Long-wave infrared lens

Abstract

The application discloses a long-wave infrared lens, comprising a first lens, a second lens and a third lens arranged in sequence along an optical axis from an object plane to an image plane, wherein the first lens is a meniscus lens with negative optical power, and the object side surface of the first lens is a convex surface; the object side surface and the image side surface of the first lens are aspherical surfaces; the long-wave infrared lens satisfies -0.7 <= (Yd-FOVd*f) / (FOVd*f) <= -0.3. The long-wave infrared lens provided by the application only uses three lenses, has a simple structure, is small in size, saves cost, and improves transmittance. The long-wave infrared lens disclosed by the application satisfies that the focal length and the overall field of view are relatively large, so that long-distance and large-field imaging are simultaneously realized, and an additional infrared camera is not needed to obtain information for software algorithm fusion, so that the problems of picture overlap or loss in the prior art are solved.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of infrared imaging technology, and in particular to a long-wave infrared lens. BACKGROUND

[0002] With the rapid development of infrared technology, infrared cameras can achieve good imaging effect at night and in harsh environments, so the market demand for them is increasing, and infrared optical lenses are an important component among them.

[0003] In order to identify objects at a long distance, a conventional infrared lens is designed with a large focal length, but such a setting will result in a smaller field of view angle of the lens and the inability to observe target objects in a larger field of view angle range around the lens. In order to identify objects at a long distance and also observe objects in a larger field of view angle around the lens, the prior art adds a wide-angle lens to the original lens with a large focal length, and then uses software to algorithmically fuse the images collected by the two lenses to obtain a large-range, long-distance picture. However, this requires two infrared cameras, which increases the cost of the lens and the core, and also increases the volume and weight occupied. In addition, due to the different field of view angles of the lenses, the image fusion using software algorithm will have picture overlap or missing phenomenon, which will also affect the response rate of the imaging system. SUMMARY

[0004] The present application provides a long-wave infrared lens that reduces the volume and cost of the lens while ensuring a large focal length and field of view angle.

[0005] In a first aspect, embodiments of the present application provide a long-wave infrared lens, comprising:

[0006] a first lens, a second lens and a third lens arranged in order along an optical axis from an object plane to an image plane;

[0007] the first lens is a meniscus lens with negative optical power, and the object side of the first lens is a convex surface;

[0008] the object side and the image side of the first lens are aspherical surfaces;

[0009] the long-wave infrared lens satisfies:

[0010] -0.7≤(Yd-FOVd*f) / (FOVd*f)≤-0.3;

[0011] wherein f is the focal length of the long-wave infrared lens, Yd is the maximum image height, and FOVd is the field of view angle corresponding to the maximum image height.

[0012] Optionally, the second lens has positive optical power, and the object side and / or the image side of the second lens is a convex surface.

[0013] Optionally, the third lens has positive refractive power, and the object side surface and / or the image side surface is convex.

[0014] Optionally, the distance from the optical axis center of the object side surface of the first lens to the image surface is TTL, and 3.1≤TTL / f≤6.2.

[0015] Optionally, the focal length of the first lens is f1, the focal length of the second lens is f2, and the focal length of the third lens is f3, and -2.3

[0016] Optionally, at least one of the object side surface and the image side surface of the first lens, the object side surface and the image side surface of the second lens, and the object side surface and the image side surface of the third lens is a binary surface.

[0017] Optionally, the object side surface or the image side surface of the third lens is a binary surface.

[0018] Optionally, the material of the first lens is germanium glass, and the materials of the second lens and the third lens are chalcogenide glass.

[0019] Optionally, the long-wave infrared lens further comprises a diaphragm.

[0020] The diaphragm is located in the optical path between the first lens and the second lens.

[0021] Alternatively, the diaphragm is located in the optical path between the second lens and the third lens.

[0022] Optionally, the focal length f of the long-wave infrared lens satisfies f≥6mm.

[0023] The field of view FOV of the long-wave infrared lens satisfies FOV≥150°.

[0024] The long-wave infrared lens provided by the embodiment of the present application only uses three lenses, has a simple structure, small volume, saves cost, and improves the transmittance. Moreover, the first lens is set as a meniscus lens with negative refractive power, the object side surface of the first lens is convex, the object side surface and the image side surface of the first lens are both aspherical surfaces, the long-wave infrared lens satisfies -0.7≤(Yd-FOVd*f) / (FOVd*f)≤-0.3, the focal length of the long-wave infrared lens in the central region is large (the focal length can be more than 6mm), the long-wave infrared lens can identify a long-distance object, the overall field of view of the long-wave infrared lens is also large (the field of view can be more than 150°), the surrounding situation can be observed, and thus an additional infrared camera does not need to be set to obtain information for software algorithm fusion, the problems of picture overlap or loss in the prior art are solved, and the response rate of the imaging system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A structure schematic diagram of a long-wave infrared lens provided by an embodiment of the present application under normal temperature state is shown in FIG. 1.

[0026] Figure 2 An MTF schematic diagram of the long-wave infrared lens provided by the embodiment of the present application under normal temperature (20℃) state is shown in FIG. 2.

[0027] Figure 3 An MTF schematic diagram of the long-wave infrared lens provided by the embodiment of the present application under low temperature (-40℃) state is shown in FIG. 3.

[0028] Figure 4 An MTF schematic diagram of the long-wave infrared lens provided by the embodiment of the present application under high temperature (80℃) state is shown in FIG. 4.

[0029] Figure 5 A spot diagram schematic diagram of the long-wave infrared lens provided by the embodiment of the present application under normal temperature (20℃) state is shown in FIG. 5.

[0030] Figure 6 A relative luminance schematic diagram of the long-wave infrared lens provided by the embodiment of the present application under normal temperature (20℃) state is shown in FIG. 6. DETAILED DESCRIPTION

[0031] The present application will be further described below in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0032] Figure 1 A structure schematic diagram of a long-wave infrared lens provided by an embodiment of the present application under normal temperature state is shown in FIG. 1. Figure 1 As shown in FIG. 1, the long-wave infrared lens provided by the embodiment of the present application comprises a first lens 110, a second lens 120 and a third lens 130 arranged in sequence along the optical axis from the object plane to the image plane, the first lens 110 is a meniscus lens with negative focal power, the object side of the first lens 110 is a convex surface, and the object side and the image side of the first lens 110 are both aspheric surfaces. The long-wave infrared lens satisfies: -0.7≤(Yd-FOVd*f) / (FOVd*f)≤-0.3; wherein f is the focal length of the long-wave infrared lens, Yd is the maximum image height, and FOVd is the field of view angle corresponding to the maximum image height.

[0033] Optical power is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam; it characterizes the ability of an optical system to deflect light. The larger the absolute value of the optical power, the stronger its ability to bend light; the smaller the absolute value, the weaker its ability to bend light. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., one surface of the lens), a single lens, or a system of multiple lenses (i.e., a lens group).

[0034] In the long-wave infrared lens provided in this embodiment, each lens can be fixed in a lens barrel. Figure 1 (not shown in the image). For example... Figure 1 As shown, in this embodiment, the first lens 110 is a meniscus lens with negative optical power, its object side is convex and its image side is concave. Both the object side and the image side of the first lens 110 are aspherical, which helps to make the long-wave infrared lens have a larger focal length in the central region (the focal length can reach more than 6mm), so that it can identify distant objects; at the same time, it can also make the overall field of view of the long-wave infrared lens larger (the field of view can reach more than 150°), so that the surrounding situation can be observed.

[0035] As a feasible implementation method, the long-wave infrared lens is set to satisfy -0.7≤(Yd-FOVd*f) / (FOVd*f)≤-0.3, where f is the focal length of the long-wave infrared lens, Yd is the maximum image height of the long-wave infrared lens on the image plane, and FOVd is the field of view (in radians) corresponding to the maximum image height.

[0036] By rationally setting the relationship between the above three factors, the requirements for long focal length and wide field of view of the lens can be further met, thereby realizing the characteristics of long-wave infrared lenses that can see both far and wide.

[0037] In summary, the long-wave infrared lens provided in this embodiment of the invention uses only three lenses, resulting in a simple structure, small size, and cost savings while improving long-wave transmittance. Furthermore, by setting the first lens 110 as a meniscus lens with negative optical power, its object-side surface is convex, and both the object-side and image-side surfaces of the first lens 110 are aspherical. Simultaneously, the long-wave infrared lens satisfies -0.7≤(Yd-FOVd*f) / (FOVd*f)≤-0.3, resulting in a larger focal length (up to 6mm or more) in the central region, enabling the identification of distant objects. Moreover, the overall field of view of the long-wave infrared lens is also large (up to 150° or more), allowing observation of the surrounding environment. Therefore, there is no need for an additional infrared camera to acquire information for software algorithm fusion, solving the problems of image overlap or missing elements in existing technologies and improving the response rate of the imaging system.

[0038] Continue to refer to Figure 1 Optionally, the second lens 120 has positive optical power, and its object side and / or image side is convex.

[0039] The second lens 120 is configured to have positive optical power and at least one side of it is convex, which helps to correct aberrations and ensures that the image quality of the long-wave infrared lens meets the imaging requirements.

[0040] Continue to refer to Figure 1 Optionally, the third lens 130 has positive optical power, and its object side and / or image side is convex.

[0041] By setting the third lens 130 to have positive optical power and its object side and / or image side to be convex, it helps to further correct aberrations, so that the image quality of the long-wave infrared lens meets the imaging requirements.

[0042] As a feasible implementation, the distance from the center of the optical axis on the object side of the first lens 110 to the image plane is TTL, where 3.1≤TTL / f≤6.2.

[0043] The distance TTL from the center of the optical axis on the object side of the first lens 110 to the image plane can be understood as the total length of the long-wave infrared lens. By reasonably setting the total length of the long-wave infrared lens, the entire long-wave infrared lens structure can be made compact and highly integrated, thereby realizing the miniaturization design of the long-wave infrared lens.

[0044] As a feasible implementation, the focal length of the first lens 110 is f1, the focal length of the second lens 120 is f2, and the focal length of the third lens 130 is f3, wherein -2.3 < f1 / f < -1.8; 1.4 < f2 / f < 5.7; 1.2 < f3 / f < 2.4.

[0045] By rationally allocating the focal length of each lens, aberrations can be corrected, ensuring that the long-wave infrared lens has good image quality.

[0046] As a possible implementation, at least one of the object-side and image-side surfaces of the first lens 110, the second lens 120, and the third lens 130 is a binary surface.

[0047] Among them, the binary surface has the functions of achromatic aberration and thermal aberration aberration. By setting at least one side of at least one lens in the long-wave infrared lens as a binary surface, chromatic aberration can be effectively corrected, thereby improving the image quality of the long-wave infrared lens.

[0048] As a feasible implementation, the object-side or image-side of the third lens 130 is a binary surface.

[0049] Wherein, by setting the object side or the image side of the third lens 130 as a binary surface, the chromatic aberration can be better corrected, so as to further improve the image quality of the long-wave infrared lens.

[0050] As a feasible implementation, the material of the first lens 110 is germanium glass, and the materials of the second lens 120 and the third lens 130 are chalcogenide glass.

[0051] Wherein, by setting the material of the first lens 110 as germanium glass, and the materials of the second lens 120 and the third lens 130 as chalcogenide glass, the long-wave infrared lens has a passive athermalization function, so that the imaging quality of the long-wave infrared lens is unchanged in a wide temperature range of-40℃ to +80℃, and the use requirement of the long-wave infrared lens in the environment with large temperature change is met.

[0052] In summary, the long-wave infrared lens provided by the embodiment of the present application sets the material of the first lens 110 as germanium glass, and the materials of the second lens 120 and the third lens 130 as chalcogenide glass, and combines the use of the binary surface, so that the influence of temperature on the imaging of the lens is eliminated, the lens has a passive athermalization function, and the imaging quality of the long-wave infrared lens is unchanged in a wide temperature range of-40℃ to +80℃. At the same time, through the cooperation of the materials and the optical power of each lens, the number of lenses is reduced to 3 to realize athermalization design, which not only reduces the material cost, but also improves the transmittance of the system.

[0053] Continuing to refer to Figure 1 Optionally, the long-wave infrared lens provided by the embodiment of the present application further comprises a diaphragm 140, which is located in the optical path between the first lens 110 and the second lens 120, or the diaphragm 140 is located in the optical path between the second lens 120 and the third lens 130.

[0054] Wherein, by setting the diaphragm 140 between the first lens 110 and the second lens 120, or between the second lens 120 and the third lens 130, the front and rear light rays can be collected, and the total length of the optical system can be shortened.

[0055] It should be noted that in other embodiments, the diaphragm can also be set at other positions according to actual needs, and the embodiment of the present application does not limit this.

[0056] Optionally, the focal length f of the long-wave infrared lens provided by the embodiment of the present application satisfies f≥6mm, and the field of view FOV satisfies FOV≥150°.

[0057] The long-wave infrared lens provided by the embodiment of the present application has a focal length of more than 6 mm, meets the requirement of a large focal length, and can identify a remote object; meanwhile, the field of view FOV is more than 150°, the overall field of view is large, and the surrounding situation can be observed; thus, the long-wave infrared lens can both see far and see wide.

[0058] It should be noted that the long-wave infrared lens provided by the embodiment of the present application can further include other structures, and a person skilled in the art can set the long-wave infrared lens according to actual requirements, for example, the long-wave infrared lens further includes a detector, the detector is used to receive a light beam passing through the long-wave infrared lens, and convert the light beam into an electrical signal, so as to facilitate subsequent acquisition of imaging information of a target object according to the electrical signal.

[0059] Continuing to refer to Figure 1 Optionally, in an actual application scenario, the image side of the third lens 130 of the long-wave infrared lens provided by the embodiment of the present application is further provided with a detector protection window 150 to protect a detector (not shown in the figure). As shown in Figure 1 The incident light enters through the object side of the first lens 110, passes through the diaphragm 140, and then passes through the second lens 120, the third lens 130 and the detector protection window 150 to finally converge on an imaging surface.

[0060] For example, Table 1 details the specific optical data parameters of each lens in the long-wave infrared lens provided by the embodiment of the present application at room temperature in a feasible implementation manner, and the optical data parameters in Table 1 correspond to Figure 1 the long-wave infrared lens shown in the figure.

[0061] The first lens 110 is a meniscus lens with negative optical power, and the object side thereof is a convex surface; the object side and the image side of the first lens 110 are both provided as aspherical surfaces; the second lens 120 has positive optical power, the object side thereof is a plane, and the image side thereof is a convex surface; the third lens 130 can have positive optical power, the object side thereof is a convex surface, the image side thereof is a convex surface, and the object side thereof adopts a binary surface; and the diaphragm 140 is located between the first lens 110 and the second lens 120.

[0062] Table 1 Optical data parameters of long-wave infrared lens

[0063]

[0064]

[0065] The surface number is determined by the order of the surfaces of each lens. For example, surface number 1 represents the object side of the first lens 110, surface number 2 represents the image side of the first lens 110, and so on. Surface number 8 represents the object side of the detector protection window 150, and surface number 9 represents the image side of the detector protection window 150. The radius of curvature represents the degree of curvature of the lens surface. A positive value indicates that the surface bends towards the image surface, and a negative value indicates that the surface bends towards the object surface. "Infinity" indicates that the surface is flat. The spacing represents the central axial distance from the current surface to the next surface. The units for both the radius of curvature and the spacing are millimeters (mm).

[0066] Its even-order aspherical surface shape satisfies the following equation:

[0067]

[0068] Where z is the distance from the even-order aspherical surface to its vertex along the optical axis, r is the height from the optical axis, c is the curvature 1 / R, R is the radius of curvature at the vertex of the lens, and k is the conic coefficient -e 2 a2, a3, a4, a5, a6, a7, and a8 are the higher-order coefficients of the aspherical surface.

[0069] For example, Table 2 details the conic coefficient k and higher-order coefficients a2, a3, a4, a5, a6, a7, a8 of the aspherical lens surface in this embodiment according to a feasible implementation.

[0070] Table 2 Aspherical parameters of each lens in the long-wave infrared lens

[0071] Page number [a2] [a3] [a4] [a5] [a6] [a7] [a8] 1 -5.04E-04 1.45E-05 -1.68E-06 8.10E-08 -2.25E-09 3.22E-11 -1.81E-13 2 -9.81E-04 8.98E-05 -1.94E-05 2.16E-06 -1.33E-07 4.28E-09 -5.56E-11 5 1.99E-05 2.40E-06 -2.46E-07 5.28E-09 -7.57E-11 -4.22E-13 1.55E-14 6 -2.87E-05 -1.14E-06 3.28E-08 -8.89E-10 1.15E-11 -8.83E-14 2.78E-16

[0072] Where -5.04E-04 indicates that the coefficient a2 of surface number 1 is -5.04 * 10. -4 And so on.

[0073] Optionally, the binary surface shape satisfies the following equation:

[0074]

[0075] Where λ0 is the designed center wavelength, and n0 is the refractive index corresponding to the center wavelength of the material;

[0076]

[0077] Where M is the diffraction order, N is the order of the polynomial coefficients in the series, Ai is the coefficient of the 2ith power, and ρ is the normalized radial aperture coordinate.

[0078] For example, Table 3 details the phase of the binary plane in this embodiment with a feasible implementation.

[0079] Table 3: Phase of binary surfaces in long-wave infrared lens

[0080] Page number R1 A1 A2 A3 A4 6 10.00 -7.94E+01 1.23E+01 -2.36E+01 1.28E+01

[0081] wherein R1 is the normalized radius of the binary surface.

[0082] In the embodiment, the focal length, the field of view angle and the maximum image height satisfy (Yd-FOVd*f) / (FOVd*f)=-0.46; the total length of the optical lens TTL and the focal length f satisfy TTL / f=4.4; the focal lengths of the three lenses and the focal length of the optical lens satisfy f1 / f=-1.7, f2 / f=1.6, f3 / f=1.3.

[0083] The long-wave infrared lens provided by the embodiment has a working waveband of 8-12 μm, an F number of 1.0, is adapted to a 640*480_12 μm uncooled detector, has a focal length of 6.5 mm and a maximum full field of view angle of 155.8°.

[0084] Further, Figure 2 The MTF diagram of the long-wave infrared lens provided by the embodiment under a normal temperature (20℃) state, Figure 3 The MTF diagram of the long-wave infrared lens provided by the embodiment under a low temperature (-40℃) state, Figure 4 The MTF diagram of the long-wave infrared lens provided by the embodiment under a high temperature (80℃) state, wherein the MTF diagram can represent the comprehensive imaging quality of the long-wave infrared lens under the normal temperature (20℃), the low temperature (-40℃) and the high temperature (80℃) states, as shown in Figures 2-4 As shown in the figure, the transfer function of the 42 line pairs / mm in the MTF curve of the long-wave infrared lens under the normal temperature (20℃), the low temperature (-40℃) and the high temperature (80℃) states is basically above 0.3, which can meet the required image quality requirement.

[0085] Figure 5 The spot diagram of the long-wave infrared lens provided by the embodiment under a normal temperature (20℃) state, wherein the spot diagram is one of the most commonly used evaluation methods in modern optical design. The spot diagram refers to that many light rays emitted by a point light source are incident on the optical system, and due to aberration, the intersection points with the image plane are no longer concentrated at the same point, but form a dispersed diagram scattered in a certain range. As shown in Figure 5 As shown in the figure, the long-wave infrared lens provided by the embodiment has a relatively concentrated and uniformly distributed dispersion diagram in the entire long-wave band, which can meet the requirement of high-resolution imaging.

[0086] Figure 6A relative luminance diagram of the long-wave infrared lens provided by the embodiment of the present application under normal temperature (20 DEG C) condition is shown in the figure, which represents the relative luminance values corresponding to different fields of view, as shown in the figure, the relative luminance of the long-wave infrared lens provided by the embodiment of the present application is greater than 90% in the whole field of view in the working waveband, and the brightness is uniform. Figure 6

[0087] In summary, the long-wave infrared lens provided by the embodiment of the present application has a large relative aperture, the MTF is close to the diffraction limit at high and low temperatures, the imaging is clear, and the imaging requirement of high resolution can be met.

[0088] It should be noted that the above are only the preferred embodiments of the present application and the technical principles applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, re-adjustments, mutual combinations and substitutions without departing from the protection scope of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims.​

Claims

1. A long-wave infrared lens, characterized in that, include: A first lens, a second lens, and a third lens are arranged sequentially from the object plane to the image plane along the optical axis; The first lens is a meniscus lens with negative optical power, and its object side is convex. Both the object-side surface and the image-side surface of the first lens are aspherical. The second lens has positive optical power, and the third lens has positive optical power; The long-wave infrared lens satisfies: -0.7≤(Yd-FOVd×f) / (FOVd×f)≤-0.3; Where f is the focal length of the long-wave infrared lens, Yd is the maximum image height, and FOVd is the field of view corresponding to the maximum image height.

2. The long-wave infrared lens according to claim 1, characterized in that, The object-side surface and / or image-side surface of the second lens are convex.

3. The long-wave infrared lens according to claim 1, characterized in that, The object-side surface and / or image-side surface of the third lens are convex.

4. The long-wave infrared lens according to claim 1, characterized in that, The distance from the center of the optical axis on the object side of the first lens to the image plane is TTL, where 3.1≤TTL / f≤6.

2.

5. The long-wave infrared lens according to claim 1, characterized in that, The focal length of the second lens is f2, and the focal length of the third lens is f3, wherein 1.4 < f2 / f < 5.7; 1.2 < f3 / f < 2.

4.

6. The long-wave infrared lens according to claim 1, characterized in that, At least one of the object-side and image-side surfaces of the first lens, the second lens, and the third lens is a binary surface.

7. The long-wave infrared lens according to claim 6, characterized in that, The object-side or image-side of the third lens is a binary surface.

8. The long-wave infrared lens according to claim 1, characterized in that, The first lens is made of germanium-based glass, while the second and third lenses are made of chalcogenide glass.

9. The long-wave infrared lens according to claim 1, characterized in that, The long-wave infrared lens also includes an aperture stop; The aperture stop is located in the optical path between the first lens and the second lens; Alternatively, the aperture stop may be located in the optical path between the second lens and the third lens.

10. The long-wave infrared lens according to claim 1, characterized in that, The focal length f of the long-wave infrared lens satisfies f≥6mm; The field of view (FOV) of the long-wave infrared lens satisfies FOV≥150°.

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