Large-aperture high-resolution short-wave infrared imaging optical system

Abstract

This invention relates to a large-aperture, high-resolution short-wave infrared imaging optical system, comprising a primary reflector, a secondary reflector, a first meniscus positive lens, a first meniscus negative lens, a second meniscus positive lens, a first biconvex positive lens, a biconcave negative lens, a second biconvex positive lens, and a filter arranged coaxially in sequence. The optical system employs a catadioptric optical structure, achieving a large aperture and long focal length. The system has a light-transmitting aperture of 240mm and a focal length of 1200mm, improving the system's target detection and identification capabilities, and is suitable for high-altitude, long-range reconnaissance. The system has been optimized to reduce the obstruction ratio and improve light energy utilization, while effectively reducing the number of lenses and simplifying the optical system structure. This achieves miniaturization and weight reduction of the long-focal-length airborne short-wave infrared imaging optical system, and is compatible with the latest 1280x1024 high-resolution short-wave infrared detectors.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically to a large-aperture, high-resolution short-wave infrared imaging optical system. Background Technology

[0002] The short-wave infrared band (0.9μm-2.5μm) possesses excellent atmospheric transmission characteristics, falling within the atmospheric transmission window and effectively penetrating obstacles such as fog and smoke. This band of imaging technology combines the high resolution of visible light with the thermal sensing capabilities of mid-wave infrared, filling the spectral gap between visible and mid-wave infrared imaging. Compared to visible light imaging, short-wave infrared exhibits superior imaging performance under harsh weather conditions, complementing thermal imaging systems to achieve all-weather observation capabilities. Furthermore, short-wave infrared technology can be used for imaging and analyzing the laser spot of laser designators and laser rangefinders, enabling automatic calibration of the laser energy center coordinates and detection of optical axis drift, providing crucial technical support for airborne optoelectronic systems.

[0003] Chinese patents CN115421284A and CN214540209U disclose two types of short-wave infrared lenses. Both of these short-wave infrared lenses are transmission systems, which have the disadvantages of short focal length and small aperture, making them difficult to apply in long-distance imaging applications.

[0004] Chinese patent application No. 202210850852.4 discloses a miniaturized catadioptric short-wave infrared imaging optical system. This optical system is compatible with short-wave infrared detectors with a resolution of 640x512 and a pixel size of 15μm. The technical parameters are: operating wavelength: 0.9μm~1.7μm; F#: 5.0; focal length: 500mm; field of view: 1.10°x0.88°. This optical system cannot be applied to the newly released high-resolution short-wave infrared detectors with a resolution of 1280x1024 and a pixel size of 10μm.

[0005] Chinese patent application No. 202211379582.X discloses a lightweight airborne short-wave infrared imaging optical system. This system features a primary reflector with an aperture of 80mm and a total weight of 190g. Its small aperture and light weight enable miniaturization and weight reduction of the airborne short-wave infrared imaging optical system. It is compatible with short-wave infrared detectors with a resolution of 640x512 and a pixel size of 15μm. The achieved technical parameters are: operating wavelength: 0.9μm~1.7μm; F#: 5.0; focal length: 400mm; field of view: 1.38°x1.10°. However, this optical system cannot be applied to the newly released high-resolution short-wave infrared detectors with a resolution of 1280x1024 and a pixel size of 10μm. Summary of the Invention

[0006] To address the technical challenges of current short-wave infrared optical systems, such as short focal length and small aperture, which make them difficult to adapt to large-scale, high-resolution detectors, this invention provides a large-aperture, high-resolution short-wave infrared imaging optical system.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a large-aperture, high-resolution short-wave infrared imaging optical system, characterized in that, along the optical path propagation direction, the optical system comprises a primary reflector, a secondary reflector, a first meniscus positive lens, a first meniscus negative lens, a second meniscus positive lens, a first biconvex positive lens, a biconcave negative lens, a second biconvex positive lens, and a planar filter arranged coaxially in sequence. The reflecting surface of the primary reflector is concave and faces the object side, the reflecting surface of the secondary reflector is convex and faces the image side, and the concave surfaces of the first meniscus positive lens, the first meniscus negative lens, and the second meniscus positive lens are all arranged facing the image plane. The first meniscus positive lens and the first meniscus negative lens form a first cemented lens I, and the first biconvex positive lens and the biconcave negative lens form a second cemented lens II.

[0008] Furthermore, the reflecting surface of the primary reflector is a parabolic surface with a central opening, the reflecting surface of the secondary reflector is a quadratic surface, and the surfaces of all lenses except the primary and secondary reflectors are spherical.

[0009] Furthermore, the quadratic surface coefficient of the secondary reflector is -2.318.

[0010] Furthermore, the primary reflector has an aperture of 240 mm, and the secondary reflector has an aperture of 62 mm.

[0011] Furthermore, by using an axially moving second biconvex positive lens, the optical system achieves image plane defocus compensation within a temperature range of -40℃ to +60℃, as well as system defocus compensation caused by changes in the distance of the observed scene.

[0012] Furthermore, the primary reflector is made of low-expansion microcrystalline glass, the secondary reflector is made of low-expansion microcrystalline glass, the first meniscus positive lens is made of H-BAF3, the first meniscus negative lens is made of H-ZF2, the second meniscus positive lens is made of H-K12, the first biconvex positive lens is made of H-QF3, the biconcave negative lens is made of H-ZLAF90, the second biconvex positive lens is made of H-ZF62, and the planar filter is made of quartz.

[0013] Furthermore, each lens of the optical system satisfies the following condition: -0.08≤f1 / f≤-0.05, -0.22≤f2 / f≤-0.18, 0.04≤f3 / f≤0.07, -0.06≤f4 / f≤-0.04, 0.15≤f5 / f≤0.25, 0.1≤f6 / f≤0.15, -0.02≤f7 / f≤-0.01, 0.05≤f8 / f≤0.07; Where: f is the focal length of the short-wave infrared imaging optical system; f1 is the effective focal length of the secondary mirror; f2 is the effective focal length of the main reflector; f3 is the effective focal length of the first meniscus positive lens; f4 is the effective focal length of the first meniscus negative lens; f5 is the effective focal length of the second meniscus positive lens; f6 is the effective focal length of the first biconvex positive lens; f7 is the effective focal length of the biconcave negative lens; f8 is the effective focal length of the second biconvex positive lens.

[0014] Furthermore, the secondary reflector and the first cemented lens I satisfy the following condition: 0.65 ≤ d 13 / TTL≤0.75, where d 13 The distance between the secondary mirror and the first meniscus positive lens is TTL, which is the total length of the optical system, i.e., the distance from the front surface of the secondary mirror to the center of the image plane.

[0015] Furthermore, the air gap between the primary reflector and the secondary reflector is 180.67 mm, the air gap between the secondary reflector and the first meniscus positive lens is 203.0 mm, the air gap between the first meniscus negative lens and the second meniscus positive lens is 4.55 mm, the air gap between the second meniscus positive lens and the first biconvex positive lens is 2.0 mm, the air gap between the biconcave negative lens and the second biconvex positive lens is 26.1 mm, the air gap between the second biconvex positive lens and the planar filter is 8.0 mm, and the air gap between the planar filter and the image plane is 10.0 mm.

[0016] Furthermore, the technical parameters achieved by the optical system are: operating wavelength: 0.9μm~1.7μm; F # Lens: 5.0; Focal length: 1200mm; Field of view: 0.61° x 0.49°; System obstruction ratio: 0.26; Wherein, F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0017] The present invention has at least the following beneficial effects: 1. This invention adopts a catadioptric optical structure to realize a long focal length and large aperture short-wave infrared optical system with a focal length of 1200mm and an aperture of 240mm. This greatly improves the detection and identification capability of the short-wave infrared system for distant targets. It is suitable for high-altitude long-range reconnaissance and solves the technical problem that it is difficult to achieve long focal length and large aperture in transmission optical systems due to the difficulty, long melting cycle and high price of large aperture optical glass materials.

[0018] 2. This invention reduces the system's obstruction ratio to 0.26 by optimizing the bending direction of the primary and secondary mirrors, the setting of each meniscus lens and the cemented lens, as well as the optical power and surface curvature of each lens. This reduces energy loss caused by secondary mirror obstruction and improves light energy utilization. At the same time, it effectively reduces the number of lenses and simplifies the optical system structure, thereby achieving miniaturization and weight reduction of the long-focal-length airborne short-wave infrared imaging optical system. It can also be adapted to the latest high-resolution short-wave infrared detectors with a resolution of 1280x1024 and a pixel size of 10μm.

[0019] 3. In the optical system of this invention, all lenses except the primary and secondary mirrors have spherical surfaces, which effectively reduces system error sensitivity and improves assembly efficiency while ensuring system imaging quality, thereby reducing production costs. Attached Figure Description

[0020] Figure 1 This is the optical path diagram of the short-wave infrared imaging optical system of the present invention.

[0021] Figure 2 The graph shows the transfer function of the shortwave infrared imaging optical system of this invention.

[0022] Figure 3 This is a dot diagram of the short-wave infrared imaging optical system of the present invention.

[0023] Figure 4 This is a field curvature and distortion diagram of the shortwave infrared imaging optical system of the present invention.

[0024] Figure 5 This is a relative illumination diagram of the image plane of the short-wave infrared imaging optical system of the present invention.

[0025] Among them, 1 is a secondary reflector, 2 is a primary reflector, 3 is a first meniscus positive lens, 4 is a first meniscus negative lens, 5 is a second meniscus positive lens, 6 is a first biconvex positive lens, 7 is a biconcave negative lens, 8 is a second biconvex positive lens, 9 is a planar filter, and 10 is the image plane. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention. In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicating orientation or positional relationship, are only for the purpose of describing the present invention and are not intended to indicate or imply that the device or element referred to must have a specific orientation.

[0027] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only, referring to the order in which lenses of this type appear. They are used to distinguish between them in description and have no special meaning. They should not be interpreted as indicating or implying relative importance.

[0028] Throughout the manual, the same reference numerals refer to the same components. The accompanying drawings are for illustrative purposes only and are not drawn to scale.

[0029] As is common knowledge, the direction closer to object space is called the object side, and the direction closer to image space is called the image side. From the object side to the image side, the two surfaces of a lens are the incident surface and the exit surface, respectively. The object side refers to the side where the light rays enter, and the image side refers to the side where they exit. Of the two surfaces of each lens, the surface facing the object side is called the object-side surface, and the surface facing the image side is called the image-side surface.

[0030] like Figure 1 As shown, a large-aperture, high-resolution short-wave infrared imaging optical system comprises a secondary reflector 1, a primary reflector 2, a first meniscus positive lens 3, a first meniscus negative lens 4, a second meniscus positive lens 5, a first biconvex positive lens 6, a biconcave negative lens 7, a second biconvex positive lens 8, and a planar filter 9, arranged coaxially from the object side to the image side.

[0031] The primary reflector 2 has a concave reflector facing the object side, the secondary reflector 1 has a convex reflector facing the image side, and the concave surfaces of the first meniscus positive lens 3, the first meniscus negative lens 4, and the second meniscus positive lens 5 are all curved toward the image plane.

[0032] The first meniscus positive lens 3 and the first meniscus negative lens 4 form the first cemented lens I, and the first biconvex positive lens 6 and the biconcave negative lens 7 form the second cemented lens II.

[0033] Furthermore, the reflecting surface of the primary reflector 2 is a parabolic surface with a central opening, and the reflecting surface of the secondary reflector 1 is a quadratic surface with a quadratic surface coefficient of -2.318.

[0034] Except for primary mirror 2 and secondary mirror 1, all other lenses have spherical surfaces.

[0035] The primary reflector 2 has an aperture of 240mm, the secondary reflector 1 has an aperture of 62mm, and the system blocking ratio is 0.26.

[0036] Preferably, the primary reflector 2 is made of low-expansion microcrystalline glass, the secondary reflector 1 is made of low-expansion microcrystalline glass, the first meniscus positive lens 3 is made of H-BAF3, the first meniscus negative lens 4 is made of H-ZF2, the second meniscus positive lens 5 is made of H-K12, the first biconvex positive lens 6 is made of H-QF3, the biconcave negative lens 7 is made of H-ZLAF90, the second biconvex positive lens 8 is made of H-ZF62, and the planar filter 9 is made of quartz.

[0037] In the optical system, the second biconvex positive lens 8 is moved axially to achieve image plane defocus compensation within the temperature range of -40℃ to +60℃ and system defocus compensation caused by changes in the distance of the observed scene, thereby ensuring clear imaging of objects at different distances under different ambient temperature conditions.

[0038] The light transmission path of the optical system is as follows: light from the external scene is reflected by the primary mirror 2 and then reaches the secondary mirror 1. After being reflected by the secondary mirror 1, it reaches the first cemented lens I. After being converged by the first cemented lens I, it reaches the second meniscus positive lens 5. After being converged by the second meniscus positive lens 5, it reaches the second cemented lens II. After being diverged by the second cemented lens II, it reaches the second biconvex positive lens 8. After being converged by the second biconvex positive lens 8, it passes through the planar filter 9 and is imaged on the image plane 10.

[0039] Furthermore, the secondary reflector 1 satisfies the following condition: -0.08≤f1 / f≤-0.05, where f is the focal length of the short-wave infrared imaging optical system and f1 is the effective focal length of the secondary reflector 1; The primary reflector 2 satisfies the following condition: -0.22≤f2 / f≤-0.18, where f is the focal length of the short-wave infrared imaging optical system and f2 is the effective focal length of the primary reflector 2; The first meniscus positive lens 3 satisfies the following condition: 0.04≤f3 / f≤0.07, where f is the focal length of the short-wave infrared imaging optical system and f3 is the effective focal length of the first meniscus positive lens 3; The first meniscus negative lens 4 satisfies the following condition: -0.06≤f4 / f≤-0.04, where f is the focal length of the shortwave infrared imaging optical system and f4 is the effective focal length of the first meniscus negative lens 4. The second meniscus positive lens 5 satisfies the following condition: 0.15≤f5 / f≤0.25, where f is the focal length of the short-wave infrared imaging optical system and f5 is the effective focal length of the second meniscus positive lens 5; The first biconvex positive lens 6 satisfies the following condition: 0.1≤f6 / f≤0.15, where f is the focal length of the short-wave infrared imaging optical system and f6 is the effective focal length of the first biconvex positive lens 6; The biconcave negative lens 7 satisfies the following condition: -0.02≤f7 / f≤-0.01, where f is the focal length of the short-wave infrared imaging optical system and f7 is the effective focal length of the biconcave negative lens 7; The second biconvex positive lens 8 satisfies the following condition: 0.05≤f8 / f≤0.07, where f is the focal length of the short-wave infrared imaging optical system and f8 is the effective focal length of the second biconvex positive lens 8.

[0040] The secondary reflector 1 and the first cemented lens I satisfy the following condition: 0.65 ≤ d 13 / TTL≤0.75, where d 13 TTL is the distance between the secondary mirror 1 and the first meniscus positive lens 3, and TTL is the total length of the optical system, which is the distance from the front surface of the secondary mirror 1 to the center of the image plane 10.

[0041] Specifically, the air gap between the primary reflector 2 and the secondary reflector 1 is 180.67 mm, the air gap between the secondary reflector 1 and the first meniscus positive lens 3 is 203.0 mm, the air gap between the first meniscus negative lens 4 and the second meniscus positive lens 5 is 4.55 mm, the air gap between the second meniscus positive lens 5 and the first biconvex positive lens 6 is 2.0 mm, the air gap between the biconcave negative lens 7 and the second biconvex positive lens 8 is 26.1 mm, the air gap between the second biconvex positive lens 8 and the filter 9 is 8.0 mm, and the air gap between the planar filter 9 and the image plane 10 is 10.0 mm.

[0042] As shown in Table 1, the technical parameters achieved by the optical system are: operating wavelength: 0.9μm~1.7μm; F # F: 5.0; Focal length: 1200mm; Field of view: 0.61° x 0.49°; Primary mirror aperture: 240mm, Secondary mirror aperture: 62mm; TTL distance from the front surface of the secondary mirror to the image plane: 297mm; System obstruction ratio: 0.26. Wherein, F... # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0043] Table 1 Technical Specifications of the Optical System of the Invention Table 2 lists detailed data for an embodiment of the optical system according to the present invention, including the surface shape, radius of curvature, thickness, and material of each lens. The units for the radius of curvature and thickness of the lens are mm. In Table 2, "radius" represents the radius of curvature of the surface. Its sign is determined by taking the intersection of the surface and the principal optical axis as the starting point and the center of the surface as the ending point. If the direction of the connecting line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the surface is planar, its radius of curvature is infinite. In Table 2, "thickness" gives the distance between two adjacent surfaces on the optical axis. Its sign is determined by taking the vertex of the current surface as the starting point and the vertex of the next surface as the ending point. If the direction of the connecting line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the material between the two surfaces is infrared material, the thickness represents the lens thickness; if there is no material between the two surfaces, it represents the air gap between the two lenses.

[0044] Table 2 Detailed data of the optical system in the embodiments of the present invention The optical system of this embodiment is simulated in optical design software, such as... Figure 2 It can be seen that when the characteristic frequency corresponding to the short-wave infrared detector is 50 lp / mm, the minimum transfer function of the short-wave infrared optical system in this embodiment is greater than 0.35, resulting in excellent imaging quality. For example... Figure 3 It can be seen that the diameter of the blur spot in the short-wave infrared optical system of this embodiment is smaller than the detector pixel diameter, which meets the usage requirements. For example... Figure 4 It can be seen that the distortion of the short-wave infrared optical system in this embodiment is less than 2.2%, which meets the usage requirements. For example... Figure 5 It can be seen that the image edge illuminance of the short-wave infrared optical system in this embodiment is 92% of the center illuminance, and the image surface illuminance uniformity is good.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A large-aperture, high-resolution short-wave infrared imaging optical system, characterized in that, Along the direction of light propagation, the optical system consists of a primary reflector (2), a secondary reflector (1), a first meniscus positive lens (3), a first meniscus negative lens (4), a second meniscus positive lens (5), a first biconvex positive lens (6), a biconcave negative lens (7), a second biconvex positive lens (8), and a planar filter (9) arranged coaxially in sequence. The reflecting surface of the primary reflector (2) is concave and faces the object side. The reflecting surface of the secondary reflector is convex and faces the image side. The concave surfaces of the first meniscus positive lens (3), the first meniscus negative lens (4), and the second meniscus positive lens (5) are all arranged facing the image plane (10). The first meniscus positive lens (3) and the first meniscus negative lens (4) form a first cemented lens I, and the first biconvex positive lens (6) and the biconcave negative lens (7) form a second cemented lens II.

2. The large-aperture, high-resolution short-wave infrared imaging optical system according to claim 1, characterized in that, The reflecting surface of the primary reflector (2) is a parabolic surface with a central opening, and the reflecting surface of the secondary reflector (1) is a quadratic surface. Except for the primary reflector (2) and the secondary reflector (1), the surfaces of all other lenses are spherical.

3. The large-aperture, high-resolution short-wave infrared imaging optical system according to claim 2, characterized in that, The quadratic surface coefficient of the secondary reflector (1) is -2.

318.

4. The large-aperture, high-resolution short-wave infrared imaging optical system according to claim 1, characterized in that, The primary reflector (2) has an aperture of 240 mm, and the secondary reflector (1) has an aperture of 62 mm.

5. The large-aperture, high-resolution, short-wave infrared imaging optical system of claim 1, wherein, The optical system achieves image plane defocus compensation within the temperature range of -40℃ to +60℃ and system defocus compensation caused by changes in the distance of the observed scene by using the second biconvex positive lens (8) with axial movement.

6. The large-aperture, high-resolution, short-wave infrared imaging optical system of claim 1, wherein, The primary reflector (2) is made of low-expansion microcrystalline glass, the secondary reflector (1) is made of low-expansion microcrystalline glass, the first meniscus positive lens (3) is made of H-BAF3, the first meniscus negative lens (4) is made of H-ZF2, the second meniscus positive lens (5) is made of H-K12, the first biconvex positive lens (6) is made of H-QF3, the biconcave negative lens (7) is made of H-ZLAF90, the second biconvex positive lens (8) is made of H-ZF62, and the planar filter (9) is made of quartz.

7. The large-aperture, high-resolution short-wave infrared imaging optical system according to claim 1, characterized in that, Each lens in the optical system satisfies the following condition: -0.08≤f1 / f≤-0.05, -0.22≤f2 / f≤-0.18, 0.04≤f3 / f≤0.07, -0.06≤f4 / f≤-0.04, 0.15≤f5 / f≤0.25, 0.1≤f6 / f≤0.15, -0.02≤f7 / f≤-0.01, 0.05≤f8 / f≤0.07; Where: f is the focal length of the short-wave infrared imaging optical system; f1 is the effective focal length of the secondary mirror (1); f2 is the effective focal length of the main reflecting mirror (2); f3 is the effective focal length of the first meniscus positive lens (3); f4 is the effective focal length of the first meniscus negative lens (4); f5 is the effective focal length of the second meniscus positive lens (5); f6 is the effective focal length of the first biconvex positive lens (6); f7 is the effective focal length of the biconcave negative lens (7); f8 is the effective focal length of the second biconvex positive lens (8).

8. The large-aperture, high-resolution, short-wave infrared imaging optical system of claim 1, wherein, The secondary reflector (1) and the first cemented lens I satisfy the following condition: 0.65 ≤ d 13 / TTL≤0.75, where d 13 TTL is the distance between the secondary mirror (1) and the first meniscus positive lens (3), and TTL is the total length of the optical system, i.e., the distance from the front surface of the secondary mirror (1) to the center of the image plane (10).

9. The large-aperture, high-resolution short-wave infrared imaging optical system according to claim 1, characterized in that, The air gap between the primary reflector (2) and the secondary reflector (1) is 180.67 mm, the air gap between the secondary reflector (1) and the first meniscus positive lens (3) is 203.0 mm, the air gap between the first meniscus negative lens (4) and the second meniscus positive lens (5) is 4.55 mm, the air gap between the second meniscus positive lens (5) and the first biconvex positive lens (6) is 2.0 mm, the air gap between the biconcave negative lens (7) and the second biconvex positive lens (8) is 26.1 mm, the air gap between the second biconvex positive lens (8) and the planar filter (9) is 8.0 mm, and the air gap between the planar filter (9) and the image plane (10) is 10.0 mm.

10. The large-aperture, high-resolution, short-wave infrared imaging optical system of claim 1, wherein, The technical parameters achieved by the optical system are: operating wavelength: 0.9μm~1.7μm; F # Lens: 5.0; Focal length: 1200mm; Field of view : 0.61° x 0.49°; System occlusion ratio: 0.26; Wherein, F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

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