A long-wave infrared zoom system with large magnification ratio

Abstract

The application provides a long-wave refrigeration infrared zoom system with a large zoom ratio, and aims at solving the technical problems that the existing refrigeration infrared zoom system has a small zoom ratio, a long system, a large number of lenses, and difficult correction of chromatic aberration and thermal aberration when a large relative aperture is achieved. The long-wave refrigeration infrared zoom system with a large zoom ratio provided by the application is organically combined by 9 lenses made of multiple materials, the control of chromatic aberration and thermal aberration of the lens is achieved, and the imaging quality at each focal length position is close to the diffraction limit; more importantly, on the basis, the reasonable distribution of the optical power of a zoom group and a compensation group is achieved, and the zoom ratio is greatly improved under the premise of ensuring the imaging quality of the long-wave refrigeration infrared zoom lens.

Description

Technical Field

[0001] This invention relates to a long-wave cooled infrared zoom system, specifically a long-wave cooled infrared zoom system with a large zoom ratio. Background Technology

[0002] Long-wave infrared zoom lenses are core optical components in photoelectric detection technology. Among them, cooled long-wave infrared lenses have significant performance advantages over uncooled ones. Cooled long-wave infrared lenses use active cooling technology to reduce the operating temperature of the focal plane array to extremely low levels, which can significantly suppress the thermal noise of the detector itself. This enables high-sensitivity and high-precision detection of weak long-wave infrared radiation. They perform exceptionally well in high-end applications such as long-range target identification and complex background suppression, and have been widely used in military reconnaissance, precision guidance, and space remote sensing.

[0003] Chinese patent CN114326065A discloses a high zoom ratio long-wavelength cooled continuous zoom lens, which adopts a five-element structure, has a focal length of 20-280mm, a zoom ratio of 14x, an f / 2 aperture, and a total optical system length of 427.63mm. However, it uses 10 optical glass elements, making its structure relatively complex. Chinese patent CN113866967A discloses a low-cost, lightweight, mid-wavelength infrared continuous zoom optical system, which is a 3x zoom system with a focal length of 30-90mm and an f / 2 aperture. It uses four germanium lenses plus aspherical and diffractive surfaces, but the zoom ratio of this system is relatively small. The literature (Zhou P W, Yu Y, Li FM, et al. An infrared zoom imaging system with large zoomratio based on linear motion mechanism [J]. Journal of Infrared and Millimeter Waves, 2023, 42 (6): 843-851.) discloses a continuous zoom system with a focal length of 6-330mm and a large zoom ratio of 55x, with a constant F-number of 2. However, the operating wavelength of this continuous zoom system is in the mid-wave band, i.e., 3.7-4.8µm. Chinese patent publication number CN203981958U discloses a cooled continuous zoom lens with a focal length of 15-300mm, but its operating wavelength is in the mid-wave band. Currently, there is no long-wave cooled infrared zoom system in the field with a focal length coverage of 15-300mm to achieve a large relative aperture (F / 2). In addition, existing long-wave infrared zoom systems mostly use germanium single crystal as the main material, supplemented by a small amount of zinc selenide. However, single-crystal germanium has limited chromatic aberration correction capability in the long-wave band and a large temperature coefficient of refractive index, resulting in significant image plane shift in high and low temperature environments.

[0004] In summary, existing cooled infrared zoom systems, when achieving large relative apertures, suffer from drawbacks such as small zoom ratio, long system length, excessive number of lenses, and difficulty in correcting chromatic aberration and thermal aberration. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of existing cooled infrared zoom systems when achieving a large relative aperture, such as small zoom ratio, long system length, large number of lenses, and difficulty in correcting chromatic aberration and thermal aberration, and to provide a long-wave cooled infrared zoom system with a large zoom ratio.

[0006] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0007] A high zoom ratio long-wave cooled infrared zoom system is characterized by comprising a front fixed group, a zoom group, a compensation group, a rear fixed group, a secondary imaging group, and a detector arranged sequentially from the object side to the image side.

[0008] The front fixed assembly has positive optical power and includes a first lens; the first lens is a meniscus germanium single crystal positive lens with its convex surface facing the object side, and both its front and rear surfaces are spherical.

[0009] The zoom group has negative optical power, and the optical power is less than or equal to -0.04; the zoom group includes a second lens and a third lens arranged sequentially along the object-to-image direction; the second lens is a meniscus positive chalcogenide glass lens with its convex surface facing the object side, its front surface is spherical and its rear surface is aspherical; the third lens is a biconcave germanium single crystal negative lens, its front surface is aspherical and its rear surface is spherical;

[0010] The compensation group has a positive optical power, and the optical power is greater than or equal to 0.04; the compensation group includes a fourth lens and a fifth lens arranged sequentially along the object-to-image direction; the fourth lens is a meniscus zinc selenide negative lens with its convex surface facing the object side, its front surface is spherical and its rear surface is aspherical; the fifth lens is a biconvex germanium single crystal positive lens, its front surface is aspherical and its rear surface is spherical.

[0011] The rear fixing group has positive optical power and includes a sixth lens and a seventh lens arranged sequentially along the object-to-image direction; the sixth lens is a meniscus zinc selenide positive lens with its convex surface facing the object, its front surface is aspherical and its rear surface is spherical; the seventh lens is a meniscus germanium single crystal negative lens with its convex surface facing the object, its front surface is aspherical and its rear surface is spherical.

[0012] The secondary imaging group has positive optical power and includes an eighth lens and a ninth lens arranged sequentially along the object-to-image direction; the eighth lens is a biconvex chalcogenide glass positive lens with a spherical front surface and an aspherical rear surface; the ninth lens is a meniscus germanium single crystal positive lens with its convex surface facing the object side, and its aspherical front surface and spherical rear surface.

[0013] The detector is a long-wavelength cooled detector, and its focusing plane is located at the image plane of the secondary imaging group.

[0014] Furthermore, the total travel distance of the variable magnification group is 118.801 mm.

[0015] Furthermore, the total travel distance of the compensation group is 65.713 mm.

[0016] Furthermore, the rear fixing assembly can move within ±2mm along the optical axis.

[0017] Furthermore, the aspherical surfaces of the second, third, fourth, fifth, sixth, seventh, eighth, and ninth lenses are even-order aspherical surfaces, and even-order aspherical surfaces satisfy the following formula:

[0018]

[0019] in It is the sag along the optical axis. It is a radial coordinate perpendicular to the optical axis. It is the vertex curvature. It is the conic coefficient. are even-degree aspherical coefficients, i is the term number of the even-degree aspherical polynomial, and n is the highest term number of the even-degree aspherical polynomial.

[0020] Furthermore, the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, and ninth lens all do not contain diffraction surfaces.

[0021] Furthermore, the short focal length of the large zoom ratio long-wave cooled infrared zoom system is 14.7mm, the long focal length is 310mm, the distance from the rear surface of the ninth lens to the detector window glass is 19.96mm, and the total optical path length of the system is 380mm.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] 1. The present invention provides a high zoom ratio long-wave cooled infrared zoom system, which uses nine lenses of various materials in an organic combination to achieve control of lens chromatic aberration and thermal aberration, so that the imaging quality at each focal length position is close to the diffraction limit; more importantly, based on this, the present invention greatly improves the zoom ratio while ensuring the imaging quality of the long-wave cooled infrared zoom lens by reasonably allocating the optical power of the zoom group and the compensation group.

[0024] 2. This invention specifically uses chalcogenide glass or zinc selenide in the zoom group, compensation group, post-fixation group, and secondary imaging group, and adopts a hybrid lens design combining germanium single crystal and chalcogenide glass or zinc selenide. The low refractive index temperature coefficient of chalcogenide glass or zinc selenide is used to offset the thermal defocusing caused by germanium single crystal, so that the difference in MTF value at different temperatures is controlled within an acceptable range, thereby realizing a passive calorimetric + active electro-focusing mode for compensation.

[0025] 3. The present invention provides a high zoom ratio long-wave cooled infrared zoom system with a constant F number of 2 and a zoom ratio of 21x. The focal length can be adjusted in the range of 14.7mm to 310mm, and can be widely used in military reconnaissance, precision guidance, space remote sensing and other fields. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an embodiment of a high zoom ratio long-wave cooled infrared zoom system according to the present invention;

[0027] Figure 2 This is a short-focal-length optical path diagram according to an embodiment of the present invention;

[0028] Figure 3 This is a central focal optical path diagram according to an embodiment of the present invention;

[0029] Figure 4 This is a long-focal-length optical path diagram according to an embodiment of the present invention;

[0030] Figure 5 The optical transfer function diagram is shown for a focal length of 14.7mm in this embodiment of the invention.

[0031] Figure 6 This is a dot plot of the focal length of 14.7mm in an embodiment of the present invention;

[0032] Figure 7 The field curvature and distortion diagrams are shown for a focal length of 14.7mm according to an embodiment of the present invention.

[0033] Figure 8 This is an optical transfer function diagram for a focal length of 150mm according to an embodiment of the present invention;

[0034] Figure 9 This is a dot plot of the focal length of 150mm in an embodiment of the present invention;

[0035] Figure 10 The field curvature and distortion diagrams are shown for a focal length of 150mm in this embodiment of the invention.

[0036] Figure 11 This is an optical transfer function diagram for a focal length of 310mm according to an embodiment of the present invention;

[0037] Figure 12This is a dot plot of the focal length of 310mm in an embodiment of the present invention;

[0038] Figure 13 The field curvature and distortion diagrams are shown for a focal length of 310mm in this embodiment of the invention.

[0039] Figure 14 The optical transfer function diagram of the present invention at -40°C is shown when the focal length is 14.7mm according to an embodiment of the invention.

[0040] Figure 15 The optical transfer function diagram of the present invention at 60°C is shown when the focal length is 14.7 mm according to an embodiment of the invention.

[0041] Figure 16 This is an optical transfer function diagram at -40°C when the focal length is 310mm, according to an embodiment of the present invention.

[0042] Figure 17 The optical transfer function diagram of the present invention is shown at 60°C when the focal length is 310mm.

[0043] The annotations in the attached figures are explained as follows:

[0044] 1-First lens, 2-Second lens, 3-Third lens, 4-Fourth lens, 5-Fifth lens, 6-Sixth lens, 7-Seventh lens, 8-Eighth lens, 9-Ninth lens, 10-Detector. Detailed Implementation

[0045] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0046] like Figure 1 As shown, a high zoom ratio long-wave cooled infrared zoom system includes a front fixed group, a zoom group, a compensation group, a rear fixed group, a secondary imaging group, and a detector 10 arranged sequentially from the object side to the image side.

[0047] The front fixed assembly has positive optical power and includes a first lens 1; the first lens 1 is a meniscus positive lens with its convex surface facing the object side, the material of the first lens 1 is germanium single crystal, and its front surface S1 is spherical and its rear surface S2 is also spherical.

[0048] To achieve a larger zoom ratio, in the design process of the long-wavelength cooled infrared zoom lens, this invention rationally allocates the optical power of the zoom group and the compensation group by controlling the vertical magnification of the zoom group at the telephoto position and the vertical magnification of the zoom group at the short focal position. The allocation result is that the zoom group has negative optical power, and its optical power must be less than or equal to -0.04, while the compensation group has positive optical power, and its optical power must be greater than or equal to 0.04.

[0049] The zoom group includes a second lens 2 and a third lens 3 arranged sequentially along the object-to-image direction. The second lens 2 is a meniscus positive lens with its convex surface facing the object side. It is made of chalcogenide glass, with a spherical front surface S3 and an aspherical rear surface S4. The third lens 3 is a biconcave negative lens made of germanium single crystal, with an aspherical front surface S5 and a spherical rear surface S6. The third lens 3 is used to achieve negative optical power in the zoom group. The combination of the positive and negative lenses effectively corrects spherical aberration, and the use of chalcogenide glass in the second lens 2 can counteract the thermal defocusing caused by the germanium single crystal in the third lens 3.

[0050] The compensation group includes a fourth lens 4 and a fifth lens 5 arranged sequentially along the object-to-image direction. The fourth lens 4 is a meniscus negative lens with its convex surface facing the object side. The material of the fourth lens 4 is zinc selenide, with its front surface S7 being spherical and its rear surface S8 being aspherical. The fifth lens 5 is a biconvex positive lens, made of germanium single crystal, with its front surface S9 being aspherical and its rear surface S10 being spherical. The fifth lens 5 is used to achieve the positive optical power of the compensation group, while the fourth lens 4 is mainly used to correct chromatic aberration and thermal aberration during zooming.

[0051] The rear fixed assembly has positive optical power and includes a sixth lens 6 and a seventh lens 7 arranged sequentially from the object side to the image side. The sixth lens 6 is a meniscus positive lens with its convex surface facing the object side. The material of the sixth lens 6 is zinc selenide, with its front surface S11 being aspherical and its rear surface S12 being spherical. The seventh lens 7 is a meniscus negative lens with its convex surface facing the object side. The material of the seventh lens 7 is germanium single crystal, with its front surface S13 being aspherical and its rear surface S14 being spherical. The sixth lens 6 is used to achieve the positive optical power of the rear fixed assembly, while the seventh lens 7 is mainly used to correct chromatic aberration and thermal aberration during zooming.

[0052] The secondary imaging group has positive optical power and includes an eighth lens 8 and a ninth lens 9 arranged sequentially from the object side to the image side. The eighth lens 8 is a biconvex positive lens made of chalcogenide glass, with a spherical front surface S15 and an aspherical rear surface S16. The ninth lens 9 is a meniscus positive lens with its convex surface facing the object side, made of germanium single crystal, with an aspherical front surface S17 and a spherical rear surface S18. The ninth lens 9 is used to achieve the positive optical power of the secondary imaging group, while the eighth lens 8 is mainly used to correct thermal differences during zooming.

[0053] Detector 10 is a long-wavelength cooled detector, and its focusing plane is located at the image plane of the secondary imaging group. In this embodiment, the resolution of detector 10 is 640*512, and the pixel size is 15µm.

[0054] The zoom group has a total travel distance of 118.801 mm, used to change the field of view of the long-wave cooled infrared zoom system. The compensation group has a total travel distance of 65.713 mm, used to compensate for image plane position shifts that occur during zoom group movement.

[0055] Preferably, the rear fixing group can move within ±2mm along the optical axis to compensate for the thermal difference under high and low temperature environments, thereby achieving a passive calorimetric mode combined with active electro-focusing.

[0056] The high zoom ratio long-wavelength cooled infrared zoom system of this invention has a short focal length of 14.7mm and a long focal length of 310mm. The distance from the rear surface of the ninth lens 9 to the window glass of the detector 10 is 19.96mm, and the total optical path length of the system is 380mm. The zoom lens operates in the 7.7μm~9.5μm wavelength range and is compatible with a 640*512@15µm long-wavelength cooled detector.

[0057] like Figures 2-4 The diagrams shown are the short-focus optical path diagram, the medium-focus optical path diagram, and the long-focus optical path diagram of the high zoom ratio long-wave cooled infrared zoom system in this embodiment.

[0058] The aspherical surfaces of the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 are all even-order aspherical surfaces, satisfying the following even-order aspherical polynomial:

[0059]

[0060] in It is the sag along the optical axis. It is a radial coordinate perpendicular to the optical axis. It is the vertex curvature. It is the conic coefficient. are even-degree aspherical coefficients, i is the term number of the even-degree aspherical polynomial, and n is the highest term number of the even-degree aspherical polynomial.

[0061] Preferably, in this embodiment, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, and the ninth lens 9 do not contain diffraction surfaces to avoid the influence of stray light.

[0062] It is worth noting that in this invention, the front surface of each lens refers to the surface facing the object, and the rear surface refers to the surface facing the image. In this embodiment, the parameters of each lens are shown in Table 1:

[0063] Table 1 Parameters of each lens

[0064]

[0065] In this embodiment, the aspherical coefficients and parameters of each lens are shown in Table 2:

[0066] Table 2 Aspheric coefficients and parameters of each lens

[0067]

[0068] Figures 5-7 The figures show the optical transfer function, dot plot, field curvature, and distortion of the high zoom ratio long-wavelength cooled infrared zoom system in this embodiment at a short focal length of 14.7mm. Figures 8-10 The figures show the optical transfer function, dot plot, field curvature, and distortion of the high zoom ratio long-wave cooled infrared zoom system in this embodiment at a mid-range focal length of 150mm. Figures 11-13 These are the optical transfer function, dot plot, field curvature, and distortion diagrams of the high zoom ratio long-wave cooled infrared zoom system in this embodiment at a focal length of 310mm. Figures 5-13 It can be seen that the imaging quality of the large zoom ratio long-wave cooled infrared zoom system in this embodiment can meet the actual usage requirements of infrared zoom lenses.

[0069] Figure 14 The image shows the optical transfer function of the high zoom ratio long-wave cooled infrared zoom system in this embodiment at a short focal length of 14.7mm at -40℃. Figure 15 The optical transfer function of the high zoom ratio long-wave cooled infrared zoom system in this embodiment at 60°C with a short focal length of 14.7mm. Figure 16 This is the optical transfer function graph of the high zoom ratio long-wave cooled infrared zoom system in this embodiment at a focal length of 310mm and at -40℃. Figure 17 The optical transfer function (OTF) of the high zoom ratio long-wavelength cooled infrared zoom system in this embodiment is shown at 60°C with a focal length of 310mm. Figures 14-17 It can be seen that the optical transfer function of the large zoom ratio long-wave cooled infrared zoom system in this embodiment can meet the imaging requirements under high and low temperature environments in the range of -40℃ to +60℃.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A high zoom ratio long-wave cooled infrared zoom system, characterized in that: It includes a front fixation group, a zoom group, a compensation group, a rear fixation group, a secondary imaging group, and a detector (10), arranged sequentially from the object side to the image side. The front fixed group has positive optical power and includes a first lens (1); the first lens (1) is a meniscus germanium single crystal positive lens with the convex surface facing the object side, and both its front and rear surfaces are spherical. The zoom group has a negative optical power, and the optical power is less than or equal to -0.04; the zoom group includes a second lens (2) and a third lens (3) arranged sequentially along the object-to-image direction; the second lens (2) is a meniscus positive chalcogenide glass lens with its convex surface facing the object, its front surface is spherical and its rear surface is aspherical; the third lens (3) is a biconcave germanium single crystal negative lens, its front surface is aspherical and its rear surface is spherical; The compensation group has a positive optical power and the optical power is greater than or equal to 0.04; the compensation group includes a fourth lens (4) and a fifth lens (5) arranged sequentially along the object-to-image direction; the fourth lens (4) is a meniscus zinc selenide negative lens with its convex surface facing the object side, its front surface is spherical and its rear surface is aspherical; the fifth lens (5) is a biconvex germanium single crystal positive lens, its front surface is aspherical and its rear surface is spherical; The rear fixed group has positive optical power and includes a sixth lens (6) and a seventh lens (7) arranged sequentially along the object-to-image direction; the sixth lens (6) is a meniscus zinc selenide positive lens with its convex surface facing the object, its front surface is aspherical and its rear surface is spherical; the seventh lens (7) is a meniscus germanium single crystal negative lens with its convex surface facing the object, its front surface is aspherical and its rear surface is spherical. The secondary imaging group has positive optical power and includes an eighth lens (8) and a ninth lens (9) arranged sequentially along the object-to-image direction; the eighth lens (8) is a biconvex chalcogenide glass positive lens with a spherical front surface and an aspherical rear surface; the ninth lens (9) is a meniscus germanium single crystal positive lens with its convex surface facing the object side, with an aspherical front surface and a spherical rear surface. The detector (10) is a long-wavelength cooled detector, and its focusing plane is located at the image plane of the secondary imaging group.

2. The high zoom ratio long-wave cooled infrared zoom system according to claim 1, characterized in that: The total travel distance of the zoom group is 118.801 mm.

3. The high zoom ratio long-wave cooled infrared zoom system according to claim 2, characterized in that: The total travel distance of the compensation group is 65.713 mm.

4. A high zoom ratio long-wave cooled infrared zoom system according to any one of claims 1-3, characterized in that: The rear fixing assembly can move within ±2mm along the optical axis.

5. The high zoom ratio long-wave cooled infrared zoom system according to claim 4, characterized in that: The aspherical surfaces of the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), and the ninth lens (9) are even-order aspherical surfaces, and even-order aspherical surfaces satisfy the following formula: ； in It is the sag along the optical axis. It is a radial coordinate perpendicular to the optical axis. It is the vertex curvature. It is the conic coefficient. are even-degree aspherical coefficients, i is the term number of the even-degree aspherical polynomial, and n is the highest term number of the even-degree aspherical polynomial.

6. The high zoom ratio long-wave cooled infrared zoom system according to claim 5, characterized in that: The first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), and the ninth lens (9) do not contain diffraction surfaces.

7. The high zoom ratio long-wave cooled infrared zoom system according to claim 6, characterized in that: The short focal length of the large zoom ratio long-wave cooled infrared zoom system is 14.7 mm, the long focal length is 310 mm, the distance from the rear surface of the ninth lens (9) to the window glass of the detector (10) is 19.96 mm, and the total optical path length of the system is 380 mm.

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