Space laser communication receiving system and control method thereof, space communication device

Abstract

This invention provides a space laser communication receiving system and its control method, as well as a space communication device, belonging to the field of optical communication technology. The system includes: a space light receiving module, an optical amplification module, and a unidirectional isolation module, disposed on the main optical path between the space light receiving module and the optical amplification module, including at least two cascaded optical circulators; a first power detection unit for receiving leakage light signals after reverse penetration of the cascaded defense line; a second power detection unit for receiving the reverse echo signal generated by the optical amplification module; and a main control unit, communicatively connected to the first and second power detection units, for performing optical path safety protection and / or closed-loop adjustment of isolation of the space laser communication receiving system based on the optical power of the leakage light signal and the reverse echo signal. This invention improves the system's isolation capability against reverse echo light to a higher level.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a space laser communication receiving system and its control method, as well as a space communication device. Background Technology

[0002] Currently, space laser communication has become a key development area in fields such as satellite communication and deep space exploration due to its technological advantages, including narrow beam width, good directionality, small antenna size, large information capacity, low power consumption, small size, and light weight. Technically, light waves are an excellent transmission medium that is non-absorbent and non-scattering, lossless, and interference-free, making laser communication extremely cost-effective.

[0003] With the development of space laser communication technology, low-noise amplifiers, as a core component of the receiver, directly affect communication quality. Erbium-doped fiber amplifiers (EDBFAs) are currently widely used in space laser communication. However, in existing technologies, the isolation of low-noise EDBFAs is typically only about 60 dB. This means that when the signal light is amplified, a reverse-propagating echo light is generated inside the amplifier. This echo light is output from the EDBFA's input port in the reverse direction and propagates back along the original optical path. If this echo light is not effectively suppressed, it will enter the upstream optical receiving antenna, forming interference noise, directly reducing the signal-to-noise ratio of the communication link and deteriorating communication quality. In addition, high-energy echo light may cause performance degradation or even physical damage to the optical components inside the optical head of the front-end laser communication payload. Summary of the Invention

[0004] This invention provides a space laser communication receiving system and its control method, as well as a space communication device, which improves the system's isolation capability against back echo light to a higher level and realizes intelligent monitoring and active protection of the echo light status.

[0005] In a first aspect, the present invention provides a space laser communication receiving system, comprising: Spatial light receiving module, used to receive input spatial light signals; The optical amplifier module is used to amplify the power of the input optical signal; A unidirectional isolation module is disposed on the main optical path between the spatial light receiving module and the optical amplification module, and includes at least two cascaded optical circulators. The first power detection unit is connected to the reverse light exhaust end of the unidirectional isolation module near the first stage of the spatial light receiving module, and is used to receive the leaked light signal after reverse penetration of the cascaded defense line. The second power detection unit is connected to the reverse light exhaust end of the unidirectional isolation module near the first stage of the optical amplification module, and is used to receive the reverse echo signal generated by the optical amplification module. The main control unit is communicatively connected to the first power detection unit and the second power detection unit, respectively, and is used to perform optical path safety protection and / or isolation closed-loop adjustment of the space laser communication receiving system based on the optical power of the leaked light signal and the reverse echo signal.

[0006] In some embodiments, the unidirectional isolation module includes at least a first optical circulator and a second optical circulator; The first port of the first optical circulator is optically connected to the spatial light receiving module, the second port is optically connected to the first port of the second optical circulator, and the third port is optically connected to the first power detection unit to form the reverse light output end near the first stage of the spatial light receiving module. The second port of the second optical circulator is optically connected to the optical input port of the optical amplification module, and the third port is optically connected to the second power detection unit to form the reverse light exhaust port near the first stage of the optical amplification module.

[0007] In some embodiments, the optical amplification module includes a pump light source and is communicatively connected to the main control unit; and / or, an optical switch is connected in series between the unidirectional isolation module and the optical amplification module, and the control terminal of the optical switch is communicatively connected to the main control unit.

[0008] In some embodiments, it also includes: Multiple temperature control components are thermally coupled to their respective optical circulators and communicatively connected to the main control unit.

[0009] In some embodiments, the spatial light receiving module and the unidirectional isolation module, the cascaded nodes within the unidirectional isolation module, and the unidirectional isolation module and the optical amplification module are all physically connected by polarization-maintaining optical fibers.

[0010] In some embodiments, it also includes: At least one backup isolation branch is connected in parallel with the unidirectional isolation module; The first optical path switcher and the second optical path switcher are respectively located on the optical input side and optical output side of the unidirectional isolation module, and are both communicatively connected to the main control unit to select the backup isolation branch.

[0011] In some embodiments, the optical amplification module is an erbium-doped fiber amplifier, and both the first power detection unit and the second power detection unit include at least a photodetector. The system also includes a coherent demodulation module, which is optically connected to the optical output end of the optical amplification module and is used to demodulate space communication data from the amplified optical signal.

[0012] In a second aspect, the present invention also provides a control method for a space laser communication receiving system, for controlling the space laser communication receiving system as described in the first aspect, the method comprising: Acquire the first electrical signal output by the first power detection unit; wherein, the first electrical signal represents the optical power of the leaked light signal after reverse penetration of the cascaded defense line; Acquire the second electrical signal output by the second power detection unit; wherein, the second electrical signal represents the optical power of the reverse echo signal generated by the optical amplification module; Based on the first electrical signal and the second electrical signal, the space laser communication receiving system is subjected to optical path safety protection and / or isolation closed-loop adjustment.

[0013] In some embodiments, optical path security protection includes: When the optical power of the reverse echo signal is greater than or equal to a preset safe power threshold, an emergency cut-off action is initiated. The cutting-off action includes: cutting off the driving current of the pump light source in the optical amplification module; or triggering an optical switch connected in series between the unidirectional isolation module and the optical amplification module to cut off the optical path.

[0014] In some embodiments, closed-loop adjustment of isolation degree includes: A temperature compensation command is generated when the optical power of the leaked optical signal deviates from the minimum range and shows an upward trend. According to the temperature compensation command, the temperature adjustment component thermally coupled to the corresponding optical circulator is controlled to change the physical temperature until the optical power of the leaked optical signal returns to the minimum value range.

[0015] In some embodiments, it also includes: When the optical power of the leaked optical signal is greater than or equal to the preset limit leakage threshold, it is determined that the current cascaded isolation optical path has experienced a hardware failure, and the system controls the switch to the backup isolation branch.

[0016] In some embodiments, it also includes: Obtain the main optical path input power of the spatial light receiving module; The dynamic reflectivity is obtained based on the input power of the main optical path and the optical power of the reverse echo signal. The aging trend of the space laser communication receiving system is obtained based on the time series fitting curve characteristics of the dynamic reflectivity.

[0017] Thirdly, the present invention also provides a space communication device, including the space laser communication receiving system as described in the first aspect.

[0018] This invention employs at least two cascaded optical circulators as unidirectional isolation modules. Compared to single-stage isolation devices, its total reverse isolation is the sum of the isolation of the two devices, reaching, for example, over 90 dB. This significantly suppresses the interference and damage of the optical amplification module's echo to the front-end spatial light receiving module. By setting a second power detection unit and a first power detection unit at two key nodes—the first-stage reverse light exhaust end near the optical amplification module and the second-stage reverse light exhaust end after penetrating the entire defense line—graded and refined monitoring of the original echo intensity and residual leakage intensity is achieved. This provides the main control unit with comprehensive and accurate status perception data, enabling it not only to determine whether the echo is too strong but also whether the isolation module itself has failed. This provides a physical basis and data prerequisite for subsequent intelligent control, effectively overcoming the shortcomings of blind protection. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a space laser communication receiving system provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of another space laser communication receiving system provided in an embodiment of the present invention; Figure 3 This is a flowchart illustrating a control method for a space laser communication receiving system provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this 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 this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] Figure 1 This is a schematic diagram of the structure of a space laser communication receiving system provided in an embodiment of the present invention. Figure 1As shown, the space laser communication receiving system includes a space light receiving module 101, an optical amplification module 107, a unidirectional isolation module 102, a first power detection unit 104, a second power detection unit 105, and a main control unit 108. The space light receiving module 101 is used to receive input space light signals; the optical amplification module 107 is used to amplify the power of the input light signals; the unidirectional isolation module 102 is disposed on the main optical path between the space light receiving module 101 and the optical amplification module 107, and includes at least two cascaded optical circulators. Figure 1 An exemplary illustration shows a unidirectional isolation module 102 comprising two cascaded optical circulators; a first power detection unit 104 is connected to the reverse light exhaust end of the unidirectional isolation module 102 near the first stage of the space light receiving module 101, for receiving the leaked light signal after reverse penetration of the cascaded defense line; a second power detection unit 105 is connected to the reverse light exhaust end of the unidirectional isolation module 102 near the first stage of the optical amplification module 107, for receiving the reverse echo signal generated by the optical amplification module 107; a main control unit 108 is communicatively connected to the first power detection unit 104 and the second power detection unit 105, for performing optical path safety protection and / or isolation closed-loop adjustment of the space laser communication receiving system based on the optical power of the leaked light signal and the reverse echo signal.

[0023] Specifically, a space laser communication receiving system refers to a complete device installed on space platforms such as satellites, spacecraft, and space stations to receive free-space laser signals emitted from other space platforms or ground stations and convert them into electrical signals to extract information. The space light receiving module 101 refers to the optical components at the system front end responsible for capturing and converging free-space incident laser signals. It may include optical antennas, converging lenses, space fiber optic coupling devices, etc., and its output end outputs the coupled fiber-guided optical signal. The optical amplification module 107 refers to a component used to boost the power of the optical signal transmitted in the main optical path. It contains a gain medium, such as erbium-doped fiber, and a pump source. The unidirectional isolation module 102 refers to a combination of devices that allows the optical signal to pass through in only one direction, i.e., from the space light receiving module 101 to the optical amplification module 107, with low loss, while greatly suppressing the reverse transmission of light. A cascaded optical circulator refers to a structure that connects two or more optical circulators in series. The optical circulator has three ports: light enters from the first port and exits from the second port, and light entering from the second port exits from the third port.

[0024] The first power detection unit 104 and the second power detection unit 105 refer to independent photoelectric conversion components used to receive and measure the optical power of the leakage light signal in a specific branch and convert it into an electrical signal output. The reverse light output end refers to the port on the optical circulator in the unidirectional isolation module 102 specifically used for outputting reverse-transmitted light, such as the third port of the circulator. This port has no output for forward-transmitted light; for light transmitted back from the subsequent stage, this port is its preset low-loss output channel. The leakage light signal refers to the echo light transmitted in reverse from the direction of the optical amplification module 107. After penetrating the reverse isolation defenses of the two cascaded optical circulators, a very small amount of light still passes back through the optical circulator near the stage of the spatial light receiving module 101, outputting a weak light signal from its reverse light output end. The magnitude of this signal reflects the overall reverse isolation performance of the cascaded isolation module. The reverse echo signal refers to the echo optical signal generated inside the optical amplification module 107 and output in the reverse direction from its input port towards the main optical path, i.e., the spatial light receiving module 101. This signal is directly extracted from the reverse light output end of the optical circulator located near the optical amplification module 107. The main control unit 108 refers to the electronic component in the system responsible for data acquisition, logic judgment, and control command generation. It can be a microcontroller, field-programmable gate array, digital signal processor, or embedded computer.

[0025] The laser signal transmitted in free space is first captured by the space light receiving module 101 and coupled into the optical fiber. Subsequently, the forward-transmitting optical signal enters the unidirectional isolation module 102, which consists of at least two cascaded optical circulators, as shown below. Figure 1 As shown, the forward light passes through the first-stage optical circulator and the second-stage optical circulator in sequence, and finally enters the optical amplification module 107 for power amplification. The amplified signal is then output to the subsequent demodulation circuit. At the same time, the optical amplification module 107 inevitably generates a reverse-transmitted echo light during operation. This echo light is output in reverse from the incident end of the optical amplification module 107, first entering the second port of the optical circulator stage closest to the optical amplification module 107 in the unidirectional isolation module 102. This reverse echo light is mainly output from its third port, that is, the reverse light exhaust end connected to the second power detection unit 105, and is received by the second power detection unit 105. This achieves the first splitting and detection of the echo light energy.

[0026] However, since the isolation of the optical circulator is not infinite, a small amount of reverse echo light will still leak through this stage of the optical circulator and continue to enter the second port of the previous stage optical circulator in reverse. Similarly, this leaked light will be output from the third port of the previous stage optical circulator, i.e., the reverse light exhaust port connected to the first power detection unit 104, and received by the first power detection unit 104. This realizes the detection of extremely weak leaked light signals after penetrating the entire cascaded isolation defense line. The main control unit 108 is communicatively connected to the first power detection unit 104 and the second power detection unit 105, respectively, to acquire in real time the first electrical signal representing the optical power of the leaked light signal and the second electrical signal representing the optical power of the reverse echo signal. The main control unit 108 has a preset logic algorithm that determines the current working state of the system based on the different values ​​and trends of these two key parameters, such as whether the reverse isolation capability has decreased or whether the echo intensity has increased abnormally, and executes the corresponding control strategy accordingly.

[0027] Therefore, this embodiment of the invention uses at least two cascaded optical circulators as unidirectional isolation modules 102. Compared to a single-stage isolation device, its total reverse isolation is the sum of the isolation of the two devices, for example, it can reach more than 90 dB, thereby greatly suppressing the interference and damage of the echo of the optical amplification module 107 to the front-end spatial light receiving module 101. By setting a second power detection unit 105 and a first power detection unit 104 at two key nodes, namely the first-stage reverse light exhaust end near the optical amplification module 107 and the second-stage reverse light exhaust end after penetrating the entire defense line, respectively, the graded and refined monitoring of the original echo intensity and residual leakage intensity is realized. This provides the main control unit 108 with comprehensive and accurate status perception data, enabling it not only to determine whether the echo is too strong, but also whether the isolation module itself has failed, providing a physical basis and data premise for subsequent intelligent control, and effectively overcoming the defects of blind protection.

[0028] In some embodiments, the unidirectional isolation module 102 includes at least a first optical circulator 103 and a second optical circulator 106; the first port of the first optical circulator 103 is optically connected to the spatial light receiving module 101, the second port is optically connected to the first port of the second optical circulator 106, and the third port is optically connected to the first power detection unit 104 to form a reverse light exhaust terminal near the spatial light receiving module 101; the second port of the second optical circulator 106 is optically connected to the optical input terminal of the optical amplification module 107, and the third port is optically connected to the second power detection unit 105 to form a reverse light exhaust terminal near the optical amplification module 107.

[0029] Specifically, the first optical circulator 103 refers to the optical circulator located closer to the spatial light receiving module 101 in the cascaded structure. The second optical circulator 106 refers to the optical circulator located closer to the optical amplification module 107 in the cascaded structure. For a standard three-port optical circulator, its port characteristics are that light input from the first port can only be output from the second port; light input from the second port can only be output from the third port.

[0030] The first port of the first optical circulator 103 is connected to the output of the spatial light receiving module 101 via an optical fiber, allowing forward signal light to enter the first optical circulator 103 and exit from its second port. The second port of the first optical circulator 103 is connected to the first port of the second optical circulator 106 via an optical fiber, allowing forward light to enter the second optical circulator 106 and exit from its second port. The second port of the second optical circulator 106 is connected to the input of the optical amplification module 107, thus establishing a complete, low-loss forward main optical path.

[0031] The reverse echo light generated by the optical amplification module 107 first enters from the second port of the second optical circulator 106. According to the circulator's characteristics, this echo light is mainly output from its third port, which is optically connected to the second power detection unit 105. Therefore, the second power detection unit 105 measures the most direct and strongest reverse echo signal. Tiny leaky light that penetrates the isolation capability of the second optical circulator 106 will be output in reverse from the first port of the second optical circulator 106 and enter the second port of the first optical circulator 103. After entering the first optical circulator 103, this leaky light will be output from its third port, which is optically connected to the first power detection unit 104. Therefore, the first power detection unit 104 measures the extremely weak leaky light signal that has finally leaked through the two-stage isolation.

[0032] Therefore, this embodiment of the invention integrates three key functions into a single optical path structure in a simple, efficient and low-insertion-loss manner: low-loss transmission of the forward signal, main path shunt detection of the reverse echo, and secondary shunt detection of residual reverse leakage. This connection ensures that the first power detection unit 104 and the second power detection unit 105 can acquire two detection signals with different physical meanings, namely the original echo and the residual leakage, without crosstalk or overlap, providing a clear and unambiguous signal source for the subsequent high-precision and high-reliability state judgment of the main control unit 108.

[0033] In some embodiments, the optical amplification module 107 includes a pump light source and is communicatively connected to the main control unit 108; and / or, a light switch is connected in series between the unidirectional isolation module 102 and the optical amplification module 107, and the control terminal of the light switch is communicatively connected to the main control unit 108.

[0034] Specifically, the pump source is one of the core components of the optical amplification module 107, such as an erbium-doped fiber amplifier. It is used to emit pump light of a specific wavelength to excite the gain medium, such as the population inversion in erbium-doped fiber, thereby amplifying the signal light. Its operating state, such as the magnitude of the drive current, directly determines whether the optical amplification module 107 works and the magnitude of the amplification gain. Communication connection refers to the electrical signal connection between the main control unit 108 and the optical amplification module 107, enabling the main control unit 108 to send control commands, such as reducing the drive current or cutting off power to the optical amplification module 107. An optical switch is an optical path control device that can, under the control of an electrical signal, switch its internal optical path on or off in a very short time. Serial connection refers to directly connecting the optical switch to the fiber optic link of the main optical path, so that all forward-transmitted light and reverse echo must pass through this device.

[0035] The main control unit 108 receives the second electrical signal fed back by the second power detection unit 105 in real time. This signal represents the optical power of the reverse echo signal. The main control unit 108 has multiple preset power thresholds, including a danger threshold. When the main control unit 108 determines, through comparison, that the current optical power of the reverse echo signal is greater than or equal to the preset safe power threshold, i.e., it has reached a danger level, it determines that the echo generated by the optical amplification module 107 has posed a substantial threat to the sensitive front-end devices. At this time, the main control unit 108 will immediately generate and send an emergency cut-off command. This command, through its communication connection with the optical amplification module 107, directly acts on the pump light source inside the optical amplification module 107, instantly cutting off the driving current of the pump light source, causing the optical amplification module 107 to lose its amplification capability, thereby eliminating the continuous generation of echoes from the source. Alternatively, the system connects a high-speed optical switch in series between the unidirectional isolation module 102 and the optical amplification module 107. When the main control unit 108 determines that emergency protection is needed, it sends a command to the control terminal of the optical switch, triggering the optical switch to cut off the physical optical path within microseconds, thereby preventing any echo from the downstream stage from continuing to propagate to the front end.

[0036] Therefore, this embodiment of the invention, by introducing a main control unit 108 to directly control the pump light source or a series high-speed optical switch, achieves extremely fast response speed and can complete the protective action before the echo energy causes irreversible damage to the front-end optical components, thus realizing true active safety protection. At the same time, it provides two independent cutoff methods, enhancing the system's redundancy and reliability.

[0037] In some embodiments, the space laser communication receiving system further includes multiple temperature regulation components, which are thermally coupled to corresponding optical circulators and communicatively connected to the main control unit 108.

[0038] Specifically, a temperature regulating component refers to a device that can change its own temperature according to an electrical signal command and heat or cool an object it is attached to or in contact with through thermal coupling. For example, a semiconductor thermoelectric cooler, whose temperature changes alter the physical properties of the optical crystal inside the optical circulator it is thermally coupled to. Thermal coupling refers to the efficient heat exchange between the temperature regulating component and the optical circulator through thermally conductive materials or direct physical contact, enabling the temperature changes of the temperature regulating component to be quickly and accurately transmitted to the optical circulator.

[0039] The core component of the optical circulator, enabling non-reciprocal rotation, is extremely sensitive to temperature. In space applications, drastic temperature changes can cause the circulator's operating point to deviate from its design value, significantly reducing its isolation. The system includes multiple temperature regulation components, each thermally coupled to a corresponding optical circulator. The main control unit 108 monitors the signal from the first power detection unit 104 in real time, as this signal represents residual leakage after penetrating two levels of defense and is the ultimate indicator of overall isolation effectiveness. When the main control unit 108 detects that the optical power of the leaked light signal continues to rise, deviating from the theoretically achievable minimum range, it determines that the current operating temperature of the circulator has deviated from the optimal isolation point. The main control unit 108 then generates a temperature compensation command and sends it to the temperature regulation component of each optical circulator. The temperature regulation component heats or cools according to the command, changing the physical temperature of the optical circulator it is coupled to. The main control unit 108 continuously monitors the feedback from the first power detection unit 104 until the optical power of the leaked light signal decreases again and stabilizes within the minimum minimum range.

[0040] Therefore, this embodiment of the invention utilizes the residual leakage light signal measured by the first power detection unit 104 as a real-time feedback signal for the isolation level of the entire cascaded isolation system, and drives the temperature regulation component to perform dynamic compensation. This achieves self-closed-loop control of the optical circulator's operating point, solving the problem of performance drift of passive isolation devices under extreme temperature differences in space, and ensuring that the system always maintains optimal isolation. This closed-loop regulation does not require an additional temperature sensor, directly using optical performance as the feedback target, making it more direct and accurate. It effectively avoids the risk of decreased isolation due to temperature drift, which could lead to communication quality degradation or damage to front-end devices, greatly improving the system's environmental adaptability and long-term reliability during on-orbit operation.

[0041] In some embodiments, the spatial light receiving module 101 to the unidirectional isolation module 102, the cascaded nodes within the unidirectional isolation module 102, and the unidirectional isolation module 102 and the optical amplification module 107 are all physically connected by polarization-maintaining optical fiber.

[0042] Specifically, polarization-maintaining fiber refers to specially designed optical fibers with a stress structure inside the fiber core, which can force the polarization state of the transmitted light wave to remain unchanged during long-distance transmission. In space laser communication, the polarization state of the optical signal itself may carry information, or the subsequent coherent demodulation equipment may be highly sensitive to it. The optical fiber connection from the output end of the space light receiving module 101 to the input end of the unidirectional isolation module 102, the cascaded optical fiber connection between the first optical circulator 103 and the second optical circulator 106 inside the unidirectional isolation module 102, and the optical fiber connection from the output end of the unidirectional isolation module 102, i.e., the second port of the second optical circulator 106, to the input end of the optical amplification module 107, all require the use of polarization-maintaining fiber, rather than ordinary single-mode fiber.

[0043] Space laser communication systems, especially those employing coherent detection, require extremely high stability of the polarization state of the optical signal. Ordinary single-mode optical fibers, when affected by environmental factors such as temperature changes, mechanical bending, and vibration, will randomly alter the polarization state of the transmitted light, leading to signal corruption or coherent demodulation failure. This invention, by forcibly using polarization-maintaining fibers in all critical forward optical path stages, ensures that the polarization characteristics of the optical signal remain distorted from the moment the space light is coupled into the fiber until it enters the optical amplification module 107. This is crucial for guaranteeing the communication quality of subsequent stages and the stable operation of the unidirectional isolation module 102.

[0044] Figure 2 This is a schematic diagram of another space laser communication receiving system provided in an embodiment of the present invention. Figure 2 As shown, based on the above embodiment, the space laser communication receiving system further includes at least one backup isolation branch 109, a first optical path switcher 111, and a second optical path switcher 112. The at least one backup isolation branch 109 is connected in parallel with the unidirectional isolation module 102. The first optical path switcher 111 and the second optical path switcher 112 are respectively located on the optical input side and the optical output side of the unidirectional isolation module 102, and are both communicatively connected to the main control unit 108 for selecting the backup isolation branch 109.

[0045] Specifically, the backup isolation branch 109 refers to a redundant optical path that is connected in parallel with the primary unidirectional isolation module 102, which consists of at least two cascaded optical circulators, in the optical path. This branch also contains devices with reverse isolation capabilities, such as another set of cascaded circulators, used to replace the primary branch in the event of a hardware failure. The first optical path switcher 111 and the second optical path switcher 112 refer to optical switching devices with multiple input or output ports. The first optical path switcher 111 is located on the optical input side of the primary unidirectional isolation module 102, with its input terminal connected to the spatial light receiving module 101, and its two output terminals connected to the input terminals of the primary isolation module and the backup isolation branch 109, respectively. The second optical path switcher 112 is located on the optical output side of the primary unidirectional isolation module 102, with its two input terminals connected to the output terminals of the primary isolation module and the backup isolation branch 109, respectively, and its output terminal connected to the optical amplification module 107.

[0046] During normal operation, the main control unit 108 controls the first optical path switcher 111 and the second optical path switcher 112 to connect the optical path to the primary unidirectional isolation module 102. Simultaneously, the main control unit 108 continuously monitors the feedback signal from the first power detection unit 104, i.e., the optical power of the residual leaked optical signal. Since this signal reflects the health status of the entire cascaded isolation module, when the main control unit 108 determines that the optical power of the leaked optical signal is greater than or equal to a preset leakage threshold far exceeding the normal value, it indicates that one or two circulators in the current primary unidirectional isolation module 102 may have experienced irreversible hardware failure due to radiation damage, mechanical faults, or other reasons, resulting in a severe loss of its isolation capability. At this time, the main control unit 108 immediately sends a switching command to the first optical path switcher 111 and the second optical path switcher 112. These two switches operate synchronously, switching the optical path from the primary isolation module to the backup isolation branch 109, thereby restoring the system's normal isolation function.

[0047] Therefore, by introducing a backup isolation branch 109 and an optical path switcher, this embodiment of the invention can automatically and quickly perform a primary-backup switch when the performance of the primary isolation module is detected to have failed, which greatly improves the mission reliability and redundancy of the entire space laser communication receiving system and avoids the scrapping of the entire receiving terminal due to the failure of a single circulator.

[0048] In some embodiments, the optical amplification module 107 is an erbium-doped fiber amplifier, the first power detection unit 104 and the second power detection unit 105 both include at least a photodetector, and the system also includes a coherent demodulation module, which is optically connected to the optical output end of the optical amplification module 107 and used to demodulate space communication data from the amplified optical signal.

[0049] Specifically, the erbium-doped fiber amplifier is a concrete implementation of the optical amplification module 107. It uses erbium-doped fiber as the gain medium and directly amplifies signal light in the 1530 nm to 1565 nm band under pump light excitation. The photodetector refers to the core sensing element in the first power detection unit 104 and the second power detection unit 105, used to convert the received optical power signal into a proportional current or voltage signal. The coherent demodulation module refers to the functional module located after the optical amplification module 107. It mixes the amplified optical signal with locally generated, highly stable local oscillator light, and by detecting the phase difference, frequency difference, and polarization state between the two, it can highly sensitively demodulate the carried space communication data from the complex modulated optical signal. The optical amplification module 107 is specifically implemented as an erbium-doped fiber amplifier, adapted for C-band space laser communication. The core photosensitive element of the first power detection unit 104 and the second power detection unit 105 is explicitly defined as a photodetector, such as a PIN photodiode or an avalanche photodiode. The amplified optical signal enters the coherent demodulation module, where it is coherently mixed with the local oscillator light to finally demodulate the space communication data.

[0050] Therefore, this embodiment of the invention specifically defines the optical amplification module 107 as an erbium-doped fiber amplifier, utilizing its advantages of high gain, low noise, and good compatibility with standard polarization-maintaining fiber in the C-band. By defining the detection unit as a photodetector and adding a coherent demodulation module, a complete space laser communication receiving front-end with highly integrated intelligent sensing and control capabilities is realized. For example, the circulator's operating wavelength can be from 1520 nm to 1580 nm, the transmit / receive isolation is better than 50 dB, the mode field core diameter is 10.1 ± 0.4 μm @ 1550 nm, and the numerical aperture (NA) is 0.125. Additionally, the main control unit 108 can also be integrated into the space light receiving module 101. Figure 1 Solid lines represent optical transmission paths, while dashed lines represent...

[0051] This invention also provides a control method for a space laser communication receiving system. Figure 3 This is a flowchart illustrating a control method for a space laser communication receiving system according to an embodiment of the present invention. The control method for the space laser communication receiving system can be used to control the space laser communication receiving system as described in the above embodiment. Figure 3 As shown, the control method of the space laser communication receiving system includes the following steps: S201. Obtain the first electrical signal output by the first power detection unit; wherein, the first electrical signal represents the optical power of the leaked light signal after reverse penetration of the cascaded defense line.

[0052] S202. Obtain the second electrical signal output by the second power detection unit; wherein, the second electrical signal represents the optical power of the reverse echo signal generated by the optical amplification module.

[0053] S203. Based on the first electrical signal and the second electrical signal, perform optical path safety protection and / or isolation closed-loop adjustment on the space laser communication receiving system.

[0054] Specifically, the first electrical signal refers to the digital signal value generated by the photodetector inside the first power detection unit 104 and which can be read by the main control unit 108 after analog-to-digital conversion. The amplitude of the signal is strictly proportional to the optical power of the leaked light signal received by the first power detection unit 104. Therefore, the first electrical signal functionally characterizes the optical power of the leaked light signal.

[0055] The second electrical signal refers to the digital signal value generated by the photodetector inside the second power detection unit 105 and which can be read by the main control unit 108 after analog-to-digital conversion. The amplitude of the signal is strictly proportional to the optical power of the reverse echo signal received by the second power detection unit 105. Therefore, the second electrical signal functionally represents the optical power of the reverse echo signal.

[0056] Optical path safety protection refers to a series of proactive intervention measures implemented by the main control unit 108 to protect sensitive front-end optical devices from damage when it detects potential destructive risks at the optical path level, especially high-power back echoes. These measures include, but are not limited to, cutting off the pump source power supply and triggering a high-speed optical switch to cut off the physical optical path. Isolation closed-loop adjustment refers to the process by which the main control unit 108 uses the optical power of the leaked optical signal fed back by the first electrical signal as the controlled variable, and adjusts the operating state of the unidirectional isolation module 102 in real time by controlling actuators, such as temperature regulation components, so that the optical power of the leaked optical signal always tends to and stabilizes at the minimum value representing the best isolation performance.

[0057] First, the main control unit 108 initiates a high-speed data acquisition task. Through its internal analog-to-digital converter interface, it periodically reads the signal line communicating with the first power detection unit 104, thereby acquiring the first electrical signal output by the first power detection unit 104. At this time, the value stored in the register inside the main control unit 108 reflects in real-time the optical power of the leaked optical signal output by the reverse light-exhausting end of the unidirectional isolation module 102 near the spatial light receiving module 101. Simultaneously, the main control unit 108 performs a synchronous data acquisition operation. Through another internal analog-to-digital converter interface, it periodically reads the signal line communicating with the second power detection unit 105, thereby acquiring the second electrical signal output by the second power detection unit 105. At this time, the value stored in the register inside the main control unit 108 reflects in real-time the optical power of the reverse echo signal generated by the optical amplification module 107, output by the reverse light-exhausting end of the unidirectional isolation module 102 near the optical amplification module 107.

[0058] After acquiring the two key electrical signals, the embedded control algorithm running inside the main control unit 108 begins operation. This algorithm uses the first and second electrical signals as input variables, performing comprehensive calculations and logical comparisons. Based on the results of these calculations and comparisons, the control algorithm generates corresponding control commands and outputs them through the general-purpose input / output port or dedicated communication interface of the main control unit 108. If the determination result indicates that optical path safety protection is required, an emergency cut-off command is output; if the determination result indicates that isolation compensation is required, a temperature adjustment command is output. In this way, the main control unit 108 performs optical path safety protection and / or isolation closed-loop adjustment actions on the space laser communication receiving system according to the first and second electrical signals.

[0059] Therefore, in this embodiment of the invention, the detection signals of the two key nodes before and after the unidirectional isolation module 102, namely the first electrical signal and the second electrical signal, are incorporated into the intelligent control logic executed by the main control unit 108. Compared with the traditional method of acting on a single alarm signal, it can handle two different abnormal situations at the same time, namely the echo enhancement caused by the sudden change in the state of the optical amplification module 107 itself, and the slow decrease in isolation caused by environmental factors or device aging.

[0060] In some embodiments, optical path safety protection includes: triggering an emergency cut-off action when the optical power of the reverse echo signal is greater than or equal to a preset safety power threshold; wherein the cut-off action includes: cutting off the driving current of the pump light source in the optical amplification module 107; or triggering an optical switch connected in series between the unidirectional isolation module 102 and the optical amplification module 107 to cut off the optical path.

[0061] Specifically, the preset safe power threshold refers to a modifiable power threshold stored within the main control unit 108. This value represents the risk boundary. When the optical power of the reverse echo signal reaches or exceeds this value, the system is considered to be in a dangerous state requiring immediate intervention. The setting of this threshold must be based on the damage resistance threshold of the optical components in the front-end spatial light receiving module 101, with a certain safety margin. The emergency cut-off action refers to a rapid response hardware-level operation performed to eliminate dangerous echoes. This action has the highest control authority and can bypass or interrupt the normal software control process, directly acting on power devices or optical path actuators. Cutting off the driving current of the pump source in the optical amplification module 107 refers to interrupting the current path supplied to the pump laser inside the optical amplification module 107 through hardware or software methods. This is the most direct way to stop the generation of echoes from the energy source. The trigger pulse sent to a high-speed optical switch connected in series between the unidirectional isolation module 102 and the optical amplification module 107 cuts off the optical path and sends an electrical trigger pulse to the optical switch device, causing its internal physical optical path to instantly change from the on state to the off state. This physically blocks the path of the echo to the front end. Even if the optical amplification module 107 itself is still generating an echo, the echo cannot pass through the cut-off optical switch in reverse.

[0062] During system operation, the main control unit 108 dynamically compares the value of the second electrical signal representing the optical power of the reverse echo signal acquired in real time with the preset safe power threshold stored internally. When the main control unit 108 determines through comparison that the optical power of the reverse echo signal represented by the currently acquired second electrical signal is greater than or equal to the preset safe power threshold, the logic circuit inside the main control unit 108 will immediately set an emergency state flag. Setting this flag will trigger an interrupt service routine, which bypasses the regular polling schedule and directly executes the instruction to trigger an emergency cutoff action.

[0063] The emergency cut-off action specifically includes two physical operations that can be executed in parallel or selectively. The first operation is that the main control unit 108 sends an invalid level signal directly to the enable control terminal of the driver of the pump light source in the optical amplification module 107 through its dedicated high-speed output pin. Upon receiving the invalid level, the driver immediately shuts off its power output stage, thereby cutting off the driving current of the pump light source in the optical amplification module 107 within microseconds. The pump light disappears, the amplification of the signal light by the optical amplification module 107 stops, and the generated reverse echo also rapidly decays to zero. The second operation is that the main control unit 108 simultaneously or individually sends a high-voltage trigger pulse to the control electrode of the optical switch connected in series between the unidirectional isolation module 102 and the optical amplification module 107. This pulse drives the micro-actuator inside the optical switch to switch its optical path from a closed state to an open state, thereby physically cutting off the light transmission channel.

[0064] In some embodiments, isolation closed-loop adjustment includes generating a temperature compensation command when the optical power of the leaked optical signal deviates from the minimum range and shows an upward trend; and driving a temperature adjustment component thermally coupled to the corresponding optical circulator to change the physical temperature according to the temperature compensation command until the optical power of the leaked optical signal returns to the minimum range.

[0065] Specifically, the minimum range refers to the allowable fluctuation range near the theoretically lowest achievable value of the optical power of the leaked light signal. Due to inherent noise in the optical system and detection circuit, this value is not a constant point, but a small interval containing upper and lower boundaries. This interval is the control target of the isolation closed-loop adjustment process. The upward trend refers to the monotonically increasing statistical characteristic of the optical power of the leaked light signal over multiple consecutive sampling periods. The temperature compensation command refers to the digital control command issued by the main control unit 108. This command includes the control target, such as which specific temperature regulation component is being used, the control direction (e.g., heating or cooling), and the control step size (e.g., the magnitude of temperature change or duty cycle). The temperature regulation component thermally coupled to the corresponding optical circulator refers to the temperature regulation component that is physically tightly fitted to the first optical circulator 103 or the second optical circulator 106 to achieve efficient heat conduction. Each optical circulator is equipped with its own independent temperature regulation component.

[0066] The main control unit 108 continuously monitors the first electrical signal from the first power detection unit 104, i.e., the optical power of the leaked light signal, with a relatively slow time constant. The algorithm aims to search for and maintain the minimum value of this power. When the main control unit 108 identifies that the current value of the optical power of the leaked light signal not only exceeds the preset minimum range, but also that its rate of change for multiple consecutive cycles shows a monotonically increasing trend, the algorithm determines that the current isolation operating point of the system has undergone an unfavorable shift. Based on this determination, the main control unit 108 generates a temperature compensation command. The generation logic of this command follows the principle of directional probing. For example, the algorithm first presets a small positive temperature change. Then, the main control unit 108 sends the command to the temperature regulation component thermally coupled to the corresponding optical circulator, for example, applying a very small positive drive current to the semiconductor thermoelectric cooler coupled to the first optical circulator 103, so that it slightly heats the first optical circulator 103.

[0067] After applying the temperature compensation command, the main control unit 108 immediately enters the observation phase and continues to read the first electrical signal. If the observed optical power of the leaked light signal begins to decrease after heating, the algorithm determines that the heating direction is correct and will continue to apply the next temperature compensation command in this direction. Conversely, if the observed leakage light power further increases, the algorithm determines that the heating direction is incorrect and will generate a reverse temperature compensation command, i.e., a cooling command, in the next iteration. Through the iterative optimization process, the main control unit 108 drives the temperature regulation component to continuously change the physical temperature of the coupled optical circulator until the optical power value of the leaked light signal falls back into and stabilizes within the minimum range. At this point, the algorithm considers the system to have returned to the optimal isolation state and stops outputting compensation commands.

[0068] In some embodiments, the control method of the space laser communication receiving system further includes: when the optical power of the leaked optical signal is greater than or equal to a preset limit leakage threshold, determining that the current cascaded isolation optical path has experienced a hardware failure, and controlling the switch to the backup isolation branch 109.

[0069] Specifically, the preset limit leakage threshold refers to a power critical value stored inside the main control unit 108 that is much higher than the upper limit of the minimum value range. This threshold is different from the aforementioned preset safe power threshold. It is not used to trigger protection actions, but rather to diagnose whether the hardware has suffered a permanent and irreversible failure. Hardware failure refers to mechanical damage, performance mutation, or complete physical damage to the optical components in the unidirectional isolation module 102, such as the first optical circulator 103 or the second optical circulator 106, making it impossible to restore its original isolation performance by external means such as adjusting the temperature. Control switching to the backup isolation branch 109 means that the main control unit 108 sends synchronous gating commands to the first optical path switcher 111 and the second optical path switcher 112, changing the internal optical path connection state of these two optical switches, and guiding the forward-transmitting optical signal from the currently operating unidirectional isolation module 102 to the backup isolation branch 109 connected in parallel.

[0070] In some embodiments, the control method of the space laser communication receiving system further includes: acquiring the main optical path input power of the space optical receiving module 101; acquiring the dynamic reflectivity based on the main optical path input power and the optical power of the reverse echo signal; and acquiring the aging trend of the space laser communication receiving system based on the time series fitting curve characteristics of the dynamic reflectivity.

[0071] Specifically, the main optical path input power refers to the total optical power value measured at the output end of the spatial optical receiving module 101 or on the main optical path immediately following it, after being received by the module and coupled into the optical fiber. This power value represents the intensity of the effective spatial signal light received by the system. Dynamic reflectivity refers to the ratio of the optical power of the back echo signal to the main optical path input power. This ratio updates in real time as the main optical path input power and the back echo signal optical power change. This parameter eliminates the influence of incident signal intensity fluctuations on the absolute echo power, more accurately reflecting the intrinsic reflection and noise characteristics within the optical amplification module 107 and the unidirectional isolation module 102. The time series refers to a series of data points of dynamic reflectivity arranged in chronological order. This dataset records the evolution trajectory of this parameter within the system cycle. The fitting curve characteristics refer to the parameters of the mathematical model obtained after mathematical fitting of the time series data, such as least squares linear fitting. For example, for linear fitting, the slope represents the rate of change of dynamic reflectivity, and the intercept represents the initial state. The aging trend refers to the direction and rate at which the physical performance of the optical amplification module 107 and the unidirectional isolation module 102 gradually degrades over time, as inferred from the characteristics of the fitted curve.

[0072] First, the main control unit 108 needs to acquire an additional reference signal. It splits a small portion of the light from the main optical path using an optical splitter and guides it to an additional third power detection unit, which is also communicatively connected to the main control unit 108. In this way, the main control unit 108 can acquire the main optical path input power of the spatial light receiving module 101, i.e., the absolute value of the signal strength currently received by the system. Next, the main control unit 108 performs a calculation with the second electrical signal, which is synchronously read and represents the optical power of the reverse echo signal, and the newly acquired main optical path input power. Specifically, it calculates the latter divided by the former, thereby obtaining the dynamic reflectivity based on the main optical path input power and the optical power of the reverse echo signal. This calculation eliminates interference caused by signal strength changes, yielding a health indicator that purely reflects the system's internal losses and reflection characteristics. Finally, the main control unit 108 stores the dynamic reflectivity calculated each time and its corresponding timestamp. As the system runs, these data points form a time series. The main control unit 108 periodically performs mathematical processing on this time series to obtain the characteristics of the dynamic reflectivity time series fitting curve, such as the slope of the fitted straight line, to determine the system's health status. If the slope is positive, it indicates that the dynamic reflectivity is increasing over time. Furthermore, based on the magnitude and trend of the slope, the aging trend of the equipment can be obtained, such as predicting how many months it will take for the dynamic reflectivity to increase to the level that triggers an alarm threshold.

[0073] Therefore, by adopting dynamic reflectivity as a normalized index, the embodiments of the present invention make the echo data measured under different input optical power and different operating modes comparable. At the same time, by predicting the aging trend of the equipment based on the characteristics of the fitted curve, the waste of resources caused by premature replacement can be avoided, and online failure caused by late replacement can also be prevented.

[0074] This invention also provides a space communication device, including the space laser communication receiving system described in the above embodiments, and therefore possesses the beneficial effects described in the above embodiments, which will not be repeated here. Specifically, the space communication device refers to a complete-scale communication payload mounted on spacecraft such as satellites, space stations, or deep space probes, used to perform space-to-ground or inter-satellite information interaction in vacuum and extremely high and low temperature environments. The aforementioned space laser communication receiving system is integrated into the space communication device as a core subsystem.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these modifications or substitutions do 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 laser communication receiving system, characterized in that, include: Spatial light receiving module, used to receive input spatial light signals; The optical amplifier module is used to amplify the power of the input optical signal; A unidirectional isolation module is disposed on the main optical path between the spatial light receiving module and the optical amplification module, and includes at least two cascaded optical circulators. The first power detection unit is connected to the reverse light exhaust end of the unidirectional isolation module near the first stage of the spatial light receiving module, and is used to receive the leaked light signal after reverse penetration of the cascaded defense line. The second power detection unit is connected to the reverse light exhaust end of the unidirectional isolation module near the first stage of the optical amplification module, and is used to receive the reverse echo signal generated by the optical amplification module. The main control unit is communicatively connected to the first power detection unit and the second power detection unit, respectively, and is used to perform optical path safety protection and / or isolation closed-loop adjustment of the space laser communication receiving system based on the optical power of the leaked light signal and the reverse echo signal.

2. The space laser communication receiving system according to claim 1, characterized in that, The unidirectional isolation module includes at least a first optical circulator and a second optical circulator. The first port of the first optical circulator is optically connected to the spatial light receiving module, the second port is optically connected to the first port of the second optical circulator, and the third port is optically connected to the first power detection unit to form the reverse light output end near the first stage of the spatial light receiving module. The second port of the second optical circulator is optically connected to the optical input port of the optical amplification module, and the third port is optically connected to the second power detection unit to form the reverse light exhaust port near the first stage of the optical amplification module.

3. The space laser communication receiving system according to claim 1 or 2, characterized in that, The optical amplification module includes a pump light source and is communicatively connected to the main control unit; and / or, an optical switch is connected in series between the unidirectional isolation module and the optical amplification module, and the control terminal of the optical switch is communicatively connected to the main control unit.

4. The space laser communication receiving system according to claim 1 or 2, characterized in that, Also includes: Multiple temperature control components are thermally coupled to their respective optical circulators and communicatively connected to the main control unit.

5. The space laser communication receiving system according to claim 1 or 2, characterized in that, The spatial light receiving module and the unidirectional isolation module, as well as the cascaded nodes within the unidirectional isolation module and the unidirectional isolation module and the optical amplification module, are all physically connected using polarization-maintaining optical fibers.

6. The space laser communication receiving system according to claim 1 or 2, characterized in that, Also includes: At least one backup isolation branch is connected in parallel with the unidirectional isolation module; The first optical path switcher and the second optical path switcher are respectively located on the optical input side and optical output side of the unidirectional isolation module, and are both communicatively connected to the main control unit to select the backup isolation branch.

7. The space laser communication receiving system according to claim 1 or 2, characterized in that, The optical amplification module is an erbium-doped fiber amplifier. The first power detection unit and the second power detection unit each contain at least a photodetector. The system also includes a coherent demodulation module, which is optically connected to the optical output end of the optical amplification module and is used to demodulate space communication data from the amplified optical signal.

8. A control method for a space laser communication receiving system, characterized in that, The method for controlling the space laser communication receiving system as described in any one of claims 1-7 includes: Acquire the first electrical signal output by the first power detection unit; wherein, the first electrical signal represents the optical power of the leaked light signal after reverse penetration of the cascaded defense line; Acquire the second electrical signal output by the second power detection unit; wherein, the second electrical signal represents the optical power of the reverse echo signal generated by the optical amplification module; Based on the first electrical signal and the second electrical signal, the space laser communication receiving system is subjected to optical path safety protection and / or isolation closed-loop adjustment.

9. The control method for the space laser communication receiving system according to claim 8, characterized in that, Implement optical path security protection, including: When the optical power of the reverse echo signal is greater than or equal to a preset safe power threshold, an emergency cut-off action is initiated. The cutting-off action includes: cutting off the driving current of the pump light source in the optical amplification module; or triggering an optical switch connected in series between the unidirectional isolation module and the optical amplification module to cut off the optical path.

10. The control method for the space laser communication receiving system according to claim 8, characterized in that, Perform closed-loop adjustment of isolation, including: A temperature compensation command is generated when the optical power of the leaked optical signal deviates from the minimum range and shows an upward trend. According to the temperature compensation command, the temperature adjustment component thermally coupled to the corresponding optical circulator is controlled to change the physical temperature until the optical power of the leaked optical signal returns to the minimum value range.

11. The control method for the space laser communication receiving system according to any one of claims 8-10, characterized in that, Also includes: When the optical power of the leaked optical signal is greater than or equal to the preset limit leakage threshold, it is determined that the current cascaded isolation optical path has experienced a hardware failure, and the system controls the switch to the backup isolation branch.

12. The control method for the space laser communication receiving system according to any one of claims 8-10, characterized in that, Also includes: Obtain the main optical path input power of the spatial light receiving module; The dynamic reflectivity is obtained based on the input power of the main optical path and the optical power of the reverse echo signal. The aging trend of the space laser communication receiving system is obtained based on the time series fitting curve characteristics of the dynamic reflectivity.

13. A space communication device, characterized in that, Including the space laser communication receiving system as described in any one of claims 1-7.

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