Free space optical communication system, device and method

Abstract

The invention relates to the technical field of laser communication, in particular to a free space optical communication system, device and method. According to the free space optical communication system provided by the invention, the space light beam is firstly coupled with the multimode optical fiber, and the characteristic that the diameter of a fiber core of the multimode optical fiber is larger is utilized, so that the coupling efficiency is improved, and the energy loss in the coupling process can be effectively reduced. Then, a mode demultiplexer is used, and a mode conversion technology is adopted to separate and convert multiple modes of light in the multimode optical fiber, so that the obtained LP01 mode is separated and converted into a fundamental mode of the single-mode optical fiber to serve as an output optical signal, and the problem that the modes of the multimode optical fiber and the single-mode optical fiber are not matched is solved through the mode conversion technology; and finally, the converted fundamental mode signal in the single-mode fiber is used for communication, so that a high-speed communication module can be better matched.

Description

[Technical field]

[0001] The present invention relates to the field of laser communication technology, and in particular to a free-space optical communication system, device and method. [Background technology]

[0002] Free-space optical communication combines the advantages of microwave communication and optical fiber communication, and has the advantages of wide bandwidth, large capacity, high speed, anti-interference, miniaturization and high security. Traditional free-space optical communication systems using multimode optical fiber face limitations in transmission speed, which makes them less compatible with high-speed optical communication modules. Therefore, in order to facilitate information processing and long-distance transmission, and to combine with existing communication technologies, free-space optical communication requires the use of single-mode optical fiber for coupling. When using single-mode optical fiber for coupling, the coupling efficiency of the space beam-single-mode optical fiber is an important parameter in the laser communication system. The higher the coupling efficiency, the smaller the energy loss in the coupling process, which determines the communication efficiency and communication distance of the communication system.

[0003] However, it is extremely difficult to achieve a high coupling efficiency in practical applications. In long-distance space optical communication links, it will be affected by many factors such as atmospheric turbulence, communication beam divergence angle, receiving port diameter, field of view and mechanical platform vibration. In addition, the core diameter of single-mode optical fiber is extremely small, about 9 microns, which further increases the difficulty of coupling. [Summary of the invention]

[0004] In order to solve the technical problem of low coupling efficiency of a space light beam to a single-mode optical fiber in an existing space optical communication system, the present invention provides a free-space optical communication system, device and method.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a free space optical communication system, comprising at least two laser communication terminals, wherein a communication link for spatial light beam propagation is formed between the laser communication terminals, and the laser communication terminals comprise: a coupling module and a multimode optical fiber supporting linear polarization mode transmission, wherein the coupling module is used to couple the spatial light beam into the multimode optical fiber; a mode demultiplexer, wherein the input end of the mode demultiplexer is connected to the multimode optical fiber, and is used to separate the multiple modes of light received by the multimode optical fiber and convert them into base mode signals in the corresponding multiple single-mode optical fibers, and define the base mode signal of the single-mode optical fiber after the LP01 mode conversion in the multimode optical fiber is completed as the output optical signal; a single-mode optical fiber, which is connected to the LP01 mode conversion output port of the mode demultiplexer, and is used to receive and transmit the output optical signal; and a photoelectric detection module, wherein the photoelectric detection module is connected to the mode demultiplexer through the single-mode optical fiber, and is used to convert the output optical signal into an electrical signal.

[0006] Preferably, the mode demultiplexer is implemented by multi-plane light conversion technology or photon lantern technology.

[0007] Preferably, an optical circulator is provided between the output end of the coupling module and the multimode optical fiber.

[0008] Preferably, the system further comprises an erbium-doped fiber amplifier, which is arranged between the photoelectric detection module and the mode demultiplexer and is used to amplify the output optical signal after mode conversion.

[0009] Preferably, the photoelectric detection module comprises an optical filter and a coherent light receiver connected in sequence.

[0010] Preferably, the coupling module is provided with a light source component, and the light source component is used to emit beacon light. The coupling module is also provided with a beacon light processing module for receiving, detecting and processing the beacon light.

[0011] Preferably, the coupling module also includes a beam splitter and a coupling lens, the beacon light processing module includes a position sensitive detector, the focus of the coupling lens is aligned with the end face center of the multimode optical fiber, the beam splitter is located on the side of the coupling lens close to the multimode optical fiber, the beacon light is focused by the coupling lens and reflected by the beam splitter to the position sensitive detector, and the spatial light beam is focused by the coupling lens and coupled to the multimode optical fiber.

[0012] Preferably, the multimode optical fiber is a few-mode optical fiber.

[0013] In order to solve the above technical problems, the present invention provides another technical solution as follows: a free space optical communication device, comprising the above free space optical communication system.

[0014] In order to solve the above technical problems, the present invention provides another technical solution as follows: a free space optical communication method, applied to the above free space optical communication system, comprising the following steps: coupling a spatial light beam into a multimode optical fiber; separating the spatial light beam received by the multimode optical fiber and converting it into a base mode signal of a single mode optical fiber; selecting the base mode signal of the single mode optical fiber converted by the LP01 mode as the output optical signal; and receiving, transmitting and processing the output optical signal.

[0015] Compared with the prior art, the free-space optical communication system, device and method provided by the present invention have the following beneficial effects:

[0016] 1. A free-space optical communication system provided by an embodiment of the present invention first couples a space light beam with a multi-mode optical fiber, utilizing the larger core diameter of the multi-mode optical fiber to improve the coupling efficiency and effectively reduce the energy loss during the coupling process. Then, a mode demultiplexer is used to separate and convert the multiple modes of light in the multi-mode optical fiber using mode conversion technology, and the LP01 mode is separated and converted into the base mode of the single-mode optical fiber as the output optical signal. This mode conversion technology solves the problem of mode mismatch between the multi-mode optical fiber and the single-mode optical fiber. Finally, the base mode signal in the converted single-mode optical fiber is used for communication, which can better match the high-speed communication module.

[0017] 2. In a free-space optical communication system provided by an embodiment of the present invention, a mode demultiplexer is implemented by multi-plane optical conversion technology or photon lantern technology. Both technologies can separate different modes in a multi-mode optical fiber and convert them into base mode signals. In particular, the photon lantern technology has very low loss during mode conversion, and theoretically can achieve zero loss.

[0018] 3. In a free-space optical communication system provided by an embodiment of the present invention, an optical circulator is arranged between the output end of the coupling module and the multimode optical fiber. The setting of the optical circulator enables each laser communication terminal to use the same optical system for communication, thereby avoiding the problem of non-coaxial communication reception and transmission during assembly and debugging, and realizing full-duplex communication of the laser communication terminal without adding laser emitting devices. The optical circulator also has a compact structure and a small size, and can be easily integrated into the free-space optical communication system.

[0019] 4. A free-space optical communication system provided by an embodiment of the present invention further includes an erbium-doped fiber amplifier, which is arranged between the photoelectric detection module and the mode demultiplexer. The output optical signal obtained after mode conversion can enter the erbium-doped fiber amplifier for amplification, which can minimize signal attenuation, thereby improving the quality and distance of signal transmission.

[0020] 5. In a free space optical communication system provided by an embodiment of the present invention, a photoelectric detection module includes an optical filter and a coherent optical receiver connected in sequence. The output optical signal is first filtered by the optical filter, and then the filtered optical signal is directed to the coherent optical receiver. Inside the receiver, the optical signal is mixed with the local oscillator light to achieve coherent detection and converted into an electrical signal. Subsequently, the signal is collected by an oscilloscope and processed by a digital signal processor.

[0021] 6. In a free-space optical communication system provided by an embodiment of the present invention, a coupling module is provided with a light source component and a beacon light processing module for emitting and processing beacon light. The beacon light can be provided to play a guiding and calibrating role. By emitting and receiving the beacon light, the transmission path and coupling position of the space light beam can be accurately determined, thereby improving the coupling efficiency and accuracy.

[0022] 7. A free-space optical communication system provided by an embodiment of the present invention, wherein the coupling module further includes a beam splitter and a coupling lens, the beacon light processing module includes a position sensitive detector, the focus of the coupling lens is aligned with the end face center of the multimode optical fiber, the beam splitter is located on the side of the coupling lens close to the multimode optical fiber, the beacon light is focused by the coupling lens and reflected to the position sensitive detector by the beam splitter, and the spatial light beam is focused by the coupling lens and coupled to the multimode optical fiber. The coupling lens can efficiently couple the spatial light beam to the multimode optical fiber, and by accurately designing and adjusting the parameters of the coupling lens, the optimal focusing and matching of the spatial light beam can be achieved, thereby reducing the loss of light energy and improving the coupling efficiency. The cooperation of the beam splitter and the position sensitive detector can use the beacon light to monitor the position change of the spatial light beam near the focus of the coupling lens in real time, and adjust the position or focal length of the coupling lens as needed, thereby improving the optical coupling efficiency. The robustness of the coupling module can also be enhanced.

[0023] 8. In a free-space optical communication system provided by an embodiment of the present invention, the multimode optical fiber is preferably a few-mode optical fiber. The core diameter of the few-mode optical fiber is larger than that of the single-mode optical fiber, and a higher coupling efficiency can be obtained. At the same time, compared with general multi-mode optical fibers, since the number of light wave modes supported by the few-mode optical fiber is limited, and the propagation characteristics of these modes in the optical fiber are relatively stable, problems such as inter-modal dispersion can be more effectively avoided, which enables the few-mode optical fiber to maintain a high signal quality during transmission. The modes in the few-mode optical fiber can be effectively separated and converted into the fundamental mode signal of the single-mode optical fiber, thereby supporting high-speed and large-capacity data transmission. The few-mode optical fiber has lower signal attenuation and is more suitable for long-distance and high-speed transmission. Therefore, it can be appropriately selected according to the specific application to further improve the quality of the optical output signal.

[0024] 9. The embodiment of the present invention further provides a free space optical communication device, which has the same beneficial effects as the above-mentioned free space optical communication system, and will not be described in detail here.

[0025] 10. The embodiment of the present invention further provides a free space optical communication method, which has the same beneficial effects as the above-mentioned free space optical communication system, and will not be described in detail here.

Brief Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 It is a schematic diagram of the framework of a free space optical communication system provided by the first embodiment of the present invention.

[0028] Figure 2 It is a schematic diagram of the framework of a laser communication terminal of a free space optical communication system provided by the first embodiment of the present invention.

[0029] Figure 3a This is a simulation diagram of the relationship between radial deviation and coupling efficiency of few-mode fiber and single-mode fiber.

[0030] Figure 3b This is a simulation diagram of the relationship between the axial deviation and coupling efficiency of few-mode fiber and single-mode fiber.

[0031] Figure 4 It is a table diagram of the test data of each mode light after mode conversion by the mode demultiplexer.

[0032] Figure 5 It is a schematic diagram of the framework of the photoelectric detection module of the free space optical communication system provided by the first embodiment of the present invention.

[0033] Figure 6 4 is a schematic diagram of a free space optical communication system provided by the second embodiment of the present invention.

[0034] Figure 7 It is a schematic diagram of the framework of a laser communication terminal of a free space optical communication system provided by the second embodiment of the present invention.

[0035] Figure 8 It is a schematic diagram of the framework of a free-space optical communication device provided by the third embodiment of the present invention.

[0036] Fig. 9 4 is a schematic diagram of a free space optical communication device provided in accordance with a fourth embodiment of the present invention.

[0037] Fig.10 4 is a flowchart of steps S1 to S4 of a free-space optical communication method provided in a fifth embodiment of the present invention.

[0038] Description of the accompanying drawings:

[0039] 1. Free space optical communication system; 2. Free space optical communication system; 3. Free space optical communication device; 4. Free space optical communication device;

[0040] 10. Laser communication terminal; 11. Coupling module; 12. Few-mode optical fiber; 13. Mode demultiplexer; 15. Single-mode optical fiber; 16. Photoelectric detection module; 17. Optical circulator; 18. Erbium-doped fiber amplifier; 20. Laser communication terminal; 21. Multimode optical fiber;

[0041] 100, spatial light beam; 110, beam splitter; 111, position sensitive detector; 112, coupling lens; 113, light source assembly; 114, beacon light; 160, optical filter; 161, coherent light receiver. [Specific implementation method]

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] See also Figure 1 and Figure 2 The first embodiment of the present invention provides a free space optical communication system 1, comprising: at least two laser communication terminals 10, a communication link for propagation of a spatial light beam 100 is formed between the laser communication terminals 10; the laser communication terminals 10 include:

[0044] A coupling module 11 and a few-mode optical fiber 12 supporting linear polarization mode transmission, wherein the coupling module 11 is used to couple the spatial light beam 100 into the few-mode optical fiber 12;

[0045] A mode demultiplexer 13, the input end of which is connected to the few-mode optical fiber 12, for separating the multiple modes of light received by the few-mode optical fiber 12 and converting them into the fundamental mode signals in the corresponding multiple single-mode optical fibers, and defining the fundamental mode signal of the single-mode optical fiber after the LP01 mode conversion in the few-mode optical fiber 12 is completed as the output optical signal;

[0046] The single-mode optical fiber 15 is connected to the LP01 mode conversion output port of the mode demultiplexer 13 and is used to receive and transmit output optical signals;

[0047] The photoelectric detection module 16 is connected to the mode demultiplexer 13 via the single-mode optical fiber 15 and is used to convert the output optical signal into an electrical signal.

[0048] It can be understood that the laser communication terminal 10 is responsible for transmitting and receiving laser signals to achieve high-speed and safe data transmission. Each laser communication terminal 10 sends and receives data at the same time, thereby achieving full-duplex communication and ensuring fast, efficient and two-way data flow.

[0049] It can be understood that in this embodiment, the laser communication terminal 10 supports the use of few-mode optical fiber 12 to send and receive signals. When the laser communication terminal 10 is used as a receiving end, compared with directly coupling the spatial beam 100 with the single-mode optical fiber 15, the coupling module 11 first couples the spatial beam 100 with the few-mode optical fiber 12, utilizing the larger core diameter of the few-mode optical fiber 12, improving the coupling efficiency, and effectively reducing the energy loss during the coupling process. In addition, under the conditions of atmospheric turbulence effects, pointing errors, and platform vibration, the stability of the energy received by the few-mode optical fiber 12 is also better than that of the single-mode optical fiber 15.

[0050] For example, the core diameter of the few-mode fiber 12 is 18.5 microns, and the core diameter of the single-mode fiber 15 is 9 microns, and the coupling efficiency of the two is calculated respectively. The simulation results obtained are as follows: Figure 3a and Figure 3b As shown, Figure 3a The ordinate represents the coupling efficiency η, and the abscissa represents the radius length r of the few-mode fiber 12 and the single-mode fiber 15. b , it can be seen that the coupling efficiency of the few-mode fiber 12 and the single-mode fiber 15 varies with the radial deviation; Figure 3b The ordinate represents the coupling efficiency η, and the abscissa represents the axial deviation ΔZ of the few-mode optical fiber 12 and the single-mode optical fiber 15. It can be seen that the coupling efficiency of the few-mode optical fiber 12 and the single-mode optical fiber 15 changes with the axial deviation. Taking 50% coupling efficiency as an example, the multimode optical fiber 21 can ensure that the coupling efficiency is not less than 50% in the presence of a 6.7 micron radial deviation or a ±339 micron axial deviation. To ensure the same coupling efficiency, the single-mode optical fiber 15 has an allowable radial deviation and axial deviation of 3.3 microns and ±81 microns, respectively. It can be understood that as the core diameter of the few-mode optical fiber 12 increases, while ensuring the same coupling efficiency, its allowable radial deviation and axial deviation range will further increase. Compared with the coupling efficiency of the spatial light beam 100 directly to the single-mode optical fiber 15, the coupling efficiency of the spatial light beam 100 to the few-mode optical fiber 12 will also be further improved.

[0051] It can be understood that the mode demultiplexer 13 is used to separate and convert the multiple modes of light in the few-mode optical fiber 12 using mode conversion technology to obtain the fundamental mode signal that can be received by the single-mode optical fiber 15, and then the single-mode optical fiber 15 transmits it. This solves the technical problem of mismatch between the few-mode optical fiber 12 and the single-mode optical fiber 15, so that the free-space optical communication system 1 in this embodiment can have the advantages of the high coupling rate of the few-mode optical fiber 12 and the long-distance signal transmission and high-speed signal transmission of the single-mode optical fiber 15. At the same time, compared with the existing method of using adaptive optical technology to improve the coupling efficiency, the mode demultiplexer 13 in this embodiment is used as a passive device to improve the coupling efficiency, is not limited by the system bandwidth, and performs more stably in complex environments, and can realize high-speed and stable free-space optical communication in turbulent atmospheres.

[0052] It can be understood that in order to further improve the coupling efficiency, adaptive optical technology can also be used at the transmitting end in the laser communication terminal 10 to correct the distorted wavefront, improve the quality of the spatial beam 100, and then couple the spatial beam 100 with the few-mode optical fiber 12.

[0053] It can be understood that the single-mode optical fiber 15 is connected to the LP01 mode conversion output port of the mode demultiplexer 13. The LP01 mode receives most of the total power received by the few-mode optical fiber 12, and the signal strength is the largest and the jitter is the smallest. At the same time, the coupling efficiency of the spatial light beam 100 is improved by using the few-mode optical fiber 12, which further improves the quality of the fundamental mode signal separated and converted by the mode demultiplexer 13. Therefore, the LP01 mode is selected to be separated and converted into the fundamental mode in the single-mode optical fiber 15 as the output optical signal, which can achieve high-speed and low bit error rate signal transmission.

[0054] It can be understood that directly selecting the fundamental mode signal of the LP01 mode conversion as the output optical signal without detecting and processing the fundamental mode signals of other mode conversions can not only ensure the reliability of communication, but also has less difficulty in actual technical implementation, which can greatly improve communication efficiency and reduce communication costs.

[0055] It can be understood that the free-space optical communication system 1 is also provided with a stepper motor (not shown) for adjusting and controlling the position of optical components such as the coupling module 11 or the few-mode fiber 12 to ensure optimal coupling between the spatial light beam 100 and the few-mode fiber 12.

[0056] As a specific embodiment, two laser communication terminals 10 are set at a horizontal interval of 1 km in the city to form a free space optical communication system 1. Among them, the wavelength of the spatial light beam 100 is 1550nm, and the divergence angle is 500μrad; the wavelength of the beacon light is 850nm, and the divergence angle is 8mrad; the receiving aperture of the coupling module 11 is 50mm; the accuracy of the stepper motor is 80μrad. The few-mode optical fiber 12 is designed to support and transmit four linear polarization modes: LP01, LP11, LP02 and LP21. Multiple photodetectors are used to simultaneously collect the four mode optical signals of LP01, LP11, LP02, and LP21 after mode conversion by the mode demultiplexer 13. The test data is as follows Figure 4As shown, the photodetector completes a sampling every 1ms, where the energy fluctuation range of the LP01 mode is 5.9dB, the energy jitter variance is 0.8, the average received energy is -8.2dBm, and the probability that the received energy falls within the central 3dB range is 93.09%. The energy fluctuation range of the LP02 mode is 11.8dB, the energy jitter variance is 1.3, the average received energy is -25.2dBm, and the probability that the received energy falls within the central 3dB range is 74.85%. The energy fluctuation range of the LP11 mode is 8.3dB, the energy jitter variance is 1.2, the average received energy is -14.2dBm, and the probability that the received energy falls within the central 3dB range is 77.49%. The energy of the LP21 mode has exceeded the range, the processed data has errors, the detector sensitivity is -60dB, the data below -60dB has been abandoned, the fluctuation range of the original data is greater than 50dB, the energy jitter variance is 2.4, the average received energy is -62.3dBm, and the probability that the received energy falls within the central 3dB range is 17.29%. The power meter measured the energy of the FMF before mode demultiplexing to be -5.0dBm, and the total received average energy after mode demultiplexing was -7.1dBm. The received energy of the LP01 mode is the largest among the four modes, accounting for 78.82% of the total received energy, and the jitter variance and fluctuation range of the LP01 mode are also the smallest. This shows that after 1km atmospheric link transmission, the LP01 mode is still dominant. Moreover, the LP01 mode can still maintain high energy intensity and small energy fluctuation characteristics after demultiplexing. Therefore, the LP01 mode has high stability at the demultiplexing end. According to the test, the base mode signal converted from the LP01 mode can complete 20Gbps data transmission with a bit error rate better than 10 -6 .

[0057] Further, the mode demultiplexer 13 is implemented by multi-plane light conversion technology or photon lantern technology.

[0058] It can be understood that both the multi-plane optical conversion technology and the photon lantern technology can separate and convert different modes in the few-mode optical fiber 12 into fundamental mode signals, and both have low losses, further ensuring the reliability of selecting the LP01 mode separation and conversion into the fundamental mode in the single-mode optical fiber 15 as the output optical signal.

[0059] It can be understood that the multi-plane optical conversion technology has a wider working bandwidth, can achieve efficient mode conversion within a wider wavelength range, and has the advantages of simple structure and low loss.

[0060] Preferably, in this embodiment, photon lantern technology is selected to realize mode conversion. Photon lantern technology has lower insertion loss and can achieve zero loss in theory, which can further ensure the reliability of output optical signal transmission. At the same time, photon lantern devices also have the advantages of small size, strong anti-electromagnetic interference performance, low crosstalk, etc.

[0061] Furthermore, an optical circulator 17 is provided between the output end of the coupling module 11 and the few-mode optical fiber 12 .

[0062] It can be understood that the setting of the optical circulator 17 enables each laser communication terminal 10 to use the same optical system for communication, and the sending and receiving of the space light beam 100 can be realized by the same laser emitting device, thereby avoiding the problem of non-coaxial communication reception and sending during the assembly and debugging process, and realizing full-duplex communication between laser communication terminals 10 without adding another independent laser emitting device. In addition, the optical circulator also has a compact structure and a small size, which can be easily integrated in the free space optical communication system 1, simplifying the design of the system. At the same time, the optical circulator 17 has excellent port isolation performance, which can ensure the transmission efficiency and accuracy of the optical signal, and has a low insertion loss, which can reduce the energy loss of the optical signal during the transmission process.

[0063] Specifically, see Figure 2 When the laser communication terminal 10 is used as a receiving end, the optical signal enters through port 2 of the optical circulator 17 and is output from port 3. In this embodiment, the spatial light beam 100 enters port 2 of the optical circulator 17 after being focused by the coupling lens 112, and is output from port 3 to the least-mode optical fiber 12. When the laser communication terminal 10 is used as a transmitting end, the optical signal enters through port 1 and is output from port 2.

[0064] Furthermore, the system also includes an erbium-doped fiber amplifier 18, which is arranged between the photoelectric detection module 16 and the mode demultiplexer 13, and is used to amplify the output optical signal after the mode conversion.

[0065] It can be understood that the output optical signal obtained after mode conversion can enter the erbium-doped fiber amplifier 18 through the single-mode optical fiber 15 to be amplified, which can minimize the attenuation of the signal, thereby improving the quality and distance of signal transmission.

[0066] Please further combine Figure 5 The photoelectric detection module 16 includes an optical filter 160 and a coherent light receiver 161 which are connected in sequence.

[0067] It can be understood that the output optical signal is first filtered by the optical filter 160, and then the filtered optical signal is directed to the coherent optical receiver 161, where the optical signal is mixed with the local oscillator light to achieve coherent detection and converted into an electrical signal, which is then collected by an oscilloscope and processed by a digital signal processor.

[0068] Please continue reading Figure 2 The coupling module 11 is provided with a light source assembly 113, and the light source assembly 113 is used to emit a beacon light 114. The coupling module 11 is also provided with a beacon light processing module (not shown) for receiving, detecting and processing the beacon light 114.

[0069] It can be understood that the beacon light 114 plays a role of guidance and calibration in the coupling module 11. By transmitting and receiving the beacon light 114, the transmission path and coupling position of the spatial light beam 100 can be accurately determined, further improving the coupling efficiency and accuracy.

[0070] Furthermore, the coupling module 11 includes a beam splitter 110 and a coupling lens 112, the beacon light processing module includes a position sensitive detector 111, the focus of the coupling lens 112 is aligned with the end face center of the few-mode fiber 12, the beam splitter 110 is located on the side of the coupling lens 112 close to the few-mode fiber 12, the beacon light 114 is focused by the coupling lens 112 and reflected by the beam splitter 110 to the position sensitive detector 111, and the spatial light beam 100 is focused by the coupling lens 112 and coupled to the few-mode fiber 12.

[0071] It can be understood that the coupling lens 112 can efficiently couple the spatial light beam 100 into the few-mode optical fiber 12. By precisely designing and adjusting the parameters of the coupling lens 112, optimal focusing and matching of the spatial light beam 100 can be achieved, thereby reducing the loss of light energy and improving coupling efficiency.

[0072] Specifically, the coupling lens 112 can be a transmitting-end coupling lens 112 , a receiving-end coupling lens 112 , or a transmitting-receiving integrated coupling lens 112 according to the communication role of the laser communication terminal 10 .

[0073] It can be understood that when an optical circulator 17 is provided between the output end of the coupling module 11 and the few-mode optical fiber 12 , the focus alignment of the coupling lens 112 needs to take into account the influence of the optical circulator on the optical signal.

[0074] It can be understood that the cooperation of the beam splitter 110 and the position sensitive detector 111 can use the beacon light to monitor the position change of the space light beam 100 near the focus of the coupling lens 112 in real time, and adjust the position or focal length of the coupling lens 112 as needed, thereby improving the light coupling efficiency. The robustness of the coupling module 11 can also be enhanced. In practical applications, the position of the space light beam 100 may change due to environmental interference, device aging and other factors. By monitoring and feeding back these changes in real time through the position sensitive detector 111, potential problems can be discovered and corrected in a timely manner, thereby ensuring the stable operation of the system.

[0075] See also Figure 6 and Figure 7 The second embodiment of the present invention provides another free-space optical communication system 2, which includes at least two laser communication terminals 20. The laser communication terminal 20 is different from the above-mentioned laser communication terminal 10 only in that the few-mode optical fiber 12 in the laser communication terminal 10 is replaced by a multi-mode optical fiber 21.

[0076] It can be understood that the core diameter of the multimode optical fiber 21 is large, and coupling the spatial light beam 100 with the multimode optical fiber 21 first can obtain a higher coupling efficiency than directly coupling the spatial light beam 100 with the single-mode optical fiber, thereby further improving the quality of signal transmission. In addition, the free-space optical communication system 2 also has all the beneficial effects of the free-space optical communication system 1 described above, which will not be described in detail here.

[0077] See also Figure 8 The third embodiment of the present invention provides a free-space optical communication device 3, including the free-space optical communication system 1 provided in the first embodiment, which has the same beneficial effects as the above-mentioned free-space optical communication system 1 and will not be described in detail here.

[0078] See also Fig. 9 The fourth embodiment of the present invention provides a free space optical communication device 4, including the free space optical communication system 2 provided in the second embodiment, which has the same beneficial effects as the above-mentioned free space optical communication system 2 and will not be described in detail here.

[0079] See also Fig.10 A fifth embodiment of the present invention provides a free space optical communication method, which is applied to the above-mentioned free space optical communication system 1 or free space optical communication system 2, and includes the following steps:

[0080] Step S1: coupling the spatial beam into a multimode optical fiber;

[0081] Step S2: separating the spatial light beam received by the multi-mode optical fiber and converting it into a fundamental mode signal of the single-mode optical fiber;

[0082] Step S3: selecting the fundamental mode signal of the single-mode optical fiber converted by the LP01 mode as the output optical signal;

[0083] Step S4: receiving, transmitting and processing the output optical signal.

[0084] It can be understood that the free-space optical communication method of this embodiment has the same beneficial effects as the free-space optical communication system 1 or the free-space optical communication system 2 described above, and will not be described in detail herein.

[0085] In the embodiments provided by the present invention, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that determining B according to A does not mean determining B only according to A, and B can also be determined according to A and / or other information.

[0086] It should be understood that the "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. Those skilled in the art should also be aware that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0087] In various embodiments of the present invention, it should be understood that the size of the serial numbers of the above-mentioned processes does not mean the necessary order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0088] The flow chart and block diagram in the accompanying drawings of the present invention illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementation schemes, the functions marked in the box can also occur in a sequence different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, which is determined based on the functions involved. It should be particularly noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs a specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0089] Compared with the prior art, the free-space optical communication system, device and method provided by the present invention have the following beneficial effects:

[0090] 1. A free-space optical communication system provided by an embodiment of the present invention first couples a space light beam with a multi-mode optical fiber, utilizing the larger core diameter of the multi-mode optical fiber to improve the coupling efficiency and effectively reduce the energy loss during the coupling process. Then, a mode demultiplexer is used to separate and convert the multiple modes of light in the multi-mode optical fiber using mode conversion technology, and the LP01 mode is separated and converted into the base mode of the single-mode optical fiber as the output optical signal. This mode conversion technology solves the problem of mode mismatch between the multi-mode optical fiber and the single-mode optical fiber. Finally, the base mode signal in the converted single-mode optical fiber is used for communication, which can better match the high-speed communication module.

[0091] 2. In a free-space optical communication system provided by an embodiment of the present invention, a mode demultiplexer is implemented by multi-plane optical conversion technology or photon lantern technology. Both technologies can separate different modes in a multi-mode optical fiber and convert them into base mode signals. In particular, the photon lantern technology has very low loss during mode conversion, and theoretically can achieve zero loss.

[0092] 3. In a free-space optical communication system provided by an embodiment of the present invention, an optical circulator is arranged between the output end of the coupling module and the multimode optical fiber. The setting of the optical circulator enables each laser communication terminal to use the same optical system for communication, thereby avoiding the problem of non-coaxial communication reception and transmission during assembly and debugging, and realizing full-duplex communication of the laser communication terminal without adding laser emitting devices. The optical circulator also has a compact structure and a small size, and can be easily integrated into the free-space optical communication system.

[0093] 4. A free-space optical communication system provided by an embodiment of the present invention further includes an erbium-doped fiber amplifier, which is arranged between the photoelectric detection module and the mode demultiplexer. The output optical signal obtained after mode conversion can enter the erbium-doped fiber amplifier for amplification, which can minimize signal attenuation, thereby improving the quality and distance of signal transmission.

[0094] 5. In a free space optical communication system provided by an embodiment of the present invention, a photoelectric detection module includes an optical filter and a coherent optical receiver connected in sequence. The output optical signal is first filtered by the optical filter, and then the filtered optical signal is directed to the coherent optical receiver. Inside the receiver, the optical signal is mixed with the local oscillator light to achieve coherent detection and converted into an electrical signal. Subsequently, the signal is collected by an oscilloscope and processed by a digital signal processor.

[0095] 6. In a free-space optical communication system provided by an embodiment of the present invention, a coupling module is provided with a light source component and a beacon light processing module for emitting and processing beacon light. The beacon light can be provided to play a guiding and calibrating role. By emitting and receiving the beacon light, the transmission path and coupling position of the space light beam can be accurately determined, thereby improving the coupling efficiency and accuracy.

[0096] 7. A free-space optical communication system provided by an embodiment of the present invention, wherein the coupling module further includes a beam splitter and a coupling lens, the beacon light processing module includes a position sensitive detector, the focus of the coupling lens is aligned with the end face center of the multimode optical fiber, the beam splitter is located on the side of the coupling lens close to the multimode optical fiber, the beacon light is focused by the coupling lens and reflected to the position sensitive detector by the beam splitter, and the spatial light beam is focused by the coupling lens and coupled to the multimode optical fiber. The coupling lens can efficiently couple the spatial light beam to the multimode optical fiber, and by accurately designing and adjusting the parameters of the coupling lens, the optimal focusing and matching of the spatial light beam can be achieved, thereby reducing the loss of light energy and improving the coupling efficiency. The cooperation of the beam splitter and the position sensitive detector can use the beacon light to monitor the position change of the spatial light beam near the focus of the coupling lens in real time, and adjust the position or focal length of the coupling lens as needed, thereby improving the optical coupling efficiency. The robustness of the coupling module can also be enhanced.

[0097] 8. In a free-space optical communication system provided by an embodiment of the present invention, the multimode optical fiber is preferably a few-mode optical fiber. The core diameter of the few-mode optical fiber is larger than that of the single-mode optical fiber, and a higher coupling efficiency can be obtained. At the same time, compared with general multi-mode optical fibers, since the number of light wave modes supported by the few-mode optical fiber is limited, and the propagation characteristics of these modes in the optical fiber are relatively stable, problems such as inter-modal dispersion can be more effectively avoided, which enables the few-mode optical fiber to maintain a high signal quality during transmission. The modes in the few-mode optical fiber can be effectively separated and converted into the fundamental mode signal of the single-mode optical fiber, thereby supporting high-speed and large-capacity data transmission. The few-mode optical fiber has lower signal attenuation and is more suitable for long-distance and high-speed transmission. Therefore, it can be appropriately selected according to the specific application to further improve the quality of the optical output signal.

[0098] 9. The embodiment of the present invention further provides a free space optical communication device, which has the same beneficial effects as the above-mentioned free space optical communication system, and will not be described in detail here.

[0099] 10. The embodiment of the present invention further provides a free space optical communication method, which has the same beneficial effects as the above-mentioned free space optical communication system, and will not be described in detail here.

[0100] The above is a detailed introduction to a free-space optical communication system, device and method disclosed in an embodiment of the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A free space optical communication system, characterized in that: The laser communication terminal comprises at least two laser communication terminals, wherein a communication link of spatial beam propagation is formed between the laser communication terminals, and the laser communication terminal comprises: A coupling module and a multimode optical fiber supporting linear polarization mode transmission, wherein the coupling module is used to couple the spatial light beam into the multimode optical fiber; A mode demultiplexer, the input end of which is connected to the multi-mode optical fiber, for separating the multiple modes of light received by the multi-mode optical fiber and converting them into base mode signals in the corresponding multiple single-mode optical fibers, and defining the base mode signal of the single-mode optical fiber after the LP01 mode conversion in the multi-mode optical fiber is completed as the output optical signal; A single-mode optical fiber connected to the LP01 mode conversion output port of the mode demultiplexer, for receiving and transmitting the output optical signal; A photoelectric detection module, wherein the photoelectric detection module is connected to the mode demultiplexer via the single-mode optical fiber and is used for converting the output optical signal into an electrical signal.

2. The free space optical communication system according to claim 1, wherein: The mode demultiplexer is implemented by multi-plane light conversion technology or photon lantern technology.

3. The free space optical communication system according to claim 1, wherein: An optical circulator is arranged between the output end of the coupling module and the multimode optical fiber.

4. The free space optical communication system according to claim 1, wherein: The system further comprises an erbium-doped fiber amplifier, which is arranged between the photoelectric detection module and the mode demultiplexer and is used for amplifying the output optical signal after mode conversion.

5. The free space optical communication system according to claim 1, wherein: The photoelectric detection module includes an optical filter and a coherent light receiver connected in sequence.

6. The free space optical communication system according to claim 1, wherein: The coupling module is provided with a light source component, and the light source component is used to emit beacon light. The coupling module is also provided with a beacon light processing module for receiving, detecting and processing the beacon light.

7. The free space optical communication system according to claim 6, wherein: The coupling module also includes a beam splitter and a coupling lens, the beacon light processing module includes a position sensitive detector, the focus of the coupling lens is aligned with the end face center of the multimode optical fiber, the beam splitter is located on the side of the coupling lens close to the multimode optical fiber, the beacon light is focused by the coupling lens and reflected by the beam splitter to the position sensitive detector, and the spatial light beam is focused by the coupling lens and coupled to the multimode optical fiber.

8. The free space optical communication system according to claim 1, wherein: The multimode optical fiber is a few-mode optical fiber.

9. A free space optical communication device, characterized in that: The free space optical communication system comprises the free space optical communication system as claimed in any one of claims 1 to 8.

10. A free space optical communication method, applied to the free space optical communication system according to any one of claims 1 to 8, characterized in that: The following steps are involved: coupling a spatial beam into a multimode optical fiber; Separate the spatial light beam received by the multimode optical fiber and convert it into the fundamental mode signal of the single-mode optical fiber; Selecting the fundamental mode signal of the single-mode optical fiber converted by the LP01 mode as the output optical signal; Receive, transmit and process the output optical signal.

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