A method and system for fiber nutation coupling

Abstract

The application provides an optical fiber nutation coupling method and system, and relates to the technical field of laser communication.The method comprises the following steps: through a light splitting device and a light spot position monitor, the optical axis consistency of a receiving optical fiber is calibrated, and the scanning area of a nutation scanning fast mirror is controlled in a first scanning area; when it is detected that light power enters the receiving optical fiber, the nutation scanning fast mirror is controlled to scan by using an automatic coupling scanning algorithm until the light power value of the light power entering the receiving optical fiber is stabilized in a predetermined range, and a second scanning area is determined; and dynamic coupling scanning is performed in the second scanning area, so that the light power stably enters the receiving optical fiber. By using the method and system provided by the application, the working efficiency and the alignment accuracy of optical fiber coupling can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of laser communication technology, and in particular to a fiber optic nutation coupling method and system. Background Technology

[0002] Spaceborne laser communication technology, with its advantages of narrow beam width, large information capacity, high transmission rate, wide coverage, and strong security, has become the core development direction of next-generation high-speed space communication. As spaceborne laser terminal technology matures, the demand for its commercial application is increasingly urgent. In spaceborne laser communication systems, it is necessary to efficiently couple the weak signal light transmitted in free space to a single-mode fiber with a core diameter of only 9μm to achieve high-speed photoelectric conversion and low bit error rate communication. However, limited by the extreme on-orbit environment and complex dynamic interference, existing technologies struggle to meet the requirements for high-precision and high-stability space-optical-fiber dynamic coupling, mainly in the following aspects:

[0003] During satellite operation, the release of mechanical stress caused by drastic changes in the space environment, such as temperature and gravity, can easily lead to micrometer-level static alignment shifts between the fiber optic receiver end face and the focused spot. Such fixed deviations directly reduce coupling efficiency, and traditional ground-based coaxial calibration methods are unsuitable for dynamic operation in orbit.

[0004] Meanwhile, influenced by factors such as vibrations of the space laser transmission platform, the focused laser spot will experience dynamic random jitter. This jitter is particularly pronounced in space-to-ground laser communication links, where beam jitter occurs as the laser travels through the atmosphere to the satellite platform's acquisition, tracking, and pointing (ATP) system's receiver. The jitter is primarily caused by three factors: tracking system residuals, beam jitter due to atmospheric turbulence, and harmonic vibrations transmitted from the satellite platform to the ATP system. If left uncontrolled, the dynamic offset caused by beam jitter can lead to excessive coupling power loss, far exceeding the communication system's tolerance.

[0005] Furthermore, existing nutation search algorithms (such as helical scanning) sacrifice steady-state tracking accuracy when increasing the nutation radius to improve lock-loss tolerance, and cannot directly monitor the spot-fiber alignment status in real time, resulting in dynamic adjustment lag. Existing technologies rely on fixed parameter compensation, which is difficult to cope with the real-time changes in the causes of static / dynamic alignment offsets in the on-orbit environment.

[0006] Therefore, there is an urgent need to develop a dynamic adaptive space light-single-mode fiber coupling method to solve the static / dynamic alignment deviation problem between the focused spot and the receiving fiber, ensure the quality of free-space laser communication, and provide a core solution for the engineering application of spaceborne laser communication systems. Summary of the Invention

[0007] The purpose of this invention is to provide an optical fiber nutation coupling method and system to solve the technical problems existing in the prior art.

[0008] Firstly, to solve the above-mentioned technical problems, the present invention provides an optical fiber nutation coupling method, comprising:

[0009] Using a beam splitter, the transmitted light of the incident light enters the nutating scanning fast-reflection mirror along the direction of the incident light, and the reflected light of the incident light enters the spot position monitor along a direction perpendicular to the incident light.

[0010] To keep the reflected light spot at the center of the spot position monitor, the optical axis of the spot position monitor and the receiving fiber is calibrated to determine the first scanning area.

[0011] Keep the reflected light spot at the center of the spot position monitor and control the nutation scanning fast-reflection mirror to perform a coverage scan in the first scanning area;

[0012] When the optical power entering the receiving fiber is detected to be no less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to scan until the optical power value coupled into the receiving fiber is no less than the second power threshold, and the second scanning area is determined.

[0013] The nutation scanning fast-reflection mirror is controlled to perform dynamic coupling scanning in the second scanning area.

[0014] The method of this invention locks the coupling scanning range within a defined first scanning area through optical axis consistency calibration, and then reduces the scanning area to a second scanning area with stable received power through an automatic coupling scanning algorithm. This method can efficiently complete the adaptive dynamic coupling of space light to optical fiber.

[0015] Furthermore, a photodetector is installed on the end face of the receiving optical fiber to detect the optical power entering the receiving optical fiber. The fast reflector controller adaptively and dynamically adjusts the scanning mode of the nutation scanning fast reflector based on the real-time detection and feedback of the optical power obtained by the receiving optical fiber from the photodetector.

[0016] Preferably, the photodetector adopts split monitoring with a split ratio of 95:5. The main path retains 95% of the optical power, while the monitoring path only takes 5%, ensuring the quality of the main signal and reducing the monitoring optical power to the nW level.

[0017] Furthermore, the method for calibrating the optical axis consistency of the spot position monitor and the receiving fiber is as follows:

[0018] Step a1: Adjust the incident light and the spot position monitor so that the reflected light of the incident light is focused and kept at the center position of the spot position monitor;

[0019] Step a2: Set the nutation scanning fast reflection mirror to the zero position and keep it stationary. Adjust the position of the receiving fiber in the vertical plane so that the transmitted light enters the receiving fiber after being reflected by the nutation scanning fast reflection mirror, and the optical power is maximized.

[0020] Step a3: Adjust the axial position of the receiving fiber and the position of the nutation scanning fast reflection mirror to maximize the optical power entering the receiving fiber.

[0021] Step a4, repeat steps a2 and / or a3 until it is confirmed that the optical power of the receiving fiber is maximized, and set the voltage value of the corresponding nutation scanning fast mirror to the ground reference zero position;

[0022] Step a5: Fix the positions of the spot position monitor, the receiving fiber, and the nutation scanning fast-reflection mirror;

[0023] Step a6: After the system is launched into orbit, the nutation scanning fast mirror is finely adjusted again by the fast mirror controller according to the ground reference zero position, so that the optical power incident on the receiving optical fiber reaches the maximum, and the voltage value of the nutation scanning fast mirror is set to the spaceborne reference zero position at this time.

[0024] By calibrating the optical axis consistency of the system, the scanning area can be quickly narrowed down and determined within a certain range corresponding to the reference zero position, which can greatly improve scanning efficiency.

[0025] Furthermore, the first scanning area refers to the circular region centered on the initial position A of the center of the light spot reflected by the nutated scanning fast-reflection mirror, with a radius equal to the optical axis of the light spot position monitor and the receiving optical fiber after optical axis alignment calibration.

[0026]

[0027] in, Indicates the radius of the first scan region. This indicates the system alignment residual. Indicates the system vibration error. This indicates the error in system stress variation.

[0028] Coverage scanning within a defined, small area can improve scanning efficiency and accuracy. Using helical scanning within this area avoids the chain reaction of increased nutation radius, reduced accuracy, and dynamic adjustment lag that can occur with helical scanning over larger areas. Using raster scanning within a defined area improves resolution and scanning efficiency and is easier to control.

[0029] Furthermore, the automatic coupling scanning algorithm refers to the neighbor comparison determination method. When the receiving fiber end face detects that the optical power has reached the first power threshold, it can be determined that there is an overlap between the receiving spot and the fiber end face. Using the neighbor comparison determination method, the center of the spot can be accurately moved in the direction that allows the fiber end face to obtain more optical power.

[0030] Furthermore, the specific method for automatic coupling scanning using the adjacent comparison determination method is as follows:

[0031] Step b1: Record the optical power value obtained by the receiving fiber when the center of the light spot reflected by the nutated scanning fast mirror is located at position B when the optical power entering the receiving fiber is detected to be not less than the first power threshold, and use it as the initial power comparison value.

[0032] Step b2: Starting from position B, control the nutation scanning fast-reflection mirror to move the center of the light spot sequentially to the comparison positions of position B, and record the optical power value obtained by the receiving fiber at each comparison position. The comparison positions include positions directly above, directly to the right, directly below, and directly to the left of position B, which are at a preset distance from position B.

[0033] Step b3: Compare the optical power values ​​obtained by the receiving fiber at position B and each of the comparison positions to obtain the position E of the optical spot center with the largest optical power.

[0034] Step b4: Control the nutation scanning fast mirror to move the current spot center position to the spot center position E, and at the same time use the optical power value obtained by the receiving fiber when the spot center is at the spot center position E as the new power comparison value.

[0035] Step b5: Starting from the center position E of the light spot, repeat steps b2 to b4 until a new power comparison value not less than the second power threshold is obtained after a preset number of times, and determine a preset number of light spot center screening positions.

[0036] Step b6: Determine the second scanning area based on the spot center selection position measured in step b5.

[0037] Furthermore, the preset number is at least three.

[0038] Furthermore, the second scanning area refers to the circular area defined by the three spot center screening positions being concentric.

[0039] By using the neighbor comparison method, a stable optical power region smaller than the first scanning region can be determined to ensure stable operation of the system.

[0040] By continuing to use the neighbor determination method in the optical power stable region, the position of the receiving light spot can be adjusted in real time to maximize the power entering the receiving light spot and maintain the maximum coupling efficiency.

[0041] Secondly, based on the same inventive concept, the present invention also provides an optical fiber nutation coupling system, the system comprising:

[0042] The beam splitting module is used to use a beam splitting device to make the transmitted light of the incident light enter the nutating scanning fast reflection mirror along the direction of the incident light, and to make the reflected light of the incident light enter the spot position monitor along the direction perpendicular to the incident light.

[0043] The monitoring module is used to monitor whether the reflected light spot remains at the center position of the spot position monitor;

[0044] An optical fiber module, comprising a receiving optical fiber and a photodetector, is used to receive a light beam and detect the optical power entering the receiving optical fiber;

[0045] The calibration module is used to calibrate the optical axis consistency of the spot position monitor and the receiving fiber to determine the first scanning area;

[0046] The control module controls the nutation scanning fast mirror to perform coverage scanning in the first scanning area. When the optical power obtained by the receiving fiber is not less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to perform scanning until a second scanning area is determined so that the optical power obtained by the receiving fiber is not less than the second power threshold. In the second scanning area, dynamic coupling is used to make the incident light continuously enter the receiving fiber.

[0047] The scanning module is used to perform scanning in the first and second scanning areas using a nutation scanning fast-reflection mirror.

[0048] Furthermore, the system also includes:

[0049] The shaping module is used to control the diameter and direction of the incident light, so that the incident light is incident directly onto the first incident surface of the beam splitter.

[0050] By adopting the above technical solution, the present invention has the following beneficial effects:

[0051] This invention provides a fiber optic nutation coupling method and system to solve the problem of efficient and stable alignment between free-space light and the receiving fiber. Since the end face of the receiving fiber is extremely small (micrometer-scale), and its position is unknown for spatial light, the method first uses a beam splitter and a spot position monitor to calibrate the system's optical axis, defining the coupling scanning range within a certain area. A coverage scan is then performed within this area to quickly locate the light spot on the receiving fiber end face. An automatic coupling scanning algorithm is then used to adjust the nutation scanning fast-reflection mirror based on the optical power received from the receiving fiber, ensuring the light spot consistently moves in the direction of increasing received power. This rapidly narrows the coupling scanning area to a region where the received optical power is stable. Within this stable power region, dynamic coupling scanning is performed to couple the received light spot into the receiving fiber. This invention significantly improves the efficiency and alignment accuracy of fiber optic coupling, ensuring the communication receiving system continuously and stably receives high-quality optical signals. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0053] Figure 1 A flowchart of an optical fiber nutation coupling method provided in an embodiment of the present invention;

[0054] Figure 2 This is a basic working principle diagram of the fiber optic automatic coupling system provided in an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of the coupling region division in the automatic coupling process provided in an embodiment of the present invention;

[0056] Figure 4 A schematic diagram of a method for determining adjacent positions using the neighbor comparison method is provided for an embodiment of the present invention;

[0057] Figure 5 A schematic diagram illustrating the principle of the objective lens post-scanning method is provided for embodiments of the present invention;

[0058] Figure 6 A schematic diagram of the grating scanning process is provided for embodiments of the present invention;

[0059] Figure 7 This is a block diagram of an optical fiber nutation coupling system provided in an embodiment of the present invention.

[0060] Figure label:

[0061] 1-Uncertain area; 2-Spot coverage area; 3-Stable optical power area; 4-Directly above; 5-Directly to the right; 6-Directly below; 7-Directly to the left. Detailed Implementation

[0062] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] The present invention will be further explained below with reference to specific embodiments.

[0064] It should also be noted that the specific embodiments or implementation methods described below are a series of optimized settings listed by the present invention to further explain the specific content of the invention, and these settings can be combined or used in conjunction with each other.

[0065] To facilitate understanding of the specific embodiments, the basic principle of the fiber optic nutation coupling system is first explained, such as... Figure 2 As shown, the fiber optic automatic coupling system is a closed-loop control system that uses the deviation signal extracted from the photodetector to control the deflection of a nutating scanning fast reflector (piezoelectric ceramic). Its working principle is as follows: the emitted light received by the optical antenna is focused by the coupling lens, and then the reflector mounted on the piezoelectric ceramic (i.e., the nutating scanning fast reflector) changes the light's transmission path, causing the focal plane of the reflected light to coincide with the end face of the single-mode fiber. The photodetector converts the optical signal coupled into the single-mode fiber into an electrical signal. The controller issues control commands based on the strength of the electrical signal, causing the driver to move the piezoelectric ceramic plate to produce a minute displacement, corresponding to a minute change in the scanning angle of the reflector. This adjusts the position of the coupling spot relative to the fiber end face, ultimately finding the optimal coupling position. Based on the above basic working principle, this invention provides an efficient and stable automatic coupling method and system.

[0066] Example 1:

[0067] like Figure 1 As shown, this embodiment provides a fiber optic nutation coupling method, including:

[0068] Using a beam splitter, the transmitted light of the incident light enters the nutating scanning fast-reflection mirror along the direction of the incident light, and the reflected light of the incident light enters the spot position monitor along a direction perpendicular to the incident light.

[0069] To keep the reflected light spot at the center of the spot position monitor, the optical axis of the spot position monitor and the receiving fiber is calibrated to determine the first scanning area.

[0070] Keep the reflected light spot at the center of the spot position monitor and control the nutation scanning fast-reflection mirror to perform a coverage scan in the first scanning area;

[0071] When the optical power entering the receiving fiber is detected to be no less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to scan until the optical power value coupled into the receiving fiber is no less than the second power threshold, and the second scanning area is determined.

[0072] The nutation scanning fast-reflection mirror is controlled to perform dynamic coupling scanning in the second scanning area.

[0073] Since it is impossible to directly observe the alignment between the receiving light spot and the end face of the receiving optical fiber during actual operation, the method of this invention introduces a beam splitter to obtain reflected light of the same origin as the signal light entering the receiving optical fiber, and introduces a light spot position monitor to monitor the position of the light spot of the same origin reflected light. Using the fixed position of the reflected light spot as a reference, the optical axis of the signal light in the receiving optical fiber is uniformly calibrated. In this way, the coupling scanning range can be initially determined within a small area, avoiding the situation where the coupling scanning cannot find the receiving optical fiber in a large area and the receiving light spot cannot couple into the receiving optical fiber for a long time.

[0074] The beam splitter utilizes the beam splitting characteristics of reflection and transmission at the coating interface (such as metal or dielectric films) to distribute light intensity according to a specific ratio (e.g., 50% transmission + 50% reflection, 80% transmission + 20% reflection, 95% transmission + 5% reflection, etc.). In this embodiment, a cubic beam splitter prism is used, with the beam splitting surface fixed at 45 degrees to the horizontal. When the incident light is perpendicularly incident on the outer surface of the cube, after passing the beam splitting surface, the transmitted light continues along the incident direction to the nutating scanning fast-reflecting mirror, while the reflected light is reflected at a 45-degree angle by the reflecting surface and enters the spot position monitor perpendicular to the incident light direction.

[0075] The light spot position monitor features high precision and high resolution, enabling accurate detection and positioning of target objects to monitor and identify the location of reflected light spots. Through a photosensitive material at the center of the monitor, the optical signal is converted into an electrical signal, which is then used to monitor the position and intensity of the light spot.

[0076] In this embodiment, the method for calibrating the optical axis consistency of the spot position monitor and the receiving optical fiber is as follows:

[0077] Step a1: Adjust the incident light and the spot position monitor so that the reflected light of the incident light is focused and kept at the center position of the spot position monitor.

[0078] The position of the reflected light spot can be observed using auxiliary equipment or computer software. Furthermore, to focus the reflected light at the center of the spot position detector, the incident light and the system focal length can be adjusted. A beam shaping device, such as a beam reducer, changes the divergence or convergence angle of the beam while simultaneously reducing its diameter, ensuring the beam enters the beam splitter at an appropriate size and angle. An autocollimator ensures the accuracy of the incident angle.

[0079] After adjusting and focusing the reflected light to the center position, keep the light source, beam splitter, and spot position monitor stationary, and use this as a reference to adjust the optical axis of the received signal light to the receiving fiber.

[0080] Step a2: Set the nutation scanning fast reflection mirror to the zero position and keep it stationary. Adjust the position of the receiving fiber in the vertical plane so that the transmitted light enters the receiving fiber after being reflected by the nutation scanning fast reflection mirror, and the optical power is maximized.

[0081] In this embodiment, a photodetector is provided on the end face of the receiving optical fiber to detect the optical power entering the receiving optical fiber.

[0082] In practical implementation, the photodetector is configured by splitting the received light at a 95:5 splitting ratio using an optical fiber beam splitter, ensuring that 95% of the light enters the receiving fiber and 5% enters the photodetector. The photodetector can detect 1nW of optical power. By monitoring the splitting power in real time, the power entering the receiving fiber endface can be calculated without affecting the main signal transmission. The optical power detected by the photodetector can be viewed in real time using auxiliary equipment or computer software.

[0083] The position of the receiving optical fiber in the vertical plane refers to its position on the horizontal X-axis and vertical Y-axis in the longitudinal plane coordinate system. By fixing the position of the nutating scanning fast reflector, the position of the receiving optical fiber in the vertical plane is adjusted so that the reflected light from the nutating scanning fast reflector is incident on the receiving optical fiber and its photodetector. At this point, the optical power can be monitored by the photodetector. Further adjustments are made to the longitudinal X-axis and Y-axis positions of the fiber to maximize the optical power value. With the nutating scanning fast reflector now fixed at zero and the receiving optical fiber in the vertical plane position, the next step of alignment can begin.

[0084] Step a3: Adjust the axial position of the receiving fiber and the position of the nutation scanning fast reflection mirror to maximize the optical power entering the receiving fiber.

[0085] Step a4, repeat steps a2 and / or a3 until it is confirmed that the optical power of the receiving fiber is maximized, and set the voltage value of the corresponding nutation scanning fast mirror to the ground reference zero position;

[0086] Step a5: Fix the positions of the spot position monitor, the receiving fiber, and the nutation scanning fast-reflection mirror;

[0087] By adjusting the position and axial position of the receiving optical fiber in the vertical plane, and adjusting the focal length of the automatic coupling scanning system, and further adjusting the position of the nutating scanning fast reflector in the vertical plane and the scanning angle, the optical power incident on the receiving optical fiber and photodetector is maximized. The physical positions of each module are fixed, and the reference zero position of the nutating scanning fast reflector is set. At this point, the optical axes of the two optical paths—the incident light to the spot position monitor and to the receiving optical fiber—are aligned, completing the consistency calibration on the ground and thus determining the first scanning area.

[0088] Step a6: After the system is launched into orbit, the nutation scanning fast mirror is finely adjusted again by the fast mirror controller according to the ground reference zero position, so that the optical power incident on the receiving optical fiber reaches the maximum, and the voltage value of the nutation scanning fast mirror is set to the spaceborne reference zero position at this time.

[0089] Due to various objective factors such as slight deformation of mechanical structures and drastic changes in ambient temperature, the position of the receiving light spot may change slightly from the ground to the spacecraft, affecting the alignment efficiency and accuracy of the receiving fiber and the receiving light spot. Therefore, in the spacecraft on-orbit environment, it is necessary to recalibrate the reference zero position of the nutation scanning fast reflector and the first scanning area corresponding to the new reference zero position to improve alignment efficiency and accuracy.

[0090] Due to residuals in the tracking system, beam jitter caused by atmospheric turbulence, harmonic vibrations transmitted from the satellite platform to the ATP system, and slight deformations of the mechanical structure caused by changes in temperature and stress on the satellite platform, the received light spot will dynamically change within the Field of Uncertainty (FOU) around the fiber end face. Optical axis consistency calibration can only define the range of this uncertain region. For the received light spot, the position of the fiber end face within this uncertain region is still uncertain, and coupling scanning is still required to find the optimal coupling position.

[0091] like Figure 3 The diagram showing the coupling scanning area division indicates that the shaded circular area centered at O ​​represents the receiving fiber end face. Since the position of the receiving fiber end face is uncertain for the receiving spot, the automatic coupling area of ​​the fiber can be divided into three parts.

[0092] An uncertain region 1 is defined with the initial center position A of the received light spot as the center. This region represents the possible location of the receiving fiber end face relative to the center of the light spot. The nutation scanning fast-reflection mirror is controlled to perform a coverage scan within the uncertain region 1, preferably using spiral scanning or grating scanning to quickly locate the receiving fiber end face.

[0093] During the coverage scan, the photodetector on the end face of the receiving fiber feeds back the detected optical power to the fast-reflection mirror controller in real time. When the receiving spot overlaps with the end face of the receiving fiber, the photodetector detects the optical power. When the photodetector on the end face of the receiving fiber detects that the optical power entering the receiving fiber is not less than a first power threshold, such as... Figure 3 When the center of the light spot shown is at position B, the radius is the sum of the radius of the receiving fiber end face and the radius of the receiving light spot, with the center at position O of the receiving fiber end face as the center (e.g., ...). Figure 3 The distance from the midpoint 0 to point B is divided into a light spot coverage area 2. Within this area, the photodetector on the receiving fiber end face can detect the optical power. However, at position B, the receiving light spot cannot accurately know the specific location of the entire receiving fiber end face.

[0094] Preferably, the first power threshold is set to 10% of the optical power obtained by the receiving fiber under ideal conditions. This can ensure that the receiving light spot is coupled into the receiving fiber and avoid misjudgment. Ideal conditions refer to the state in which the receiving light spot and the end face of the receiving fiber are completely aligned.

[0095] To more accurately align the receiving light spot with the ground end face of the receiving fiber, starting from position B, an automatic coupling scanning algorithm is used to control the nutating scanning fast-reflection mirror to scan until the optical power coupled into the receiving fiber is not less than the second power threshold. Assuming that the center of the light spot is located at point C at this point, the second scanning area is determined, i.e. Figure 3 The optical power stabilization region 3 is shown. It should be noted that... Figure 3 This diagram is for illustrative purposes only; the division of each region in the diagram is unknown to the receiving light spot. Since the uncertainty of the receiving light spot's position is an objective phenomenon—it dynamically changes within a certain range and is not subject to human control—an automatic coupling scanning algorithm is needed to find a coupling scanning region that allows the system to operate stably. This enables the coupling scan to dynamically and stably couple the received signal light into the receiving optical fiber.

[0096] Preferably, the second power threshold is set as the minimum optical power that allows the entire communication system to operate stably. It is typically 40% to 50% of the optical power obtained by the receiving fiber under ideal conditions, so that the system can maintain stable operation in the second scanning area while ensuring the scanning efficiency and robustness of the coupled scanning system.

[0097] In this embodiment, the first scanning region, also known as the uncertain region 1, refers to a circular region with the initial position A of the center of the light spot reflected by the nutated scanning fast reflection mirror as the center and the radius as the following formula, after the optical axis consistency calibration of the light spot position monitor and the receiving optical fiber is performed:

[0098]

[0099] in, Indicates the radius of the first scan region. This indicates the system alignment residual. Indicates the system vibration error. This indicates the error in system stress variation.

[0100] The main application scenario of this embodiment is laser communication between spacecraft and the ground. The range of the uncertain region 1 is mainly affected by the system alignment residual. System vibration error and system stress variation error When the three error sources are known or easily obtainable, the radius of the first scan region can be estimated using these three errors. In other embodiments, other error sources may have a greater impact, requiring corresponding modifications to the formula for estimating the radius of the first scan region.

[0101] In practical implementation, when the aforementioned error is difficult to obtain, empirical values ​​can be used instead. In this embodiment, the uncertain region 1 can be replaced by a range of ±200 μrad near the reference zero position of the fast-reflection mirror. The initial position A is the position of the center of the reflected light spot initially captured by the nutation scanning fast-reflection mirror.

[0102] In this embodiment, the automatic coupling scanning algorithm uses the neighbor comparison method, which is a sorting comparison algorithm. Since coverage scanning can only guarantee no missed scans, the obtained position is not necessarily the optimal coupling position. Furthermore, the automatic coupling system in this embodiment uses a back-scanning method with a curved scanning image plane, which can cause defocusing errors of the focused beam at the fiber end face. To overcome these factors, the neighbor comparison method is used for precise two-dimensional translational positioning. The neighbor comparison method uses the current center position of the light spot as the center and compares the light intensity at positions one step above, below, left, and right to determine the direction of light spot movement, ensuring that the light spot always moves along the direction of increasing light intensity. For example... Figure 4 The diagram shows the adjacent comparison method. The circles in the diagram do not represent the size of the received light spot, but only the direction and distance of the received light spot moving sequentially. The distance between two adjacent center circles represents a moving step. The diameter of the received light spot is greater than the moving step.

[0103] In this embodiment, the specific method for automatic coupling scanning using the adjacent comparison determination method is as follows:

[0104] Step b1: Record the optical power value obtained by the receiving fiber when the center of the light spot reflected by the nutated scanning fast mirror is located at position B when the optical power entering the receiving fiber is detected to be not less than the first power threshold, and use it as the initial power comparison value.

[0105] Step b2: Starting from position B, control the nutation scanning fast-reflection mirror to move the center of the light spot sequentially to the comparison positions of position B, and record the optical power value obtained by the receiving fiber at each comparison position. The comparison positions include positions 4 directly above, 5 directly to the right, 6 directly below, and 7 directly to the left of position B, which are at a preset distance from position B.

[0106] The preset distance is the coupling tracking scan step size. By setting a small tracking scan step size, the receiving light spot is moved up, down, left, and right by one tracking scan step size by the deflection of the two-dimensional piezoelectric ceramic in the nutation scanning fast reflector, and the voltage magnitude obtained at each position is recorded. The scanning position of the fast reflector is recorded by the voltage magnitude.

[0107] The smaller tracking scanning step size can be set empirically to a value that is small compared to the radius of the receiving spot, typically in the nanometer range. In the adjacent comparison determination method, when the receiving spot moves to each comparison position with this step size, it can completely cover the scanned area, and there are no missed scan areas between the positions.

[0108] To further improve scanning efficiency and accuracy, the tracking step length can be calculated using a formula. Taking raster scanning as an example, the calculation method is illustrated below. Figure 5 Schematic diagram of the principle of post-objective scanning method and Figure 6 Schematic diagram of the raster scanning process. Figure 6 The small and medium circles indicate the position of the center of the light spot during movement, and do not represent the size of the entire light spot. Assume the length of the raster scanning area is... Then it can be expressed as:

[0109]

[0110] in, Let be the distance from the point of reflection of the coupled light on the reflector to the focal point. This represents the maximum scanning angle of the nutating scanning fast-reflection mirror. According to Rayleigh diffraction theory, the diffraction-limited resolution angle of the coupled scanning system is... for:

[0111] ,

[0112] in, For aperture shape factor, For the wavelength of the coupled light wave, This refers to the aperture size of the coupling lens.

[0113] The number of scan points in a single line can be obtained from the above formula. for:

[0114] ,

[0115] Therefore, the scanning step size for:

[0116] ,

[0117] In this embodiment, a circular coupling lens is used as an example. Take 1.22.

[0118] As can be seen from the above process, the tracking scan step size mainly depends on the wavelength of the coupled optical wave in the system. The aperture size of the coupling lens The maximum scanning angle of the nutation scanning fast-reflection mirror In other embodiments, the tracking step size can be calculated using corresponding methods and formulas according to the actual situation.

[0119] Step b3: Compare the optical power values ​​obtained by the receiving optical fiber at position B and each of the comparison positions to obtain the position E of the optical spot center with the largest optical power.

[0120] Step b4: Control the nutation scanning fast mirror to move the current spot center position back to the spot center position E, and at the same time use the optical power value obtained by the receiving fiber when the spot center is at the spot center position E as the new power comparison value.

[0121] Step b5: Starting from the center position E of the light spot, repeat steps b2-b4 until a new power comparison value not less than the second power threshold is obtained after a preset number of times, and determine the preset number of light spot center screening positions.

[0122] In this embodiment, the preset number is at least three. Steps b2-b4 are repeated until a preset number of optical power comparison values ​​that allow the system to operate stably are obtained, i.e., not less than the second power threshold. The corresponding spot center position is the spot center screening position. The preset number of times corresponds one-to-one with the preset number of spot center screening positions. After obtaining at least three spot center screening positions through the above steps, the second scanning area can be determined.

[0123] The second scanning area refers to the circular area defined by the three spot center screening positions being concentric, corresponding to... Figure 3 In the optical power stabilization region 3, the second scanning region is the area of ​​dynamic coupling scanning of the receiving system under stable operating conditions. Within the second scanning region, the nutation scanning fast-reflecting mirror is controlled to perform dynamic coupling scanning to overcome the dynamic offset caused by beam jitter, ensuring that the optical power coupled into the receiving fiber is stabilized above the second power threshold, and the system remains in a stable operating state.

[0124] Within the second scanning area, the adjacent comparison judgment scanning method can continue to be used to adjust the position of the light spot and the optical fiber in real time, so as to maximize the power entering the receiving optical fiber, find the optimal coupling position, and keep the coupling efficiency at its maximum.

[0125] Example 2:

[0126] like Figure 7 As shown, this embodiment provides an optical fiber nutation coupling system, the system including:

[0127] The beam splitting module is used to use a beam splitting device to make the transmitted light of the incident light enter the nutating scanning fast reflection mirror along the direction of the incident light, and to make the reflected light of the incident light enter the spot position monitor along the direction perpendicular to the incident light.

[0128] The monitoring module is used to monitor whether the reflected light spot remains at the center position of the spot position monitor;

[0129] An optical fiber module, comprising a receiving optical fiber and a photodetector, is used to receive a light beam and detect the optical power entering the receiving optical fiber;

[0130] The calibration module is used to calibrate the optical axis consistency of the spot position monitor and the receiving fiber to determine the first scanning area;

[0131] The control module controls the nutation scanning fast mirror to perform coverage scanning in the first scanning area. When the optical power obtained by the receiving fiber is not less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to perform scanning until a second scanning area is determined so that the optical power obtained by the receiving fiber is not less than the second power threshold. In the second scanning area, dynamic coupling is used to make the incident light continuously enter the receiving fiber.

[0132] The scanning module is used to perform scanning in the first and second scanning areas using a nutation scanning fast-reflection mirror.

[0133] In addition to the modules mentioned above, the system also includes the following components to adjust the direction and diameter of the incident light:

[0134] The shaping module is used to control the diameter and direction of the incident light, so that the incident light is incident directly onto the incident surface of the beam splitter.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fiber optic nutation coupling method, characterized in that, include: Using a beam splitter, the transmitted light of the incident light enters the nutating scanning fast-reflection mirror along the direction of the incident light, and the reflected light of the incident light enters the spot position monitor along a direction perpendicular to the incident light. To keep the reflected light spot at the center of the spot position monitor, the optical axis of the spot position monitor and the receiving fiber is calibrated to determine the first scanning area. Keep the reflected light spot at the center of the spot position monitor and control the nutation scanning fast-reflection mirror to perform a coverage scan in the first scanning area; When the optical power entering the receiving fiber is detected to be no less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to scan until the optical power value coupled into the receiving fiber is no less than the second power threshold, and the second scanning area is determined. The nutation scanning fast-reflection mirror is controlled to perform dynamic coupling scanning in the second scanning area; The method for calibrating the optical axis consistency of the spot position monitor and the receiving fiber is as follows: Step a1: Adjust the incident light and the spot position monitor so that the reflected light of the incident light is focused and kept at the center position of the spot position monitor; Step a2: Set the nutation scanning fast reflection mirror to the zero position and keep it stationary. Adjust the position of the receiving fiber in the vertical plane so that the transmitted light enters the receiving fiber after being reflected by the nutation scanning fast reflection mirror, and the optical power is maximized. Step a3: Adjust the axial position of the receiving fiber and the position of the nutation scanning fast reflection mirror to maximize the optical power entering the receiving fiber. Step a4, repeat steps a2 and / or a3 until the optical power of the receiving fiber is at its maximum, and set the voltage value of the corresponding nutation scanning fast mirror to the ground reference zero position; Step a5: Fix the positions of the spot position monitor, the receiving fiber, and the nutation scanning fast-reflection mirror; Step a6: After the system is launched into orbit, the nutation scanning fast mirror is finely adjusted again by the fast mirror controller according to the ground reference zero position, so that the optical power incident on the receiving optical fiber reaches the maximum, and the voltage value of the nutation scanning fast mirror is set to the spaceborne reference zero position at this time. The first scanning area refers to the circular region centered on the initial position A of the light spot reflected by the nutated scanning fast reflection mirror, with the following formula as the radius, after the optical axis alignment of the light spot position monitor and the receiving optical fiber is calibrated: in, Indicates the radius of the first scan region. This indicates the system alignment residual. Indicates the system vibration error. This indicates the error in system stress variation.

2. The method according to claim 1, characterized in that, A photodetector is provided on the end face of the receiving optical fiber to detect the optical power entering the receiving optical fiber.

3. The method according to claim 1, characterized in that, The automatic coupling scan algorithm refers to the neighbor comparison determination method.

4. The method according to claim 3, characterized in that, The specific method for automatic coupling scanning using the adjacent comparison determination method is as follows: Step b1: Record the optical power value obtained by the receiving fiber when the center of the light spot reflected by the nutated scanning fast mirror is located at position B when the optical power entering the receiving fiber is detected to be not less than the first power threshold, and use it as the initial power comparison value. Step b2: Starting from position B, control the nutation scanning fast-reflection mirror to move the center of the light spot sequentially to the comparison positions of position B, and record the optical power value obtained by the receiving fiber at each comparison position. The comparison positions include positions directly above, directly to the right, directly below, and directly to the left of position B, which are at a preset distance from position B. Step b3: Compare the optical power values ​​obtained by the receiving fiber at position B and each of the comparison positions to obtain the position E of the optical spot center with the largest optical power. Step b4: Control the nutation scanning fast mirror to move the current spot center position to the spot center position E, and at the same time use the optical power value obtained by the receiving fiber when the spot center is at the spot center position E as the new power comparison value. Step b5: Starting from the center position E of the light spot, repeat steps b2 to b4 until a new power comparison value not less than the second power threshold is obtained after a preset number of times, and determine a preset number of light spot center screening positions. Step b6: Determine the second scanning area based on the spot center selection position measured in step b5.

5. The method according to claim 4, characterized in that, The preset number is at least three.

6. The method according to claim 5, characterized in that, The second scanning area refers to the circular area defined by the three light spot center screening positions being concentric.

7. A fiber optic nutation coupling system employing the method described in any one of claims 1-6, characterized in that, include: The beam splitting module is used to use a beam splitting device to make the transmitted light of the incident light enter the nutating scanning fast reflection mirror along the direction of the incident light, and to make the reflected light of the incident light enter the spot position monitor along the direction perpendicular to the incident light. The monitoring module is used to monitor whether the reflected light spot remains at the center position of the spot position monitor; An optical fiber module, comprising a receiving optical fiber and a photodetector, is used to receive a light beam and detect the optical power entering the receiving optical fiber; The calibration module is used to calibrate the optical axis consistency of the spot position monitor and the receiving fiber to determine the first scanning area; The control module controls the nutation scanning fast mirror to perform coverage scanning in the first scanning area. When the optical power obtained by the receiving fiber is not less than the first power threshold, the automatic coupling scanning algorithm is used to control the nutation scanning fast mirror to perform scanning until a second scanning area is determined so that the optical power obtained by the receiving fiber is not less than the second power threshold. In the second scanning area, dynamic coupling is used to make the incident light continuously enter the receiving fiber. The scanning module is used to perform scanning in the first and second scanning areas using a nutation scanning fast-reflection mirror.

8. The system according to claim 7, characterized in that, Also includes: The shaping module is used to control the diameter and direction of the incident light, so that the incident light is incident directly onto the first incident surface of the beam splitter.

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