Two-piece long-wave infrared lens

Abstract

The invention discloses a two-piece long-wave infrared lens which comprises a first lens and a second lens which are sequentially arranged from an object plane to an image plane, the first lens and the second lens are both meniscus lenses which protrude towards the object side and have positive focal power, at least one of the object side face and the image side face of the first lens is a binary plane, and at least one of the object side face and the image side face of the second lens is a convex plane. The object side surface and the image side surface of the second lens are aspheric surfaces; and the proportional relation among the focal length, the maximum image height and the field angle is reasonably set. According to the lens, good imaging is ensured, the size and weight are reduced, the cost is reduced, the response rate is improved, and a large clear photographing range can be ensured when an object is remotely recognized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical lenses, and in particular relates to a two-piece long-wave infrared lens. Background Art

[0002] With the rapid development of infrared technology, infrared cameras can achieve good imaging effects at night and in harsh environments, which has led to an increasing market demand for them, and infrared optical lenses are an important component.

[0003] Far infrared rays are in the wavelength range of 8um to 12um, and are emitted from humans, animals or other objects as heat (i.e., as infrared rays). This makes far infrared rays widely used, for example, for imaging in dark places or for observing temperature distribution. Conventional infrared lenses use more lenses to clearly identify objects, but such a setting will cause the size of the lens to become larger, increasing the cost; and a large number of lenses will not only lead to a large volume but also slow propagation, affecting the response rate of the imaging system; in addition, existing conventional infrared lenses are difficult to simultaneously achieve long-distance object recognition and expand the range of clear photography. Therefore, a two-piece long-wave infrared lens is proposed. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned problems and to propose a two-piece long-wave infrared lens, which helps to reduce volume and weight, reduce costs, increase response rate, and can identify distant objects and expand the range of clear photography while ensuring good imaging.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a two-piece long-wave infrared lens, comprising a first lens and a second lens arranged in sequence from an object plane to an image plane, wherein:

[0007] The first lens and the second lens are both meniscus lenses convex to the object side and have positive power, at least one of the object side surface and the image side surface of the first lens is a binary surface, and the object side surface and the image side surface of the second lens are both aspherical surfaces;

[0008] The two-piece long-wave infrared lens also meets the following conditions:

[0009] 0.01≤(Yd-FOV*f) / (FOV*f)≤0.1;

[0010] Where, f is the focal length of the two-element long-wave infrared lens, in mm; Yd is the maximum image height, in mm; FOV is the field of view corresponding to the maximum image height, in degrees.

[0011] Preferably, the two-piece long-wave infrared lens also meets the following conditions:

[0012] 1≤TTL / f≤3;

[0013] Wherein, TTL is the distance from the center of the optical axis of the object side of the first lens to the image plane, in mm.

[0014] Preferably, the two-piece long-wave infrared lens also meets the following conditions:

[0015] 1.2≤|f1 / f|≤1.7; 1.2≤|f2 / f|≤1.7;

[0016] Wherein, f1 is the focal length of the first lens, and f2 is the focal length of the second lens, both in mm.

[0017] Preferably, at least one of the object-side surface and the image-side surface of the second lens is a binary surface.

[0018] Preferably, the two-piece long-wave infrared lens also meets the following conditions:

[0019] f≥34mm, FOV≥15.9°.

[0020] Preferably, both the first lens and the second lens are chalcogenide glass lenses.

[0021] Preferably, the two-piece long-wave infrared lens further includes an aperture and a protective glass, wherein the aperture is located on the object side of the first lens and the protective glass is located on the image side of the second lens.

[0022] Preferably, the operating wavelength band of the two-piece long-wave infrared lens is 8 μm to 12 μm.

[0023] Preferably, the radius of curvature of the object side surface of the first lens is 28±5%, and the radius of curvature of the image side surface is 34.6±5%; the radius of curvature of the object side surface of the second lens is 17.8±5%, and the radius of curvature of the image side surface is 18.1±5%, the unit is mm.

[0024] Preferably, the aspheric surface satisfies the even aspheric surface type, and the formula is as follows:

[0025]

[0026] Among them, z1(r) is the vector height of the even-order aspheric surface at position r, r is the height from the optical axis, c is the curvature, which is equal to 1 / R, R is the radius of curvature, k is the cone coefficient, and a 2 、a 3 、a 4 、a 5 、a 6 、a 7 、a 8 is the aspheric high-order coefficient;

[0027] The formula for a two-dimensional surface is as follows:

[0028]

[0029] in,

[0030]

[0031] Among them, z2(r) is the vector height of the binary surface at position r, λ 0 is the central wavelength, n 0 is the refractive index corresponding to the central wavelength, M is the diffraction order, i=1~N, N is the order of the polynomial coefficients in the series, Ai is the coefficient of the 2i-th power, ρ is the normalized radial aperture coordinate, HOR is the horizontal angle, int is the rounding function, and φ is the additional phase.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The long-wave infrared lens uses only two lenses, and by setting the proportional relationship between the focal length, the maximum image height and the field of view angle, for example, the first lens and the second lens are both meniscus lenses with positive focal power, the object side surface of which is convex, and at least one of the object side surface and the image side surface of the first lens is a binary surface, so that the overall length of the lens can be shortened so that it can be compactly stored in a housing such as a lens barrel, and the range of clear photography can be expanded by extending the focal length and improving the brightness of the optical system, and distant objects can be identified. The focal length reaches more than 34m, and the field of view FOV reaches more than 15°; in addition, by setting the materials of the first lens and the second lens to be chalcogenide glass combined with the use of binary surfaces, chromatic aberration can be effectively corrected, thereby improving the image quality of the long-wave infrared lens, and the influence of temperature on the lens imaging can be eliminated, so that the lens has the function of passive heat elimination, thereby making the long-wave infrared lens have unchanged imaging quality within a wide temperature range of -40°C to +80°C, simple structure, small and lightweight, cost saving, and improved transmittance and response rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the two-piece long-wave infrared lens of the present invention;

[0035] Figure 2 It is a schematic diagram of the MTF of the present invention at room temperature (20°C);

[0036] Figure 3 It is a schematic diagram of the MTF of the present invention at a low temperature (-40°C);

[0037] Figure 4 It is a schematic diagram of the MTF of the present invention at a high temperature (+80°C);

[0038] Figure 5Schematic diagram of the diffuse spots of the present invention at room temperature (20°C);

[0039] Figure 6 It is a schematic diagram of relative illumination of the present invention at room temperature (20°C).

[0040] Reference numerals: L1, first lens; L2, second lens; STO, aperture; CG, cover glass; IMA, image plane. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the technical field of this application. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0043] like Figure 1-6 As shown, a two-piece long-wave infrared lens comprises a first lens L1 and a second lens L2 arranged in sequence from the object plane to the image plane, wherein:

[0044] The first lens L1 and the second lens L2 are both meniscus lenses convex to the object side and have positive refractive power, at least one of the object side surface and the image side surface of the first lens L1 is a binary surface, and the object side surface and the image side surface of the second lens L2 are both aspherical surfaces;

[0045] The two-piece long-wave infrared lens also meets the following conditions:

[0046] 0.01≤(Yd-FOV*f) / (FOV*f)≤0.1;

[0047] Where, f is the focal length of the two-element long-wave infrared lens, in mm; Yd is the maximum image height, in mm; FOV is the field of view corresponding to the maximum image height, in degrees.

[0048] The two-piece long-wave infrared lens provided in this embodiment can fix each lens on the lens barrel ( Figure 1 (not shown). Figure 1As shown, in this embodiment, by setting the first lens L1 to have positive focal power, the object side surface is convex, and the image side surface is concave. And at least one of the object side surface and the image side surface of the first lens L1 is a binary surface. Chromatic aberration can be effectively corrected, thereby improving the image quality of the infrared lens. By setting the second lens L2 to have positive focal power, the object side surface is convex, and the image side surface is concave, it is helpful to correct aberration, so that the image quality of the infrared lens meets the imaging requirements. At the same time, the long-wave infrared lens is set to meet 0.01≤(Yd-FOV*f) / (FOV*f)≤0.1. The problem of low imaging quality in the prior art is solved, and it is impossible to cooperate with the infrared sensor to clearly distinguish the object imaging, and at the same time, the response rate of the imaging lens system can be improved. Among them, the optical focal length is equal to the difference between the image side beam convergence and the object side beam convergence, which characterizes the ability of the optical system to deflect light. The larger the absolute value of the optical focal length, the stronger the ability to bend light, and the smaller the absolute value of the optical focal length, the weaker the ability to bend light. When the focal length is positive, the refraction of light is convergent; when the focal length is negative, the refraction of light is divergent. The long-wave infrared lens provided by the present invention uses only two lenses, has a simple structure, a small size, saves costs and improves transmittance.

[0049] In one embodiment, the two-piece long-wave infrared lens also meets the following conditions:

[0050] 1≤TTL / f≤3;

[0051] Wherein, TTL is the distance from the center of the optical axis of the object side of the first lens L1 to the image plane, in mm. Wherein, TTL is the total length of the lens. By reasonably setting the total length of the long-wave infrared lens, the entire long-wave infrared lens can be ensured to have a compact structure and high integration, thereby realizing the miniaturization design of the long-wave infrared lens.

[0052] In one embodiment, the two-piece long-wave infrared lens also meets the following conditions:

[0053] 1.2≤|f1 / f|≤1.7; 1.2≤|f2 / f|≤1.7;

[0054] Wherein, f1 is the focal length of the first lens L1, and f2 is the focal length of the second lens L2, in mm. By reasonably allocating the focal lengths of the lenses, it is beneficial to correct aberrations and ensure that the long-wave infrared lens has good image quality.

[0055] In one embodiment, at least one of the object side surface and the image side surface of the second lens L2 is a binary surface. By setting the object side surface or the image side surface of the second lens L2 as a binary surface, chromatic aberration can be better corrected, thereby further improving the image quality of the long-wave infrared lens.

[0056] In one embodiment, the two-piece long-wave infrared lens also meets the following conditions:

[0057] f≥34mm, FOV≥15.9°.

[0058] Among them, the focal length reaches more than 34mm, which meets the demand for a larger focal length and can identify distant objects; at the same time, the FOV reaches more than 15°, which can view distant objects; thus realizing the characteristics of long-wave infrared lenses that can see far and see clearly.

[0059] In one embodiment, the first lens L1 and the second lens L2 are both chalcogenide glass lenses. The materials of the first lens L1 and the second lens L2 are chalcogenide glass, so that the long-wave infrared lens has a passive athermalization function, and thus the imaging quality of the long-wave infrared lens remains unchanged within a wide temperature range of -40°C to +80°C, meeting the use requirements of the long-wave infrared lens in an environment with large temperature changes.

[0060] In one embodiment, the two-piece long-wave infrared lens further includes an aperture STO and a protective glass CG, wherein the aperture STO is located on the object side of the first lens L1, and the protective glass CG is located on the image side of the second lens L2. By arranging the aperture STO on the object side of the first lens L1, the front and rear light rays can be converged, thereby shortening the total length of the optical system. The protective glass CG can protect the detector (not shown in the figure).

[0061] In one embodiment, the operating wavelength range of the two-piece long-wave infrared lens is 8 μm to 12 μm.

[0062] In one embodiment, the radius of curvature of the object side surface of the first lens L1 is 28±5%, and the radius of curvature of the image side surface is 34.6±5%; the radius of curvature of the object side surface of the second lens L2 is 17.8±5%, and the radius of curvature of the image side surface is 18.1±5%, in mm. This helps to ensure the image quality while shortening the total length of the optical system.

[0063] In one embodiment, the aspheric surface satisfies an even aspheric surface type, and the formula is as follows:

[0064]

[0065] Among them, z1(r) is the vector height of the even-order aspheric surface at position r, r is the height from the optical axis, c is the curvature, which is equal to 1 / R, R is the radius of curvature, k is the cone coefficient, and a 2 、a 3 、a 4 、a 5 、a 6 、a 7 、a 8 is the aspheric high-order coefficient;

[0066] The formula for a two-dimensional surface is as follows:

[0067]

[0068] in,

[0069]

[0070] Among them, z2(r) is the vector height of the binary surface at position r, λ 0 is the central wavelength, n 0 is the refractive index corresponding to the central wavelength, M is the diffraction order, i=1~N, N is the order of the polynomial coefficients in the series, Ai is the coefficient of the 2i-th power, ρ is the normalized radial aperture coordinate, HOR is the horizontal angle, int is the rounding function, and φ is the additional phase.

[0071] The long-wave infrared lens provided by the present invention is provided with a first lens L1 and a second lens L2 made of chalcogenide materials, and is combined with the use of a binary surface, wherein the binary surface has the functions of achromatism and athermalization. By providing at least one mirror surface 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, and being able to eliminate the influence of temperature on lens imaging, so that the lens has the function of passive athermalization, thereby ensuring that the imaging quality of the long-wave infrared lens remains unchanged within a wide temperature range of -40°C to +80°C. Meanwhile, by coordinating the materials and the focal length of each lens, the number of lenses is reduced to two to achieve an athermal design, thereby reducing the material cost and improving the transmittance and response rate of the system. The focal length reaches more than 34m, meeting the requirement of a larger focal length, and can identify distant objects. Meanwhile, the FOV reaches more than 15°, so that distant objects can be viewed. Thus, the long-wave infrared lens is provided with the characteristics of being able to see far and clearly.

[0072] It should be noted that the long-wave infrared lens provided in the embodiment of the present invention may also include other structures, and those skilled in the art may configure them according to actual needs. For example, the long-wave infrared lens may further include a detector, which is used to receive the light beam passing through the long-wave infrared lens and convert the light beam into an electrical signal, so as to obtain imaging information of the target object based on the electrical signal later.

[0073] For ease of understanding, a detailed description is given below through specific embodiments.

[0074] The long-wave infrared lens provided in this embodiment includes a first lens L1, a second lens L2, an aperture STO and a protective glass CG. The aperture STO is located in the optical path between the object plane and the first lens L1. In actual application scenarios, a protective glass CG is also provided on the image side of the second lens L2 to protect the detector (not shown in the figure). The first lens L1 is a meniscus lens with positive focal power, whose object side surface is convex and whose image side surface is concave, and the object side surface of the first lens L1 is set as an aspherical surface, and the image side surface is set as a binary surface; the second lens L2 has positive focal power, whose object side surface is convex and whose image side surface is concave, and both the object side surface and the image side surface of the second lens L2 are set as aspherical surfaces. The incident light passes through the aperture STO and enters from the object side surface of the first lens L1, passes through the second lens L2, and then passes through the protective glass CG and finally converges on the imaging surface IMA.

[0075] The specific optical parameters of each lens at room temperature are shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] Among them, the surface numbers are numbered according to the surface order of each lens. For example, the surface number S1 represents the object side surface of the first lens L1, S2 represents the image side surface of the first lens L1, S3 represents the object side surface of the second lens L2, S4 represents the image side surface of the second lens L2, S5 is the object side surface of the protective glass CG, and S6 is the image side surface of the protective glass CG. The curvature radius represents the curvature of the lens surface. A positive value represents that the mirror surface is bent toward the image side, and a negative value represents that the mirror surface is bent toward the object side. Among them, "Infinity" represents that the mirror surface is a plane. The spacing represents the central axial distance from the current mirror surface to the next mirror surface (i.e., the adjacent mirror surface), and the units of the curvature radius and the spacing are both millimeters (mm).

[0080] The cone coefficient k and the high-order coefficient a of each lens surface in this embodiment are 2 、a 3 、a 4 、a 5 、a 6 、a 7 、a 8 , as shown in Table 2.

[0081] Table 2

[0082]

[0083] Wherein, ρ=r / R1, R1 is the normalized radius of the binary surface.

[0084] According to the above data, in this embodiment, (Yd-FOV*f) / (FOV*f)=0.04; TTL / f=1.3; f1 / f=1.5, f2 / f=1.7 are satisfied. The working band of the long-wave infrared lens provided in this embodiment is 8μm~12μm, the F number is 1.0 and it is suitable for 640*512_12μm uncooled detector, the focal length is 35mm, and the FOV is 15.9°.

[0085] Furthermore, Figure 2 This is a schematic diagram of the MTF of the long-wave infrared lens provided in this embodiment at room temperature (20°C). Figure 3 This is a schematic diagram of the MTF of a long-wave infrared lens at low temperature (-40°C). Figure 4 is the MTF diagram of the long-wave infrared lens at high temperature (80°C), where the MTF diagram can represent the comprehensive imaging quality of the long-wave infrared lens at room temperature (20°C), low temperature (-40°C) and high temperature (80°C). Figure 2-4 As shown, when the long-wave infrared lens is at room temperature (20°C), low temperature (-40°C) and high temperature (80°C), the transfer function of the MTF curve at 42 line pairs / mm is above 0.3, which can meet the required image quality requirements.

[0086] Figure 5 The schematic diagram of the diffuse spot of the long-wave infrared lens provided in this embodiment at room temperature (20°C) is shown. The diffuse spot is one of the most commonly used evaluation methods in modern optical design. The diffuse spot refers to the diffuse pattern formed by the intersection of many light rays emitted by a point light source and the image plane after passing through the optical system, which is no longer concentrated at the same point due to aberration. Figure 5 As shown, the long-wave infrared lens provided in this embodiment has a relatively concentrated and evenly distributed diffusion pattern in the entire long-wave band, which can meet the needs of high-resolution imaging.

[0087] Figure 6 The relative illumination diagram of the long-wave infrared lens provided in this embodiment at room temperature (20° C.) represents the relative illumination values ​​corresponding to different fields of view, such as Figure 6 As shown, the long-wave infrared lens provided in this embodiment has a relative illumination of more than 90% in the entire field of view in the working band, and the brightness is uniform.

[0088] In summary, the long-wave infrared lens provided by the present invention has a large relative aperture, an MTF close to the diffraction limit at high and low temperatures, and a clear image, which can meet the requirements of high-resolution imaging.

[0089] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above-described embodiments only express the more specific and detailed embodiments described in this application, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of this application, which all belong to the protection scope of this application. Therefore, the protection scope of the patent application shall be based on the attached claims.

Claims

1. A two-piece long-wave infrared lens, characterized in that: The two-piece long-wave infrared lens comprises a first lens (L1) and a second lens (L2) which are arranged in sequence from the object plane to the image plane, wherein: The first lens (L1) and the second lens (L2) are both meniscus lenses convex toward the object side and having positive optical power, at least one of the object side surface and the image side surface of the first lens (L1) is a binary surface, and the object side surface and the image side surface of the second lens (L2) are both aspherical surfaces; The two-piece long-wave infrared lens also meets the following conditions: 0.01≤(Yd-FOV*f) / (FOV*f)≤0.1; Among them, f is the focal length of the two-piece long-wave infrared lens, in mm; Yd is the maximum image height, in mm; FOV is the field of view corresponding to the maximum image height, in degrees.

2. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The two-piece long-wave infrared lens also meets the following conditions: 1≤TTL / f≤3; Wherein, TTL is the distance from the center of the optical axis of the object side surface of the first lens (L1) to the image plane, in mm.

3. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The two-piece long-wave infrared lens also meets the following conditions: 1.2≤|f1 / f|≤1.7; 1.2≤|f2 / f|≤1.7; Wherein, f1 is the focal length of the first lens (L1), and f2 is the focal length of the second lens (L2), and the unit is mm.

4. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: At least one of the object-side surface and the image-side surface of the second lens (L2) is a binary surface.

5. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The two-piece long-wave infrared lens also meets the following conditions: f≥34mm, FOV≥15.9°.

6. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The first lens (L1) and the second lens (L2) are both chalcogenide glass lenses.

7. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The two-piece long-wave infrared lens further comprises an aperture stop (STO) and a protective glass (CG), wherein the aperture stop (STO) is located on the object side of the first lens (L1), and the protective glass (CG) is located on the image side of the second lens (L2).

8. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The working band of the two-piece long-wave infrared lens is 8 μm to 12 μm.

9. The two-piece long-wave infrared lens as claimed in claim 1, characterized in that: The curvature radius of the object side surface of the first lens (L1) is 28±5%, and the curvature radius of the image side surface is 34.6±5%; the curvature radius of the object side surface of the second lens (L2) is 17.8±5%, and the curvature radius of the image side surface is 18.1±5%, the unit is mm.

10. The two-piece long-wave infrared lens according to any one of claims 1 to 9, characterized in that: The aspheric surface satisfies the even aspheric surface type, and the formula is as follows: Wherein, z1(r) is the vector height of the even-order aspheric surface at position r, r is the height from the optical axis, c is the curvature, which is equal to 1 / R, R is the radius of curvature, k is the cone coefficient, and a2, a3, a4, a5, a6, a7, and a8 are the high-order coefficients of the aspheric surface; The formula for the two-dimensional surface is as follows: in, Among them, z2(r) is the vector height of the binary surface at position r, λ0 is the central wavelength, n0 is the refractive index corresponding to the central wavelength, M is the diffraction order, i=1~N, N is the order of the polynomial coefficients in the series, Ai is the coefficient of the 2i-th power, ρ is the normalized radial aperture coordinate, HOR is the horizontal angle, int is the integer function, and φ is the additional phase.

Images