An ultra-short focal length athermal infrared lens

Abstract

The application belongs to the field of infrared optical technology and discloses an ultrashort-focus athermal infrared lens, which comprises a first lens and a second lens arranged in sequence from an object side to an image side, the first lens is a negative-power lens, and the second lens is a positive-power lens; along an optical axis from the object side to the image side, two surfaces of the first lens are a first object side surface and a first image side surface in sequence, two surfaces of the second lens are a second object side surface and a second image side surface in sequence, the first object side surface and the second image side surface are aspheric surfaces, and the first image side surface and the second object side surface are binary surfaces. The application adopts two lenses in total, and through reasonable power distribution, combination of aspheric surfaces and design of binary surfaces, the application can be applied to a long-wave infrared band, has the characteristics of a wide field of view, a short focal length and wide coverage of a field of view, has strong thermal stability, can meet the demand of a working temperature of-40 DEG C to 80 DEG C, and is suitable for a detector with 256*192 image elements and 12 mu m image element size.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of infrared optical technology, and particularly relates to an ultra-short-focus athermal infrared lens. BACKGROUND

[0002] Wide-angle infrared lenses have the characteristics of short focal length and wide field coverage, and are applied more and more widely. The edge resolution of the image surface is not high, and the aberration is difficult to correct. The shorter the focal length is, the more difficult the design is to control the imaging quality.

[0003] In addition, the ambient temperature will affect the refractive index of the lens material, causing the change of optical power and the shift of the best image surface, image blurring, contrast reduction, and optical imaging quality reduction, ultimately affecting the imaging performance of the lens. In order to realize the image surface shift of the infrared optical system when working in a wide temperature range, the athermal technology must be used to make the optical system have good imaging quality in a larger range. In the passive athermal technology of optics, in order to obtain a wider working temperature range, the number of lenses is often large, resulting in large volume, complex structure and high cost.

[0004] Therefore, while ensuring athermalization, how to realize short focal length and ensure good resolution is a difficult problem to be solved in this field at present. SUMMARY

[0005] In order to solve the above problems, the application provides an ultra-short-focus athermal infrared lens, and the specific technical scheme is as follows.

[0006] An ultra-short-focus athermal infrared lens comprises a first lens and a second lens arranged in sequence from an object side to an image side, the first lens is a negative power lens, and the second lens is a positive power 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, and the two surfaces of the second lens are a second object side surface and a second image side surface in sequence, the first image side surface and the second object side surface are both binary surfaces, and the first object side surface and the second image side surface are both aspheric surfaces.

[0007] Preferably, the aspheric surfaces of the first object side surface and the second image side surface both satisfy the following formula,

[0008]

[0009] In the formula, Z is the distance sag of the aspheric surface from the vertex of the aspheric surface when the height r is at a position 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 and E are high-order aspheric coefficients.

[0010] Preferably, the first lens and the second lens are both IRG206 materials.

[0011] Preferably, the fitting curvature radius of the first object side S1 of the first lens is -31.637mm, the fitting curvature radius of the first image side S2 is 7.638mm, the fitting curvature radius of the second object side S3 of the second lens is 7.736mm, and the fitting curvature radius of the second image side S4 is -10.031mm.

[0012] Preferably, the central thickness of the first lens is 2mm, and the central thickness of the second lens is 4.184mm.

[0013] Preferably, an aperture stop is arranged between the first lens and the second lens, the distance between the first lens and the aperture stop is 3.116mm, and the distance between the aperture stop and the second lens is 0.498mm.

[0014] Preferably, the first image side is a binary surface, and the expression thereof is

[0015]

[0016] wherein M is a diffraction order, the diffraction order is 1, B1, B2, B3 are binary surface phase coefficients, and for the first image side, B1=5.62, B2=4.04, and B3=1.14, and the normalized radius ρ is 1.8.

[0017] For the first image side, B1=5.62, B2=4.04, and B3=1.14, and the normalized radius ρ is 1.8.

[0018] Preferably, the second object side is a binary surface, and the expression thereof is

[0019]

[0020] wherein M is a diffraction order, the diffraction order is 1, B1, B2, B3 are binary surface phase coefficients, and for the second object side, B1=-22.625, B2=8.921, and B3=-2.174, and the normalized radius ρ is 3.3.

[0021] Preferably, the working waveband of the lens is 8μm-12μm, the F number is 1.0, the horizontal field of view is 90°, and the vertical field of view is 60°.

[0022] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0023] The infrared athermalization lens provided by the application adopts two lenses, the number of lenses is less, through reasonable refractive power distribution, combining aspheric surface and binary surface design, the infrared athermalization lens can be applied to a long-wave infrared band, has a large field of view, short focal length, wide coverage of the field of view, and the focal length can be as short as 1.9 mm, and the average MTF of the MTF in the full field of view is greater than 0.30@42lp / mm at normal temperature. The infrared athermalization lens provided by the application has strong thermal stability, can meet the demand of a working temperature of-40℃ to 80℃, and is suitable for a target surface detector with 256*192 pixels and a pixel size of 12μm. BRIEF DESCRIPTION OF DRAWINGS

[0024] 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.

[0025] Figure 1 The optical path diagram of the infrared athermalization lens in the specific embodiment of the application;

[0026] Figure 2 The MTF diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0027] Figure 3 The Spot diagram of the athermalization infrared lens in a 20℃ working environment in the specific embodiment of the application;

[0028] Figure 4 The MTF diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0029] Figure 5 The Spot diagram of the athermalization infrared lens in a-40℃ working environment in the specific embodiment of the application;

[0030] Figure 6 The MTF diagram of the athermalization infrared lens in an 80℃ working environment in the specific embodiment of the application;

[0031] Figure 7 The Spot diagram of the athermalization infrared lens in an 80℃ working environment in the specific embodiment of the application.

[0032] Fig. number: 1, first lens; 2, diaphragm; 3, second lens; 4, silicon protective window; 5, detector image surface. DETAILED DESCRIPTION

[0033] Clearly, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0034] As shown in the accompanying drawings of the embodiments of the present application, the present embodiments provide an ultra-short focal length athermal infrared lens, which comprises two lenses, sequentially comprising a first lens 1 and a second lens 3 along the optical axis from the object side to the image side. The first lens 1 has a negative focal power, and the second lens 3 has a positive focal power. Figure 1

[0035] The parameters of the two lenses are shown in Table 1.

[0036] The fitting curvature radius of the first object side S1 of the first lens is -31.637 mm, the fitting curvature radius of the first image side S2 is 7.638 mm, the fitting curvature radius of the second object side S3 of the second lens is 7.736 mm, and the fitting curvature radius of the second image side S4 is -10.031 mm. The central thickness of the first lens 1 is 2 mm, and the central thickness of the second lens 3 is 4.184 mm. An aperture 2 is arranged between the first lens 1 and the second lens 3, the distance between the first lens 1 and the aperture 2 is 3.116 mm, and the distance between the aperture 2 and the second lens 3 is 0.498 mm. The first lens 1 and the second lens 3 are both IRG206 materials.

[0037] Table 1: Parameters of the first lens and the second lens

[0038]

[0039] As a preferred embodiment of the present application, the first object side S1 and the second image side S4 are both aspheric surfaces, and satisfy the following formula,

[0040]

[0041] In the formula, Z is the distance from the vertex of the aspheric surface when the aspheric surface is at a height r along the optical axis, h is the height, c=1 / R, R is the fitting radius of the near-axis curvature of the mirror surface, k is the conic coefficient, A, B, C, D, and E are high-order aspheric coefficients, and the aspheric surface data of each lens is shown in Table 2.

[0042] Table 2: Aspheric surface coefficient data of each lens

[0043]

[0044] In the formula, Z is the distance from the vertex of the aspheric surface when the aspheric surface is at a height r along the optical axis, h is the height, c=1 / R, R is the fitting radius of the near-axis curvature of the mirror surface, k is the conic coefficient, A, B, C, D, and E are high-order aspheric coefficients, and the aspheric surface data of each lens is shown in Table 2. ​

[0045]

[0046] M is a diffraction order, the diffraction order is 1, B1, B2, B3 are binary surface phase coefficients, for the first image side

[0047] the surface, B1=5.62, B2=4.04, B3=1.14, and the normalized radius p is 1.8.

[0048] The second object side surface S3 is a binary surface, and its expression is

[0049]

[0050] wherein M is a diffraction order, the diffraction order is 1, B1, B2, B3 are binary surface phase coefficients, for the second object side surface, B1=-22.625, B2=8.921, B3=-2.174, and the normalized radius p is 3.3.

[0051] In the embodiment, the lens has good imaging quality and strong thermal stability in the temperature range of-40℃ to 80℃ through the reasonable design of the material of the two lenses as chalcogenide glass, the optical power of the two lenses, aspheric surface and binary surface.

[0052] Figure 2 、 Figure 4 、 Figure 6 respectively, are the MTF diagrams of the athermal infrared lens in the working environments of 20℃, -40℃ and 80℃. 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. Figure 3 、 Figure 5 、 Figure 7 respectively, are the Spot diagrams of the athermal infrared lens in the working environments of 20℃, -40℃ and 80℃. 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 80℃, has good comprehensive imaging quality, and has strong thermal stability.

[0053] From the above, the athermal infrared lens composed of the above lenses provided in the embodiment achieves the following optical indexes.

[0054] Working waveband: 8μm-12μm;

[0055] Focal length: f'=1.9mm;

[0056] Resolution: 256x192 12pm;

[0057] F number: 1.0;

[0058] Horizontal field of view: 90°, vertical field of view: 60°;

[0059] The infrared athermalization lens provided by the embodiment adopts two lenses in total, the infrared athermalization lens adopts two lenses in total, the number of lenses is small, through reasonable power distribution, combined with the design of aspheric surface and binary surface, it can be applied to the long-wave infrared band, has a large field of view, a short focal length, a wide coverage rate of the field of view, and the focal length can be as short as 1.9 mm, and the average MTF of the MTF in the full field of view at normal temperature is greater than 0.30@42lp / mm. The infrared lens provided by the present application has strong thermal stability and can meet the demand of the working temperature of-40℃ to 80℃, and is suitable for a target surface detector with 256x192 pixels and a pixel size of 12pm.

[0060] 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 ultra-compact athermal infrared lens characterized in that, The lens comprises a first lens and a second lens arranged in sequence from an object side to an image side, the first lens is a negative lens, and the second lens is a positive lens; along an optical axis from the object side to the image side, two surfaces of the first lens are a first object side surface and a first image side surface in sequence, and two surfaces of the second lens are a second object side surface and a second image side surface in sequence, the first object side surface and the second image side surface are aspheric surfaces, and the first image side surface and the second object side surface are binary surfaces; A fitting curvature radius of the first object side surface S1 of the first lens is -31.637 mm, a fitting curvature radius of the first image side surface S2 is 7.638 mm, a fitting curvature radius of the second object side surface S3 of the second lens is 7.736 mm, and a fitting curvature radius of the second image side surface S4 is -10.031 mm; a center thickness of the first lens is 2 mm, and a center thickness of the second lens is 4.184 mm; an aperture stop is arranged between the first lens and the second lens, a distance between the first lens and the aperture stop is 3.116 mm, and a distance between the aperture stop and the second lens is 0.498 mm; and an effective focal length of the lens is 1.9 mm.

2. The ultra- short throw athermal infrared lens of claim 1, wherein, The aspheric surfaces of the first object side surface and the second image side surface satisfy the following formula, In the formula, Z is a distance vector height of an aspheric surface at a position of a height r along an optical axis direction from a vertex of the aspheric surface; c=1 / R, R is a paraxial curvature fitting radius of a mirror surface; k is a conic coefficient; A, B, C, D and E are high-order aspheric coefficients.

3. The ultra- short throw athermal infrared lens of claim 1, wherein, The first lens and the second lens are both IRG206 materials.

4. The ultra- short throw athermal infrared lens of claim 1, wherein, The first image side surface is a binary surface, and an expression of the first image side surface is In the formula, M is a diffraction order, the diffraction order is 1, B1, B2 and B3 are binary phase coefficients, for the first image side surface, B1=5.62, B2=4.04 and B3=1.14, and a normalized radius p is 1.

8.

5. The ultra- short throw athermal infrared lens of claim 1, wherein, The second object side surface is a binary surface, and an expression of the second object side surface is In the formula, M is a diffraction order, the diffraction order is 1, B1, B2 and B3 are binary phase coefficients, for the second object side surface, B1=-22.625, B2=8.921 and B3=-2.174, and a normalized radius p is 3.

3.

6. The ultra- short throw athermal infrared lens of claim 1, wherein, The working waveband of the lens is 8 μm-12 μm, an F number is 1.0, a horizontal field of view angle is 90°, and a vertical field of view angle is 60°.

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