Mid-wave infrared spectral imaging lens

Abstract

The present invention relates to the field of optical lenses, and provides a mid-wave infrared spectral imaging lens. From the object surface to the image surface, it sequentially includes a first lens, a second lens, a third lens, a Dewar window, and a filter, which are arranged coaxially; the first lens, the second lens, and the third lens are all aspherical lenses; the first lens has a positive optical power, and the focal length of the first lens satisfies 245 mm ≤ f1 ≤ 250 mm; the second lens has a negative optical power, and the focal length of the second lens satisfies -30 mm ≤ f2 ≤ -25 mm; the third lens has a positive optical power, and the focal length of the third lens satisfies 20 mm ≤ f3 ≤ 25 mm. The solution of this application reduces the number of lenses by introducing aspherical lenses, and solves the defect that the existing mid-wave infrared spectral imaging lens is difficult to simultaneously meet the requirements of large field of view, high energy utilization rate, and high-resolution spectral imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and in particular to a mid-wave infrared spectral imaging lens. Background Art

[0002] 3.0μm - 5.0μm is the atmospheric window of mid-wave infrared. The mid-wave infrared radiation of natural scenes includes its own thermal radiation and sunlight reflection. The thermal radiation of high-temperature objects is mainly concentrated in short-wave and mid-wave infrared. In industry, mid-wave infrared can be used for thermal imaging detection and can be applied to reconnaissance, guided weapons, night vision equipment, etc.

[0003] When the field of view angle of a mid-wave infrared lens is larger, more targets can be observed and the field of view is wider. However, as the field of view angle of the lens increases, the image quality of the edge field of view will deteriorate. At the same time, in order to obtain the spectral characteristics of the target at night, high energy utilization rate and high resolution need to be satisfied. It is difficult for the existing mid-wave infrared lenses in the prior art to meet the requirements of high energy utilization rate and high resolution while increasing the lens field of view. Summary of the Invention

[0004] The present invention provides a mid-wave infrared spectral imaging lens to solve the deficiency that the existing spectral imaging technology is difficult to simultaneously meet the requirements of large field of view, high energy utilization rate and high resolution. The solution of the present application can increase the lens field of view while meeting the requirements of high resolution and high energy utilization rate by reducing the number of lenses, and keep the image quality at a relatively high level.

[0005] The present invention provides a mid-wave infrared spectral imaging lens for mid-wave infrared spectral imaging, which sequentially includes a first lens, a second lens, a third lens, a Dewar window and a filter arranged coaxially from the object plane to the image plane;

[0006] The first lens, the second lens and the third lens are all aspherical lenses;

[0007] The first lens has a positive optical power, and the focal length of the first lens satisfies 245 mm ≤ f1 ≤ 250 mm; the second lens has a negative optical power, and the focal length of the second lens satisfies -30 mm ≤ f2 ≤ -25 mm; the third lens has a positive optical power, and the focal length of the third lens satisfies 20 mm ≤ f3 ≤ 25 mm.

[0008] According to the mid-wave infrared spectral imaging lens provided by the present invention, the central thickness of the first lens satisfies 2 mm ≤ t1 ≤ 4 mm; the central thickness of the second lens satisfies 4 mm ≤ t2 ≤ 6 mm; the central thickness of the third lens satisfies 11 mm ≤ t3 ≤ 13 mm.

[0009] According to the mid-wave infrared spectral imaging lens provided by the present invention, the side of the first lens close to the object plane is an even aspherical surface, and the side close to the image plane is a second-order aspherical surface;

[0010] The side of the second lens close to the object surface is an even aspheric surface, and the side close to the image surface is an even aspheric surface;

[0011] The side of the third lens close to the object surface is an even aspheric surface, and the side close to the image surface is an even aspheric surface.

[0012] For the mid-wave infrared spectral imaging lens provided by the present invention, the aspheric surface profiles of the first lens, the second lens, and the third lens conform to the following formula:

[0013]

[0014] Where Z is the sag height, c is the curvature, r is the radial distance from a certain point on the lens to the optical axis, k is the conic coefficient, and a2, a3, and a4 are all aspheric coefficients.

[0015] For the mid-wave infrared spectral imaging lens provided by the present invention, the side of the first lens close to the object surface satisfies:

[0016] a2 = -2.41E -6 , a3 = 1.40E -9 , a4 = -7.55E -13 , k = -1.91.

[0017] The side of the first lens close to the image surface satisfies:

[0018] a2 = a3 = a4 = 0, k = -10.

[0019] For the infrared lens provided by the present invention, the side of the second lens close to the object surface satisfies:

[0020] a2 = -2.94E -6 , a3 = -3.87E -8 , a4 = -4.31E -11 , k = -1.89.

[0021] The side of the second lens close to the image surface satisfies:

[0022] a2 = 3.04E -6 , a3 = -1.05E -8 , a4 = 3.84E -11 , k = 0.67.

[0023] For the infrared lens provided by the present invention, the side of the third lens close to the object surface satisfies:

[0024] a2 = -1.04E -5 , a3 = 1.40E -8 , a4 = -1.27E-11 , k = 4.08.

[0025] On the side of the third lens close to the image plane, the following conditions are satisfied:

[0026] a2 = a3 = a4 = 0, k = 1.16.

[0027] For the mid-wave infrared spectral imaging lens provided by the present invention, the material of the first lens is germanium, the material of the second lens is germanium, the material of the third lens is silicon, the material of the Dewar window includes any one of silicon and germanium, and the material of the filter is germanium.

[0028] For the mid-wave infrared spectral imaging lens provided by the present invention, the aperture stop is arranged at the Dewar window.

[0029] In the mid-wave infrared spectral imaging lens provided by the solution of the present application, the second lens and the third lens are arranged to converge the light beam, achieving the effect of improving the field of view and expanding the vision. At the same time, a first lens is arranged in front of the second lens and the third lens. The first lens can diverge the input light beam to avoid excessive convergence of the light beam by the second lens and the third lens in the subsequent process. It can be seen that only three lenses are arranged in the solution of the present application, and the focal length adjustment and material selection of the three lenses meet the actual requirements. The fewer the number of lenses, the less energy loss generated when the light beam passes through the lenses, enabling more energy of the light beam to be used for imaging, thereby improving the imaging quality. At the same time, the first lens, the second lens, and the third lens are all aspherical lenses, which have a better converging or diverging effect on the light beam, can better improve the optical performance of the infrared lens, effectively reduce the aberration of the image, and further improve the imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 is a schematic optical path diagram of the mid-wave infrared spectral imaging lens provided by an embodiment of the present invention;

[0032] Figure 2 is one of the performance schematic diagrams of the mid-wave infrared spectral imaging lens provided by an embodiment of the present invention;

[0033] Figure 3 is the second performance schematic diagram of the infrared lens provided by an embodiment of the present invention;

[0034] Figure 4It is the third performance schematic diagram of the infrared lens provided by the embodiment of the present invention;

[0035] Figure 5 It is the fourth performance schematic diagram of the infrared lens provided by the embodiment of the present invention.

[0036] Wherein:

[0037] 1 - First lens; 2 - Second lens; 3 - Third lens; 4 - Dewar window; 5 - Filter. Specific embodiments

[0038] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0039] Figure 1 It is the optical path schematic diagram of the mid-wave infrared spectral imaging lens provided by the embodiment of the present invention.

[0040] As Figure 1 shown, this embodiment provides a mid-wave infrared spectral imaging lens for mid-wave infrared spectral imaging, which sequentially includes a first lens 1, a second lens 2, a third lens 3, a Dewar window 4, and a filter 5 arranged coaxially from the object plane to the image plane;

[0041] The first lens, the second lens, and the third lens are all aspherical lenses;

[0042] The first lens has a positive optical power, and the focal length f1 of the first lens satisfies 245 mm ≤ f1 ≤ 250 mm;

[0043] The second lens has a negative optical power, and the focal length f2 of the second lens satisfies -30 mm ≤ f2 ≤ -25 mm;

[0044] The third lens has a positive optical power, and the focal length f3 of the third lens satisfies 20 mm ≤ f3 ≤ 25 mm.

[0045] In practice, the mid-wave infrared spectral imaging lens in this embodiment may include an object plane and an image plane. During use, the imaging light beam can enter from the object plane of the infrared lens and form an image on the image plane. That is, the user can observe the object to be observed on the image plane of the infrared lens.

[0046] In practical applications, the Dewar window is equivalent to a cold stop during use, which can limit the light beam, control the entry of light, and control the imaging range.

[0047] A filter is an optical element used to select light in a specific wavelength band. It can selectively transmit or reflect light of a specific wavelength through its optical properties. When light passes through the filter, due to the different refractive indices or propagation speeds of light with different wavelengths in the material, they will be separated into different spectral components, thereby achieving precise control and processing of light for spectral imaging.

[0048] In implementation, the first lens, the second lens, and the third lens in this embodiment are all aspherical lenses. Compared with the spherical lenses in the related art, aspherical lenses have a better converging or diverging effect on light. Therefore, a better imaging effect can be achieved with a smaller number of lenses.

[0049] The total length of the infrared lens provided in this embodiment can be 98.15 millimeters (mm), and the image field can be designed to be 15.36×15.36 millimeters. It can be adapted to a mid-wave detector with 1024×1024 pixels and a pixel size of 15 micrometers. When used in combination, the filter of the infrared lens can be attached to the surface of the detector for spectral imaging.

[0050] In this embodiment, the optical power and focal length of the three lenses are also limited. The first lens has a positive optical power, that is, the first lens is a positive lens, or in other words, the first lens is a convex lens, which can converge the incident light.

[0051] The second lens has a negative optical power, that is, the first lens is a negative lens, or in other words, the second lens is a concave lens, which can diverge the incident light.

[0052] The third lens has a positive optical power, that is, the third lens is a positive lens, or in other words, the third lens is a convex lens, which can converge the incident light.

[0053] In practical applications, the focal length of the first lens can be between 245 millimeters and 250 millimeters, preferably 248 millimeters.

[0054] The focal length of the second lens can be between -30 millimeters and -25 millimeters, preferably -28 millimeters.

[0055] The focal length of the third lens can be between 20 millimeters and 25 millimeters, preferably 21.4 millimeters.

[0056] In the infrared lens provided by the solution of this embodiment, the first lens and the third lens are provided to converge the light beam, achieving the effect of increasing the field of view. At the same time, a second lens is provided in front of the first lens and the third lens. The second lens can diverge the input light beam to avoid excessive convergence of the light beam by the first lens and the third lens. It can be seen that only three lenses are provided in the solution of this application, and the three lenses cooperate with each other through focal length adjustment. The small number of lenses can reduce the energy loss generated when the light beam passes through the lenses, enabling more energy of the light beam to be used for imaging, thereby improving the imaging quality. At the same time, the first lens, the second lens, and the third lens are all aspherical lenses, which have a better converging or diverging effect on the light beam, can better improve the optical performance of the infrared lens, effectively reduce the aberration of imaging, and further improve the imaging quality.

[0057] In an exemplary embodiment, the central thickness t1 of the first lens satisfies 2 mm ≤ t1 ≤ 4 mm;

[0058] The central thickness t2 of the second lens satisfies 4 mm ≤ t2 ≤ 6 mm;

[0059] The central thickness t3 of the third lens satisfies 11 mm ≤ t3 ≤ 13 mm.

[0060] The central thickness of the lens refers to the central thickness of the material in the central part of the lens, and measures the central thickness at the highest or lowest point of the two surfaces of the lens. In practical applications, by controlling the central thickness of the three lenses, the optical path length of the light passing through the lens can be accurately controlled. The optical path length here can affect the converging or diverging effect of the lens on the light on the one hand, and also affect the energy loss of the light when propagating in the lens on the other hand. Therefore, in this embodiment, by controlling the central thickness of the three lenses within a certain range, the relationship between the control effect of the lens on the light and the energy loss of the light can be balanced, so as to achieve the highest control effect on the premise of minimizing energy loss.

[0061] On the other hand, in this embodiment, the radius of curvature of each surface of the three lenses can also be limited. The radius of curvature is a quantity describing the degree of curve bending change at a certain point on the curve. In this embodiment, while controlling the central thickness of the lens, the radius of curvature of the lens can be limited to control the edge central thickness of the lens. On the one hand, the relationship between the control effect of the lens on the light passing through the edge and the energy loss of the light can be balanced. On the other hand, the radius of curvature can also control the aberration of the lens. The obtained infrared lens can have a large image field with low distortion. In addition, the spherical aberration and the diffraction spot can be less than 1 pixel, and the diffraction function is close to the diffraction limit. The modulation transfer function (MTF) of the infrared lens is better than 0.55@33 lp / mm.

[0062] In an exemplary embodiment, the side of the first lens close to the object surface is an even aspheric surface, and the side close to the image surface is a second-order aspheric surface;

[0063] The side of the second lens close to the object surface is an even aspheric surface, and the side close to the image surface is an even aspheric surface;

[0064] The side of the third lens close to the object surface is an even aspheric surface, and the side close to the image surface is a second-order aspheric surface.

[0065] An even aspheric surface is an aspheric surface with an even-power series polynomial as an additional polynomial. Its expression usually includes a reference quadric surface and an additional polynomial, which is used to characterize the deviation between the aspheric surface and its reference quadric surface.

[0066] The second-order aspheric surface is a subclass of the aspheric surface. It is the most widely used in optical systems and has a special position. The second-order aspheric surface can be further divided into an aspheric surface with a pair of anastigmatic points and an aspheric surface without anastigmatic points.

[0067] In this embodiment, the precise control of the incident mid-wave infrared spectrum is achieved through the cooperation of the even aspheric surface and the second-order aspheric surface.

[0068] Specifically, in this embodiment, the side of the first lens close to the object surface is an even aspheric surface, and the side close to the image surface is a second-order aspheric surface.

[0069] The side of the second lens close to the object surface is an even aspheric surface, and the side close to the image surface is an even aspheric surface.

[0070] The side of the third lens close to the object surface is an even aspheric surface, and the side close to the image surface is a second-order aspheric surface.

[0071] The following Table 1 exemplifies the various parameter indicators of the three lenses in the solution of this embodiment.

[0072] Table 1

[0073] Surface Surface profile Radius of curvature (mm) Central thickness 1 Even aspheric surface 67.11 2.69 2 Second-order aspheric surface 71.46 23.93 3 Even aspheric surface -27.29 4.65 4 Even aspheric surface -47.24 0.5 5 Even aspheric surface -228.47 12.98 6 Second-order aspheric surface -44.21 13.53 7 Plane Infinity 2 8 Plane Infinity 14.03 9 Plane Infinity 0.5

[0074] Among them, surface 1 in Table 1 refers to the side of the first lens close to the object surface, surface 2 refers to the side of the first lens close to the image surface; surface 3 refers to the side of the second lens close to the object surface, surface 4 refers to the side of the second lens close to the image surface; surface 5 refers to the side of the third lens close to the object surface, surface 6 refers to the side of the third lens close to the image surface, surface 7 refers to the side of the Dewar window close to the object surface, surface 8 refers to the side of the Dewar window close to the image surface, and surface 9 refers to the filter.

[0075] In addition, the central thickness of surface 1 in Table 1 above refers to the central thickness of the first lens, the central thickness of surface 2 refers to the vertical distance from the center on the image side of the first lens to the center on the object side of the second lens, the central thickness of surface 3 refers to the central thickness of the second lens, the central thickness of surface 4 refers to the vertical distance from the center on the image side of the second lens to the center on the object side of the third lens, the central thickness of surface 5 refers to the central thickness of the third lens, the central thickness of surface 6 refers to the vertical distance from the center on the image side of the third lens to the object side of the Dewar window, the central thickness of surface 7 refers to the central thickness of the Dewar window, the central thickness of surface 8 refers to the vertical distance from the Dewar window to the filter, and the central thickness of surface 9 refers to the central thickness of the filter.

[0076] In an exemplary embodiment, the aspherical surface profiles of the first lens, the second lens, and the third lens conform to the following formula:

[0077]

[0078] where Z is the sagittal height, c is the curvature, r is the radial distance from a point on the lens to the optical axis, k is the conic constant, and a2, a3, and a4 are all aspherical coefficients.

[0079] In practical applications, the sagittal height of a lens usually refers to the vertical distance from the intersection point of a light ray and the principal optical axis of the lens to the lens. By precisely calculating and controlling the sagittal height, optical properties such as the focusing ability and imaging quality of the lens can be optimized.

[0080] The curvature of a lens is an important parameter describing the degree of curvature of the lens surface. In implementation, by precisely controlling the curvature of the lens, performance indicators such as imaging quality, resolution, and contrast can be optimized.

[0081] The conic constant of a lens determines the shape of the lens surface. The larger the absolute value of the conic constant, the greater the deviation of the lens surface from a spherical surface. Therefore, by adjusting the conic constant, optical properties of the lens such as reducing aberration and improving imaging quality can be optimized.

[0082] In an exemplary embodiment, the following is satisfied on the object side of the first lens close to the object surface:

[0083] a2 = -2.41E -6 a3 = 1.40E -9 a4 = -7.55E -13 k = -1.91.

[0084] The following is satisfied on the image side of the first lens close to the image surface:

[0085] a2 = a3 = a4 = 0, k = -10.

[0086] In an exemplary embodiment, the side of the second lens close to the object plane satisfies:

[0087] a2 = -2.94E -6 , a3 = -3.87E -8 , a4 = -4.31E -11 , k = -1.89.

[0088] The side of the second lens close to the image plane satisfies:

[0089] a2 = 3.04E -6 , a3 = -1.05E -8 , a4 = 3.84E -11 , k = 0.67.

[0090] In an exemplary embodiment, the side of the third lens close to the object plane satisfies:

[0091] a2 = -1.04E -5 , a3 = 1.40E -8 , a4 = -1.27E -11 , k = 4.08.

[0092] The side of the third lens close to the image plane satisfies:

[0093] a2 = a3 = a4 = 0, k = 1.16.

[0094] In an exemplary embodiment, the material of the first lens includes germanium, the material of the second lens includes germanium, the material of the third lens includes silicon, the material of the Dewar window includes any one of silicon and germanium, and the material of the filter includes germanium.

[0095] In practice, germanium material and silicon material have good light conduction performance. Using them as the main materials of the infrared lens can reduce the energy loss during the transmission of the light beam in the infrared lens and improve the imaging quality.

[0096] Figure 2 is one of the performance diagrams of the infrared lens provided by the embodiment of the present invention.

[0097] Figure 3 is the second performance diagram of the infrared lens provided by the embodiment of the present invention.

[0098] Figure 4 is the third performance diagram of the infrared lens provided by the embodiment of the present invention.

[0099] Figure 5 is the fourth performance diagram of the infrared lens provided by the embodiment of the present invention.

[0100] Among them, as Figure 2and Figure 3 As shown, when the infrared lens is used in conjunction with a 1024×1024 detector, the pixel center pitch is 15 microns. It can be seen that at a Nyquist frequency of 33 lp / mm, the MTF of the full field of view is greater than 0.55, and the optical transfer function is close to the diffraction limit.

[0101] As Figure 4 and Figure 5 shown, the field curvature of the infrared lens is less than 0.1 mm, the imaging distortion is less than 2%, and the imaging quality is good.

[0102] In practical applications, the telescope in this embodiment is in the mid-wave infrared spectrum band of 3.7 microns to 4.8 microns. The maximum field of view angle of the telescope can reach 40 degrees, the F number is 2, the focal length of the telescope is 45 mm, and the imaging distortion of the telescope is less than 2%.

[0103] In an exemplary embodiment, the aperture of the telescope is disposed on the image plane side of the Dewar window, so that it can be ensured that all light rays can pass through the aperture, and unnecessary stray light can be avoided from entering the system, and thus 100% matching of the aperture can be achieved.

[0104] The specific implementation method of the telescope provided in this embodiment can be implemented with reference to the above embodiments, and will not be elaborated here.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Mid-wave infrared spectral imaging lens, characterized in that, For mid-wave infrared spectral imaging, it successively includes a first lens, a second lens, a third lens, a Dewar window, and a filter arranged coaxially from the object plane to the image plane; The first lens, the second lens, and the third lens are all aspherical lenses; The first lens has a positive optical power, and the focal length f1 of the first lens satisfies 245 mm ≤ f1 ≤ 250 mm; The second lens has a negative optical power, and the focal length f2 of the second lens satisfies -30 mm ≤ f2 ≤ -25 mm; The third lens has a positive optical power, and the focal length f3 of the third lens satisfies 20 mm ≤ f3 ≤ 25 mm; The aspherical surface profiles of the first lens, the second lens, and the third lens conform to the following formula: Where Z is the sag height, c is the curvature, r is the radial distance from a certain point on the lens to the optical axis, k is the conic coefficient, and a2, a3, and a4 are all aspherical coefficients; The side of the first lens close to the object plane satisfies: a2 = -2.41E -6 , a3 = 1.40E -9 , a4 = -7.55E -13 , k = -1.91; The side of the first lens close to the image plane satisfies: a2 = a3 = a4 = 0, k = -10; The side of the second lens close to the object plane satisfies: a2 = -2.94E -6 , a3 = -3.87E -8 , a4 = -4.31E -11 , k = -1.89; The side of the second lens close to the image plane satisfies: a2 = 3.04E -6 , a3 = -1.05E -8 , a4 = 3.84E -11 , k = 0.67; The side of the third lens close to the object plane satisfies: a2 = -1.04E -5 , a3 = 1.40E -8 , a4 = -1.27E -11 , k = 4.08; The side of the third lens close to the image plane satisfies: a2 = a3 = a4 = 0, k = 1.

16.

2. The mid-wave infrared spectral imaging lens according to claim 1, wherein The central thickness t1 of the first lens satisfies 2 mm ≤ t1 ≤ 4 mm; The central thickness t2 of the second lens satisfies 4 mm ≤ t2 ≤ 6 mm; The central thickness t3 of the third lens satisfies 11 mm ≤ t3 ≤ 13 mm.

3. The mid-wave infrared spectral imaging lens according to claim 1, wherein The side of the first lens close to the object plane is an even aspherical surface, and the side close to the image plane is a second-order aspherical surface; The side of the second lens close to the object plane is an even aspherical surface, and the side close to the image plane is an even aspherical surface; The side of the third lens close to the object plane is an even aspherical surface, and the side close to the image plane is an even aspherical surface.

4. The mid-wave infrared spectral imaging lens according to claim 1, wherein The material of the first lens is germanium, the material of the second lens is germanium, the material of the third lens is silicon, the material of the Dewar window is germanium, and the material of the filter is germanium.

5. The mid-wave infrared spectral imaging lens according to any one of claims 1-4, characterized in that, The aperture stop of the lens is arranged at the Dewar window.

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