A 10x continuous zoom mid-wave cooled infrared optical system

Abstract

This invention discloses a 10x continuous zoom mid-wave cooled infrared optical system, comprising a front fixed group (1), a zoom group (2), a middle fixed group (3), a compensation group (4), a first plane mirror (5), a second plane mirror (6), a rear fixed group (7), a secondary imaging fixed group (8), a cooled detector cold stop (9), and a focal plane (10), arranged sequentially along the optical path on the same optical axis. The optical system contains nine lenses, with the zoom group and compensation group each containing only one lens. Furthermore, the entrance pupil is close to the first lens at long focal lengths, resulting in a compact system structure, small size, high light transmittance, and corrosion resistance. Additionally, since mid-infrared aspherical surfaces can be machined using diamond single-point turning, the machining difficulty is low, leading to low overall machining costs.

Description

Technical Field

[0001] This invention belongs to the field of optical system technology, specifically relating to a 10x continuous zoom mid-wave cooled infrared optical system. Background Technology

[0002] Infrared imaging technology is widely used in target detection, identification, and tracking due to its advantages such as all-weather operation and strong environmental adaptability. Mid-wave cooled detectors, with their high sensitivity, have broad application prospects in related military fields. Especially in application scenarios that require both wide-field-of-view target search and narrow-field-of-view tracking and identification of long-distance targets, it is usually necessary to ensure that the target remains clearly imaged within the zoom range and that the target of interest is not lost during zooming. In such cases, the optical system must have continuous zoom capability within the required focal length range.

[0003] With advancements in infrared device fabrication, infrared component processing capabilities, and optical design, mid-wave infrared continuous zoom optical systems with larger zoom ratios and smaller size and weight have been proposed. Chinese patent application CN110673314A discloses a negative-compensation large-target mid-wave cooled infrared continuous zoom optical system, which includes one diffractive lens, with the first lens being relatively large. Chinese patent application CN106950684A discloses an integrated infrared dual-band 20× zoom optical system, which uses three diffractive lenses, increasing processing difficulty and reducing light transmittance. Chinese patent application CN103389570A discloses a mid-wave infrared continuous zoom optical system with a high zoom ratio, employing a cross-arrangement of zoom lenses A and B with compensation lenses C and D for zooming. This system cannot be folded and has a relatively long axial dimension.

[0004] As can be seen from the existing technologies described above, current continuous zoom mid-wave cooled infrared optical system designs utilize diffractive lenses to reduce the number of lenses used. However, this inevitably affects the system's light transmittance. Furthermore, because the micro-nano fabricated structures of diffractive lenses are more susceptible to corrosion, higher demands are placed on the corrosion resistance design of the entire system. In addition, the existing technologies do not consider miniaturization factors, such as controlling the size of the first lens in the telephoto mode, nor do they consider the advantages that a folding layout brings to system miniaturization. Summary of the Invention

[0005] In view of the above, the purpose of this invention is to provide a 10x continuous zoom mid-wave cooled infrared optical system. This optical system includes 9 lenses, with the zoom group and compensation group each containing only 1 lens. Furthermore, the entrance pupil is close to the first lens at long focal lengths, resulting in a compact system structure and small size.

[0006] To achieve the aforementioned objective, an embodiment provides a 10x continuous zoom mid-wave cooled infrared optical system, comprising focal lengths arranged sequentially along the optical path on the same optical axis. f 1. Front fixed group (1), focal length is f 2 zoom group (2), focal length is f 3 intermediate fixed group (3), focal length is f The compensation group (4), the first plane mirror (5), the second plane mirror (6), and the focal length are 4 f The rear fixed group (7) of 7 has a focal length of f The secondary imaging fixing group (8), the cooled detector cold aperture (9), and the focal plane (10) are of group 8, wherein the rear fixing group (7) includes a focal length of 8. f 71 The rear fixed group first lens (71) and focal length are f 72 The second lens (72) of the rear fixed group, and the secondary imaging fixed group (8) include a focal length of f 81 The first lens (81) of the secondary imaging fixed group has a focal length of f 82 The second lens (82) of the secondary imaging fixed group and the focal length is f 83 The third lens (83) of the secondary imaging fixed group, the optical imaging system satisfies the following conditions:

[0007] ;

[0008] in, f This indicates the focal length of an optical imaging system.

[0009] Preferably, the system adopts a secondary imaging structure, with the primary imaging located between the rear fixed group (7) and the secondary imaging fixed group (8), and the secondary imaging located on the focal plane (10).

[0010] Preferably, the front fixed group (1), the zoom group (2), the middle fixed group (3), the compensation group (4), the first plane mirror (5), the second plane mirror (6), and the rear fixed group (7) form a single imaging group;

[0011] The object side of the zoom group (2) and the image side of the intermediate fixed group (3) in the single imaging group adopt a flattened ellipsoidal design, the image side of the zoom group (2) and the object side of the intermediate fixed group (3) adopt an even-order aspherical design, and the surfaces of the remaining lenses in the single imaging group adopt a standard spherical design.

[0012] Preferably, both the zoom group (2) and the compensation group (4) are implemented using a single lens, and the intermediate fixed group (3) between the zoom group (2) and the compensation group (4) contains a single lens.

[0013] Preferably, the secondary imaging fixation group (8) serves as the secondary imaging group;

[0014] The secondary imaging group uses a three-piece refractive mirror group, namely the first lens (81), the second lens (82), and the third lens (83) of the secondary imaging fixed group are all single-piece refractive mirrors. The image side of the first lens (81) and the object side of the second lens (82) of the secondary imaging fixed group are designed with even-order aspherical surfaces, while the surfaces of the other lenses in the secondary imaging group are designed with standard spherical surfaces.

[0015] Preferably, the system can achieve continuous zoom within a focal length range of 50-500mm for targets in the 3.7-4.8μm mid-infrared band by controlling the movement of the zoom group (2) and the compensation group (4) to perform large-scale search and small-scale observation.

[0016] Preferably, the pixel array of the focal plane (10) is 640×512, and the F number is 3≤F≤5.

[0017] Preferably, the front fixed group (1) adopts a single lens with a diameter of less than 120mm. The light path is refracted back through the first plane mirror (5) and the second plane mirror (6) to form a U-shaped optical system.

[0018] Preferably, when the focal length of the optical system f When the distance is within the range of 50-500mm, the distance s1 between the front fixed group (1) and the zoom group (2) is 111.379-236.684mm, the distance s2 between the zoom group (2) and the middle fixed group (3) is 9.082-134.387mm, the distance s3 between the middle fixed group (3) and the compensation group (4) is 65.745-162.738mm, and the distance s4 between the compensation group (4) and the first plane mirror (5) is 47.603-144.597mm.

[0019] Preferably, the exit pupil of the secondary imaging fixed group (8) in the system coincides with the cold aperture (9) of the cooled detector.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0021] (1) The optical system of the present invention uses a cooled mid-infrared detector. Therefore, the exit pupil of the secondary imaging fixed group in the optical system needs to be matched with the cold aperture of the cooled detector to achieve 100% efficiency of the cold aperture of the cooled detector. At the same time, the system adopts a secondary imaging structure. Under the premise that the exit pupil is matched with the cold aperture of the cooled detector, it is possible for the entrance pupil to be located near the first lens, which effectively reduces the overall aperture of the optical system.

[0022] (2) The optical system of the present invention consists of 9 optical lenses, which do not contain diffraction surfaces, only 4 even-order aspherical lenses, and the rest are spherical lenses. The system has a simple structure, high light transmittance, and corrosion resistance. Furthermore, since the mid-infrared aspherical surface can be machined by diamond single-point turning, the machining difficulty is low and the overall machining cost is low.

[0023] (3) In the optical system of the present invention, both the zoom group and the compensation group are implemented with one lens, which is simple in structure and makes it easier to realize the driving process when the zoom group and the compensation group move to the corresponding focus position.

[0024] (4) The optical system of the present invention adopts a secondary imaging design. The primary imaging structure realizes the zoom function, and the secondary imaging structure compensates for the remaining aberrations, so that the system can achieve near-diffraction limit imaging at key points during the zoom process of 50~500mm.

[0025] (5) The optical system of the present invention adopts a U-shaped design layout, which leaves sufficient space for the placement of the mid-infrared cooled detector. The system layout is reasonable and the structure is compact, and the volume and weight of the entire system are miniaturized. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the optical structure of an optical system provided in an embodiment of the present invention at a short focal length of 50mm;

[0028] Figure 2 This is a schematic diagram of the optical structure of an optical system provided in an embodiment of the present invention at a focal length of 200mm.

[0029] Figure 3 This is a schematic diagram of the optical structure of an optical system provided in an embodiment of the present invention at a medium telephoto focal length of 350mm.

[0030] Figure 4 This is a schematic diagram of the optical structure of an optical system provided in an embodiment of the present invention at a focal length of 500mm;

[0031] Figure 5 The zoom curve of an optical system provided in an embodiment of the present invention;

[0032] Figure 6 The optical transfer function curve of an optical system provided in an embodiment of the present invention at a short focal length of 50mm;

[0033] Figure 7 The optical transfer function curve of an optical system provided in an embodiment of the present invention at a focal length of 200mm;

[0034] Figure 8 The optical transfer function curve of an optical system provided in an embodiment of the present invention at a medium telephoto focal length of 350mm;

[0035] Figure 9 The optical transfer function curve of an optical system provided in an embodiment of the present invention at a focal length of 500mm;

[0036] Reference numerals: 1-Front fixed group, 2-Magnification group, 3-Intermediate fixed group, 4-Compensation group, 5-First plane mirror, 6-Second plane mirror, 7-Rear fixed group, 8-Secondary imaging fixed group, 9-Cooled detector cold aperture, 10-Focal plane, 71-Rear fixed group first lens, 72-Rear fixed group second lens, 81-Secondary imaging fixed group first lens, 82-Secondary imaging fixed group second lens, 83-Secondary imaging fixed group third lens. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0038] like Figures 1-4 As shown, an embodiment of a 10x continuous zoom mid-wave cooled infrared optical system includes a front fixed group 1, a zoom group 2, an intermediate fixed group 3, a compensation group 4, a plane mirror 5, a plane mirror 6, a rear fixed group 7, a secondary imaging fixed group 8, a cooled detector 9, and a focal plane 10, all arranged sequentially along the optical path on the same optical axis. The front fixed group 1, zoom group 2, intermediate fixed group 3, compensation group 4, plane mirror 5, plane mirror 6, and rear fixed group 7 form a primary imaging group, and the secondary imaging fixed group 8 forms a secondary imaging group. The rear fixed group 7 includes a first lens 71 and a second lens 72, and the secondary imaging fixed group 8 includes a first lens 81, a second lens 82, and a third lens 83. This optical system satisfies the following conditions:

[0039]

[0040] in, f Indicates that the optical imaging system is in f =500mm focal length, f 1 indicates the focal length of the front fixed group 1. f 2 indicates the focal length of zoom group 2. f 3 indicates the focal length of the middle fixed group 3. f 4 represents the focal length of compensation group 4. f 7 indicates the focal length of the rear fixed group 7. f 8 represents the focal length of the fixed group 8 in the secondary imaging.

[0041] Rear fixed group 7 meets the following conditions:

[0042]

[0043] in, f 7 indicates the focal length of the rear fixed group 7. f 71 This indicates the focal length of the rear fixed group 71. f 72 This indicates the focal length of the rear fixed group 72.

[0044] The secondary imaging fixation group (8) meets the following conditions:

[0045]

[0046] in, f 8 represents the focal length of the secondary imaging fixed group (8). f 81 This indicates the focal length of the secondary imaging fixed group (81). f 82 This indicates the focal length of the secondary imaging fixed group (82). f 83 This indicates the focal length of the secondary imaging fixed group (83).

[0047] In the optical system, the incident light rays pass sequentially through the front fixed group 1, the zoom group 2, the intermediate fixed group 3, and the compensation group 4 to be projected onto the first plane mirror 5. After passing through the first plane mirror 5, the light rays are projected onto the second plane mirror 6, and then converged onto the primary image plane by the rear fixed group 7. After passing through the primary image plane, the light rays are projected onto the secondary imaging fixed group 8, and then converged by the secondary imaging fixed group 8. After passing through the cooled detector cold stop 9, the light rays finally converge onto the focal plane 10.

[0048] In this embodiment, the optical lens materials mainly use commonly used silicon, germanium, zinc sulfide, and chalcogenide glass. Both the zoom group 2 and the compensation group 4 are implemented using a single lens, and the intermediate fixed group 3 between the zoom group 2 and the compensation group 4 contains a single lens. The exit pupil of the secondary imaging fixed group (8) coincides with the cold stop 9 of the cooled detector. The pixel array of the focal plane 10 is 640×512, and the F-number is 3≤F≤5.

[0049] In this embodiment, the object-side surface of the zoom group 2 and the image-side surface of the intermediate fixed group 3 in the primary imaging group are designed with flattened ellipsoids, while the image-side surface of the zoom group 2 and the object-side surface of the intermediate fixed group 3 are designed with even-order aspherical surfaces. The surfaces of the remaining lenses in the primary imaging group are designed with standard spherical surfaces. The secondary imaging group uses a three-element refractive mirror group, namely, the first lens 81, the second lens 82, and the third lens 83 of the secondary imaging fixed group are all single-element refractive mirrors. The image-side surface of the first lens 81 and the object-side surface of the second lens 82 of the secondary imaging fixed group are designed with even-order aspherical surfaces, while the surfaces of the remaining lenses in the secondary imaging group are designed with standard spherical surfaces.

[0050] In this embodiment, zoom group 2 and compensation group 4 serve as a moving group. When zooming is required, a control signal is generated by the circuit to control the motor, moving zoom group 2 and compensation group 4 to the corresponding zoom position, thereby achieving mid-wave infrared imaging at different focal lengths. Specifically, it is applicable to the 3.7-4.8μm mid-wave infrared band. Continuous zooming within a focal length range of 50-500mm can be achieved through zooming, enabling large-scale searches and fine observations in small areas. During 10x zoom, the distance between the zoom group and the compensation group satisfies the following condition:

[0051]

[0052] Wherein, s1 is the spacing range between the front fixed group 1 and the zoom group 2, s2 is the spacing range between the zoom group 2 and the intermediate fixed group 3, s3 is the spacing range between the intermediate fixed group 3 and the compensation group 4, and s4 is the spacing range between the compensation group 4 and the first plane mirror 5. Specifically, the spacing values ​​at several key focal lengths of 50mm, 200mm, 350mm, and 500mm are shown in Table 1, and the corresponding structural diagrams are as follows. Figure 1-4 As shown:

[0053]

[0054] The embodiment also provides an optical system with specific optical parameters, the corresponding specific optical parameters are shown in Table 2:

[0055]

[0056] In the aforementioned optical system, the object-side surface of the zoom group 2 and the image-side surface of the intermediate fixed group 3 in the primary imaging group adopt an ellipsoidal design, with the conic coefficient of the object-side surface of the zoom group 2 being 10.008 and that of the image-side surface of the intermediate fixed group 3 being 10.017. The image-side surface of the zoom group 2 and the object-side surface of the intermediate fixed group 3 adopt an even-order aspherical design, with the conic coefficient of the image-side surface of the zoom group 2 being 10.028, and the higher-order aspherical coefficients being a4 = -1.162E-007, a6 = 5.148E-011, and a8 = -3.292E-014; the conic coefficient of the object-side surface of the intermediate fixed group 3 is 9.307, and the higher-order aspherical coefficients are a4 = -8.589E-008, a6 = 2.799E-011, and a8 = -1.042E-014. The remaining lens surfaces in the primary imaging group all adopt a standard spherical design.

[0057] The secondary imaging fixing group 8 adopts a three-element refractive mirror group, in which the image-side surface of the first lens 81 and the object-side surface of the second lens 82 of the secondary imaging fixing group are designed with even-order aspherical surfaces. The conicity of the image-side surface of the first lens 81 of the secondary imaging fixing group is 0.795, and the higher-order aspherical coefficients are a4 = 2.132E-004, a6 = 9.868E-006, and a8 = -5.507E-008; the conicity of the object-side surface of the secondary imaging fixing group 82 is 1.385, and the higher-order aspherical coefficients are a4 = -3.866E-005, a6 = 2.655E-006, and a8 = -7.939E-008; the surfaces of the remaining lenses in the secondary imaging group are all designed with standard spherical surfaces.

[0058] The optical system provided in this embodiment comprises nine lenses and does not include a diffraction surface, resulting in a simple structure. The secondary imaging structure makes it possible for the entrance pupil to be located near the first lens when the exit pupil of the mid-wave cooled infrared optical system needs to coincide with the cold stop 9 of the cooled detector, thus minimizing the aperture of the first lens in the optical system. In this embodiment, the exit pupil of the mid-wave cooled infrared optical system coincides with the cold stop 9, and in telephoto mode, the entrance pupil is close to the first lens, resulting in a smaller overall optical system aperture. The aperture of the first lens is less than 120mm, and the system adopts a U-shaped layout, making it compact. This system, in conjunction with changes in the azimuth and pitch angles of the optical system, can track targets at different spatial angles and operating distances. By calibrating the corresponding positions of the zoom group and compensation group at a certain focal length, the zoom curve is obtained as shown below. Figure 5 As shown, during the zoom process, the motion curves of the zoom group and the compensation group are smooth without inflection points, and the constraint relationship between the zoom group and the compensation group is non-linear.

[0059] Figures 6-9The optical transfer function curves of the optical system at several key points during the zoom process from 50 to 500mm are shown. It can be seen that the MTF of each field of view is greater than 0.17 at different focal lengths, which meets the imaging requirements of the optical system at different focal lengths.

[0060] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A 10x continuous zoom mid-wave cooled infrared optical system, characterized in that, This includes focal lengths arranged sequentially along the same optical axis and the optical path. f 1. Front fixed group (1), focal length is f 2 zoom group (2), focal length is f 3 intermediate fixed group (3), focal length is f The compensation group (4), the first plane mirror (5), the second plane mirror (6), and the focal length are 4 f The rear fixed group (7) of 7 has a focal length of f The secondary imaging fixing group (8), the cooled detector cold aperture (9), and the focal plane (10) are of group 8, wherein the rear fixing group (7) includes a focal length of 8. f 71 The rear fixed group first lens (71) and focal length are f 72 The second lens (72) of the rear fixed group, and the secondary imaging fixed group (8) include a focal length of f 81 The first lens (81) of the secondary imaging fixed group has a focal length of f 82 The second lens (82) of the secondary imaging fixed group and the focal length is f 83 The third lens (83) of the secondary imaging fixed group, the optical imaging system satisfies the following conditions: ； in, f This indicates the focal length of an optical imaging system.

2. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The system adopts a secondary imaging structure, with the primary imaging located between the rear fixed group (7) and the secondary imaging fixed group (8), and the secondary imaging located on the focal plane (10).

3. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The front fixed group (1), the zoom group (2), the middle fixed group (3), the compensation group (4), the first plane mirror (5), the second plane mirror (6), and the rear fixed group (7) form a primary imaging group; The object side of the zoom group (2) and the image side of the intermediate fixed group (3) in the single imaging group adopt a flattened ellipsoidal design, the image side of the zoom group (2) and the object side of the intermediate fixed group (3) adopt an even-order aspherical design, and the surfaces of the remaining lenses in the single imaging group adopt a standard spherical design.

4. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, Both the zoom group (2) and the compensation group (4) are implemented using a single lens, and the intermediate fixed group (3) between the zoom group (2) and the compensation group (4) contains a single lens.

5. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The secondary imaging fixed group (8) serves as the secondary imaging group; The secondary imaging group uses a three-piece refractive mirror group, namely the first lens (81), the second lens (82), and the third lens (83) of the secondary imaging fixed group are all single-piece refractive mirrors. The image side of the first lens (81) and the object side of the second lens (82) of the secondary imaging fixed group are designed with even-order aspherical surfaces, while the surfaces of the other lenses in the secondary imaging group are designed with standard spherical surfaces.

6. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The system can achieve continuous zoom within a focal length range of 50-500mm for targets in the 3.7-4.8μm mid-infrared band by controlling the movement of the zoom group (2) and the compensation group (4) to perform large-scale search and small-scale observation.

7. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The pixel array of the focal plane (10) is 640×512, and the F number is 3≤F≤5.

8. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The front fixed group (1) uses a single lens with a diameter of less than 120mm. The light path is refracted back through the first plane mirror (5) and the second plane mirror (6) to form a U-shaped optical system.

9. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, When the focal length of the optical system f When the distance is within the range of 50-500mm, the distance s1 between the front fixed group (1) and the zoom group (2) is 111.379-236.684mm, the distance s2 between the zoom group (2) and the middle fixed group (3) is 9.082-134.387mm, the distance s3 between the middle fixed group (3) and the compensation group (4) is 65.745-162.738mm, and the distance s4 between the compensation group (4) and the first plane mirror (5) is 47.603-144.597mm.

10. The 10x continuous zoom mid-wave cooled infrared optical system according to claim 1, characterized in that, The exit pupil of the secondary imaging fixed group (8) in the system coincides with the cold aperture (9) of the cooled detector.

Images