A satellite laser link anti-sun interception and communication transceiver system

Abstract

This invention discloses a satellite laser link anti-solar interference tracking and communication transceiver system, belonging to the field of space laser communication. The system includes a narrowband optical window, a telescope, a fine tracking mechanism, a beam splitter, an objective lens, a four-quadrant detector and processing circuitry, a coupler, and a laser. By innovatively using spatial light filtering combined with signal light intensity modulation, the four-quadrant detector serves as the system's acquisition, tracking, and communication unit. It receives mid-to-long-wave infrared intensity-modulated signal light from the target terminal, filtering the solar background light entering the four-quadrant detector. Combined with the space narrowband filter window in the system, it achieves the three major functions of laser link acquisition, tracking, and communication, and possesses anti-solar interference capability.

Description

Technical Field

[0001] This invention relates to a satellite laser link anti-solar interference detection and communication transceiver system, belonging to the field of space laser communication. Background Technology

[0002] With the continuous breakthroughs in on-orbit verification of satellite laser communication technology and the advancement of reliability and availability improvement, laser terminals, represented by high-orbit Internet satellites, have begun to undertake the task of all-weather business data transmission. However, due to the lack of effective means of anti-solar interference tracking and communication, laser terminals currently adopt an active avoidance strategy during periods of solar interference (the angle between the solar incidence angle and the communication line of sight is less than 3°). Solar interference mainly affects laser terminals in two ways: (1) The sun, as a strong noise source, reduces the signal-to-noise ratio or even annihilates the signal, leading to a decrease in tracking and communication performance of the laser terminal or even loss of function; (2) The sun, as a strong heat source, will cause a significant temperature rise or a large gradient when the external heat flow of the sun enters the telescope along the laser terminal channel during solar interference. This harsh thermal environment will inevitably affect the coaxiality, astigmatism angle and image quality of the laser terminal. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a satellite laser link anti-solar interference acquisition, tracking and communication transceiver system. Based on a four-quadrant detector, it realizes the three major functions of laser terminal acquisition, tracking and communication, and has the ability to work against solar interference.

[0004] The technical solution of this invention is:

[0005] A satellite laser link anti-solar interference tracking and communication transceiver system includes a narrowband optical window, a telescope, a fine tracking mechanism, a beam splitter, an objective lens, a four-quadrant detector and processing circuit, a coupler and a laser;

[0006] The laser is used to generate the emitted signal light;

[0007] The coupler converts the emitted signal light from an optical fiber beam into a spatial beam, and then transmits it to the beam splitter.

[0008] The beam splitter transmits the emitted signal light to the fine tracking mechanism and transmits the target signal light reflected by the fine tracking mechanism to the objective lens;

[0009] The objective lens focuses the target light signal and forms a light spot on the photosensitive surface of the four-quadrant detector.

[0010] The narrowband optical window filters the target signal light emitted by the target terminal, and the effective target signal light within the bandwidth range is transmitted to the telescope.

[0011] The telescope converges the target signal light and transmits it to the reflector, and expands the transmitted signal light emitted from the reflector and transmits it to the target terminal.

[0012] The reflector reflects the target signal light from the telescope into the fine tracking mechanism, and reflects the transmitted signal light from the fine tracking mechanism into the telescope.

[0013] The precision tracking mechanism tracks the incident target signal light and adjusts it according to the received angular offset to keep the target signal light locked within the field of view.

[0014] The four-quadrant detector performs four-quadrant photoelectric conversion on the received target optical signal, forming four electrical signals which are then transmitted to the processing circuit.

[0015] The processing circuit receives four electrical signals, performs position error calculation and communication signal extraction, and then controls the precision tracking mechanism to perform reverse compensation based on the angle offset obtained from the position error calculation, thereby achieving target acquisition and tracking.

[0016] Furthermore, the processing circuit calculates the position of the light spot based on the proportion of energy distribution in each quadrant of the four-quadrant detector to determine the spatial position of the target, specifically:

[0017] The tracking controller establishes a Cartesian coordinate system with the center of the four-quadrant detector as the origin. The specific location of the detected target is reduced to the deviation of the light spot relative to the center within the detector's Cartesian coordinate system. The magnitude of this deviation is:

[0018]

[0019] Among them, P A P B P C P D I1 represents the optical power of the light spot in the four quadrants, I2, I3, and I4 represent the photocurrent generated in each quadrant of the four-quadrant detector, and Δx and Δy represent the offset of the light spot relative to the center in the X-axis direction and the Y-axis direction, respectively, which are the position errors and also give the position of the light spot.

[0020] Furthermore, based on the position error, the tracking controller calculates the angular offset of the received beam, specifically as follows:

[0021]

[0022] Where Δθ represents the angle between the Z-axis and the incident direction of the beam, and f′ represents the focal length of the objective lens. x , Δθ y This indicates the angular offset of the light beam in the X-axis direction and the angular offset in the Y-axis direction.

[0023] Furthermore, the optical signals generated in each quadrant of the four-quadrant detector are first amplified by the TIA circuit, then shaped, and the deviation of the light spot relative to the center is calculated.

[0024] Furthermore, the processing circuit extracts the communication signal by performing analog-to-digital conversion on the signals of each quadrant of the four-quadrant detector, followed by power division processing, equalization, clock data recovery, soft decision and decoding to recover the baseband signal.

[0025] Furthermore, the performance requirements for the laser are as follows: wavelength stability less than 0.1 pm, output power greater than 1 W, power stability less than 0.5 dB, linewidth less than 100 kHz, and relative intensity noise less than -140 dB / Hz.

[0026] Furthermore, the four-quadrant detector is of the HgCdTe type, with the following performance requirements: quantum efficiency greater than 60%, response time not greater than 10 ns, dynamic range not less than 40 dB, and dark current less than 10 dB. -4 A / cm 2 .

[0027] Furthermore, the optical path of the transmitted signal light is as follows: after passing through the coupler, the transmitted signal light completes the conversion from an optical fiber beam to a spatial beam, and after being transmitted through a beam splitter, reflected by a fine tracking mechanism and a reflector, it is sent into the telescope, and after being expanded by the telescope, it is sent to the target terminal.

[0028] Furthermore, the optical path of the target signal light is as follows: the target signal light from the target terminal is filtered through a narrow-band optical window, and the effective signal light is incident on the telescope. After the telescope's beam shrinking and the reflector reversing the optical path, it is reflected by the fine tracking mechanism, reflected by the beam splitter, and converged by the objective lens before reaching the four-quadrant detector. The four-quadrant detector calculates the angular offset and sends it to the fine tracking mechanism. The fine tracking mechanism calculates the execution quantity based on the angular offset and provides real-time compensation for the tracking deviation to achieve acquisition and tracking. At the same time, the four-quadrant detector and processing circuit effectively filter the modulated optical signal and complete demodulation and decoding.

[0029] Furthermore, the narrow-band optical window suppresses solar background light outside the center wavelength of the target optical signal by ±3nm, with a suppression ratio of 40dB.

[0030] The advantages of this invention compared to the prior art are:

[0031] (1) The present invention uses a four-quadrant detector as the system’s acquisition, tracking and communication unit, replacing the traditional discrete multi-optical axis system, and realizes that the acquisition light, tracking light and communication light are strictly coaxial.

[0032] (2) The present invention uses a four-quadrant detector as the system’s capture, tracking and communication unit to receive the medium and long-wave infrared intensity modulation signal light sent by the target terminal, thereby filtering the solar background light entering the four-quadrant detector. Combined with the space narrowband filter window in the system, the laser link can achieve anti-solar interference capture, tracking and communication. Attached Figure Description

[0033] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0034] Figure 1 This is an optical path diagram of a satellite laser link anti-solar interference detection and communication transceiver system according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the satellite laser link anti-sun interception and communication transceiver system according to an embodiment of the present invention. Detailed Implementation

[0036] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0037] To address the challenge of laser terminals being unable to acquire, track, and communicate during solar interference, this invention presents a satellite laser link anti-solar interference acquisition and communication system. Employing mid-to-long-wave infrared bands, it innovatively utilizes a single four-quadrant detector to achieve laser terminal acquisition, tracking, and communication functions, while also possessing anti-solar interference capabilities.

[0038] The system is like Figure 1 As shown, it includes a narrow-band light window (i.e. Figure 1 The system comprises a narrowband filter, a telescope, a fine tracking mechanism, a beam splitter, an objective lens, a four-quadrant detector (QD) and processing circuitry, a coupler, and a laser. The tracking and communication wavelength is 10.6 μm, and the QD is an HgCdTe type four-quadrant detector. The two core components of this system are a 10.6 μm laser and an HgCdTe type QD detector.

[0039] When selecting a 10.6μm laser, the main specifications should meet the following requirements: wavelength stability less than 0.1pm, output power greater than 1W, power stability less than 0.5dB, linewidth less than 100kHz, and relative intensity noise less than -140dB / Hz.

[0040] When selecting an HgCdTe type four-quadrant detector, the main specifications must meet the following requirements: quantum efficiency greater than 60%, response time not greater than 10 ns, dynamic range not less than 40 dB, and dark current less than 10 ns. -4 A / cm 2 .

[0041] Transmitted optical signal flow: After passing through the coupler, the transmitted signal light completes the conversion from fiber optic beam to spatial beam. Then, after being transmitted through the beam splitter, reflected by the fine tracking mechanism and the reflector, it is sent into the telescope. After being expanded by the telescope, it is sent to the target terminal.

[0042] Received optical signal flow: The 10.6μm wavelength signal light from the target terminal is filtered through a narrowband optical window, and the effective signal light within the bandwidth is converged to the telescope. This system is designed with a narrowband optical window bandpass filtering range of 10.6μm ± 3nm and an out-of-band suppression ratio of 40dB. The signal light passing through the narrowband optical window is then focused by the telescope's beam convergence and reflector, reflected by the precision tracking mechanism, reflected by the beam splitter, and converged by the objective lens. The precisely tracked and stabilized beam ensures that the beam effectively reaches the photosensitive surface of the four-quadrant detector. The detector calculates the deviation of the tracked target light signal, and the precision tracking mechanism receives the detector's error signal in real time, keeping the beam locked within the precision tracking field of view to ensure the light spot is always stably aligned with the center of the subsequent optical path, thus achieving the tracking function. Simultaneously, the four-quadrant detector and its processing circuit effectively filter the modulated optical signal, complete demodulation and decoding, and realize the communication function.

[0043] The principle of this system is as follows: Figure 2 As shown, the tracking method is as follows: the signal light collected by the four-quadrant detector is amplified by the pre-amplifier circuit TIA and shaped by the analog signal processing circuit to generate a direction error signal. The optical signal is then converted from analog to digital to extract the position error, which is used as a feedback signal to execute tracking control. The spot position detection steps are as follows:

[0044] 1) After the laser beam passes through the objective lens, it forms a light spot on the photosensitive surface of the four-quadrant detector. Since the light power falling in each quadrant is proportional to the area of ​​the light spot in that quadrant, the brightness center position of the target can be calculated based on the proportion of energy distribution in each quadrant, so as to determine the spatial position of the target.

[0045] 2) Establish a rectangular coordinate system with the center of the four-quadrant detector as the origin. The specific orientation of the detected target in the detector's rectangular coordinate system can be reduced to calculating the magnitude and direction of the deviation of the light spot from the center of the photodetector in each of the four quadrants. The calculation method is as follows:

[0046]

[0047] Among them, P A P B P C P D I1, I2, I3, and I4 represent the optical power of the light spot in the four quadrants, and I1, I2, I3, and I4 represent the photocurrent generated in each quadrant of the four-quadrant detector.

[0048] 3) After calculation, the offsets Δx and Δy in the X and Y directions are output. Based on the offset of the light spot position, the offset angle of the received beam can be calculated. The precision tracking control unit calculates the actuation parameters based on the obtained position and angle offsets, which are used to drive the actuator for tracking control, realizing the system's capture and tracking functions. The beam angle offset is calculated as follows:

[0049]

[0050] Where Δθ represents the angle between the z-axis and the incident direction of the beam, f′ represents the focal length of the objective lens, Δx represents the distance between the center of the spot and the y-axis, and Δy represents the distance between the center of the spot and the x-axis.

[0051] The communication method of this system is as follows: the signals of each quadrant of the four-quadrant detector are converted by A / D to obtain the optical power value of each quadrant for position error signal calculation. At the same time, the power is distributed to the communication receiver, and then the baseband signal is recovered after equalization, clock / data recovery, soft decision and decoding, so as to realize the communication reception function.

[0052] The above method enables a single branch to perform three functions: acquisition, tracking, and communication. This replaces the traditional method of using multiple beam splitters and fast mirrors to continuously adjust the beam splitting ratio, which divides the signal into acquisition and tracking branches and communication branches, effectively reducing the systematic error caused by coaxiality issues.

[0053] This system is designed with a telescope having an effective aperture of 100mm and a narrow-band filter optical window, achieving a suppression ratio of 40dB for solar background light beyond the center wavelength of ±3nm. The receiving field of view of the four-quadrant detector branch is designed to be 300μrad. Based on the above specifications, the system faces a solar constant illuminance of 1380W / m². 2 At normal incidence, the solar background light power detected by the four-quadrant detector is approximately -50 dBm, which is below the QD detector's saturation threshold of -30 dBm. Further electrical filtering of the received optical signal extracts the useful intensity-modulated optical signal, which is then used for demodulation and decoding.

[0054] During communication detection, the signals from each quadrant of the four-quadrant detector are converted by an A / D converter, and then added together in the digital domain to obtain the data signal. This data signal undergoes equalization, clock / data recovery, and decoding. To ensure communication and tracking stability, temperature noise compensation for the four-quadrant detector is also required. The received signal is first converted to a digital signal by a high-speed A / D converter and then transmitted to the FPGA for digital demodulation. In the FPGA, the data signal is first equalized by a digital filter to eliminate inter-symbol interference caused by the channel and the preceding receiving circuit. The equalized signal is then clocked using a digital algorithm and resampled to synchronize the received signal clock with the signal processor's clock. Finally, a soft-decision method is used to recover the data and perform subsequent decoding and other data processing. Using soft-decision circuitry improves the receiving sensitivity by approximately 2dB compared to traditional hard-decision circuits. Due to the low frequency of the tracking and data signals, the high-resolution analog-to-digital converter chip and digital processing circuitry used in this scheme are easy to implement.

[0055] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A satellite laser link anti-solar interference detection and communication transceiver system, characterized in that, It includes a narrowband optical window, a telescope, a fine tracking mechanism, a beam splitter, objective lenses, a four-quadrant detector and processing circuitry, couplers, and a laser; The laser is used to generate the emitted signal light; The coupler converts the emitted signal light from an optical fiber beam into a spatial beam, and then transmits it to the beam splitter. The beam splitter transmits the emitted signal light to the fine tracking mechanism and transmits the target signal light reflected by the fine tracking mechanism to the objective lens; The objective lens focuses the target light signal and forms a light spot on the photosensitive surface of the four-quadrant detector. The narrowband optical window filters the target signal light emitted by the target terminal, and the effective target signal light within the bandwidth range is transmitted to the telescope. The telescope converges the target signal light and transmits it to the reflector, and expands the transmitted signal light emitted from the reflector and transmits it to the target terminal. The reflector reflects the target signal light from the telescope into the fine tracking mechanism, and reflects the transmitted signal light from the fine tracking mechanism into the telescope. The precision tracking mechanism tracks the incident target signal light and adjusts it according to the received angular offset to keep the target signal light locked within the field of view. The four-quadrant detector performs four-quadrant photoelectric conversion on the received target optical signal, forming four electrical signals which are then transmitted to the processing circuit. The processing circuit receives four electrical signals, performs position error calculation and communication signal extraction, and then controls the precision tracking mechanism to perform reverse compensation based on the angle offset obtained from the position error calculation, thereby achieving target acquisition and tracking.

2. The satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The processing circuit calculates the position of the light spot based on the proportion of energy distribution in each quadrant of the four-quadrant detector, in order to determine the spatial position of the target. Specifically: The tracking controller establishes a Cartesian coordinate system with the center of the four-quadrant detector as the origin. The specific location of the detected target is reduced to the deviation of the light spot relative to the center within the detector's Cartesian coordinate system. The magnitude of this deviation is: Among them, P A P B P C P D I1 represents the optical power of the light spot in the four quadrants, I2, I3, and I4 represent the photocurrent generated in each quadrant of the four-quadrant detector, and Δx and Δy represent the offset of the light spot relative to the center in the X-axis direction and the Y-axis direction, respectively, which are the position errors and also give the position of the light spot.

3. The satellite laser link anti-solar interference detection and communication transceiver system according to claim 2, characterized in that, Based on the position error, the tracking controller calculates the angular offset of the received beam, specifically: Where Δθ represents the angle between the Z-axis and the incident direction of the beam, and f′ represents the focal length of the objective lens. x , Δθ y This indicates the angular offset of the light beam in the X-axis direction and the angular offset in the Y-axis direction.

4. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 2, characterized in that, The optical signals generated by each quadrant of the four-quadrant detector are first amplified by the TIA circuit, then shaped, and the deviation of the light spot from the center is calculated.

5. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The processing circuit extracts the communication signal by performing analog-to-digital conversion on the signals of each quadrant of the four-quadrant detector, followed by power division processing, equalization, clock data recovery, soft decision and decoding to recover the baseband signal.

6. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The performance requirements for the laser are: wavelength stability less than 0.1 pm, output power greater than 1W, power stability less than 0.5 dB, linewidth less than 100 kHz, and relative intensity noise less than -140 dB / Hz.

7. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The four-quadrant detector uses the HgCdTe type, with the following performance requirements: quantum efficiency greater than 60%, response time not greater than 10 ns, dynamic range not less than 40 dB, and dark current less than 10 dB. -4 A / cm 2 .

8. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The optical path of the transmitted signal light is as follows: after passing through the coupler, the transmitted signal light completes the conversion from an optical fiber beam to a spatial beam, and after being transmitted through a beam splitter, reflected by a fine tracking mechanism and a reflector, it is sent into the telescope, and after being expanded by the telescope, it is sent to the target terminal.

9. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The optical path of the target signal light is as follows: After the target signal light from the target terminal is filtered by a narrow-band optical window, the effective signal light is incident on the telescope. After the telescope's beam shrinking and the reflector reversing the optical path, it is reflected by the fine tracking mechanism, reflected by the beam splitter, and converged by the objective lens before reaching the four-quadrant detector. The four-quadrant detector calculates the angular offset and sends it to the fine tracking mechanism. The fine tracking mechanism calculates the execution quantity based on the angular offset and provides real-time compensation for the tracking deviation to achieve acquisition and tracking. At the same time, the four-quadrant detector and processing circuit effectively filter the modulated optical signal and complete demodulation and decoding.

10. A satellite laser link anti-solar interference detection and communication transceiver system according to claim 1, characterized in that, The narrow-band optical window suppresses solar background light outside the center wavelength of the target optical signal by ±3nm, with a suppression ratio of 40dB.

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