Symmetrical afocal scanning optical system

Abstract

The invention relates to the technical field of optical scanning, and discloses an afocal optical system for scanning. Comprising an X-direction scanning galvanometer, a front lens group, a rear lens group and a Y-direction scanning galvanometer, the front lens group and the rear lens group are symmetrically arranged about a light convergence surface, the front lens group is located on the light emitting side of the X-direction scanning galvanometer, the rear lens group is located on the light emitting side of the front lens group, and the Y-direction scanning galvanometer is located on the light emitting side of the rear lens group; the front lens group comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged along the light propagation direction; the rear lens group comprises a sixth lens, a seventh lens, an eighth lens, a ninth lens and a tenth lens which are sequentially arranged along the light propagation direction; wherein the focal length value of the afocal optical system is very large, that is, the focal power approaches to 0, so that after incident circular collimated light passes through the X-direction scanning galvanometer, the front lens group, the rear lens group and the Y-direction scanning galvanometer, the emergent light is still circular collimated light.

Description

Technical Field

[0001] This application relates to the field of optical scanning system technology, and more particularly to a focalless optical system for scanning. Background Technology

[0002] In laser scanning systems, existing scanning direction control structures typically arrange the mirrors controlling X-direction deflection and the mirrors controlling Y-direction deflection in a close arrangement. This is because when the beam aperture is large or the rotation angle is large, a larger mirror is needed to ensure the complete beam spot falls on the second mirror (in the Y direction), or the distance between the two mirrors needs to be reduced, which may not meet the requirements in some applications. Summary of the Invention

[0003] This application provides a symmetrical afocalless scanning optical system, aiming to solve the design problem of the relay optical system between the reflector controlling the X-direction deflection and the reflector controlling the Y-direction deflection in existing laser scanning systems under the conditions of large-angle scanning or large-aperture beam use. The embodiment of this application provides an afocalless optical system for scanning, including an X-direction scanning galvanometer, a front mirror group, a rear mirror group, and a Y-direction scanning galvanometer. The front mirror group and the rear mirror group are symmetrically arranged about the light converging plane. The front mirror group is located on the light-emitting side of the X-direction scanning galvanometer, the rear mirror group is located on the light-emitting side of the front mirror group, and the Y-direction scanning galvanometer is located on the light-emitting side of the rear mirror group. The front lens group includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the direction of light propagation. The rear lens group includes a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the direction of light propagation. The first lens in the front lens group and the tenth lens in the rear lens group are symmetrical about the light convergence plane. The second lens in the front lens group and the ninth lens in the rear lens group are symmetrical about the light convergence plane. The third lens in the front lens group and the eighth lens in the rear lens group are symmetrical about the light convergence plane. The fourth lens in the front lens group and the seventh lens in the rear lens group are symmetrical about the light convergence plane. The fifth lens in the front lens group and the sixth lens in the rear lens group are symmetrical about the light convergence plane. The difference between the optical power of the afocal optical system and 0 is within a preset range, so that after the incident circular collimated light passes through the X-direction scanning galvanometer, the front mirror group, the rear mirror group, and the Y-direction scanning galvanometer, the outgoing light is still circular collimated light.

[0004] This invention solves the problem in existing laser scanning systems where the installation distance between the reflector controlling X-direction deflection and the reflector controlling Y-direction deflection is usually very small by placing a focal-free optical system between two reflectors. This system satisfies the scanning angle requirements and increases the distance between the X and Y reflectors.

[0005] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0006] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0007] Figure 1 This is a schematic diagram of the structure of an afocalless optical system for scanning provided in an embodiment of this application; Figure 2 This is an optical path diagram of the scanning mirror deflection provided in an embodiment of this application; Figure 3 This is a schematic diagram of the front mirror assembly provided in one embodiment of this application; Figure 4 This is a schematic diagram of the rear mirror assembly provided in one embodiment of this application; Figure 5 This is a schematic diagram of an implementation example provided in this application; Figure 6 This is a system dot diagram provided in one embodiment of this application; Figure 7 This is an MTF curve diagram corresponding to the system provided in one embodiment of this application; Figure 8 This is a focal color difference diagram corresponding to the system provided in one embodiment of this application; Figure 9 This is an image of the emitted light spot when the galvanometer of the system provided in one embodiment of this application is deflected at different angles.

[0008] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0009] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0010] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0011] It should be understood that, in order to clearly describe the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0012] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0013] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0014] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0015] In laser scanning systems, current designs often involve closely arranging the mirrors controlling X-direction deflection and the mirrors controlling Y-direction deflection. This is because when the beam aperture is large or the rotation angle is large, a larger mirror is needed to ensure the complete beam spot falls on the second mirror (in the Y direction), or the distance between the two mirrors needs to be reduced. This may not meet the requirements in some applications.

[0016] Please refer to Figures 1-9This application provides a focal-free optical system for scanning, including an X-direction scanning galvanometer 1, a front mirror group 100, a rear mirror group 200, and a Y-direction scanning galvanometer 13. The front mirror group 100 and the rear mirror group 200 are symmetrically arranged about a light-converging surface 7. The front mirror group 100 is located on the light-emitting side of the X-direction scanning galvanometer 1, the rear mirror group 200 is located on the light-emitting side of the front mirror group 100, and the Y-direction scanning galvanometer 13 is located on the light-emitting side of the rear mirror group 200. The front mirror group 100 includes a first lens 2, a second lens 3, a third lens 4, a fourth lens 5, and a fifth lens 6 arranged sequentially along the light propagation direction. The rear mirror group 200 includes a sixth lens 8, a seventh lens 9, and an eighth lens 10 arranged sequentially along the light propagation direction. The system comprises a ninth lens 11 and a tenth lens 12. The first lens in the front lens group is symmetrical to the tenth lens in the rear lens group about the light convergence plane; the second lens in the front lens group is symmetrical to the ninth lens in the rear lens group about the light convergence plane; the third lens in the front lens group is symmetrical to the eighth lens in the rear lens group about the light convergence plane; the fourth lens in the front lens group is symmetrical to the seventh lens in the rear lens group about the light convergence plane; and the fifth lens in the front lens group is symmetrical to the sixth lens in the rear lens group about the light convergence plane. The difference between the optical power of the afocal optical system and 0 is within a preset range, ensuring that the incident circular collimated light, after passing through the X-direction scanning galvanometer, the front lens group, the rear lens group, and the Y-direction scanning galvanometer, still results in a circular collimated light output.

[0017] In some embodiments, the laser wavelength of the system is 1020nm-1050nm, the incident beam aperture is 15mm, the output beam aperture is also 15mm, and the beam deflection can be within the range of ±5°.

[0018] The initial structure of the front lens group, consisting of the first lens 2 to the fifth lens 6, can be optimized according to the structural parameters in the table below to obtain a front lens group that meets the requirements. By inverting the front lens group, the rear lens group structure (including the sixth lens 8 to the tenth lens 12) is obtained. The combination of the front lens group and the rear lens group constitutes the provided afocalless scanning system.

[0019] Specifically, the afocal optical system provided in this application aims to solve the problems of beam cross-section distortion, aberration correction difficulties and energy loss in traditional afocal systems. Through symmetrical lens group design and galvanometer position optimization, it achieves the maintenance of the outgoing beam shape and high-precision scanning of incident circular collimated light.

[0020] The scanning galvanometer includes an X-axis scanning galvanometer (controlling horizontal scanning) and a Y-axis scanning galvanometer (controlling vertical scanning). The symmetrical lens group is divided into a front lens group (5 lenses) and a rear lens group (5 lenses), mirror-symmetrically arranged about the "light convergence surface," achieving afocal characteristics through optical power balance. The component layout and optical path sequence (along the light propagation direction) are: X-axis scanning galvanometer (incident side) → front lens group lenses (lenses 1-5) → rear lens group lenses (lenses 6-10) → Y-axis scanning galvanometer (exit side). The front and rear lens groups form a mirror structure with the "light convergence surface" as the plane of symmetry (e.g., the first lens of the front lens group is symmetrical to the tenth lens of the rear lens group, the second to the ninth, and so on).

[0021] The optimization of galvanometer position and the guarantee of scanning accuracy are achieved through the following measures: The X galvanometer is located on the incident side of the front mirror group. It first deflects the incident collimated light in the horizontal direction. After passing through the front and rear mirror groups, it is deflected in the vertical direction by the Y galvanometer located on the exit side of the rear mirror group. After the beam is corrected by the symmetry system, the independence of the X and Y scanning directions is ensured, and mutual interference is reduced.

[0022] The optical system workflow includes: Incident stage: Circular collimated light is deflected by the X-direction galvanometer and enters the front lens group; Front lens group processing: Five lenses correct aberrations in the beam, ensuring the light passes through the focal plane. The rear lens group (symmetrical to the front lens group) compensates for the optical power of the front lens group, ensuring the total optical power is close to zero; Outgoing stage: After deflection by the Y-direction galvanometer, the outgoing light remains circularly collimated, completing high-precision scanning. The front lens group is designed to be image-side telecentric, meaning the principal ray is perpendicular to the focal plane, and it provides good correction for aberrations such as distortion and field curvature. The rear lens group is the inverted version of the front lens group, therefore the beam angle is... When the beam is incident at an angle, the angle of the emitted light after passing through the front and rear mirror groups remains the same. .

[0023] The system provided in this application offers at least the following advantages: Beam shape preservation: The symmetrical structure ensures consistent magnification in the X and Y directions, avoiding circular beam distortion and improving scanning accuracy; Efficient aberration correction: Balanced optical power and symmetrical lens group design effectively suppress aberrations such as coma and astigmatism, simplifying optical design; Optimized galvanometer configuration: The X / Y galvanometers are located on both sides of the symmetrical system, reducing additional aberrations introduced by scanning and improving system stability; Achievement of focusless characteristics: The total optical power is close to zero, ensuring that both incident and outgoing light are collimated, meeting the stringent requirements of laser scanning systems for beam collimation. Through the above-mentioned symmetrical focusless optical system design, the core defects of traditional focusless systems are effectively solved, providing a reliable optical architecture for high-precision laser scanning (such as 3D imaging and industrial processing).

[0024] In some embodiments, the optical power distributions of the first lens, second lens, third lens, fourth lens, and fifth lens in the front lens group are positive, positive, negative, negative, and positive, respectively.

[0025] The optical power distribution of the front lens group is designed in the order of "positive, positive, negative, negative, positive". The optical power balance within the front lens group is achieved through a specific combination of optical power symbols, which provides a basis for the symmetrical design of the rear lens group, ensures that the total optical power of the entire system is close to zero, and suppresses aberrations.

[0026] Optical power distribution rule: The optical power symbols of the 5 lenses in the front lens group are positive, positive, negative, negative, positive in sequence (that is, the 1st, 2nd, and 5th lenses have positive optical power, and the 3rd and 4th lenses have negative optical power).

[0027] Positive power lenses (element 1, 2, and 5) are used to converge light rays, while negative power lenses (element 3 and 4) are used to diverge light rays. The combination of "positive-positive-negative-negative-positive" creates a "converging-diverging-converging" optical path modulation, preventing excessive convergence or divergence of the beam caused by a single power level. The total optical power of the front lens group is the sum of the optical powers of each lens. The optical power distribution of the rear lens group is symmetrical to that of the front lens group (i.e., the optical power distribution of the rear lens group is positive, negative, negative, positive, positive, mirror image of the front lens group), ensuring that the total optical power cancels each other out, achieving a focusless characteristic.

[0028] In some embodiments, if the focal length of the front lens group is f1, the focal length of the first lens is f2, the focal length of the second lens is f3, the focal length of the third lens is f4, the focal length of the fourth lens is f5, and the focal length of the fifth lens is f6, where: 0.5 <f1 / f2<1.5;1<f1 / f3<2;-4<f1 / f4<-1;-0.5<f1 / f5<0;1<f1 / f6<3。

[0029] By limiting the ratio range between the overall focal length f1 of the front lens group and the focal lengths (f2 to f6) of each individual lens in the afocal system, and by reasonably allocating the optical power of each lens, the total optical power of the system is ensured to approach 0 after the front and rear lens groups are symmetrically matched, while aberrations are corrected to maintain the circular collimation characteristics of the outgoing light.

[0030] The focal length ratio of each lens needs to be optimized using optical design software (such as Zemax) to ensure that the light angles of the front and rear lens groups are at the plane of symmetry, avoiding aberrations such as astigmatism and field curvature, and ultimately ensuring that the incident circular collimated light remains circular collimated light after passing through the scanning galvanometer and lens group.

[0031] In some embodiments, the thickness of the first lens is d1, the thickness of the second lens is d2, the thickness of the third lens is d3, the thickness of the fourth lens is d4, and the thickness of the fifth lens is d5, wherein: 10 < f1 / d1 < 30; 5 < f1 / d2 < 25; 25 < f1 / d3 < 35; 5 < f1 / d4 < 25; 10 < f1 / d5 < 20.

[0032] In some embodiments, the air thickness between the first lens and the second lens in the front lens group is a first thickness; the air thickness between the second lens and the third lens in the front lens group is a second thickness; the air thickness between the third lens and the fourth lens in the front lens group is a third thickness; the air thickness between the fourth lens and the fifth lens in the front lens group is a fourth thickness; the air gap between the fifth lens and the light converging surface is a fifth thickness; the first thickness is d12, the second thickness is d23, the third thickness is d34, the fourth thickness is d45, and the fifth thickness is d56; wherein: 5 < d1 / d12 < 15; 0.1 < d2 / d23 < 1; 0.01 < d3 / d34 < 0.5; 5 < d4 / d45 < 15; 0.05 < d5 / d56 < 0.5.

[0033] In some embodiments, the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens, and tenth lens are made of optical materials. The selection of optical materials is based on the system wavelength or spectral width. The chromatic aberration of the system is corrected by matching the Abbe number and refractive index of the materials. The materials used in the laser system have high transmittance to reduce light energy loss.

[0034] In some embodiments, the drive control of the X-direction scanning galvanometer and the Y-direction scanning galvanometer is achieved by acquiring a preset scanning trajectory, calculating the real-time deflection angle of the X-direction scanning galvanometer and the Y-direction scanning galvanometer based on the optical parameters of the afocal optical system, and controlling the X-direction scanning galvanometer and the Y-direction scanning galvanometer to deflect according to the real-time deflection angle through a closed-loop control algorithm, so that the scanning trajectory of the emitted light meets the preset requirements.

[0035] In some embodiments, the coaxiality calibration of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth lenses during assembly involves positioning the lenses of the front and rear lens groups using a reference optical axis, measuring the optical axis offset of each lens using optical inspection equipment, and adjusting the position and angle of the lenses according to the optical axis offset, so that the offset of the optical axes of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth lenses from the reference optical axis meets the system performance tolerance requirements.

[0036] This invention employs a symmetrical arrangement of the front and rear mirror groups about the light convergence plane, with corresponding lenses symmetrically distributed. This allows for precise balance of the optical system's power, ensuring that the incident circularly collimated light maintains its circular collimation after scanning, preventing beam cross-section distortion and improving scanning accuracy and beam quality. The symmetrical structure facilitates aberration correction. By optimizing lens parameters and combining appropriate optical materials, it corrects aberrations across a wide spectrum at large scanning angles, ensuring the performance of subsequent optical systems. It can further optimize system aberrations, reduce reliance on complex aspherical or special materials, and lower processing and debugging costs. The symmetrical layout facilitates modular design and assembly of the optical system, improves mechanical stability, and is suitable for scanning equipment with high requirements for size and reliability (such as LiDAR and 3D scanners).

[0037] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A focalless optical system for scanning, characterized in that, It includes an X-direction scanning galvanometer, a front mirror group, a rear mirror group, and a Y-direction scanning galvanometer. The front mirror group and the rear mirror group are symmetrically arranged about the light converging surface. The front mirror group is located on the light-emitting side of the X-direction scanning galvanometer, the rear mirror group is located on the light-emitting side of the front mirror group, and the Y-direction scanning galvanometer is located on the light-emitting side of the rear mirror group. The front lens group includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the direction of light propagation. The rear lens group includes a sixth lens, a seventh lens, an eighth lens, a ninth lens, and a tenth lens arranged sequentially along the direction of light propagation. The first lens in the front lens group and the tenth lens in the rear lens group are symmetrical about the light convergence plane. The second lens in the front lens group and the ninth lens in the rear lens group are symmetrical about the light convergence plane. The third lens in the front lens group and the eighth lens in the rear lens group are symmetrical about the light convergence plane. The fourth lens in the front lens group and the seventh lens in the rear lens group are symmetrical about the light convergence plane. The fifth lens in the front lens group and the sixth lens in the rear lens group are symmetrical about the light convergence plane. The difference between the optical power of the afocal optical system and 0 is within a preset range, so that after the incident circular collimated light passes through the X-direction scanning galvanometer, the front mirror group, the rear mirror group, and the Y-direction scanning galvanometer, the outgoing light is still circular collimated light.

2. The system according to claim 1, characterized in that, The optical power distributions of the first lens, second lens, third lens, fourth lens, and fifth lens in the front lens group are positive, positive, negative, negative, and positive, respectively.

3. The system according to claim 2, characterized in that, If the focal length of the front lens group is f1, the focal length of the first lens is f2, the focal length of the second lens is f3, the focal length of the third lens is f4, the focal length of the fourth lens is f5, and the focal length of the fifth lens is f6, then: 0.5 <f1 / f2<1.5; 1 <f1 / f3<2; -4 <f1 / f4<-1; -0.5 <f1 / f5<0; 1 <f1 / f6<3。 4. The system according to claim 3, characterized in that, The thickness of the first lens is d1, the thickness of the second lens is d2, the thickness of the third lens is d3, the thickness of the fourth lens is d4, and the thickness of the fifth lens is d5, wherein: 10 < f1 / d1 < 30; 5 < f1 / d2 < 25; 25 < f1 / d3 < 35; 5 < f1 / d4 < 25; 10 < f1 / d5 < 20.

5. The system according to claim 4, characterized in that, The air thickness between the first and second lenses in the front lens group is the first thickness; the air thickness between the second and third lenses in the front lens group is the second thickness; the air thickness between the third and fourth lenses in the front lens group is the third thickness; the air thickness between the fourth and fifth lenses in the front lens group is the fourth thickness; the air gap between the fifth lens and the light converging surface is the fifth thickness; the first thickness is d12, the second thickness is d23, the third thickness is d34, the fourth thickness is d45, and the fifth thickness is d56; wherein: 5 < d1 / d12 < 15; 0.1 < d2 / d23 < 1; 0.01 < d3 / d34 < 0.5; 5 < d4 / d45 < 15; 0.05 < d5 / d56 < 0.

5.

6. The system according to claim 1, characterized in that, The first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens and tenth lens are made of optical materials. The selection of optical materials is based on the system wavelength or spectral width, and the chromatic aberration of the system is corrected by matching the Abbe number and refractive index of the materials.

7. The system according to claim 1, characterized in that, The drive control of the X-direction scanning galvanometer and the Y-direction scanning galvanometer is achieved by acquiring a preset scanning trajectory, calculating the real-time deflection angle of the X-direction scanning galvanometer and the Y-direction scanning galvanometer based on the optical parameters of the afocal optical system, and controlling the X-direction scanning galvanometer and the Y-direction scanning galvanometer to deflect according to the real-time deflection angle through a closed-loop control algorithm, so that the scanning trajectory of the emitted light meets the preset requirements.

8. The system according to claim 1, characterized in that, The coaxiality calibration of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth lenses during assembly involves positioning the lenses of the front and rear lens groups using a reference optical axis, measuring the optical axis offset of each lens using optical testing equipment, and adjusting the position and angle of the lenses according to the optical axis offset to ensure that the offset of the optical axes of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth lenses from the reference optical axis meets the system performance tolerance requirements.

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