Long-wave infrared lens for high-definition components

Abstract

The invention discloses a long-wave infrared lens adapted to a high-definition component, comprising a lens group, a detector protection window and a detector arranged in sequence from the object side to the image side along the optical axis, the lens group comprising a first lens, an aperture stop, a focusing lens group and a second lens, the focusing lens group comprising at least one focusing lens, at least one surface of the first lens, the focusing lens and the second lens is a non-spherical surface, at least one surface is a spherical surface and at least one surface is a diffraction surface. A long-wave infrared lens adapted to a high-definition component according to an embodiment of the present invention can effectively correct aberrations and improve imaging quality.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging, and in particular to a long-wave infrared lens adapted to a high-definition component. Background Art

[0002] At present, the mainstream infrared detector array sizes are: 384×288, 640×512, 1024×768, etc. With the continuous advancement of infrared detection technology, the array size of the infrared detector focal plane continues to increase, while the pixel size is gradually reduced. However, most of the long-wave infrared lens optical systems on the market are designed for small array detectors, with a relatively small image height, and cannot be adapted to high-definition components with a relatively large detector array, such as infrared detectors with an array size of 1280×1024. The use of long-wave infrared lenses with small image heights with large array detectors will cause a waste of detector resources, and the output image will have dark corners and black edges.

[0003] In order to achieve excellent imaging quality, most infrared lenses currently use more spherical lenses to correct aberrations. Too many lenses will increase signal attenuation, and further increase the weight and cost of the lens. In addition, since the use environment of long-wave infrared lenses is mostly harsh, the temperature range is large, and the refractive index temperature coefficient of infrared lens materials is much larger than that of visible light materials, temperature changes will cause the best image plane to shift, resulting in image blur and thus reduced imaging quality.

[0004] Therefore, it is necessary to develop a long-wave infrared lens adapted to high-definition components based on the shortcomings of existing technologies, so that it can adapt to large-array infrared detectors while ensuring good imaging quality within a wide temperature range. Summary of the invention

[0005] The object of the present invention is to provide a long-wave infrared lens adapted to a high-definition component, which can effectively correct aberrations and improve imaging quality.

[0006] A long-wave infrared lens adapted for a high-definition component according to an embodiment of the present invention comprises a lens group, a detector protection window and a detector arranged in sequence along an optical axis from the object side to the image side, the lens group comprises a first lens, an aperture stop, a focusing lens group and a second lens, the focusing lens group comprises at least one focusing lens, at least one surface of the first lens, the focusing lens and the second lens is a non-spherical surface, at least one surface is a spherical surface and at least one surface is a diffraction surface.

[0007] According to some embodiments of the present invention, the first lens, the aperture stop, the focusing lens group and the second lens are arranged in sequence from the object side to the image side along the optical axis.

[0008] According to some embodiments of the present invention, at least one surface of the first lens and the at least one focusing lens is a spherical surface and at least one surface is an aspherical lens, and one surface of the second lens is a diffractive surface.

[0009] According to some embodiments of the present invention, the focusing lens group includes a first focusing lens and a second focusing lens which are sequentially arranged along the optical axis from the object side to the image side.

[0010] Optionally, the aperture stop is closely arranged on the surface of the first focusing lens facing the object.

[0011] Optionally, the surface of the first lens facing the object side is aspherical, the surface of the first lens facing the image side is spherical, the surface of the first focusing lens facing the object side is spherical, the surface of the first focusing lens facing the image side is aspherical, the surface of the second focusing lens facing the object side is spherical, the surface of the second focusing lens facing the image side is aspherical, the surface of the second lens facing the object side is spherical, and the surface of the second lens facing the image side is a diffraction surface.

[0012] Optionally, the diffraction surface of the second lens is a diffraction surface based on an even-order aspherical substrate.

[0013] According to some embodiments of the present invention, the focusing lens group is movable along the optical axis, and the optical axis movement amount ΔL1 of the focusing lens group satisfies: -8.5mm≤ΔL1≤0.9mm.

[0014] According to some embodiments of the present invention, the lens group is movable relative to the detector along the optical axis, and the movement amount ΔL2 of the lens group satisfies: -4.8mm≤ΔL2≤0.8mm.

[0015] According to some embodiments of the present invention, the number of pixels of the detector in the horizontal direction is greater than or equal to 1280, and the number of pixels in the vertical direction is greater than or equal to 1024; the pixel spacing a of the detector satisfies: 6μm≤a≤15μm.

[0016] Therefore, the high-definition component adapted according to the embodiment of the present invention can effectively correct aberrations and improve imaging quality through the mixed design of spherical, aspherical and diffractive surfaces of different lens surfaces, while effectively reducing the number of system lenses, reducing the volume of the system, and reducing the weight of the system; the reasonable design of the aspherical surface and the diffractive surface is conducive to the turning process of the diamond lathe, and the surface shape is high in precision, ensuring the imaging quality. In addition, the whole group focusing or the focusing lens group focusing method can be used to ensure that the imaging distance is from 0.2m to infinity. Clear imaging can be achieved, and the lens can be ensured to be clear in the temperature range of -40℃ to 60℃. The lens F number is equal to 1, the focal length is 30mm, and the image circle diameter is 25mm, which meets the market demand for long-wave infrared lenses that can adapt to 1280×1024 high-definition detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of a long-wave infrared lens adapted to a high-definition component according to an embodiment of the present invention;

[0018] Figure 2 The MTF curve of a long-wave infrared lens adapted to a high-definition component at 20° C. according to an embodiment of the present invention;

[0019] Figure 3 The MTF curve of the long-wave infrared lens adapted to the high-definition component at -40°C according to one embodiment of the present invention;

[0020] Figure 4 The MTF curve of a long-wave infrared lens adapted to a high-definition component at 60° C. according to an embodiment of the present invention.

[0021] Reference numerals:

[0022] 100: Long-wave infrared lens for high-definition components;

[0023] 10: Lens group;

[0024] 1: First lens;

[0025] 2: focusing lens group, 21: first focusing lens, 22: second focusing lens;

[0026] 3: Second lens;

[0027] 4: Aperture stop;

[0028] 20: detector protection window, 30: detector;

[0029] S1: the surface of the first lens facing the object side, S2: the surface of the first lens facing the image side, S3: the surface of the first focusing lens facing the object side, S4: the surface of the first focusing lens facing the image side, S5: the surface of the second focusing lens facing the object side, S6: the surface of the second focusing lens facing the image side, S7: the surface of the second lens facing the object side, S8: the surface of the second lens facing the image side. DETAILED DESCRIPTION

[0030] The long-wave infrared lens 100 adapted to high-definition components proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0031] The following describes a long-wave infrared lens 100 adapted for high-definition components according to an embodiment of the present invention with reference to the accompanying drawings.

[0032] like Figure 1 As shown, the long-wave infrared lens 100 adapted for high-definition components according to an embodiment of the present invention may include a lens group 10, a detector protection window 20, and a detector 30 arranged in sequence from the object side to the image side along the optical axis. It should be noted that the object side refers to the incident side of the light, and the image side refers to the emitting side. "Along the optical axis from the object side to the image side" means Figure 1 In the direction from front to back.

[0033] The lens group 10 includes a first lens 1, an aperture stop 4, a focusing lens group 2 and a second lens 3. The focusing lens group 2 includes at least one focusing lens, that is, the focusing lens group 2 may include one focusing lens or the focusing lens group 2 may include multiple focusing lenses. Figure 1 In the example shown, the focusing lens group 2 includes two focusing lenses, namely a first focusing lens 21 and a second focusing lens 22. The first focusing lens 21 and the second focusing lens 22 are arranged in sequence along the direction of the optical axis from the object side to the image side, that is, the first focusing lens 21 is arranged in front of the second focusing lens 22.

[0034] Optionally, the focusing lens group 2 may be disposed between the first lens 1 and the second lens 3. It is understandable that the focusing lens group 2 may not be disposed between the first lens 1 and the second lens 3. For example, the focusing lens group 2 may be disposed in front of the first lens 1 or behind the second lens 3. The number of focusing lenses of the focusing lens group 2 and the specific position of the focusing lens group 2 may be set according to actual needs. Figure 1 As shown, the first lens 1, the aperture stop 4, the focusing lens group 2 and the second lens 3 are arranged in sequence from the object side to the image side along the optical axis.

[0035] At least one surface of the first lens 1, the focusing lens and the second lens 3 is a diffraction surface, at least one surface is a spherical surface and at least one surface is a diffraction surface. Specifically, each lens has two opposite surfaces, namely a surface facing the object side and a surface facing the image side. The lens group 10 includes multiple lenses such as the first lens 1, the focusing lens and the second lens 3. Then the lens group 10 has multiple lens surfaces, including at least one aspherical surface, at least one spherical surface and at least one diffraction surface. The use of aspherical surfaces in an optical system can reduce the number of lenses in the system, effectively eliminate spherical aberration and coma, reduce light energy loss, and improve imaging quality; the diffraction surface is conducive to achromatization. A lens with a diffraction surface refers to a lens with a diffraction surface processed on the lens surface. The dispersion characteristics (material independence and negative value) of the diffraction optical element are very conducive to achromatization, and can form a refractive-diffractive hybrid optical system with good achromatic performance with the refractive element. At the same time, the diffraction optical element has a negative thermal difference characteristic, which is conducive to the thermal difference elimination of the optical system.

[0036] Therefore, according to the embodiment of the present invention, the long-wave infrared lens 100 adapted to the high-definition component can effectively correct aberrations and improve the imaging quality through the mixed design of spherical, aspherical and diffractive surface types of different lens surfaces, while effectively reducing the number of system lenses, reducing the volume of the system, and reducing the weight of the system; the reasonable design of the aspherical surface type and the diffractive surface is conducive to the turning process of the diamond lathe, and the surface type has high precision, which ensures the imaging quality. In addition, the whole group focusing or the focusing lens group 2 can be used to ensure that the imaging distance can be clearly imaged from 0.2m to infinity, and at the same time ensure that the lens can be clearly imaged within the temperature range of -40℃ to 60℃. The lens F number is equal to 1, the focal length is 30mm, and the image circle diameter is 25mm, which meets the market demand for a long-wave infrared lens 100 that can adapt to the 1280×1024 high-definition detector 30.

[0037] In some embodiments of the present invention, at least one surface of the first lens 1 and the at least one focusing lens is a spherical surface and at least one surface is an aspherical lens, and one surface of the second lens 3 is a diffraction surface. Specifically, at least one of the first lens 1 and the focusing lens is an aspherical lens and at least one is a spherical lens, so that the lens group 10 includes at least one spherical surface and at least one aspherical surface, or the two surfaces of at least one lens in the first lens 1 and the focusing lens are spherical and aspherical surfaces, respectively. Other lenses can be arranged as needed. For example, the two side surfaces of the first lens 1 can be spherical and aspherical surfaces, respectively, and the two side surfaces of the focusing lens can be spherical and aspherical surfaces, respectively.

[0038] In some specific examples of the present invention, the focusing lens group 2 includes a first focusing lens 21 and a second focusing lens 22 arranged in sequence from the object side to the image side along the optical axis. The aperture stop 4 is closely arranged on the surface of the first focusing lens 21 facing the object side. The surface S1 of the first lens 1 facing the object side is an aspherical surface, the surface S2 of the first lens facing the image side is a spherical surface, the surface S3 of the first focusing lens 21 facing the object side is a spherical surface, the surface S4 of the first focusing lens 21 facing the image side is an aspherical surface, the surface S5 of the second focusing lens 22 facing the object side is a spherical surface, the surface S6 of the second focusing lens 22 facing the image side is an aspherical surface, the surface S7 of the second lens 3 facing the object side is a spherical surface, and the surface S8 of the second lens 3 facing the image side is a diffraction surface. Further, the diffraction surface of the second lens 3 can be a diffraction surface based on an even-order aspherical substrate.

[0039] In a specific example of the present invention, the optical data of the lens of this embodiment is shown in Table 1 below. In Table 1, the surface serial number refers to the serial numbering of each surface from the object side of the first lens 1 to the image side of the detector protection window 20 along the optical axis from the object plane to the image plane. Table 1 also includes: the surface shape of each surface, the radius of curvature R of each surface, the thickness of each lens or the interval d between two adjacent lenses, and the material of each lens, wherein S9 and S10 are two surfaces of the detector protection window 20 respectively, S9 is the surface of the detector protection window 20 facing the object side, and S10 is the surface of the detector protection window 20 facing the image side. Surfaces S9 and S10 can both be planes, so their radius of curvature is infinite (infinity), and surface serial number S11 is the imaging surface (optical light converges on this surface through the front optical system), that is, the surface of the detector 30.

[0040] Table 1

[0041]

[0042] In some embodiments of the present invention, the focusing lens group 2 is movable along the optical axis direction, that is, the focusing lens group 2 is movable along the optical axis direction. Figure 1 The front-to-back direction shown is movable to achieve a close-range focusing function and compensate for image plane defocus caused by temperature changes, wherein the optical axis movement ΔL1 of the focusing lens group 2 satisfies: -8.5mm≤ΔL1≤0.9mm, and the negative sign indicates that the movement direction is opposite to the light propagation direction. Specifically, the maximum movement of the focusing lens group 2 in the forward direction can be 8.5mm, and the maximum movement of the focusing lens group 2 in the backward direction can be 0.9mm.

[0043] In some embodiments of the present invention, the lens group 10 is movable relative to the detector 30 along the optical axis, that is, the first lens 1, the aperture stop 4, the focusing lens group 2 and the second lens 3 are movable as a whole along the optical axis. In this way, the distance between the entire lens and the detector 30 can be adjusted by the whole group focusing method to achieve close-range focusing and compensate for the image plane defocus caused by temperature changes, wherein the movement amount ΔL2 of the lens group 10 satisfies: -4.8mm≤ΔL2≤0.8mm. The negative sign indicates that the movement direction is opposite to the light propagation direction. Specifically, the maximum movement amount of the lens group 10 in the forward movement direction can be 4.8mm, and the maximum movement amount of the lens group 10 in the backward movement direction can be 0.8mm. Therefore, by adopting the whole group focusing or focusing by the focusing lens group, it is possible to achieve clear imaging from 0.2m to infinity at an imaging distance, and at the same time ensure that the lens can achieve clear imaging within the temperature range of -40℃ to 60℃. The lens has an F number of 1, a focal length of 30mm, and an image circle diameter of 25mm, meeting the market demand for a long-wave infrared lens that can be adapted to 1280×1024 high-definition detectors.

[0044] In the embodiment of the present invention, the surface S1 of the first lens 1 facing the object side, the surface S4 of the first focusing lens 22 facing the image side, and the surface S6 of the second focusing lens 22 facing the image side can all adopt an even-order aspherical surface type, the surface S8 of the second lens 3 facing the image side is a diffraction surface, and the other surfaces can all adopt a spherical surface type, wherein the expression of the even-order aspherical surface type is as follows:

[0045]

[0046] In the above expressions, Z is the distance vector height from the fixed focus of the aspheric surface when the aspheric surface is at a height of R along the optical axis, C0=1 / R, R is the radius of curvature of each aspheric surface, K is the cone coefficient, Y is the distance from the point on the aspheric surface to the optical axis, A, B, C, D... are the coefficients of the higher-order terms, specifically, A, B, C, D... are the coefficients of the second-order term, the fourth-order term, the sixth-order term, the eighth-order term... respectively.

[0047] The surface parameters of each aspheric surface in this embodiment are listed in the following Table 2. Table 2 shows the even-order aspheric coefficients of surfaces S1, S4, S6, and S8, wherein other order coefficients are not used, for example, the second-order coefficients and the eighth-order coefficients are not used, that is, A and D are both zero:

[0048] Table 2

[0049] Surface serial number Cone coefficient The fourth-order coefficient Sixth-order coefficient S1 0 -4.49e-07 -2.14e-09 S4 0 1.87e-07 -9.77e-10 S6 0 -5.05e-06 1.30e-08 S8 0 9.41e-06 -1.70e-08

[0050] In this embodiment, the rear surface S8 of the second lens 3 is a diffractive surface based on an even-order aspheric substrate, and its aspheric surface parameters are listed in Table 2. The diffractive surface parameters of the rear surface of the second lens 3 in this embodiment are listed in Table 3.

[0051] Table 3

[0052]

[0053] The number of pixels of the detector 30 in the horizontal direction is greater than or equal to 1280, and the number of pixels in the vertical direction is greater than or equal to 1024; the pixel spacing a of the detector 30 satisfies: 6μm≤a≤15μm.

[0054] According to the embodiment of the present invention, the long-wave infrared lens 100 adapted to the high-definition component is as follows: Figure 2-Figure 4 The figure shows the MTF (Modulation Transfer Function) curves of the long-wave infrared lens 100 adapted to the high-definition component at three different temperatures of -40°C, 20°C, and 60°C. Each curve in the curve refers to the MTF curve of different fields of view (differentiated by image height, such as the central field of view is 0mm, and there are 2mm, 4mm, 8.6mm, 10.1mm and the edge field of view is 12.33mm, etc.). Each field of view has two directions, the meridian and the sagittal. Figure 2-Figure 4 The solid lines in the figure are the test results of the meridian direction of different viewing fields, and the dotted lines are the test results of the sagittal direction of different viewing fields. Figure 2-Figure 4 The modulation transfer function curve of the optical system shown is close to the diffraction limit of the optical system, and the overall curve is relatively gentle and does not change much, indicating that the imaging quality is good. It can be seen from the above curve graph that the long-wave infrared lens 100 adapted to the high-definition component according to the embodiment of the present invention has good imaging quality at -40°C-60°C, that is, the long-wave infrared lens 100 adapted to the high-definition component according to the embodiment of the present invention can work under the ambient temperature conditions of -40°C-60°C. The performance indicators that can be achieved by the long-wave infrared lens 100 adapted to the high-definition component according to one embodiment of the present invention are as follows: focal length: 30mm; relative aperture: 1.0; working wavelength: 8μm~12μm; field of view range: 18.4°(H)×14.7°(V); image circle diameter: 25mm; adapted detector 30 specifications: 1280×1024,15μm; working temperature range: -40°C~60°C; closest imaging distance: 0.2m.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A long-wave infrared lens adapted for high-definition components, characterized in that: It comprises a lens group, a detector protection window and a detector which are sequentially arranged along the optical axis from the object side to the image side, the lens group comprises a first lens, an aperture stop, a focusing lens group and a second lens, the focusing lens group comprises a first focusing lens and a second focusing lens which are sequentially arranged along the optical axis from the object side to the image side, the surface of the first lens facing the object side is an even-order aspheric surface, the surface of the first lens facing the image side is a spherical surface, the surface of the first focusing lens facing the object side is a spherical surface, the surface of the first focusing lens facing the image side is an even-order aspheric surface, the surface of the second focusing lens facing the object side is a spherical surface, the surface of the second focusing lens facing the image side is an even-order aspheric surface, the surface of the second lens facing the object side is a spherical surface, and the surface of the second lens facing the image side is a diffraction surface; The lens group as a whole can move relative to the detector along the optical axis, and the movement amount ΔL2 of the lens group satisfies: -4.8mm≤ΔL2≤0.8mm, where the negative sign indicates that the movement direction is opposite to the light propagation direction; The number of pixels in the horizontal direction of the detector is greater than or equal to 1280, and the number of pixels in the vertical direction is greater than or equal to 1024; The first lens is a negative power lens, the first focusing lens is a positive power lens, the second focusing lens is a positive power lens, and the second lens is a positive power lens.

2. The long-wave infrared lens adapted for high-definition components according to claim 1, characterized in that: The first lens, the aperture stop, the focusing lens group and the second lens are arranged in sequence from the object side to the image side along the optical axis.

3. The long-wave infrared lens adapted for high-definition components according to claim 1, characterized in that: The aperture stop is closely arranged on the surface of the first focusing lens facing the object.

4. The long-wave infrared lens adapted for high-definition components according to claim 1, characterized in that: The diffractive surface of the second lens is a diffractive surface based on an even-order aspherical substrate.

5. The long-wave infrared lens adapted for high-definition components according to claim 1, characterized in that: The focusing lens group is movable along the optical axis, and the optical axis movement amount ΔL1 of the focusing lens group satisfies: -8.5mm≤ΔL1≤0.9mm.

6. The long-wave infrared lens adapted for high-definition components according to claim 1, characterized in that: The detector pixel spacing a satisfies: 6 μm≤a≤15 μm.

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