A Compact Afocal System Based on a Multi-Faceted Optical Element

Abstract

The present invention relates to a compact afocal system based on a multi-faceted coaxial optical element, comprising: a first optical path module and a second optical path module; the first optical path module and the second optical path module are arranged coaxially in sequence along the object side to the image side direction; the first optical path module and the second optical path module are respectively total reflection optical transmission modules, and the first optical path module and the second optical path module are arranged with coincident foci; the first optical path module has a first entrance pupil and a first exit pupil; the second optical path module has a second entrance pupil and a second exit pupil; the first optical path module receives external light through the first entrance pupil and outputs it through the first exit pupil; the second optical path module receives the light output from the first exit pupil through the second entrance pupil and outputs it in the form of parallel light through the second exit pupil.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a compact afocal system based on a multi-faceted coaxial optical element. Background Art

[0002] An afocal system is also known as a telecentric system or an afocal system. Generally, it is considered that an afocal system has no net focusing or net divergence of light beams. At present, afocal systems are widely used in telescopic optical systems, laser optical systems, space remote sensing and other fields. With the continuous development of science and technology, they are gradually developing towards high performance, small volume, low cost, and short production cycle.

[0003] Existing design methods for afocal systems are mostly traditional transmissive or catadioptric. Traditional transmissive optical systems are realized by dispersive optical elements, and the systems have the disadvantages of large volume, difficult chromatic aberration correction, and long production cycle; traditional catadioptric optical systems are based on the Cassegrain system, which has the advantages of high imaging quality and no chromatic aberration, but there are problems such as long focal length and large aperture, making it difficult to achieve a small volume. In addition, for afocal systems composed of different combinations of optical materials, due to the temperature performance differences of various optical materials, temperature changes will cause changes in the sizes of optical elements, which will further affect the imaging quality. Therefore, the athermal design of the system also has a great impact on the imaging quality.

[0004] Chinese Patent CN111367067B discloses a totally reflective afocal optical system. This system is designed based on the reflective optical system design method and uses four reflective elements to form an off-axis optical system. However, it uses an off-axis design method to form an off-axis four-reflection optical system, but this off-axis four-reflection optical system makes the alignment tolerance of each optical element more stringent, increasing the alignment difficulty and complexity. Summary of the Invention

[0005] The purpose of the present invention is to provide a compact afocal system based on a multi-faceted coaxial optical element.

[0006] To achieve the above-mentioned invention purpose, the present invention provides a compact afocal system based on a multi-faceted coaxial optical element, including: a first optical path module and a second optical path module;

[0007] Along the object side to the image side direction, the first optical path module and the second optical path module are coaxially arranged in sequence;

[0008] The first optical path module and the second optical path module are respectively total reflection optical transmission modules, and the first optical path module and the second optical path module are arranged with coincident foci;

[0009] The first optical path module has a first entrance pupil and a first exit pupil;

[0010] The second optical path module has a second entrance pupil and a second exit pupil;

[0011] The first optical path module receives external light through the first entrance pupil and outputs it through the first exit pupil;

[0012] The second optical path module receives the light output from the first exit pupil through the second entrance pupil and outputs it in the form of parallel light through the second exit pupil.

[0013] According to one aspect of the present invention, the first optical path module includes: a first reflecting element and a second reflecting element;

[0014] Along the object side to the image side direction, the first reflecting element and the second reflecting element are coaxial and arranged with a gap;

[0015] The first entrance pupil is arranged on the first reflecting element, and the first exit pupil is arranged on the second reflecting element;

[0016] One side of the second reflecting element adjacent to the first reflecting element is a first front reflecting surface for receiving the light passing through the first entrance pupil;

[0017] One side of the first reflecting element adjacent to the second reflecting element is a first rear reflecting surface for receiving the light reflected by the first front reflecting surface and making the light exit from the first exit pupil;

[0018] The first front reflecting surface includes a plurality of coaxial first annular front reflecting surfaces;

[0019] The first rear reflecting surface includes a plurality of coaxial first annular rear reflecting surfaces.

[0020] According to one aspect of the present invention, the second optical path module includes: a third reflecting element and a fourth reflecting element;

[0021] Along the object side to the image side direction, the third reflecting element and the fourth reflecting element are coaxial and arranged with a gap;

[0022] The second entrance pupil is arranged on the third reflecting element, and the second exit pupil is arranged on the fourth reflecting element;

[0023] One side of the fourth reflecting element adjacent to the third reflecting element is a second front reflecting surface for receiving the light passing through the second entrance pupil;

[0024] One side of the third reflecting element adjacent to the fourth reflecting element is a second rear reflecting surface for receiving the light reflected by the second front reflecting surface and making the light exit from the second exit pupil;

[0025] The second front reflecting surface includes a plurality of coaxial second annular front reflecting surfaces;

[0026] The second rear reflecting surface includes a plurality of coaxial second annular rear reflecting surfaces.

[0027] According to one aspect of the present invention, the number of the first annular front reflecting surfaces and the first annular rear reflecting surfaces is the same, and respectively satisfies: 2 ≤ X ≤ 9; wherein, X represents the number of the first annular front reflecting surfaces and the first annular rear reflecting surfaces;

[0028] The number of the second annular front reflecting surfaces and the second annular rear reflecting surfaces is the same, and respectively satisfies: 2 ≤ Y ≤ 9; wherein, Y represents the number of the second annular front reflecting surfaces and the second annular rear reflecting surfaces.

[0029] According to one aspect of the present invention, the first annular front reflecting surface and the first annular rear reflecting surface are a plane, a quadratic surface or an aspheric surface;

[0030] The second annular front reflecting surface and the second annular rear reflecting surface are a plane, a quadratic surface or an aspheric surface.

[0031] According to one aspect of the present invention, the first annular front reflecting surface and the first annular rear reflecting surface adopt a high-order aspheric reflecting surface, and are respectively provided with a high-reflectivity film layer;

[0032] The second annular front reflecting surface and the second annular rear reflecting surface adopt a high-order aspheric reflecting surface, and are respectively provided with a high-reflectivity film layer;

[0033] The reflectivity of the high-reflectivity film layer is greater than 98%.

[0034] According to one aspect of the present invention, the first reflecting element, the second reflecting element, the third reflecting element and the fourth reflecting element are made of the same material.

[0035] According to one aspect of the present invention, the first entrance pupil and the second exit pupil are respectively arc-shaped through holes, wherein, along the circumferential direction of the first reflecting element, a plurality of the first entrance pupils are arranged at intervals, and along the circumferential direction of the fourth reflecting element, a plurality of the second exit pupils are arranged at intervals;

[0036] The first exit pupil and the second entrance pupil are respectively circular through holes, wherein, the first exit pupil is located at the middle position of the second reflecting element, and the second entrance pupil is located at the middle position of the third reflecting element.

[0037] According to one aspect of the present invention, the second reflecting element and the third reflecting element are independent of each other, or, the second reflecting element and the third reflecting element are integral.

[0038] According to one aspect of the present invention, the field of view angle of the compact afocal system is greater than or equal to 10°.

[0039] The working wavelength band of the compact afocal system includes visible light band, near-infrared band, mid-infrared band and far-infrared band.

[0040] According to one solution of the present invention, a compact afocal system based on multi-faceted coaxial optical elements of the present invention realizes many advantages such as high performance, small volume, low cost, athermalization, and short production cycle.

[0041] According to one solution of the present invention, a compact afocal system based on multi-faceted coaxial optical elements of the present invention uses a first reflecting element, a second reflecting element, a third reflecting element and a fourth reflecting element to reflect light. After multiple folding reflections on the annular reflecting surfaces of each multi-faceted coaxial optical element, the light exits in the form of parallel light. That is, the afocal system of the present invention is a total reflection system, without chromatic aberration, and is suitable for the use requirements of each wavelength band.

[0042] According to one solution of the present invention, a compact afocal system based on multi-faceted coaxial optical elements of the present invention, multiple coaxial annular reflecting surfaces of the first front reflecting surface are all processed on the second reflecting element, multiple coaxial annular reflecting surfaces of the first rear reflecting surface are all processed on the first reflecting element, multiple coaxial annular reflecting surfaces of the second front reflecting surface are all processed on the fourth reflecting element, and multiple coaxial annular reflecting surfaces of the second rear reflecting surface are all processed on the third reflecting element. The design method based on multi-faceted coaxial optical elements makes the structure of the afocal system more compact, reduces the difficulty of processing and alignment. And because the coaxial annular reflecting surfaces of the multi-faceted coaxial optical elements are all located on the substrate of the same material, the reflectivity and thermal properties are consistent. Therefore, the optical performance of a compact afocal system based on multi-faceted coaxial optical elements can be maximized. In addition, some adjacent reflecting elements can be optionally set as an integral body, which can further effectively reduce the number of reflecting elements, making the structure more compact and the volume smaller.

[0043] According to one solution of the present invention, a compact afocal system based on multi-faceted coaxial optical elements of the present invention can optimize the angles and spherical parameters of the coaxial annular reflecting surfaces of each multi-faceted coaxial optical element through a computer, so that the field of view angle is greater than or equal to 10°, and the imaging quality under each field of view is close to the diffraction limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic structural diagram of a compact afocal system showing an embodiment according to the present invention;

[0045] Figure 2Schematically shows the transfer function curve of the compact afocal system according to Embodiment 1 of the present invention;

[0046] Figure 3 Schematically shows the field curvature and distortion curves of the compact afocal system according to Embodiment 1 of the present invention. Detailed implementation manners

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0048] When describing the embodiments of the present invention, the orientation or positional relationships expressed by the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" are based on the orientation or positional relationships shown in the relevant drawings. It is 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. Therefore, the above terms should not be construed as limiting the present invention.

[0049] The present invention will be described in detail below with reference to the drawings and specific implementation manners. The implementation manners cannot be elaborated one by one here, but the implementation manners of the present invention are not limited to the following implementation manners.

[0050] As Figure 1 shown, according to an embodiment of the present invention, a compact afocal system based on a multi-faceted coaxial optical element of the present invention includes: a first optical path module 1 and a second optical path module 2. In this embodiment, along the object side to the image side direction, the first optical path module 1 and the second optical path module 2 are coaxially arranged in sequence; wherein, the first optical path module 1 and the second optical path module 2 are respectively total reflection optical transmission modules, and the first optical path module 1 and the second optical path module 2 are arranged with coincident foci. In this embodiment, the first optical path module 1 has a first entrance pupil 1a and a first exit pupil 1b; the second optical path module 2 has a second entrance pupil 2a and a second exit pupil 2b. In this embodiment, the first optical path module 1 receives external light through the first entrance pupil 1a and outputs it through the first exit pupil 1b; the second optical path module 2 receives the light output from the first exit pupil 1b through the second entrance pupil 2a and outputs it in the form of parallel light through the second exit pupil 2b.

[0051] Through the above settings, the compact structure of the present invention is effectively ensured, and the installation difficulty between the optical elements is reduced. Without alignment, the position accuracy between the reflecting surfaces can be ensured, effectively improving the production efficiency of the present invention.

[0052] As Figure 1 shown, according to an embodiment of the present invention, the first optical path module 1 includes: a first reflecting element 11 and a second reflecting element 12. In this embodiment, along the object side to the image side direction, the first reflecting element 11 and the second reflecting element 12 are coaxial and arranged at intervals. Among them, the first entrance pupil 1a is provided on the first reflecting element 11, and the first exit pupil 1b is provided on the second reflecting element 12; the side of the second reflecting element 12 adjacent to the first reflecting element 11 is the first front reflecting surface 121, which is used to receive the light passing through the first entrance pupil 1a. In this embodiment, the side of the first reflecting element 11 adjacent to the second reflecting element 12 is the first rear reflecting surface 111, which is used to receive the light reflected by the first front reflecting surface 121 and make the light exit from the first exit pupil 1b.

[0053] As Figure 1 shown, according to an embodiment of the present invention, the first front reflecting surface 121 includes a plurality of coaxial first annular front reflecting surfaces 121a; the first rear reflecting surface 111 includes a plurality of coaxial first annular rear reflecting surfaces 111a. When there are multiple first annular front reflecting surfaces 121a and first annular rear reflecting surfaces 111a respectively, multiple reflections of external light can be realized, so as to realize multiple compressions of the optical path and then realize the output of line light. For example, the first front reflecting surface 121 includes X first annular front reflecting surfaces 121a, and the first rear reflecting surface 111 includes X coaxial first annular rear reflecting surfaces 111a. Among them, the external light directly irradiates on the first first annular front reflecting surface 121a through the first entrance pupil 1a. Under the reflection of the first first annular front reflecting surface 121a, the light can be reflected on the first first annular rear reflecting surface 111a. Under the reflection of the first first annular rear reflecting surface 111a, the light can be reflected on the second first annular front reflecting surface 121a. Under the reflection of the second first annular front reflecting surface 121a, the light can be reflected on the second first annular rear reflecting surface 111a, and so on. Under the reflection of the Xth first annular front reflecting surface 121a, the light can be reflected on the Xth first annular rear reflecting surface 111a, and under the reflection of the Xth first annular rear reflecting surface 111a, the light can exit through the first exit pupil 1b.

[0054] In this embodiment, the edges of adjacent first annular front reflection surfaces 121a are connected to each other by using a transition surface to suppress stray light, and the relative position accuracy of adjacent first annular front reflection surfaces 121a is within 1 μm. The edges of adjacent first annular rear reflection surfaces 111a are connected to each other by using a transition surface to suppress stray light, and the relative position accuracy of adjacent first annular rear reflection surfaces 111a is within 1 μm. Through the above settings, the light reflection efficiency and accuracy of the present invention are effectively ensured.

[0055] As Figure 1 shown, according to an embodiment of the present invention, the second optical path module 2 includes: a third reflection element 21 and a fourth reflection element 22. In this embodiment, along the object side to the image side direction, the third reflection element 21 and the fourth reflection element 22 are coaxially arranged with a gap; wherein, the second entrance pupil 2a is provided on the third reflection element 21, and the second exit pupil 2b is provided on the fourth reflection element 22. In this embodiment, the side of the fourth reflection element 22 adjacent to the third reflection element 21 is the second front reflection surface 221, which is used to receive the light passing through the second entrance pupil 2a; the side of the third reflection element 21 adjacent to the fourth reflection element 22 is the second rear reflection surface 211, which is used to receive the light reflected by the second front reflection surface 221 and make the light exit from the second exit pupil 2b. In this embodiment, the second front reflection surface 221 includes a plurality of coaxial second annular front reflection surfaces 221a; the second rear reflection surface 211 includes a plurality of coaxial second annular rear reflection surfaces 211a. When a plurality of second annular front reflection surfaces 221a and second annular rear reflection surfaces 211a are respectively provided, multiple reflections of the light output by the first optical path module 1 can be realized, so as to realize the output of line light after multiple compressions of the optical path. For example, the second front reflection surface 221 includes Y second annular front reflection surfaces 221a, and the second rear reflection surface 211 includes Y coaxial second annular rear reflection surfaces 211a. Among them, the light emitted through the first exit pupil 1b directly irradiates on the first second annular front reflection surface 221a through the second entrance pupil 2a. Under the reflection of the first second annular front reflection surface 221a, the light can be reflected on the first second annular rear reflection surface 211a. Under the reflection of the first second annular rear reflection surface 211a, the light can be reflected on the second second annular front reflection surface 221a. Under the reflection of the second second annular front reflection surface 221a, the light can be reflected on the second second annular rear reflection surface 211a, and so on. Under the reflection of the Yth second annular front reflection surface 221a, the light can be reflected on the Yth second annular rear reflection surface 211a, and under the reflection of the Yth second annular rear reflection surface 211a, the light can be emitted parallel through the second exit pupil 2b.

[0056] In this embodiment, the edges of adjacent second annular front reflecting surfaces 221a are connected to each other by using transition surfaces to suppress stray light, and the relative position accuracy of adjacent first annular front reflecting surfaces 121a is within 1 μm. The edges of adjacent second annular rear reflecting surfaces 211a are connected to each other by using transition surfaces to suppress stray light, and the relative position accuracy of adjacent first annular rear reflecting surfaces 111a is within 1 μm. Through the above settings, the light reflection efficiency and accuracy of the present invention are effectively ensured.

[0057] Through the above settings, the compact afocal system of the present invention is a total reflection system without chromatic aberration. Based on the optical elements with multiple annular reflecting surfaces coaxially and co - body on the same reflecting surface, the structure of the present invention is more compact, reducing the difficulty of processing and alignment. And since the coaxial annular reflecting surfaces of the multi - toroidal co - body optical elements are all located on the same substrate with consistent reflectivity and thermal properties, therefore, the optical performance of a compact afocal system based on multi - toroidal co - body optical elements can be maximally improved.

[0058] As Figure 1 shown, according to an embodiment of the present invention, the number of the first annular front reflecting surfaces 121a and the first annular rear reflecting surfaces 111a is the same, and they respectively satisfy: 2 ≤ X ≤ 9; where X represents the number of the first annular front reflecting surfaces 121a and the first annular rear reflecting surfaces 111a. In this embodiment, the number of the first annular front reflecting surfaces 121a and the first annular rear reflecting surfaces 111a is respectively set to 2. Of course, they can also be respectively set to 3, 4, 5, etc. according to needs.

[0059] In this embodiment, the number of the second annular front reflecting surfaces 221a and the second annular rear reflecting surfaces 211a is the same, and they respectively satisfy: 2 ≤ Y ≤ 9; where Y represents the number of the second annular front reflecting surfaces 221a and the second annular rear reflecting surfaces 211a; in this embodiment, the number of the second annular front reflecting surfaces 221a and the second annular rear reflecting surfaces 211a is respectively set to 2. Of course, they can also be respectively set to 3, 4, 5, etc. according to needs.

[0060] As Figure 1 shown, according to an embodiment of the present invention, the first annular front reflecting surfaces 121a and the first annular rear reflecting surfaces 111a are planes, quadratic surfaces or aspherical surfaces; the second annular front reflecting surfaces 221a and the second annular rear reflecting surfaces 211a are planes, quadratic surfaces or aspherical surfaces.

[0061] With the above settings, the surface profiles of the respective annular reflecting surfaces (i.e., the first annular front reflecting surface 121a, the first annular rear reflecting surface 111a, the second annular front reflecting surface 221a, and the second annular rear reflecting surface 211a) can be selectively set as needed, so as to optimize their light reflection efficiency and coma aberration correction ability.

[0062] As Figure 1 shown, according to an embodiment of the present invention, the first annular front reflecting surface 121a and the first annular rear reflecting surface 111a adopt high-order aspherical reflecting surfaces, and are respectively provided with high-reflectivity film layers; in this embodiment, the high-reflectivity film layers are completely covered on the first annular front reflecting surface 121a and the first annular rear reflecting surface 111a. In this embodiment, the transition surfaces for connecting adjacent first annular front reflecting surfaces 121a and connecting adjacent first annular rear reflecting surfaces 111a are annular planes, and anti-glare paint is sprayed on the transition surfaces to further suppress stray light. In this embodiment, the second annular front reflecting surface 221a and the second annular rear reflecting surface 211a adopt high-order aspherical reflecting surfaces, and are respectively provided with high-reflectivity film layers. In this embodiment, the high-reflectivity film layers are completely covered on the second annular front reflecting surface 221a and the second annular rear reflecting surface 211a. In this embodiment, the transition surfaces for connecting adjacent second annular front reflecting surfaces 221a and connecting adjacent second annular rear reflecting surfaces 211a are annular planes, and anti-glare paint is sprayed on the transition surfaces to further suppress stray light. In this embodiment, the reflectivity of the high-reflectivity film layer is greater than 98%. In this embodiment, the high-reflectivity film layer can adopt a silver film.

[0063] With the above settings, by setting the surface profiles of the respective annular reflecting surfaces (i.e., the first annular front reflecting surface 121a, the first annular rear reflecting surface 111a, the second annular front reflecting surface 221a, and the second annular rear reflecting surface 211a) to high-order aspherical surfaces, the multiple degrees of freedom of the high-order aspherical surfaces can be further effectively utilized, so that each reflecting element has the advantages of strong aberration correction ability and light weight.

[0064] In addition, by providing high-reflectivity coatings on the respective annular reflecting surfaces (i.e., the first annular front reflecting surface 121a, the first annular rear reflecting surface 111a, the second annular front reflecting surface 221a, and the second annular rear reflecting surface 211a), the reflection efficiency of the present invention can be more effectively improved, and its light transmission ability is further improved.

[0065] As Figure 1As shown, according to an embodiment of the present invention, the first reflecting element 11, the second reflecting element 12, the third reflecting element 21, and the fourth reflecting element 22 are made of the same material. In this embodiment, the first reflecting element 11, the second reflecting element 12, the third reflecting element 21, and the fourth reflecting element 22 can be made of aerospace aluminum alloy material Al6061, aluminum matrix silicon carbide, etc.

[0066] By preparing each reflecting element with the same material, it can effectively ensure that each reflecting element has the same physical properties in the same environment, and then can more effectively ensure the efficiency and ability of light transmission, especially providing a reliable and effective guarantee for ensuring the final output of parallel light by the second optical path module 2. In addition, preparing each reflecting element with the same material is also convenient for rapid manufacturing.

[0067] Through the above settings, the materials used for each reflecting element also have the advantages of good thermal stability and strong environmental adaptability.

[0068] As Figure 1 shown, according to an embodiment of the present invention, the first entrance pupil 1a and the second exit pupil 2b are respectively arc-shaped through holes. Among them, along the circumferential direction of the first reflecting element 11, a plurality of (for example, 2, 3, 4, etc.) first entrance pupils 1a are arranged at intervals. Along the circumferential direction of the fourth reflecting element 22, a plurality of (for example, 2, 3, 4, etc.) second exit pupils 2b are arranged at intervals. In this embodiment, the first entrance pupil 1a is arranged close to the edge of the first reflecting element 11, and they are arranged at equal intervals from each other. Among them, in the radial direction of the first reflecting element 11, the inner diameter of the first entrance pupil 1a is greater than the diameter of the first annular rear reflecting surface 111a (S03). In this embodiment, the second exit pupil 2b is arranged close to the edge of the fourth reflecting element 22, and they are arranged at equal intervals from each other. Among them, in the radial direction of the fourth reflecting element 22, the inner diameter of the second exit pupil 2b is greater than the diameter of the second annular front reflecting surface 221a (S06).

[0069] In this embodiment, the first exit pupil 1b and the second entrance pupil 2a are respectively circular through holes. Among them, the first exit pupil 1b is located at the middle position of the second reflecting element 12, and the second entrance pupil 2a is located at the middle position of the third reflecting element 21.

[0070] As Figure 1As shown, according to an embodiment of the present invention, the second reflecting element 12 and the third reflecting element 21 are independent of each other. Through the above arrangement, the positions between the first optical path module 1 and the second optical path module 2 can be flexibly set, making the structural arrangement more convenient. In another embodiment, the second reflecting element 12 and the third reflecting element 21 are integrated, so that the second reflecting element 12 and the third reflecting element 21 form one element, with a front reflecting surface 121 and a second rear reflecting surface 211 distributed on the same element, further making the structure of the present invention more compact and beneficial to the miniaturization of the present invention.

[0071] As Figure 1 shown, according to an embodiment of the present invention, the field of view angle of the compact afocal system of the present invention is greater than or equal to 10°.

[0072] As Figure 1 shown, according to an embodiment of the present invention, the working wavelength band of the compact afocal system of the present invention includes the visible light band, the near-infrared band, the mid-infrared band, and the far-infrared band.

[0073] Through the above arrangement, the compact afocal system of the present invention has a wide application range and can be scaled proportionally to meet the needs of different optical systems.

[0074] As Figure 1 shown, according to an embodiment of the present invention, the absolute value calculation formula of the beam compression ratio or visual magnification or angular magnification of the compact afocal system of the present invention is:

[0075]

[0076] where M is the beam compression ratio or visual magnification or angular magnification of the compact afocal system of the present invention, f1 is the focal length of the first optical path module 1, and f2 is the focal length of the second optical path module 2.

[0077] To further illustrate the present invention, an example of the present invention is given.

[0078] Example 1

[0079] The imaging quality of the compact afocal system of the present invention based on the multi-faceted coaxial optical element is close to the diffraction limit. The following system technical indicators are selected for example verification:

[0080] Among them, the focal length of the first optical path module 1 is 63.85 mm, the focal length of the second optical path module 2 is 30 mm, the visual magnification is 0.47, and the working wavelength is 450 - 750 nm.

[0081] In this embodiment, the first front reflecting surface 121 includes two coaxial first annular front reflecting surfaces 121a. For convenience of description, the first of the two first annular front reflecting surfaces 121a is denoted as S01, and the second is denoted as S02. Among them, the second first annular front reflecting surface 121a (S02) is located inside the first first annular front reflecting surface 121a (S01).

[0082] The first rear reflecting surface 111 includes two coaxial first annular rear reflecting surfaces 111a. For convenience of description, the first of the two first annular rear reflecting surfaces 111a is denoted as S03, and the second is denoted as S04. Among them, the second first annular rear reflecting surface 111a (S04) is located inside the first first annular rear reflecting surface 111a (S03).

[0083] The second front reflecting surface 221 includes two coaxial second annular front reflecting surfaces 221a. For convenience of description, the first of the two second annular front reflecting surfaces 221a is denoted as S05, and the second is denoted as S06. Among them, the second second annular front reflecting surface 221a (S06) is located outside the first second annular front reflecting surface 221a (S05).

[0084] The second rear reflecting surface 211 includes two coaxial second annular rear reflecting surfaces 211a. For convenience of description, the first of the two second annular rear reflecting surfaces 211a is denoted as S07, and the second is denoted as S08. Among them, the second second annular rear reflecting surface 211a (S08) is located outside the first second annular rear reflecting surface 211a (S07).

[0085] Based on the above system technical indicators and combined with computer software optimization design, the annular reflecting surfaces of each reflecting element in the compact afocal system of the multi-faceted coaxial optical element of the present invention are designed, and the optimized parameters of each annular reflecting surface in Table 1 are obtained.

[0086] Face Number Face Type Radius of Curvature / mm Spacing / mm Diameter / mm Quadratic Surface Coefficient S01 Asphere -59.178893 -9.512918 62 0.177132 S03 Asphere -272.354769 11.512493 49.5 -4.066977 S02 Asphere -225.377067 -11.935698 49.5 -6.688110 S04 Asphere -66.002279 24.082335 29 -3.513439 S08 Asphere -26.106191 -4.85 26 -3.271509 S06 Asphere -298.700349 4.700688 20.6 91.868744 S07 Asphere -796.362795 -4.895 19.6 -336.061652 S05 Asphere -27.197604 9.756 11 -18.506535

[0087] Table 1

[0088] In this embodiment, the first annular front reflecting surfaces 121a (S01, S02), the first annular rear reflecting surfaces 111a (S03, S04), the second annular front reflecting surfaces 221a (S05, S06), and the second annular rear reflecting surfaces 211a (S07, S08) all adopt high-order aspherical surfaces, and the aspherical surfaces are obtained according to the following formula:

[0089]

[0090] Among them, c is the basic curvature at the vertex; k is the conic constant; r is the radial coordinate in the direction perpendicular to the optical axis; A2, A4, A6, A8, A 10 , A 12 , A 14 and A 16 are aspheric coefficients.

[0091] Furthermore, through computer software optimization design, the aspheric coefficients of each annular reflecting surface when applied to visible light are optimized, and the optimized parameters in Table 2 are obtained.

[0092]

[0093]

[0094] Table 2

[0095] Referring to Figure 2 the transfer function curve graph of a compact afocal system based on a multi-faceted coaxial optical element in this embodiment shown in Figure 2 it can be seen that the modulation function values in each field of view are close to the diffraction limit.

[0096] Referring to Figure 3 the field curvature and distortion curve graph of a compact afocal system based on a multi-faceted coaxial optical element in this embodiment shown in

[0097] The above content is only an example of the specific solution of the present invention. For the equipment and structures not described in detail therein, it should be understood that the existing general equipment and general methods in the art are adopted for implementation.

[0098] The above description is only one solution of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A compact afocal system based on a multi-faceted coaxial optical element, characterized in that, Comprising: A first optical path module (1) and a second optical path module (2); Along the object side to the image side direction, the first optical path module (1) and the second optical path module (2) are arranged coaxially in sequence; The first optical path module (1) and the second optical path module (2) are respectively total reflection type optical transmission modules, and the first optical path module (1) and the second optical path module (2) are arranged with coincident foci; The first optical path module (1) has a first entrance pupil (1a) and a first exit pupil (1b); The second optical path module (2) has a second entrance pupil (2a) and a second exit pupil (2b); The first optical path module (1) receives external light through the first entrance pupil (1a) and outputs it through the first exit pupil (1b); The second optical path module (2) receives the light output from the first exit pupil (1b) through the second entrance pupil (2a), and outputs it in the form of parallel light through the second exit pupil (2b); The first optical path module (1) includes: a first reflecting element (11) and a second reflecting element (12); Along the object side to the image side direction, the first reflecting element (11) and the second reflecting element (12) are arranged coaxially and at intervals; The first entrance pupil (1a) is arranged on the first reflecting element (11), and the first exit pupil (1b) is arranged on the second reflecting element (12); One side of the second reflecting element (12) adjacent to the first reflecting element (11) is a first front reflecting surface (121), which is used to receive the light passing through the first entrance pupil (1a); One side of the first reflecting element (11) adjacent to the second reflecting element (12) is a first rear reflecting surface (111), which is used to receive the light reflected by the first front reflecting surface (121) and make the light exit from the first exit pupil (1b); The first front reflecting surface (121) includes a plurality of coaxial first annular front reflecting surfaces (121a); The first rear reflecting surface (111) includes a plurality of coaxial first annular rear reflecting surfaces (111a); The second optical path module (2) includes: a third reflecting element (21) and a fourth reflecting element (22); Along the object side to the image side direction, the third reflecting element (21) and the fourth reflecting element (22) are arranged coaxially and at intervals; The second entrance pupil (2a) is arranged on the third reflecting element (21), and the second exit pupil (2b) is arranged on the fourth reflecting element (22); One side of the fourth reflecting element (22) adjacent to the third reflecting element (21) is a second front reflecting surface (221), which is used to receive the light passing through the second entrance pupil (2a); One side of the third reflecting element (21) adjacent to the fourth reflecting element (22) is a second rear reflecting surface (211), which is used to receive the light reflected by the second front reflecting surface (221) and make the light exit from the second exit pupil (2b); The second front reflecting surface (221) includes a plurality of coaxial second annular front reflecting surfaces (221a); The second rear reflection surface (211) includes a plurality of coaxial second annular rear reflection surfaces (211a); The edges of adjacent first annular front reflection surfaces (121a) are connected to each other by using a transition surface, the edges of adjacent first annular rear reflection surfaces (111a) are connected to each other by using a transition surface, the edges of adjacent second annular front reflection surfaces (221a) are connected to each other by using a transition surface, and the edges of adjacent second annular rear reflection surfaces (211a) are connected to each other by using a transition surface. Among them, the transition surface is provided with extinction paint; The relative position accuracy of adjacent first annular front reflection surfaces (121a) is within 1 μm, and the relative position accuracy of adjacent first annular rear reflection surfaces (111a) is within 1 μm; The second reflection element (12) and the third reflection element (21) are independent of each other, or the second reflection element (12) and the third reflection element (21) are integrated.

2. The compact afocal system according to claim 1, characterized in that, The number of the first annular front reflection surfaces (121a) and the first annular rear reflection surfaces (111a) is the same, and respectively satisfies: 2 ≤ X ≤ 9; where X represents the number of the first annular front reflection surfaces (121a) and the first annular rear reflection surfaces (111a); The number of the second annular front reflection surfaces (221a) and the second annular rear reflection surfaces (211a) is the same, and respectively satisfies: 2 ≤ Y ≤ 9; where Y represents the number of the second annular front reflection surfaces (221a) and the second annular rear reflection surfaces (211a).

3. The compact afocal system according to claim 2, wherein, The first annular front reflection surface (121a) and the first annular rear reflection surface (111a) are plane, quadratic surface or aspheric surface; The second annular front reflection surface (221a) and the second annular rear reflection surface (211a) are plane, quadratic surface or aspheric surface.

4. The compact afocal system according to claim 3, characterized in that, The first annular front reflection surface (121a) and the first annular rear reflection surface (111a) adopt high-order aspheric reflection surfaces, and are respectively provided with high-reflectivity film layers; The second annular front reflection surface (221a) and the second annular rear reflection surface (211a) adopt high-order aspheric reflection surfaces, and are respectively provided with high-reflectivity film layers; The reflectivity of the high-reflectivity film layer is greater than 98%.

5. The compact afocal system according to claim 4, characterized in that The first reflection element (11), the second reflection element (12), the third reflection element (21) and the fourth reflection element (22) are made of the same material.

6. The compact afocal system according to claim 5, wherein The first entrance pupil (1a) and the second exit pupil (2b) are respectively arc-shaped through holes. Among them, along the circumferential direction of the first reflection element (11), a plurality of the first entrance pupils (1a) are arranged at intervals, and along the circumferential direction of the fourth reflection element (22), a plurality of the second exit pupils (2b) are arranged at intervals; The first exit pupil (1b) and the second entrance pupil (2a) are respectively circular through holes. Among them, the first exit pupil (1b) is located at the middle position of the second reflection element (12), and the second entrance pupil (2a) is located at the middle position of the third reflection element (21).

7. The compact afocal system according to claim 6, wherein The field of view angle of the described compact afocal system is greater than or equal to 10°; The working wavelength band of the described compact afocal system includes the visible light band, the near-infrared band, the mid-infrared band, and the far-infrared band.

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