Medium-wave athermalization infrared lens and imaging device

Abstract

The invention discloses a medium-wave athermalization infrared lens, the focal length is 50 mm, the medium-wave athermalization infrared lens comprises a first lens, a second lens and a third lens which are sequentially arranged in the optical axis transmission direction, the first lens and the third lens are meniscus positive lenses, the convex surfaces of the meniscus positive lenses face the object side, and the convex surfaces of the meniscus positive lenses face the object side. The second lens is a meniscus negative lens of which the convex surface faces the object side; the air interval between the first lens and the second lens is 7 mm, and the air interval between the second lens and the third lens is 5.66 mm. The medium-wave athermalization infrared lens can be suitable for a refrigeration type detector with the pixel number of 640 * 512 and the pixel size of 15 microns, the number of lenses is small, the structure is simple, and imaging is clear. The invention further discloses an imaging device.

Description

Technical Field

[0001] The present application belongs to the field of infrared lens technology, and specifically relates to a medium-wave athermal infrared lens and an imaging device. Background Art

[0002] With the continuous advancement of focal plane technology, the pixel scale of the focal plane continues to increase and the pixel size continues to decrease, which means that the optical system can effectively increase the field of view while maintaining the focal length.

[0003] For example, a 640×512 pixel detector can produce high-definition images while doubling the field of view while maintaining the same focal length compared to a 320×256 pixel detector. However, traditional lenses used for 640×512 detectors typically require a larger number of lenses to achieve high-definition imaging performance. Summary of the Invention

[0004] The technical problem to be solved by this application is that the traditional lens used for 640×512 detectors has a large number of lenses. In order to solve this technical problem, a medium-wave athermal infrared lens and imaging device that can be applied to a 640×512 detector and has a small number of lenses is provided.

[0005] The technical solutions proposed in this application are: A medium-wavelength athermal infrared lens having a focal length of 50 mm, comprising a first lens, a second lens, and a third lens arranged in sequence along an optical axis transmission direction, wherein the first lens and the third lens are both positive meniscus lenses with a convex surface facing the object side, and the second lens is a negative meniscus lens with a convex surface facing the object side; An air gap between the first lens and the second lens is 7 mm, and an air gap between the second lens and the third lens is 5.66 mm.

[0006] Furthermore, the center thickness of the first lens is 4.5 mm, the radius of curvature of the object side surface is 33.36 mm, and the radius of curvature of the image side surface is 43.17 mm; the center thickness of the second lens is 2.5 mm, the radius of curvature of the object side surface is 140.8 mm, and the radius of curvature of the image side surface is 61.16 mm; the center thickness of the third lens is 2.5 mm, the radius of curvature of the object side surface is 74.66 mm, and the radius of curvature of the image side surface is 320.81 mm.

[0007] Furthermore, the focal length of the first lens is 45.709 mm, and the optical power is 0.22; the focal length of the second lens is -36.608 mm, and the optical power is -0.027; the focal length of the third lens is 39.85 mm, and the optical power is 0.025.

[0008] Furthermore, the first lens and the third lens are both made of silicon glass, and the second lens is made of germanium.

[0009] Furthermore, the image side surface of the third lens is an aspheric surface, satisfying the aspheric surface formula: Among them, Z is the distance vector height from the aspheric surface vertex when the aspheric surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror surface; k is the cone coefficient; A, B, C, and D are high-order aspheric coefficients.

[0010] Furthermore, the medium-wave athermal infrared lens has an operating band of 3.7 μm to 4.8 μm, an operating temperature of -40°C to 60°C, an F number of 4.0, and a field of view of 10.9°×8.8°.

[0011] An imaging device comprises the medium-wave athermal infrared lens according to any one of claims 1 to 6 and a detector for receiving images formed by the medium-wave athermal infrared lens.

[0012] Furthermore, the number of pixels of the detector is 640×512, the pixel size is 15 μm, and the detector is a refrigerated infrared detector.

[0013] Furthermore, the total optical length of the imaging device is 58 mm, and the back focus is 35.84 mm.

[0014] The above-mentioned medium-wave athermal infrared lens can be applied to a 640×512 detector, and the medium-wave athermal infrared lens only includes three lenses, which simplifies the structure and reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application.

[0016] Figure 1 A schematic diagram of the optical path of an imaging device provided in one embodiment of the present application; Figure 2 This is the MTF diagram of the medium-wave athermal infrared lens provided in one embodiment of the present application at 20°C; Figure 3 This is a spot diagram of the medium-wave athermal infrared lens provided in one embodiment of the present application at 20°C; Figure 4 This is the MTF diagram of the medium-wave athermal infrared lens provided in one embodiment of the present application at 60°C; Figure 5This is a spot diagram of the medium-wave athermal infrared lens provided in one embodiment of the present application at 60°C; Figure 6 This is the MTF diagram of the medium-wave athermal infrared lens provided in one embodiment of the present application at -40°C; Figure 7 This is a spot diagram of a medium-wave athermal infrared lens provided in one embodiment of the present application at -40°C.

[0017] Description of labels: 11. First lens; 12. Second lens; 13. Third lens; 21. Protective window; 22. Aperture stop; 23. Image plane. DETAILED DESCRIPTION

[0018] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0019] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0021] In order to facilitate understanding of the technical solution of the present application, the number of lenses in a conventional lens applied to a 640×512 detector is explained here: the number of lenses in a conventional lens may be more than 5, which is a relatively large number of lenses.

[0022] Based on this, the present application provides an imaging device comprising a medium-wavelength athermal infrared lens and a detector for receiving images captured by the medium-wavelength athermal infrared lens. The medium-wavelength athermal infrared lens has a focal length of 50mm, an F-number of 4.0, a field of view of 10.9°×8.8°, an operating temperature range of -40°C to 60°C, and an operating wavelength range of 3.7μm to 4.8μm. The detector is a cooled infrared detector with a pixel count of 640×512 and a pixel size of 15μm.

[0023] like Figure 1 As shown, in one embodiment, a medium-wavelength athermal infrared lens comprises a first lens 11, a second lens 12, and a third lens 13, arranged in sequence along the optical axis. Both the first lens 11 and the third lens 13 are positive meniscus lenses with their convex surfaces facing the object side, while the second lens 12 is a negative meniscus lens with its convex surface facing the object side. The air gap between the first lens 11 and the second lens 12 is 7 mm, while the air gap between the second lens 12 and the third lens 13 is 5.66 mm.

[0024] Furthermore, the focal length of the first lens 11 is 45.709 mm, and the optical power is 0.22; the focal length of the second lens 12 is -36.608 mm, and the optical power is -0.027; the focal length of the third lens 13 is 39.85 mm, and the optical power is 0.025.

[0025] Furthermore, the center thickness of the first lens 11 is 4.5 mm, the radius of curvature of the object side surface is 33.36 mm, and the radius of curvature of the image side surface is 43.17 mm; the center thickness of the second lens 12 is 2.5 mm, the radius of curvature of the object side surface is 140.8 mm, and the radius of curvature of the image side surface is 61.16 mm; and the center thickness of the third lens 13 is 2.5 mm, the radius of curvature of the object side surface is 74.66 mm, and the radius of curvature of the image side surface is 320.81 mm.

[0026] It is understandable that Figure 1 For example, the optical axis transmission direction is from left to right, the left side is the object side, and the right side is the image side. For example, the S1 surface of the first lens 11 is the object side surface, and the S2 surface is the image side surface. The same is true for other lenses, which will not be described in detail here. For details, please refer to Table 1 and Table 2.

[0027] Table 1 Lens parameters Table 2 Focal length of each lens As can be seen from Table 1, in a specific embodiment, the first lens 11 and the third lens 13 are both made of silicon glass, and the second lens 12 is made of germanium.

[0028] The above-mentioned medium-wave athermal infrared lens can be applied to a 640×512 detector, and the medium-wave athermal infrared lens only includes three lenses, which simplifies the structure and reduces the cost.

[0029] In one embodiment, the image-side surface of the third lens 13 is an aspheric surface and satisfies the aspheric surface formula: Where Z is the distance from the aspheric surface vertex to the aspheric surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror surface; k is the conic coefficient; A, B, C, and D are the higher-order aspheric coefficients. Additionally, the aspheric surface data for the third lens 13 is shown in Table 3.

[0030] Table 3 Aspheric surface data In one embodiment, the detector includes a protective window 21, an aperture 22, and an image plane 23, arranged sequentially along the optical axis. From left to right, the light beam first passes through the first lens 11, the second lens 12, and the third lens 13, and then passes through the protective window 21 and the aperture 22 to form an image on the image plane 23. In practice, the air gap between the third lens 13 and the protective window 21 is 17.79 mm.

[0031] Furthermore, the total optical length of the imaging device (the distance from the S1 surface of the first lens element 11 to the image plane 23) is 58 mm, and the back focus (the distance from the S6 surface of the third lens element 13 to the image plane 23) is 35.84 mm. This indicates that the imaging device has a short total optical length and a small size, which facilitates a compact design.

[0032] See also Figures 2 to 7 , Figure 2 This is the MTF diagram of the MW athermal infrared lens at 20°C. Figure 3 This is the spot diagram of the MW athermal infrared lens at 20°C; Figure 4 This is the MTF diagram of the MW athermal infrared lens at 60°C. Figure 5 This is the spot diagram of the MW athermal infrared lens at 60°C; Figure 6 This is the MTF diagram of the MW athermal infrared lens at -40℃. Figure 7 This is the spot diagram of the medium-wave athermal infrared lens at -40°C. In the MTF diagram, the horizontal axis represents different spatial frequencies, the vertical axis represents the modulation degree, and the cutoff resolution is 33lp / mm. Figures 2 to 7 It can be seen that the medium-wave athermal infrared lens has good image quality and can adapt to the temperature range of -40℃~60℃.

[0033] In summary, the medium-wavelength athermalized infrared lens provided in this application has an operating band of 3.7μm to 4.8μm, a focal length of 50mm, an F-number of 4.0, a field of view of 10.9°×8.8°, and is suitable for cooled detectors with a pixel count of 640×512 and a pixel size of 15μm. It has a small number of lenses, a simple structure, and produces clear images. Furthermore, this medium-wavelength athermalized infrared lens utilizes the differences in thermal properties of different optical materials. By combining a variety of optical materials with different properties and lens arrangements, it can achieve temperature compensation, thereby realizing an athermal design.

[0034] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A medium-wave athermal infrared lens, characterized in that: The focal length is 50 mm. The medium-wave athermal infrared lens includes a first lens, a second lens, and a third lens arranged in sequence along the optical axis transmission direction. The first lens and the third lens are both positive meniscus lenses with a convex surface facing the object side, and the second lens is a negative meniscus lens with a convex surface facing the object side. An air gap between the first lens and the second lens is 7 mm, and an air gap between the second lens and the third lens is 5.66 mm.

2. The medium-wave athermal infrared lens according to claim 1, characterized in that: The center thickness of the first lens is 4.5 mm, the radius of curvature of the object side is 33.36 mm, and the radius of curvature of the image side is 43.17 mm; the center thickness of the second lens is 2.5 mm, the radius of curvature of the object side is 140.8 mm, and the radius of curvature of the image side is 61.16 mm; the center thickness of the third lens is 2.5 mm, the radius of curvature of the object side is 74.66 mm, and the radius of curvature of the image side is 320.81 mm.

3. The medium-wave athermal infrared lens according to claim 1, characterized in that: The focal length of the first lens is 45.709 mm, and the optical power is 0.22; the focal length of the second lens is -36.608 mm, and the optical power is -0.027; the focal length of the third lens is 39.85 mm, and the optical power is 0.

025.

4. The medium-wave athermal infrared lens according to claim 1, characterized in that: The first lens and the third lens are both made of silicon glass, and the second lens is made of germanium.

5. The medium-wave athermal infrared lens according to claim 1, characterized in that: The image side surface of the third lens is aspherical, satisfying the aspherical surface formula: Among them, Z is the distance vector height from the aspheric surface vertex when the aspheric surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror surface; k is the cone coefficient; A, B, C, and D are high-order aspheric coefficients.

6. The medium-wave athermal infrared lens according to claim 1, characterized in that: The medium-wave athermal infrared lens has an operating band of 3.7 μm to 4.8 μm, an operating temperature of -40°C to 60°C, an F number of 4.0, and a field of view of 10.9°×8.8°.

7. An imaging device, characterized in that: The invention comprises the medium-wave athermal infrared lens according to any one of claims 1 to 6 and a detector for receiving images formed by the medium-wave athermal infrared lens.

8. The imaging device according to claim 7, wherein The number of pixels of the detector is 640×512, the pixel size is 15 μm, and the detector is a refrigerated infrared detector.

9. The imaging device according to claim 7, wherein The total optical length of the imaging device is 58 mm, and the back focus is 35.84 mm.

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