Focusing method and focusing system

Abstract

The present invention relates to the technical field of optical systems, and in particular to a focusing method and a focusing system. The focusing method comprises: arranging a focusing system; determining a theoretical focal length; determining an offset of a focus on a focal plane, determining a theoretical focus position based on the offset and the theoretical focal length, and positioning a camera at the theoretical focus position; utilizing a light source to emit parallel light transmitted in a first direction to form a light spot on a camera target surface; rotating the light source by a certain angle to cause the light spot to be displaced on the camera target surface, and obtaining an actual distance between a lens and a camera based on the rotation angle and the light spot displacement. L , according to the actual distance L The error between the actual focal length and the theoretical focal length is to move the first wedge to adjust the equivalent thickness of the double wedge structure so that the actual distance L The error between the focal length and the theoretical focal length is equivalent to zero. The present invention is beneficial to improving the focusing accuracy and improving the stability and reliability of the optical axis during the focusing process.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical systems, and in particular relates to a focusing method and a focusing system. Background Art

[0002] With the development of satellite internet, deep space exploration, and satellite-to-ground laser communications, free-space optical communication (FSOC) technology has attracted widespread attention due to its advantages such as high bandwidth, low latency, and strong anti-interference capabilities. In FSOC systems, the receiver must focus and couple spatial light into a single-mode fiber (SMF) to achieve high-quality communication. However, in practical applications, optical systems are susceptible to wavefront distortion due to a variety of factors, including systematic errors introduced during system manufacturing and assembly, as well as alignment errors caused by space environmental factors such as launch vibration and on-orbit thermal effects. This can reduce fiber coupling efficiency and, in severe cases, even disrupt the communication link.

[0003] Current research focuses on alignment errors during fiber coupling, including the reduction in coupling efficiency caused by defocusing. Compared to traditional imaging systems, focusing at the receiving end of laser communications is more challenging, as the incident light must be precisely coupled into the single-mode fiber, placing stringent demands on optical axis stability. For example, for a single-mode fiber with a wavelength of 1550nm, when the lateral offset reaches 0.67 times the mode field diameter, the coupling efficiency drops to 10%. Therefore, there is an urgent need to explore structures with high stability and high-precision focusing capabilities to effectively improve the system's beam coupling efficiency and overall communication performance.

[0004] The current mainstream focusing solutions are mainly achieved through the following methods: using a zoom lens group to change the effective focal length of the system through relative movement between multiple lenses to achieve focusing; using a liquid lens to quickly change the optical focal length to complete focusing by adjusting the curvature of the liquid interface; the axial translation lens method moves the entire lens group along the optical axis to move the focus back and forth; and the axial translation fiber solution directly moves the position of the fiber end face to adapt to different focusing positions. These methods each achieve focal length adjustment and focus compensation functions by changing the spatial position of key optical elements or receiving surfaces in the system.

[0005] The zoom lens group has a wide focusing range and is suitable for a variety of application scenarios, but its structure is complex, the size is large, the installation and adjustment accuracy requirements are high, and the response speed is slow; the liquid lens has a fast response, a compact structure, and does not require a mechanical structure, which is suitable for miniaturized systems, but is easily affected by gravity and temperature changes, has wavefront aberrations, and is difficult to achieve large-aperture applications; the axial translation lens has a simple structure, low cost, and is easy to implement, but requires high-precision mechanical control, and has problems with poor stability and limited response speed; the axial moving optical fiber method also has a simple structure and can achieve rapid focusing through piezoelectric elements, but it has extremely high requirements for displacement accuracy, is prone to coupling loss, and piezoelectric drive may have directional coupling interference, affecting system stability; Overall, these methods have certain limitations in terms of system stability and environmental adaptability. Summary of the Invention

[0006] In view of this, the present invention aims to provide a focusing method and a focusing system, which are beneficial to improving the focusing accuracy and improving the stability and reliability of the optical axis during the focusing process.

[0007] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0008] The present invention provides a focusing method, comprising: arranging a focusing system, wherein the focusing system comprises a light source, a lens, a double wedge structure, and a camera arranged in sequence along a first direction, wherein the double wedge structure comprises a first wedge and a second wedge spaced apart along the first direction, and the first wedge is movable relative to the second wedge to adjust the equivalent thickness of the double wedge structure; and adjusting the focal length of the lens according to the focal length of the lens. f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length According to the spacing between the first optical wedge and the second optical wedge in the first direction △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane , based on the offset and theoretical focal length Determine the theoretical focus position and position the camera at the theoretical focus position; use the light source to emit parallel light transmitted along the first direction to form a light spot on the camera target surface; rotate the light source by a certain angle to cause the light spot to shift on the camera target surface, and obtain the actual distance between the lens and the camera based on the rotation angle and the light spot displacement. L , according to the actual distance L With theoretical focal length Move the first wedge to adjust the equivalent thickness of the double wedge structure so that the actual distance L With theoretical focal length The error between them is equivalent to zero.

[0009] Furthermore, according to the focal length of the lens f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length Including: Determine the theoretical focal length according to formula 1 , Formula 1 is as follows: .

[0010] Furthermore, according to the distance between the first optical wedge and the second optical wedge in the first direction △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane Includes: Determine the offset according to Formula 2 , Formula 2 is as follows: ;in, represents the exit angle, .

[0011] Furthermore, the actual distance between the lens and the camera is obtained according to the rotation angle and the spot displacement. L Including: Get the actual distance according to formula 3 L , Formula 3 is as follows: L=x / θ ,in, x is the light spot displacement, θ is the rotation angle.

[0012] Furthermore, the corresponding relationship between N different rotation angles and spot displacement is obtained, and N actual distances are obtained according to formula 3 L , N actual distances L Take the average value as the final actual distance L .

[0013] Furthermore, according to the actual distance L With theoretical focal length The error between moving the first optical wedge includes: L With theoretical focal length The error between the two is used to obtain the thickness of the double wedge structure to be adjusted , according to the thickness to be adjusted Determine the amount of movement of the first optical wedge , waiting for the movement Move the first wedge by the amount.

[0014] Further, to wait for the movement After moving the first optical wedge by the movement amount, the method further includes: rotating the light source to a position where parallel light is emitted along the first direction, fine-tuning the movement of the first optical wedge by adjusting the light intensity of the light spot in the image formed by the camera, and stopping the movement of the first optical wedge when the light intensity reaches a maximum value to achieve optimal focus.

[0015] Furthermore, according to the actual distance L With theoretical focal length The error between the two is used to obtain the thickness of the double wedge structure to be adjusted Including: Obtain the thickness to be adjusted according to formula 4 , Formula 4 is as follows: ,in, n is the refractive index of the double wedge structure; according to the thickness to be adjusted Determine the amount of movement of the first optical wedge Including: Obtain the amount to be moved according to formula 5 , Formula 5 is as follows: ,in, α It is a wedge angle.

[0016] Another aspect of the present invention provides a focusing system, which is used to implement the above-mentioned focusing method. The focusing system includes: an angle measurement component and a light source, a lens, a double optical wedge structure, and a camera arranged in sequence along a first direction; wherein the light source is used to emit parallel light, the angle measurement component is used to measure the angle of the light source, the lens is used to receive the parallel light and output a focused light beam, the double optical wedge structure includes a first optical wedge and a second optical wedge that are spaced apart and have parallel wedge surfaces, the wedge surface of the first optical wedge is opposite to the wedge surface of the second optical wedge, wherein the first optical wedge is movable relative to the second optical wedge in a direction parallel to the wedge surface to adjust the equivalent thickness of the double optical wedge structure, and the camera is used to receive the focused light beam.

[0017] Furthermore, the angle measuring assembly includes a reflector and a Leica goniometer. The reflector is arranged on the light source, and the Leica goniometer cooperates with the reflector to measure the angle of the light source.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects: the focusing method provided by the present invention first positions the camera at a theoretical focal position. The determination of the theoretical focal position not only relies on a theoretical focal length determined based on the lens and the two optical wedges in the double optical wedge structure, but also takes into account the influence of the air gap between the first optical wedge and the second optical wedge on the focus offset. In addition, after the camera is positioned at the theoretical focal position, the position of the camera is further fine-tuned to further improve the focusing accuracy. Specifically, the correspondence between the rotation angle and the light spot displacement is obtained by rotating the light source, and then the actual distance between the lens and the camera is obtained based on the correspondence between the rotation angle and the light spot displacement. The equivalent thickness of the double optical wedge structure is adjusted according to the difference between the theoretical focal length and the actual distance so that the error between the actual distance and the theoretical focal length is zero or close to zero (equivalent to zero). After such fine-tuning, the position of the camera is a relatively accurate focus position.

[0019] The focusing method provided by the present invention can achieve high-precision focusing while maintaining the stability of the optical axis during the adjustment process. The system structure adopted for the adjustment is simple and easy to install and adjust, and has excellent optical axis holding ability and low positioning sensitivity. It can achieve continuous and controllable focal length adjustment while maintaining the stability of the optical axis direction, significantly improving the optical axis stability and focusing accuracy. Compared with the traditional axial translation focusing method, the method has the advantages of compact structure, simple installation and adjustment, high error tolerance and small introduced wavefront aberration. It is particularly suitable for application scenarios with high requirements on optical axis consistency and focusing reliability, such as free-space laser communication and high-precision imaging. The air gap compensation mechanism further enhances the operating stability of the system in complex environments, and has high engineering practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 A schematic structural diagram of the focusing system according to an embodiment of the present invention;

[0022] Figure 2 A flowchart of a focusing method according to an embodiment of the present invention;

[0023] Figure 3 A schematic diagram illustrating an optical axis eccentricity caused by an air gap in a double wedge structure according to an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the linear relationship between the actual offset and the displacement of the first optical wedge according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0027] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0028] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0030] refer to Figures 1 to 3The present invention provides a focusing method, which is implemented based on the focusing system provided by the invention. The focusing system includes: an angle measurement component and a light source 1, a lens 5, a double optical wedge structure and a camera 10 arranged in sequence along a first direction X; wherein the light source 1 is used to emit parallel light, the angle measurement component is used to measure the angle of the light source 1, the lens 5 is used to receive the parallel light and output a focused light beam, the double optical wedge structure includes a first optical wedge 6 and a second optical wedge 8 that are spaced apart and have wedge surfaces parallel to each other, the wedge surface of the first optical wedge 6 is opposite to the wedge surface of the second optical wedge 8, wherein the first optical wedge 6 is movable relative to the second optical wedge 8 in a direction parallel to the wedge surface to adjust the equivalent thickness of the double optical wedge structure, and the camera 10 is used to receive the focused light beam.

[0031] The first direction X is parallel to the extension direction of the preset optical axis of the focusing system.

[0032] In some embodiments, the light source 1 can be a collimator, and the focusing system further includes a high-precision rotation platform 2, on which the collimator is disposed. The high-precision rotation platform 2 is used to drive the collimator to rotate to change the optical axis direction of the parallel light.

[0033] Furthermore, the angle measuring assembly includes a reflector 4 and a Leica goniometer 3. The reflector 4 is arranged on the light source 1, and the Leica goniometer 3 is arranged on the side of the reflector 4 away from the light source 1. The Leica goniometer 3 cooperates with the reflector 4 to measure the rotation angle of the light source 1. It should be noted that when the optical axis direction of the parallel light emitted by the light source 1 is parallel to the first direction X, the rotation angle of the light source 1 is zero.

[0034] In some embodiments, the focusing system further includes a first optical wedge bracket 7 and a driving unit 12. The driving unit 12 can be a one-dimensional translation stage. The first optical wedge 6 is disposed on the first optical wedge bracket 7. The first optical wedge bracket 7 is connected to the free end of the driving unit 12. The driving unit 12 is used to drive the first optical wedge 6 to move in a direction parallel to the wedge surface.

[0035] In other embodiments, the driving unit 12 may also be a stepping motor, a DC motor, a linear motor or a piezoelectric motor.

[0036] In some embodiments, the surfaces of first optical wedge 6 and second optical wedge 8 may be coated with an anti-reflection coating, an anti-reflection coating, a high-reflection coating, or a filter coating to enhance optical performance within a specific wavelength range, thereby further improving the light utilization and performance of the system within a specific spectral band.

[0037] In some embodiments, the focusing system further includes a lateral translation stage 9 with position feedback, and the camera 10 is disposed on the lateral translation stage 9 .

[0038] In some embodiments, the first optical wedge 6 and the second optical wedge 8 are made of the same material. The material of the first optical wedge 6 can be optical glass, calcium fluoride, sapphire, plastic optical material, or optical resin.

[0039] In some embodiments, the focusing system further includes a computer 11 , the camera 10 is connected to the computer 11 , and the computer 11 is used to process data output by the camera 10 .

[0040] The focusing method provided by the present invention includes: arranging a focusing system, wherein the focusing system includes a light source 1, a lens 5, a double optical wedge structure, and a camera 10 arranged in sequence along a first direction X, wherein the double optical wedge structure includes a first optical wedge 6 and a second optical wedge 8 spaced apart along the first direction X, and the first optical wedge 6 is movable relative to the second optical wedge 8 to adjust the equivalent thickness of the double optical wedge structure, thereby achieving adjustment of the optical path difference; according to the focal length of the lens 5 f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length According to the spacing between the first optical wedge 6 and the second optical wedge 8 in the first direction X △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane , based on the offset and theoretical focal length Determine the theoretical focus position and position the camera 10 at the theoretical focus position; use the light source 1 to emit parallel light transmitted along the first direction X to form a light spot on the target surface of the camera 10; rotate the light source 1 by a certain angle to cause the light spot to shift on the target surface of the camera 10, and obtain the actual distance between the lens 5 and the camera 10 based on the rotation angle and the light spot displacement. L , according to the actual distance L With theoretical focal length The error between the two is to move the first optical wedge 6 to adjust the equivalent thickness of the double optical wedge structure so that the actual distance L With theoretical focal length The error between them is equivalent to zero.

[0041] The focusing system provided by the present invention has a simple structure and is easy to assemble and adjust. The wavefront aberration introduced by the focusing method is small, the optical axis offset is small, and the focusing accuracy is high, and the system is suitable for high-precision optical systems.

[0042] Introducing offset The reason is that although the double optical wedge structure has good focusing ability, in actual application, the air gap between the first optical wedge 6 and the second optical wedge 8 will affect the system performance. If the air gap between the first optical wedge 6 and the second optical wedge 8 is too small, the first optical wedge 6 may come into contact with the second optical wedge 8 during movement, causing component damage and affecting system reliability. If the gap is too large or uneven, it is easy to cause excessive optical axis offset or tilt of the optical axis direction. Therefore, it is necessary to ensure that there is a certain air gap between the first optical wedge 6 and the second optical wedge 8. In order to reduce the impact of the focus offset caused by the air gap on the system performance, the focus offset can be regarded as an initial system error and compensated by adjusting the position of the camera 10. The offset This is the focus offset caused by the air gap. It is used as the initial error of the system to correct it, further reducing the error caused by the system structure.

[0043] Theoretical focal length is the theoretical focal length of the receiving system composed of the lens 5 and the double wedge optical structure. The focusing range of the present invention is , ,in, is the adjustable overall thickness range of the double wedge structure, and the focusing accuracy of the double wedge structure is , ,in, δl The minimum resolution of the driving unit 12 for moving the first optical wedge 6 is α is the wedge angle of the first optical wedge 6 or the second optical wedge 8 . It should be noted that the wedge angle of the first optical wedge 6 is consistent with the wedge angle of the second optical wedge 8 .

[0044] Furthermore, according to the focal length of lens 5 f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length Including: Determine the theoretical focal length according to formula 1 , Formula 1 is as follows: .

[0045] Furthermore, according to the spacing between the first optical wedge 6 and the second optical wedge 8 in the first direction X △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane Includes: Determine the offset according to Formula 2 , Formula 2 is as follows: ;in, represents the exit angle, .

[0046] Furthermore, the actual distance between the lens 5 and the camera 10 is obtained according to the rotation angle and the spot displacement. L Including: Get the actual distance according to formula 3 L , Formula 3 is as follows: L=x / θ ,in, x is the light spot displacement, θ is the rotation angle.

[0047] Furthermore, the corresponding relationship between N different rotation angles and spot displacement is obtained, and N actual distances are obtained according to formula 3 L , N actual distances L Take the average value as the final actual distance L , N is a positive integer greater than 1.

[0048] Furthermore, according to the actual distance L With theoretical focal length The error between moving the first optical wedge 6 includes: L With theoretical focal length The error between the two is used to obtain the thickness of the double wedge structure to be adjusted , according to the thickness to be adjusted Determine the amount of movement of the first optical wedge 6 , waiting for the movement The first optical wedge 6 is moved by a movement amount φ.

[0049] Further, to wait for the movement After moving first optical wedge 6 by the desired amount, the process further includes rotating light source 1 to a position where it emits parallel light traveling in a first direction X, fine-tuning the movement of first optical wedge 6 based on the intensity of the light spot imaged by camera 10, and stopping the movement of first optical wedge 6 when the intensity reaches a maximum value to achieve optimal focus. Specifically, optimal focus is considered achieved when the peak intensity reaches a maximum value, indicating that the target plane of camera 10 is accurately aligned with the focal plane of the system. If this condition is not met, fine-tuning first optical wedge 6 continues until the peak intensity reaches a maximum value to achieve precise focus.

[0050] Furthermore, according to the actual distance L With theoretical focal length The error between the two is used to obtain the thickness of the double wedge structure to be adjusted Including: Obtain the thickness to be adjusted according to formula 4 , Formula 4 is as follows: ,in, n is the refractive index of the double wedge structure; according to the thickness to be adjusted Determine the amount of movement of the first optical wedge 6 Including: Obtain the amount to be moved according to formula 5 , Formula 5 is as follows: ,in, α It is a wedge angle.

[0051] It should be noted that in actual use, after the camera 10 is positioned at the focal point using the focusing method provided by the present invention, the camera 10 must be disassembled and the receiving end of the optical fiber used to collect light must be positioned at the focal point. In some cases, the light source 1 must also be removed and replaced with a tracking system. The lens, double wedge structure, and optical fiber must be aligned behind the tracking system. The tracking system is used to guide spatial light to the lens. In some cases, the tracking system is a pointing, acquisition, and tracking (PAT) subsystem.

[0052] A specific embodiment of a focusing method is provided below.

[0053] In some embodiments, the light source 1 is a collimator, the operating wavelength of the collimator can be 1550 nm, the materials of the first optical wedge 6 and the second optical wedge 8 can both be optical glass, the refractive index of the first optical wedge 6 and the second optical wedge 8 at a wavelength of 1550 nm is both 1.429, the wedge angle can be 15°, the one-dimensional translation stage is an electric translation stage, the effective stroke of the one-dimensional translation stage can be 12 mm, and the minimum resolution of the one-dimensional translation stage can be 0.2 μm. In this way, high-precision linear movement can be achieved.

[0054] refer to Figure 2 , the focusing method comprises the following steps:

[0055] Step S1: The focal length of the lens 5 can be calibrated using the collimator, the lens 5 and the camera 10. The average value of multiple focal lengths can be taken as the focal length of the lens 5. f , measured focal length f The double wedge structure is then placed in the optical path to complete the initial adjustment. The initial equivalent thickness of the double wedge structure is 10.700 mm, and the width of the air gap is 0.5 mm. Using the aforementioned formula 1, the theoretical focal length is 103.213 mm. The camera 10 can be roughly positioned at the focal position determined by the theoretical focal length.

[0056] Step S2, calculate the offset according to the above formula 2 , offset 0.061mm, according to the offset Fine-adjust the position of the camera 10 to compensate for the offset and position the camera 10 at the theoretical focus position;

[0057] Step S3: Use the high-precision rotation stage 2 to rotate the collimator at a small angle, and use the Leica goniometer 3 and the reflector 4 to accurately measure the rotation angle. θ , the spot displacement on the target surface of camera 10x The center of mass position can be extracted through image processing algorithms. 500 consecutive acquisitions are performed to obtain 500 sets of rotation angles. θ and spot displacement x , and then 500 actual distance values ​​are obtained. The average value of the 500 actual distance values ​​is taken as the actual distance L. The actual distance L is 0.748 mm. According to the above formula 3, the actual distance L between the lens 5 and the camera 10 is 102.868 mm.

[0058] Step S4: Based on the difference between the actual distance L and the theoretical focal length, the required thickness of the double-wedge structure is calculated to be 1.149 mm. The first optical wedge 6 is linearly moved 4.440 mm along its inclined surface using a one-dimensional translation stage, thereby completing the thickness adjustment of the double-wedge structure.

[0059] Step S5: Determine whether the camera 10 is in optimal focus by measuring the peak intensity of the light spot in the image. When the peak intensity reaches a maximum value, optimal focus is achieved, indicating that the target surface of the camera 10 is accurately aligned with the focal plane of the system. If this condition is not met, continue to fine-tune the position of the first optical wedge 6 until the peak intensity is maximized, thereby achieving precise focus.

[0060] Step S6: After the camera 10 is positioned at the optimal focus, the focusing process ends.

[0061] In this embodiment, the focus accuracy of the double wedge structure is 0.016 μm, and the focus adjustment range is 0.932 mm.

[0062] like Figure 4 As shown in the experiment, the actual offset There is a good linear relationship between the displacement of the first optical wedge 6 and the regression fit is R 2 All exceed 0.996. The offset caused by the 0.5mm wide air gap The calculated offset is 0.062 mm. The relative error of (0.061mm) is only 1.64%, which verifies the accuracy of the air gap compensation model (Formula 2).

[0063] In addition, the offset in another specific embodiment Zemax is used for simulation, and the offset obtained by simulation is The offset is 0.0190 mm, calculated using the above formula 2 The relative error between the two is only 0.529%, which further verifies the accuracy of the air gap compensation model (Formula 2).

[0064] In response to the requirements for optical axis stability and focusing accuracy during the focusing process in a laser communication receiving end system, the present invention provides a focusing system and method to achieve continuous adjustment of the focal plane position, thereby ensuring that the spatial light beam is stably and efficiently coupled into the single-mode optical fiber. The system is suitable for application scenarios where the free-space optical communication receiving end has high requirements for optical axis consistency and focusing accuracy.

[0065] It should be noted that, in addition to being used for focusing at the receiving end of a free-space laser communication system, the present invention can also be widely used in telescopes, microscopes, lidar systems, infrared imaging instruments, fiber-coupled light source devices, medical instruments or other precision optical measurement and detection equipment to achieve high-precision beam focusing.

[0066] The present invention adopts an adjustment method of a double wedge structure to avoid introducing obvious optical axis offset during the focusing process, thereby improving the stability and error tolerance of the system in complex environments. In addition, the present invention also proposes an air gap compensation mechanism to correct the initial optical axis eccentricity problem caused by the air gap in the double wedge structure installation, thereby further improving the system focusing accuracy and coupling stability. Compared with traditional focusing technologies, the present invention has the following advantages: high optical axis stability, using a double wedge structure for focusing, there is no need to move the camera during the focusing process, fundamentally reducing the optical axis offset, and effectively improving the optical axis stability and reliability of the focusing process; the air gap model compensates for the optical axis offset, by establishing a calculation compensation model for the optical axis offset caused by the air gap, by accurately calculating the initial optical axis offset caused by the air gap and correcting it, thereby further reducing the overall optical axis offset error of the system; it has strong error tolerance, can better cope with actuator errors and external interference in actual operating environments, and is suitable for complex free-space optical communication environments and precision optical scenes.

[0067] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0068] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A focusing method, characterized in that: include: Arranging a focusing system, the focusing system comprising a light source, a lens, a double optical wedge structure, and a camera arranged in sequence along a first direction, wherein the double optical wedge structure comprises a first optical wedge and a second optical wedge spaced apart along the first direction, the first optical wedge being movable relative to the second optical wedge to adjust an equivalent thickness of the double optical wedge structure; According to the focal length of the lens f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length ; According to the distance between the first optical wedge and the second optical wedge in the first direction △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane , based on the offset and theoretical focal length Determine the theoretical focus position and position the camera at the theoretical focus position; Using a light source to emit parallel light transmitted along a first direction to form a light spot on a target surface of a camera; The light source is rotated by a certain angle to displace the light spot on the camera target surface, and the actual distance between the lens and the camera is obtained according to the rotation angle and the light spot displacement. L , according to the actual distance L With theoretical focal length The error between the two is to move the first optical wedge to adjust the equivalent thickness of the double optical wedge structure so that the actual distance L With the theoretical focal length The error between them is equivalent to zero.

2. The focusing method according to claim 1, wherein: According to the focal length of the lens f , the initial equivalent thickness of the double wedge structure d 0 and the refractive index of the double wedge structure n Determine the theoretical focal length include: Determine the theoretical focal length according to formula 1 , the formula 1 is as follows: .

3. The focusing method according to claim 1, wherein: According to the distance between the first optical wedge and the second optical wedge in the first direction △d , the refractive index of the double wedge structure n and wedge angle α Determine the offset of the focus on the focal plane include: Determine the offset using Formula 2 , the formula 2 is as follows: ; in, represents the exit angle, .

4. The focusing method according to claim 1, wherein: The actual distance between the lens and the camera is obtained according to the rotation angle and the spot displacement L Including: Get the actual distance according to formula 3 L , the formula 3 is as follows: L=x / θ ,in, x is the light spot displacement, θ is the rotation angle.

5. The focusing method according to claim 4, wherein: Obtain the corresponding relationship between N different rotation angles and spot displacement, and obtain N actual distances according to the formula 3 L , the N actual distances L Take the average value as the final actual distance L .

6. The focusing method according to claim 1, wherein: According to the actual distance L With theoretical focal length The error between moving the first optical wedge includes: L With theoretical focal length The error between the two obtains the thickness of the double wedge structure to be adjusted , according to the thickness to be adjusted Determine the amount of movement of the first optical wedge , waiting for the movement The first optical wedge is moved by a movement amount.

7. The focusing method according to claim 6, wherein: Amount to be moved After moving the first optical wedge by a moving amount, the method further comprises: The light source is rotated to a position where parallel light is emitted along a first direction, and the first optical wedge is moved by fine-tuning the intensity of the light spot in the camera image. When the light intensity reaches a maximum value, the movement of the first optical wedge is stopped to achieve optimal focus.

8. The focusing method according to claim 6, wherein: According to the actual distance L With theoretical focal length The error between the two obtains the thickness of the double wedge structure to be adjusted include: Obtain the thickness to be adjusted according to Formula 4 , the formula 4 is as follows: ,in, n is the refractive index of the double wedge structure; According to the thickness to be adjusted Determine the amount of movement of the first optical wedge Including: Obtain the amount to be moved according to formula 5 , Formula 5 is as follows: ,in, α It is a wedge angle.

9. A focusing system, characterized in that: The focusing system is used to implement the focusing method according to any one of claims 1 to 8, and the focusing system includes: An angle measurement assembly and a light source, a lens, a double wedge structure, and a camera arranged in sequence along a first direction; The light source is used to emit parallel light, the angle measuring assembly is used to measure the angle of the light source, the lens is used to receive the parallel light and output a focused light beam, the double optical wedge structure includes a first optical wedge and a second optical wedge that are spaced apart and have parallel wedge surfaces, the wedge surface of the first optical wedge is directly opposite to the wedge surface of the second optical wedge, the first optical wedge is movable relative to the second optical wedge in a direction parallel to the wedge surface to adjust the equivalent thickness of the double optical wedge structure, and the camera is used to receive the focused light beam.

10. The focusing system according to claim 9, wherein: The angle measuring assembly includes a reflector and a Leica goniometer. The reflector is arranged on the light source. The Leica goniometer cooperates with the reflector to measure the angle of the light source.

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