A Compact Mid-Wave Infrared Lens and a Mid-Wave Infrared Imaging System with the Same

Abstract

The present invention provides a compact medium-wave infrared lens and a medium-wave infrared imaging system having the same. The infrared lens comprises six lenses arranged sequentially along the optical axis from the object side to the image side. The first lens is a meniscus lens with positive optical power, with its convex surface facing the object side; the second lens is a meniscus lens with negative optical power, with its convex surface facing the object side; the third lens is a meniscus lens with positive optical power, with its convex surface facing the object side; the fourth lens is a meniscus lens with positive optical power, with its convex surface facing the image side; the fifth lens is a meniscus lens with negative optical power, with its convex surface facing the image side; and the sixth lens is a biconvex lens. The present invention can solve the technical problem in the prior art that, under strict size constraints, the image quality design, athermalization design, and quenching reflection design of the lens cannot be optimized.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a compact medium-wave infrared lens and a medium-wave infrared imaging system having the same. Background Art

[0002] Cooled medium-wave infrared imaging systems have outstanding application advantages in the military due to their wavelength characteristics and the high sensitivity of their cooling components. As a key component of medium-wave infrared imaging systems, the design of medium-wave infrared lenses has corresponding special features. Military lenses generally require an operating temperature range of -40°C to 60°C. However, due to the large thermal expansion coefficient and temperature variation coefficient of the infrared lens material, changes in ambient temperature can significantly alter the refractive index, surface curvature, thickness, and spacing between adjacent lenses. This can cause severe defocusing in the infrared lens. To reduce size and weight and improve design reliability, optical passive athermalization is generally used to address these issues. Furthermore, the design of cooled medium-wave infrared lenses also requires additional consideration of special issues such as aperture matching and cold reflection.

[0003] With the widespread adoption of miniaturized cooling devices, the size of medium-wavelength cooled infrared lenses is becoming increasingly smaller. Within these strict size constraints, lens design challenges arise in image quality, athermalization, and cooling reflection reduction. This requires the use of specialized lens material combinations and structural types, as well as balanced aberration parameters, to achieve optimal lens design and processing. Summary of the Invention

[0004] The present invention provides a compact medium-wave infrared lens and a medium-wave infrared imaging system having the same, which can solve the technical problem in the prior art that the image quality design, athermal difference design and refrigeration reflection design of the lens cannot reach a better state under strict size restrictions.

[0005] According to one aspect of the present invention, a compact medium-wave infrared lens is provided, comprising six lenses arranged in sequence along the optical axis from the object side to the image side, wherein the first lens is a meniscus lens with positive optical power, with the convex surface facing the object side; the second lens is a meniscus lens with negative optical power, with the convex surface facing the object side; the third lens is a meniscus lens with positive optical power, with the convex surface facing the object side; the fourth lens is a meniscus lens with positive optical power, with the convex surface facing the image side; the fifth lens is a meniscus lens with negative optical power, with the convex surface facing the image side; and the sixth lens is a biconvex lens.

[0006] Preferably, the convex surface of the first lens and the side opposite to the convex surface are both spherical surfaces; the convex surface of the second lens is spherical, and the side opposite to the convex surface is aspherical; the convex surface of the third lens is spherical, and the side opposite to the convex surface is aspherical; the convex surface of the fourth lens is aspherical, and the side opposite to the convex surface is spherical; the convex surface of the fifth lens is a diffraction aspherical surface, and the side opposite to the convex surface is spherical.

[0007] Preferably, the materials of the first lens, the fourth lens and the sixth lens are all silicon.

[0008] Preferably, the material of the second lens is germanium.

[0009] Preferably, the third lens and the fifth lens are both made of chalcogenide glass.

[0010] Preferably, the focal length range of the first lens is 35.5 to 39.5 mm, the focal length range of the second lens is -34.62 to -30.62 mm, the focal length range of the third lens is 47.41 to 51.41 mm, the focal length range of the fourth lens is 8.38 to 12.38 mm, the focal length range of the fifth lens is -42.08 to -38.08 mm, and the focal length range of the sixth lens is 16.25 to 20.25 mm.

[0011] Preferably, the center thickness range of the first lens is 7 to 9 mm, the center thickness range of the second lens is 2.7 to 4.7 mm, the center thickness range of the third lens is 5.4 to 7.4 mm, the center thickness range of the fourth lens is 7 to 9 mm, the center thickness range of the fifth lens is 6 to 8 mm, and the center thickness range of the sixth lens is 2.4 to 4.4 mm.

[0012] Preferably, the convex surface curvature radius of the first lens is in the range of 41 to 43 mm, and the curvature radius of the side opposite to the convex surface is in the range of 67 to 69 mm; the convex surface curvature radius of the second lens is in the range of 59 to 61 mm, and the curvature radius of the side opposite to the convex surface is in the range of 34 to 36 mm; the convex surface curvature radius of the third lens is in the range of 33 to 35 mm, and the curvature radius of the side opposite to the convex surface is in the range of 51 to 53 mm; the convex surface curvature radius of the fourth lens is in the range of -14 to -12 mm, and the curvature radius of the side opposite to the convex surface is in the range of -13 to -11 mm; the convex surface curvature radius of the fifth lens is in the range of -12 to -10 mm, and the curvature radius of the side opposite to the convex surface is in the range of -19 to -17 mm; the first convex surface curvature radius of the sixth lens is in the range of 48 to 50 mm, and the second convex surface curvature radius opposite to the first convex surface is in the range of -29 to -27 mm.

[0013] Preferably, the spacing between the first lens and the second lens is in the range of 1 to 3 mm, the spacing between the second lens and the third lens is in the range of 1 to 3 mm, the spacing between the third lens and the fourth lens is in the range of 36 to 38 mm, the spacing between the fourth lens and the fifth lens is in the range of 1 to 3 mm, and the spacing between the fifth lens and the sixth lens is in the range of 0.1 to 1 mm.

[0014] According to another aspect of the present invention, a medium-wave infrared imaging system is provided, comprising any of the above-mentioned compact medium-wave infrared lenses.

[0015] The technical solution of the present invention, through the combination of six lenses arranged in a specific sequence, and the introduction of aspheric and aspheric diffractive surfaces on specific surfaces, can effectively correct the aberrations of the optical system and achieve the purpose of optical passive athermalization. By adopting a secondary imaging method, the aperture of the front lens is effectively compressed. The lens of the present invention can achieve optimal image quality design, athermalization design, and quenching reflection design within strict size constraints (requiring a long focal length, a small F number, a short total length, and a large back focus), thereby achieving good and stable imaging quality within a temperature range of -40°C to 60°C, while also having a simple structure, a small size, and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are included to provide a further understanding of the embodiments of the present invention, constitute a part of the specification, illustrate the embodiments of the present invention, and together with the description, explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0017] Figure 1 A schematic structural diagram of a compact medium-wave infrared lens provided according to an embodiment of the present invention is shown;

[0018] Figure 2 The optical transfer function diagram of the medium-wave infrared lens provided according to an embodiment of the present invention at 20° C. is shown.

[0019] The above drawings include the following reference numerals:

[0020] 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. 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 only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] Unless otherwise specifically stated, the relative arrangement of the parts and steps, the numerical expressions and the numerical values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values should be interpreted as being merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0024] like Figure 1 As shown, the present invention provides a compact medium-wave infrared lens, comprising six lenses arranged in sequence from the object side to the image side along the optical axis, wherein the first lens 1 is a meniscus lens with positive optical power, with the convex surface facing the object side; the second lens 2 is a meniscus lens with negative optical power, with the convex surface facing the object side; the third lens 3 is a meniscus lens with positive optical power, with the convex surface facing the object side; the fourth lens 4 is a meniscus lens with positive optical power, with the convex surface facing the image side; the fifth lens 5 is a meniscus lens with negative optical power, with the convex surface facing the image side; and the sixth lens 6 is a biconvex lens.

[0025] The present invention utilizes a combination of six lenses arranged in a specific sequence, along with aspheric and aspheric diffractive surfaces introduced on specific surfaces, to effectively correct optical system aberrations and achieve passive optical athermalization. By employing a secondary imaging method, the aperture of the front lens is effectively reduced. The lens of the present invention achieves optimal image quality, athermalization, and quenching design within strict size constraints (requiring a long focal length, a small F-number, a short total length, and a large back focus), thereby achieving good and stable imaging quality within a temperature range of -40°C to 60°C, while maintaining a simple structure, compact size, and high reliability.

[0026] According to one embodiment of the present invention, the convex surface of the first lens 1 and the surface opposite to the convex surface are both spherical surfaces; the convex surface of the second lens 2 is spherical, and the surface opposite to the convex surface is aspherical; the convex surface of the third lens 3 is spherical, and the surface opposite to the convex surface is aspherical; the convex surface of the fourth lens 4 is aspherical, and the surface opposite to the convex surface is spherical; the convex surface of the fifth lens 5 is a diffraction aspherical surface, and the surface opposite to the convex surface is spherical.

[0027] According to one embodiment of the present invention, the materials of the first lens 1, the fourth lens 4 and the sixth lens 6 are all silicon; the material of the second lens 2 is germanium; and the material of the third lens 3 and the fifth lens 5 are all chalcogenide glass.

[0028] Specifically, the third lens 3 is made of chalcogenide glass HW15_MW, and the fifth lens 5 is made of chalcogenide glass HW14_MW.

[0029] Through the above setup, the six lenses are made of three materials: in addition to silicon and germanium, two chalcogenide glass materials, HW14_MW and HW15_MW, are also used.

[0030] According to one embodiment of the present invention, the focal length range of the first lens 1 is 35.5 to 39.5 mm, the focal length range of the second lens 2 is -34.62 to -30.62 mm, the focal length range of the third lens 3 is 47.41 to 51.41 mm, the focal length range of the fourth lens 4 is 8.38 to 12.38 mm, the focal length range of the fifth lens 5 is -42.08 to -38.08 mm, and the focal length range of the sixth lens 6 is 16.25 to 20.25 mm.

[0031] According to one embodiment of the present invention, the center thickness of the first lens 1 ranges from 7 to 9 mm, the center thickness of the second lens 2 ranges from 2.7 to 4.7 mm, the center thickness of the third lens 3 ranges from 5.4 to 7.4 mm, the center thickness of the fourth lens 4 ranges from 7 to 9 mm, the center thickness of the fifth lens 5 ranges from 6 to 8 mm, and the center thickness of the sixth lens 6 ranges from 2.4 to 4.4 mm.

[0032] According to one embodiment of the present invention, the convex surface of the first lens element 1 has a curvature radius in a range of 41 to 43 mm, and the curvature radius of the surface opposite to the convex surface is in a range of 67 to 69 mm; the convex surface of the second lens element 2 has a curvature radius in a range of 59 to 61 mm, and the curvature radius of the surface opposite to the convex surface is in a range of 34 to 36 mm; the convex surface of the third lens element 3 has a curvature radius in a range of 33 to 35 mm, and the curvature radius of the surface opposite to the convex surface is in a range of 51 to 53 mm; the convex surface of the fourth lens element 4 has a curvature radius in a range of -14 to -12 mm, and the curvature radius of the surface opposite to the convex surface is in a range of -13 to -11 mm; the convex surface of the fifth lens element 5 has a curvature radius in a range of -12 to -10 mm, and the curvature radius of the surface opposite to the convex surface is in a range of -19 to -17 mm; the first convex surface of the sixth lens element 6 has a curvature radius in a range of 48 to 50 mm, and the second convex surface opposite to the first convex surface has a curvature radius in a range of -29 to -27 mm.

[0033] According to one embodiment of the present invention, the spacing between the first lens 1 and the second lens 2 is in the range of 1 to 3 mm, the spacing between the second lens 2 and the third lens 3 is in the range of 1 to 3 mm, the spacing between the third lens 3 and the fourth lens 4 is in the range of 36 to 38 mm, the spacing between the fourth lens 4 and the fifth lens 5 is in the range of 1 to 3 mm, and the spacing between the fifth lens 5 and the sixth lens 6 is in the range of 0.1 to 1 mm.

[0034] Through the above arrangement, the axial size of the optical system is greatly compressed. At the same time, since a baffle correction mechanism is required between the lens and the detector in practical application, the back focus of the optical system is significantly increased.

[0035] The technical solution of the present invention is described in detail below with reference to specific embodiments.

[0036] like Figure 1 As shown, in this embodiment, the compact medium-wave infrared lens of the present invention includes six lenses arranged in sequence from the object side to the image side along the optical axis. The first lens 1 is a meniscus lens with positive optical power, with its convex surface facing the object side, and the convex surface of the first lens 1 and the side opposite to the convex surface are both spherical surfaces; the second lens 2 is a meniscus lens with negative optical power, with its convex surface facing the object side, the convex surface of the second lens 2 is spherical, and the side opposite to the convex surface is aspherical; the third lens 3 is a meniscus lens with positive optical power, with its convex surface facing the object side, the convex surface of the third lens 3 is spherical, and the side opposite to the convex surface is aspherical; the fourth lens 4 is a meniscus lens with positive optical power, with its convex surface facing the image side, the convex surface of the fourth lens 4 is aspherical, and the side opposite to the convex surface is spherical; the fifth lens 5 is a meniscus lens with negative optical power, with its convex surface facing the image side, the convex surface of the fifth lens 5 is a diffractive aspherical surface, and the side opposite to the convex surface is spherical; and the sixth lens 6 is a biconvex lens.

[0037] In this embodiment, the first lens 1, the fourth lens 4 and the sixth lens 6 are made of silicon, the second lens 2 is made of germanium, the third lens 3 is made of chalcogenide glass HW15_MW, and the fifth lens 5 is made of chalcogenide glass HW14_MW.

[0038] Among them, the focal length of the first lens 1 is 37.5 mm, the focal length of the second lens 2 is -32.62 mm, the focal length of the third lens 3 is 49.41 mm, the focal length of the fourth lens 4 is 10.38 mm, the focal length of the fifth lens 5 is -40.08 mm, and the focal length of the sixth lens 6 is 18.25 mm.

[0039] With the above configuration, the main optical parameters of the infrared lens of this embodiment are as follows:

[0040] Working band: 3.7μm~4.8μm;

[0041] Focal length: 137mm;

[0042] F number: 2.5;

[0043] Field of view: 4°×3.2°;

[0044] Total length of the optical system (distance from the convex surface of the first lens 1 to the image plane): 114.5 mm;

[0045] Optical system back focus (the distance from the second convex surface of the sixth lens 6 to the image plane): 33.3 mm.

[0046] like Figure 2 As shown, the meridian curve T and the sagittal curve S (part of the curves overlap) at field angles of 0°, 1.9°, 2.7° and the diffraction limit are shown. It can be seen that the meridian curve T and the sagittal curve S at different field angles are close to the diffraction limit meridian curve T and the sagittal curve S. Therefore, the medium-wave infrared lens of the present invention can achieve good imaging quality in the temperature range of -40°C to 60°C.

[0047] The compact medium-wave infrared lens disclosed herein is compatible with medium-wave infrared cooled detectors. Its aperture setting meets the 100% cold aperture efficiency typically required by cooled detectors. Its optical system utilizes a secondary imaging method, effectively reducing the aperture of the front-end lens. Due to space limitations, the optical design significantly reduced the axial dimensions of the optical system. Furthermore, the requirement for a baffle correction mechanism between the lens and the detector in practical applications significantly increases the back focus of the optical system. The optical system consists of six lenses, incorporating three aspheric surfaces and one diffractive aspheric surface. Three materials are used: silicon and germanium, commonly used in infrared optics, as well as two new domestically produced chalcogenide glass materials, HW14_MW and HW15_MW. By combining the glass materials in a specific order and introducing the aspheric and diffractive surfaces on specific surfaces, the optical system can effectively correct for aberrations and achieve passive optical athermalization. The lens achieves excellent and stable imaging quality within a temperature range of -40°C to 60°C, while maintaining a simple structure, compact size, and high reliability.

[0048] According to another aspect of the present invention, a medium-wave infrared imaging system is provided, comprising any of the above-mentioned compact medium-wave infrared lenses.

[0049] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0050] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0051] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A compact medium-wave infrared lens, characterized in that: The optical system comprises six lenses arranged in sequence from the object side to the image side along the optical axis, wherein the first lens (1) is a meniscus lens with positive focal power, with its convex surface facing the object side; the second lens (2) is a meniscus lens with negative focal power, with its convex surface facing the object side; the third lens (3) is a meniscus lens with positive focal power, with its convex surface facing the object side; the fourth lens (4) is a meniscus lens with positive focal power, with its convex surface facing the image side; the fifth lens (5) is a meniscus lens with negative focal power, with its convex surface facing the image side; and the sixth lens (6) is a biconvex lens. The convex surface of the first lens (1) and the side opposite to the convex surface are both spherical surfaces; the convex surface of the second lens (2) is spherical, and the side opposite to the convex surface is aspherical; the convex surface of the third lens (3) is spherical, and the side opposite to the convex surface is aspherical; the convex surface of the fourth lens (4) is aspherical, and the side opposite to the convex surface is spherical; the convex surface of the fifth lens (5) is a diffraction aspherical surface, and the side opposite to the convex surface is spherical; The focal length range of the first lens (1) is 35.5 to 39.5 mm, the focal length range of the second lens (2) is -34.62 to -30.62 mm, the focal length range of the third lens (3) is 47.41 to 51.41 mm, the focal length range of the fourth lens (4) is 8.38 to 12.38 mm, the focal length range of the fifth lens (5) is -42.08 to -38.08 mm, and the focal length range of the sixth lens (6) is 16.25 to 20.25 mm; The center thickness of the first lens (1) is in the range of 7 to 9 mm, the center thickness of the second lens (2) is in the range of 2.7 to 4.7 mm, the center thickness of the third lens (3) is in the range of 5.4 to 7.4 mm, the center thickness of the fourth lens (4) is in the range of 7 to 9 mm, the center thickness of the fifth lens (5) is in the range of 6 to 8 mm, and the center thickness of the sixth lens (6) is in the range of 2.4 to 4.4 mm; The convex surface curvature radius of the first lens (1) ranges from 41 to 43 mm, and the curvature radius of the side opposite to the convex surface ranges from 67 to 69 mm; the convex surface curvature radius of the second lens (2) ranges from 59 to 61 mm, and the curvature radius of the side opposite to the convex surface ranges from 34 to 36 mm; the convex surface curvature radius of the third lens (3) ranges from 33 to 35 mm, and the curvature radius of the side opposite to the convex surface ranges from 51 to 53 mm; the convex surface curvature radius of the fourth lens (4) ranges from -14 to -12 mm, and the curvature radius of the side opposite to the convex surface ranges from -13 to -11 mm; the convex surface curvature radius of the fifth lens (5) ranges from -12 to -10 mm, and the curvature radius of the side opposite to the convex surface ranges from -19 to -17 mm; the first convex surface curvature radius of the sixth lens (6) ranges from 48 to 50 mm, and the second convex surface curvature radius opposite to the first convex surface ranges from -29 to -27 mm; The spacing between the first lens (1) and the second lens (2) is in the range of 1 to 3 mm, the spacing between the second lens (2) and the third lens (3) is in the range of 1 to 3 mm, the spacing between the third lens (3) and the fourth lens (4) is in the range of 36 to 38 mm, the spacing between the fourth lens (4) and the fifth lens (5) is in the range of 1 to 3 mm, and the spacing between the fifth lens (5) and the sixth lens (6) is in the range of 0.1 to 1 mm.

2. The compact medium-wave infrared lens according to claim 1, characterized in that: The materials of the first lens (1), the fourth lens (4) and the sixth lens (6) are all silicon.

3. The compact medium-wave infrared lens according to claim 2, characterized in that: The material of the second lens (2) is germanium.

4. The compact medium-wave infrared lens according to claim 3, characterized in that: The materials of the third lens (3) and the fifth lens (5) are both chalcogenide glass.

5. A medium-wave infrared imaging system, characterized in that: The compact medium-wave infrared lens according to any one of claims 1 to 4.

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