Low-sensitivity long-focal-length extremely-short-total-length medium-wave infrared zoom optical system

Abstract

The invention relates to the technical field of infrared optical imaging, in particular to a low-sensitivity long-focal-length extremely-short-total-length medium-wave infrared zoom optical system, and aims to solve the problems that an existing medium-wave infrared zoom system is difficult to achieve long-focal-length zoom and has low sensitivity under the requirement conditions of large zoom ratio and extremely-short total length. The system is coaxially provided with a front fixed group, a zoom group, a compensation group, a rear fixed group, a secondary imaging group and a medium wave refrigeration detector along the direction of an optical axis, the front fixed group comprises a double-meniscus monocrystalline silicon lens and a double-meniscus monocrystalline germanium lens; the zoom group is a double-concave single crystal germanium lens; the compensation group is a double-convex monocrystalline silicon lens; the rear fixing group is a double-meniscus single crystal germanium lens; the secondary imaging group comprises a double-convex single crystal germanium lens, a straight surface single crystal germanium lens, a double-meniscus single crystal germanium lens and a meniscus single crystal silicon lens; the medium-wave refrigeration detector is coaxially and sequentially provided with a protection window, a cold diaphragm and a detector target surface, the protection window is located on one side close to an object space, and the detector target surface coincides with an image surface.

Description

Technical Field

[0001] The invention relates to the technical field of infrared optical imaging, and in particular to a low-sensitivity, long-focal-length, extremely-short-total-length medium-wave infrared zoom optical system. Background Art

[0002] With the rapid development of infrared imaging technology and the increasing number of long-distance observation tasks, such as target tracking, photography and security monitoring, research on large-zoom infrared zoom systems has been carried out at home and abroad. Various infrared zoom systems have been launched and widely used in military and civilian fields. In today's world where there are stringent requirements on the size and weight of airborne optoelectronic systems, the simplicity and lightness of optical lenses have become a crucial technical problem.

[0003] However, the refrigerated medium-wave infrared continuous zoom system with a zoom ratio of 30 times or more disclosed in the prior art, in order to achieve long focal length zoom without deflecting the optical path, the total length is usually in the range of 650mm to 750mm, which cannot meet the needs of working in a small space. In addition, as long as the system involves the three elements of large zoom ratio, long focal length zoom, and extremely short total length, its tolerance sensitivity is bound to be high, which makes engineering application more difficult. Therefore, it is particularly important to develop a low-sensitivity, long focal length, and extremely short total length medium-wave infrared zoom optical system.

[0004] The Chinese patent publication number is "CN117784381A", and the patent name is "High zoom ratio medium wave cooling continuous zoom optical system". The system includes a front fixed group, a zoom group, a first compensation group, a second compensation group, a field stop, a secondary imaging group, and a medium wave cooling detector arranged coaxially in sequence. The zoom group, the first compensation group, and the second compensation group are linked to achieve continuous zoom, realizing a 40x medium wave infrared continuous zoom optical system with a focal length of 15 to 600mm and a total length of about 235mm. Although the problem of the large zoom ratio and long focal length continuous zoom system being too long is solved, the zoom focal length range is shortened. At the same time, the three-group linkage zoom form increases the complexity of the system's zoom, and the addition of too many aspherical surfaces leads to excessive system tolerance sensitivity, which is not feasible for engineering applications. Summary of the invention

[0005] In order to solve the problem that the existing medium-wave infrared zoom system is difficult to achieve long focal length zoom and has low sensitivity under the requirements of large zoom ratio and extremely short total length, the present invention provides a low-sensitivity medium-wave infrared zoom optical system with long focal length and extremely short total length.

[0006] To solve the above problems, the present invention provides the following technical solutions:

[0007] A low-sensitivity, long-focal-length, extremely short-total-length medium-wave infrared zoom optical system, characterized in that a front fixing group, a zoom group, a compensation group, a rear fixing group, a secondary imaging group and a medium-wave cooling detector are coaxially arranged along the optical axis direction of the system;

[0008] The front fixed group includes a double meniscus single crystal silicon lens with positive optical power and a double meniscus single crystal germanium lens with positive optical power, which are used to quickly converge the light beam;

[0009] The zoom group is a double concave single crystal germanium lens with negative optical power;

[0010] The compensation group is a biconvex single crystal silicon lens with positive optical power;

[0011] The rear fixed group is a double meniscus single crystal germanium lens with positive optical power;

[0012] The secondary imaging group comprises a double convex single crystal germanium lens with negative optical power, a straight single crystal germanium lens with positive optical power, a double meniscus single crystal germanium lens with positive optical power, and a meniscus single crystal silicon lens with positive optical power;

[0013] The medium wave cooling detector is coaxially provided with a protection window, a cold aperture and a detector target surface in sequence, wherein the protection window is located on the side close to the object, and the detector target surface coincides with the image surface.

[0014] The positions of the two lenses, the biconcave single crystal germanium lens and the biconvex single crystal silicon lens, can be moved, and continuous zooming can be achieved through double-group linkage.

[0015] The front and rear surfaces S1 and S2 of the double meniscus single crystal silicon lens in the front fixing group are both spherical surfaces; the front surface S3 of the double meniscus single crystal germanium lens is spherical, and the rear surface S4 is aspherical.

[0016] The front surface S5 of the biconcave single crystal germanium lens of the zoom group is a spherical surface, and the rear surface S6 thereof is a diffraction surface.

[0017] The front surface S7 of the biconvex single crystal silicon lens of the compensation group is an aspherical surface, and the rear surface S8 is a diffraction surface.

[0018] The front surface S9 of the double meniscus single crystal germanium lens of the rear fixed group is a spherical surface, and the rear surface S10 is a diffraction surface.

[0019] The front surface S11 of the double convex single crystal germanium lens of the secondary imaging group is spherical, and its rear surface S12 is aspherical; the front and rear surfaces S13 and S14 of the straight single crystal germanium lens are both spherical; the front and rear surfaces S15 and S16 of the double meniscus single crystal germanium lens are both spherical; the front surface S17 of the meniscus single crystal silicon lens is aspherical, and its rear surface S18 is spherical.

[0020] The beneficial effects of the present invention are:

[0021] 1. When the present invention is in use, the positions of the diffraction surface and the aspheric surface are reasonably arranged to shorten the distance that the zoom group and the compensation group move when the system is continuously zooming, thereby reducing the total length of the optical system, so that the total length of the system is only 337 mm, which is significantly shorter than that of zoom lenses of similar specifications.

[0022] 2. At the same time, the number of lenses in the entire optical system is reduced to 9, reducing the overall volume of the system, achieving a 30x zoom ratio medium-wave infrared zoom system and a continuous change of focal length from 30 to 900mm. Compared with zoom lenses of similar specifications, the system solves the problem of insufficient detection capability of long-distance targets due to shortened focal length variation range while ensuring an extremely short total length, and the problem of the refractive-reflective optical path system commonly used by similar lenses, which causes a large energy loss due to the addition of two reflectors, resulting in the system's dimensions being too large and complicated.

[0023] 3. When in use, the present invention uses an independent component desensitization design to reduce the overall tolerance sensitivity of the system. Compared with zoom lenses of similar specifications, the feasibility of actual engineering applications is higher.

[0024] The present invention realizes long focal length zooming while ensuring low sensitivity, large zoom ratio and extremely short total length, and has good imaging quality, and can better meet the needs of working in a narrow space. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a long focal length structure of a medium-wave infrared zoom optical system with low sensitivity and very short total length provided by an embodiment of the present invention;

[0026] Figure 2 A schematic diagram of the focusing structure of a medium-wave infrared zoom optical system with a low sensitivity, long focal length and extremely short total length provided by an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of a short-focus structure of a medium-wave infrared zoom optical system with a long focal length and extremely short total length and low sensitivity provided by an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the MTF of the telephoto structure of a medium-wave infrared zoom optical system with a long focal length and extremely short total length and low sensitivity provided by an embodiment of the present invention;

[0029] Figure 5 A schematic diagram of the MTF of the focal structure of the low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system provided by an embodiment of the present invention;

[0030] Figure 6 A schematic diagram of the MTF of the short-focus structure of a medium-wave infrared zoom optical system with a long focal length and extremely short total length and low sensitivity provided by an embodiment of the present invention;

[0031] Numbers in the figure: 1, front fixing group; 2, zoom group; 3, compensation group; 4, rear fixing group; 5, secondary imaging group; 6, medium wave cooled detector; 11, double meniscus single crystal silicon positive lens; 12, double meniscus single crystal germanium positive lens; 21, double concave single crystal germanium negative lens; 31, double convex single crystal silicon positive lens; 41, double meniscus single crystal germanium positive lens; 51, double convex single crystal germanium negative lens; 52, double convex single crystal germanium positive lens; 53, double meniscus single crystal germanium positive lens; 54, meniscus single crystal silicon positive lens; 61, protective window; 62, cold aperture; 63, detector target surface. DETAILED DESCRIPTION

[0032] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] like Figure 1 As shown, a low-sensitivity, long-focal-length, extremely short-total-length medium-wave infrared zoom optical system comprises a front fixed group 1, a zoom group 2, a compensation group 3, a rear fixed group 4, a secondary imaging group 5 and a medium-wave cooled detector 6 which are coaxially arranged from left to right along the optical axis.

[0034] The front fixing group 1 comprises a double meniscus single crystal silicon lens 11 with positive optical power and a double meniscus single crystal germanium lens 12 with positive optical power, which are used to quickly converge the light beam. The front and rear surfaces S1 and S2 of the double meniscus single crystal silicon lens 11 are both spherical. The front surface S3 of the double meniscus single crystal germanium lens 12 is a spherical surface, and the rear surface S4 is an aspherical surface.

[0035] The zoom group 2 is a double concave single crystal germanium lens 21 with negative focal power, the front surface S5 is a spherical surface, and the rear surface S6 is a diffraction surface, which is used to change the focal length of the entire system to achieve 30 times continuous zoom;

[0036] The compensation group 3 is a biconvex single crystal silicon lens 31 with positive optical power, a front surface S7 of which is an aspherical surface and a rear surface S8 of which is a diffraction surface, and is used to compensate for the image plane position.

[0037] The rear fixing group 4 is a double meniscus single crystal germanium lens 41 with positive optical power, the front surface S9 is a spherical surface, and the rear surface S10 is a diffraction surface.

[0038] The secondary imaging group 5 comprises a biconvex single crystal germanium lens 51 with negative optical power, a straight-faced single crystal germanium lens 52 with positive optical power, a double meniscus single crystal germanium lens 53 with positive optical power, and a meniscus single crystal silicon lens 54 with positive optical power. Among them, the front surface S11 of the biconvex single crystal germanium lens 51 is a spherical surface, and the rear surface S12 thereof is an aspherical surface; the front and rear surfaces S13 and S14 of the straight-faced single crystal germanium lens 52 are both spherical surfaces; the front and rear surfaces S15 and S16 of the double meniscus single crystal germanium lens 53 are both spherical surfaces; the front surface S17 of the meniscus single crystal silicon lens 54 is an aspherical surface, and the rear surface S18 thereof is a spherical surface.

[0039] The medium wave cooling detector 6 comprises a protective window 61, a cold aperture 62 and a detector target surface 63 which are coaxially arranged from left to right along the optical axis and packaged together. The protective window 61 is located on the side close to the object, and the detector target surface 63 coincides with the image plane. Among them, the front and rear surfaces S19 and S20 of the protective window 61 are both planes. The detector resolution is 640×512, and the pixel size is 15um. In order to ensure a compact structure, the aperture position coincides with the detector cold aperture, ensuring 100% cold aperture efficiency and improving imaging quality.

[0040] The biconcave single crystal germanium lens 21 and the biconvex single crystal silicon lens 31 are moved to achieve a 30x zoom ratio, a 30-900mm long focal length zoom, and change their positions accordingly according to environmental changes, thereby achieving temperature compensation, and finally receiving images through a medium wave cooling detector.

[0041] Example:

[0042] like Figure 1 As shown, when the system described in this example is in the telephoto state, the air gap between the double meniscus single crystal germanium lens 12 and the lens 21 is 114.310 mm, the air gap between the biconcave single crystal germanium lens 21 and the biconvex single crystal silicon lens 31 is 3.144 mm, and the air gap between the biconvex single crystal silicon lens 31 and the double meniscus single crystal germanium lens 41 is 60.804 mm.

[0043] like Figure 2 As shown, when the system described in this example is in the mid-focus state, the air gap between the double-menus shaped single-crystal germanium lens 12 and the double-concave single-crystal germanium lens 21 is 112.963 mm, the air gap between the double-concave single-crystal germanium lens 21 and the double-convex single-crystal silicon lens 31 is 16.721 mm, and the air gap between the double-convex single-crystal silicon lens 31 and the double-menus shaped single-crystal germanium lens 41 is 48.571 mm.

[0044] like Figure 3As shown, when the system described in this example is in a short-focus state, the air gap between the double-menus shaped single-crystal germanium lens 12 and the double-concave single-crystal germanium lens 21 is 34.200 mm, the air gap between the double-concave single-crystal germanium lens 21 and the double-convex single-crystal silicon lens 31 is 114.093 mm, and the air gap between the double-convex single-crystal silicon lens 31 and the double-menus shaped single-crystal germanium lens 41 is 29.965 mm.

[0045] In this embodiment, the space interval between the double meniscus single crystal germanium lens 41 and the double convex single crystal germanium negative lens 51 is 21.415 mm, the air interval between the double convex single crystal germanium negative lens 51 and the double convex single crystal germanium positive lens 52 is 2.612 mm, the air interval between the double convex single crystal germanium positive lens 52 and the positive double meniscus single crystal germanium lens 53 is 6.513 mm, the air interval between the positive double meniscus single crystal germanium lens 53 and the positive meniscus single crystal germanium lens 54 is 2.052 mm, the air interval between the positive meniscus single crystal germanium lens 54 and the cold aperture is 5.864 mm, and the air interval between the cold aperture 62 and the detector target surface 63 is 19.80 mm.

[0046] The above-mentioned low-sensitivity long focal length extremely short total length medium-wave infrared zoom optical system, wherein the aspherical surface satisfies the following expression:

[0047] z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis;

[0048] k is the cone coefficient;

[0049] α2, α3, and α4 are high-order aspheric coefficients.

[0050] The diffraction surface satisfies the following expression:

[0051] φ=Ah 2 +Bh 4 +Ch 6 +Dh 8 ;

[0052] Among them, A, B, C, and D are diffraction coefficients.

[0053] The parameters of each lens of the continuous zoom optical system of the present invention are shown in Table 1:

[0054] Table 1

[0055] Surface name type Curvature radius / mm Thickness / mm Material S1 Spherical 185.842 36.577 SILICON S2 Spherical 361.215 19.558 S3 Spherical 357.678 15.174 GERMANIUM S4 Aspheric 225.873 114.310 S5 Spherical -472.320 10.782 GERMANIUM S6 Diffraction surface 75.590 3.144 S7 Aspheric 107.750 5.061 SILICON S8 Diffraction surface -258.926 60.804 S9 Spherical -13.703 1.668 GERMANIUM S10 Diffraction surface -17.144 21.415 S11 Spherical 72.051 2.956 SILICON S12 Aspheric -54.578 2.612 S13 Spherical 1159.399 1.231 GERMANIUM S14 Spherical 622.162 6.513 S15 Spherical -11.662 2.132 GERMANIUM S16 Spherical -18.587 2.052 S17 Aspheric -183.147 4.029 SILICON S18 Spherical -19.596 2.422 S19 flat - 1.000 GERMANIUM S20 flat - 1.942 S21 flat - 0.500 GERMANIUM Cold light stop flat - 19.800 Image plane flat - -

Claims

1. Low-sensitivity long focal length extremely short total length medium-wave infrared zoom optical system, characterized by: The system is coaxially arranged along the optical axis direction with a front fixing group (1), a zoom group (2), a compensation group (3), a rear fixing group (4), a secondary imaging group (5) and a medium wave cooling detector (6); The front fixed group (1) comprises a double meniscus single crystal silicon lens (11) with positive optical power and a double meniscus single crystal germanium lens (12) with positive optical power; The variable power group (2) is a double concave single crystal germanium lens (21) with negative optical power; The compensation group (3) is a biconvex single crystal silicon lens (31) with positive optical power; The rear fixed group (4) is a double meniscus single crystal germanium lens (41) with positive optical power; The secondary imaging group (5) comprises a double convex single crystal germanium lens (51) with negative optical power, a straight single crystal germanium lens (52) with positive optical power, a double meniscus single crystal germanium lens (53) with positive optical power, and a meniscus single crystal silicon lens (54) with positive optical power; The medium wave cooling detector (6) is coaxially provided with a protection window (61), a cold aperture (62) and a detector target surface (63) in sequence, wherein the protection window (61) is located on a side close to the object, and the detector target surface (63) coincides with the image plane.

2. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The positions of the two lenses, the biconcave single crystal germanium lens (21) and the biconvex single crystal silicon lens (31), can be moved, and continuous zooming can be achieved through dual-group linkage.

3. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The front and rear surfaces S1 and S2 of the double meniscus-shaped single crystal silicon lens (11) in the front fixing group (1) are both spherical surfaces; the front surface S3 of the double meniscus-shaped single crystal germanium lens (12) is a spherical surface, and the rear surface S4 is an aspherical surface.

4. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The front surface S5 of the biconcave single crystal germanium lens (21) of the zoom group (2) is a spherical surface, and the rear surface S6 is a diffraction surface.

5. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The front surface S7 of the biconvex single crystal silicon lens (31) of the compensation group (3) is an aspherical surface, and the rear surface S8 is a diffraction surface.

6. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The front surface S9 of the double meniscus single crystal germanium lens (41) of the rear fixing group (4) is a spherical surface, and the rear surface S10 is a diffraction surface.

7. The low-sensitivity, long focal length, extremely short total length medium-wave infrared zoom optical system according to claim 1, characterized in that: The front surface S11 of the biconvex single crystal germanium lens (51) of the secondary imaging group (5) is a spherical surface, and the rear surface S12 thereof is an aspherical surface; the front and rear surfaces S13 and S14 of the straight single crystal germanium lens (52) are both spherical surfaces; the front and rear surfaces S15 and S16 of the double meniscus single crystal germanium lens (53) are both spherical surfaces; the front surface S17 of the meniscus single crystal silicon lens (54) is an aspherical surface, and the rear surface S18 thereof is a spherical surface.

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