A middle wave athermal infrared lens and an imaging device

Abstract

The application discloses a middle-wave athermal infrared lens with a focal length of 50 mm, which comprises a first lens, a second lens and a third lens arranged in sequence along the transmission direction of the optical axis, wherein the first lens and the third lens are both convex moon positive lenses with the convex surface facing the object side, and the second lens is a convex moon negative lens with the convex surface facing the object side; the air gap between the first lens and the second lens is 7 mm, and the air gap between the second lens and the third lens is 5.66 mm. The middle-wave athermal infrared lens can be applied to a refrigeration type detector with 640*512 pixels and a pixel size of 15 microns, has a small number of lenses, a simple structure and clear imaging. The application further discloses an imaging device.

Description

Technical Field

[0001] This application belongs to the field of infrared lens technology, specifically relating to a mid-wave thermally ablated infrared lens and imaging device. Background Technology

[0002] With the continuous advancement of focal plane technology, the pixel scale of the focal plane is constantly increasing while the pixel size is constantly decreasing. This means that the optical system can effectively increase the field of view while maintaining the same focal length.

[0003] For example, compared to a 320×256 detector, a 640×512 pixel detector not only acquires high-definition images but also doubles the field of view while maintaining the same focal length. However, traditional lenses used in 640×512 detectors typically employ 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 traditional lenses used in 640×512 detectors have a large number of lenses. To solve this technical problem, a mid-wave thermally ablated differential infrared lens and imaging device that can be used in 640×512 detectors and has a smaller number of lenses is provided.

[0005] The technical solution proposed in this application is as follows: A mid-wave pyrometric infrared lens with a focal length of 50mm includes a first lens, a second lens, and a third lens arranged sequentially along the optical axis. The first lens and the third lens are both positive meniscus lenses with their convex surfaces facing the object side, and the second lens is a negative meniscus lens with its convex surfaces facing the object side. The air gap between the first lens and the second lens is 7 mm, and the air gap between the second lens and the third lens is 5.66 mm.

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

[0007] Furthermore, the first lens has a focal length of 45.709 mm and an optical power of 0.022; the second lens has a focal length of -36.608 mm and an optical power of -0.027; and the third lens has a focal length of 39.85 mm and an optical power of 0.025.

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

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

[0010] Furthermore, the operating wavelength of the mid-wave thermally ablated differential infrared lens is 3.7μm~4.8μm, the operating temperature is -40℃~60℃, the F number is 4.0, and the field of view is 10.9°×8.8°.

[0011] An imaging device includes the aforementioned mid-wave athermalized infrared lens and a detector for receiving images from the mid-wave athermalized infrared lens.

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

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

[0014] The aforementioned mid-wave pyrometric infrared lens can be applied to a 640×512 detector. Moreover, this mid-wave pyrometric infrared lens only includes three lenses, which simplifies the structure and reduces costs due to the small number of lenses. Attached Figure Description

[0015] The accompanying drawings are provided to further understand this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof.

[0016] Figure 1 This is a schematic diagram of the optical path of an imaging device provided in an embodiment of this application; Figure 2 MTF image of a mid-wave thermally ablated differential infrared lens at 20°C, provided in an embodiment of this application; Figure 3 A dot plot of a mid-wave thermally ablation differential infrared lens provided in an embodiment of this application at 20°C; Figure 4 MTF diagram of a mid-wave thermally ablated differential infrared lens at 60°C, provided in an embodiment of this application; Figure 5 A dot plot of a mid-wave thermally ablated differential infrared lens at 60°C, provided in an embodiment of this application; Figure 6 MTF plot of a mid-wave thermally ablated differential infrared lens provided in an embodiment of this application at -40°C; Figure 7 A dot plot of a mid-wave thermally ablation differential infrared lens provided in an embodiment of this application at -40°C.

[0017] Label Explanation: 11. First lens; 12. Second lens; 13. Third lens; 21. Protective window; 22. Aperture stop; 23. Image plane. Detailed Implementation

[0018] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0019] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] To facilitate understanding of the technical solution of this application, the number of lenses in a conventional lens used with a 640×512 detector is explained here: the conventional lens may have more than 5 lenses, which is a relatively large number of lenses.

[0022] Based on this, this application provides an imaging device, which includes a mid-wave thermochromic infrared lens and a detector for receiving the image captured by the mid-wave thermochromic infrared lens. The mid-wave thermochromic 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 of -40℃ to 60℃, and an operating wavelength of 3.7μm to 4.8μm. The detector is a cooled infrared detector with 640×512 pixels and a pixel size of 15μm.

[0023] like Figure 1 As shown, in one embodiment, the mid-wave thermally ablated differential infrared lens includes a first lens 11, a second lens 12, and a third lens 13 arranged sequentially along the optical axis transmission direction. The first lens 11 and the third lens 13 are both meniscus positive lenses with their convex surfaces facing the object side, and the second lens 12 is a meniscus negative lens with its convex surfaces facing the object side; the air gap between the first lens 11 and the second lens 12 is 7 mm, and the air gap between the second lens 12 and the third lens 13 is 5.66 mm.

[0024] Furthermore, the first lens 11 has a focal length of 45.709 mm and an optical power of 0.022; the second lens 12 has a focal length of -36.608 mm and an optical power of -0.027; and the third lens 13 has a focal length of 39.85 mm and an optical power of 0.025.

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

[0026] Understandably, with Figure 1 For example, the optical axis direction is from left to right, with the left side being the object side and the right side being the image side. For instance, the S1 surface of the first lens 11 is the object side surface and the S2 surface is the image side surface. The same applies to other lenses, which will not be elaborated here. For details, please refer to Table 1 and Table 2.

[0027] Table 1 Parameters of each lens Table 2 Focal length of each lens As can be seen from Table 1, in one 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 aforementioned mid-wave pyrometric infrared lens can be applied to a 640×512 detector. Moreover, this mid-wave pyrometric infrared lens only includes three lenses, which simplifies the structure and reduces costs due to the small number of lenses.

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

[0030] Table 3 Aspherical 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. The light beam passes sequentially from left to right through a first lens 11, a second lens 12, and a third lens 13, and then sequentially through the protective window 21 and the aperture 22 to form an image on the image plane 23. In practical applications, 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 11 to the image plane 23) is 58 mm, and the back clipping (the distance from the S6 surface of the third lens 13 to the image plane 23) is 35.84 mm. It can be determined that the imaging device has a short total optical length and a small size, which is beneficial for achieving miniaturized design of the device.

[0032] Please see Figures 2 to 7 , Figure 2 This is the MTF plot of the mid-wave thermally ablated differential infrared lens at 20℃. Figure 3 This is a dot plot of the mid-wave thermally ablated differential infrared lens at 20℃; Figure 4 This is the MTF plot of the mid-wave thermally ablated differential infrared lens at 60℃. Figure 5 This is a dot plot of the mid-wave thermally ablated differential infrared lens at 60℃; Figure 6 This is the MTF plot of the mid-wave thermally ablated differential infrared lens at -40℃. Figure 7 This is a dot plot of the mid-wave pyrometric infrared lens at -40℃. In the MTF plot, the horizontal axis represents different spatial frequencies, the vertical axis represents modulation density, and the cutoff resolution is 33 lp / mm for all values. Combined with... Figures 2 to 7 It can be seen that the mid-wave thermal differential infrared lens has excellent image quality and can adapt to a temperature range of -40℃ to 60℃.

[0033] In summary, the mid-wave thermal differential infrared lens provided in this application operates in the 3.7μm~4.8μm band, has a focal length of 50mm, an F-number of 4.0, and a field of view of 10.9°×8.8°. It 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 mid-wave thermal differential infrared lens utilizes the differences in thermal properties of different optical materials. Through the combination of various optical materials with different properties and the arrangement of the lenses, temperature compensation can be achieved, thus realizing a thermal-free design.

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

Claims

1. A mid-wave thermally ablated differential infrared lens, characterized in that, With a focal length of 50mm, the mid-wave thermally ablated infrared lens is composed of a first lens, a second lens, and a third lens arranged sequentially along the optical axis. The first lens and the third lens are both positive meniscus lenses with their convex surfaces facing the object side, and the second lens is a negative meniscus lens with its convex surfaces facing the object side. The air gap between the first lens and the second lens is 7 mm, and the air gap between the second lens and the third lens is 5.66 mm. The first lens has a center thickness of 4.5 mm, an object-side radius of curvature of 33.36 mm, and an image-side radius of curvature of 43.17 mm; the second lens has a center thickness of 2.5 mm, an object-side radius of curvature of 140.8 mm, and an image-side radius of curvature of 61.16 mm; the third lens has a center thickness of 2.5 mm, an object-side radius of curvature of 74.66 mm, and an image-side radius of curvature of 320.81 mm.

2. The mid-wave thermally ablated differential infrared lens according to claim 1, characterized in that, The first lens has a focal length of 45.709 mm and an optical power of 0.022; the second lens has a focal length of -36.608 mm and an optical power of -0.027; and the third lens has a focal length of 39.85 mm and an optical power of 0.

025.

3. The mid-wave thermally ablated differential infrared lens according to claim 1, characterized in that, The first lens and the third lens are both made of silicon glass, while the second lens is made of germanium.

4. The mid-wave thermally ablated differential infrared lens according to claim 1, characterized in that, The image-side surface of the third lens is aspherical, satisfying the aspherical formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, and D are higher-order aspherical coefficients.

5. The mid-wave thermally ablated differential infrared lens according to claim 1, characterized in that, The mid-wave thermal differential infrared lens operates in the wavelength range of 3.7μm to 4.8μm, has an operating temperature range of -40℃ to 60℃, an F-number of 4.0, and a field of view of 10.9° × 8.8°.

6. An imaging device, characterized in that, It includes the mid-wave athermalized infrared lens as described in any one of claims 1-5 and the detector that receives the image from the mid-wave athermalized infrared lens.

7. The imaging apparatus according to claim 6, characterized in that, The detector has 640×512 pixels, a pixel size of 15μm, and is a cooled infrared detector.

8. The imaging apparatus according to claim 6, characterized in that, The imaging device has an optical length of 58 mm and a back cutoff of 35.84 mm.

Images