Compact secondary imaging type medium-wave infrared optical imaging system
The compact mid-wave infrared optical imaging system designed with 7 lenses solves the problems of large size and many lenses in the mid-wave infrared imaging system, achieving high-quality imaging and stable work in a wide temperature range, reducing costs.
Patent Information
- Application Number
- CN202422369841.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-27
- Publication Date
- 2025-07-08
- Estimated Expiration
- 2034-09-27
AI Technical Summary
The existing mid-wave infrared imaging system has large size, many lenses, low imaging quality, and narrow operating temperature range, which limits its use scenarios and increases deployment costs.
It adopts a 7-piece lens design, including three front and four rear lenses, combined with even aspherical and folded hybrid lenses, and is designed with a compact optical system, which is applicable to a wide temperature range and high imaging quality.
The system is designed with a compact design, and the imaging quality is improved, and the temperature range is extended to -40℃ to 60℃, reducing production costs and maintaining high image quality over a wide temperature range.
Smart Images
Figure CN223078539U_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of optical technology, and particularly to a compact secondary imaging mid-wave infrared optical imaging system. Background Art
[0002] As an extension and expansion of human visual ability, infrared imaging technology is of great significance for application scenarios such as all-weather monitoring, remote sensing mapping, and non-contact temperature measurement systems. Based on the characteristics and properties of the images formed by the system, the design of mid-wave infrared optical imaging systems is often restricted by factors such as materials, system geometric dimensions, the specifications of the infrared detection module matched with it, and environmental temperature, etc. When ensuring that the image quality meets the indicators, the geometric dimensions of mid-wave infrared imaging systems are often large, the number of lenses is large, the aperture is small, and the operating temperature range of the system is narrow. Existing solutions often choose to design the total length and aperture of the system to be large or use a large number of lenses. The former leads to too large component dimensions of the system, making manufacturing and assembly and debugging difficult, and the latter leads to low transmittance of the system, obvious ghost images, etc. This undoubtedly limits the usage scenarios of the system and significantly increases the cost of deploying the system. Summary of the Invention
[0003] To solve the problems of large size, many lenses, and low imaging quality of infrared imaging systems in the prior art, a compact secondary imaging mid-wave infrared optical imaging system is provided. This system performs optical imaging through 7 lenses, has a small geometric size, a large aperture, a wide applicable temperature range, and high imaging quality.
[0004] A compact secondary imaging mid-wave infrared optical imaging system includes 7 lenses and a detector module.
[0005] The 7 lenses sequentially include, from the object side to the imaging plane along the system optical axis: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens; the detector module sequentially includes, from the object side to the imaging plane along the system optical axis: a detector window, a cold stop, a germanium filter, and a detector rear focal plane.
[0006] The first lens has a positive optical power; the second lens has a negative optical power; the third lens is a positive meniscus lens with a positive optical power; the fourth lens is a positive meniscus lens with a positive optical power; the fifth lens is a negative meniscus lens with a negative optical power; the sixth lens is a negative meniscus lens with a positive optical power; the seventh lens has a positive optical power.
[0007] The incident light converges 2 mm before the fourth lens after passing through the first lens, the second lens, and the third lens in sequence, and then passes through the fourth lens, the fifth lens, the sixth lens, the seventh lens, the detector window, the cold stop, and the germanium filter in sequence, and is imaged on the detector rear focal plane.
[0008] Advantageous Effects
[0009] The present application provides a compact secondary imaging mid-wave infrared optical imaging system, specifically a secondary imaging mid-wave infrared optical imaging system with high contrast and low distortion at the secondary image plane and a working temperature range from -40°C to +60°C. The focal length of this system is 80 mm and its structure is compact. The system consists of seven lenses, divided into two groups. The front group is composed of three lenses, designed with a relatively large aperture and large curvature, aiming to obtain a relatively large image-side numerical aperture at the primary image plane, thereby compressing the overall geometric size of the system. The rear group is composed of four lenses, which play the role of secondary imaging and reducing higher-order spherical aberration, distortion, and chromatic dispersion.
[0010] The total length and the maximum aperture of the system are respectively controlled within 180 mm and 60 mm, and only seven lenses are used, with a compact structure, which makes up for the defects of the existing technical solutions to a certain extent. Moreover, due to the relatively small geometric structure, the production cost of the system is also well controlled. Some lens surfaces are designed with even aspheres, significantly reducing various higher-order aberrations, such that the modulation transfer function @42 lp / mm at the secondary image plane within the field of view of 2ω = 6° is greater than 0.1 at -40°C to 60°C (temperature sampling interval is 20°C), and the distortion is less than ±0.055% within the field of view of 2ω = 6°. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 It is a schematic structural diagram of a compact secondary imaging mid-wave infrared optical imaging system according to a specific embodiment of the present application;
[0012] Figure 2 It is a MTF curve graph of a compact secondary imaging mid-wave infrared optical imaging system according to a specific embodiment of the present application at different temperatures;
[0013] Figure 3 It is a graph of the change of distortion of a compact secondary imaging mid-wave infrared optical imaging system according to a specific embodiment of the present application with the field of view. SPECIFIC EMBODIMENTS
[0014] The following will be combined with Figures 1 to 3 , to illustrate this embodiment; a compact secondary imaging mid-wave infrared optical imaging system includes seven lenses and a detector module;
[0015] The seven lenses include, in sequence along the optical axis of the system from the object side to the imaging plane: the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7; the detector module includes, in sequence along the optical axis of the system from the object side to the imaging plane: the detector window P1, the cold stop STO, the germanium filter P2, and the detector rear focal plane IMA;
[0016] The first lens L1 has a positive focal power, and its object side is convex; the second lens L2 has a negative focal power, and its object side is concave; the third lens L3 is a positive meniscus lens with a positive focal power; the fourth lens L4 is a positive meniscus lens with a positive focal power, and its object side is concave; the fifth lens L5 is a negative meniscus lens with a negative focal power; the sixth lens L6 is a negative meniscus lens with a positive focal power; the seventh lens L7 has a positive focal power, and its image side is convex;
[0017] The incident light converges 2 mm in front of the fourth lens L4 after passing through the first lens L1, the second lens L2, and the third lens L3, and then passes through the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, the detector window P1, the cold stop STO, and the germanium filter P2, and forms an image on the detector rear focal plane IMA.
[0018] Specifically, as Figure 1 shown, the first lens L1, the second lens L2, and the third lens L3 form the front lens group, and the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 form the rear lens group; the front group consists of three lenses and adopts a design with a larger aperture and a larger curvature, aiming to obtain a larger image-side numerical aperture at the first image plane, thereby reducing the overall geometric size of the system; the rear group consists of four lenses, which play the role of secondary imaging and reducing higher-order spherical aberration, distortion, and chromatic aberration.
[0019] Furthermore, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are even aspherical lenses, and the sixth lens L6 is a diffractive-refractive hybrid lens.
[0020] Furthermore, the aperture of the cold stop STO is 12.300 mm; the size of the detector rear focal plane IMA is 12.288 mm × 12.288 mm.
[0021] Furthermore, both the germanium filter P2 and the detector window IMA are zero-focal-power flats, and the germanium filter P2 and the detector window IMA are arranged in parallel with each other.
[0022] Furthermore, the surfaces of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are all coated with infrared antireflection films, and the average transmittance of the seven lenses is greater than or equal to 99%.
[0023] Further, the first front surface S1 and the first rear surface S2 of the first lens are both spherical surfaces; the second front surface S3 of the second lens is a spherical surface, and the second rear surface S4 of the second lens is an aspherical surface; the third front surface S5 of the third lens is an aspherical surface, and the third rear surface S6 of the third lens is a spherical surface; the fourth front surface S7 of the fourth lens is a spherical surface, and the fourth rear surface S8 of the fourth lens is an aspherical surface; the fifth front surface S9 of the fifth lens is a spherical surface, and the fifth rear surface S10 of the fifth lens is an aspherical surface; the sixth front surface S11 of the sixth lens is a binary diffractive spherical surface, and the sixth rear surface S12 of the sixth lens is a spherical surface; the seventh front surface S13 and the seventh rear surface S14 of the seventh lens are both spherical surfaces.
[0024] Further, the thickness of the first lens L1 is 4.143 mm, the radius of curvature of the first front surface S1 is 126.862 mm, the radius of curvature of the first rear surface S2 is 1922.569 mm, and the distance between the first rear surface S2 and the second front surface S3 is 0.999 mm; the thickness of the second lens L2 is 1.998 mm, the radius of curvature of the second front surface S3 is 4024.611 mm, the radius of curvature of the second rear surface S4 is 149.92 mm, and the distance between the second rear surface S4 and the third front surface S5 is 1.006 mm; the thickness of the third lens L3 is 12.968 mm, the radius of curvature of the third front surface S5 is 58.863 mm, the radius of curvature of the third rear surface S6 is 326.518 mm, and the distance between the third rear surface S6 and the fourth front surface S7 is 46.33 mm; the thickness of the fourth lens L4 is 9.015 mm, the radius of curvature of the fourth front surface S7 is -9.967 mm, the curvature of the fourth rear surface S8 is -14.864 mm, and the distance between the fourth rear surface S8 and the fifth front surface S9 is 20.32 mm; the thickness of the fifth lens L5 is 11.833 mm, the radius of curvature of the fifth front surface S9 is -77.638 mm, the radius of curvature of the fifth rear surface S10 is -99.942 mm, and the distance between the fifth rear surface S10 and the sixth front surface S11 is 3.864 mm; the thickness of the sixth lens L6 is 1.998 mm, the radius of curvature of the sixth front surface S11 is 91.276 mm, the radius of curvature of the sixth rear surface S12 is 246.527 mm, and the distance between the sixth rear surface S12 and the seventh front surface S13 is 0.996 mm; the thickness of the seventh lens L7 is 5.261 mm, the radius of curvature of the seventh front surface S13 is 62.886 mm, the radius of curvature of the seventh rear surface S14 is -57.828 mm, and the distance between the seventh rear surface S14 and the front surface of the detector window is 4.919 mm; the thickness of the detector window P1 is 2.5 mm, the front and rear surfaces of the germanium filter P2 are both flat, the curvatures of the front and rear surfaces of the germanium filter P2 are both 0, the distance between the rear surface of the detector window P1 and the cold stop STO is 1.85 mm; the distance between the cold stop STO and the front surface of the germanium filter P2 is 25.2 mm; the thickness of the germanium filter P2 is 0.8 mm, the front and rear surfaces of the germanium filter P2 are both flat, the curvatures of the front and rear surfaces of the germanium filter are both 0, and the distance between the rear surface of the germanium filter P2 and the detector rear focal plane IMA is 4 mm.
[0025] Further, the first lens L1 and the fourth lens L4 are lenses made of silicon; the second lens L2 and the sixth lens L6 are lenses made of germanium; the third lens L3 and the seventh lens L7 are lenses made of zinc selenide; the fifth lens L5 is a lens made of sapphire.
[0026] Furthermore, the system focal length is 81.25 mm, the field of view 2ω = 6°, and the image space F-number is 1.65. The image space F-number is the ratio of the paraxial effective focal length conjugated to infinity to the paraxial entrance pupil diameter.
[0027] The system uses a binary lens and reasonably selects the lens and barrel materials, achieving achromatic aberration correction and athermalization design of the optical system, and realizing high-quality imaging in the temperature range of -40°C to 60°C. Figure 2 It is the MTF curve graph of a compact secondary imaging mid-wave infrared optical imaging system in six configurations (temperature sampling interval is 20°C) of the specific embodiment of this application from -40°C to 60°C. It can be seen from the figure that the MTF@42lp / mm of the system in each configuration is greater than 0.1, and the fluctuation is small when the temperature changes. The system can operate stably below -40°C to 60°C.
[0028] Figure 3 It is the graph of the change of distortion of a compact secondary imaging mid-wave infrared optical imaging system in the specific embodiment of this application with the field of view. It can be seen from the figure that the maximum distortion of the system is 0.055%.
[0029] The present invention provides a compact secondary imaging mid-wave infrared optical imaging system. The system design is carried out by using the secondary imaging method, so that the cold stop efficiency of the system reaches 100%, and the vignetting coefficient of the full field of view (2ω = 6°) is 1; the use of multiple aspherical surfaces ensures the high image quality of the imaging system, meeting the requirement of stable operation of the system in a wide temperature range.
Claims
1. A compact secondary imaging mid-wave infrared optical imaging system, characterized in that: It includes seven lenses and a detector module; The seven lenses, along the system optical axis from the object side to the imaging plane, sequentially include: a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens; the detector module, along the system optical axis from the object side to the imaging plane, sequentially includes: a detector window, a cold stop, a germanium filter, and a detector rear focal plane; The first lens has a positive focal power; the second lens has a negative focal power; the third lens is a positive meniscus lens with a positive focal power; the fourth lens is a positive meniscus lens with a positive focal power; the fifth lens is a negative meniscus lens with a negative focal power; the sixth lens is a negative meniscus lens with a positive focal power; the seventh lens has a positive focal power; The incident light converges 2 mm before the fourth lens after passing through the first lens, the second lens, and the third lens in sequence, and then passes through the fourth lens, the fifth lens, the sixth lens, the seventh lens, the detector window, the cold stop, and the germanium filter in sequence, and is imaged on the detector rear focal plane.
2. The compact secondary imaging mid-wave infrared optical imaging system according to claim 1, characterized in that: The first front surface and the first rear surface of the first lens are both spherical surfaces; the second front surface of the second lens is a spherical surface, and the second rear surface of the second lens is an aspherical surface; the third front surface of the third lens is an aspherical surface, and the third rear surface of the third lens is a spherical surface; the fourth front surface of the fourth lens is a spherical surface, and the fourth rear surface of the fourth lens is an aspherical surface; the fifth front surface of the fifth lens is a spherical surface, and the fifth rear surface of the fifth lens is an aspherical surface; the sixth front surface of the sixth lens is a binary diffractive spherical surface, and the sixth rear surface of the sixth lens is a spherical surface; the seventh front surface and the seventh rear surface of the seventh lens are both spherical surfaces.
3. The compact secondary imaging mid-wave infrared optical imaging system according to claim 2, characterized in that: The thickness of the first lens is 4.143 mm, the radius of curvature of the first front surface is 126.862 mm, the radius of curvature of the first rear surface is 1922.569 mm, and the distance between the first rear surface and the second front surface is 0.999 mm; the thickness of the second lens is 1.998 mm, the radius of curvature of the second front surface is 4024.611 mm, the radius of curvature of the second rear surface is 149.92 mm, and the distance between the second rear surface and the third front surface is 1.006 mm; the thickness of the third lens is 12.968 mm, the radius of curvature of the third front surface is 58.863 mm, the radius of curvature of the third rear surface is 326.518 mm, and the distance between the third rear surface and the fourth front surface is 46.33 mm; the thickness of the fourth lens is 9.015 mm, the radius of curvature of the fourth front surface is -9.967 mm, the curvature of the fourth rear surface is -14.864 mm, and the distance between the fourth rear surface and the fifth front surface is 20.32 mm; the thickness of the fifth lens is 11.833 mm, the radius of curvature of the fifth front surface is -77.638 mm, the radius of curvature of the fifth rear surface is -99.942 mm, and the distance between the fifth rear surface and the sixth front surface is 3.864 mm; the thickness of the sixth lens is 1.998 mm, the radius of curvature of the sixth front surface is 91.276 mm, the radius of curvature of the sixth rear surface is 246.527 mm, and the distance between the sixth rear surface and the seventh front surface is 0.996 mm; the thickness of the seventh lens is 5.261 mm, the radius of curvature of the seventh front surface is 62.886 mm, the radius of curvature of the seventh rear surface is -57.828 mm, and the distance between the seventh rear surface and the front surface of the detector window is 4.919 mm; the thickness of the detector window is 2.5 mm. The front surface and the rear surface of the germanium filter are both flat, and the curvatures of the front surface and the rear surface of the germanium filter are both 0. The distance between the rear surface of the detector window and the cold stop is 1.85 mm; the distance between the cold stop and the front surface of the germanium filter is 25.2 mm; the thickness of the germanium filter is 0.8 mm. The front surface and the rear surface of the germanium filter are both flat, and the curvatures of the front surface and the rear surface of the germanium filter are both 0. The distance between the rear surface of the germanium filter and the detector rear focal plane is 4 mm.
4. A compact secondary imaging mid-wave infrared optical imaging system according to claim 3, characterized in that: The aperture of the cold stop is 12.300 mm; the size of the detector rear focal plane is 12.288 mm × 12.288 mm.
5. The compact secondary imaging mid-wave infrared optical imaging system according to claim 3, wherein: The first lens and the fourth lens are made of silicon; the second lens and the sixth lens are made of germanium; the third lens and the seventh lens are made of zinc selenide; the fifth lens is made of sapphire.
6. A compact secondary imaging mid-wave infrared optical imaging system according to claim 5, characterized in that: The surfaces of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are all coated with infrared antireflection films, and the average transmittance of the seven lenses is greater than or equal to 99%.
7. A compact secondary imaging mid-wave infrared optical imaging system according to claim 6, characterized in that: The second lens, the third lens, the fourth lens and the fifth lens are even aspherical lenses, and the sixth lens is a diffractive-refractive hybrid lens.
8. A compact secondary imaging mid-wave infrared optical imaging system according to claim 1, characterized in that: Both the germanium filter and the detector window are plano lenses with zero optical power, and the germanium filter and the detector window are arranged parallel to each other.
9. The compact secondary imaging mid-wave infrared optical imaging system according to claim 1, wherein: The system focal length is 81.25 mm, the field of view angle 2ω = 6°, and the F number is 1.65.