A lightweight airborne short-wave infrared imaging optical system

Abstract

The present invention discloses a lightweight airborne short-wave infrared imaging optical system. The optical system comprises a secondary reflector, a primary reflector, a first cemented lens, a first negative meniscus lens, and a second cemented lens, which are coaxially arranged from the object side to the image side. The primary reflector has a central aperture, and its reflective surface is a parabola facing the object side, while the reflective surface of the secondary reflector is a quadratic surface facing the image side. The present invention employs a catadioptric optical structure. By optimizing the curvature direction of each meniscus lens, the arrangement of the cemented lenses, and the optical power and surface curvature of each lens, the number of lenses is effectively reduced, the optical system structure is simplified, and the miniaturization and lightweighting of the airborne short-wave infrared imaging optical system are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of short-wave infrared imaging optical systems, in particular to a lightweight airborne short-wave infrared imaging optical system. Background Art

[0002] Shortwave infrared (SWIR) refers to infrared radiation with a wavelength of 0.9μm to 2.5μm. This wavelength falls within the atmospheric transmission window, resulting in excellent atmospheric transmission. Located between visible light and medium-wave infrared, SWIR can provide information unavailable to visible light and medium-wave infrared, while also possessing the imaging characteristics of both. This fills the spectral gap between visible light and medium-wave infrared imaging.

[0003] The short-wave infrared band is longer than the visible light band, is less affected by atmospheric scattering, has a stronger ability to penetrate haze and smoke, and has atmospheric obstacle penetration capabilities similar to thermal infrared. Its imaging effect in harsh climatic conditions and battlefield environments is significantly better than visible light imaging. It complements thermal imaging and can achieve all-weather adaptability to the greatest extent.

[0004] Shortwave infrared imaging systems can image the laser spot of currently used laser designators and laser rangefinders. In addition to observing the laser spot, they can also automatically mark the coordinates of the laser spot's energy center, confirming whether the laser rangefinder's optical axis has drifted. Shortwave infrared technology has broad application prospects, and equipping airborne optoelectronic systems with shortwave infrared imaging systems is of great significance.

[0005] It can be seen that it is very necessary to design and develop short-wave infrared imaging optical systems, and lightweight airborne short-wave infrared imaging optical systems are even more difficult to design. Summary of the Invention

[0006] In order to solve the technical problem that current short-wave infrared optical systems are difficult to achieve miniaturization and lightweighting, the present invention provides a lightweight airborne short-wave infrared imaging optical system.

[0007] In order to achieve the above object, the specific scheme adopted by the present invention is:

[0008] A lightweight airborne short-wave infrared imaging optical system comprises a secondary reflector, a primary reflector, a first cemented lens, a first meniscus negative lens, and a second cemented lens, which are coaxially arranged in sequence from the object side to the image side. The primary reflector has a central opening, and the reflecting surface of the primary reflector is a parabola facing the object side; the reflecting surface of the secondary reflector is a quadratic surface facing the image side; light from an external scene is reflected by the primary reflector and reaches the secondary reflector, and then reflected by the secondary reflector and reaches the first cemented lens. After being converged by the first cemented lens, the light reaches the first meniscus negative lens, and then diverges after being diverged by the first meniscus negative lens and reaches the second cemented lens. After being converged by the second cemented lens, the light is imaged on the imaging surface.

[0009] Furthermore, the first cemented lens is formed by cementing a first meniscus positive lens and a biconvex positive lens; and the second cemented lens is formed by cementing a second meniscus positive lens and a second meniscus negative lens.

[0010] Furthermore, the first meniscus positive lens, the first meniscus negative lens, the second meniscus positive lens and the second meniscus negative lens are all arranged to bend toward the image side.

[0011] Furthermore, the quadratic surface coefficient of the secondary reflector is -1.629.

[0012] Furthermore, the diameter of the primary reflector is 80 mm, and the diameter of the secondary reflector is 22 mm.

[0013] Furthermore, the secondary reflector and the first cemented lens satisfy the following condition: 0.55≤d13 / TTL≤0.60, wherein d13 is the distance between the secondary reflector and the first meniscus positive lens, and TTL is the distance from the front surface of the secondary reflector to the center of the imaging plane.

[0014] Furthermore, the material of the primary reflector is quartz, the material of the secondary reflector is quartz, the material of the first meniscus positive lens is H-ZF62, the material of the double convex positive lens is H-ZK9B, the material of the first meniscus negative lens is H-ZLAF76, the material of the second meniscus positive lens is H-QK3L, and the material of the second meniscus negative lens is H-ZLAF66.

[0015] Furthermore, by axially moving the second cemented lens, clear imaging of objects at different distances can be achieved under different ambient temperature conditions, with a total moving stroke of 3.0 mm.

[0016] Furthermore, the optical system satisfies the following conditions: -0.1≤f1 / f≤-0.05, -0.3≤f2 / f≤-0.2, 0.4≤f3 / f≤0.5, 3.5≤f4 / f≤3.7, -0.2≤f5 / f≤-0.1, 0.06≤f6 / f≤0.15, -0.1≤f7 / f≤-0.05;

[0017] Wherein, f is the focal length of the short-wave infrared imaging optical system, f1 is the effective focal length of the secondary reflector, f2 is the effective focal length of the primary reflector, f3 is the effective focal length of the first meniscus positive lens, f4 is the effective focal length of the biconvex positive lens, f5 is the effective focal length of the first meniscus negative lens, f6 is the effective focal length of the second meniscus positive lens, and f7 is the effective focal length of the second meniscus negative lens.

[0018] Furthermore, the technical parameters achieved by the optical system are: working band: 0.9μm~1.7μm; F#: 5.0; focal length: 400mm; field of view: 1.38°×1.10°; where F#=f / D, D is the incident pupil diameter.

[0019] Beneficial effects:

[0020] 1) The present invention adopts a catadioptric optical structure, with the primary reflector adopting a parabola and the secondary reflector adopting a quadratic surface. Through the reasonable distribution of the optical power of the primary reflector and the secondary reflector, the system obstruction ratio is less than 0.28, which effectively improves the utilization rate of light energy, thereby improving the sensitivity of the system, which is conducive to the detection and identification of long-distance targets.

[0021] 2) By optimizing the material combination of the primary reflector, secondary reflector, and rear lens groups, as well as the optical power and surface curvature, a short-wavelength imaging optical system with a focal length of 400mm is achieved using only two reflectors and five lenses, effectively reducing the number of lenses and simplifying the optical system structure. The primary reflector of the optical system has an aperture of 80mm and a total weight of 190g. Its small aperture and light weight enable the miniaturization and lightweighting of the airborne short-wavelength infrared imaging optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the optical path diagram of the short-wave infrared imaging optical system.

[0023] Figure 2 This is the transfer function diagram of the short-wave infrared imaging optical system.

[0024] Figure 3 This is the point diagram of the short-wave infrared imaging optical system.

[0025] Figure 4 This is the field curvature and distortion diagram of the short-wave infrared imaging optical system.

[0026] Markings in the diagram: 1. Secondary reflector, 2. Primary reflector, 3. First meniscus positive lens, 4. Biconvex positive lens, 5. First meniscus negative lens, 6. Second meniscus positive lens, 7. Second meniscus negative lens, 8. Imaging surface. DETAILED DESCRIPTION

[0027] The present invention is 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 if there are terms such as "upper", "lower", "front", "back", "left", "right" and the like indicating directions or positional relationships, they are only used in conjunction with the appended drawings of this application. Figure 1Accordingly, for the purpose of describing the present invention, the terms "first," "second," and "third" are used for descriptive purposes only, referring to the order in which lenses of that type appear, and are not to be construed as indicating or implying relative importance.

[0028] like Figure 1 A lightweight airborne short-wave infrared imaging optical system comprises a secondary reflector 1, a primary reflector 2, a first meniscus positive lens 3, a biconvex positive lens 4, a first meniscus negative lens 5, a second meniscus positive lens 6, and a second meniscus negative lens 7, which are coaxially arranged from the object side to the image side. Light from the external scene is reflected by the primary reflector 2 and reaches the secondary reflector 1. After being reflected by the secondary reflector 1, it reaches the first cemented lens. After being converged by the first cemented lens, it reaches the first meniscus negative lens 5. After being diverged by the first meniscus negative lens 5, it reaches the second cemented lens. After being converged by the second cemented lens, it forms an image on the imaging surface 8. The reflecting surface of the primary reflector 2 is a parabola with a central opening and faces the object side. The reflecting surface of the secondary reflector 1 is a quadratic surface. The first meniscus positive lens 3, the first meniscus negative lens 5, the second meniscus positive lens 6, and the second meniscus negative lens 7 are all arranged to bend toward the image side.

[0029] As common sense, the direction close to the object space is the object side, and the direction close to the image space is the image side. From the object side to the image side, the two sides of the lens are the incident side and the exit side respectively.

[0030] The first meniscus positive lens 3 and the biconvex positive lens 4 form a first cemented lens, and the second meniscus positive lens 6 and the second meniscus negative lens 7 form a second cemented lens.

[0031] The quadratic surface coefficient of the secondary reflector 1 is -1.629.

[0032] The diameter of the primary reflector 2 is 80 mm, and the diameter of the secondary reflector 1 is 22 mm.

[0033] Preferably, the material of the main reflector 2 is quartz, the material of the secondary reflector 1 is quartz, the material of the first meniscus positive lens 3 is H-ZF62, the material of the double convex positive lens 4 is H-ZK9B, the material of the first meniscus negative lens 5 is H-ZLAF76, the material of the second meniscus positive lens 6 is H-QK3L, and the material of the second meniscus negative lens 7 is H-ZLAF66.

[0034] The system uses an axially movable second cemented lens 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.

[0035] In detail, the secondary reflector 1 satisfies the following conditions: -0.1≤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;

[0036] The main reflector 2 satisfies the following conditions: -0.3≤f2 / f≤-0.2, where f is the focal length of the short-wave infrared imaging optical system and f2 is the effective focal length of the main reflector 2;

[0037] The first meniscus positive lens 3 satisfies the following condition: 0.4≤f3 / f≤0.5, 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;

[0038] The biconvex positive lens 4 satisfies the following condition: 3.5≤f4 / f≤3.7, where f is the focal length of the short-wave infrared imaging optical system and f4 is the effective focal length of the biconvex positive lens 4;

[0039] The first meniscus negative lens 5 satisfies the following condition: -0.2≤f5 / f≤-0.1, where f is the focal length of the short-wave infrared imaging optical system and f5 is the effective focal length of the first meniscus negative lens 5;

[0040] The second meniscus positive lens 6 satisfies the following condition: 0.06≤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 second meniscus positive lens 6;

[0041] The second meniscus negative lens 7 satisfies the following condition: -0.1≤f7 / f≤-0.05, where f is the focal length of the short-wave infrared imaging optical system and f7 is the effective focal length of the second meniscus negative lens 7 .

[0042] The secondary reflector 1 and the first cemented lens I meet the following condition: 0.55≤d13 / TTL≤0.60, where d13 is the distance between the secondary reflector 1 and the first meniscus positive lens 3, and TTL is the distance from the front surface of the secondary reflector 1 to the center of the imaging surface 8.

[0043] The technical parameters achieved by the optical system are: operating wavelength: 0.9μm to 1.7μm; F#: 5.0; focal length: 400mm; field of view: 1.38° × 1.10°; primary reflector aperture: 80mm; and TTL distance from the front surface of the secondary reflector to the image plane: 136mm. The F# calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0044] Further, such as Figure 1The air gap between the primary reflector 2 and the secondary reflector 1 is 70 mm, the air gap between the secondary reflector 1 and the first meniscus positive lens 3 is 80 mm, the air gap between the biconvex positive lens 4 and the first meniscus negative lens 5 is 2.0 mm, the air gap between the first meniscus negative lens 5 and the second meniscus positive lens 6 is 10.5 mm, and the air gap between the second meniscus negative lens 7 and the image plane 8 is 13.6 mm.

[0045]

[0046]

[0047] Table 1 shows the technical indicators achieved by the present invention, wherein the calculation formula of F# (optical system F number) is f / D, f is the focal length of the optical system, and D is the incident pupil diameter.

[0048] Table 2 lists detailed data of an optical system embodiment according to the present invention, including the surface shape, radius of curvature, thickness, and material of each lens. The units of the radius of curvature and thickness of the lens are both in mm. The "radius" in Table 2 represents the radius of curvature of the surface. The positive and negative values ​​are determined by taking the intersection of the surface and the principal optical axis as the starting point and the center of the curved surface of the surface as the end point. If the direction of the connecting line is the same as the direction of light propagation, the value is positive; otherwise, the value is negative. If the surface is a plane, the radius of curvature of the surface is infinite. The "thickness" in Table 2 gives the distance between two adjacent surfaces on the optical axis. The positive and negative values ​​are determined by taking the vertex of the current surface as the starting point and the vertex of the next surface as the end point. If the direction of the connecting line is the same as the direction of light propagation, the value is positive; otherwise, the value 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, the thickness represents the air space between the two lenses.

[0049]

[0050]

[0051] like Figure 2 It can be seen that when the spatial frequency corresponding to the short-wave infrared detector is 33lp / mm, the minimum value of the system transfer function is greater than 0.5, and the imaging quality is excellent.

[0052] like Figure 3 It can be seen that the diffuse spot diameter of the short-wave infrared optical system is smaller than the detector pixel diameter, which meets the use requirements.

[0053] like Figure 4 It can be seen that the distortion of the short-wave infrared optical system is less than 2.2%, which meets the use requirements.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made based on the essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lightweight airborne short-wave infrared imaging optical system, characterized in that: The lens comprises a secondary reflector, a primary reflector, a first cemented lens, a first meniscus negative lens, and a second cemented lens, which are coaxially arranged in sequence from the object side to the image side. The primary reflector has a central opening, and the reflecting surface of the primary reflector is a parabola facing the object side. The reflecting surface of the secondary reflector is a quadratic surface facing the image side. The light from the external scene is reflected by the primary reflector and reaches the secondary reflector. After being reflected by the secondary reflector, it reaches the first cemented lens. After being converged by the first cemented lens, it reaches the first negative meniscus lens. After being diverged by the first negative meniscus lens, it reaches the second cemented lens. After being converged by the second cemented lens, it forms an image on the imaging surface. The first cemented lens is formed by cementing a first meniscus positive lens and a biconvex positive lens; the second cemented lens is formed by cementing a second meniscus positive lens and a second meniscus negative lens; The first meniscus positive lens, the first meniscus negative lens, the second meniscus positive lens and the second meniscus negative lens are all arranged to bend toward the image side; The optical system satisfies the following conditions: -0.1≤f1 / f≤-0.05, -0.3≤f2 / f≤-0.2, 0.4≤f3 / f≤0.5, 3.5≤f4 / f≤3.7, -0.2≤f5 / f≤-0.1, 0.06≤f6 / f≤0.15, -0.1≤f7 / f≤-0.05; Wherein, f is the focal length of the short-wave infrared imaging optical system, f1 is the effective focal length of the secondary reflector, f2 is the effective focal length of the primary reflector, f3 is the effective focal length of the first meniscus positive lens, f4 is the effective focal length of the biconvex positive lens, f5 is the effective focal length of the first meniscus negative lens, f6 is the effective focal length of the second meniscus positive lens, and f7 is the effective focal length of the second meniscus negative lens.

2. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: The quadratic surface coefficient of the secondary reflector is -1.

629.

3. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: The diameter of the primary reflector is 80 mm, and the diameter of the secondary reflector is 22 mm.

4. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: The secondary reflector and the first cemented lens meet the following condition: 0.55≤d13 / TTL≤0.60, where d13 is the distance between the secondary reflector and the first meniscus positive lens, and TTL is the distance from the front surface of the secondary reflector to the center of the imaging surface.

5. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: The material of the primary reflector is quartz, the material of the secondary reflector is quartz, the material of the first meniscus positive lens is H-ZF62, the material of the double convex positive lens is H-ZK9B, the material of the first meniscus negative lens is H-ZLAF76, the material of the second meniscus positive lens is H-QK3L, and the material of the second meniscus negative lens is H-ZLAF66.

6. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: By axially moving the second cemented lens, clear imaging of objects at different distances can be achieved under different ambient temperature conditions, with a total moving stroke of 3.0 mm.

7. The lightweight airborne short-wave infrared imaging optical system according to claim 1, characterized in that: The technical parameters of the optical system are as follows: working band: 0.9μm~1.7μm; F#: 5.0; focal length: 400mm; Field of view: 1.38°×1.10°; Where F#=f / D, D is the diameter of the entrance pupil.

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