An airborne infrared warning optical system based on a fisheye lens

Abstract

The application discloses an airborne infrared warning optical system based on a fisheye lens, and solves the problems of a small warning field of view and poor temperature adaptability of an existing airborne infrared warning system. The optical system comprises, from left to right, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a refrigeration type mid-wave infrared detector. The left side of the first lens is an object plane, and the right side of the sixth lens is the refrigeration type mid-wave infrared detector. The first lens is a meniscus negative lens. The second lens is a meniscus negative lens. The third lens is a meniscus positive lens. The fourth lens is a meniscus positive lens. The fifth lens is a double-concave negative lens, and the sixth lens is a double-convex positive lens. The application has the advantages of compact size, small distortion and excellent imaging performance, and can realize normal imaging warning in a temperature range of-55 DEG C to 70 DEG C without an external focusing mechanism, thereby improving the field of view and sensitivity of the airborne infrared warning.

Description

Technical Field

[0001] This invention belongs to the field of infrared optical system design, specifically relating to an airborne infrared warning optical system based on a fisheye lens. Background Technology

[0002] To improve the battlefield survivability and cost-effectiveness of armed helicopters, helicopter platforms must enhance their optoelectronic countermeasures capabilities.

[0003] Airborne infrared warning systems, as a crucial component of airborne terminal defense systems, are capable of rapidly and accurately detecting the location and other information of approaching infrared targets. Typical requirements include a large sensing and warning range (field of view not less than 180°) and a long sensing distance. Airborne infrared warning optical systems based on fisheye lenses can meet these requirements. However, the large field of view of this type of optical system increases the difficulty of aberration correction. Furthermore, to achieve high detection efficiency, a cooled infrared detector is used, requiring 100% matching between the optical system's exit pupil and the detector's cold stop to suppress the impact of stray light outside the field of view on the sensing and warning effectiveness. Additionally, due to the high temperature refractive index of infrared optical glass materials, temperature changes can severely degrade the warning system's performance. Patent CN105044887 B discloses a cooled, large relative aperture ultra-wide-angle infrared optical system with a field of view of only 120° and lacking thermalization, thus failing to meet the aforementioned airborne warning requirements.

[0004] In summary, currently available airborne infrared warning systems have limitations. Therefore, researching an optical system with a large warning field of view, wide temperature adaptability, and applicable to airborne infrared warnings is an important problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention proposes an airborne infrared warning optical system based on a fisheye lens, which can detect and warn of approaching infrared targets within a 180° range, while achieving wide temperature adaptability and miniaturization of the optical system.

[0006] The technical solution for realizing the present invention is as follows: an airborne infrared warning optical system based on a fisheye lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a cooled mid-wave infrared detector arranged from left to right; the left side of the first lens is the object plane, and the right side of the sixth lens is the cooled mid-wave infrared detector; the cooled mid-wave infrared detector includes a cooled mid-wave infrared detector protective window and a cooled mid-wave infrared detector filter arranged sequentially from left to right along the incident direction of light, and a cold stop is provided on the rear surface of the cooled mid-wave infrared detector filter.

[0007] Compared with the prior art, the significant advantages of this invention are:

[0008] (1) The lens of the airborne infrared warning optical system based on the fisheye lens of the present invention uses 6 optical lenses. By selecting optical structure, selecting optical materials and using high-order aspherical surfaces, the field of view of the optical system reaches 180°, the relative aperture of the system reaches 1 / 2, and the f-Theta distortion of the optical system is ≤1%, which greatly improves the warning field of view and relative aperture of the optical system, and improves the angle measurement accuracy and detection sensitivity of the system.

[0009] (2) Compared with the existing airborne infrared alarm systems, which mostly have a field of view of 90°, the airborne platform equipped with an airborne infrared alarm optical system based on a fisheye lens of the present invention can significantly reduce the number of equipment, thus saving platform resources and equipment costs.

[0010] (3) The airborne infrared warning optical system based on fisheye lens of the present invention uses only two 8th order aspherical lenses. Compared with the optical system with global aspherical design, it is easier to achieve a lightweight and miniaturized structure, and requires fewer lenses, resulting in lower cost and making it more suitable for mass production and mass equipment on airborne platforms.

[0011] (4) The airborne infrared warning optical system based on fisheye lens of the present invention adopts a passive calorimetric design. By selecting a material combination with matching linear expansion coefficients of lens barrel material and infrared glass material, clear imaging of the target can be achieved in the full temperature range of -55℃ to 70℃. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of an optical system according to an embodiment of the present invention.

[0013] Figure 2 This is a schematic diagram of the structure of the optical system in embodiment two of the present invention.

[0014] Figure 3(a) is a dot plot of the optical system of an embodiment of the present invention at an ambient temperature of -55°C.

[0015] Figure 3(b) is a dot plot of the optical system of the present invention at an ambient temperature of 20°C.

[0016] Figure 3(c) is a dot plot of the optical system of the present invention at an ambient temperature of 70°C.

[0017] Figure 4(a) shows the MTF curve of the optical system of this embodiment at an ambient temperature of -55°C.

[0018] Figure 4(b) shows the MTF curve of the optical system of this embodiment at an ambient temperature of 20°C.

[0019] Figure 4(c) shows the MTF curve of the optical system of this embodiment at an ambient temperature of 70°C.

[0020] Figure 5(a) shows the distortion curve of the optical system of this embodiment at an ambient temperature of -55°C.

[0021] Figure 5(b) shows the distortion curve of the optical system of this embodiment at an ambient temperature of 20°C.

[0022] Figure 5(c) shows the distortion curve of the optical system of this embodiment at an ambient temperature of 70°C.

[0023] Explanation of reference numerals in the attached drawings: 1-First lens, 2-Second lens, 3-Third lens, 4-Fourth lens, 5-Fifth lens, 6-Sixth lens, 7-Cooled mid-wave infrared detector, 701-Cooled mid-wave infrared detector protective window, 702-Cooled mid-wave infrared detector filter, 8-Optical mirror, IMA-Image plane. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0026] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixing," etc., should be interpreted broadly. For example, "fixing" can mean a fixed connection, a detachable connection, or an integral part; "connection" can mean a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible to those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0029] The following section will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention, using this design example as an example.

[0030] Combination Figure 1 An airborne infrared warning optical system based on a fisheye lens includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a cooled mid-wave infrared detector arranged along the incident direction of light from left to right. The cooled mid-wave infrared detector includes a protective window, a filter, and a cold stop arranged in sequence. The optical system is provided with an aperture stop, which has the same size as the cold stop and is positioned coincidentally.

[0031] An airborne infrared warning optical system based on a fisheye lens, wherein the left side of the first lens is the object plane and the right side of the cold stop of the cooled mid-wave detector is the image plane; the first lens is a meniscus negative lens bent towards the image side, the second lens is a meniscus negative lens bent towards the object side, the third lens is a meniscus positive lens bent towards the object side, the fourth lens is a meniscus positive lens bent towards the image side, the fifth lens is a biconcave negative lens, and the sixth lens is a biconvex positive lens.

[0032] The first lens, second lens, third lens, fourth lens, fifth lens, and sixth lens satisfy the following relationships: -5.0≤f1 / f≤-4.0, -6.4≤f2 / f≤-6.0, 13.0≤f3 / f≤13.4, 18.6≤f4 / f≤19.0, -7.5≤f5 / f≤-6.5, 4.0≤f6 / f≤4.6; where f is the focal length of the optical system, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, f5 is the focal length of the fifth lens, and f6 is the focal length of the sixth lens.

[0033] Furthermore, the center thickness of the first lens is 6.0mm to 6.6mm, and its front surface (i.e., the left surface) and rear surface (i.e., the right surface) are spherical; the center thickness of the second lens is 7.8mm to 8.2mm, and its front surface and rear surface are spherical; the center thickness of the third lens is 7.8mm to 8.2mm, and its front surface and rear surface are spherical; the center thickness of the fourth lens is 3.8mm to 4.2mm, its front surface is an even-order aspherical, and its rear surface is spherical; the center thickness of the fifth lens is 3.3mm to 4.0mm, and its front surface and rear surface are spherical; the center thickness of the sixth lens is 4.5mm to 5.5mm, its front surface is spherical, and its rear surface is an even-order aspherical.

[0034] Furthermore, the air gap between the first lens and the second lens is 21.0 mm to 21.6 mm, the air gap between the second lens and the third lens is 11.5 mm to 12.5 mm, the air gap between the third lens and the fourth lens is 103.0 mm to 104.0 mm, the distance between the fourth lens and the fifth lens is 15.5 mm to 16.5 mm, the distance between the fifth lens and the sixth lens is 1.0 mm to 2.0 mm, and the distance between the sixth lens and the protective window of the cooled mid-wave infrared detector is 6.0 mm to 8.0 mm.

[0035] Furthermore, the second and third lenses can be configured with planar reflectors with different deflection angles according to the system's outer envelope size constraints.

[0036] Furthermore, the optical system operates in the mid-wave infrared band; a cooled mid-wave infrared detector protective glass, made of single-crystal silicon, is disposed on the right side of the sixth lens. A cooled mid-wave infrared detector filter, made of single-crystal germanium, is disposed on the right side of the cooled mid-wave infrared detector protective glass.

[0037] Furthermore, the f-theta distortion of the optical system is <1%.

[0038] Furthermore, the first lens is made of single-crystal germanium, the second lens is made of single-crystal silicon, the third lens is made of zinc sulfide, the fourth lens is made of zinc selenide, the fifth lens is made of single-crystal germanium, and the sixth lens is made of single-crystal silicon.

[0039] Example 1

[0040] like Figure 1As shown, this embodiment provides an airborne infrared warning optical system based on a fisheye lens, 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, and an aperture stop (STOP) arranged sequentially from left to right along the light incident direction. The left side of the first lens 1 is the object plane, and the right side of the sixth lens 6 is a cooled mid-wave infrared detector 7. The cooled mid-wave infrared detector 7 includes a cooled mid-wave infrared detector protective window 701 and a cooled mid-wave infrared detector filter 702 arranged sequentially from left to right along the light incident direction. A cold aperture stop is disposed on the rear surface of the cooled mid-wave infrared detector filter 702, and the aperture stop (STOP) coincides with the position of the cold aperture stop.

[0041] The first lens 1 is a meniscus negative lens bent towards the image side, made of single-crystal germanium; the second lens 2 is a meniscus negative lens bent towards the object side, made of single-crystal silicon; the third lens 3 is a meniscus positive lens bent towards the object side, made of zinc sulfide; the fourth lens 4 is a meniscus positive lens bent towards the image side, made of zinc selenide; the fifth lens 5 is a biconcave negative lens made of single-crystal germanium; and the sixth lens 6 is a biconvex positive lens made of single-crystal silicon.

[0042] Lens 1, 2, 3, 4, 5, and 6 satisfy the following relationships: -5.0 ≤ f1 / f ≤ -4.0, -6.4 ≤ f2 / f ≤ -6.0, 13.0 ≤ f3 / f ≤ 13.4, 18.6 ≤ f4 / f ≤ 19.0, -7.5 ≤ f5 / f ≤ -6.5, 4.0 ≤ f6 / f ≤ 4.6; where f is the focal length of the optical system, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, f5 is the focal length of the fifth lens, and f6 is the focal length of the sixth lens.

[0043] This invention discloses an airborne infrared warning optical system based on a fisheye lens. It utilizes non-high-order spherical surfaces to achieve a large aperture, wide field of view, and miniaturization. Specifically, the first lens 1 has a center thickness of 6.0mm–6.6mm, with both its front and rear surfaces being spherical; the second lens 2 has a center thickness of 7.8mm–8.2mm, with both its front and rear surfaces being spherical; the third lens 3 has a center thickness of 7.8mm–8.2mm, with both its front and rear surfaces being spherical; the fourth lens 4 has a center thickness of 3.8mm–4.2mm, with its front surface being an eighth-order aspherical and its rear surface being spherical; the fifth lens 5 has a center thickness of 3.3mm–4.0mm, with both its front and rear surfaces being spherical; and the sixth lens 6 has a center thickness of 4.5mm–5.5mm, with its front surface being spherical and its rear surface being an eighth-order aspherical.

[0044] The air gap between the first lens 1 and the second lens 2 is 21.0 mm to 21.6 mm; the air gap between the second lens 2 and the third lens 3 is 11.5 mm to 12.5 mm; the air gap between the third lens 3 and the fourth lens 4 is 103.0 mm to 104.0 mm; the air gap between the fourth lens 4 and the fifth lens 5 is 15.5 mm to 16.5 mm; the air gap between the fifth lens 5 and the sixth lens 6 is 1.0 mm to 2.0 mm; and the air gap between the sixth lens 6 and the cooled mid-wave infrared detector 7 is 6.0 mm to 8.0 mm.

[0045] The cooled mid-wave infrared detector has a total of 1280×1024 pixels, and the size of each pixel is 15μm×15μm.

[0046] The air gap between the cooled mid-wave infrared detector protective window 701 and the cooled mid-wave infrared detector filter 702 in the cooled mid-wave infrared detector 7 is 1.5 mm, and the air gap between the cooled mid-wave infrared detector filter and the image plane IMA is 30 mm. The cooled mid-wave infrared detector protective window 701 is made of flat glass with a center thickness of 1.6 mm and is made of monocrystalline silicon. The cooled mid-wave infrared detector filter 702 is made of flat glass with a center thickness of 0.3 mm and is made of monocrystalline germanium.

[0047] The following are the various numerical data related to the airborne infrared warning optical system based on a fisheye lens involved in this embodiment:

[0048] Table 1. Specific parameters of each lens in the optical system of this embodiment (unit: mm)

[0049]

[0050] Table 2 Aspheric Coefficients of the Optical System in the Example Implementation

[0051] Aspheric coefficient Fourth lens Sixth lens A4 -2.48E-06 5.59E-07 A6 -1.88E-09 -1.51E-09 A8 -1.86E-12 2.04E-12

[0052] In this embodiment of the invention, an airborne infrared warning optical system based on a fisheye lens has an optical total length of 229 mm, a maximum aperture of 67 mm, a field of view of 182°, an F number of 2, and operates in the mid-wave infrared band.

[0053] In this embodiment, the structural material of the fixed optical system is aluminum alloy with an expansion coefficient of 2.36×10-5. By cooperating with the lens material of the optical system, good imaging quality can be guaranteed without adjusting the focal plane position of the optical system when the ambient temperature varies within the range of -55℃ to 70℃.

[0054] like Figures 3(a) to 3(c)As shown, the RMS radius of the imaging spot of the optical system at ambient temperatures of -55℃, 20℃, and 70℃ ranges from 2.8μm to 5.7μm for different fields of view, which is less than half the size of a single pixel (15μm). Furthermore, the spot radius is relatively uniform, indicating that the spot quality is similar across the entire field of view. Figures 4(a) to 4(c) As shown, the optical system exhibits transfer functions greater than 0.47 at different fields of view at ambient temperatures of -55℃, 20℃, and 70℃, approaching the diffraction limit, indicating good imaging quality. Figures 5(a) to 5(b) As shown, the maximum f-Theta distortion of the optical system is only 0.75% when the ambient temperatures are -55℃, 20℃, and 70℃, respectively, indicating that the optical system has extremely low distortion and high angle measurement accuracy and detection sensitivity.

[0055] This invention provides an airborne infrared warning optical system based on a fisheye lens, which has advantages such as a large field of view, large relative aperture, high optical transfer function, and minimal f-Theta distortion, enabling high angle measurement accuracy and detection sensitivity. The airborne infrared warning optical system based on a fisheye lens of this invention employs a design combining four spherical lenses and two eighth-order aspherical lenses, achieving a compact and lightweight structure with fewer lenses required, lower cost, and greater suitability for mass production, making it suitable for mass deployment on airborne platforms. Furthermore, by selecting a material combination with matching coefficients of linear expansion for the lens barrel and infrared glass, this invention achieves clear imaging of targets across the entire temperature range of -55℃ to 70℃ without the need for an additional focusing mechanism.

[0056] Analysis of the embodiments shows that the optical system is compact and has good imaging, meeting the requirements of airborne infrared alarm systems for a large sensing range, long sensing distance, and small size.

[0057] Example 2

[0058] like Figure 2 As shown, the difference from Embodiment 1 is that, based on Embodiment 1, an optical reflector 8 is set between the third lens 3 and the fourth lens 4. The first lens 1, the second lens 2, and the third lens 3 are located on the incident optical axis of the optical reflector 8, while the fourth lens 4, the fifth lens 5, the sixth lens 6, and the cooled mid-wave infrared detector 7 are located on the exit optical axis of the optical reflector 8. The angle between the incident optical axis and the exit optical axis of the optical reflector 8 is 103.23°, which compresses the volume of the entire optical system and meets the requirements for use in scenarios with strict space requirements.

[0059] In this embodiment, the angle between the incident optical axis and the outgoing optical axis of the optical reflector 8 can be replaced by other angles without modifying parameters such as the radius of curvature, thickness, and material in the optical system.

Claims

1. An airborne infrared warning optical system based on fisheye lens, characterized in that: The optical system comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a refrigeration type mid-wave infrared detector arranged from left to right; the left side of the first lens is an object plane, and the right side of the sixth lens is the refrigeration type mid-wave infrared detector; the refrigeration type mid-wave infrared detector comprises a refrigeration type mid-wave infrared detector protective window and a refrigeration type mid-wave infrared detector filter which are arranged in sequence from left to right along the light incidence direction, and a cold light stop is arranged on the rear surface of the refrigeration type mid-wave infrared detector filter; The first lens is a meniscus negative lens which is bent towards the image side, the second lens is a meniscus negative lens which is bent towards the object side, the third lens is a meniscus positive lens which is bent towards the object side, the fourth lens is a meniscus positive lens which is bent towards the image side, the fifth lens is a double-concave negative lens, and the sixth lens is a double-convex positive lens. The central thickness of the first lens is 6.0mm-6.6mm, the front surface of the first lens is a spherical surface with a curvature radius of 48.2mm, and the rear surface of the first lens is a spherical surface with a curvature radius of 25.4mm; the central thickness of the second lens is 7.8mm-8.2mm, the front surface of the second lens is a spherical surface with a curvature radius of -81.5mm, and the rear surface of the second lens is a spherical surface with a curvature radius of 919.0mm; the central thickness of the third lens is 7.8mm-8.2mm, the front surface of the third lens is a spherical surface with a curvature radius of -146.7mm, and the rear surface of the third lens is a spherical surface with a curvature radius of -53.8mm; the central thickness of the fourth lens is 3.8mm-4.2mm, the front surface of the fourth lens is an even aspheric surface with a curvature radius of 85.4mm, and the rear surface of the fourth lens is a spherical surface with a curvature radius of 234.0mm; the central thickness of the fifth lens is 3.3mm-4.0mm, the front surface of the fifth lens is a spherical surface with a curvature radius of -207.5mm, and the rear surface of the fifth lens is a spherical surface with a curvature radius of 208.3mm; and the central thickness of the sixth lens is 4.5mm-5.5mm, the front surface of the sixth lens is a spherical surface with a curvature radius of 203.0mm, and the rear surface of the sixth lens is an even aspheric surface with a curvature radius of -68.1mm.

2. The fisheye lens based airborne infrared warning optical system according to claim 1, characterized in that: The optical system further comprises an aperture stop arranged in the refrigeration type mid-wave infrared detector.

3. The fisheye lens based airborne infrared warning optical system according to claim 2, characterized in that: The first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens satisfy the following relationship: -5.0≤f1 / f≤-4.0, -6.4≤f2 / f≤-6.0, 13.0≤f3 / f≤13.4, 18.6≤f4 / f≤19.0, -7.5≤f5 / f≤-6.5, and 4.0≤f6 / f≤4.6; wherein f is the focal length of the optical system, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, f5 is the focal length of the fifth lens, and f6 is the focal length of the sixth lens.

4. The fisheye lens based airborne infrared warning optical system according to claim 3, characterized in that: The air gap between the first lens and the second lens is 21.0mm-21.6mm, the air gap between the second lens and the third lens is 11.5mm-12.5mm, the air gap between the third lens and the fourth lens is 103.0mm-104.0mm, the air gap between the fourth lens and the fifth lens is 15.5mm-16.5mm, the air gap between the fifth lens and the sixth lens is 1.0mm-2.0mm, and the air gap between the sixth lens and the refrigeration type mid-wave infrared detector is 6.0mm-8.0mm.

5. The fisheye lens based airborne infrared warning optical system according to claim 4, characterized in that: The air gap between the first lens and the second lens is 21.3mm, the air gap between the second lens and the third lens is 12.0mm, the air gap between the third lens and the fourth lens is 103.4mm, the air gap between the fourth lens and the fifth lens is 15.9mm, the air gap between the fifth lens and the sixth lens is 1.5mm, and the air gap between the sixth lens and the refrigeration type mid-wave infrared detector is 7.2mm.

6. The airborne infrared warning optical system based on fisheye lens according to any one of claims 1-5, characterized in that: The optical system works in a mid-wave infrared wave band.

7. The fisheye lens based airborne infrared warning optical system according to claim 6, characterized in that: The f-theta distortion of the optical system is less than or equal to 1%.

8. The fisheye lens based airborne infrared warning optical system according to claim 7, characterized in that: The first lens is made of single crystal germanium material, the second lens is made of single crystal silicon material, the third lens is made of zinc sulfide material, the fourth lens is made of zinc selenide material, the fifth lens is made of single crystal germanium material, and the sixth lens is made of single crystal silicon material.

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