplitude, and high frequency and low amplitude.

[0005] Existing precision tracking systems mostly employ a single-level control architecture, relying on CMOS sensors for position feedback and using two microprocessors to handle centroid calculation and control algorithms respectively, with the optical sensor (FSM) acting as the actuator to achieve optical axis alignment. While this design achieves functional division to some extent, the communication latency between the two processors limits the improvement of the system's suppression bandwidth, making it difficult to meet the requirements of high-speed, high-precision communication. Furthermore, traditional centroid algorithms have limited anti-interference capabilities in complex environments, making it difficult to guarantee long-term stable performance in space applications. Summary of the Invention

[0006] The purpose of this invention is to address the issues of fine tracking suppression bandwidth and positioning accuracy in space laser communication APT systems. This invention provides a space laser communication fine tracking component employing a two-stage fine tracking closed-loop control system. These two stages are a first-stage fine tracking closed-loop control system and a second-stage fine tracking closed-loop control system, used to effectively improve the fine tracking interference suppression bandwidth. The first-stage fine tracking closed-loop control system utilizes spot centroid tracking technology and a high-speed CMOS detector suitable for space applications, achieving a 4K processing speed and reducing system latency. Camera image processing, spot positioning, and FSM closed-loop control are implemented on a single FPGA programmable processor, effectively reducing control latency and improving the fine tracking suppression bandwidth. An improved Fourier spot positioning algorithm is employed, considering both algorithm performance and computational latency, achieving high positioning accuracy while improving the anti-interference performance of the spot positioning algorithm. The second-stage precision tracking closed-loop control system employs fiber optic nutation coherent tracking technology to reduce the influence of background stray light and facilitates the integration of tracking and communication. It utilizes the optical energy signal detected by a space optical coherent communication receiver as feedback to improve the tracking signal-to-noise ratio. Simultaneously, it employs a MEMS mirror as the tracking actuator to achieve low power consumption and integration. Neural network PID controller parameters are used to enhance the adaptability of the control system.

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

[0008] A space laser communication precision tracking component is characterized by including a first-stage precision tracking closed-loop control system using spot centroid tracking technology, a second-stage precision tracking closed-loop control system using fiber optic nutation coherent tracking technology, and an FPGA programmable processor (5).

[0009] The first-stage precision tracking closed-loop control system includes an FSM fast reflector (1), a beam splitter (2), a CMOS camera (3), a first ADC analog-to-digital converter (4), and a first DAC digital-to-analog converter (6);

[0010] The beam splitter (2) is used to split the incident beam into a reflected beam and a transmitted beam. The CMOS camera (3) captures the spot image of the reflected beam and converts it into an analog electrical signal, which is then transmitted to the ADC analog-to-digital converter (4). The first ADC analog-to-digital converter (4) converts the analog signal transmitted by the CMOS camera into a digital signal and transmits it to the FPGA programmable processor (5). The FPGA programmable processor (5) receives the digital image signal transmitted by the first ADC analog-to-digital converter (4), performs image processing and spot positioning, calculates the miss distance, and then generates a control signal based on the miss distance. The first DAC digital-to-analog converter (6) converts the digital control signal generated by the FPGA back into an analog signal to drive the FSM fast reflector (1). The FSM fast reflector (1) adjusts the angle of the reflector according to the control signal, thereby changing the direction of the beam, compensating for the miss distance of the beam, and ensuring that the receiving and transmitting beam axes remain aligned.

[0011] The second-stage precision tracking closed-loop control system includes a MEMS mirror (7), a nutation device (8), an EDFA optical amplifier (9), an optical mixer (10), a photodetector (11), a second ADC analog-to-digital converter (12), a local oscillator laser (13), a PCT piezoelectric ceramic (14), and a second DAC digital-to-analog converter (15).

[0012] The nutation device (8) has a built-in single-mode fiber for fiber coupling of the incident spatial light signal, and performs nutation operation by driving the end face of the single-mode fiber to periodically couple the signal light; the EDFA optical amplifier (9) is located after the nutation device (8) and is used to amplify the weak light signal coupled through the fiber with low noise. After being mixed with the local oscillator light signal generated by the local oscillator laser (13) by the optical mixer (10), the mixed light signal is converted into an electrical signal by the photodetector (11), and then converted into an electrical signal by the second ADC analog-to-digital converter (12). The digital signal is input to the FPGA programmable processor (5). The FPGA programmable processor (5) receives the digital signal transmitted by the second ADC analog-to-digital converter (12), processes it, calculates the miss distance, and generates a control signal based on the miss distance to control the PCT piezoelectric ceramic (14) to perform nutation control on the nutation device (8). At the same time, it controls the MEMS mirror (7) based on the miss distance to align the light and light receiving axes. The second DAC digital-to-analog converter (15) converts the control signal of the FPGA programmable processor into an analog signal to drive the MEMS mirror (7).

[0013] Preferably, the CMOS in the first-stage precision tracking closed-loop control system is a 320×256 element short-wave infrared InGaAs array detector with four-channel output, supporting programmable windowing, a frame rate of not less than 2kHz, continuously adjustable integration time, an on-chip integrated temperature sensor, and a built-in TEC thermoelectric cooler to accurately control the chip's operating temperature. It meets the requirements of GM2 level in the General Specification for Semiconductor Optoelectronic Modules GJB 8120-2013, with an operating temperature range of -35℃ to 50℃ and a maximum operating time of 1000 hours. The single-event lockout threshold, measured according to QJ 10005-2008 Guidelines for Heavy Ion Single-Event Effect Testing of Aerospace Semiconductor Devices, is ≥50MeV, meeting the requirements for long-term space applications.

[0014] Preferably, the ADC analog-to-digital converter in the first-stage precision tracking closed-loop control system has a 14-bit output and a conversion rate of not less than 25 MSPS.

[0015] Preferably, the FSM fast reflector in the first-stage precision tracking closed-loop control system is driven by a piezoelectric ceramic, which is small in size, has a large driving force, high resolution, and fast response.

[0016] Preferably, the spot positioning and fine tracking closed-loop control method used in the first-stage fine tracking closed-loop control system implements camera image processing, spot positioning, and FSM closed-loop control on a single FPGA programmable processor, effectively reducing control latency and improving fine tracking suppression bandwidth. It includes the following steps:

[0017] (1) Spatial light is reflected by a fast reflector (FSM) onto the photosensitive surface of the CMOS camera;

[0018] (2) The CMOS camera converts the optical signal into an analog electrical signal, and then transmits the analog electrical signal to the ADC;

[0019] (3) The ADC converts the analog signal into a digital signal and transmits it to the FPGA programmable processor;

[0020] (4) The FPGA programmable processor performs image digital signal analysis and processing, realizes camera image processing, spot positioning, calculates the center position of the spot, further obtains the miss distance, and then realizes FSM closed-loop control based on the miss distance, and outputs control signals to DAC.

[0021] (5) The DAC converts the digital signal into an analog signal and transmits it to the FSM fast reflector so that it rotates to align the receiving and transmitting axes.

[0022] Preferably, the first-stage precision tracking closed-loop control system employs an improved Fourier phase-shift spot positioning algorithm, which considers both the performance and computational delay of the spot positioning algorithm, thereby improving its anti-interference performance while maintaining high positioning accuracy. It includes the following steps:

[0023] (1) The FPGA drives the CMOS camera and reads the image data transmitted from the ADC;

[0024] (2) An adaptive threshold segmentation algorithm is adopted to reduce background light interference;

[0025] (3) A sliding window is used to identify star points, and the maximum value window is used as the region of interest to eliminate star point interference;

[0026] (4) The Fourier phase shift algorithm is used to achieve sub-pixel level spot positioning.

[0027] The Fourier phase shift algorithm estimates the displacement difference between the sampled image and the ideal image by analyzing the phase frequency response curve of the sampled signal, based on the phase shift characteristics of the Fourier transform. From the Fourier phase shift characteristics, we can obtain the distance between the sampling origin and the true center point. The phase function relationship with the sampled signal is as follows:

[0028]

[0029] Therefore, the Fourier phase-shifting spot localization algorithm uses the maximum point of the spot image as the origin, performs DFT on its x-axis and y-axis sequences respectively, and calculates the offsets in the x-axis and y-axis directions to determine the center position of the spot. Due to the characteristics of the Fourier transform, the Fourier phase-shifting algorithm is not easily affected by DC components and is insensitive to low-frequency noise; the accuracy of the phase slope measurement depends on multiple frequency samples. It can be seen that if... If the error is caused by the random signal N(ω), then as shown in the following equation, the influence of low-frequency noise in the Fourier phase-shifting method is limited.

[0030]

[0031] The MEMS mirror in the second-stage precision tracking closed-loop control system has significantly reduced mass, size and power consumption. The highly integrated MEMS mirror can be mass-produced at low cost, enabling the miniaturization and integration of precision tracking components.

[0032] The nutation device in the second-stage precision tracking closed-loop control system uses a single-mode optical fiber to couple spatial optical signals. It uses a small-range nutation optical fiber to find and continuously approach the peak optical power. It is relatively insensitive to atmospheric scintillation and fading, easily achieves integrated tracking and communication, and is not easily affected by background stray light.

[0033] Preferably, the PCT piezoelectric ceramic driven nutation device in the second-stage precision tracking closed-loop control system performs high-frequency nutation.

[0034] Preferably, the EDFA optical amplifier in the second-stage precision tracking closed-loop control system is a low-noise optical amplifier that amplifies weak optical signals with low noise.

[0035] Preferably, the optical mixer in the second-stage fine tracking closed-loop control system coherently mixes the signal light with the local oscillator light and obtains the intensity envelope fluctuation of the signal light using the coherent demodulation method. This fully leverages the advantages of high coherent detection sensitivity and good filtering performance to improve the tracking signal-to-noise ratio, and the high tracking bandwidth enables higher tracking accuracy.

[0036] Preferably, neural network PID controller parameters are used to improve the adaptability of the control system. Traditional PID controllers struggle to control complex nonlinear controlled objects, while deep neural networks can achieve nonlinear mapping between input and output, and possess strong learning and adaptive capabilities. A five-layer BP neural network is used to tune the PID parameters. The actual input and output of the control system, as well as their error, are used as network inputs, and the three control parameters of the PID controller are used as network outputs. The variance of the input and output is used as the error function to learn the network.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1) This invention employs a two-stage precision tracking system. By combining first-stage spot positioning and tracking technology with second-stage spatial nutation coherent tracking technology, it achieves precise control and tracking of the spot position in space laser communication. This two-stage system architecture effectively improves the suppression bandwidth and accuracy of precision tracking, solving the problem that traditional single-stage systems cannot simultaneously meet the requirements of high bandwidth and high accuracy.

[0039] 2) The first-stage fine tracking system employs spot centroid tracking technology, implementing camera image processing, spot positioning, and FSM closed-loop control on a single FPGA programmable processor, effectively reducing control latency and improving the fine tracking suppression bandwidth. Simultaneously, an improved Fourier phase-shift spot positioning algorithm is used, considering both spot positioning accuracy and computational latency, ensuring high positioning accuracy while enhancing the anti-interference capability of the spot positioning algorithm.

[0040] 3) The second-stage precision tracking system adopts fiber optic nutation tracking technology, using the nutation device as a position detector to reduce the influence of background stray light, and using the light energy signal detected by the spatial optical coherent communication receiver as feedback to improve the tracking signal-to-noise ratio. At the same time, MEMS mirrors are used as tracking actuators to achieve low power consumption and integration.

[0041] 4) A neural network PID controller was introduced. By utilizing the nonlinear mapping capability and self-learning capability of the neural network, dynamic tuning of the PID control parameters was achieved, which improved the adaptability and control accuracy of the control system to complex nonlinear controlled objects. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0043] Figure 2 This is the control flowchart of the present invention.

[0044] Figure 3 This is a flowchart of the light spot positioning method of the present invention.

[0045] Figure 4 This is a block diagram of the ATP control system.

[0046] Figure 5 This is a schematic diagram of the Fourier phase shift algorithm.

[0047] Figure 6 This is a schematic diagram of a BP neural network. Detailed Implementation

[0048] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and detailed descriptions. The following embodiments or drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0049] like Figure 1 As shown, this embodiment of a high-performance space laser communication precision tracking component adopts a two-stage precision tracking closed-loop control system, which effectively improves the precision tracking suppression bandwidth. The first-stage precision tracking closed-loop control system includes an FSM fast reflector (1), a beam splitter (2), a CMOS camera (3), an ADC analog-to-digital converter (4), an FPGA programmable processor (5), and a DAC digital-to-analog converter (6). The second-stage precision tracking closed-loop control system includes a MEMS mirror (7), a nutation device (8), an EDFA optical amplifier (9), an optical mixer (10), a photodetector (11), an ADC analog-to-digital converter (12), a local oscillator laser (13), a PCT piezoelectric ceramic (14), and a DAC digital-to-analog converter (15).

[0050] In this embodiment, the first-stage precision tracking closed-loop control system adopts spot positioning and tracking technology. The CMOS camera is used for laser imaging and converts the light signal into an analog electrical signal, which is then transmitted to the ADC digital-to-analog converter. The ADC converts the analog signal transmitted by the CMOS camera into a digital signal and transmits it to the FPGA programmable processor. The FPGA programmable processor drives the CMOS camera, processes the obtained image information data, calculates the spot position to calculate the miss distance, and then controls the FSM fast reflector to align the light and light receiving axes according to the miss distance. The DAC converts the control signal of the FPGA programmable processor into an analog signal to drive the FSM fast reflector.

[0051] In this embodiment, the second-stage precision tracking closed-loop control system adopts spatial nutation coherent tracking technology. In the nutation device, a single-mode fiber couples the incident spatial light, converting the spatial light signal into an optical fiber signal. The end face of the single-mode fiber is driven to nutate, periodically coupling the signal light. An EDFA optical amplifier amplifies the weak light signal with low noise. An optical mixer mixes the amplified optical signal with the local oscillator light generated by the local oscillator laser. A photodetector converts the optical signal into an electrical signal, and an ADC analog-to-digital converter converts the analog signal from the photodetector into a digital signal. An FPGA drives a PCT piezoelectric ceramic to control the nutation of the nutation device and processes the signal from the photodetector, calculates the miss distance, and controls the MEMS mirror to align the receiving and emitting axes based on the miss distance. A DAC digital-to-analog converter converts the control signal from the FPGA programmable processor into an analog signal to drive the MEMS mirror.

[0052] In this embodiment, the CMOS in the first-stage precision tracking closed-loop control system is a 320×256 element short-wave infrared InGaAs array detector. This detector mainly consists of an InGaAs focal plane array detector chip, a TEC thermoelectric cooler, a temperature sensor, a hermetically sealed housing, and a glass window. The InGaAs focal plane array detector chip has a hybrid structure, formed by flip-chip interconnection of a high-sensitivity InGaAs detector array (PDA) and a high-speed, low-noise CMOS readout circuit (ROIC). The CMOS chip consists of 320x256 readout circuits, each containing 256 pixel channels. Each channel includes a charge amplification circuit, a CDS gain circuit, a sample-and-hold circuit, a column buffer circuit, and control circuit logic. The input stage adopts a CTIA structure with multiple charge-to-voltage conversion gain levels and integrated anti-halo and correlated double sampling (CDS) noise reduction functions. This detector features a large array with small pixels, high imaging resolution, four-channel output, programmable windowing, continuously adjustable integration time, an on-chip integrated temperature sensor, and a built-in TEC thermoelectric cooler to accurately control the chip's operating temperature. It meets the GM2 level requirements of the General Specification for Semiconductor Optoelectronic Modules (GJB8120-2013), with an operating temperature range of -35℃ to 50℃ and a maximum operating time of 1000 hours. It exhibits good radiation resistance, with a single-event lockout threshold ≥50MeV as measured according to the Guidelines for Heavy Ion Single-Event Effect Testing of Aerospace Semiconductor Devices (QJ10005-2008), meeting the requirements for long-term space applications. In this embodiment, the CMOS uses a 32×32 element window, a frame rate of 4kHz, and an operating clock of 12.5MHz.

[0053] In this embodiment, the ADC (Digital-to-Analog Converter) in the first-stage precision tracking closed-loop control system is the AD9245 chip from Analog Devices, a high-precision, high-speed, low-power chip suitable for processing small signals, with a 14-bit output that meets the accuracy requirements. In this embodiment, the ADC sampling frequency is 25 MSPS.

[0054] In this embodiment, the FPGA programmable processor is the Xilinx Kintex-7 series XC7K325T-2FFG900I. The product includes CLB modules that can be used to implement conventional logic and distributed RAM. In addition, it includes programmable modules such as I / O, BlockRAM, DSP, MMCM, and GTX, which can easily implement various specific applications.

[0055] In this embodiment, the FSM fast reflector in the first-stage precision tracking closed-loop control system uses the PI S-330 model fast reflector, which has a resolution of 20 nrad, excellent position stability, sub-millisecond response time, and a linear error of less than 0.2%. It employs a piezoelectric ceramic actuator made of all-ceramic insulating material, resulting in a longer service life and insensitivity to humidity and high operating temperatures.

[0056] In this embodiment, the ADC in the first-stage fine tracking closed-loop control system uses Analog Devices' 16-bit digital-to-analog converter chip AD5766BCPZ-RL7 to generate analog control signals to control the two fine tracking FSM fast reflectors.

[0057] The first-stage fine-tracking closed-loop control system employs a spot-positioning fine-tracking closed-loop control method that implements camera image processing, spot positioning, and FSM closed-loop control on a single FPGA programmable processor, effectively reducing control latency and improving fine-tracking suppression bandwidth. It includes the following steps:

[0058] (1) Spatial light is reflected by a fast reflector (FSM) onto the photosensitive surface of the CMOS camera;

[0059] (2) The CMOS camera converts the optical signal into an analog electrical signal, and then transmits the analog electrical signal to the ADC;

[0060] (3) The ADC converts the analog signal into a digital signal and transmits it to the FPGA programmable processor;

[0061] (4) The FPGA programmable processor performs image digital signal analysis and processing, realizes camera image processing, spot positioning, calculates the center position of the spot, further obtains the miss distance, and then realizes FSM closed-loop control based on the miss distance, and outputs control signals to DAC.

[0062] (5) The DAC converts the digital signal into an analog signal and transmits it to the FSM fast reflector so that its rotation angle is used to align the receiving and transmitting axes.

[0063] The first-stage precision tracking closed-loop control system employs an improved Fourier phase-shift spot positioning algorithm. This algorithm considers both performance and computational delay, achieving high positioning accuracy while enhancing its anti-interference capabilities. It includes the following steps:

[0064] (1) The FPGA drives the CMOS camera and reads the image data transmitted from the ADC;

[0065] (2) An adaptive threshold algorithm is used to reduce background light interference;

[0066] (3) A sliding window is used to identify star points, and the maximum value window is used as the region of interest to eliminate star point interference;

[0067] (4) The Fourier phase shift algorithm is used to achieve sub-pixel level spot positioning.

[0068] The Fourier phase-shift algorithm, based on the phase-shift characteristics of the Fourier transform, estimates the displacement difference between the sampled image and the ideal image by analyzing the phase-frequency response curve of the sampled signal, thereby obtaining sub-pixel-level positioning accuracy. Let the real symmetric function be f(ξ), then its phase-frequency response curve can be obtained. When we sample a real symmetric function, we often cannot sample exactly its center of symmetry, such as... Figure 5 As shown, the extreme points of the sampling are taken as zero points, and it is assumed that they deviate from the center of symmetry. Therefore, the relationship between the actual sampling function and the ideal sampling function can be obtained as follows:

[0069]

[0070] From the time-shifting properties of the Fourier transform, we can obtain:

[0071]

[0072] Sampling C(x) at N points yields C(n), and performing a discrete Fourier transform on it yields C(k). Given... We can obtain:

[0073]

[0074] Therefore, we can obtain the offset of the extreme point relative to the center point by performing a DFT on the sampling function, and thus obtain the center position.

[0075] An ideal light spot exhibits a Gaussian energy distribution on a plane perpendicular to the propagation direction, thus its energy distribution is symmetrical along both the x and y axes. A CMOS detector samples this energy in the spatial domain, resulting in a symmetrical ideal light spot sampling signal. We select the extreme points of the sampling signal and perform DFT along both the x and y axes to obtain the offsets of these extreme points relative to the center point in both directions, thereby determining the center position of the light spot. The Fourier phase-shift algorithm achieves sub-pixel level positioning accuracy and is less susceptible to DC offset and low-frequency noise.

[0076] The MEMS mirror in the second-stage precision tracking closed-loop control system has significantly reduced mass, size and power consumption. The highly integrated MEMS mirror can be mass-produced at low cost, enabling the miniaturization and integration of precision tracking components.

[0077] The nutation device in the second-stage precision tracking closed-loop control system uses a single-mode optical fiber to couple spatial optical signals. It uses a small-range nutation optical fiber to find and continuously approach the peak optical power. It is relatively insensitive to atmospheric scintillation and fading, easily achieves integrated tracking and communication, and is not easily affected by background stray light.

[0078] The PCT piezoelectric ceramic driven nutation device in the second-stage precision tracking closed-loop control system performs high-frequency nutation.

[0079] The EDFA optical amplifier in the second-stage precision tracking closed-loop control system is a low-noise optical amplifier that amplifies weak optical signals with low noise.

[0080] The optical mixer in the second-stage fine tracking closed-loop control system coherently mixes the signal light with the local oscillator light and obtains the intensity envelope fluctuation of the signal light by using coherent demodulation. It fully leverages the advantages of high coherent detection sensitivity and good filtering performance to improve the tracking signal-to-noise ratio, and has a high tracking bandwidth, which can achieve higher tracking accuracy.

[0081] The high-performance space laser communication precision tracking component employs neural network PID controller parameters to improve the adaptability of the control system. Traditional PID controllers struggle to control complex nonlinear controlled objects, while deep neural networks can achieve nonlinear mapping between input and output, and possess strong learning and adaptive capabilities. A five-layer BP neural network is used to tune the PID parameters; the BP neural network is a multi-layer feedforward neural network that uses the back propagation algorithm. Figure 6 The actual inputs rin(k), output youout(k), and their error error(k) of the control system shown are used as network inputs, and the three control parameters of the PID controller are used as network outputs. The variance of the input and output is used as the error function to learn the network. The sigmoid function is selected as the activation function.

[0082]

[0083] This invention significantly improves the tracking suppression bandwidth by combining a two-stage precision tracking system. The first-stage system enhances basic tracking performance by optimizing the spot localization algorithm and reducing control delay; the second-stage system further enhances tracking accuracy and stability through spatial nutation coherent tracking technology. Together, these two systems deliver bandwidth performance far exceeding expectations. The introduction of the improved Fourier phase-shift spot localization algorithm and fiber optic nutation tracking technology significantly enhances the system's resistance to interference factors such as background stray light and atmospheric scintillation. Simultaneously, these technologies improve system stability and reliability, enabling the system to maintain efficient and stable communication performance in complex and variable space environments. By employing highly integrated MEMS mirrors and low-power hardware design, the precision tracking component achieves miniaturization, integration, and low power consumption. This not only reduces the overall system cost but also improves portability and deployability, providing strong support for the widespread application of space laser communication. The application of a neural network PID controller allows the control system to dynamically adjust PID parameters according to actual operating conditions, improving the system's adaptability and control accuracy. This is of great significance for improving the reliability and stability of space laser communication.

[0084] Comparative Example 1:

[0085] The camera and fine tracking are accomplished by two software programs, which are located on two separate FPGA programmable processors. There is a significant transmission delay between the two programs, resulting in a low fine tracking suppression bandwidth, which cannot achieve higher performance.

[0086] Comparative Example 2:

[0087] The spot localization algorithm uses a relatively simple centroid algorithm. When faced with spot images distorted by factors such as atmospheric turbulence, thermal deformation of the optomechanical structure, and background light, it cannot effectively locate the center of the spot, resulting in a large positional error. It cannot adapt to the problems that may arise from long-term operation in orbit.

[0088] Matters not covered in this invention are common knowledge.

[0089] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A space laser communication precision tracking component, characterized in that: It includes a first-stage fine tracking closed-loop control system using spot centroid tracking technology, a second-stage fine tracking closed-loop control system using fiber optic nutation coherent tracking technology, and an FPGA programmable processor (5); The first-stage precision tracking closed-loop control system includes an FSM fast reflector (1), a beam splitter (2), a CMOS camera (3), a first ADC analog-to-digital converter (4), and a first DAC digital-to-analog converter (6); The beam splitter (2) is used to split the incident beam into a reflected beam and a transmitted beam. The CMOS camera (3) captures the spot image of the reflected beam and converts it into an analog electrical signal, which is then transmitted to the ADC analog-to-digital converter (4). The first ADC analog-to-digital converter (4) converts the analog signal transmitted by the CMOS camera into a digital signal and transmits it to the FPGA programmable processor (5). The FPGA programmable processor (5) receives the digital image signal transmitted by the first ADC analog-to-digital converter (4), performs image processing and spot positioning, calculates the miss distance, and then generates a control signal based on the miss distance. The first DAC digital-to-analog converter (6) converts the digital control signal generated by the FPGA back into an analog signal to drive the FSM fast reflector (1). The FSM fast reflector (1) adjusts the angle of the reflector according to the control signal, thereby changing the direction of the beam, compensating for the miss distance of the beam, and ensuring that the receiving and transmitting beam axes remain aligned. The second-stage precision tracking closed-loop control system includes a MEMS mirror (7), a nutation device (8), an EDFA optical amplifier (9), an optical mixer (10), a photodetector (11), a second ADC analog-to-digital converter (12), a local oscillator laser (13), a PCT piezoelectric ceramic (14), and a second DAC digital-to-analog converter (15). The nutation device (8) incorporates a single-mode fiber for fiber coupling of the incident spatial light signal and performs nutation operation on the end face of the single-mode fiber to periodically couple the signal light. The EDFA optical amplifier (9) is located after the nutation device (8) and is used for low-noise amplification of the weak light signal coupled through the fiber. After being mixed with the local oscillator light signal generated by the local oscillator laser (13) by the optical mixer (10), the mixed light signal is converted into an electrical signal by the photodetector (11), and then converted into a digital signal by the second ADC analog-to-digital converter (12). The digital signal is transmitted to the FPGA programmable processor (5). The FPGA programmable processor (5) receives the digital signal transmitted by the second ADC analog-to-digital converter (12), processes it, calculates the miss distance, and generates a control signal based on the miss distance to control the PCT piezoelectric ceramic (14) to perform nutation control on the nutation device (8). At the same time, it controls the MEMS mirror (7) based on the miss distance to align the light and light receiving axes. The second DAC digital-to-analog converter (15) converts the control signal of the FPGA programmable processor into an analog signal to drive the MEMS mirror (7).

2. The space laser communication precision tracking component according to claim 1, characterized in that: The CMOS camera (3) is a 320×256 element short-wave infrared InGaAs array detector with four-channel output, programmable windowing, frame rate not less than 2KHz, continuously adjustable integration time, on-chip integrated temperature sensor and TEC thermoelectric cooler. It meets the GM2 level requirements in GJB 8120-2013 specification, with an operating temperature range of -35℃ to 50℃ and a single-particle lockout threshold ≥50MeV.

3. The space laser communication precision tracking component according to claim 1, characterized in that: The first-stage fine tracking closed-loop control system adopts a spot positioning fine tracking closed-loop control method, which includes implementing camera image processing, spot positioning and FSM closed-loop control on FPGA, and adopting an improved Fourier phase-shift spot positioning algorithm to improve positioning accuracy and anti-interference performance.

4. The space laser communication precision tracking component according to claim 2, characterized in that: The spot localization algorithm includes the following steps: (1) The FPGA drives the CMOS camera and reads the image data transmitted from the ADC; (2) An adaptive threshold segmentation algorithm is adopted to reduce the influence of background light; (3) Use a sliding window to select the region with the highest grayscale as the region of interest to eliminate star point interference; (4) The Fourier phase shift algorithm is used to achieve sub-pixel spot positioning and has strong anti-interference ability.

5. The space laser communication precision tracking component according to claim 1, characterized in that, The MEMS mirror (7) in the second-stage precision tracking closed-loop control system has significantly reduced mass, volume and power consumption. The nutation device (8) couples spatial optical signals through single-mode fiber and uses PCT piezoelectric ceramic (14) for high-frequency nutation. The EDFA optical amplifier (9) is a low-noise optical amplifier. The optical mixer (10) achieves coherent demodulation to improve the tracking signal-to-noise ratio and bandwidth.

6. The space laser communication precision tracking component according to claim 1, characterized in that, It also includes a neural network PID controller, which uses a five-layer BP neural network to tune the PID parameters in order to improve the adaptability of the control system. The activation function of the BP neural network is the Sigmoid function.

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