A small, lightweight, low-distortion, athermalized infrared optical system

Abstract

The present application relates to a kind of small light weight, low distortion athermal infrared optical system, the optical system is coaxially arranged in order from object side to image side by crescent positive lens, first crescent negative lens, diaphragm, second crescent negative lens, double convex positive lens is composed, by the optimization setting of interval between each lens, the reasonable distribution of each lens power and the cooperation of lens optical material, by 4 pieces of lens, small light weight, low distortion athermal infrared optical system applicable to resolution 1024x768 detector is realized, total weight is 75g, the maximum distortion of edge field is less than 0.5%.Without additionally setting the focusing mechanism for compensating the imaging quality decline caused by temperature change of optical system, athermalization in-55 ℃~+70 ℃ wide temperature range is realized, effectively simplifies system structure, improves product reliability.The whole system has high imaging quality, the total length of optical system is small, and the system rear intercept is long, which is beneficial to the design of rear-end detector mounting structure.

Description

Technical Field

[0001] This invention relates to the field of uncooled infrared optical systems, and more specifically to a small, lightweight, low-distortion, athermal infrared optical system. Background Technology

[0002] With technological advancements, the pixel size of uncooled infrared systems is continuously decreasing, their sensitivity is constantly improving, while their price is gradually decreasing. Furthermore, because they do not require a cooling system, the systems can be miniaturized, leading to their increasingly widespread application in security monitoring, automotive, and other fields. However, uncooled systems have lower temperature sensitivity and poorer detection capabilities. To improve these aspects, infrared optical systems require large relative apertures to enhance light-gathering capabilities. Simultaneously, to adapt to the environmental temperature requirements of different regions, a calorimetric design is necessary.

[0003] There are three main methods for achieving athermalization in infrared optical systems: active mechanical athermalization, passive mechanical athermalization, and passive optical athermalization. Active mechanical athermalization uses a temperature sensor to measure changes in ambient temperature, calculates the resulting image plane displacement, and then uses a motor to drive the lens along the optical axis to achieve temperature compensation. Passive mechanical athermalization utilizes the interaction of materials with high and low expansion systems. By adjusting the lengths of these materials, the expansion and contraction of different expansion systems move one or more lenses within the infrared optical system along the optical axis, thus achieving temperature compensation. Passive optical athermalization leverages the differences in thermal properties of various optical materials, combining different optical and structural materials to achieve temperature compensation.

[0004] Mechanically active athermalized optical systems require motor drive, which is not conducive to the miniaturization design of optical systems and has low reliability. Mechanically passive athermalized optical systems require an inner cylinder of high-expansion material and an outer cylinder of low-expansion material in their structural design, making the structure relatively complex. Optically passive athermalized optical systems are achieved by using a variety of materials. By matching the photothermal coefficients of the optical materials and distributing the optical power of the lenses, the optical system can maintain the image plane displacement within the system's focal depth range over a wide temperature range. It has the characteristics of simple structure, reliability, high assembly efficiency, and suitability for mass production.

[0005] Chinese Patent Application No. 202211379583.4 discloses a low-distortion wide-angle long-wave uncooled infrared optical system with passive pyrolysis. This system consists of four lenses, with an operating wavelength of 8μm to 12μm; an f / 1.0 aperture; a focal length of 45mm; a field of view of 19.4° × 15.5°; an image diameter of Φ19.7mm; an operating temperature range of -55℃ to +70℃; and a total length of less than 70mm. The system has a large target area and can be used with a 1280 × 1024 uncooled infrared detector with a pixel size of 12μm.

[0006] Chinese patent application number 201811315703.8 discloses a miniaturized, high-resolution, wide-temperature, athermal infrared optical system. This system consists of six lenses, has a circular field of view of 83.5°, an F-number of 1, and is matched with a 15μm pixel, 1024×768 detector. The distortion is ultimately less than 3% within a 74° field of view and less than 5% across the entire field of view. While the system has a large field of view, it requires a large number of lenses and is relatively long.

[0007] Chinese Patent Application No. 202111523925.0 discloses a 35mm focal length pyrometric infrared lens and its assembly and imaging methods. The system consists of four lenses and achieves the following technical specifications: operating wavelength: 8μm~12μm; focal length: f′=35mm; resolution: 1280×1024, 12μm; F-number: 1; horizontal field of view: 24.75°, vertical field of view: 19.91°; distortion: less than 1%; temperature range: -40℃ to 80℃. The system has a short backstop of 10.81mm, which places high demands on the design of the detector's mounting structure. Summary of the Invention

[0008] To address the technical challenges of traditional uncooled and athermalized infrared optical systems being bulky, heavy, and exhibiting significant distortion when adapted to large-area infrared detectors, this invention provides a small, lightweight, low-distortion athermalized infrared optical system.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A small, lightweight, low-distortion, athermal infrared optical system is disclosed. The optical system comprises a meniscus positive lens, a first meniscus negative lens, an aperture, a second meniscus negative lens, and a biconvex positive lens arranged coaxially from the object side to the image side. The concave surfaces of the meniscus positive lens and the first meniscus negative lens are oriented towards the image plane, while the concave surface of the second meniscus negative lens is oriented away from the image plane and towards the object side.

[0011] Furthermore, the aperture stop is located between the first meniscus negative lens and the second meniscus negative lens, with the distance between the first meniscus negative lens and the aperture stop on the optical axis being 5mm, and the distance between the aperture stop and the second meniscus negative lens on the optical axis being 5mm.

[0012] Furthermore, the meniscus positive lens, the second meniscus negative lens, and the biconvex positive lens are all made of chalcogenide glass IRG206, and the first meniscus negative lens is made of zinc selenide ZNSE.

[0013] Furthermore, the meniscus lens satisfies the following condition: 0.9≤f1 / f≤1.2, where f is the focal length of the optical system and f1 is the effective focal length of the meniscus lens;

[0014] The first meniscus negative lens satisfies the following condition: -1.2≤f2 / f≤-0.9, where f is the focal length of the optical system and f2 is the effective focal length of the first meniscus negative lens;

[0015] The second meniscus negative lens satisfies the following condition: 5.0≤f4 / f≤6.0, where f is the focal length of the optical system and f4 is the effective focal length of the second meniscus negative lens;

[0016] The biconvex positive lens is subject to the following condition: 0.7≤f5 / f≤1.0, where f is the focal length of the optical system and f5 is the effective focal length of the biconvex positive lens.

[0017] Furthermore, a protective glass is provided in front of the image plane, the distance on the optical axis between the second meniscus negative lens and the biconvex positive lens is T45, the distance on the optical axis between the biconvex positive lens and the protective glass is T56, and the thickness of the biconvex positive lens on the optical axis is CT5, satisfying the following condition: 4.0≤(T45+T56) / CT5≤4.5.

[0018] Furthermore, the surface of the meniscus positive lens facing the image, the surface of the first meniscus negative lens facing the image, and the surface of the second meniscus negative lens facing the image are all aspherical.

[0019] Furthermore, the surface of the biconvex positive lens facing the object side is a diffractive aspherical surface.

[0020] Furthermore, the technical parameters achieved by the optical system are: operating wavelength: 8μm~12μm; F # : 1.2; Focal length: 35mm; Field of view: 19.9°×15.0°, Image plane diameter: Φ15.4mm; Wherein, F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0021] Furthermore, the total length from the front surface of the meniscus positive lens to the image plane is less than 55 mm, and the back cutoff of the system, i.e. the distance between the back surface of the biconvex positive lens and the image plane on the optical axis, is 19.58 mm.

[0022] Beneficial effects:

[0023] 1. The optical system of this invention achieves a small, lightweight, low-distortion, and pyrothermal infrared optical system with a focal length of 35mm, an image plane diameter of 15.4mm, and distortion of less than 0.5% by optimizing the spacing between lenses, rationally allocating the optical power of each lens, and coordinating the optical materials of the lenses. The total weight of the four lenses is 75g, the total length of the optical system is 54.9mm, and the back focal length of the system is 19.58mm. The long back focal length is beneficial to the design of the back-end detector mounting structure.

[0024] 2. By combining different optical materials, this invention achieves a passive, calorimetric optical system that can produce good images within a wide temperature range of -55℃ to +70℃. This eliminates the need for a separate focusing mechanism to compensate for the decrease in image quality caused by temperature changes in the optical system, effectively simplifying the system structure and improving product reliability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the optical system of the present invention;

[0026] Figure 2 The optical transfer function (MTF) curve of the optical system of the present invention at room temperature (20°C) is shown.

[0027] Figure 3 The optical transfer function (MTF) curve of the optical system of the present invention at a low temperature of -55°C is shown.

[0028] Figure 4 The optical transfer function (MTF) curve of the optical system of the present invention at a high temperature of +70°C is shown.

[0029] Figure 5 This is a dot plot of the optical system of the present invention at room temperature (20°C);

[0030] Figure 6 This is a dot plot of the optical system of the present invention at a low temperature of -55°C;

[0031] Figure 7 This is a dot plot of the optical system of the present invention at a high temperature of +70°C;

[0032] Figure 8 Field curvature and distortion diagram of the optical system of this invention;

[0033] Figure 9 The relative illumination curve of the image plane of the optical system of this invention.

[0034] Among them, 1 is a meniscus positive lens, 2 is a first meniscus negative lens, 3 is an aperture stop STO, 4 is a second meniscus negative lens, 5 is a biconvex positive lens, 6 is a detector window protective glass, and 7 is an image plane. Detailed Implementation

[0035] To make the above features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right" and other terms indicating orientation or positional relationship are only used to correspond to the drawings of this application for the purpose of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation.

[0037] The terms “first,” “second,” and “third” are used for descriptive purposes only, referring to the order in which lenses of this type appear, and should not be construed as indicating or implying relative importance.

[0038] Throughout the manual, the same reference numerals refer to the same components. The accompanying drawings are for illustrative purposes only and are not drawn to scale.

[0039] As is common knowledge, the direction closer to object space is called the object side, and the direction closer to image space is called the image side. From the object side to the image side, the two sides of the lens are, respectively, the incident surface and the exit surface. The object side refers to the side where the light rays enter, and the image side refers to the side where they exit. "From the object side to the image side along the optical axis" means... Figure 1 The direction from left to right. Of the two surfaces of each lens, the surface facing the object is called the object surface, and the surface facing the image is called the image surface.

[0040] like Figure 1 The small, lightweight, low-distortion, athermal infrared optical system shown consists of a meniscus positive lens 1, a first meniscus negative lens 2, an aperture 3, a second meniscus negative lens 4, and a biconvex positive lens 5 arranged sequentially from the object side to the image side.

[0041] Furthermore, the meniscus positive lens 1, the first meniscus negative lens 2, the second meniscus negative lens 4, and the biconvex positive lens 5 are arranged coaxially from the object side to the image side.

[0042] Furthermore, the aperture stop 3 is located between the first meniscus negative lens 2 and the second meniscus negative lens 4. The distance between the first meniscus negative lens 2 and the aperture stop 3 on the optical axis is 5mm, and the distance between the aperture stop 3 and the second meniscus negative lens 4 on the optical axis is 5mm.

[0043] Furthermore, the concave surfaces of the meniscus positive lens 1 and the first meniscus negative lens 2 are both bent towards the image plane 7, and the radius of curvature of each lens surface is positive. The concave surface of the second meniscus negative lens 4 is bent towards the object side away from the image plane, and the radius of curvature of the lens surface is negative.

[0044] Preferably, the meniscus positive lens 1, the second meniscus negative lens 4, and the biconvex positive lens 5 are all made of chalcogenide glass IRG206, and the first meniscus negative lens 2 is made of zinc selenide ZNSE.

[0045] The specific light transmission path of the optical system of the present invention is as follows: the light emitted by the infrared radiation of the external scene is converged by the meniscus positive lens 1 and reaches the first meniscus negative lens 2. After the first meniscus negative lens 2 diverges, it passes through the aperture 3 and reaches the second meniscus negative lens 4. After the second meniscus negative lens 4 diverges, it reaches the biconvex positive lens 5. After the biconvex positive lens 5 converges, it passes through the protective glass 6 and is imaged on the image plane 7.

[0046] Preferably, the meniscus lens 1 satisfies the following condition: 0.9≤f1 / f≤1.2, where f is the focal length of the optical system and f1 is the effective focal length of the meniscus lens 1;

[0047] The first meniscus negative lens 2 satisfies the following condition: -1.2≤f2 / f≤-0.9, where f is the focal length of the optical system and f2 is the effective focal length of the first meniscus negative lens (2);

[0048] The second meniscus negative lens (4) satisfies the following condition: 5.0≤f4 / f≤6.0, where f is the focal length of the optical system and f4 is the effective focal length of the second meniscus negative lens (4);

[0049] The biconvex positive lens (5) is subject to the following condition: 0.7≤f5 / f≤1.0, where f is the focal length of the optical system and f5 is the effective focal length of the biconvex positive lens (5).

[0050] Furthermore, in the aforementioned small, lightweight, low-distortion, and pyroelectric infrared optical system, the distance on the optical axis between the second meniscus negative lens 4 and the biconvex positive lens 5 is T45, the distance on the optical axis between the biconvex positive lens 5 and the protective glass 6 is T56, and the thickness of the biconvex positive lens 5 on the optical axis is CT5, satisfying the following condition: 4.0≤(T45+T56) / CT5≤4.5.

[0051] The technical specifications achieved by this invention are shown in Table 1. The formula for calculating F# (F-number of the optical system) is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0052] Table 1 Technical Specifications of the Optical System of the Invention

[0053]

[0054]

[0055] Detailed data for the optical system of the present invention with a focal length of 35mm are shown in Table 2, which includes the surface shape, radius of curvature, thickness, and material of each lens. The units for the radius of curvature and thickness of the lens are mm, and the radius of curvature of spherical and aspherical surfaces refers to the radius of curvature at the intersection of the lens surface and the optical axis.

[0056] In Table 2, the "Surface Number" is counted along the direction of light propagation. For example, the incident surface of the meniscus positive lens 1 is numbered S1, and the exit surface is numbered S2. Other mirror surfaces are numbered similarly. The curved surfaces of the meniscus positive lens 1, the first meniscus negative lens 2, the second meniscus negative lens 4, and the biconvex positive lens 5 along the object-to-image direction are respectively marked as S1, S2, S3, S4, S5, S6, S7, and S8. The "Radius" in Table 2 represents the radius of curvature of the surface. Its sign is determined by taking the intersection of the surface and the principal optical axis as the starting point and the center of the surface as the ending point. If the direction of the connecting line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the surface is planar, its radius of curvature is infinite. The "Thickness" in Table 2 gives the distance between two adjacent surfaces on the optical axis. Its sign is determined by taking the vertex of the current surface as the starting point and the vertex of the next surface as the ending point. If the direction of the connecting line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the material between the two surfaces is infrared material, then the thickness represents the lens thickness; if there is no material between the two surfaces, it represents the air gap between the two lenses.

[0057] Table 2 Detailed data of the optical system in the embodiments of the present invention

[0058]

[0059]

[0060] The small, lightweight, low-distortion, and athermal infrared optical system of the present invention comprises aspherical surfaces, namely, the surface S2 of the meniscus positive lens 1 facing the image side, the surface S4 of the first meniscus negative lens 2 facing the image side, and the surface S6 of the second meniscus negative lens 4 facing the image side.

[0061] Furthermore, the surface equations of the above-mentioned aspherical surfaces are as follows:

[0062]

[0063] Where z is the distance vector from the vertex of the aspherical surface at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspherical coefficient, B is the sixth-order aspherical coefficient, and C is the eighth-order aspherical coefficient.

[0064] Table 3 lists the aspherical coefficients of the image-side surface S2 of the meniscus positive lens 1, the image-side surface S4 of the first meniscus negative lens 2, and the image-side surface S6 of the second meniscus negative lens 4 according to the present invention. The table uses scientific notation; for example, -7.849043e-006 represents -7.849043 × 10⁻⁶. -6 .

[0065] Table 3 Aspheric coefficients of the present invention

[0066]

[0067] Furthermore, the object-side surface S7 of the biconvex positive lens 5 is aspherical. A continuous relief structure is machined on the aspherical substrate using diamond turning to form a diffraction surface, which satisfies the following equation:

[0068]

[0069] Where z is the distance vector from the vertex of the aspherical surface at a height of r along the optical axis, c is the curvature (c = 1 / R), where R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspherical coefficient, B is the sixth-order aspherical coefficient, and C is the eighth-order aspherical coefficient; HOR is the diffraction order, C1, C2, and C3 are the diffraction surface coefficients, λ0 is the design center wavelength, n is the refractive index of the lens, and n0 is the air refractive index.

[0070] Table 4 lists the diffraction aspheric coefficients of the object-side surface S7 of the biconvex positive lens 5 according to the present invention.

[0071] Table 4. Diffraction non-surface coefficients of the present invention

[0072]

[0073] After simulation using optical design software, such as Figure 2 , Figure 3 , Figure 4 As shown, when using an uncooled detector with a pixel size of 12μm and a pixel count of 1024×768, corresponding to a spatial frequency of 42lp / mm, the optical system transfer function is greater than 0.32 at room temperature, low temperature, and high temperature. Figure 5 , Figure 6 , Figure 7As shown, the dot plots of the system at room temperature, low temperature, and high temperature are all smaller than the diameter of the Ally disk; as Figure 8 The figure shows the field curvature and distortion diagrams of this optical system. As can be seen from the figure, the maximum distortion at the edge of the field of view is less than 0.5%. Figure 9 The figure shows the relative illuminance curve of the image plane of the optical system. As can be seen from the figure, the illuminance of the edge field of view is 96%, and the uniformity of the image plane illuminance is good.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A small, lightweight, low-distortion, athermalized infrared optical system, characterized in that, The optical system consists of a meniscus positive lens (1), a first meniscus negative lens (2), an aperture stop (3), a second meniscus negative lens (4), and a biconvex positive lens (5) arranged coaxially from the object side to the image side. The concave surfaces of the meniscus positive lens (1) and the first meniscus negative lens (2) are positioned facing the image plane (7), while the concave surface of the second meniscus negative lens (4) is positioned facing away from the image plane (7) and towards the object side. The meniscus positive lens (1) satisfies the following condition: 0.9 ≤ f 1 / f ≤1.2, where f For the focal length of the optical system, f 1 is the effective focal length of the meniscus positive lens (1); The first meniscus negative lens (2) satisfies the following condition: -1.2 ≤ f 2 / f ≤-0.9, where f For the focal length of the optical system, f 2 is the effective focal length of the first meniscus negative lens (2); The second meniscus negative lens (4) satisfies the following condition: 5.0 ≤ f 4 / f ≤6.0, where f For the focal length of the optical system, f 4 is the effective focal length of the second meniscus negative lens (4); The biconvex positive lens (5) is satisfied under the following condition: 0.7 ≤ f 5 / f ≤1.0, where f For the focal length of the optical system, f 5 is the effective focal length of the biconvex positive lens (5).

2. The small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The aperture stop (3) is located between the first meniscus negative lens (2) and the second meniscus negative lens (4). The distance between the first meniscus negative lens (2) and the aperture stop (3) on the optical axis is 5 mm, and the distance between the aperture stop (3) and the second meniscus negative lens (4) on the optical axis is 5 mm.

3. The small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The meniscus positive lens (1), the second meniscus negative lens (4), and the biconvex positive lens (5) are all made of chalcogenide glass IRG206, and the first meniscus negative lens (2) is made of zinc selenide ZNSE.

4. The small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, A protective glass (6) is provided in front of the image plane (7). The distance between the second meniscus negative lens (4) and the biconvex positive lens (5) on the optical axis is T45. The distance between the biconvex positive lens (5) and the protective glass (6) on the optical axis is T56. The thickness of the biconvex positive lens (5) on the optical axis is CT5, which satisfies the following condition: 4.0≤(T45+T56) / CT5≤4.

5.

5. A small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The surface of the meniscus positive lens (1) facing the image side, the surface of the first meniscus negative lens (2) facing the image side, and the surface of the second meniscus negative lens (4) facing the image side are all aspherical.

6. The small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The surface of the biconvex positive lens facing the object side is a diffractive aspherical surface.

7. A small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The technical parameters achieved by the optical system are: operating wavelength: 8μm~12μm; F # : 1.2; Focal length: 35mm; Field of view: 19.9° x 15.0°, Image plane diameter: Φ15.4mm; where, F # The calculation formula is f / D , f The focal length of the optical system. D The diameter is the entrance pupil.

8. A small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that, The total length from the front surface of the meniscus lens (1) to the image plane (7) is less than 55 mm, and the back intercept of the system is 19.58 mm.

Images