A large aperture athermal infrared lens

Abstract

The application discloses a large-aperture athermal infrared lens, which comprises a first lens, a diaphragm, a second lens and a third lens arranged in sequence from an object side to an image side, wherein the first lens and the third lens are positive lenses, and the second lens is a negative 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 aspheric surfaces. The application adopts three lenses, and through reasonable focal power distribution, combination of aspheric 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 a 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 athermal infrared lens. BACKGROUND

[0002] With the development of science and technology, infrared imaging technology has been widely applied in the fields of national defense, industry, medical treatment and the like. Infrared detection has certain ability of penetrating smoke, fog, haze, snow and the like and ability of identifying camouflage, is not blinded by 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 the thermal expansion and contraction of the lens barrel material, so as to cause the change of the optical power of the optical system and the shift of the best image plane, and finally cause the image generated by the optical system to be blurred, the contrast to be reduced, and the imaging quality to be reduced, thereby affecting the imaging performance of the lens. Therefore, when the infrared optical system works in a wide temperature range, if the image plane does not shift, the athermal technology must be used to make the optical system have good imaging quality in a larger range.

[0003] In the prior art, the optical athermal technology mainly includes three kinds of mechanical-electrical active type, mechanical passive type and optical passive type. The former two types will cause the optical system to be complex, so as to increase the volume and weight of the system. In order to obtain a wider working temperature range, the optical passive type often has a large number of lenses in the system, a complex structure, or introduces a diffraction surface, so as to cause the transmittance of the optical system to be obviously reduced. As can be seen, the existing athermal technology has inconveniences. SUMMARY

[0004] In order to solve the above problems, the present application provides an athermal infrared lens, and the specific technical scheme is as follows. An athermal infrared lens includes a first lens, a diaphragm, a second lens and a third lens arranged in sequence from an object side to an image side, the first lens and the third lens are positive lenses, and the second lens is a negative 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; the expression of the first image side surface as a binary surface is,

[0005] M(B1ρ 2 +B2ρ 4 )

[0006] Wherein, M is diffraction order, the diffraction order is 1, B1, B2 are binary surface phase coefficients, for the first image side surface, B1=-14.082939, B2=4.0068351, the normalized radius ρ is 20.

[0007] Preferably, the aspheric surface of the second image side surface and the third image side surface satisfy the following formula,

[0008]

[0009] In the formula, Z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height r along the optical axis direction; 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 coefficients.

[0010] Preferably, the first lens and the third lens are both IRG206 materials, and the second lens is ZNSE material.

[0011] Preferably, the fitting curvature radius of the first object side surface S1 of the first lens is 96.31mm, the fitting curvature radius of the first image side surface S2 is 544.75mm, the fitting curvature radius of the second object side surface S3 of the second lens is 34.06mm, the fitting curvature radius of the second image side surface S4 is 17.15mm, the fitting curvature radius of the third object side surface S5 of the third lens is 26.63mm, and the fitting curvature radius of the third image side surface S6 of the third lens is 187.43mm. The center thickness of the first lens is 4.5mm, the center thickness of the second lens is 4.1mm, and the center thickness of the third lens is 7.1mm. The distance between the first lens and the diaphragm is 18.9mm, the distance between the diaphragm and the second lens is 5.74mm, and the distance between the second lens and the third lens is 5.17mm.

[0012] Preferably, the first image side surface is a binary surface, and the expression is,

[0013] M(B1ρ 2 +B2ρ 4 )

[0014] Wherein, M is diffraction order, the diffraction order is 1, B1, B2 are binary surface phase coefficients, for the first image side surface, B1=-14.082939, B2=4.0068351, the normalized radius ρ is 20.

[0015] Preferably, the working waveband of the lens is 8μm-12μm, the F number is 0.85, the horizontal field of view angle is 17.67°, and the vertical field of view angle is 14.18°.

[0016] The technical scheme of the present application has the following beneficial effects compared with the prior art:

[0017] The infrared athermalization lens provided by the application adopts three lenses, the number of lenses is less, and through reasonable refractive power distribution, combination of aspheric surface 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 response sensitivity, and the average MTF of the MTF in the full field of view at normal temperature is >0.30@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

[0018] 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.

[0019] Figure 1 The optical path diagram of the infrared athermalization lens in the specific embodiment of the application;

[0020] Figure 2 The MTF diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0021] Figure 3 The Spot diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0022] Figure 4 The MTF diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0023] Figure 5 The Spot diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0024] Figure 6 The MTF diagram of the athermalization infrared lens in a 60℃ working environment in the specific embodiment of the application;

[0025] Figure 7 The Spot diagram of the athermalization infrared lens in a 60℃ working environment in the specific embodiment of the application;

[0026] Figure 8 The distortion diagram of the athermalization infrared lens in the specific embodiment of the application.

[0027] Figure number: 1, first lens; 2, diaphragm; 3, second lens; 4, third lens; 5, silicon protective window; 6, detector image surface. DETAILED DESCRIPTION

[0028] 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 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.

[0029] 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 and the second lens 3 have negative focal power, and the third lens 4 has positive focal power.

[0030] 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 96.31 mm, the fitting curvature radius of a first image side S2 is 544.75 mm, the fitting curvature radius of a second object side S3 of the second lens 3 is 34.06 mm, the fitting curvature radius of a second image side S4 is 17.15 mm, the fitting curvature radius of a third object side S5 of the third lens 4 is 26.63 mm, and the fitting curvature radius of a third image side S6 of the third lens 4 is 187.43 mm. The central thickness of the first lens 1 is 4.5 mm, the central thickness of the second lens 3 is 4.1 mm, and the central thickness of the third lens 4 is 7.1 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 18.9 mm, the distance between the diaphragm 2 and the second lens 3 is 5.74 mm, and the distance between the second lens 3 and the third lens 4 is 5.17 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.

[0031] Table 1: Parameters of the first lens to the third lens

[0032]

[0033]

[0034] 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 both are aspherical surfaces, and satisfy the following formula,

[0035]

[0036] In the formula, Z is the distance from the vertex of the aspherical surface to the height r of the aspherical 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 aspherical surface coefficients, and the aspherical surface data of each lens is shown in Table 1.

[0037] The first image side surface S2 of the first lens 1 is a binary surface, and its expression is

[0038] M(B1ρ 2 +B2ρ 4 )

[0039] 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 =-14.082939 and B2 = 4.0068351, and the normalized radius p is 20.

[0040] 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 aspherical surface, and the binary surface.

[0041] Figure 2 、 Figure 4 、 Figure 6 The Spot diagrams of the athermal infrared lens in the working environments of 20℃, -40℃ and 60℃ are shown in FIGS. 5, 6 and 7 respectively. Figure 3 、 Figure 5 、 Figure 7 The MTF diagrams of the athermal infrared lens in the working environments of 20℃, -40℃ and 60℃ are shown in FIGS. 8, 9 and 10 respectively, the horizontal axis represents different spatial frequencies, and the vertical axis represents modulation. All the field of view 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. From 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 smaller 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. From Figure 8 It can be seen that the distortion of the infrared lens provided in the embodiment is less than 3%, so the distortion is very small.

[0042] From the above, it can be seen that the athermal infrared lens provided in the embodiment composed of the above lenses achieves the following optical indicators.

[0043] Working waveband: 8μm-12μm;

[0044] Focal length: f′=35mm;

[0045] Resolution: 640x512 17um;

[0046] F number: 0.85;

[0047] Horizontal field of view: 17.67°, vertical field of view: 14.18°;

[0048] The infrared athermalization lens provided by the embodiment adopts three lenses in total, the number of lenses is less, through reasonable refractive power distribution, in combination with the design of aspheric surface and binary surface, the infrared athermalization lens can be applied to a long-wave infrared band, has characteristics of large aperture, large target surface, high image quality, high reaction sensitivity and the like, and the average MTF of MTF in a full field of view at normal temperature is greater than 0.30@30lp / mm. The infrared lens provided by the embodiment has strong thermal stability, can meet the demand of a working temperature of-40℃ to 60℃, and is suitable for a target surface detector with 640x512 image elements and 17um image element size.

[0049] 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. A thermally ablated infrared lens, characterized in that, The infrared thermal aberration lens employs three lenses: a first lens, an aperture, a second lens, and a third lens, arranged sequentially from the object side to the image side. The first and third lenses are positive power lenses, and the second lens is a negative power lens. Along the optical axis from the object side to the image side, the two surfaces of the first lens are, in sequence, the first object-side surface and the first image-side surface; the two surfaces of the second lens are, in sequence, the second object-side surface and the second image-side surface; and the two surfaces of the third lens are, in sequence, the third object-side surface and the third image-side surface. The first image-side surface is a binary surface, while the second and third image-side surfaces are aspherical. The expression for the first image-side surface as a binary surface is: Where M is the diffraction order, the diffraction order is 1, B1 and B2 are the phase coefficients of the binary plane, for the first image side, B1 = -14.082939, B2 = 4.0068351, and the normalization radius ρ is 20. The fitted radius of curvature of the first object-side surface of the first lens is 96.31 mm, and the fitted radius of curvature of the first image-side surface is 544.75 mm. The fitted radius of curvature of the second object-side surface of the second lens is 34.06 mm, and the fitted radius of curvature of the second image-side surface is 17.15 mm. The fitted radius of curvature of the third object-side surface of the third lens is 26.63 mm, and the fitted radius of curvature of the third image-side surface of the third lens is 187.43 mm. The center thickness of the first lens is 4.5 mm, the center thickness of the second lens is 4.1 mm, and the center thickness of the third lens is 7.1 mm. The distance between the first lens and the aperture stop is 18.9 mm, the distance between the aperture stop and the second lens is 5.74 mm, and the distance between the second lens and the third lens is 5.17 mm.

2. The thermally ablated infrared lens according to claim 1, characterized in that, The aspherical surfaces of the second and third image sides both satisfy the following formula. In the formula, Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R, where R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; and A, B, C, D, and E are higher-order aspherical coefficients.

3. The thermally ablated infrared lens according to claim 1, characterized in that, Both the first lens and the third lens are made of IRG206 material, and the second lens is made of ZNSE material.

4. The thermally ablated infrared lens according to claim 1, characterized in that, The lens operates in the 8μm-12μm band, has an F-number of 0.85, a horizontal field of view of 17.67°, and a vertical field of view of 14.18°.

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