Miniaturized three-reflection refrigeration type infrared optical system based on LEO detector

Abstract

A miniaturized three-reflection refrigeration type infrared optical system based on an LEO detector is characterized in that an image plane of a thermal imager is rotated by 90 degrees through a three-time reflection mode, so that the LEO type refrigeration infrared detector is rotated by 90 degrees to be installed, the problem that the transverse size is too large due to the structure of the detector is solved, and the miniaturized design of the whole thermal imager is realized. Based on the scheme, the optical system can reach 100% cold diaphragm efficiency, the system adopts a secondary imaging structure to reduce the aperture of the system, the optical path is reflected through the reflector to adapt to the installation requirement in a special space, and the diffractive optical element and the aspheric surface are used for athermalization and achromatism.

Description

Technical Field

[0001] The invention relates to a miniaturized three-reflection cooling type infrared optical system based on a LEO detector, which can be applied to airborne and vehicle-mounted optical pod infrared thermal imagers. Background Art

[0002] At present, the most widely used airborne infrared optical systems are mainly divided into straight optical systems and folding optical systems. Among them, all optical lenses of the straight optical system are coaxial, with a small lateral width and a large axial length. It is mostly used in occasions with a short focal length ( Figure 1 ); The folding optical system adds two reflectors to compress the light path to achieve a smaller axial size and a larger lateral width. It is mostly used in long-focal-length thermal imagers and can compress the larger axial size caused by the longer focal length ( Figure 2 ).

[0003] Currently, in airborne environments, due to the wide lateral dimensions of LEO detectors and small axial and longitudinal dimensions, most infrared optical systems based on LEO detectors are straight-tube optical systems. LEO detectors cannot take advantage of their small size and light weight when used in folding optical systems. If the size advantage is to be taken advantage of, the LEO detector needs to be rotated 90°, but the aspect ratio of the image plane cannot be changed. As a result, the image plane of the detector itself needs to be rotated 90°, and the detector needs to be specially customized. For LEO detectors that have been widely used, rotating the image plane will reduce reliability. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and solve the problem of excessive lateral dimensions caused by the structure of the detector itself.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A miniaturized three-reflection refrigerated infrared optical system based on LEO detectors rotates the image plane of the thermal imager 90° by three reflections, so that the LEO type refrigerated infrared detector can be installed by rotating it 90°, solving the problem of excessive lateral size caused by the detector's own structure and realizing the miniaturization design of the thermal imager. Based on the above scheme, the optical system can achieve 100% cold aperture efficiency. The system adopts a secondary imaging structure to reduce the system aperture, and uses a reflector to fold the optical path to meet the installation requirements in special spaces. Diffractive optical elements and aspherical surfaces are used to eliminate heat and color differences.

[0007] A miniaturized three-reflection cooling infrared optical system based on a LEO detector, comprising a front fixed lens group, a zoom lens group, a compensation lens group, a rear fixed lens group, a secondary imaging lens group, a cold light bar, a detector focal plane, and three reflectors;

[0008] The light passes through the front fixed lens group, the zoom lens group, the compensation lens group, the rear fixed lens group, the secondary imaging lens group, and the cold light barrier in sequence, and is projected onto the focal plane of the detector;

[0009] The front fixed lens group provides the initial image point for the optical system, and the zoom lens group and the compensation lens group move according to the preset curve to achieve field of view transformation; the rear fixed lens group converges the light to form an image on the primary image plane, and the secondary imaging lens group projects the primary image plane onto the focal plane of the detector; the cold light bar serves as the actual light bar and exit pupil of the optical system;

[0010] Three reflectors are located between the rear fixed lens group and the secondary imaging lens group to reflect the light three times.

[0011] A design method based on the above miniaturized three-reflection refrigeration infrared optical system comprises:

[0012] Arrange the components in the order that the light is projected onto the focal plane of the detector after passing through the front fixed lens group, the zoom lens group, the compensation lens group, the rear fixed lens group, the secondary imaging lens group, and the cold light barrier;

[0013] The distance between the rear fixed group and the secondary imaging mirror group is enlarged so that three reflectors can be placed within the distance.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention rotates the image plane of the optical system by 90° through the design of the optical system. Without rotating the image plane inside the LEO detector, the detector can be directly rotated by 90° for installation to shorten the lateral width of the thermal imager and meet the use requirements.

[0016] (2) The present invention is based on materials such as silicon, germanium, and zinc selenide. After optimized design, it adopts a secondary imaging structure and utilizes aspheric surfaces and diffraction surfaces to reduce the system aperture and simplify the system structure. The optical path is refracted through three reflections. While compressing the volume of the optical path, the image plane of the optical system is rotated 90°, so that the LEO detector is installed on the main frame of the optical system in a manner of rotating 90°. This reduces the volume and weight while improving the structural stability.

[0017] (3) The optical system of the present invention has a focal length of 15 mm to 300 mm and is composed of 8 lenses and 3 reflectors. It is designed to achieve 100% cold light barrier efficiency and has good imaging quality.

[0018] (4) The difficulty of the optical system involved in the present invention lies in the adjustment of the angle relationship between the three reflectors. By setting up an optical path and adjusting the installation method, the relative angle error between the three reflectors can be reduced to within 10", effectively solving the problem of reduced imaging quality of the thermal imager due to the adjustment error. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a straight optical system and LEO detector.

[0020] Figure 2 It is a refracting optical system and LEO detector.

[0021] Figure 3 It is a three-reflection optical system.

[0022] Figure 4 This is an object-image relationship diagram.

[0023] Figure 5 This is the optical path diagram of the optical system of the present invention.

[0024] Figure 6 This is an optical system diagram of the present invention.

[0025] Figure 7 This is a schematic diagram of the optical path of the present invention. Figure 7 a is the first diagram for establishing a vertical light path. Figure 7 b is the first picture of reflector adjustment. Figure 7 c is the second diagram for establishing a vertical light path. Figure 7 d is the second picture of the reflector adjustment.

[0026] Figure numerals: 1-front fixed lens group A, 2-front fixed lens group B, 3-zooming lens group, 4-compensation lens group, 5-rear fixed lens group A, 6-rear fixed lens group B, 7-secondary imaging lens A, 8-secondary imaging lens B, 9-cold light bar, 10-detector focal plane. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] A miniaturized three-reflection refrigerated infrared optical system based on a LEO detector comprises a front fixed lens group A1, a front fixed lens group B2, a zoom lens group 3, a compensation lens group 4, a rear fixed lens group A5, a rear fixed lens group B6, a secondary imaging lens A7, a secondary imaging lens B8, a cold light bar 9, a detector focal plane 10, and three reflectors.

[0029] Among them, the front fixed lens group A1 and the front fixed lens group B2 constitute the front fixed lens group, which provide the initial image point for the optical system, the zoom lens group 3 and the compensation lens group 4 move according to the preset curve to realize the field of view transformation; the rear fixed lens group A5 and the rear fixed lens group B6 constitute the rear fixed lens group, which converges the light on the primary image plane through the rear fixed lens group; the secondary imaging lens A7 and the secondary imaging lens B8 constitute the secondary imaging lens group, which projects the primary image plane onto the detector focal plane 10, and 9 is the cold light bar, which serves as the actual light bar and exit pupil of the system and is located between the secondary imaging lens group and the detector focal plane 10.

[0030] After one reflection, the target object will form left and right mirror images. Each image plane of the optical system will form left and right and top and bottom mirror images. The algorithm supports left and right mirror images and top and bottom mirror images, but does not support image plane rotation (image plane rotation will change the aspect ratio of the image plane). Therefore, if the thermal imager is to form a positive image, the top and bottom mirror images and left and right mirror images must be an even number of times.

[0031] If the image plane is rotated 90° by reflection, at least three reflections are required. Therefore, the optical system of the present invention adopts a three-reflection structure, combined with a secondary imaging optical system, and cooperates with an algorithm to perform a left-right mirror image, achieving the effect of 6 left-right mirror images and 2 upper-lower mirror images. Finally, the optical system forms a positive image, and the object-image relationship is as follows: Figure 4 shown.

[0032] Figure 4 In the figure, Z is the propagation direction of light. The light beam emitted by the target satisfies the left-hand rule before entering the optical system, and satisfies the right-hand rule after passing through the optical system. Therefore, a left-right mirror image is generated. After the left-right mirror image is completed through the algorithm, the system can form a normal image.

[0033] The design is carried out according to the secondary imaging optical system design method, and the position of the reflector is reserved. The final designed optical system is as follows Figure 5 and Figure 6 shown.

[0034] Specific:

[0035] First, a secondary imaging optical system that meets the requirements is designed. The front group (including front fixed lens group A, front fixed lens group B, zoom lens group, compensation lens group, rear fixed lens group A, and rear fixed lens group B) images the infinite target, and the rear group (including secondary imaging lens A and secondary imaging lens B) performs secondary imaging on the primary image surface. Silicon, germanium, zinc selenide and other materials are used, and aspheric surfaces are added to the germanium lens for optimization to meet the requirements of the optical system.

[0036] Then, the distance between the rear fixed lens group and the secondary imaging lens group is increased so that three reflectors can be placed at this distance, and the reflector aperture is planned (the reflector aperture is reduced by setting a reasonable focal length ratio). A diffraction surface is added to the germanium sheet of the rear fixed lens group, and the ring zone coefficient and the planned radius are set. After the final design is completed, in this embodiment, the number of front fixed lens groups is 2, the number of zoom lens groups is 1, the number of compensation lens groups is 1, the number of rear fixed lens groups is 2, the reflectors are 3, and the number of secondary imaging lens groups is 2. Among them, there are 2 aspherical surfaces (front fixed lens group B and zoom lens group) and 2 diffraction surfaces (rear fixed lens group B and secondary imaging lens B). While satisfying the cold light bar matching, the system imaging quality reaches the diffraction limit.

[0037] When the light passes through each reflector, it needs to be folded 90° (such as Figure 4 As shown in the figure, the normal of the reflector forms an angle of 45° with the light beam, and the incident angle of the light beam passing through the reflector is 45°. When the reflector angle deviates by a°, the reflection angle will deviate by 2a°, and after passing through three reflectors, it will deviate by 8a°. Therefore, the precise adjustment of the reflector angle is a prerequisite for the normal operation of the optical system.

[0038] according to Figure 2 In the secondary reflection optical form and detector placement shown in the figure, the object is in the positive direction on the image plane after passing through the optical system. Figure 3 The three-reflection optical form and detector position shown in the figure, after the target is reflected three times, the object image relationship is as follows Figure 4 As shown, Figure 2 Compared with the traditional optical design, the image is rotated 90°. However, the image is required to remain positive during use, so the Figure 3 As shown, Figure 2 Compared with the detector, the detector is rotated 90°. At this time, the object forms a positive image on the detector surface, and the detector is rotated 90° ( Figure 3 ), compared with before rotation ( Figure 2 ), the lateral size is reduced, which is conducive to the miniaturization of the whole machine.

[0039] At the same time, the three reflectors rotate the target image by 90°, so that the optical axis of the detector and the incident optical axis of the optical system have a height difference in the height direction ( Figure 3 right), and Figure 2 Compared with the method of directly rotating the detector 90°, the height size of the thermal imager is not increased.

[0040] This design builds an optical path and installs and fixes each reflector in turn, such as Figure 7As shown, the four surfaces of the reference prism are all reflective surfaces, and the verticality of two adjacent surfaces is 0.5". Through light pipe collimation (the light beam emitted by the light pipe, after passing through the reflective surface of the reference prism, returns to the light pipe, forming an observable cross image on the light pipe, and the center of the image coincides with the visual scale of the light pipe), the optical axes of light pipe 1 and light pipe 2 are adjusted to a verticality of 5" (including the error of the light pipe degree) ( Figure 7 a); Secondly, remove the reference prism and fix the reflector 1 structure between the two light pipes. Light pipe 1 and reflector 1 structure are aligned, and at the same time, the light beam emitted by light pipe 2 enters light pipe 1 after being reflected by the reflector, forming another observable cross image on light pipe 1 ( Figure 7 b). By adjusting the relative angle between the reflector 1 and the reflector 1 mounting structure (the structure is fixed), the two cross images are adjusted to overlap and the reflector is fixed.

[0041] according to Figure 7 c. Align the two light tubes to the same reflective surface, and then restore the installed reflector 1 and its structure to Figure 7 d, adjust the reflector 2 according to the above method until each reflector is installed in sequence, wherein the error generated by the previously installed reflector will not be accumulated, but will be compensated by the reference established when the next reflector is installed and adjusted, and the final deviation angle of the outgoing light beam is the error angle (5") of the optical path construction. The deflection angle of the outgoing light beam is twice the angle deviation of the reflector, that is, 10".

[0042] The technical parameters of the optical system of the present invention are as follows:

[0043] Wavelength: 3.7μm~4.8μm;

[0044] Field of view: 35.4°×28.7°~1.84°×1.47°;

[0045] Focal length: f = 15mm ~ 300mm;

[0046] Detector pixel: 15μm×15μm;

[0047] Number of pixels: 640×512;

[0048] Cold aperture diameter: Φ10mm;

[0049] F-number:4.

[0050] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

[0051] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, 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 shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A miniaturized three-reflection cooling infrared optical system based on LEO detector, characterized in that: It comprises a front fixed lens group, a variable magnification lens group (3), a compensation lens group (4), a rear fixed lens group, a secondary imaging lens group, a cold light bar (9), a detector focal plane (10), and three reflecting mirrors; The light is sequentially projected onto the detector focal plane (10) after passing through the front fixed lens group, the variable magnification lens group (3), the compensation lens group (4), the rear fixed lens group, the secondary imaging lens group, and the cold light barrier; The front fixed lens group provides an initial image point for the optical system, the zoom lens group (3) and the compensation lens group (4) move according to a preset curve to achieve field of view transformation; the rear fixed lens group converges light to form an image on the primary image plane, and the secondary imaging lens group projects the primary image plane onto the detector focal plane (10); the cold light bar (9) serves as the actual light bar and exit pupil of the optical system; Three reflectors are located between the rear fixed lens group and the secondary imaging lens group to reflect the light three times.

2. The miniaturized three-reflection refrigeration type infrared optical system according to claim 1, characterized in that: The front fixed lens group A (1) and the front fixed lens group B (2) constitute a front fixed lens group; the rear fixed lens group A (5) and the rear fixed lens group B (6) constitute a rear fixed lens group; the secondary imaging lens A (7) and the secondary imaging lens B (8) constitute a secondary imaging lens group.

3. The miniaturized three-reflection refrigeration type infrared optical system according to claim 2, characterized in that: The front fixed lens group B (2) and the variable magnification lens group (3) are aspherical surfaces, and the rear fixed lens group B (6) and the secondary imaging lens B (8) are diffraction surfaces.

4. The miniaturized three-reflection refrigeration type infrared optical system according to claim 1, characterized in that: The normal of each reflector forms an angle of 45° with the light beam, and the incident angle of the light when passing through the reflector is 45°.

5. The miniaturized three-reflection refrigeration type infrared optical system according to claim 1, characterized in that: By constructing an optical path, each reflector is installed and fixed in turn.

6. A design method for the miniaturized three-reflection refrigeration infrared optical system according to claim 1, characterized in that: include: The components are arranged in the order that the light is projected onto the focal plane (10) of the detector after passing through the front fixed lens group, the variable magnification lens group (3), the compensation lens group (4), the rear fixed lens group, the secondary imaging lens group, and the cold light barrier in sequence; The distance between the rear fixed group and the secondary imaging mirror group is increased so that three reflectors can be placed within the distance.

7. The design method of a miniaturized three-reflection cooling infrared optical system according to claim 6, characterized in that: The front fixed lens group A (1) and the front fixed lens group B (2) constitute a front fixed lens group; the rear fixed lens group A (5) and the rear fixed lens group B (6) constitute a rear fixed lens group; the secondary imaging lens A (7) and the secondary imaging lens B (8) constitute a secondary imaging lens group.

8. The design method of a miniaturized three-reflection cooling infrared optical system according to claim 7, characterized in that: The front fixed lens group B (2) and the variable magnification lens group (3) are aspherical surfaces, and the rear fixed lens group B (6) and the secondary imaging lens B (8) are diffraction surfaces.

9. The design method of a miniaturized three-reflection cooling infrared optical system according to claim 6, characterized in that: The normal of each reflector forms an angle of 45° with the light beam, and the incident angle of the light when passing through the reflector is 45°.

10. The design method of a miniaturized three-reflection cooling infrared optical system according to claim 6, characterized in that: By constructing an optical path, each reflector is installed and fixed in turn.

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