A compensation device and method for the optical path mechanical displacement of an inter-satellite communication satellite laser terminal

Abstract

The present invention discloses a device and method for compensating for mechanical displacement in the optical path of an intersatellite communication satellite laser terminal. The device comprises: a laser signal is received by an optical head and then enters a receiving optical path. In the receiving optical path, the optical signal is reflected by a fast reflector (FSM) and then transmits through a color separator. It is then reflected by a deflection mirror and passes through a narrowband color filter. The filtered light beam is split into two beams by a beam splitter. The majority of the laser signal is reflected by liquid crystal on silicon (LCOS), focused by a coupling lens, and then coupled into a receiving optical fiber and transmitted to a signal processor to complete signal reception. The remaining small portion of light enters a tracking camera module. The tracking and aiming module of the satellite terminal adjusts the angle of the FSM according to the position of the light spot to compensate for vibration during satellite operation. Compared to traditional single-point scanning methods, the method of the present invention significantly reduces the number of search steps. The compensation process, which traditionally requires tens of thousands of steps, is compressed to just a few hundred steps, allowing the system to complete self-calibration in tens or even seconds, effectively shortening the system self-calibration time.

Description

Technical Field

[0001] The present invention relates to the technical field of laser communication detection, and in particular to a compensation device and a compensation method for mechanical displacement of an optical path of an inter-satellite communication satellite laser terminal. Background Art

[0002] Common intersatellite laser communication terminals such as Figure 1 As shown in the figure, the operating wavelengths of the signal transmission and reception modules are 1540nm and 1560nm, respectively. When the terminal transmits data, the laser emits a 1540nm laser beam. After being collimated by a lens, the beam is reflected by FSM2, the dichroic filter, and FSM1 before being emitted. When the terminal receives data, the 1560nm laser beam is reflected by FSM1, transmitted through the dichroic filter, reflected by a deflection mirror, passed through a narrowband filter, and split into two beams by a beam splitter. Most of the incident light is reflected by FSM3 and coupled into the receiving optical fiber. A small amount of light enters the tracking camera module, which is used to control tracking and aiming between communication terminals.

[0003] like Figure 2 This is a simplified schematic diagram of the optical signal coupling module in a common intersatellite laser communication terminal's receiving module. This module generally consists of three components: a fast steering mirror (FSM), a coupling lens, and a single-mode fiber. When the optical signal coupling module is in operation, the optical signal received by the optical head is reflected by the FSM and coupled into the single-mode fiber through the coupling lens. Vibration during terminal transmission and operation can cause displacement of the receiving fiber, reducing received power. Therefore, intersatellite laser communication terminals require periodic self-calibration to compensate for this displacement.

[0004] Traditional intersatellite laser communication terminals typically use a single-point scanning method to compensate for receiving fiber displacement. This involves varying the tilt angle of the FSM (Faster Scanning Module) to control the focused beam's spiral traversal within the focal plane behind the coupling lens, repositioning it on the receiving fiber's end face. Because the uncertainty region after receiving fiber displacement is two-dimensional, the time complexity of the traditional single-beam spiral search is quadratic. As receiving fiber displacement increases, the system's self-calibration time increases rapidly, reducing the system's communication time and rate. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a compensation device for the mechanical displacement of the optical path of an intersatellite communication satellite laser terminal, which solves the problem of long system self-calibration time caused by using a single-beam scanning method to compensate for the displacement of the receiving optical fiber in traditional intersatellite laser communication terminals. The present invention also provides a compensation method for the mechanical displacement of the optical path of an intersatellite communication satellite laser terminal.

[0006] Technical solution: According to a first aspect of the present invention, a device for compensating for mechanical displacement of an optical path in an intersatellite communication satellite laser terminal is provided. The device includes an optical head for receiving an incident laser signal. The optical head is reflected by a fast reflector (FSM), transmits a color separator, and then reflects through a deflection mirror and a narrow-band filter. The filtered light beam is split into two beams by a beam splitter. Most of the laser signal is reflected by liquid crystal on silicon (LCOS), focused by a coupling lens, and coupled to the end face of a receiving optical fiber. The signal is then transmitted to a signal processor in the satellite communication terminal to complete signal reception. The remaining light enters a tracking camera module. The tracking and aiming module in the satellite communication terminal adjusts the angle of the FSM according to the position of the light spot to compensate for vibration, ensuring that the system can always receive optical signals with maximum efficiency.

[0007] The liquid crystal on silicon (LCOS) is used to display different phase holograms and to split and deflect the light spot on the rear focal plane of the coupling lens.

[0008] Furthermore, it includes: the signal processor is connected to an optical power meter, and part of the light received by the signal processor enters the optical power meter, which is used as a feedback signal for receiving optical fiber vibration compensation, and decodes the other part of the light received by the signal processor, thereby completing the signal reception.

[0009] On the other hand, the present invention also provides a method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal, the method comprising:

[0010] The signal processor in the S1 satellite communication terminal determines whether the focused light spot at the rear focus of the coupling lens is relatively displaced from the end face of the receiving optical fiber, that is, the focused light spot is not on the end face of the receiving optical fiber. If there is no relative displacement, the laser signal is continued to be received. Otherwise, the current hologram is traversed and scanned in a spiral phase according to the displacement of the light spot.

[0011] After the spiral stage S2 is completed, the sector stepping stage scanning is entered, and finally the diffraction jump scanning is performed until the compensation of the receiving optical fiber displacement is completed;

[0012] After S3 completes the compensation for the receiving optical fiber position offset, the LCOS displays the compensated grating hologram, and the satellite communication terminal continues to receive optical signals until the received optical power drops to a certain value again, then goes to step S1 for the next compensation.

[0013] Further, including:

[0014] In step S2, the focused light spot rotates in a spiral around the initial position and searches outward until any diffraction light spot is detected, thereby ending the scanning at this stage. The diffraction light spot is a plurality of equidistant multi-order light spots formed after the incident laser signal is modulated by the LCOS wavefront. The plurality of equidistant multi-order light spots are on a straight line that passes through the rear focus of the coupling lens, and the point spacing satisfies the grating equation.

[0015] Further, including:

[0016] After completing the scan at this stage, the horizontal direction is used as the reference baseline to determine the approximate azimuth angle Φ of the current relative displacement between the receiving fiber end face and the back focus of the coupling lens. The azimuth angle is the angle between the line connecting the receiving fiber end face and the back focus of the coupling lens and the horizontal direction.

[0017] Further, including:

[0018] In step S3, after the spiral stage ends, the sector-shaped stepping stage scanning is entered, including: at this time, the receiving optical fiber end face is positioned between the focus spot arrays, and each time the focus spot array midpoint and the spot spacing are increased, the spot array is rotated left and right by a certain angle for scanning, and the scanning range is the sector-shaped area. After each scan, the spot array angle corresponding to the maximum power in the scan is updated to a new azimuth angle Φ, and the azimuth angle is corrected. This process is repeated until a sufficiently sharp spot is found, that is, when a local maximum value is found, the relative displacement intermediate value r is determined, and the sector-shaped stepping scanning stage is terminated. The maximum power is the maximum power measured during the process of rotating the spot array left and right by one angle at a fixed spot spacing. Further, it includes:

[0019] The method for determining the relative displacement intermediate value r is:

[0020] By continuously increasing the dot spacing, a power maximum is found, that is, a certain diffraction order gradually hits the receiving fiber. At this time, the position of the +1-order focused light spot relative to the focus after the coupling lens is r. At this time, the possible positions of the receiving fiber end face can be traversed according to the grating equation to determine the position of the receiving fiber.

[0021] Further, including:

[0022] In step S3, the diffraction jump scan includes: utilizing the geometric relationship between the diffraction orders as a priori conditions to perform jump scans between different diffraction orders. Specifically, the azimuth angle Φ is fixed, and only the relative displacement of the light spot is changed by 2r, and a search is performed within its neighborhood. After the search is completed, the relative displacement of the light spot is changed to 3r, and the search is performed again within its neighborhood. Similarly, the relative displacement of the light spot is changed to 4r, 5r, and so on until the optical fiber position is found. At this time, the absolute value of the relative displacement is determined to be approximately R. At this time, the displacement of the +1-order focused light spot relative to the back focus of the coupling lens is R. That is, the +1-order light spot is incident on the receiving optical fiber, and the relative displacement between the receiving optical fiber and the back focus of the coupling lens is roughly determined.

[0023] Further, including:

[0024] The geometric relationship between the diffraction orders is expressed as:

[0025] D≈R=m*fλ / T

[0026] Where m is the diffraction order, f is the focal length of the coupling lens, T is the period of the blazed grating hologram displayed on the LCOS, and λ is the wavelength of the laser;

[0027] The method for determining the absolute value of relative displacement D is:

[0028] Let the first-order spot offset r = fλ / T, and traverse the displacement of the first-order spot. If the +N-level spot hits the end face of the receiving fiber at this time, the first-order spot offset is changed to Nr, that is, D≈R=Nr, N∈[...,-4,-3,-2,-1,1,2,3,4,...].

[0029] Further, including:

[0030] In step S3, until the best optical fiber coupling efficiency compensation effect is achieved, the steps include:

[0031] After determining the approximate azimuth angle Φ of the fiber displacement and the approximate absolute value R of the relative displacement, the final fine search stage is entered. Within a circle with a radius of 5 μm around the current maximum position, the search is carried out in a 1 / 10 step size in its neighborhood. When D = R, the best fiber coupling efficiency compensation effect is achieved.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0033] Fast Compensation: LCOS reduces the time complexity of the self-calibration process from the traditional quadratic complexity to linear complexity, significantly improving self-calibration speed. Compared to traditional single-point scanning methods, this method significantly reduces the number of search steps. The compensation process, which traditionally requires tens of thousands of steps, is compressed to just a few hundred, allowing the system to complete self-calibration in tens or even seconds, effectively shortening the system's self-calibration time.

[0034] Efficient Coupling: The application of LCOS in the optical path enables more precise control of the direction and splitting of the light beam, thereby improving coupling efficiency. The holographic design of LCOS enables multi-directional compensation of the light beam, allowing the system to maintain efficient optical signal reception under different conditions.

[0035] Improved stability: Through algorithm design tailored to LCOS, an automatic coupling speed far faster than traditional FSM is achieved. This improves system stability, enabling it to more quickly adapt to disturbances caused by factors such as satellite mechanical vibration, maintaining normal system operation.

[0036] Improved communication rate: This invention effectively improves the communication rate of intersatellite laser communication systems. By reducing the self-calibration time, the system's communication time is increased, thereby supporting a wider range of intersatellite laser communication network applications.

[0037] Enhanced adaptability: This invention uses LCOS holographic design and self-calibration methods to make the system more adaptable. The system can more flexibly cope with optical path misalignment under different conditions, improving the system's robustness and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of an intersatellite laser communication terminal in the prior art;

[0039] Figure 2 This is a simplified schematic diagram of a receiving module in an intersatellite laser communication terminal in the prior art;

[0040] Figure 3 This is a system structure diagram of the LCOS-based inter-satellite laser communication according to an embodiment of the present invention;

[0041] Figure 4 This is a flowchart of satellite terminal self-calibration according to an embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram of a satellite terminal self-calibration process according to an embodiment of the present invention;

[0043] Figure 6 Schematic diagram of the frequency distribution of coupling steps for Monte Carlo simulation of various search methods according to the embodiments of the present invention, wherein (a) is a schematic diagram of the distribution when the search step is greater than 10,000 steps, and (b) is a schematic diagram of the distribution when the search step is less than 1,000 steps;

[0044] Figure 7 Schematic diagrams of the three stages of the self-calibration process according to an embodiment of the present invention, wherein (a) is a schematic diagram of the spiral calibration stage, (b) is a schematic diagram of the sector step calibration stage, and (c) is a schematic diagram of the diffraction jump calibration stage;

[0045] Figure 8 Schematic diagram of the azimuth angle α and the absolute value of the relative displacement D according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention and not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0047] 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.

[0048] According to a first aspect of the present invention, a device for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal is provided. Figure 3 and Figure 4 The device includes an optical head that receives an incident laser signal. After being reflected by a fast-reflecting mirror (FSM), the signal passes through a color separator and then a narrow-band filter. The filtered light beam is split into two by a beam splitter. Most of the laser signal is reflected by liquid crystal on silicon (LCOS), focused by a coupling lens, and then coupled to the end face of the receiving fiber. This is then transmitted to a signal processor for signal reception. A small portion of the light enters a tracking camera module. The tracking and aiming module in the satellite communication terminal adjusts the FSM angle based on the position of the light spot, ensuring the system always receives the light signal with maximum efficiency. The LCOS is used to display different phase holograms and split the light spot on the rear focal plane of the coupling lens.

[0049] The satellite terminal itself vibrates during operation. The tracking and aiming module is used to compensate for vibration at the receiving end. Its operating principle is to infer the vibration direction based on the changes in the spot shape on the tracking camera's CMOS image sensor. The FSM angle is then adjusted to compensate for the vibration, ensuring that the tracking camera's imaging spot remains constant. A portion of the optical signal entering the signal processor is connected to an optical power meter to measure the current received optical power, primarily serving as feedback for receiving fiber vibration compensation. Another portion decodes the received optical signal to complete signal reception. The control circuit is the communication terminal's host computer. The signal processing, tracking and aiming, and fast coupling modules are relatively independent but controlled by the control circuit.

[0050] In this embodiment, the signal processor is connected to an optical power meter, and part of the light received by the signal processor enters the optical power meter, which is used as a feedback signal for receiving optical fiber vibration compensation, decoding the other part of the light received by the signal processor, and thus completing the signal reception.

[0051] During normal operation, the satellite communication terminal system behaves similarly to a typical intersatellite laser communication module. The FSM2 is used to mitigate high-frequency disturbances caused by factors such as mechanical vibration of the satellite. This system uses a 1560nm wavelength laser for receiving signals. During operation, the FSM2's angle is constantly adjusted based on the relative positions of the satellites and mechanical vibration of the satellites themselves to minimize transmission loss.

[0052] When the system receives a signal, the hologram solidified during the self-calibration phase of the LCOS7 display acts as a reflector. The laser with a wavelength of 1560nm is reflected by the FSM2 and then transmits through the color separator 3. It is then reflected by the deflection mirror 4 and passes through the narrow-band filter 5. The filtered light beam is split into two beams by the beam splitter 6. Most of the light is reflected by the LCOS7, focused by the coupling lens 8, and coupled to the optical fiber at the signal receiving end, and transmitted to the signal processor 9 to complete the signal reception.

[0053] Another small portion of light enters the tracking camera module 10, and the control circuit adjusts the FSM2 angle according to the light spot position to ensure that the system can always receive the light signal with maximum efficiency.

[0054] Traditional solutions also use FSM in the place of LCOS. This invention replaces the FSM at mark 7 with LCOS, ensuring backward compatibility with FSM. FSM2 is used to compensate for high-speed vibration, consistent with traditional solutions. Because LCOS has a slower response speed than FSM, it is not used as a replacement.

[0055] In this embodiment of the present invention, FSM2 and LCOS7 are not connected. Instead, they are controlled by the satellite link establishment and tracking module to achieve real-time alignment between satellite terminals. Ideally, the light beam entering the receiving module should be incident along the optical axis, with the light spot on the tracking camera centered. However, satellite vibration during operation can cause the angle of the received beam to shift, which in turn causes the position of the light spot on the tracking camera to change. The satellite tracking module adjusts the angle of FSM2 based on this offset.

[0056] LCOS7, part of the self-calibration module, compensates for receiver fiber displacement caused by satellite vibration. After FSM2 adjustment, the beam entering the receiver module always propagates along the optical axis. However, satellite vibration can cause relative displacement between the receiver fiber and the coupling lens's focused spot. LCOS7 adjusts the focused spot's position to restore efficient coupling.

[0057] The optical head 1 in this embodiment is a customized optical head with high sensitivity and wavelength adaptability, manufactured by companies such as the Changchun Institute of Optics, Fine Mechanics and Physics and the Xi'an Institute of Optics and Fine Mechanics. This optical head can effectively receive laser signals and ensure stable performance across different wavelength ranges.

[0058] Fast Mirror FSM2: This device uses the S-335 fast mirror from Puai Nano. This device enables high-speed and high-precision control of the beam direction and is used to compensate for the mechanical resonance of the system.

[0059] Color separation filter 3: The color separation filter DMLP1500L from Solebo is used. This filter is used to separate the input and output laser signals of different wavelengths to achieve full-duplex communication.

[0060] Reflecting mirror 4: Select the high reflectivity mirror from Edmund Optics, model #47-114. This mirror is used to reflect the laser signal and fold the optical path.

[0061] Narrowband filter 5: This filter is provided by Edmund Optics, model #65-779. This filter is used to select optical signals within a specific wavelength range to ensure that the system only receives signals of the target wavelength.

[0062] Beam splitter 6: Use the beam splitter from Sorebo, model BS039. This beam splitter is used to split the optical signal into two beams, one of which is used for coupling lens focusing, and the other small part is used for tracking the camera module.

[0063] LCOS7 spatial light modulator: The LCOS device, model X15213, manufactured by Hamamatsu Corporation was selected. As an alternative to fast-steering mirrors (FSMs), LCOS can precisely control the light beam by displaying different phase holograms, improving self-calibration efficiency.

[0064] Coupling lens 8: Custom high-precision coupling lens, manufactured by Jingcui Optics. This lens is used to focus the light beam and improve the coupling efficiency of the optical fiber.

[0065] Signal processor 9: uses self-developed coherent optical QPSK coded optical communication system to achieve signal modulation and demodulation;

[0066] Tracking camera module 10: A Cinogy light spot analyzer, model CinCam CMOS-1201EL, was selected. This module monitors the light spot position in real time and adjusts the LCOS through control circuitry to ensure the system always receives optical signals with maximum efficiency.

[0067] On the other hand, the present invention also provides a method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal, the method comprising the following steps:

[0068] After S1 completes signal reception, LCOS displays a hologram of the current optical path;

[0069] During the self-calibration of the satellite communication terminal system, LCOS7 and the signal processor at the receiving end 9 form a feedback loop, and the hologram displayed on the LCOS7 is iterated by the receiving power at the receiving end, thereby realizing the rapid compensation of the optical path displacement. Figure 5 As shown in FIG, the schematic diagram represents the spot position change trajectory during the self-calibration process, where ① is the spiral traversal scanning stage, ② is the fan-shaped step scanning stage, and ③ is the diffraction jump scanning stage.

[0070] The signal processor in the S2 satellite communication terminal determines whether the focused light spot of the coupling lens has relative displacement with the end face of the receiving optical fiber. If there is no relative displacement, it continues to receive the laser signal. Otherwise, it performs a spiral stage traversal scan of the current hologram based on the offset of the light spot.

[0071] Ideally, the receiving fiber is at the back focus of the coupling lens, and the focused light spot is also at that back focus, hitting the receiving fiber end face, achieving maximum coupling efficiency. However, mechanical vibrations in the satellite terminal can cause the receiving fiber to shift, leaving the focused light spot still at the back focus, significantly reducing coupling efficiency. Displaying a grating hologram on the LCOS monitor controls the position of the focused light spot, ensuring that it re-imports the receiving fiber end face.

[0072] Because the initial position of the focused spot is at the focal point of the coupling lens, the position of the focused spot is described by the angle α between the line connecting the focused spot and the focal point and the horizontal direction, and the distance D between the focused spot and the back focus. The position of the receiving fiber is determined in the same way. The basic logic of the search is to first determine Φ≈α and then determine R≈D. The self-calibration process is mainly as follows:

[0073] The position of an object in the polar coordinate system is determined by two parameters: the angle Φ between the line connecting the object and the origin and the horizontal direction, and the length R of the line connecting the object and the origin. In this scenario, the origin is the back focus of the coupling lens, which is the initial position of the focused light spot. Its position is determined by Φ = 0 and R = 0.

[0074] After the receiving optical fiber is displaced, its position is determined by Φ=α and R=D.

[0075] When searching, first find Φ so that the azimuth angle of the focused spot Φ = α; then, search in the radial direction. When R = D, the search is completed.

[0076] Specifically: The first stage of self-calibration is the same as the traditional method of self-calibrating the system through a fast mirror to achieve optical path displacement compensation, and a spiral traversal scan is performed. That is, by displaying blazed gratings of different directions and periods on the LCOS, the direction of light beam transmission is changed, the light spot rotates around the initial position, and continuously searches outward. LCOS can simulate optical elements, such as displaying a hologram of a blazed grating. When light hits the LCOS, it will hit the same blazed grating, and the wavefront will change in the same way. At this time, the LCOS can be regarded as an equivalent blazed grating. Here, different grating holograms are displayed on the LCOS to achieve beam splitting and deflection.

[0077] This method differs from traditional techniques in that the termination conditions for the spiral traversal search process are different. Traditional methods continue the spiral traversal process until the beam is deflected to the receiving fiber. The greater the displacement deviation in the entire optical path, the more severe the offset between the receiving fiber and the light spot, and the longer the compensation process takes, with a quadratic relationship. Once the offset distance is even slightly larger, the number of search iterations can easily reach tens of thousands.

[0078] In the present invention, the spiral traversal search phase ends upon detection of any diffraction spot. The diffraction spot is formed by LCOS wavefront modulation of the incident light. At this point, the approximate azimuth angle Φ of the relative displacement of the receiving fiber can be determined. However, due to the mixing of higher-order diffraction orders, the absolute value of the relative displacement R cannot be determined. The azimuth angle is the angle between the horizontal direction and the line connecting the end face of the receiving fiber and the rear focus of the coupling lens. Once this angle is determined, the split light spots are aligned in this direction. By continuously increasing the spacing between the light spots, a maximum value is found, corresponding to a specific diffraction order impinging on the end face of the receiving fiber.

[0079] To improve algorithm stability, each time the spot spacing is increased, the dot matrix is rotated slightly left or right. This is referred to as a very small sector. After each search, the dot matrix angle corresponding to the maximum power is updated to the new azimuth angle. The spacing is increased by approximately 5 μm each time.

[0080] Specifically, in step S2, the light spot rotates in a spiral around the initial position and continuously searches outward until any diffraction spot is detected, thereby ending the scanning at this stage. The diffraction spot is a plurality of equidistant light spots formed after the incident laser signal is modulated by the LCOS wavefront. The plurality of equidistant light spots are on a straight line that passes through the rear focus of the coupling lens, and the point spacing satisfies the grating equation.

[0081] After completing the scan at this stage, the azimuth angle Φ of the relative displacement between the current receiving fiber end face and the back focus of the coupling lens is determined. Due to the mixing of high-order diffraction orders at this time, the absolute value of the relative displacement R cannot be confirmed; the azimuth angle is the angle between the line connecting the receiving fiber end face and the back focus of the coupling lens and the horizontal direction.

[0082] Higher-order diffraction orders have low energy, and due to power meter noise, it's difficult to find the center and thus determine the offset. Assuming the +10th-order spot is offset by 100 μm, then the +1st-order spot is offset by 10 μm. To find the maximum power, a precise search is performed near the +10th-order spot. Increasing the +1st-order spot's displacement by 1 μm, now 9*11=99 μm, and the new +9th-order spot appears near the original +10th-order spot. The new and old spots partially overlap, making it difficult to locate the +10th-order spot based solely on received power. Therefore, a search based on diffraction orders is performed when the new and old spots are farther apart.

[0083] After the S3 spiral stage, it enters the sector stepping stage scanning, and finally performs diffraction jump scanning until the best fiber coupling efficiency compensation effect is achieved.

[0084] After determining the azimuth angle Φ of the receiving fiber's relative displacement, the second stage of self-calibration—sector-step scanning—begins. Compared to spiral traversal, this stage requires searching only within a very small sector-shaped area, a 5μm-long arc. After each sector is searched, the search continues outward, starting from the location with the highest detected energy within that area, until a sufficiently sharp spot is found. Upon reaching a local maximum, the intermediate value of the relative displacement, r, is determined. If the receiving fiber is centered within the spot, no matter how it is rotated, the maximum cannot be found. The spot spacing must be increased with each rotation to find a local maximum, corresponding to a specific diffraction order striking the receiving fiber endface. By continuously increasing the spot spacing, a clearly recognizable power maximum is found, indicating that a specific diffraction order is gradually striking the receiving fiber. At this point, the position of the +1-order spot relative to the rear focus of the coupling lens is r. The receiving fiber's position can be determined by traversing the possible positions of the receiving fiber endface using the grating equation.

[0085] After r is determined, the sector step scanning phase ends. The location with the maximum energy detected within the region is specifically: the tracking camera module 10 monitors the received power in real time and updates the location corresponding to the current maximum value detected. The maximum detected value indicates the maximum received optical power. A sufficiently sharp light spot has an energy greater than 30dBm.

[0086] In step S3, after the spiral stage ends, the sector stepping stage scanning begins, which includes: each time the spot spacing is increased, the dot matrix is rotated left and right by an angle, that is, the sector area, and after each scan, the dot matrix angle corresponding to the maximum power is updated to the new azimuth angle Φ until a sufficiently sharp spot is found, that is, when the local maximum value is found, the relative displacement intermediate value r is determined, and the sector stepping scanning stage ends.

[0087] In step S3, the diffraction jump scan includes: using the geometric relationship between each diffraction order as a priori conditions, jumping scanning between different diffraction orders, that is, fixing the azimuth angle Φ, changing the relative displacement of the light spot to 2r, and searching within its neighborhood; after the search is completed, changing the relative displacement of the light spot to 3r, and searching again within its neighborhood; and so on, changing the relative displacement of the light spot to 4r, 5r... until the optical fiber position is found, and determining the absolute value of the relative displacement R.

[0088] Note that the first-order spot offset r = fλ / T, and traverse the displacement of the positive first-order spot. If the +N-order spot hits the end face of the receiving fiber at this time, the first-order spot offset is changed to Nr, that is, R = Nr, N∈[....,-5,-4,-3,-2,-1,1,2,3,4,5,...]. Specifically,

[0089] If the +3-level spot strikes the receiving fiber end face, the offset of the first-level spot is changed to 3r, and the +1-level spot strikes the receiving fiber end face. Since we don't know which spot strikes the receiving fiber end face, we traverse the displacement of the +1-level spot, ..., -5r, -4r, -3r, -2r, -r, r, 2r, 3r, 4r, 5r, ...

[0090] After determining the approximate azimuth angle Φ and absolute value R of the relative displacement, the final fine search phase begins. The core radius of a single-mode fiber is 5 μm, so the uncertainty region selected for the fine search ensures that the fiber end face is within it. The search is performed in 1 / 10 steps within the adjacent region, i.e., within a 5 μm radius circle around the current maximum value, to achieve optimal fiber coupling efficiency compensation.

[0091] Among them, the geometric relationship of the light spots of each diffraction order of the grating is:

[0092] R = m*fλ / T, where m is the diffraction order, f is the focal length of the coupling lens, T is the period of the blazed grating hologram displayed on the LCOS, and λ is the wavelength corresponding to the laser.

[0093] like Figure 7 As shown in the figure, the whole search process is shown. Figure 7 (a) in the figure determines the search direction through spiral search and then enters the sector step scan Figure 7 (b) in the figure, when a resolvable power maximum is detected, the diffraction jump scanning phase begins. Figure 7 In (c), the maximum power corresponds to the +1 level spot hitting the receiving fiber end face. For the convenience of display, the position of all points is the location of the +1 level spot. Figure 8 The corresponding azimuth angle Φ and relative displacement absolute value R.

[0094] like Figure 6 As shown in (a) and (b) of FIG, the present invention achieves remarkable results by introducing a liquid crystal on silicon device (LCOS) to replace the traditional fast steering mirror (FSM) and adopting a new self-calibration method.

[0095] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0096] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

[0097] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A device for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal, comprising an optical head, a receiving optical path, a tracking camera module, and a signal processor, characterized in that: After being received by the optical head, the laser signal enters the receiving optical path. In the receiving optical path, the optical signal is reflected by the fast reflector (FSM) and then transmits through the color separator. It is then reflected by the turning mirror and passes through the narrow-band color filter. The filtered light beam is split into two beams by the beam splitter. Most of the laser signal is reflected by the silicon-based liquid crystal (LCOS) and focused by the coupling lens, then coupled into the receiving optical fiber and transmitted to the signal processor to complete the signal reception. The remaining small part of the light enters the tracking camera module. The tracking and aiming module of the satellite terminal adjusts the angle of the FSM according to the position of the light spot to compensate for the vibration of the satellite during operation, ensuring that the system can always receive the optical signal with the highest efficiency. The silicon-based liquid crystal (LCOS) is used to display different phase holograms and deflect and split the light spot on the focal plane behind the coupling lens. The signal processor is connected to an optical power meter. A small portion of the light received by the signal processor enters the optical power meter and is used as a feedback signal to compensate for the position offset and vibration of the receiving optical fiber, decode the other portion of the light received by the signal processor, and thus complete the signal reception.

2. A method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal, characterized in that: The method includes: The signal processor in the S1 satellite communication terminal determines whether the focused light spot at the rear focus of the coupling lens is relatively displaced from the end face of the receiving optical fiber, that is, the focused light spot is not on the end face of the receiving optical fiber. If there is no relative displacement, the laser signal is continued to be received. Otherwise, a spiral phase traversal scan is performed on the current hologram based on the displacement of the light spot. The spiral phase traversal scan is to rotate the focused light spot in a spiral around the initial position and search outward until any diffraction light spot is detected. After the spiral stage S2 is completed, the sector stepping stage scanning is entered, and finally the diffraction jump scanning is performed until the compensation of the receiving optical fiber displacement is completed; After S3 completes the compensation for the receiving fiber position offset, the LCOS displays the compensated grating hologram, and the satellite communication terminal continues to receive optical signals until the received optical power drops to a certain value again, and then goes to step S1 for the next compensation until the best fiber coupling efficiency compensation effect is achieved; Among them, the sector-shaped stepping stage scanning is: at this time, the position of the receiving optical fiber end face is between the focused light spot arrays, and each time the distance between the midpoint and the point of the focused light spot array is increased, the array is rotated left and right by a certain angle for scanning, and the scanning range is set to a sector-shaped area; the diffraction jump scanning includes: using the geometric relationship between each diffraction order as a priori condition, jumping scanning between different diffraction orders, that is, fixing the azimuth angle Φ, only changing the relative displacement of the light spot by 2r, and searching within its neighborhood; after the search is completed, changing the relative displacement of the light spot to 3r, and searching again within its neighborhood; and so on, changing the relative displacement of the light spot to 4r, 5r... until the optical fiber position is found, and then determining the absolute value of the relative displacement R.

3. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 2, characterized in that: In step S2, after the traversal scan of the spiral stage is completed, the diffraction spot is a plurality of equidistant spots formed after the incident laser signal is modulated by the wavefront of the silicon-based liquid crystal LCOS. The plurality of equidistant spots are on a straight line that passes through the rear focus of the coupling lens, and the point spacing satisfies the grating equation.

4. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 3, characterized in that: After the traversal scan of the spiral stage is completed, the horizontal direction is used as the reference baseline to determine the approximate value Φ of the azimuth angle α of the relative displacement between the current receiving fiber end face and the back focus of the coupling lens. The azimuth angle α is the angle between the line connecting the current receiving fiber end face and the back focus of the coupling lens and the horizontal direction.

5. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 4, characterized in that: In step S2, after each sector-stepping stage scan, the dot matrix angle corresponding to the maximum power in that scan is updated to a new azimuth angle Φ, and the azimuth angle is corrected. The process is repeated until a sufficiently sharp light spot is found, that is, when a local maximum value is found, the relative displacement intermediate value r is determined, and the sector-stepping scanning stage is terminated. The maximum power value is the maximum power value measured when the dot matrix rotates left and right by one angle at a fixed light spot spacing.

6. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 5, characterized in that: The method for determining the relative displacement intermediate value r is: By continuously increasing the dot spacing, a power maximum is found, that is, a certain diffraction order gradually hits the receiving fiber. At this time, the position of the +1-order focused light spot relative to the focus after the coupling lens is r. At this time, the possible positions of the receiving fiber end face can be traversed according to the grating equation to determine the position of the receiving fiber.

7. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 6, characterized in that: The geometric relationship between the diffraction orders is expressed as: D≈R=m*fλ / T Where m is the diffraction order, f is the focal length of the coupling lens, T is the period of the blazed grating hologram displayed on the LCOS, and λ is the wavelength of the laser; The method for determining the absolute value of relative displacement D is: Let the first-order spot offset r = fλ / T, and traverse the displacement of the positive first-order spot. If the +N-order spot hits the end face of the receiving fiber at this time, the first-order spot offset is changed to Nr, that is, D≈R=Nr, N∈[...,-4,-3,-2,-1,1,2,3,4,...].

8. The method for compensating for mechanical displacement of an optical path of an intersatellite communication satellite laser terminal according to claim 7, characterized in that: In step S3, until the best optical fiber coupling efficiency compensation effect is achieved, the steps include: After determining the approximate azimuth angle Φ of the fiber displacement and the approximate absolute value R of the relative displacement, the final fine search stage begins. Within a circle with a radius of 5 μm around the current maximum position, the search is performed in a 1 / 10 step size in the vicinity. The best fiber coupling efficiency compensation effect is achieved when D = R, where D is the relative displacement value between the receiving fiber end face and the rear focus of the coupling lens before the receiving fiber is displaced.

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