Athermalization long-wave prime lens and imaging device

Abstract

The invention discloses an athermalization long-wave prime lens which has an effective focal length of 4.5 mm and an F number of 1.0. The athermalization long-wave prime 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 is a negative meniscus lens with the convex face facing the object side, the second lens is a positive meniscus lens with the convex face facing the image side, and the third lens is a biconvex lens. The first lens, the second lens and the third lens are all made of chalcogenide glass; when the temperature of the athermalization long-wave prime lens is 20 DEG C, the air interval between the first lens and the second lens is 6.45 mm, and the air interval between the second lens and the third lens is 8.6 mm. The athermalization long-wave prime lens has the advantages that the number of lenses is small, the structure is simple and compact, all the lenses are made of chalcogenide glass, and the cost is reduced while passive athermalization is achieved. 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 an athermal long-wave fixed-focus lens and an imaging device. Background Art

[0002] Long-wave infrared uncooled optical systems are widely used in both military and civilian fields. These advantages are due to their excellent anti-interference performance, long range at night, strong ability to penetrate smoke and haze, all-weather and all-day operation, and their ability to provide panoramic multi-target observation, tracking, and target recognition, as well as excellent resistance to target stealth. Consequently, increasingly high demands are placed on the imaging quality of these optical systems. Passive athermalization, based on the differences in thermal analysis parameters of optical materials within an optical system, employs a rational combination of materials to compensate for image plane displacement caused by ambient temperature changes, thereby fixing the optimal image plane and achieving an athermal design for the system. However, existing passive athermalization optical systems often utilize relatively expensive germanium lenses. Summary of the Invention

[0003] The technical problem to be solved by the present application is that the existing passive athermalized optical system uses germanium lenses, which is relatively expensive. In order to solve this technical problem, a low-cost athermalized long-wave fixed-focus lens and imaging device are provided.

[0004] The technical solutions proposed in this application are: An athermalized long-wavelength fixed-focus lens having an effective focal length of 4.5 mm and an F-number of 1.0; the athermalized long-wavelength fixed-focus lens comprises a first lens, a second lens, and a third lens arranged in sequence along the optical axis transmission direction; the first lens is a negative meniscus lens with a convex surface facing the object side; the second lens is a positive meniscus lens with a convex surface facing the image side; the third lens is a biconvex lens; and the first, second, and third lenses are all made of chalcogenide glass. Wherein, when the temperature of the athermalized long-wave fixed-focus lens is 20° C., the air gap between the first lens and the second lens is 6.45 mm, and the air gap between the second lens and the third lens is 8.6 mm.

[0005] The above-mentioned athermalized long-wave fixed-focus lens has a small number of lenses, a simple and compact structure, and all lenses are made of chalcogenide glass, which reduces costs while achieving passive athermalization.

[0006] Furthermore, when the temperature of the athermalized long-wave fixed-focus lens is 20° C.: The center thickness of the first lens is 1 mm, the radius of curvature of the object side is 9.16 mm, the aperture is 11 mm, the radius of curvature of the image side is 5.8 mm, and the aperture is 9 mm; the center thickness of the second lens is 1.1 mm, the radius of curvature of the object side is -109.7 mm, the aperture is 9.6 mm, the radius of curvature of the image side is -38.66 mm, and the aperture is 10 mm; the center thickness of the third lens is 2.29 mm, the radius of curvature of the object side is 43.91 mm, the aperture is 12.4 mm, the radius of curvature of the image side is -20.73 mm, and the aperture is 12.4 mm.

[0007] Furthermore, the object-side surface of the first lens, the object-side surface of the second lens, and the object-side surface of the third lens are all aspherical surfaces, 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 Y along the optical axis; 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.

[0008] Furthermore, the image side surface of the third light-transmitting mirror is a diffraction surface and an aperture surface, satisfying the diffraction surface expression:

[0009] Where M is the diffraction order, N is the number of the polynomial coefficients in the series, and A i is the coefficient of ρ raised to the 2ith power, where ρ is the normalized radius.

[0010] Furthermore, the object side surface of the first lens is coated with an HD film, and the image side surface of the first lens and the surfaces of the second lens and the third lens are all coated with an AR film.

[0011] Furthermore, the horizontal field angle range of the athermalized long-wave fixed-focus lens is: 2ω=42°.

[0012] An imaging device comprises the athermalized long-wave fixed-focus lens and a detector for receiving images formed by the athermalized long-wave fixed-focus lens.

[0013] Furthermore, the number of pixels of the detector is 384×288, the pixel size is 12 μm, and the detector is a non-cooled detector.

[0014] Furthermore, the total optical length of the imaging device is 29.94 mm, and the back focus is 10.5 mm. 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 a spot diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at -40°C; Figure 3 This is the MTF graph of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at -40°C; Figure 4 This is a field curvature distortion diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at -40°C; Figure 5 This is a spot diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 80°C; Figure 6 This is the MTF diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 80°C; Figure 7 This is a diagram of field curvature distortion of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 80°C; Figure 8 This is a spot diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 20°C; Figure 9 This is the MTF diagram of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 20°C; Figure 10 This is a diagram of the field curvature distortion of the athermalized long-wavelength fixed-focus lens provided in one embodiment of the present application at 20°C.

[0017] Description of labels: 11. First lens; 12. Second lens; 13. Third lens; 100. Protective window; 101. 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] The present application provides an imaging device comprising an athermalized long-wavelength fixed-focus lens and a detector for receiving images captured by the athermalized long-wavelength fixed-focus lens. The athermalized long-wavelength fixed-focus lens has an effective focal length of 4.5 mm, an F-number of 1.0, and a horizontal field of view of 2ω = 42°. The detector is an uncooled detector with 384 × 288 pixels and a pixel size of 12 μm.

[0022] like Figure 1 As shown, in one embodiment, an athermalized long-wavelength fixed-focus lens includes a first lens, a second lens, and a third lens arranged sequentially along the optical axis. The first lens is a negative meniscus lens with its convex surface facing the object side, the second lens is a positive meniscus lens with its convex surface facing the image side, and the third lens is a biconvex lens. The first, second, and third lenses are all made of chalcogenide glass. When the temperature of the athermalized long-wavelength fixed-focus lens is 20°C, the air gap between the first and second lenses is 6.45 mm, and the air gap between the second and third lenses is 8.6 mm.

[0023] Furthermore, when the temperature of the athermalized long-wave fixed-focus lens is 20°C: the center thickness of the first lens is 1 mm, the radius of curvature of the object side is 9.16 mm, the aperture of the object side is 11 mm, the radius of curvature of the image side is 5.8 mm, and the aperture of the image side is 9 mm; the center thickness of the second lens is 1.1 mm, the radius of curvature of the object side is -109.7 mm, the aperture of the object side is 9.6 mm, the radius of curvature of the image side is -38.66 mm, and the aperture of the image side is 10 mm; the center thickness of the third lens is 2.29 mm, the radius of curvature of the object side is 43.91 mm, the aperture of the object side is 12.4 mm, the radius of curvature of the image side is -20.73 mm, and the aperture of the image side is 12.4 mm.

[0024] In one embodiment, the detector includes a protective window and an image plane, arranged sequentially along the optical axis. The light beam passes from left to right through the first, second, and third lenses, and then through the protective window, forming an image on the image plane. In practice, the air gap between the third lens and the protective window is 7.65 mm. The protective window is 0.7 mm thick and made of germanium. The air gap between the protective window and the image plane is 2.15 mm.

[0025] In one embodiment, the imaging device has an overall optical length (the distance from the S1 surface of the first lens element to the image plane) of 29.94 mm, and a back focus (the distance from the S6 surface of the third lens element to the image plane) of 10.5 mm. This imaging device exhibits a short overall optical length, a compact structure, and a small size, facilitating a miniaturized device design.

[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 is the object side surface, and the S2 surface is the image side surface. The same is true for other lenses. I will not go into details here. For details, please refer to Table 1.

[0027] Table 1 Lens parameters

[0028] The above-mentioned athermalized long-wave fixed-focus lens has a small number of lenses, a simple and compact structure, and all lenses are made of chalcogenide glass, which reduces costs while achieving passive athermalization.

[0029] In one embodiment, the object-side surface of the first lens, the object-side surface of the second lens, and the object-side surface of the third lens are all aspherical surfaces and satisfy the aspherical surface formula: Where Z is the distance from the aspheric surface vertex to the aspheric surface at a height Y along the optical axis; R is the paraxial curvature fitting radius of the mirror surface; K is the conic coefficient; A, B, C, D, and E are the higher-order aspheric coefficients. In addition, the data of each aspheric surface is shown in Table 2.

[0030] Table 2 Aspheric surface data

[0031] In one embodiment, the image-side surface of the third light-transmitting mirror is a diffraction surface and an aperture surface, satisfying the diffraction surface expression:

[0032] Where M is the diffraction order, N is the number of the polynomial coefficients in the series, and A i is the coefficient of ρ raised to the 2ith power, and ρ is the normalized radius. In addition, the diffraction coefficients are shown in Table 3.

[0033] Table 3 Diffraction coefficient

[0034] In one embodiment, the object side of the first lens is coated with an HD film to improve light transmittance, reduce glare and ghosting while providing certain physical protection; the image side of the first lens and the surfaces of the second and third lenses are coated with an AR film to reduce reflections and increase light transmittance while providing certain physical protection, thereby improving imaging quality.

[0035] See also Figures 2 to 10 , Figure 2 is the spot diagram of the athermalized long-wave fixed-focus lens at -40°C. Figure 3 This is the MTF diagram of the athermalized long-wave fixed-focus lens at -40°C. Figure 4 This is the field curvature distortion diagram of the athermalized long-wavelength fixed-focus lens at -40°C; Figure 5 is the spot diagram of the athermalized long-wave fixed-focus lens at 80°C. Figure 6 This is the MTF diagram of the athermalized long-wave fixed-focus lens at 80°C. Figure 7 This is the field curvature distortion diagram of the athermalized long-wavelength fixed-focus lens at 80°C; Figure 8 is the spot diagram of the athermalized long-wave fixed-focus lens at 20°C, Figure 9 This is the MTF diagram of the athermalized long-wave fixed-focus lens at 20°C. Figure 10 This is the field curvature distortion diagram of the athermalized long-wave fixed focus lens at 20°C. In the MTF diagram, the horizontal axis represents different spatial frequencies and the vertical axis represents the modulation degree. Figures 2 to 10 It can be seen that the image quality of this athermalized long-wave fixed-focus lens is very good and it can adapt to the temperature range of -40℃~80℃.

[0036] In summary, the athermal long-wave fixed-focus lens provided by this application has an effective focal length of 4.5mm, an F number of 1.0, and a horizontal field of view angle range satisfying 2ω=42°. It is suitable for non-cooled detectors with a pixel count of 384×288 and a pixel size of 12μm. It has a small number of lenses, a simple structure, and clear imaging. At the same time, the imaging device has a total optical length of 29.94mm and a back focus of 10.5mm. It has a compact structure, light weight, and the focal length is less affected by temperature. Combined with the differences in thermal properties of different optical materials, temperature compensation can be achieved through the coordination of a variety of optical materials with different characteristics and lens arrangement structures to ensure the stability of the optical axis during temperature changes, thereby achieving an athermal design.

[0037] 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. An athermalized long-wavelength fixed-focus lens, characterized in that: The effective focal length is 4.5 mm, and the F number is 1.

0. The athermalized long-wave fixed-focus lens includes a first lens, a second lens, and a third lens arranged in sequence along the optical axis transmission direction. The first lens is a negative meniscus lens with a convex surface facing the object side, the second lens is a positive meniscus lens with a convex surface facing the image side, and the third lens is a biconvex lens. The first, second, and third lenses are all made of chalcogenide glass. Wherein, when the temperature of the athermalized long-wave fixed-focus lens is 20° C., the air gap between the first lens and the second lens is 6.45 mm, and the air gap between the second lens and the third lens is 8.6 mm.

2. The athermalized long-wavelength fixed-focus lens according to claim 1, wherein: When the temperature of the athermalized long-wave fixed-focus lens is 20°C: The center thickness of the first lens is 1 mm, the radius of curvature of the object side is 9.16 mm, the aperture is 11 mm, the radius of curvature of the image side is 5.8 mm, and the aperture is 9 mm; the center thickness of the second lens is 1.1 mm, the radius of curvature of the object side is -109.7 mm, the aperture is 9.6 mm, the radius of curvature of the image side is -38.66 mm, and the aperture is 10 mm; the center thickness of the third lens is 2.29 mm, the radius of curvature of the object side is 43.91 mm, the aperture is 12.4 mm, the radius of curvature of the image side is -20.73 mm, and the aperture is 12.4 mm.

3. The athermalized long-wavelength fixed-focus lens according to claim 1, wherein: The object-side surface of the first lens, the object-side surface of the second lens, and the object-side surface of the third lens are all aspherical surfaces, 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 Y along the optical axis; 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.

4. The athermalized long-wavelength fixed-focus lens according to claim 1, wherein: The image side surface of the third light-transmitting mirror is a diffraction surface and an aperture surface, which satisfies the diffraction surface expression: Where M is the diffraction order, N is the number of the polynomial coefficients in the series, and A i is the coefficient of ρ raised to the 2ith power, where ρ is the normalized radius.

5. The athermalized long-wavelength fixed-focus lens according to claim 1, wherein: The object side surface of the first lens is coated with an HD film, and the image side surface of the first lens and the surfaces of the second lens and the third lens are all coated with an AR film.

6. The athermalized long-wavelength fixed-focus lens according to claim 1, wherein: The horizontal field angle range of the athermal long-wave fixed-focus lens is: 2ω=42°.

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

8. The imaging device according to claim 7, wherein The number of pixels of the detector is 384×288, the pixel size is 12 μm, and the detector is a non-cooling detector.

9. The imaging device according to claim 7, wherein The total optical length of the imaging device is 29.94 mm, and the back focus is 10.5 mm.

Images