Small light-weight low-distortion athermalization infrared optical system

Abstract

The invention relates to a small-sized light-weight low-distortion athermalization infrared optical system, which consists of a meniscus positive lens, a first meniscus negative lens, a diaphragm, a second meniscus negative lens and a biconvex positive lens which are sequentially and coaxially arranged from an object space to an image space, through optimal arrangement of intervals among the lenses, reasonable distribution of focal power of the lenses and cooperation of optical materials of the lenses, the four lenses realize a small-sized light-weight low-distortion athermalization infrared optical system suitable for a detector with the resolution of 1024 * 768, the total weight is 75 g, and the maximum distortion of an edge field of view is less than 0.5%. A focusing mechanism used for compensating imaging quality reduction caused by temperature change of the optical system does not need to be additionally arranged, athermalization in the wide temperature range of-55 DEG C to + 70 DEG C is achieved, the system structure is effectively simplified, and the product reliability is improved. The whole system is high in imaging quality, the optical system is small in total length, the system back focal length is long, and the design of a back-end detector mounting structure is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of non-cooled infrared optical systems, and in particular to a small, lightweight, low-distortion, athermal infrared optical system. Background Art

[0002] With the development and progress of technology, the pixel size of uncooled infrared systems has been continuously reduced, the sensitivity has been continuously improved, and its price has been gradually reduced. In addition, because it does not require a refrigerator, the system can be miniaturized, so it is increasingly widely used in security monitoring, vehicle-mounted and other fields. However, the temperature sensitivity of uncooled systems is low and the detection capability is poor. In order to improve the temperature sensitivity and detection capability of the system, the infrared optical system is required to have a large relative aperture to improve the system's light-gathering ability. At the same time, in order to adapt to the ambient temperature requirements of different regions, the system needs to be designed without heat.

[0003] There are three main ways to achieve athermalization of infrared optical systems: mechanical active athermalization, mechanical passive athermalization, and optical passive athermalization. Mechanical active athermalization uses a temperature sensor to measure the change in ambient temperature, calculates the image plane displacement caused by the temperature change, and then uses a motor to drive the lens to move along the optical axis to achieve temperature compensation; mechanical passive athermalization uses the materials of the high expansion system and the low expansion system to cooperate with each other, adjust the length of the two materials, and expand and contract the materials of different expansion systems to make a group or the entire group of lenses in the infrared optical system move along the optical axis to achieve temperature compensation; optical passive athermalization uses the differences in thermal properties of different optical materials to achieve temperature compensation through the combination of a variety of optical materials and structural materials with different properties.

[0004] Mechanical active athermal optical systems require motor drive, which is not conducive to the miniaturization design of optical systems and has low reliability. Mechanical passive athermal optical systems require an inner cylinder made of high expansion material and an outer cylinder made of low expansion material during structural design, and the structure is relatively complex. Optical passive athermal optical systems are implemented using a variety of materials. By matching the photothermal coefficient of the optical material and the optical focal length of the distribution lens, the optical system can maintain the image plane displacement within the focal depth range of the system over a wide temperature range. It has the characteristics of simple structure, reliability, high assembly efficiency, and is suitable for mass production.

[0005] The Chinese patent application number 202211379583.4 discloses a low-distortion wide-angle long-wave uncooled infrared optical system with optical passive athermalization. The system consists of four lenses, with an operating band of 8μm to 12μm; F#: 1.0; focal length: 45mm; field of view: 19.4°×15.5°, image plane diameter: Φ19.7mm, operating temperature range: -55℃~+70℃; total length is less than 70mm. The system has a large target surface and can be adapted to a 1280×1024 uncooled infrared detector with a pixel size of 12μm.

[0006] The Chinese patent application number 201811315703.8 discloses a miniaturized high-resolution wide-temperature athermal infrared optical system, which consists of six lenses, with a circular field of view of 83.5°, an F number of 1, and a detector with 15μm pixels and 1024×768. The distortion is ultimately less than 3% within a 74° field of view and less than 5% in the full field of view. The system has a large field of view, but has a large number of lenses and a long length.

[0007] The Chinese patent application number 202111523925.0 discloses a 35mm focal length athermal infrared lens and its assembly method and imaging method. The system consists of four lenses and achieves the following technical indicators: working band: 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 back intercept of the system is 10.81mm, which is short, and has high requirements for the design of the detector installation structure. Summary of the invention

[0008] In order to solve the technical problems of large size, heavy weight and large distortion of traditional uncooled athermal infrared optical systems when adapting to large target infrared detectors, the present invention provides a small, lightweight, low-distortion athermal infrared optical system.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A small, lightweight, low-distortion, athermal infrared optical system, the optical system consists of a meniscus positive lens, a first meniscus negative lens, an aperture, a second meniscus negative lens, and a double convex positive lens coaxially arranged in sequence from the object side to the image side, the concave surfaces of the meniscus positive lens and the first meniscus negative lens are arranged toward the image plane, and the concave surface of the second meniscus negative lens is arranged away from the image plane and toward the object side.

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

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

[0013] Furthermore, the meniscus positive 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 positive 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 meets the following condition: 0.7≤f5 / f≤1.0, wherein 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 between the second meniscus negative lens and the biconvex positive lens on the optical axis is T45, the distance between the biconvex positive lens and the protective glass on the optical axis 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 side, the surface of the first meniscus negative lens facing the image side, and the surface of the second meniscus negative lens facing the image side are all aspherical surfaces.

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

[0020] Furthermore, the technical parameters of the optical system are as follows: working band: 8μm~12μm; F # : 1.2; focal length: 35mm; field of view: 19.9°×15.0°, image diameter: Φ15.4mm; where 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 system back focus, that is, the distance between the rear 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 the present invention realizes a small, lightweight, low-distortion, athermal infrared optical system with a focal length of 35 mm, an image plane diameter of 15.4 mm, and a distortion of less than 0.5% by optimizing the intervals between the lenses, reasonably distributing the focal power of the lenses, and matching the optical materials of the lenses. The total weight of the four lenses is 75 g, and the total length of the optical system is 54.9 mm. At the same time, the back intercept of the system is 19.58 mm, which is long and is conducive to the design of the rear detector installation structure;

[0024] 2. The present invention realizes an optical passive athermal optical system that can achieve good imaging in a wide temperature range of -55°C to +70°C by combining different optical materials. There is no need to set up a focusing mechanism to compensate for the degradation of imaging quality caused by temperature changes in the optical system, which effectively simplifies the system structure and improves product reliability. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0029] Figure 5 is a point diagram of the optical system of the present invention at room temperature 20°C;

[0030] Figure 6 It is a spot diagram of the optical system of the present invention at a low temperature of -55°C;

[0031] Figure 7 It is a point diagram 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 the present invention;

[0033] Fig. 9 Relative illumination curve of the image plane of the optical system of the present invention.

[0034] Among them, 1 is a meniscus positive lens, 2 is a first meniscus negative lens, 3 is an aperture STO, 4 is a second meniscus negative lens, 5 is a double convex positive lens, 6 is a detector window protection glass, and 7 is an image plane. DETAILED DESCRIPTION

[0035] In order to make the above features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings.

[0036] In the description of the present invention, it is necessary to understand that if there are terms such as "upper", "lower", "front", "back", "left", "right", etc. to indicate directions or positional relationships, they only correspond to the drawings of the present application and are for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific direction.

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

[0038] Throughout the specification, like reference numerals refer to like elements.In the drawings, the figures are by way of example only and are not drawn strictly to scale.

[0039] As common sense, the direction close to the object space is the object side, and the direction close to the image space is the image side. From the object side to the image side, the two sides of the lens are the incident side and the exit side. The object side refers to the side where the light enters, and the image side refers to the side where the light exits. "From the object side to the image side along the optical axis" is like Figure 1 The direction from left to right in the image. The surface facing the object side of the two surfaces of each lens is called the object side surface, and the surface facing the image side of the two surfaces of each lens is called the image side surface.

[0040] like Figure 1 The small, lightweight, low-distortion, athermal infrared optical system shown is composed of a meniscus positive lens 1, a first meniscus negative lens 2, an aperture 3, a second meniscus negative lens 4, and a double convex positive lens 5, which are arranged in sequence 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 coaxially arranged in sequence from the object side to the image side.

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

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

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

[0045] The specific light transmission path of the optical system of the present invention is that 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, the first meniscus negative lens 2 diverges and passes through the aperture 3 to reach the second meniscus negative lens 4, diverges through the second meniscus negative lens 4 and reaches the double convex positive lens 5, converges through the double convex positive lens 5, passes through the protective glass 6 and forms an image on the image plane 7.

[0046] Preferably, the meniscus positive 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 positive 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, wherein 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) meets the following condition: 0.7≤f5 / f≤1.0, wherein 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 described small, lightweight, low-distortion, athermal infrared optical system, 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, 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 indicators achieved by the present invention are shown in Table 1, wherein the calculation formula of F# (optical system F number) is f / D, f is the focal length of the optical system, and D is the incident pupil diameter.

[0052] Table 1 Technical indicators of the optical system of the present invention

[0053] The detailed data of the embodiment of the optical system of the present invention when the focal length is 35 mm is shown in Table 2, which includes the surface type, curvature radius, thickness, and material of each lens. The units of the curvature radius and thickness of the lens are mm, and the curvature radius of the spherical surface and the aspherical surface refers to the curvature radius at the intersection of the lens surface and the optical axis.

[0054] The "surface number" in Table 2 is counted along the direction of light propagation, such as the light beam incident surface of the meniscus positive lens 1 is numbered S1, the light beam exit surface is numbered S2, and the numbers of other mirror surfaces are similar. The curved surfaces of the meniscus positive lens 1, the first meniscus negative lens 2, the second meniscus negative lens 4, and the double convex positive lens 5 along the object-to-image direction are marked as S1, S2, S3, S4, S5, S6, S7, and S8, respectively. The "radius" in Table 2 indicates the radius of curvature of the surface, and the principle for determining the positive and negative values ​​is: the intersection of the surface and the main optical axis is taken as the starting point, and the center of the curved surface of the surface is taken as the end 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 a plane, the radius of curvature of the surface is infinite; the "thickness" in Table 2 gives the distance between two adjacent surfaces on the optical axis, and the principle for determining the positive and negative values ​​is: the vertex of the current surface is taken as the starting point, and the vertex of the next surface is taken as the end point. If the direction of the 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, the thickness represents the lens thickness. If there is no material between the two surfaces, it represents the air space between the two lenses.

[0055] Table 2 Detailed data of the optical system in the embodiment of the present invention

[0056] In the small, lightweight, low-distortion, athermal infrared optical system described in the present invention, 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 are all aspherical.

[0057] Furthermore, the surface equations of the above-mentioned aspheric surfaces are:

[0058]

[0059] Among them, z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is 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 in the direction perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, and C is the eighth-order aspheric coefficient.

[0060] Table 3 lists the aspheric coefficients of 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 according to the present invention. The table uses scientific notation. For example, -7.849043e-006 represents -7.849043×10 -6 .

[0061] Table 3 Aspheric coefficients of the present invention

[0062] Furthermore, the surface S7 of the biconvex positive lens 5 facing the object side is an aspherical surface, and a continuous relief structure is formed on the aspherical substrate by diamond turning to form a diffraction surface, which satisfies the equation:

[0063]

[0064] Among them, z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is 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 in the direction perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, and C is the eighth-order aspheric 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 refractive index of air.

[0065] Table 4 lists the diffraction aspheric coefficients of the surface S7 of the biconvex positive lens 5 facing the object side according to the present invention.

[0066] Table 4 Diffraction non-curved surface coefficients of the present invention

[0067] After optical design software simulation, such as Figure 2 , Figure 3 , Figure 4 As shown in the figure, when the uncooled detector with a pixel size of 12 μm and a pixel number of 1024×768 corresponds to a spatial frequency of 42 lp / mm, the optical system transfer function at room temperature, low temperature and high temperature is greater than 0.32; Figure 5 , Figure 6 , Figure 7 As shown in the figure, the point diagrams of the system at room temperature, low temperature and high temperature are all smaller than the diameter of the Airy disk; Figure 8 As shown in the figure, it is the field curvature and distortion diagram of the optical system. It can be seen from the figure that the maximum distortion of the edge field of view is less than 0.5%. Fig. 9As shown in FIG. 1 , it is the image plane relative illumination curve of the optical system. It can be seen from the figure that the illumination of the edge field of view is 96%, and the image plane illumination uniformity is good.

[0068] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as above in preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A small, lightweight, low-distortion, athermalized infrared optical system, characterized in that: The optical system comprises a meniscus positive lens (1), a first meniscus negative lens (2), an aperture (3), a second meniscus negative lens (4), and a double convex positive lens (5) which are coaxially arranged in sequence 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 arranged in the direction of the image plane (7), and the curvature radius of each lens surface is positive; the concave surface of the second meniscus negative lens (4) is arranged away from the image plane (7) and towards the object side, and the curvature radius of the lens surface is negative.

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

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

4. A small, lightweight, low-distortion, athermalized infrared optical system according to claim 1, characterized in that: The focal length of each lens must meet the following conditions: 0.9≤ f 1 / f ≤1.2，-1.2≤ f 2 / f ≤-0.9，5.0≤ f 4 / f ≤6.0，0.7≤ f 5 / f ≤1.0； in: f is the focal length of the optical system; f 1 is the effective focal length of the meniscus positive lens (1); f 2 is the effective focal length of the first meniscus negative lens (2); f 4 is the effective focal length of the second meniscus negative lens (4); f 5 is the effective focal length of the biconvex positive lens (5).

5. A 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, satisfying the following condition: 4.0≤(T45+T56) / CT5≤4.

5.

6. 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 surfaces.

7. A 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 aspheric surface.

8. 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 as follows: working band: 8μm~12μm; F # : 1.2; focal length: 35mm; field of view: 19.9°x15.0°, image diameter: Φ15.4mm; among which, F # The calculation formula is f / D , f is the focal length of the optical system, D is the entrance pupil diameter.

9. 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 positive lens (1) to the image plane (7) is less than 55 mm, and the system back focus, i.e., the distance between the back surface of the biconvex positive lens (5) and the image plane (7) on the optical axis, is 19.58 mm.

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