All-aluminum catadioptric large-relative-aperture athermalization long-wave infrared lens

Abstract

The invention discloses an all-aluminum catadioptric large-relative-aperture athermalization long-wave infrared lens which comprises a main lens barrel and a secondary lens barrel located in the middle of the main lens barrel. A head cover is fixedly connected to one end face of the main lens cone, main reflectors which are symmetrically arranged relative to the secondary lens cone are arranged in the main lens cone, the head cover is a spherical mirror, the main reflectors are parabolic reflectors, and the concave surface of the head cover is opposite to the convex surface of the main reflectors; a secondary reflecting mirror, a first transmitting mirror, a second transmitting mirror, a third transmitting mirror and a fourth transmitting mirror are sequentially arranged in the secondary lens cone in the light incidence direction. The primary reflector and the secondary reflector are made of aluminum alloy; the first transmitting mirror and the third transmitting mirror are both made of germanium and are respectively an aspheric lens and a diffraction surface lens. According to the lens, clear imaging can be achieved without refocusing, and the lens has the advantages of being light in weight, low in cost, capable of achieving mass production and high in reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared lenses, and particularly to an all-aluminum catadioptric large relative aperture athermalized long-wave infrared lens. Background Art

[0002] With the continuous development and increasing maturity of infrared night vision technology, infrared optical systems have been widely used in military and civilian fields because infrared lenses have many advantages, such as good anti-interference performance, all-weather and all-time operation, operability in complex environments, the ability to observe and track multiple targets, and the ability to monitor without a light source. However, the materials used in infrared lenses and mechanical materials will produce certain thermal effects. The refractive index temperature coefficient of the lens material will change with the ambient temperature, and the expansion coefficient of mechanical materials is relatively large, resulting in problems such as focal length change, image plane drift, and image quality degradation in the infrared optical system. Therefore, athermalized infrared optical systems have become an important development direction for high-precision infrared optical systems. However, most of the infrared lenses on the market have complex structures, high processing difficulties and costs, and low resolutions. In particular, all-aluminum athermalized long-wave infrared lenses are even rarer. Currently, the main methods for athermalized design of infrared systems are: mechanical passive compensation method, mechanical-electronic active compensation method, and optical passive compensation method. The first method is limited by the selection of structural materials and infrared materials, with strong limitations; the second method uses mechanical passive compensation and mechanical-electronic active compensation, with a complex system structure, low reliability, and inconvenient operation; the third method is to add diffractive optical elements to the optical system, and the production cost of diffractive elements is relatively low and can be directly processed by single-point turning. The mixed use of diffractive elements and traditional optical elements can not only increase the degree of freedom in design, better correct aberrations and eliminate thermal aberrations, improve the image quality of the system, reduce the volume, and lower the cost. Summary of the Invention

[0003] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide an all-aluminum catadioptric large relative aperture athermalized long-wave infrared lens, which compensates for the optical system changes caused by the thermal expansion and contraction of the all-aluminum reflector and the lens barrel through a refractive-diffractive hybrid lens group, solves the problem that the optical system of high-expansion coefficient materials can achieve clear imaging without focusing at temperatures from -100°C to +100°C, and the all-aluminum structure can achieve lightweight and facilitate mass production. To achieve the above objects and other advantages according to the present invention, there is provided an all-aluminum catadioptric large relative aperture athermalized long-wave infrared lens, comprising: A main lens barrel and a secondary lens barrel located in the middle part of the main lens barrel; A head cover is fixedly connected to one end surface of the main lens barrel, and a main reflector symmetrically arranged with respect to the secondary lens barrel is arranged inside the main lens barrel. The head cover is a spherical mirror, the main reflector is a parabolic reflector, and the concave surface of the head cover is arranged opposite to the convex surface of the main reflector; Inside the secondary mirror tube, a secondary reflector, a first transmissive lens, a second transmissive lens, a third transmissive lens, and a fourth transmissive lens are sequentially arranged along the light incident direction; The materials of the primary reflector and the secondary reflector are aluminum alloy; The materials of the first transmissive lens and the third transmissive lens are both germanium, and they are an aspherical lens and a diffractive lens respectively.

[0004] Preferably, the materials of the second transmissive lens and the fourth transmissive lens are IRG, and they are both aspherical lenses. The convex surface of the second transmissive lens is arranged opposite to the convex surface of the third transmissive lens, and the concave surface of the second transmissive lens is arranged opposite to the concave surface of the first transmissive lens.

[0005] Preferably, the materials of the primary mirror tube and the secondary mirror tube are both aluminum alloy mirror tubes.

[0006] Preferably, the gap between the head cover and the primary reflector is 53.75 mm, the gap between the primary reflector and the secondary reflector is 30.75 mm, the air gap between the secondary reflector and the first transmissive lens is 19.25 mm, the air gap between the first transmissive lens and the second transmissive lens is 5.69 mm, the air gap between the second transmissive lens and the third transmissive lens is 9.78 mm, and the air gap between the third transmissive lens and the fourth transmissive lens is 6.71 mm.

[0007] Preferably, it further includes a first retaining ring, a first spacer, a second spacer, a third spacer, a fourth spacer, and a second retaining ring arranged inside the secondary mirror tube; wherein, the first retaining ring is arranged on one end side of the secondary mirror tube, the second retaining ring is arranged on the other end side of the secondary mirror tube, the first spacer is arranged between the secondary reflector and the first transmissive lens, the second spacer is arranged between the first transmissive lens and the second transmissive lens, the third spacer is arranged between the second transmissive lens and the third transmissive lens, the fourth spacer is arranged between the third transmissive lens and the fourth transmissive lens, and a head cover retaining ring arranged inside the primary mirror tube.

[0008] Preferably, the distance from the center of the light exit surface of the fourth transmissive lens to the image plane is 10 mm.

[0009] Compared with the prior art, the beneficial effects of the present invention are: 1. The absolute value of the focal length of this optical system is 79.5 mm, the relative aperture is F / 1.03, the response band is 8 - 14 μm. The lens materials, mechanical materials, optical power, material thermal expansion coefficient, and mirror surface shapes of the optical system are reasonably selected, and they can compensate each other at high and low temperatures. High imaging quality can be maintained in environments of -100 °C, 20 °C, and +100 °C. The imaging resolution of the optical system is better than 640×512 (12 μm), and the MTF values are all greater than 0.22 @ 40 lp / mm. Clear imaging can be achieved without refocusing, and it has the advantages of light weight, low cost, mass producibility, and high reliability.

[0010] 2. The primary and secondary reflectors and the lens barrel of this optical system are all made of aluminum alloy materials, and the lens group is made of domestic long-wave infrared chalcogenide glass and germanium, which have the characteristics of mature technology, easy processing, and low cost.

[0011] 3. This optical system can ensure that the relative illumination of the image plane is uniform and the relative illumination consistency is greater than 87%; the maximum field angle of the optical system is 5°, the distortion is positive distortion and relatively small, and the distortion of the full field of view is less than 2.79%. At room temperature, the MTF is better than 0.28@40lp / mm.

[0012] 4. The aperture of this lens system is 80mm, the imaging resolution is better than 640×512(12μm), its back focal length is 10mm, and it is adapted to domestic long-wave infrared detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic optical path diagram of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention; Figure 2 is a schematic structural diagram of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention; Figure 3 is an illumination diagram of the optical system of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention; Figure 4 is an astigmatism and distortion diagram of the optical system of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention; Figure 5 is an optical modulation transfer function diagram of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention at 20°C; Figure 6 is an optical modulation transfer function diagram of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention at -100°C; Figure 7 is an optical modulation transfer function diagram of an all-aluminum catadioptric athermalized long-wave infrared lens with a large relative aperture according to the present invention at +100°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0015] Refer to Figure 1 、2 , a fully aluminum catadioptric large relative aperture athermalized long-wave infrared lens, comprising: a main barrel A and a secondary barrel B located in the middle part of the main barrel, both the main barrel A and the secondary barrel B are made of aluminum alloy barrels; a hood is fixedly connected to one end face of the main barrel A, a main reflector 1 symmetrically arranged with respect to the secondary barrel B is arranged inside the main barrel A, the hood is a spherical mirror, the main reflector 1 is a parabolic reflector, and the concave surface of the hood is arranged opposite to the convex surface of the main reflector 1; a secondary reflector 2, a first transmissive lens 3, a second transmissive lens 4, a third transmissive lens 5 and a fourth transmissive lens 6 are sequentially arranged inside the secondary barrel along the light incident direction; the materials of the main reflector 1 and the secondary reflector 2 are aluminum alloy, and the main reflector 1 is a parabolic reflector, 0.02 < absolute value of optical power < 0.03; the secondary reflector 2 is an aspherical reflector, 0.12 < absolute value of optical power < 0.13.

[0016] The materials of the first transmissive lens 3 and the third transmissive lens 5 are both germanium, the first transmissive lens 3 is an aspherical lens, 0.04 < absolute value of optical power < 0.05; the third transmissive lens 5 is a diffractive surface lens, 0.004 < absolute value of optical power < 0.005.

[0017] Furthermore, the materials of the second transmissive lens 4 and the fourth transmissive lens 6 are IRG206, and both are aspherical lenses. The convex surface of the second transmissive lens 4 is arranged opposite to the convex surface of the third transmissive lens 5, and the concave surface of the second transmissive lens 4 is arranged opposite to the concave surface of the first transmissive lens 3. The absolute value of the optical power of the second transmissive lens 4 ranges from 0.08 < absolute value of optical power < 0.09. The absolute value of the optical power of the fourth transmissive lens 6 ranges from 0.12 < absolute value of optical power < 0.13.

[0018] Furthermore, the passing semi-aperture of the hood is 42.5 mm and the thickness is 6 mm; the passing semi-aperture of the main reflector 1 is 40 mm and the thickness is 9 mm; the passing semi-aperture of the secondary reflector 2 is 9.8 mm and the thickness is 4 mm; the passing semi-aperture of the first transmissive lens 3 is 6.3 mm and the thickness is 5.92 mm; the passing semi-aperture of the second transmissive lens 4 is 9 mm and the thickness is 6.31 mm; the passing semi-aperture of the third transmissive lens 5 is 9 mm and the thickness is 6.06 mm; the passing semi-aperture of the fourth transmissive lens 6 is 8.3 mm and the thickness is 6.35 mm.

[0019] Further, the gap between the hood and the primary mirror 1 is 53.75 mm, the gap between the primary mirror 1 and the secondary mirror 2 is 30.75 mm, the air gap between the secondary mirror 2 and the first transmissive lens 3 is 19.25 mm, the air gap between the first transmissive lens 3 and the second transmissive lens 4 is 5.69 mm, the air gap between the second transmissive lens 4 and the third transmissive lens 5 is 9.78 mm, and the air gap between the third transmissive lens 5 and the fourth transmissive lens 6 is 6.71 mm.

[0020] Further, as Figure 2 shown, it further includes a first retaining ring a, a first spacer b, a second spacer c, a third spacer f, a fourth spacer g, and a second retaining ring h disposed in the secondary lens barrel B; wherein, the first retaining ring a is disposed on one end side of the secondary lens barrel B, the second retaining ring h is disposed on the other end side of the secondary lens barrel B, the first spacer b is disposed between the secondary mirror 2 and the first transmissive lens 3, the second spacer c is disposed between the first transmissive lens 3 and the second transmissive lens 4, the third spacer f is disposed between the second transmissive lens 4 and the third transmissive lens 5, the fourth spacer g is disposed between the third transmissive lens 5 and the fourth transmissive lens 6, and a hood retaining ring i disposed in the primary lens barrel A. The third retaining ring d and the fourth retaining ring e are used to connect and fix the lens and other mechanical structures.

[0021] Further, the distance from the center of the light exit surface of the fourth transmissive lens 6 to the image plane is 10 mm.

[0022] Further, the imaging band of this infrared lens is from 8 μm to 14 μm and the imaging resolution is better than 640×512 (12 μm).

[0023] Figure 3 This is the relative illumination diagram provided by the present invention, where the abscissa represents the field angle and the ordinate represents the normalized relative illumination value. It can be seen that the relative illumination values of all fields are greater than 87%.

[0024] Figure 4 This is the astigmatism and distortion diagram of the optical system of the present invention system. The abscissa is the percentage of optical distortion and the ordinate is the field angle of the optical system. It can be seen that the distortion of this optical system is less than 2.79%.

[0025] Figures 5 - 7 This is the modulation transfer function diagram of the optical system at different temperatures. The abscissa is the spatial modulation frequency and the ordinate is the optical modulation function. Figure 5 This is the optical modulation transfer function of this lens at room temperature of 20°C. Figure 6 This is the optical modulation transfer function of this lens at a low temperature of -100°C. Figure 7The modified optical modulation transfer function at a high temperature of +100°C shows that the lens of the present invention can maintain high imaging quality under the conditions of 20°C, -100°C, and +100°C.

[0026] In summary, this application is an athermalized infrared lens designed for a non-cooled focal plane array detector with a 640×512 (12μm) area array and a response band of 8 - 14μm. The system uses the optical passive compensation method and incorporates diffractive optical elements to achieve athermalization design for the infrared system. The primary and secondary mirrors and the lens barrel of the system are all made of aluminum alloy, achieving the goals of lightweight, low cost, mass producibility, and high reliability. In the temperature range of -100°C to +100°C, the infrared system does not defocus, ensuring clear imaging without focusing adjustment of the optical system.

[0027] The number of devices and the processing scale described here are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be obvious to those skilled in the art. Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated and described examples here.

Claims

1. An all-aluminum catadioptric large relative aperture athermalized long-wave infrared lens, characterized in that: include: A main lens barrel (A) and a secondary lens barrel (B) located in the middle of the main lens barrel; A head cover is fixedly connected to one end surface of the main lens barrel (A); a main reflector (1) is arranged symmetrically with respect to the secondary lens barrel (B) inside the main lens barrel (A); the head cover is a spherical mirror; the main reflector (1) is a parabolic reflector; and the concave surface of the head cover is arranged opposite to the convex surface of the main reflector (1); A secondary reflector (2), a first transmission mirror (3), a second transmission mirror (4), a third transmission mirror (5) and a fourth transmission mirror (6) are arranged in sequence inside the secondary lens barrel along the incident direction of light. The material of the primary reflector (1) and the secondary reflector (2) is aluminum alloy; The first transmission mirror (3) and the third transmission mirror (5) are both made of germanium and are respectively an aspherical lens and a diffractive lens.

2. The all-aluminum catadioptric large relative aperture athermal long-wave infrared lens according to claim 1, characterized in that: The second transmission mirror (4) and the fourth transmission mirror (6) are made of IRG206 and are both aspherical lenses; the convex surface of the second transmission mirror (4) is arranged opposite to the convex surface of the third transmission mirror (5); and the concave surface of the second transmission mirror (4) is arranged opposite to the concave surface of the first transmission mirror (3).

3. The all-aluminum catadioptric large relative aperture athermal long-wave infrared lens according to claim 1, characterized in that: The main lens barrel (A) and the secondary lens barrel (B) are both made of aluminum alloy.

4. The all-aluminum catadioptric large relative aperture athermalized long-wave infrared lens according to claim 1, characterized in that: The air gap between the head cover and the main reflector (1) is 53.75 mm, the air gap between the main reflector (1) and the secondary reflector (2) is 30.75 mm, the air gap between the secondary reflector (2) and the first transmission mirror (3) is 19.25 mm, the air gap between the first transmission mirror (3) and the second transmission mirror (4) is 5.69 mm, the air gap between the second transmission mirror (4) and the third transmission mirror (5) is 9.78 mm, and the air gap between the third transmission mirror (5) and the fourth transmission mirror (6) is 6.71 mm.

5. The all-aluminum catadioptric large relative aperture athermal long-wave infrared lens as claimed in claim 4, characterized in that: It also includes a first pressure ring (a), a first spacer ring (b), a second spacer ring (c), a third spacer ring (f), a fourth spacer ring (g), and a second pressure ring (h) arranged in the secondary lens barrel (B); wherein, The first pressing ring (a) is arranged at one end side of the secondary lens barrel (B), the second pressing ring (h) is arranged at the other end side of the secondary lens barrel (B), the first spacer ring (b) is arranged between the secondary reflector (2) and the first transmission mirror (3), the second spacer ring (c) is arranged between the first transmission mirror (3) and the second transmission mirror (4), the third spacer ring (f) is arranged between the second transmission mirror (4) and the third transmission mirror (5), the fourth spacer ring (g) is arranged between the third transmission mirror (5) and the fourth transmission mirror (6), and the head cover pressing ring (i) is arranged in the main lens barrel (A).

6. The all-aluminum catadioptric large relative aperture athermal long-wave infrared lens as claimed in claim 1, characterized in that: The distance between the center of the light emitting surface of the fourth transmission mirror (6) and the image plane is 10 mm.

Images