Large target surface infrared optical athermalization fixed focus lens

Abstract

The utility model discloses a big target surface infrared optical athermalization fixed focus lens. Fixed focus lens includes first lens, second lens and third lens who sets up in order along the light ray incident direction coaxially, first lens is negative focal power meniscus, and the convex surface and the concave surface are all spherical surfaces, and the convex surface is towards the object side, and the concave surface is towards the image side, second lens is positive focal power meniscus, and the convex surface is spherical surface, and is towards the object side, and the concave surface is towards the image side, and is diffraction surface, third lens is positive focal power meniscus, and the convex surface and the concave surface are all aspheric surface, and the convex surface is towards the object side, and the concave surface is towards the image side. The utility model solves the problem that the existing lens will cause the focal power change and the best ideal image surface deviation due to temperature difference, realizes optical athermalization.

Description

Technical Field

[0001] This utility model relates to the field of infrared optical lens design technology, and more specifically, to a large-target infrared optical athermalized fixed-focus lens that can be matched with various types of detectors. Background Technology

[0002] With the increasing demand for infrared lenses in both commercial and civilian applications, infrared imaging technology has been widely used in defense, industry, medical, and power detection fields, demonstrating significant application prospects and market value. The basis of infrared target and object identification is infrared radiation, enabling rapid, long-distance, all-weather observation, particularly suitable for target detection and identification at night and under adverse weather conditions. In infrared systems, temperature is a major influencing factor; changes in operating temperature inevitably lead to alterations in imaging system aberrations and image plane drift, resulting in decreased image quality. To eliminate or reduce the impact of temperature effects, thermalization techniques are typically employed, enabling infrared imaging systems to maintain clear imaging under varying temperature conditions.

[0003] There are three main methods for achieving athermalization in infrared optical systems: active mechanical athermalization, passive mechanical athermalization, and passive optical athermalization. Active mechanical athermalization uses a temperature sensor to measure changes in ambient temperature, calculates the resulting image plane displacement, and then uses a motor to drive the lens along the optical axis to achieve temperature compensation. Passive mechanical athermalization utilizes the interaction of materials from high-expansion and low-expansion systems. By adjusting the lengths of these materials, the expansion and contraction of different expansion systems move one or more lenses within the infrared optical system along the optical axis, thus achieving temperature compensation. Passive optical athermalization leverages the differences in thermal properties of various optical materials, combining different optical and structural materials to achieve temperature compensation.

[0004] Mechanically active athermalized optical systems require motor drive, which is not conducive to the miniaturization design of optical systems and has low reliability. Mechanically passive athermalized optical systems require an inner cylinder of high-expansion material and an outer cylinder of low-expansion material in their structural design, making the structure relatively complex. Optically passive athermalized optical systems are achieved by using a variety of materials. By matching the photothermal coefficients of the optical materials and distributing the optical power of the lenses, the optical system can maintain the image plane displacement within the system's focal depth range over a wide temperature range. It has the characteristics of simple structure, reliability, and high assembly efficiency, and is suitable for mass production.

[0005] Currently, passive athermal optical systems mostly utilize scarce and expensive materials such as zinc selenide and zinc sulfide. However, the high price of zinc selenide and zinc sulfide naturally leads to high product costs, limiting their application. Furthermore, current infrared fixed-focus lenses generally have a small image plane (e.g., The following are difficult to adapt to large-area infrared detectors (such as...). The above factors limit the system resolution. Furthermore, existing infrared lenses place chalcogenide materials in the first element, but their high-transmittance AR film is prone to cracking over a wide temperature range, has poor scratch resistance, and high maintenance costs. In dusty or high-temperature and high-humidity environments, it is still necessary to add a germanium window to protect the lens. Utility Model Content

[0006] In response to the above-mentioned defects or improvement needs of existing technologies, this utility model provides a large-target infrared optical athermalized fixed-focus lens that can be matched with various types of detectors, solving the problem that existing lenses will cause changes in optical power and shifts in the optimal ideal image plane due to temperature differences, and achieving optical athermalization.

[0007] To achieve the above objectives, this utility model provides an infrared optical athermalized fixed-focus lens, comprising a first lens, a second lens, and a third lens arranged coaxially along the incident direction of light; the first lens is a meniscus lens with negative optical power, both its convex and concave surfaces being spherical, with the convex surface facing the object side and the concave surface facing the image side; the second lens is a meniscus lens with positive optical power, its convex surface being spherical, facing the object side, and its concave surface facing the image side, serving as a diffraction surface; the third lens is a meniscus lens with positive optical power, both its convex and concave surfaces being aspherical, with the convex surface facing the object side and the concave surface facing the image side.

[0008] In some embodiments, the aforementioned infrared optical athermalized fixed-focus lens further includes an aperture stop; the aperture stop is disposed between the first lens and the second lens.

[0009] In some embodiments, the first lens has a first center thickness CT1, the second lens has a second center thickness CT2, and the third lens has a third center thickness CT3; wherein, 2.0 mm <CT1<3.0mm,5.0mm<CT2<6.0mm,3.0mm<CT3<4.0mm。

[0010] In some embodiments, a first air gap A1 exists between the first lens and the second lens, a second air gap A2 exists between the second lens and the third lens, and a third air gap A3 exists between the third lens and the focal plane of the aforementioned infrared optical athermalized fixed-focus lens; wherein, 0.0 mm <A1<1.0mm,40.0mm<A2<45.0mm,10.0mm<A3<15.0mm。

[0011] In some embodiments, the convex surface of the first lens has a first radius of curvature R1, the concave surface of the first lens has a second radius of curvature R2, the convex surface of the second lens has a third radius of curvature R3, the concave surface of the second lens has a fourth radius of curvature R4, the convex surface of the third lens has a fifth radius of curvature R5, and the concave surface of the third lens has a sixth radius of curvature R6; wherein, 120≤R1≤130, 110≤R2≤120, 40≤R3≤50, 60≤R4≤70, 10≤R5≤20, and 20≤R6≤30.

[0012] In some embodiments, the first lens has a first focal length f1, the second lens has a second focal length f2, and the third lens has a third focal length f3, wherein the focal length of the aforementioned infrared optical athermalized fixed-focus lens is f; wherein -6.0 <f1 / f<-7.0,1.0<f2 / f<2.0,3.0<f3 / f<4.0。

[0013] In some embodiments, the first lens is made of single-crystal germanium.

[0014] In some embodiments, both the second and third lenses are made of chalcogenide materials.

[0015] In some embodiments, the aforementioned infrared optical athermalized fixed-focus lens includes a lens barrel made of aluminum alloy, which matches the coefficient of thermal expansion of the first lens, the second lens, and the third lens.

[0016] In summary, the technical solutions conceived by this utility model have the following beneficial effects compared with the prior art:

[0017] (1) Adopting a 3-piece structure, and using aspherical aberration correction, it can meet the customer's requirement for a large target area for imaging in this system, with a total image height of [missing information]. The imaging target surface can accommodate both the conventionally used 640*512 17um detector and the 1280*1024 12um detector. Its technical advantage of being compatible with multiple detector models provides application space for different fields and closely meets market demands.

[0018] (2) Optical athermal achromatic ...

[0019] (3) The first piece uses small-volume Ge material, which is compatible with high-transmittance anti-reflection (AR) film and wear-resistant diamond-like carbon (DLC) coating. DLC coating is not easy to crack in a wide temperature range and has strong scratch resistance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a large-target infrared optical athermalized fixed-focus lens according to an embodiment of this utility model;

[0021] Figure 2 This is a schematic diagram of the MTF of the large-target infrared optical athermalized fixed-focus lens of this utility model at 20℃ (room temperature);

[0022] Figure 3 This is a schematic diagram of the MTF of the large-target infrared optical athermalized fixed-focus lens of this utility model at -40℃ (low temperature);

[0023] Figure 4 This is a schematic diagram of the MTF of the large-target infrared optical athermal fixed-focus lens of this utility model at 80℃ (high temperature). Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered exemplary in nature and not restrictive.

[0025] like Figure 1 As shown, the large-target infrared optical athermalized fixed-focus lens of this utility model embodiment includes a first lens 101, an aperture stop 103, a second lens 105, and a third lens 107. The first lens 101, the second lens 105, and the third lens 107 are arranged coaxially along the incident light direction. The aperture stop 103 is located between the first lens 101 and the second lens 105. The first lens 101 is a meniscus lens with negative optical power, where both the convex surface S1 and the concave surface S2 are spherical, with the convex surface S1 facing the object side and the concave surface S2 facing the image side. The second lens 105 is a meniscus lens with positive optical power, where the convex surface S3 is spherical and faces the object side, and the concave surface S4 faces the image side and is a diffraction surface. The third lens 107 is a meniscus lens with positive optical power, where both the convex surface S5 and the concave surface S6 are aspherical, with the convex surface S5 facing the object side and the concave surface S6 facing the image side.

[0026] In some embodiments, the first lens 101 has a first central thickness CT1, the second lens 105 has a second central thickness CT2, and the third lens 107 has a third central thickness CT3, where 2.0 mm < CT1 < 3.0 mm, 5.0 mm < CT2 < 6.0 mm, and 3.0 mm < CT3 < 4.0 mm.

[0027] In some embodiments, there is a first air gap A1 between the first lens 101 and the second lens 105, a second air gap A2 between the second lens 105 and the third lens 107, and a third air gap A3 between the third lens 107 and the focal plane of the large-format infrared optical athermalized fixed-focus lens, where 0.0 mm < A1 < 1.0 mm, 40.0 mm < A2 < 45.0 mm, and 10.0 mm < A3 < 15.0 mm. The setting of the air gaps needs to consider the balance of suppressing field curvature and off-axis aberrations while shortening the overall length. Increasing the air gap can optimize the field curvature and reduce higher-order aberrations, but it will directly increase the total track length (TTL) of the lens. Reducing the air gap may reduce the monochromatic aberration, but it may lead to a shortening of the system's overall length, causing the coupling of the optical powers of adjacent lens surfaces and making it impossible to balance aberrations such as distortion. At the same time, changing the gap may change the internal reflection optical path, and a reasonable gap setting can optimize the suppression of specific-order ghost images so that the reflected light does not focus on the sensor.

[0028] In some embodiments, the convex surface S1 of the first lens 101 has a first radius of curvature R1, the concave surface S2 of the first lens 101 has a second radius of curvature R2, the convex surface S3 of the second lens 105 has a third radius of curvature R3, the concave surface S4 of the second lens 105 has a fourth radius of curvature R4, the convex surface S5 of the third lens 107 has a fifth radius of curvature R5, and the concave surface S6 of the third lens 107 has a sixth radius of curvature R6, where 120 ≤ R1 ≤ 130, 110 ≤ R2 ≤ 120, 40 ≤ R3 ≤ 50, 60 ≤ R4 ≤ 70, 10 ≤ R5 ≤ 20, and 20 ≤ R6 ≤ 30. The principle for determining the positive and negative of the radius of curvature is: taking the intersection point of the surface and the principal optical axis as the starting point and the center of curvature of the surface as the end point, if the direction of the connection line is the same as the direction of light propagation, it is positive, otherwise it is negative; if the surface is a plane, the radius of curvature of the surface is infinite.

[0029] In some embodiments, the first lens 101 has a first focal length f1, the second lens 105 has a second focal length f2, the third lens 107 has a third focal length f3, and the focal length of the large-format infrared optical athermalized fixed-focus lens is f, where -6.0 < f1 / f < -7.0, 1.0 < f2 / f < 2.0, and 3.0 < f3 / f < 4.0.

[0030] In some embodiments, the first lens 101 is made of germanium (Ge). Germanium is divided into single-crystal germanium and polycrystalline germanium. Polycrystalline germanium has many impurities at its boundaries, which affects the non-uniformity of its refractive index. Therefore, single-crystal germanium is the preferred material for the first lens 101. In some embodiments, the second lens 105 and the third lens 107 are both made of chalcogenide materials. Among them, the chalcogenide material used in the second lens 105 utilizes diffraction technology, which reduces the cost of the lens material while also achieving the purpose of reducing thermal differences in the infrared optical system at high and low temperatures.

[0031] In some implementations, the lens barrel material of the large-target infrared optical calorimetric fixed-focus lens is aluminum alloy. By matching the thermal expansion coefficients of the lens barrel material and the lens, mechanical defocusing is avoided, making the system imaging more stable and reliable.

[0032] In some implementations, the large-area infrared athermalized fixed-focus lens has the following optical specifications:

[0033] (1) Working wavelength λ: 8um < λ < 12um;

[0034] (2) Focal length f: 50mm < f < 60mm;

[0035] (3) Relative aperture D / f: 1 / 1.4 < D / f < 1;

[0036] (4) Field of view: 2ω>20°;

[0037] (5) Maximum imaging target area of ​​the system:

[0038] (6) The total length of the optical path L ≤ 71 mm and the optical back cutoff S > 14 mm.

[0039] The modulation transfer function (MTF) of an optical system is one of the important parameters used to describe the imaging performance of the optical system. It represents the modulation transfer efficiency of the optical system at different spatial frequencies, and its value ranges from 0 to 1. Simulations using optical design software yielded the MTF curves of the large-area infrared athermalized fixed-focus lens of this embodiment at room temperature, low temperature, and high temperature, as shown below. Figures 2 to 4 As shown. The horizontal axis represents spatial frequency, with higher frequencies indicating finer details; the vertical axis represents modulation transmission efficiency, reflecting the degree of contrast retention.

[0040] Figures 2 to 4The MTF curves for eight different scenarios are given. F1: Diff.Limit represents the diffraction limit, F1(RIH)0.000mm represents 0 field of view, F2:T(RIH)5.000mm represents 0.5 field of view in the meridional direction, F2:R(RIH)5.000mm represents 0.5 field of view in the sagittal direction, F3:T(RIH)7.070mm represents 0.707 field of view in the meridional direction, F3:R(RIH)7.070mm represents 0.707 field of view in the sagittal direction, F4:T(RIH)10.000mm represents 1 field of view in the meridional direction, and F4:R(RIH)10.000mm represents 1 field of view in the sagittal direction.

[0041] As can be seen, when using an uncooled detector with a pixel size of 12μm and a pixel count of 1280×1024, corresponding to a spatial frequency of 42lp / mm, the transfer function is greater than 0.2 under normal temperature, low temperature, and high temperature conditions. Therefore, the large-target infrared optical anechoic fixed-focus lens of this embodiment has excellent optical imaging quality and good anechoic effect.

[0042] This utility model's large-target infrared optical athermalized fixed-focus lens adopts a 3-element structure. Through aspherical aberration correction, it meets customer requirements for a large target area in the system's imaging. Its compatibility with multiple detector models provides application space for various fields, closely aligning with market demands. It employs optical athermalized achromatic correction, utilizing thermal difference compensation between Ge and IG6. Through optical power distribution, the modulation transfer function decreases by less than 10% within the -40℃ to +80℃ range. By matching the thermal expansion coefficients of the lens barrel material (aluminum alloy) and the lenses, mechanical defocusing is avoided, resulting in more stable and reliable system imaging. It is well-suited for mass production and boasts a compact size. The first element uses a small-volume Ge material, compatible with high-transmittance antireflective coatings and wear-resistant diamond-like carbon (DLC) coatings. DLC coatings are less prone to cracking over a wide temperature range and exhibit strong scratch resistance.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying 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 application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more (two or more) executable instructions for implementing a particular logical function or process. Furthermore, the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functionality involved.

[0046] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A large-target infrared optical athermalized fixed-focus lens, characterized in that, The system includes a first lens, a second lens, and a third lens arranged coaxially along the incident direction of light. The first lens is a meniscus lens with negative optical power, where both the convex and concave surfaces are spherical, with the convex surface facing the object side and the concave surface facing the image side. The second lens is a meniscus lens with positive optical power, where the convex surface is spherical and faces the object side, while the concave surface faces the image side and serves as a diffraction surface. The third lens is a meniscus lens with positive optical power, where both the convex and concave surfaces are aspherical, with the convex surface facing the object side and the concave surface facing the image side.

2. The large-target infrared optical athermalized fixed-focus lens as described in claim 1, characterized in that, It also includes an aperture stop; the aperture stop is disposed between the first lens and the second lens.

3. The large-target infrared optical athermalized fixed-focus lens as described in claim 2, characterized in that, The first lens has a first center thickness CT1, the second lens has a second center thickness CT2, and the third lens has a third center thickness CT3; wherein, 2.0 mm <CT1<3.0mm,5.0mm<CT2<6.0mm,3.0mm<CT3<4.0mm。 4. The large-target infrared optical athermalized fixed-focus lens as described in claim 2, characterized in that, There is a first air gap A1 between the first lens and the second lens, a second air gap A2 between the second lens and the third lens, and a third air gap A3 between the third lens and the focal plane of the infrared optical athermalized fixed-focus lens; wherein, 0.0 mm <A1<1.0mm,40.0mm<A2<45.0mm,10.0mm<A3<15.0mm。 5. The large-target infrared optical athermalized fixed-focus lens as described in claim 2, characterized in that, The first lens has a first radius of curvature R1 on its convex surface, a second radius of curvature R2 on its concave surface, a third radius of curvature R3 on its convex surface, a fourth radius of curvature R4 on its concave surface, a fifth radius of curvature R5 on its convex surface, and a sixth radius of curvature R6 on its concave surface; wherein 120mm≤R1≤130mm, 110mm≤R2≤120mm, 40mm≤R3≤50mm, 60mm≤R4≤70mm, 10mm≤R5≤20mm, and 20mm≤R6≤30mm.

6. The large-target infrared optical athermalized fixed-focus lens as described in claim 2, characterized in that, The first lens has a first focal length f1, the second lens has a second focal length f2, the third lens has a third focal length f3, and the focal length of the infrared optical athermalized fixed-focus lens is f; wherein, -6.0 <f1 / f<-7.0,1.0<f2 / f<2.0,3.0<f3 / f<4.0。 7. The large-target infrared optical athermalized fixed-focus lens as described in any one of claims 1 to 6, characterized in that, The first lens is made of single-crystal germanium.

8. The large-target infrared optical athermalized fixed-focus lens as described in claim 7, characterized in that, Both the second lens and the third lens are made of chalcogenide materials.

9. The large-target infrared optical athermalized fixed-focus lens as described in any one of claims 1 to 6, characterized in that, It includes a lens barrel made of aluminum alloy, whose coefficient of thermal expansion is matched with that of the first lens, the second lens, and the third lens.

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