High-resolution refrigeration type medium-wave infrared imaging optical system

Abstract

The invention relates to the technical field of infrared imaging, and discloses a high-resolution refrigeration type medium-wave infrared imaging optical system which comprises an objective lens group and a relay lens group, infrared light beams from an object space can be effectively collected and focused through the designed objective lens group and relay lens group, and finally a high-resolution infrared image is formed on an imaging plane. The optical system can keep stable imaging quality in a wide temperature range from-40 DEG C to + 60 DEG C, the optical transfer function (MTF) is greater than 0.3 when the spatial frequency is 42lp / mm, and is close to the diffraction limit, and excellent temperature stability and imaging quality are shown. Besides, the system adopts a secondary imaging system design and combines germanium and silica glass materials to realize aberration correction and achromatic design, and through introduction of a high-order aspheric surface and a binary diffraction surface, high-order aberration is effectively corrected, and the structure is simplified.

Description

Technical Field

[0001] The invention belongs to the field of infrared imaging, and in particular relates to a high-resolution refrigerated medium-wave infrared imaging optical system. Background Art

[0002] The infrared imaging system mainly detects the target's own thermal radiation and uses the temperature difference between the target and the background to extract the target. The greater the temperature difference, the stronger the ability to extract the target. Therefore, the infrared imaging system is not limited by lighting conditions when detecting targets. It has the advantages of good concealment, strong anti-interference ability, long range, and all-weather operation. It is widely used in military and civilian fields such as infrared detection and security monitoring. The medium-wave infrared (MWIR) imaging system, which works in the spectral range of 3μm to 5μm and can provide rich target thermal radiation information, has become a hot spot in the research and application of infrared imaging.

[0003] There are several problems and shortcomings in the research of existing infrared imaging technology that the present invention aims to solve. First, there is no in-depth discussion of optimization measures in correcting aberrations and improving imaging quality, especially the lack of discussion on the performance stability of the system under extreme temperature conditions. Second, the compactness and weight of the system are not fully considered, which is crucial for applications on portable or mobile platforms. In addition, there is a lack of discussion on the economics and manufacturing costs of the system, which is an important consideration for large-scale production and commercial applications. Summary of the invention

[0004] The object of the present invention is to overcome the above problems and provide a high-resolution refrigerated medium-wave infrared imaging optical system, which can solve the thermal defocusing problem caused by temperature fluctuations when the existing infrared imaging system works in a wide temperature range.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The present invention provides a high-resolution refrigerated medium-wave infrared imaging optical system, comprising an objective lens group and a relay lens group, wherein the objective lens group comprises a first lens, a second lens and a third lens, and the relay lens group comprises a fourth lens, a fifth lens, a sixth lens and a seventh lens;

[0007] The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens and the seventh lens are arranged in sequence from the object side to the image side;

[0008] The light beam from the object side passes through the first lens, the second lens and the third lens in sequence to form a first intermediate image, and then passes through the fourth lens, the fifth lens, the sixth lens and the seventh lens to form a high-resolution infrared image on the final imaging plane.

[0009] A further improvement of the present invention is that the first lens, the third lens, the fourth lens and the sixth lens are made of silicon glass.

[0010] A further improvement of the present invention is that the second lens, the fifth lens and the seventh lens are made of germanium single crystal.

[0011] A further improvement of the present invention is that the object side surfaces of the second lens and the fifth lens are even-order aspherical lenses.

[0012] A further improvement of the present invention is that the image side surfaces of the third lens, the fourth lens, the sixth lens and the seventh lens are even-order aspherical lenses.

[0013] A further improvement of the present invention is that the surface shape formula of the aspheric surface is:

[0014]

[0015] Where c is the curvature, and r 0 is the radius of curvature of the optical surface; k is the cone coefficient; r is the normalized radius coordinate; A, B, C, D are the multi-term coefficients.

[0016] A further improvement of the present invention is that the object side surface of the fifth lens is a binary surface, which satisfies the expression equation of the binary surface in Zemax optical design software:

[0017] M[B 1 *p 2 +B 2 *p 4 +B 3 *p 6 +B 4 *p 8 ]

[0018] Where M is the diffraction order, the diffraction order is 1; B 1 , B 2 , B 3 , B 4 is the binary surface phase coefficient; p is the normalized radius.

[0019] A further improvement of the present invention is that a cold stop is also arranged at the rear side of the relay lens assembly.

[0020] A further improvement of the present invention is that the system includes a temperature focusing mechanism, and the distance between the second lens and the third lens is adjusted in the range of -0.082 mm to 0.126 mm.

[0021] A further improvement of the present invention is that the effective focal length of the system is 165.8 mm and the F number is 1.65.

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

[0023] The present invention provides a high-resolution refrigerated medium-wave infrared imaging optical system. Through the designed objective lens group and relay lens group, the infrared light beam from the object side can be effectively collected and focused, and finally a high-resolution infrared image is formed on the imaging plane; the optical system can maintain stable imaging quality in a wide temperature range of -40°C to +60°C, and the optical transfer function (MTF) at a spatial frequency of 42lp / mm is greater than 0.3, close to the diffraction limit, showing excellent temperature stability and imaging quality. In addition, through reasonable lens arrangement and parameter selection, a compact system structure is achieved, which not only helps to reduce the volume and weight of the system, but also improves the stability and reliability of the system.

[0024] Furthermore, this system adopts a secondary imaging system design, combined with germanium and silicon glass materials, to achieve aberration correction and achromatic design, and by introducing high-order aspheric surfaces and binary diffraction surfaces, it effectively corrects high-order aberrations and simplifies the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings described herein are only for explanation purposes and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the drawings are only schematic, used to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the various components of the present invention.

[0026] Figure 1 This is a layout diagram of the refrigerated secondary medium-wave infrared imaging system of the present invention;

[0027] Figure 2 This is the MTF curve of the system at 20°C;

[0028] Figure 3 This is the point diagram of the system at 20°C;

[0029] Figure 4 The field curvature and distortion diagram of the system at 20°C;

[0030] Figure 5 This is the MTF curve of the -40℃ system after focusing with a focusing lens;

[0031] Figure 6 This is the MTF curve of the 60℃ system after focusing with a focusing lens.

[0032] Among them: 1, the first lens; 2, the second lens; 3, the third lens; 4, the fourth lens; 5, the fifth lens; 6, the sixth lens; 7, the seventh lens; 8, the cold aperture. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0036] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0037] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0038] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0040] like Figure 1As shown, an embodiment of the present invention provides a high-resolution refrigerated medium-wave infrared imaging optical system, comprising a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7 and a cold stop 8; wherein the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 are arranged in sequence from the object side to the image side; a light beam from the object side passes through the first lens 1, the second lens 2 and the third lens 3 in sequence to form a first intermediate image, and then passes through the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 to form a high-resolution infrared image on the final imaging plane.

[0041] In this embodiment, the first lens 1, the second lens 2 and the third lens 3 are arranged in sequence from the object side to the image side to form an objective lens group, which is responsible for capturing the target and focusing it to form a first intermediate image; the fourth lens 4, the fifth lens 5, the sixth lens 6 and the seventh lens 7 are arranged in sequence from the object side to the image side to form a relay lens group, and a cold aperture stop 8 is arranged on the rear side of the relay lens group; the relay lens group uses the intermediate image generated by the objective lens group as its object plane, and after a second imaging process, the intermediate image is completely accurately imaged to the final imaging plane through the cold aperture stop 8 to achieve high-resolution imaging; the function of the cold aperture stop 8 is to limit the light beam passing through the system, reduce the influence of stray light and thermal noise, and thus improve the signal-to-noise ratio and resolution of the image.

[0042] In this embodiment, the system includes a temperature focusing mechanism, and the third lens 3 serves as a focusing lens. When the ambient temperature changes, the distance between the second lens 2 and the third lens 3 is adjusted to balance the aberration caused by temperature, wherein the distance between the second lens 2 and the third lens 3 is adjusted in the range of -0.082 mm to 0.126 mm.

[0043] In this embodiment, high-order aspheric lenses are further applied. The introduction of high-order aspheric lenses can correct high-order spherical aberration, coma and astigmatism, simplify the system structure, reduce the number of lenses, and improve the imaging quality of the system. Among them, the object side of the second lens 2 and the fifth lens 5 is an even-order aspheric lens; the image side of the third lens 3, the fourth lens 4, the sixth lens 6 and the seventh lens 7 is an even-order aspheric lens, and satisfies the aspheric formula:

[0044]

[0045] Where c is the curvature, and r 0 is the radius of curvature of the optical surface; k is the cone coefficient; r is the normalized radius coordinate; A, B, C, D are the coefficients of multiple terms, and A is zero in most cases.

[0046] It should be noted that in order to reduce costs and make the system easier to process, this system only uses quartic, sixth and octathon aspheric surfaces as optimization variables during the optimization design process.

[0047] In this embodiment, the object side surface of the fifth lens 5 is a binary surface, which satisfies the aspheric surface formula and the expression equation of the binary surface in the Zemax optical design software:

[0048] M[B 1 *p 2 +B 2 *p 4 +B 3 *p 6 +B 4 *p 8 ]

[0049] Where M is the diffraction order, the diffraction order is 1; B 1 , B 2 , B 3 , B 4 is the binary surface phase coefficient, B 1 =-1.0596E+004, B 2 =2.5884E+005, B 3 =8.8955E+007, B 4 =-1.2839E+011; p is the normalized radius, p=100.

[0050] In this embodiment, the first lens 1, the third lens 3, the fourth lens 4 and the sixth lens 6 are made of silicon glass; the second lens 2, the fifth lens 5 and the seventh lens 7 are made of germanium single crystal. The combination of germanium single crystal and silicon glass material realizes the design of aberration correction and achromatism, and improves the imaging clarity.

[0051] In this embodiment, the parameters of each lens component of the optical imaging system are shown in Table 1. The side of the lens where light is incident is the object side, and the side where light is emitted is the image side. For example, the S1 surface of the first lens 1 is the object side, and the S2 surface is the image side. Other lenses are not described here.

[0052] Table 1 Parameters of each lens

[0053]

[0054]

[0055] In this embodiment, the high-order aspheric coefficients of all aspheric lenses of the optical imaging system are as shown in Table 2. The object-side surfaces S3, S8 and S10 of the second lens 2, the fourth lens 4 and the fifth lens 5, and the image-side surfaces S6, S13 and S15 of the third lens 3, the sixth lens 6 and the seventh lens 7 are aspheric.

[0056] Table 2 Aspheric coefficients of each lens

[0057] Surface number A B C D E S3 7.274E-09 3.216E-13 -1.359E-15 7.098E-19 -2.031E-22 S6 -6.834E-06 1.612E-09 -2.519E-12 1.436E-15 -1.041E-18 S8 -2.728E-04 -1.976E-06 4.826E-07 -1.395E-08 1.352E-10 S10 1.156E-05 2.162E-06 5.675E-08 1.155E-09 -3.191E-12 S13 -1.383E-05 1.073E-07 2.337E-11 -1.549E-12 3.420E-15 S15 5.757E-05 -7.305E-08 -1.844E-10 3.516E-13 1.104E-14

[0058] The MTF diagram and point diagram of the optical system of the present invention are as follows: Figure 2 and Figure 3 As shown, Figure 2 As shown in the MTF diagram, the horizontal axis represents different spatial frequencies, the vertical axis represents the modulation degree, and all fields of view represent the MTF curve of the meridian plane. It can be seen from the figure that the MTF is close to the diffraction limit, the root mean square diameter of the diffuse spot is smaller than the Airy disk diameter, and the image quality is good.

[0059] The field curvature and distortion diagram of the optical system of the present invention at 20°C are shown in FIG. Figure 4 As shown, the maximum field of view of the optical system is 3°, the sagittal field curvature is 0.0786 mm, the meridian field curvature is 0.1320 mm, the maximum distortion is 3.002%, and the distortion type is F-Tan (Theta).

[0060] like Figure 5 and Figure 6 As shown in the figure, the MTF diagram of the optical system of the present invention after focusing by the focusing lens at -40°C and +60°C makes it possible for the optical transfer function (MTF) of the optical system to be greater than 0.3 when the spatial frequency is 42lp / mm, which is close to the diffraction limit. It can be seen that the optical system has the characteristics of use in a wide temperature range, that is, it can maintain stable and clear imaging effects in the temperature range of -40°C to +60°C.

[0061] In this embodiment, the effective focal length of the optical system is 165.8 mm, the working band is 3 μm-5 μm, and the F number is 1.65. In addition, the total length of the optical system is less than 180 mm, and the maximum aperture is less than 110 mm, achieving a compact design while meeting high-resolution and high-contrast imaging effects.

[0062] The lens of this embodiment performs aberration correction and balance in a wide spectral range by reasonably allocating the focal power and designing the optical materials, aspherical surfaces and diffraction surfaces, so that the lens has excellent image quality in a wide spectral range and achieves wide spectrum confocality. The lens of the present invention can be applied to a lens module and can be equipped with a detector with a pixel number of 1024*1024 and a pixel size of 12μm.

[0063] Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

[0064] The above content is a further detailed description of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several simple deductions or substitutions, which should be regarded as belonging to the protection scope of the present invention determined by the submitted claims.

Claims

1. A high-resolution refrigerated medium-wave infrared imaging optical system, characterized in that: The invention comprises an objective lens group and a relay lens group, wherein the objective lens group comprises a first lens (1), a second lens (2) and a third lens (3), and the relay lens group comprises a fourth lens (4), a fifth lens (5), a sixth lens (6) and a seventh lens (7); The first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6) and the seventh lens (7) are arranged in sequence from the object side to the image side; A light beam from the object side passes through a first lens (1), a second lens (2) and a third lens (3) in sequence to form a first intermediate image, and then passes through a fourth lens (4), a fifth lens (5), a sixth lens (6) and a seventh lens (7) to form a high-resolution infrared image on a final imaging plane.

2. A high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The first lens (1), the third lens (3), the fourth lens (4) and the sixth lens (6) are made of silicon glass.

3. A high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The second lens (2), the fifth lens (5) and the seventh lens (7) are made of germanium single crystal.

4. A high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The object side surfaces of the second lens (2) and the fifth lens (5) are even-order aspherical lenses.

5. The high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The image side surfaces of the third lens (3), the fourth lens (4), the sixth lens (6) and the seventh lens (7) are even-order aspherical mirrors.

6. A high-resolution refrigerated medium-wave infrared imaging optical system according to claim 4 or 5, characterized in that: The surface formula of the aspheric surface is: Where c is the curvature, and r0 is the radius of curvature of the optical surface; k is the cone coefficient; r is the normalized radius coordinate; A, B, C, and D are the multi-term coefficients.

7. The high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The object side surface of the fifth lens (5) is a binary surface, which satisfies the expression equation of the binary surface in Zemax optical design software: M[B1*p 2 +B2*p 4 +B3*p 6 +B4*p 8 ] Where M is the diffraction order, which is 1; B1, B2, B3, and B4 are binary surface phase coefficients; and p is the normalized radius.

8. The high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: A cold diaphragm (8) is also arranged on the rear side of the relay lens assembly.

9. The high-resolution refrigerated medium-wave infrared imaging optical system according to claim 1, characterized in that: The system comprises a temperature focusing mechanism, and the distance between the second lens (2) and the third lens (3) can be adjusted in a range of -0.082 mm to 0.126 mm.

10. A high-resolution refrigerated medium-wave infrared imaging optical system according to claim 9, characterized in that: The effective focal length of the system is 165.8 mm and the F number is 1.65.

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