Space-based quantum key distribution system

Abstract

The invention relates to quantum key distribution, in particular to a space-based quantum key distribution system and a QKD transmitter, the space-based quantum key distribution system takes an FPGA as a control core and comprises an electronic module and an optical module, and the electronic module is responsible for converting key information provided by a QKD processor into a modulation signal and realizing dynamic coding of a quantum state; the optical module encodes a quantum state under the action of the modulation signal, regulates and controls the quantum pulse intensity to a single photon level, and finally outputs the quantum pulse intensity to a laser communication terminal of a satellite platform to be transmitted to an optical ground station; the optical ground station comprises an uplink system and a downlink system, the uplink system provides a stable and reliable beacon for the satellite platform, and the downlink system dynamically detects and compensates wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, counteracts the influence of atmospheric disturbance on light beam quality in real time and performs single-mode optical fiber coupling; according to the technical scheme provided by the invention, the defect that space-based quantum key distribution is difficult to accurately and efficiently carry out can be effectively overcome.

Description

Technical Field

[0001] This invention relates to quantum key distribution, and more specifically to a space-based quantum key distribution system. Background Technology

[0002] Quantum key distribution (QKD) is a secure communication technology based on the principles of quantum mechanics, which theoretically provides information-theoretically secure key distribution. However, existing QKD systems are mainly deployed on terrestrial fiber optic cables or short-distance free-space links, and their transmission distance is limited by channel loss, making it difficult to achieve global coverage.

[0003] Deploying QKD systems on satellite platforms is considered a feasible solution for building a global quantum network. However, space-based QKD systems face many serious challenges: 1) Harshness of the space environment: Due to environmental factors such as severe vibrations during satellite launch, extreme temperature changes during on-orbit operation, and space radiation effects, extremely high requirements are placed on the stability and reliability of electronic devices (such as FPGAs) and precision optical devices (such as modulators and lasers) in QKD transmitters. However, most existing QKD systems are designed for laboratory environments and lack enhanced design and on-orbit adaptive calibration mechanisms for the space environment. 2) Strong interference of atmospheric channels: The satellite-to-ground link needs to cross the troposphere and stratosphere. Atmospheric turbulence will cause intensity fluctuations (scintillation) and wavefront phase distortion of the optical signal. This is fatal for ground receiving systems that need to efficiently couple optical signals into single-mode fiber (SMF). Wavefront phase distortion will cause a sharp drop in coupling efficiency, significantly increase the error rate of qubits, and may even cause the QKD protocol to fail to generate keys. Some existing ground stations use simple tracking systems and lack high-frequency, high-precision adaptive wavefront correction capabilities, which cannot maintain optimal performance in harsh atmospheric environments. 3) Evolution of security threats: The openness of the space-to-ground link makes it face unique security threats. Attackers may send strong light signals from the ground to the satellite in an attempt to blind or control the single-photon detector, or carry out other attacks on the QKD protocol implementation layer. Existing space QKD systems usually lack on-orbit, real-time security threat perception and response capabilities. 4) Bottleneck in system performance: Early space QKD systems (such as the Micius satellite) had relatively low key generation rates.

[0004] To meet the needs of practical applications, it is necessary to increase the system's clock frequency and key throughput, which requires the QKD transmitter to have high-speed electronic processing capabilities and low-jitter optical modulation technology. Summary of the Invention

[0005] (a) Technical problems to be solved In view of the above-mentioned shortcomings of the existing technology, the present invention provides a space-based quantum key distribution system, which can effectively overcome the defects of the existing technology in that it is difficult to accurately and efficiently perform space-based quantum key distribution.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A space-based quantum key distribution system, comprising a QKD transmitter and an optical ground station; The QKD transmitter, with FPGA as its control core, includes an electronic module and an optical module. The electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to realize the dynamic encoding of the quantum state. The optical module encodes the quantum state under the action of the modulation signal and regulates the quantum pulse intensity to the single-photon level, and finally outputs it to the laser communication terminal of the satellite platform to transmit to the optical ground station. The optical ground station comprises an uplink system and a downlink system. The uplink system uses multiple beacon lasers of different frequencies and employs frequency diversity technology to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations and providing a stable and reliable beacon for the satellite platform. The downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsetting the impact of atmospheric disturbances on beam quality, and performs single-mode fiber coupling.

[0007] Preferably, the QKD transmitter is connected to the QKD processor and power supply unit of the satellite platform via an electrical connector, and the QKD processor provides the QKD transmitter with key information and protocol control commands originating from the quantum random number generator.

[0008] Preferably, the electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to realize the dynamic encoding of the quantum state, including: The FPGA receives the digital data stream sent by the QKD processor through a high-speed serial transceiver and converts it into parallel control signals to drive an external digital-to-analog converter (DAC) to generate precise analog voltage signals to control the intensity modulator and phase modulator, thus producing the desired quantum state.

[0009] Preferably, the FPGA is embedded with a microprocessor soft core to form a system-on-a-chip (SoC). The microprocessor soft core interacts with the FPGA logic section through the AMBA AXI bus, runs a real-time operating system, and uniformly manages telemetry and command communication, non-volatile memory, clock tree, and ADC interface for monitoring optical power and temperature.

[0010] Preferably, the optical module includes a pulse generation unit and a calibration unit. The pulse generation unit includes a C-band distributed feedback laser, an intensity modulator, and a phase modulator. The C-band distributed feedback laser serves as a light source, and the intensity modulator and phase modulator are cascaded thereafter to generate optical pulses and encode quantum states, respectively. The calibration unit is an active photoelectric feedback control loop. A portion of the quantum pulses are directed to the calibration photodiode via a beam splitter, converting the optical power into an electrical signal. After the FPGA acquires the electrical signal, it dynamically adjusts the DC bias voltage of the intensity modulator and phase modulator using gradient search or dithering technology to compensate for intensity and phase drift caused by temperature changes.

[0011] Preferably, the optical module further includes a pulse amplification unit and a pulse attenuation unit. The pulse amplification unit uses a semiconductor optical amplifier as a fast optical switch and controls it to switch between "on" and "off" states by driving current, generating strong reference pulses and weak quantum pulses respectively. The pulse attenuation unit uses a variable optical attenuator to precisely control the optical power, so that the intensity of the weak quantum pulse is accurately attenuated to a single-photon level with an average number of photons per pulse of less than 1.

[0012] Preferably, the optical module further includes a quantum hacking protection unit, which contains a high dynamic range photodetector that continuously monitors abnormal optical power entering the optical path. Once a strong light signal suspected of being an attack is detected, the FPGA immediately triggers a response mechanism, including cutting off the drive current of the semiconductor optical amplifier to physically block the optical path, or sending an alarm to the optical ground station via a remote command link.

[0013] Preferably, the uplink system uses multiple beacon lasers of different frequencies and frequency diversity technology to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations to provide a stable and reliable beacon for the satellite platform, including: The uplink is constructed using four independent frequency beacon lasers. The four beacon lasers are frequency diversified at the transmitting end. After passing through atmospheric turbulence, due to the frequency difference, the interference patterns in the far field are uncorrelated, thus statistically averaging the scintillation effect and providing a stable and reliable beacon for the satellite platform.

[0014] Preferably, the downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsets the influence of atmospheric disturbances on beam quality, and performs single-mode fiber coupling, including: The light signals emitted by the S1 and QKD transmitters reach the optical platform via the telescope and the Coude optical path. S2. The beam is first corrected for large-scale wavefront tilt by a fast tilting mirror; S3. The corrected beam enters the core correction loop: A portion of the beam is guided by the beam splitter to the adaptive optics wavefront sensor, whose microlens array divides the wavefront into multiple sub-apertures and forms a spot array on the CCD. By calculating the centroid shift of the spot in each sub-aperture, the complete wavefront phase distortion information is reconstructed in real time. S4. The wavefront controller calculates and generates a driving signal in real time based on the wavefront phase distortion information through a closed-loop control algorithm, and applies it to the deformable mirror. Each actuator of the deformable mirror pushes and pulls its own reflective surface according to the driving signal to generate a wavefront conjugate with the atmospheric distortion, thereby canceling the influence of atmospheric disturbance on the beam quality. S5. A near-diffraction-limited beam is precisely focused by a high numerical aperture objective lens and coupled into a single-mode fiber.

[0015] (III) Beneficial Effects

[0016] Compared with existing technologies, the space-based quantum key distribution system provided by this invention has the following advantages: 1) Unprecedented link performance: By combining a high-speed QKD transmitter (2.25Gbps) with a high-order adaptive optics ground station, high key generation rate and low qubit error rate can be achieved in real space-to-ground links, which is the key to building a practical space-based quantum network; 2) Excellent environmental adaptability: The QKD transmitter's on-orbit real-time calibration function enables it to adapt to temperature fluctuations and component aging on the satellite platform, ensuring the long-term stability of quantum state preparation quality and solving the problem of long-term reliable operation of space equipment; 3) Strong anti-interference capability: The multi-beam frequency diversity beacon laser and high-frequency closed-loop wavefront correction mechanism of the optical ground station can effectively suppress the influence of atmospheric turbulence, ensuring that a stable optical link can still be established and maintained in harsh atmospheric environments, and achieving a single-mode fiber coupling efficiency of up to 45% or more. 4) Enhanced system security: The active quantum hacking protection unit integrated inside the QKD transmitter provides physical layer security monitoring and defense capabilities, greatly improving the system's resilience in the face of actual security threats; 5) High systemicity and scalability: This invention provides an end-to-end system solution from space to ground. Its modular design makes it easy to upgrade and adapt to future new QKD protocols and other laser communication tasks. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 This is a schematic diagram of the QKD transmitter in this invention; Figure 2 This is a schematic diagram of the downlink system in this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] The following describes the specific functional modules of a space-based quantum key distribution system provided by this invention, using concrete examples (such as...). Figure 1 (As shown) and its technical effects. The system's functional modules include a QKD transmitter and an optical ground station; The QKD transmitter, with FPGA as its control core, includes an electronic module and an optical module. The electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to realize the dynamic encoding of the quantum state. The optical module encodes the quantum state under the action of the modulation signal and modulates the quantum pulse intensity to the single-photon level, and finally outputs it to the laser communication terminal on the satellite platform to transmit to the optical ground station. The optical ground station comprises an uplink system and a downlink system. The uplink system uses multiple beacon lasers of different frequencies and employs frequency diversity technology to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations and providing a stable and reliable beacon for the satellite platform. The downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsetting the impact of atmospheric disturbances on beam quality, and performs single-mode fiber coupling.

[0021] I. QKD Transmitter The QKD transmitter is a complex system integrating electronics, optics, and software. Its core key lies in solving the challenges of high-speed, high-stability, and high-security quantum state preparation in space environments.

[0022] The QKD transmitter is connected to the QKD processor and power unit of the satellite platform via an electrical connector. The QKD processor provides the QKD transmitter with key information and protocol control commands originating from the quantum random number generator.

[0023] 1) Electronic Modules The electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to achieve dynamic encoding of the quantum state, including: The FPGA receives the digital data stream sent by the QKD processor through a high-speed serial transceiver (following the SpaceFibre or enhanced SpaceWire protocol, with a transmission rate of not less than 2.5Gbps), and converts it into parallel control signals to drive an external digital-to-analog converter (DAC) with an update rate of not less than 5GSa / s and an analog bandwidth of not less than 1.5GHz) to generate precise analog voltage signals to control the intensity modulator and phase modulator, and generate the required quantum states (such as the four quantum states required by the BB84 protocol).

[0024] An FPGA embeds a microprocessor soft core (such as an ARM Cortex-M) to form a system-on-a-chip (SoC). This microprocessor soft core interacts with the FPGA logic section through the AMBA AXI bus, runs a real-time operating system, and uniformly manages telemetry and command communication, non-volatile memory, clock tree, and ADC interface for monitoring optical power and temperature.

[0025] 2) Optical Modules The optical module includes a pulse generation unit and a calibration unit. The pulse generation unit includes a C-band distributed feedback laser, an intensity modulator, and a phase modulator. The C-band distributed feedback laser serves as the light source, and the intensity modulator and phase modulator are cascaded after it to generate light pulses and encode quantum states, respectively. The calibration unit is an active photoelectric feedback control loop. It guides part of the quantum pulse into the calibration photodiode through a beam splitter, converting the optical power into an electrical signal. After the FPGA acquires the electrical signal, it dynamically adjusts the DC bias voltage of the intensity modulator and phase modulator through gradient search or dithering technology to compensate for the intensity and phase drift caused by temperature changes.

[0026] Specifically, the dithering technology is implemented by superimposing a sinusoidal or square wave dithering signal with a frequency in the range of 100Hz to 10kHz and a peak value in the range of 5mV to 50mV onto the DC bias voltage of the intensity modulator or phase modulator; the FPGA, through its internally integrated digital phase-locked amplification function, synchronously demodulates the amplitude and phase of the dithering frequency component in the photodiode return signal, and generates an error signal accordingly. The DC bias voltage is dynamically adjusted through a closed-loop control algorithm to lock the modulator operating point at the extreme point of the transmission curve.

[0027] The optical module also includes a pulse amplification unit and a pulse attenuation unit. The pulse amplification unit uses a semiconductor optical amplifier (SOA) as a fast optical switch, and controls it to switch between "on" (amplification) and "off" (high attenuation) states by driving current, generating strong reference pulses and weak quantum pulses respectively. The pulse attenuation unit uses a variable optical attenuator (VOA) to precisely control the optical power, so that the intensity of weak quantum pulses is accurately attenuated to a single-photon level with an average number of photons per pulse of less than 1.

[0028] The optical module also includes a quantum hacking protection unit, which contains a high dynamic range photodetector (linear dynamic range greater than 80dB) that continuously monitors abnormal optical power entering the optical path. Once a strong optical signal suspected of being an attack is detected (the judgment condition is: the instantaneous monitored optical power exceeds the preset threshold of the average power of the quantum signal by more than 30dB, and this state lasts for more than 1μs), the FPGA immediately triggers a response mechanism (delay time less than 10μs), including cutting off the drive current of the semiconductor optical amplifier to physically block the optical path, or sending an alarm to the optical ground station via a remote command link.

[0029] In this application's technical solution, the QKD transmitter adopts a model-based design and test-driven development paradigm. The software architecture follows the European Space Standardization Cooperation (ECSS) standards, and the code undergoes automated testing through a continuous integration / continuous deployment (CI / CD) pipeline. It adheres to SOLID principles and a clean architecture to ensure high reliability and maintainability. The software is modularized, clearly separating core responsibilities such as calibration, communication, monitoring, and security.

[0030] II. Optical Ground Station The core of the optical ground station lies in suppressing the degrading effect of atmospheric turbulence on signal quality and establishing and maintaining a highly reliable satellite-to-ground link. The optical ground station is based on the 80-cm Nasmyth-type Ritchey-Chretien telescope. The optical signal received by the telescope is guided through the Coude optical path to the optical platform located in the laboratory below. The optical platform integrates the key adaptive wavefront correction system (with a control bandwidth of no less than 500Hz) and the fiber optic coupling system of this invention.

[0031] 1) Uplink system The uplink system uses multiple beacon lasers of different frequencies and frequency diversity techniques to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations to provide a stable and reliable beacon for the satellite platform, including: The uplink is constructed using four independent frequency beacon lasers (with a frequency interval of more than 10 GHz between each pair). The four beacon lasers are frequency diversified at the transmitting end. After passing through atmospheric turbulence, due to the frequency difference, the interference patterns in the far field are uncorrelated, thus statistically averaging the scintillation effect and providing a stable and reliable beacon for the satellite platform.

[0032] 2) Downlink System The downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsets the impact of atmospheric disturbances on beam quality, and performs single-mode fiber coupling, such as... Figure 2 As shown, it includes: The light signals emitted by the S1 and QKD transmitters reach the optical platform via the telescope and the Coude optical path. S2. The beam is first corrected for large-scale wavefront tilt by a fast tilting mirror; S3. The corrected beam enters the core correction loop: A portion of the beam is guided by the beam splitter to the adaptive optics wavefront sensor (Shack-Hartmann sensor, with no less than 32*32 sub-apertures and a sampling frame rate of no less than 2kHz). Its microlens array divides the wavefront into multiple sub-apertures and forms a spot array on the CCD. By calculating the centroid shift of the spot in each sub-aperture, the complete wavefront phase distortion information is reconstructed in real time (at a rate of several kilohertz). S4. The wavefront controller calculates and generates a driving signal in real time based on the wavefront phase distortion information through a closed-loop control algorithm (such as a proportional-integral controller), and applies it to the deformable mirror. Each actuator of the deformable mirror (no less than 97) pushes and pulls its own reflective surface according to the driving signal to generate a wavefront conjugate with the atmospheric distortion, thereby canceling the influence of atmospheric disturbance on the beam quality. S5. A near-diffraction-limited beam is precisely focused by a high numerical aperture objective lens and coupled into a single-mode fiber.

[0033] In the technical solution of this application, the optical ground station is designed with a modular optical platform layout and a configurable software-defined control system. By replacing the coupling optical module at the front end and adjusting the control system parameters, the optical ground station can quickly adapt to the mission requirements of different wavelengths and different protocols.

[0034] Figure 2 This is a system diagram of the downlink system in this invention, systematically illustrating the signal flow and key components of the entire receiving link. (See diagram:) From satellite: refers to optical signals transmitted downlink from satellites, typically including quantum signals and classical communication signals; 80 cm aperture: The diameter of the primary mirror of the Nasmyth-type Ritchey-Chretien telescope directly determines the system's light-gathering capability and angular resolution; Kuder optical path: an optical path that guides a beam of light from the telescope's pointing axis to a fixed position using a series of mirrors; Telescope simulator: A device that simulates parallel light (as if from an infinitely distant star) in a laboratory setting for system calibration and testing; Optical repeater: A lens group used to transmit image planes, maintain beam characteristics, and match the pupils of different components; High-speed tilt mirror: A mirror that can deflect a beam at high speed and with small amplitude to correct wavefront tilt (Tip-Tilt). Deformable mirror: A mirror whose reflective surface shape can be precisely controlled by electrical signals. It is used to correct higher-order wavefront distortion and is the core actuator for wavefront distortion correction in an adaptive wavefront correction system. Beam splitting: An optical operation that splits a beam of light into multiple beams according to wavelength or energy ratio; Fiber coupling: The process of efficiently focusing and injecting a calibrated free-space beam into a single-mode fiber, which is the interface for quantum optical signals to enter subsequent detectors; Adaptive optics wavefront sensor: measures the phase distortion of the incident light wavefront in real time, providing the feedback signal required for the correction of the deformable mirror; Focusing camera: used to monitor beam quality and focus status; Classical communication: refers to traditional laser communication, as opposed to quantum communication; Modem: A device that modulates and demodulates signals to transmit data; Optoelectronic converter: A device that converts optical signals into electrical signals.

[0035] To better illustrate the technical solution of this application, a preferred embodiment is described in detail below. In this embodiment, the system parameter configuration and performance are as follows: • Space segment (QKD transmitter): o Clock rate: 2.25GHz; o Light source wavelength: 1550.12nm (C-band); o Quantum state encoding: Using the BB84 protocol, four polarization states are generated through an intensity modulator and a phase modulator; o On-orbit calibration: Employs dithering technology with a dithering frequency of 1kHz, bias voltage control accuracy better than 0.1mV, calibration cycle ≤10s, and can compensate for phase drift within a temperature range of -20°C to +50°C; o Output pulse: The average photon number of the quantum pulse is μ=0.5, controlled by a variable optical attenuator (VOA) with an accuracy of ±0.02μ.

[0036] • Ground segment (optical ground station): o Receiving telescope: Nasmyth type Ritchey-Chretien, 80cm aperture; o Uplink beacon: 4 laser beams, frequency-spaced 20GHz, effectively suppressing atmospheric scintillation and reducing the variance of beacon light power fluctuation received by the satellite platform by approximately 50%; o Adaptive wavefront correction system: Wavefront sensor: Shack-Hartmann type, 40*40 sub-aperture, frame rate 2500Hz; Deformable mirror: 127-element continuous surface deformable mirror; Fast tilt mirror: Closed-loop bandwidth ≥ 1kHz; Control bandwidth: The closed-loop bandwidth of the entire system is ≥600Hz; o Fiber coupling: Achromatic coupling objective (numerical aperture NA=0.4) optimized for 1550.12nm wavelength is used.

[0037] • Link and performance: o Test conditions: simulated satellite overhead, elevation angle 30°, atmospheric coherence length r0≈10cm (@1550nm) under moderate turbulence conditions, link loss approximately 35dB; o Coupling efficiency: After correction by the adaptive wavefront correction system, the coupling efficiency of the downlink quantum signal to the single-mode fiber (SMF-28e) increased from <2% before correction to 46%~48%; o System performance: Under these conditions, the system achieves a net secure key rate (SKR) of 12 kbps and a stable quantum bit error rate (QBER) of 2.8%; o Security Protection: In laboratory simulated attack tests, the quantum hacker protection unit can physically block the optical path within 5μs against strong pulse attacks exceeding the normal power by 35dB, with a blocking success rate of 100%.

[0038] The embodiments show that the present invention effectively solves the core bottleneck of extremely low coupling efficiency caused by atmospheric turbulence in the space-to-ground quantum link through the synergistic effect of specific technical means, realizes an order-of-magnitude improvement in key generation capability, and achieves unexpected technical effects.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A space-based quantum key distribution system, characterized in that: Including QKD transmitters and optical ground stations; The QKD transmitter uses an FPGA as its control core and includes an electronic module and an optical module. The electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to realize the dynamic encoding of quantum states. The optical module encodes quantum states under the action of modulation signals and modulates the intensity of quantum pulses to the single-photon level, and finally outputs them to the laser communication terminal of the satellite platform to transmit to the optical ground station; The optical ground station comprises an uplink system and a downlink system. The uplink system uses multiple beacon lasers of different frequencies and employs frequency diversity technology to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations and providing a stable and reliable beacon for the satellite platform. The downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsetting the impact of atmospheric disturbances on beam quality, and performs single-mode fiber coupling.

2. The space-based quantum key distribution system according to claim 1, characterized in that: The QKD transmitter is connected to the QKD processor and power supply unit of the satellite platform via an electrical connector. The QKD processor provides the QKD transmitter with key information and protocol control commands originating from the quantum random number generator.

3. The space-based quantum key distribution system according to claim 2, characterized in that: The electronic module is responsible for converting the key information provided by the QKD processor into a modulation signal to realize the dynamic encoding of quantum states, including: The FPGA receives the digital data stream sent by the QKD processor through a high-speed serial transceiver and converts it into parallel control signals to drive an external digital-to-analog converter (DAC) to generate precise analog voltage signals to control the intensity modulator and phase modulator, thus producing the desired quantum state.

4. The space-based quantum key distribution system according to claim 3, characterized in that: The FPGA is embedded with a microprocessor soft core to form a system-on-a-chip (SoC). The microprocessor soft core interacts with the FPGA logic section through the AMBA AXI bus, runs a real-time operating system, and uniformly manages telemetry and command communication, non-volatile memory, clock tree, and ADC interface for monitoring optical power and temperature.

5. The space-based quantum key distribution system according to claim 3, characterized in that: The optical module includes a pulse generation unit and a calibration unit. The pulse generation unit includes a C-band distributed feedback laser, an intensity modulator, and a phase modulator. The C-band distributed feedback laser serves as a light source, and the intensity modulator and phase modulator are cascaded thereafter to generate optical pulses and encode quantum states, respectively. The calibration unit is an active photoelectric feedback control loop. A portion of the quantum pulses are directed to the calibration photodiode via a beam splitter, converting the optical power into an electrical signal. After the FPGA acquires the electrical signal, it dynamically adjusts the DC bias voltage of the intensity modulator and phase modulator using gradient search or dithering technology to compensate for intensity and phase drift caused by temperature changes.

6. The space-based quantum key distribution system according to claim 5, characterized in that: The optical module also includes a pulse amplification unit and a pulse attenuation unit. The pulse amplification unit uses a semiconductor optical amplifier as a fast optical switch and controls it to switch between "on" and "off" states by driving current, generating strong reference pulses and weak quantum pulses respectively. The pulse attenuation unit uses a variable optical attenuator to precisely control the optical power, so that the intensity of the weak quantum pulse is accurately attenuated to a single-photon level with an average number of photons per pulse of less than 1.

7. The space-based quantum key distribution system according to claim 6, characterized in that: The optical module also includes a quantum hacking protection unit, which contains a high dynamic range photodetector that continuously monitors abnormal optical power entering the optical path. Once a strong light signal suspected of being an attack is detected, the FPGA immediately triggers a response mechanism, including cutting off the drive current of the semiconductor optical amplifier to physically block the optical path, or sending an alarm to the optical ground station via a remote command link.

8. The space-based quantum key distribution system according to claim 1, characterized in that: The uplink system uses multiple beacon lasers of different frequencies and frequency diversity techniques to suppress scintillation caused by atmospheric turbulence, statistically averaging signal fluctuations to provide a stable and reliable beacon for the satellite platform, including: The uplink is constructed using four independent frequency beacon lasers. The four beacon lasers are frequency diversified at the transmitting end. After passing through atmospheric turbulence, due to the frequency difference, the interference patterns in the far field are uncorrelated, thus statistically averaging the scintillation effect and providing a stable and reliable beacon for the satellite platform.

9. The space-based quantum key distribution system according to claim 1, characterized in that: The downlink system dynamically detects and compensates for wavefront distortion based on a high-frequency closed-loop wavefront correction mechanism, real-time offsets the impact of atmospheric disturbances on beam quality, and performs single-mode fiber coupling, including: The light signals emitted by the S1 and QKD transmitters reach the optical platform via the telescope and the Coude optical path. S2. The beam is first corrected for large-scale wavefront tilt by a fast tilting mirror; S3. The corrected beam enters the core correction loop: A portion of the beam is guided by the beam splitter to the adaptive optics wavefront sensor, whose microlens array divides the wavefront into multiple sub-apertures and forms a spot array on the CCD. By calculating the centroid shift of the spot in each sub-aperture, the complete wavefront phase distortion information is reconstructed in real time. S4. The wavefront controller calculates and generates a driving signal in real time based on the wavefront phase distortion information through a closed-loop control algorithm, and applies it to the deformable mirror. Each actuator of the deformable mirror pushes and pulls its own reflective surface according to the driving signal to generate a wavefront conjugate with the atmospheric distortion, thereby canceling the influence of atmospheric disturbance on the beam quality. S5. A near-diffraction-limited beam is precisely focused by a high numerical aperture objective lens and coupled into a single-mode fiber.

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