Intermediate wave refrigeration optical system

Abstract

The application discloses a middle-wave refrigeration optical system, and has an optical total length of 110 mm, and comprises a lens and a detector capable of receiving an image formed by the lens. The lens is composed of a first lens, a second lens, a third lens, a fourth lens and a fifth lens arranged in sequence from an object side to an image side. The first lens is a convex moon positive lens with a convex surface facing the object side, the second lens is a convex moon negative lens with a convex surface facing the object side, the third lens is a double-convex lens, the fourth lens is a convex moon negative lens with a convex surface facing the object side, and the fifth lens is a double-convex lens. The optical system has an optical total length of 110 mm, is compact in structure, and is beneficial to the miniaturization design of the optical system.

Description

Technical Field

[0001] This application belongs to the field of infrared optical imaging equipment technology, specifically relating to a mid-wave cooled optical system. Background Technology

[0002] Infrared-cooled ultra-wide-angle optical systems cannot adopt a symmetrical structure like ordinary wide-angle optical systems. To reduce background noise, cooled infrared detectors incorporate a cold stop within their Dewar diaphragms, requiring the optical stop of the infrared optical system to be matched with the detector's cold stop. This makes aberration correction relatively difficult for cooled infrared ultra-wide-angle optical systems. Consequently, there are relatively few patents for infrared ultra-wide-angle optical systems that can be matched with cooled detectors.

[0003] For example, patent CN110161663B discloses a cooled, athermalized infrared fisheye optical system. This system uses two sets of five-element structures to achieve athermalization, giving it a certain degree of temperature adaptability. However, the system's field of view is only 102°, which is relatively small, and the total optical length reaches 148mm, making it relatively large. Summary of the Invention

[0004] Therefore, it is necessary to provide a mid-wave cooled optical system with a large field of view and a small size.

[0005] The technical solution proposed in this application is as follows: A mid-wave cooled optical system with a total optical length of 110 mm includes a lens and a detector capable of receiving the image formed by the lens. The lens is composed of a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially from the object side to the image side. The first lens is a positive meniscus lens with its convex surface facing the object side, the second lens is a negative meniscus lens with its convex surface facing the object side, the third lens is a biconvex lens, and the fourth lens is a negative meniscus lens with its convex surface facing the object side, and the fourth lens is a biconvex lens.

[0006] Furthermore, the air gap between the first lens and the second lens is 2.5 mm, the air gap between the second lens and the third lens is 37 mm, the air gap between the third lens and the fourth lens is 2 mm, and the air gap between the fourth lens and the fifth lens is 21 mm.

[0007] Further, the first lens has a center thickness of 3 mm, an object-side radius of curvature of 85.5 mm, and an image-side radius of curvature of 86.07 mm; the second lens has a center thickness of 3 mm, an object-side radius of curvature of 140.58 mm, and an image-side radius of curvature of 23.877 mm; the third lens has a center thickness of 7.86 mm, an object-side radius of curvature of 53.9 mm, and an image-side radius of curvature of -142.41 mm; the fourth lens has a center thickness of 7.22 mm, an object-side radius of curvature of 149.57 mm, and an image-side radius of curvature of 64.99 mm; and the fifth lens has a center thickness of 7.5 mm, an object-side radius of curvature of 52.59 mm, and an image-side radius of curvature of -68.62 mm.

[0008] Furthermore, the optical power ratio of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens is 520∶1∶2.3∶3.3∶1.4.

[0009] Furthermore, the lens has a focal length of 4.7mm, an F-number of 1, and a field of view of at least 155°.

[0010] Furthermore, the optical system operates at a temperature of -50 to +70°C and in a wavelength range of 3.7 to 4.8 μm.

[0011] Furthermore, the object-side surface of the second lens, all surfaces of the fourth lens, and the object-side surface of the fifth lens are aspherical surfaces, and satisfy 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; A1, A2, A3, A4, A5, and A6 are higher-order aspherical coefficients.

[0012] Furthermore, the optical system follows the following parameter design conditions: Optical power allocation conditions: ; Conditions for eliminating color difference: ; Heat dissipation difference conditions: ; in, The total optical power of the system; The incident height of the first paraxial ray in each lens group; , For each mirror, the optical power and Abbe number are: is the coefficient of linear expansion for each lens group; is the coefficient of linear expansion of the lens barrel; L is the total length of the mechanical structure.

[0013] Furthermore, the first lens is made of sapphire, the second lens is made of silicon, the third lens is made of ZnSe, the fourth lens is made of germanium, and the fifth lens is made of chalcogenide glass.

[0014] Furthermore, the detector has a resolution of 640×512 and a pixel size of 15μm.

[0015] In summary, the mid-wave cooled optical system provided in this application operates in the 3.7μm~4.8μm band, has a focal length of 4.7mm, an F-number of 1, and a field of view of at least 155°. It is also suitable for cooled detectors with a pixel count of 640×512 and a pixel size of 15μm. Furthermore, the system has a total optical length of 110mm, a compact structure, and is beneficial for miniaturization design. In addition, by utilizing the differences in thermal properties of different optical materials and through the combination of various optical materials with different properties and lens arrangement structures, temperature compensation can be achieved, thus realizing a calorimetric design. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is a schematic diagram of the structure of a mid-wave cooling optical system provided in an embodiment of this application; Figure 2 MTF plot of a mid-wave cooled optical system provided in an embodiment of this application at 20°C; Figure 3 MTF plot of a mid-wave cooling optical system provided in an embodiment of this application at -50°C; Figure 4 MTF plot of a mid-wave cooled optical system provided in an embodiment of this application at 70°C; Figure 5 This is a relative illumination diagram of a mid-wave cooled optical system provided in an embodiment of this application.

[0018] Label Explanation: 11. First lens; 12. Second lens; 13. Third lens; 14. Fourth lens; 15. Fifth lens; 21. Protective window; 22. Cold stop; 23. Image plane. Detailed Implementation

[0019] 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.

[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] In one embodiment, this application provides a mid-wave cooled optical system with a total optical length of 110 mm, an operating temperature range of -50 to +70°C, and an operating wavelength range of 3.7 to 4.8 μm. The optical system includes a lens and a detector capable of receiving the image captured by the lens. The lens has a focal length of 4.7 mm, an F-number of 1, and a field of view of at least 155°. The detector has a resolution of 640 × 512, a pixel size of 15 μm, and is a cooled infrared detector.

[0022] like Figure 1 As shown, in one embodiment, the lens comprises a convergence group, a compensation group, and a correction group arranged sequentially from the object side to the image side. The convergence group is used to converge the object-side optical fiber to the compensation group, the compensation group is used to compensate for the offset of the image plane 23, and the correction group is used to correct aberrations generated by the optical system. Specifically, the convergence group consists of a first lens 11 and a second lens 12 arranged sequentially from the object side to the image side. The first lens 11 is a meniscus positive lens with its convex surface facing the object side, and the second lens 12 is a meniscus negative lens with its convex surface facing the object side. The compensation group consists of a third lens 13 and a fourth lens 14 arranged sequentially from the object side to the image side. The third lens 13 is a biconvex lens, and the fourth lens 14 is a meniscus negative lens with its convex surface facing the object side. The correction group consists of a fifth lens 15, which is a biconvex lens.

[0023] It should be explained that in the field of infrared-cooled ultra-wide-angle optical systems, in order to reduce background noise, the cooled infrared detector in the infrared-cooled ultra-wide-angle optical system has a cold stop 22 set inside its Dewar. Therefore, the stop of the infrared optical system needs to be matched with the cold stop 22 of the detector. As a result, the infrared-cooled ultra-wide-angle optical system cannot adopt a symmetrical structure like ordinary wide-angle optical systems. This makes aberration correction of the cooled infrared ultra-wide-angle optical system relatively difficult.

[0024] In view of this, a mid-wave cooled optical system is proposed in this embodiment. Specifically, the system uses the convergence group to converge the ultra-wide-area light from the object side into the compensation group, which can achieve a wide field of view of over 155°. Furthermore, since the lens material undergoes thermal expansion when the temperature changes, the radius of curvature and thickness of the lens change, thereby altering the focal length of the lens. Therefore, the compensation group is set up to compensate for the image plane 23 offset caused by the change in focal length. Finally, the correction group corrects the aberrations generated during the imaging process, avoiding problems such as image blurring, distortion, or reduced resolution. At the same time, in the process of correcting the remaining aberrations, the correction group can compress the spatial envelope of the optical system, shorten the total optical length, and give full play to the unique advantage of the compactness of the optical system.

[0025] In one embodiment, the air gap between the first lens 11 and the second lens 12 is 2.5 mm, the air gap between the second lens 12 and the third lens 13 is 37 mm, the air gap between the third lens 13 and the fourth lens 14 is 2 mm, and the air gap between the fourth lens 14 and the fifth lens 15 is 21 mm.

[0026] Furthermore, the first lens 11 has a center thickness of 3 mm, an object-side radius of curvature of 85.5 mm, and an image-side radius of curvature of 86.07 mm; the second lens 12 has a center thickness of 3 mm, an object-side radius of curvature of 140.58 mm, and an image-side radius of curvature of 23.877 mm; the third lens 13 has a center thickness of 7.86 mm, an object-side radius of curvature of 53.9 mm, and an image-side radius of curvature of -142.41 mm; the fourth lens 14 has a center thickness of 7.22 mm, an object-side radius of curvature of 149.57 mm, and an image-side radius of curvature of 64.99 mm; and the fifth lens 15 has a center thickness of 7.5 mm, an object-side radius of curvature of 52.59 mm, and an image-side radius of curvature of -68.62 mm. Specific parameters can be found in Table 1.

[0027] In one embodiment, the power ratio of the first lens 11, the second lens 12, the third lens 13, the fourth lens 14, and the fifth lens 15 is 520:1:2.3:3.3:1.4. Further, the first lens 11 is made of sapphire, the second lens 12 is made of silicon, the third lens 13 is made of ZnSe, the fourth lens 14 is made of germanium, and the fifth lens 15 is made of chalcogenide glass. The lens also includes a lens barrel for mounting the lenses, the barrel being made of a material with a coefficient of thermal expansion of 23.6 × 10⁻⁶. -6 Aluminum alloy at / ℃.

[0028] Furthermore, to avoid the impact of temperature changes on the image quality of the system, the defocusing amount generated by the lens group must compensate for the mechanical defocusing generated by the lens barrel, so that the total defocusing amount of the system is always controlled within the system's depth of focus range, thereby achieving passive, heat-free optics. Therefore, the optical system follows these parameter design conditions: Optical power allocation conditions: ; Conditions for eliminating color difference: ; Heat dissipation difference conditions: ; in, The total optical power of the system; The incident height of the first paraxial ray in each lens group; , For each mirror, the optical power and Abbe number are: is the coefficient of linear expansion for each lens group; is the coefficient of linear expansion of the lens barrel; L is the total length of the mechanical structure.

[0029] In one embodiment, the detector includes a protective window 21, a cold aperture 22, and an image plane 23 arranged sequentially. Light passes sequentially through a converging group, a compensation group, and a correction group, and then illuminates the image plane 23 through the protective window 21 and the cold aperture 22 to form an image.

[0030] Table 1 Lens Data It should be noted that, in Figure 1 In the illustrated embodiment, taking the first lens 11 as an example, the left surface of the first lens 11 is the object-side surface, with surface number S1, and the right surface is the image-side surface, with surface number S2. Other lenses are similar and will not be described in detail here.

[0031] In one embodiment, the object-side surface of the second lens 12, all surfaces of the fourth lens 14, and the object-side surface of the fifth lens 15 are aspherical surfaces and satisfy 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; A1, A2, A3, A4, A5, and A6 are higher-order aspherical coefficients. Specific parameters can be found in Table 2.

[0032] Table 2 Aspherical Data In one embodiment, the object-side surface of the fifth lens 15 is a composite surface of an aspherical surface and a binary diffraction surface, which satisfies the equation for a binary surface in Zemax: M(B1ρ) 2+B2ρ 4 ); where M is the diffraction order, B1 and B2 are the phase coefficients of the binary surface, and ρ is the normalized radius. The binary surface data are shown in Table 3.

[0033] Table 3 Binary Surface Data Please see Figures 2 to 5 , Figure 2 This is the MTF plot of the optical system at 20℃. Figure 3 This is the MTF plot of the optical system at -50℃. Figure 4 This is the MTF plot of the optical system at 70℃. Figure 5 This is the relative illumination diagram for the optical system. In the MTF plot, the horizontal axis represents different spatial frequencies, the vertical axis represents modulation degree, and the cutoff resolution is 33 lp / mm for all values. Combined with... Figures 2 to 4 It can be seen that the optical system exhibits stable optical transfer function (MTF) over a wide temperature range of -50℃ to 70℃. At room temperature (20℃), the on-axis field of view has an MTF value greater than 0.8 at 33 lp / mm, and the MTF value at the maximum field of view (approximately 78.9° half-field angle) is greater than 0.5. Even at extreme temperatures of -50℃ and 70℃, the on-axis field of view MTF value remains greater than 0.7, and the maximum field of view MTF value is greater than 0.3, indicating that the lens maintains good image quality under wide temperature conditions, effectively overcoming the impact of temperature changes on optical performance. Combined with... Figure 5 It can be seen that, within the entire field of view (157°), the relative illuminance of this optical system uniformly decreases from 1.0 at the center to 0.7 at the edge, with no obvious vignetting and uniform illuminance distribution, effectively overcoming the cosine distortion of ultra-wide-angle lenses. 4 The problem of θ decay.

[0034] In summary, the mid-wave cooled optical system provided in this application operates in the 3.7μm~4.8μm band, has a focal length of 4.7mm, an F-number of 1, and a field of view of at least 155°. It is also suitable for cooled detectors with a pixel count of 640×512 and a pixel size of 15μm. Furthermore, the system has a total optical length of 110mm, a compact structure, and is beneficial for miniaturization design. In addition, by utilizing the differences in thermal properties of different optical materials and through the combination of various optical materials with different properties and lens arrangement structures, temperature compensation can be achieved, thus realizing a calorimetric design.

[0035] 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 cooled optical system, characterized in that, The total optical length is 110mm, including a lens and a detector capable of receiving the image formed by the lens. The lens is composed of a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially from the object side to the image side. The first lens is a positive meniscus lens with its convex surface facing the object side, the second lens is a negative meniscus lens with its convex surface facing the object side, the third lens is a biconvex lens, and the fourth lens is a negative meniscus lens with its convex surface facing the object side, and the fourth lens is a biconvex lens.

2. The mid-wave cooled optical system according to claim 1, characterized in that, The air gap between the first lens and the second lens is 2.5 mm, the air gap between the second lens and the third lens is 37 mm, the air gap between the third lens and the fourth lens is 2 mm, and the air gap between the fourth lens and the fifth lens is 21 mm.

3. The mid-wave cooled optical system according to claim 2, characterized in that, The first lens has a center thickness of 3 mm, an object-side radius of curvature of 85.5 mm, and an image-side radius of curvature of 86.07 mm; the second lens has a center thickness of 3 mm, an object-side radius of curvature of 140.58 mm, and an image-side radius of curvature of 23.877 mm; the third lens has a center thickness of 7.86 mm, an object-side radius of curvature of 53.9 mm, and an image-side radius of curvature of -142.41 mm; the fourth lens has a center thickness of... The thickness of the fifth lens is 7.22mm, the radius of curvature of the object side is 149.57mm, and the radius of curvature of the image side is 64.99mm; the center thickness of the fifth lens is 7.5mm, the radius of curvature of the object side is 52.59mm, and the radius of curvature of the image side is -68.62mm.

4. The mid-wave cooled optical system according to claim 1, characterized in that, The optical power ratio of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens is 520:1:2.3:3.3:1.

4.

5. The mid-wave cooled optical system according to claim 1, characterized in that, The lens has a focal length of 4.7mm, an F-number of 1, and a field of view of at least 155°.

6. The mid-wave cooled optical system according to claim 1, characterized in that, The optical system operates at a temperature of -50 to +70°C and in a wavelength range of 3.7 to 4.8 μm.

7. The mid-wave cooled optical system according to claim 1, characterized in that, The object-side surface of the second lens, all surfaces of the fourth lens, and the object-side surface of the fifth lens are aspherical and satisfy 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; A1, A2, A3, A4, A5, and A6 are higher-order aspherical coefficients.

8. The mid-wave cooled optical system according to claim 1, characterized in that, The optical system is designed according to the following parameters: Optical power allocation conditions: ; Conditions for eliminating color difference: ; Heat dissipation difference conditions: ; in, The total optical power of the system; The incident height of the first paraxial ray in each lens group; , For each mirror, the optical power and Abbe number are: is the coefficient of linear expansion for each lens group; is the coefficient of linear expansion of the lens barrel; L is the total length of the mechanical structure.

9. The mid-wave cooled optical system according to claim 1, characterized in that, The first lens is made of sapphire, the second lens is made of silicon, the third lens is made of ZnSe, the fourth lens is made of germanium, and the fifth lens is made of chalcogenide glass.

10. The mid-wave cooled optical system according to claim 1, characterized in that, The detector has a resolution of 640×512 and a pixel size of 15μm.

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