A miniaturized, high-resolution, wide-temperature, athermal infrared optical system

Abstract

The present invention discloses a miniaturized, high-resolution, wide-temperature, athermalized infrared optical system. The system consists of a first positive meniscus lens, a biconcave negative lens, a second positive meniscus lens, and a negative meniscus lens, coaxially arranged from the object side to the image side. The first, second, and negative meniscus lenses are all curved toward the image side. This optical system is compatible with 1280×1024 high-resolution, long-wavelength, uncooled detectors and operates within a wide temperature range of -55°C to +70°C. It avoids defocusing and image quality degradation due to ambient temperature fluctuations, achieving athermalization. The system utilizes a chalcogenide glass with a low temperature refractive index and employs passive optical athermalization, simplifying and miniaturizing the system.

Description

Technical Field

[0001] The present invention relates to the technical field of non-cooled infrared optical systems, and in particular to a miniaturized, high-resolution, wide-temperature, athermal infrared optical system. Background Art

[0002] With the rapid development of infrared night vision technology, infrared thermal imaging has garnered increasing attention, and significant progress has been made in the development of infrared detectors, its core technology. Uncooled detectors generally have lower detection efficiency than cooled ones. However, as pixel size continues to decrease and sensitivity continues to increase, their price is gradually decreasing. Uncooled infrared detectors also offer advantages such as light weight, compact size, low power consumption, high reliability, and portability. In recent years, they have shown broad application prospects in a wide range of fields, including industry, agriculture, national defense, healthcare, transportation, and environmental protection.

[0003] However, in general, the refractive index of optical materials changes with temperature, which causes the focal length of the lens or optical system to change. The temperature coefficient of infrared optical materials is much larger than that of ordinary optical glass. For example, the typical value of dn / dt of germanium single crystal is about 396×10 -6 / ℃, while the temperature coefficient of K9 glass is only 2.8×10 -6 / °C. Therefore, the impact of temperature on refractive index is particularly pronounced in infrared systems. As ambient temperature changes, the refractive index, the curvature and thickness of optical lenses, and the spacing between components all change, causing thermal defocus in the infrared optical system and degrading imaging quality. Therefore, athermalizing infrared optical systems has become a mainstream development direction for high-precision infrared optical systems.

[0004] There are three main approaches to athermalizing infrared systems. The first is mechanical passive compensation, which utilizes temperature-sensitive mechanical materials or memory alloys to induce axial displacement of one or a group of lenses, thereby compensating for image plane displacement caused by temperature changes. This method requires calculating the position of the optimal phase plane at different temperatures. Based on the displacement of the optimal phase plane, the displacement of the optimal image plane is compensated by varying the expansion and contraction of the structural materials. The second is electronic active compensation, which uses a temperature sensor to detect temperature changes, calculates the image plane displacement caused by temperature changes, and uses a motor to drive the lens to axially shift to achieve compensation. The third is optical passive compensation. Optical passive athermalization exploits the differences in the thermal properties of optical materials. By rationally combining materials with different properties, the effects of temperature are eliminated, resulting in an athermal effect. This approach offers the advantages of relatively simple structure, small size, light weight, no power supply, and excellent system reliability. Its overall efficiency is the highest, and therefore it has attracted considerable attention.

[0005] Optical systems developed using hybrid refractive / diffractive elements have unparalleled advantages in improving system imaging quality, reducing system volume and weight, and lowering costs, as diffractive optical elements have negative dispersion characteristics, negative temperature characteristics, and can achieve arbitrary phase modulation of the light wavefront. When used in conjunction with ordinary optical elements, they have unparalleled advantages in improving system imaging quality, reducing system volume and weight, and lowering costs.

[0006] Large-array infrared detectors require infrared optical lenses with large target surfaces, otherwise the infrared images produced by the system will appear to have bright corners. Therefore, when designing an infrared optical system, its target surface size should be no smaller than that of the selected infrared detector.

[0007] Existing optical passive athermalized long-wave infrared optical systems use infrared materials such as single crystal germanium, zinc selenide, and zinc sulfide. These conventional infrared materials have a large temperature coefficient. Therefore, in order to enable the system to operate within a wide temperature range, the optical system has a large number of lenses and a relatively complex structure, which is not conducive to miniaturization design. Summary of the Invention

[0008] The present invention provides a miniaturized, high-resolution, wide-temperature, athermal infrared optical system. This optical system utilizes low-temperature-coefficient chalcogenide glass, ensuring compatibility with a 1280×1024 high-resolution, long-wavelength, uncooled detector while achieving excellent imaging over a wide temperature range of -55°C to +70°C. Miniaturization is achieved due to the system's relatively small number of lenses and the absence of complex temperature compensation mechanisms.

[0009] In order to achieve the above object, the specific scheme adopted by the present invention is:

[0010] A miniaturized, high-resolution, wide-temperature, athermal infrared optical system comprises a first meniscus positive lens, a biconcave negative lens, a second meniscus positive lens, and a meniscus negative lens coaxially arranged in sequence from the object side to the image side; wherein the first meniscus positive lens, the second meniscus positive lens, and the meniscus negative lens are all arranged curved toward the image side.

[0011] Furthermore, the material used for the first meniscus positive lens is single crystal germanium; the materials used for the biconcave negative lens, the second meniscus positive lens and the meniscus negative lens are all chalcogenide glass IRG206.

[0012] Furthermore, let the focal length of the optical system be f, then the effective focal length of each lens included in the optical system of the present invention satisfies the following conditions:

[0013] The effective focal length f1 of the first meniscus positive lens satisfies: 1.0≤f1 / f≤1.2;

[0014] The effective focal length f2 of the biconcave negative lens satisfies: -0.7≤f2 / f≤-0.6;

[0015] The effective focal length f3 of the second meniscus positive lens satisfies: 0.55≤f3 / f≤0.65;

[0016] The effective focal length f4 of the meniscus negative lens satisfies: -2.9≤f4 / f≤-2.7.

[0017] Furthermore, the distance on the optical axis between the first meniscus positive lens and the biconcave negative lens is T12, the distance on the optical axis between the biconcave negative lens and the second meniscus positive lens is T23, and the thickness of the biconcave negative lens on the optical axis is CT2, then T12, T23 and CT2 satisfy: 3.2≤(T12+T23) / CT2≤3.6.

[0018] Furthermore, the surface of the biconcave negative lens facing the image side is aspherical, and the surface of the biconcave negative lens facing the image side satisfies the surface equation:

[0019]

[0020] Wherein, z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient.

[0021] Furthermore, the aspheric coefficients of the surface of the biconcave negative lens facing the image side are: k=0, A=-2.598806e-006, B=-1.788164e-009, C=2.378721e-012, and D=0.

[0022] Furthermore, the surface of the meniscus negative lens facing the object side adopts a diffractive aspheric surface, and the surface of the meniscus negative lens facing the object side satisfies the surface equation:

[0023]

[0024] Among them, z is the distance vector height from the aspheric surface vertex when the aspheric surface is at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, and C is the eighth-order aspheric coefficient; HOR is the diffraction order, C1, C2, and C3 are the diffraction surface coefficients, λ0 is the design center wavelength; n is the refractive index of the lens, and n0 is the refractive index of air.

[0025] Furthermore, the aspheric coefficients of the surface of the meniscus negative lens facing the object side are: k=0, A=-1.733180e-005, B=-3.923963e-008, C=4.173116e-011, HOR=1, C1=0.00016023, C2=-5.00616326e-007, C3=0.

[0026] Furthermore, the technical parameters achieved by the optical system are:

[0027] Working band: 8μm~12μm; F # : 1.0; focal length: 45mm; field of view: 19.4°×15.5°, image diameter: Φ19.7mm, operating temperature range: -55℃~+70℃;

[0028] Among them, F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

[0029] Furthermore, the detector adapted for the optical system is a 1280×1024 uncooled infrared detector with a pixel size of 12 μm.

[0030] Beneficial effects:

[0031] 1) In the present invention, the double concave negative lens, the second meniscus positive lens and the meniscus negative lens are all made of chalcogenide glass material with the brand IRG206. Since the refractive index temperature coefficient of chalcogenide glass IRG206 is 32×10 -6 / ℃, which is one tenth of the ordinary infrared material Ge. Therefore, the introduction of chalcogenide glass can make the defocus of the optical system caused by temperature changes smaller, achieve the purpose of athermalization in a wide temperature range while using fewer lenses, and realize miniaturization.

[0032] 2) Optical passive athermalization is adopted. Compared with active athermalization and mechanical passive athermalization, it does not require complex motion adjustment mechanisms, has a simple system structure, and improves the reliability of the optical system while reducing the overall weight.

[0033] 3) The image plane diameter of the system is Φ19.7mm, and the optical system target surface is large, which can be adapted to the current high-resolution detector with an array size of 1280×1024; the total length from the front surface of the first meniscus positive lens to the image plane is less than 70mm, which is short in total length and is conducive to lightweight structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the optical system light path diagram;

[0035] Figure 2is the transfer function diagram of the optical system at room temperature of 20℃;

[0036] Figure 3 This is the transfer function diagram of the optical system at a low temperature of -55℃;

[0037] Figure 4 The transfer function diagram of the optical system at a high temperature of +70°C;

[0038] Figure 5 Point diagram of the optical system at room temperature of 20°C;

[0039] Figure 6 Spot diagram of the optical system at low temperature of -55℃;

[0040] Figure 7 Spot diagram of the optical system at high temperature +70°C;

[0041] Among them, 1. first meniscus positive lens, 2. biconcave negative lens, 3. second meniscus positive lens, 4. meniscus negative lens, 5. image plane. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] In order to make the above features and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention. In the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "front", "back", "left", "right" and the like indicating directions or positional relationships, they are only used in conjunction with the appended drawings of this application. Figure 1 Accordingly, for the purpose of describing the present invention, the terms "first," "second," and "third" are used for descriptive purposes only, referring to the order in which lenses of that type appear, and are not to be construed as indicating or implying relative importance.

[0044] First of all, it should be noted that the direction close to the object space is the object side, and the direction close to the image space is the image side. From the object side to the image side, the two sides of the lens are the incident surface and the exit surface respectively.

[0045] like Figure 1As shown, the miniaturized, high-resolution, wide-temperature, athermal infrared optical system of the present invention comprises a first positive meniscus lens 1, a biconcave negative lens 2, a second positive meniscus lens 3, and a negative meniscus lens 4, coaxially arranged from the object side to the image side. Infrared radiation emitted by an external scene is converged by the first positive meniscus lens 1 and reaches the biconcave negative lens 2. It is then diverged by the biconcave negative lens 2 and reaches the second positive meniscus lens 3. It is then converged by the second positive meniscus lens 3 and reaches the negative meniscus lens 4. After being diverged by the negative meniscus lens 4, it forms an image on an image plane 5. The first positive meniscus lens 1, the second positive meniscus lens 3, and the negative meniscus lens 4 are all arranged to bend toward the image side.

[0046] In detail, the material used for the first meniscus positive lens 1 is single crystal germanium Ge, and the material used for the biconcave negative lens 2, the second meniscus positive lens 3, and the meniscus negative lens 4 is IRG206.

[0047] Let the focal length of the optical system be f, then the effective focal length of each lens included in the optical system of the present invention satisfies the following conditions:

[0048] The effective focal length f1 of the first meniscus positive lens 1 satisfies: 1.0≤f1 / f≤1.2;

[0049] The effective focal length f2 of the biconcave negative lens 2 satisfies: -0.7≤f2 / f≤-0.6;

[0050] The effective focal length f3 of the second meniscus positive lens 3 satisfies: 0.55≤f3 / f≤0.65;

[0051] The effective focal length f4 of the meniscus negative lens 4 satisfies: -2.9≤f4 / f≤-2.7.

[0052] Let the distance on the optical axis between the first meniscus positive lens 1 and the biconcave negative lens 2 be T12, the distance on the optical axis between the biconcave negative lens 2 and the second meniscus positive lens 3 be T23, and the thickness on the optical axis of the biconcave negative lens 2 be CT2, then T12, T23, and CT2 satisfy the following condition: 3.2≤(T12+T23) / CT2≤3.6.

[0053] Table 1 shows the technical indicators achieved by the present invention, among which F # (Optical system F number) is calculated as f / D, where D is the diameter of the entrance pupil.

[0054] Table 1 Technical indicators achieved by the present invention

[0055] parameter Technical indicators detector 1280×1024 uncooled infrared detector Pixel size 12μm Working band 8~12μm <![CDATA[F # (Optical System F Number)]]> 1.0 focal length 45mm Field of view 19.4°×15.5° Image diameter Φ19.7mm

[0056] Table 2 lists detailed data for an optical system embodiment according to the present invention, including the surface type, radius of curvature, thickness, and material of each lens. The units of the lens radius of curvature and thickness are both in mm. The radius of curvature of spherical and aspheric surfaces refers to the radius of curvature at the intersection of the lens surface and the optical axis. The "serial numbers" in Table 2 are counted along the direction of light propagation. For example, the light incident surface of the first meniscus positive lens 1 is numbered S1, the light exit surface is numbered S2, and the numbers for the other mirror surfaces are similar. The "radius" in Table 2 represents the radius of curvature of the surface. The positive or negative sign is determined by starting with the intersection of the surface with the principal optical axis and ending at the center of the surface. If the connecting line is in the same direction as the light propagation direction, the value is positive; otherwise, it is negative. If the surface is planar, the radius of curvature is infinite. The "thickness" in Table 2 gives the distance between two adjacent surfaces on the optical axis. The positive or negative sign is determined by starting with the vertex of the current surface and ending with the vertex of the next surface. If the direction of the line is the same as the direction of light propagation, it is positive; otherwise, it is negative. If the material between the two surfaces is infrared material, the thickness represents the lens thickness. If there is no material between the two surfaces, it represents the air space between the two lenses.

[0057] Table 2 Detailed data of the optical system of the present invention

[0058]

[0059] According to Table 2, the curved surfaces of the first meniscus positive lens 1, the biconcave lens 2, the second meniscus positive lens 3, and the meniscus negative lens 4 along the object-to-image direction are marked as S1, S2, S3, S4, S5, S6, S7, and S8, respectively. Among them, the curved surface S4 on the image-facing side of the biconcave negative lens 2 is an aspheric surface, and its surface equation is:

[0060]

[0061] Among them, z is the distance vector height from the aspheric surface vertex when the aspheric surface is at a height of r along the optical axis; c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface; r is the radial coordinate perpendicular to the optical axis; k is the quadratic curve constant; A is the fourth-order aspheric coefficient; B is the sixth-order aspheric coefficient; C is the eighth-order aspheric coefficient; D is the tenth-order aspheric coefficient.

[0062] Table 3 lists the aspheric coefficients of the curved surface S4 on the image side of the biconcave negative lens 2 in the present invention. It should be noted that the table uses scientific notation. For example, -2.598806e-006 represents -2.598806×10 -6 .

[0063] Table 3 Aspheric coefficients of the curved surface S4 on the image side of the biconcave negative lens 2

[0064] k A B C D 0 -2.598806e-006 -1.788164e-009 2.378721e-012 0

[0065] The curved surface S7 on the object-facing side of the meniscus negative lens 4 is an aspherical surface. A continuous relief structure is formed on the aspherical substrate by diamond turning to form a diffraction surface, which satisfies the equation:

[0066]

[0067] Wherein, z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, and C is the eighth-order aspheric coefficient; HOR is the diffraction order, C1, C2, and C3 are the diffraction surface coefficients, λ0 is the design center wavelength, n is the refractive index of the lens, and n0 is the refractive index of air.

[0068] Table 4 Diffraction aspheric coefficients of the curved surface S7 on the object side of the meniscus negative lens in the present invention.

[0069]

[0070] After optical design software simulation, such as Figure 2 、 Figure 3 、 Figure 4 As shown in the figure, when the uncooled detector with a pixel size of 12μm and a pixel number of 1280×1024 corresponds to a spatial frequency of 42lp / mm, the transfer functions at room temperature 20℃, low temperature -55℃ and high temperature 70℃ are all greater than 0.3. Figure 5 、 Figure 6 、 Figure 7 The point diagrams are respectively for the optical system at room temperature 20°C, low temperature -55°C and high temperature 70°C. It can be seen from the figures that the diffuse spot diameter of the system is smaller than the Airy disk diameter.

[0071] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Any equivalent changes or modifications made based on the essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A miniaturized, high-resolution, wide-temperature, athermal infrared optical system, characterized in that: The lens is composed of a first positive meniscus lens, a biconcave negative lens, a second positive meniscus lens, and a negative meniscus lens, which are coaxially arranged in sequence from the object side to the image side, wherein the first positive meniscus lens, the second positive meniscus lens, and the negative meniscus lens are all arranged to bend toward the image side; Let the focal length of the optical system be f, then the effective focal length of each lens included in the optical system of the present invention satisfies the following conditions: The effective focal length f1 of the first meniscus positive lens satisfies: 1.0≤f1 / f≤1.2; The effective focal length f2 of the biconcave negative lens satisfies: -0.7≤f2 / f≤-0.6; The effective focal length f3 of the second meniscus positive lens satisfies: 0.55≤f3 / f≤0.65; The effective focal length f4 of the meniscus negative lens satisfies: -2.9≤f4 / f≤-2.

7.

2. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The material used for the first meniscus positive lens is single crystal germanium; the materials used for the biconcave negative lens, the second meniscus positive lens and the meniscus negative lens are all chalcogenide glass IRG206.

3. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The distance on the optical axis between the first meniscus positive lens and the biconcave negative lens is T12, the distance on the optical axis between the biconcave negative lens and the second meniscus positive lens is T23, and the thickness of the biconcave negative lens on the optical axis is CT2. Then, T12, T23, and CT2 satisfy: 3.2≤(T12+T23) / CT2≤3.

6.

4. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The surface of the biconcave negative lens facing the image side is aspherical, and the surface of the biconcave negative lens facing the image side satisfies the surface equation: Wherein, z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient.

5. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 4, characterized in that: The aspheric coefficients of the surface of the biconcave negative lens facing the image side are: k=0, A=-2.598806e-006, B=-1.788164e-009, C=2.378721e-012, and D=0.

6. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The surface of the meniscus negative lens facing the object side adopts a diffractive aspheric surface, and the surface of the meniscus negative lens facing the object side satisfies the surface equation: Among them, z is the distance vector height from the aspheric surface vertex when the aspheric surface is at a height of r along the optical axis, c is the curvature, c = 1 / R, R represents the radius of curvature of the lens surface, r is the radial coordinate perpendicular to the optical axis, k is the quadratic curve constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, and C is the eighth-order aspheric coefficient; HOR is the diffraction order, C1, C2, and C3 are the diffraction surface coefficients, λ0 is the design center wavelength; n is the refractive index of the lens, and n0 is the refractive index of air.

7. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 6, characterized in that: The aspheric coefficients of the surface of the meniscus negative lens facing the object side are: k=0, A=-1.733180e-005, B=-3.923963e-008, C=4.173116e-011, HOR=1, C1=0.00016023, C2=-5.00616326e-007, C3=0.

8. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The technical parameters achieved by the optical system are: Working band: 8μm~12μm; F # : 1.0; Focal length: 45mm; Field of view: 19.4°×15.5°, image diameter: Φ19.7mm, operating temperature range: -55℃~+70℃; Among them, F # The calculation formula is f / D, where f is the focal length of the optical system and D is the diameter of the entrance pupil.

9. The miniaturized, high-resolution, wide-temperature, athermal infrared optical system according to claim 1, characterized in that: The detector adapted to the optical system is a 1280×1024 uncooled infrared detector with a pixel size of 12 μm.

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