A large aperture athermal infrared lens

Abstract

The application discloses a large-aperture athermal infrared lens, which comprises a first lens, a second lens and a third lens arranged in sequence from an object side to an image side, wherein the first lens is a positive lens, the second lens is a negative lens, and the third lens is a positive lens; the image side of the first lens is a binary surface, and the image sides of the second lens and the third lens are aspherical surfaces. The application adopts three lenses, and through reasonable focal power distribution, combination of aspherical surfaces and binary surface design, the application can be applied to a long-wave infrared waveband, has the characteristics of large aperture, large target surface and high imaging sensitivity, and has strong thermal stability, can meet the requirement of working temperature of-40 DEG C to 60 DEG C, and is suitable for a detector with 640*512 image elements and 17 mu m image element size.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of infrared optical technology, and particularly relates to a large-aperture athermal infrared lens. BACKGROUND

[0002] With the development of science and technology, the infrared imaging technology has been widely applied in the fields of national defense, industry, medical treatment and the like. The infrared detection has the ability of penetrating smoke, fog, haze, snow and the like and identifying camouflage, is not blinded by the strong light and flash interference in the battlefield, can realize long-distance and all-weather observation, and is particularly suitable for target detection under night and poor weather conditions. However, in the application of infrared imaging, the temperature of the external environment will affect the refractive index of the lens material, and will also cause thermal expansion and cold contraction of the lens barrel material, so as to cause the change of optical power and the shift of the best image plane, the image is blurred, the contrast is reduced, the optical imaging quality is reduced, and finally the imaging performance of the lens is affected. Therefore, when the infrared optical system works in a wide temperature range, it is required that the image plane does not shift, and the athermal technology must be used to make the optical system have good imaging quality in a larger range.

[0003] The optical athermal technology mainly includes: mechanical and electrical active type, mechanical passive type and optical passive type. The first two ways will complicate the system, increase the volume and weight. In order to obtain a wider working temperature range, the optical passive type often has a large number of lenses, a complex structure, or introduces a diffraction surface, which will cause the transmittance of the optical system to decrease obviously. As can be seen, the existing athermal technology has some inconveniences. SUMMARY

[0004] In order to solve the problems in the prior art, the present application provides an athermal infrared lens, and the specific technical scheme is as follows.

[0005] An athermal infrared lens comprises a first lens, a diaphragm, a second lens and a third lens arranged in sequence from the object side to the image side, the first lens is a positive power lens, the second lens is a negative power lens, and the third lens is a positive power lens; along the optical axis from the object side to the image side, the two surfaces of the first lens are a first object side surface and a first image side surface in sequence, the two surfaces of the second lens are a second object side surface and a second image side surface in sequence, and the two surfaces of the third lens are a third object side surface and a third image side surface in sequence, wherein the first image side surface is a binary surface, and the second image side surface and the third image side surface are aspherical surfaces.

[0006] The aspherical surfaces of the second image side surface and the third image side surface both satisfy the following formula,

[0007]

[0008] In the formula, Z is the distance from the vertex of the aspheric surface to the height r of the aspheric surface along the optical axis direction; c=1 / R, R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, E are high-order aspheric surface coefficients.

[0009] Preferably, the first lens and the third lens are both IRG206 materials, and the second lens is ZNSE material.

[0010] Preferably, the fitting curvature radius of the first object side S1 of the first lens is 59.75 mm, the fitting curvature radius of the first image side S2 is 154 mm, the fitting curvature radius of the second object side S3 of the second lens is 37.83 mm, the fitting curvature radius of the second image side S4 is 18.91 mm, the fitting curvature radius of the third object side S5 of the third lens is 41.99 mm, and the fitting curvature radius of the third image side S6 of the third lens is 319.32 mm. The center thickness of the first lens is 7.5 mm, the center thickness of the second lens is 5.2 mm, and the center thickness of the third lens is 6.5 mm. The distance between the first lens and the diaphragm is 4.92 mm, the distance between the diaphragm and the second lens is 14.92 mm, and the distance between the second lens and the third lens is 12.11 mm.

[0011] Preferably, the first image side is a binary surface, and the expression thereof is,

[0012] M(B1ρ 2 +B2ρ 4 )

[0013] Wherein, M is the diffraction order, the diffraction order is 1, B1 and B2 are binary surface phase coefficients, for the first image side, B1=-14.023712, B2=1.4035372, and the normalized radius ρ is 20.

[0014] The working waveband of the lens is 8-12 μm, the F number is 0.85, the horizontal field of view angle is 12.4°, and the vertical field of view angle is 10°.

[0015] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0016] The infrared athermalization lens provided by the application adopts three lenses in total, the number of lenses is less, and through reasonable refractive power distribution, combination of aspheric surfaces and binary surface design, the infrared athermalization lens can be applied to a long-wave infrared band, has the characteristics of large aperture, large target surface, high image quality and high reaction sensitivity. The average MTF of the MTF in the full field of view at normal temperature is >0.40@30lp / mm. The infrared athermalization lens provided by the application has strong thermal stability and can meet the demand of working temperature of-40℃ to 60℃, and is suitable for a target surface detector with 640*512 image elements and an image element size of 17μm. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 The optical path diagram of the infrared athermalization lens in the specific embodiment of the application;

[0019] Figure 2 The MTF diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0020] Figure 3 The Spot diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0021] Figure 4 The MTF diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0022] Figure 5 The Spot diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0023] Figure 6 The MTF diagram of the athermalization infrared lens in a 60℃ working environment in the specific embodiment of the application;

[0024] Figure 7 The Spot diagram of the athermalization infrared lens in a 60℃ working environment in the specific embodiment of the application;

[0025] Figure 8 The distortion diagram of the athermalization infrared lens in the specific embodiment of the application.

[0026] Fig. number: 1, first lens; 2, diaphragm; 3, second lens; 4, third lens; 5, germanium protective window; 6, detector image surface. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0028] As shown in the accompanying drawings of the embodiments of the present application, Figure 1 The present embodiment provides an athermal infrared lens, which includes three lenses, and sequentially includes a first lens 1, a diaphragm 2, a second lens 3 and a third lens 4 along an optical axis from an object side to an image side. The first lens 1 has a positive focal power, the second lens 3 has a negative focal power, and the third lens 4 has a positive focal power.

[0029] The parameters of the athermal infrared lens provided by the present embodiment are shown in Table 1. The fitting curvature radius of a first object side S1 of the first lens 1 is 59.75 mm, the fitting curvature radius of a first image side S2 is 154 mm, the fitting curvature radius of a second object side S3 of the second lens 3 is 37.83 mm, the fitting curvature radius of a second image side S4 is 18.91 mm, the fitting curvature radius of a third object side S5 of the third lens 4 is 41.99 mm, and the fitting curvature radius of a third image side S6 of the third lens 4 is 319.32 mm. The center thickness of the first lens 1 is 7.5 mm, the center thickness of the second lens 3 is 5.2 mm, and the center thickness of the third lens 4 is 6.5 mm. The diaphragm 2 is arranged between the first lens 1 and the second lens 3, the distance between the first lens 1 and the diaphragm 2 is 4.92 mm, the distance between the diaphragm 2 and the second lens 3 is 14.92 mm, and the distance between the second lens 3 and the third lens 4 is 12.11 mm. The first lens 1 and the third lens 4 are both made of IRG206 material, and the second lens 3 is made of ZNSE.

[0030] Table 1: Parameters of the first lens to the third lens

[0031]

[0032]

[0033] As a preferred embodiment of the present application, the second image side S4 of the second lens 3 and the third image side S6 of the third lens 4 are both aspherical surfaces, and satisfy the following formula,

[0034]

[0035] In the formula, Z is the distance from the vertex of the aspheric surface to the height r of the aspheric surface along the optical axis; c = 1 / R, R is the paraxial curvature fitting radius of the mirror surface; k is the conic coefficient; A, B, C, D, E are high-order aspheric surface coefficients, and the aspheric surface data of each lens is shown in Table 1.

[0036] The first image side surface S2 of the first lens 1 is a binary surface, and its expression is

[0037] M(B1ρ 2 +B2ρ 4 )

[0038] In the formula, M is the diffraction order, the diffraction order is 1, B1 and B2 are binary surface phase coefficients, for the first image side surface, B1 =-14.023712, B2 = 1.4035372, and the normalized radius p is 20.

[0039] In the embodiment, the lens has good imaging quality and strong thermal stability in the temperature range of-40℃ to 60℃ through the reasonable design of the material of the two lenses as chalcogenide glass, the material of the other lens as ZNSE, the optical power of the three lenses, the aspheric surface, and the binary surface.

[0040] Figure 2 , Figure 4 , Figure 6 respectively are the Spot diagrams of the athermal infrared lens in the working environments of 20℃, -40℃, and 60℃. Figure 3 , Figure 5 , Figure 7 respectively are the MTF diagrams of the athermal infrared lens in the working environments of 20℃, -40℃, and 60℃, the horizontal axis represents different spatial frequencies, and the vertical axis represents modulation. All the field represents the MTF curve of the meridional plane, which is the curve marked as T in the figure, and the MTF curve of the sagittal plane is the curve marked as S in the figure, and DIFF.LIMIT in the figure represents the diffraction limit. Figures 2 to 7 It can be seen that the MTF is close to the diffraction limit, the root mean square diameter of the diffraction spot is less than the diameter of the Airy disk, and the image quality is very good. Therefore, the lens of the embodiment has good resolution level in the working environments of 20℃, -40℃, and 60℃, the comprehensive imaging quality of the lens is good, and the thermal stability is strong. Figure 8 It can be seen that the distortion of the infrared lens provided in the embodiment is less than 2%, so the distortion is very small.

[0041] As can be seen from the above, the athermal infrared lens provided in the embodiment composed of the above lenses achieves the following optical indicators.

[0042] Working waveband: 8μm-12μm;

[0043] Focal length: f′=50mm;

[0044] Resolution: 640x512 17μm;

[0045] F number: 1.2;

[0046] The horizontal field of view is 12.4°, and the vertical field of view is 10°.

[0047] The infrared athermalization lens provided in the embodiment has three lenses in total, and the number of lenses is small. Through reasonable power distribution, in combination with the design of aspheric surface and binary surface, the infrared athermalization lens can be applied to the long-wave infrared band, has the characteristics of large aperture, large target surface, high image quality and high response sensitivity. The average MTF of the MTF in the full field of view at normal temperature is >0.40@30lp / mm. The infrared athermalization lens provided in the embodiment has strong thermal stability, and can meet the demand of working temperature of-40℃ to 60℃. The infrared athermalization lens is suitable for a target surface detector with 640x512 pixels and a pixel size of 17μm.

[0048] Obviously, the above embodiments are only examples for clearly illustrating the technical solutions of the present application, and are not intended to limit the implementation manners of the present application. Any modification, equivalent replacement and improvement made on the basis of the above description for those skilled in the art should be included in the protection scope of the claims of the present application.

Claims

1. An athermal infrared lens characterized by, The infrared achromatic lens comprises three lenses, The lens comprises, from the object side to the image side, a first lens, a diaphragm, a second lens and a third lens, the first lens is a positive lens, the second lens is a negative lens, and the third lens is a positive lens; from the object side to the image side along the optical axis, the two surfaces of the first lens are a first object side surface and a first image side surface in sequence, the two surfaces of the second lens are a second object side surface and a second image side surface in sequence, and the two surfaces of the third lens are a third object side surface and a third image side surface in sequence, wherein the first image side surface is a binary surface, and the second image side surface and the third image side surface are aspherical surfaces. The fitting curvature radius of the first object side surface S1 of the first lens is 59.75 mm, the fitting curvature radius of the first image side surface S2 is 154 mm, the fitting curvature radius of the second object side surface S3 of the second lens is 37.83 mm, the fitting curvature radius of the second image side surface S4 is 18.91 mm, the fitting curvature radius of the third object side surface S5 of the third lens is 41.99 mm, and the fitting curvature radius of the third image side surface S6 of the third lens is 319.32 mm; the center thickness of the first lens is 7.5 mm, the center thickness of the second lens is 5.2 mm, and the center thickness of the third lens is 6.5 mm; the distance between the first lens and the diaphragm is 4.92 mm, the distance between the diaphragm and the second lens is 14.92 mm, and the distance between the second lens and the third lens is 12.11 mm.

2. An athermal infrared lens according to claim 1, characterized in that, The aspherical surfaces of the second image side surface and the third image side surface satisfy the following formula, In the formula, Z is the distance from the vertex of the aspherical surface to the height r along the optical axis direction; c=1 / R, R is the fitting radius of the aspherical surface; k is the conic coefficient; A, B, C, D and E are high-order aspherical coefficients.

3. An athermal infrared lens according to claim 1, wherein, The first lens and the third lens are made of IRG206 material, and the second lens is made of ZNSE material.

4. An athermal infrared lens according to claim 1, wherein, The first image side surface is a binary surface, and its expression is as follows, In the formula, M is the diffraction order, the diffraction order is 1, B1 and B2 are binary phase coefficients, for the first image side surface, B1=-14.023712 and B2=1.4035372, and the normalized radius p is 20.

5. An athermal infrared lens according to claim 1, wherein The working waveband of the lens is 8-12 μm, the F number is 0.85, the horizontal field of view is 12.4°, and the vertical field of view is 10°.

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