A 25.0 mm large target infrared optical athermal lens and imaging method

Abstract

The invention relates to a 25.0 mm large-target infrared optical athermal lens and an imaging method. A positive lens A, a negative lens B and a positive lens C are arranged in sequence from left to right along a light incident direction in the lens optical system. The air interval between the positive lens A and the negative lens B is 3.250 mm, and the air interval between the negative lens B and the positive lens C is 5.273 mm. The lens has a compact structure, a small volume, is convenient to use, can be stably maintained in a high-temperature environment, automatically realizes optical athermalization, improves use efficiency, has a low production cost, and has strong practicality and economic value. The lens has a large imaging target surface that can match multiple types of detectors, can be applied to different detectors at the same time, and meets different market demands. The large target surface provides use space for different application fields, truly meets the use requirements of customers, and can be applied to and solve the problem of excessively large tolerances in mass production of detectors.

Description

Technical Field

[0001] The invention relates to a 25.0 mm large target surface infrared optical athermal lens and an imaging method. Background Art

[0002] With the current demand for infrared lenses in commercial and civilian applications, infrared imaging technology has been widely used in defense, industry, medical treatment, power detection and other fields, with great application prospects and market value. Infrared detection technology is a technology that studies the generation, conversion and application of infrared radiation. It has a certain ability to penetrate smoke, fog, etc. and recognize camouflage. It is not affected by some strong light on the battlefield. The basis of infrared recognition of targets and scenery is infrared radiation. It can quickly achieve long-distance, all-weather observation, especially suitable for detecting and identifying targets at night and under adverse weather conditions.

[0003] Among them, in the infrared system, the most influential factor is temperature. This factor mainly causes a large change in the refractive index of the infrared material, and also affects the size of the lens barrel due to thermal expansion and contraction. Its worst effect is to cause unpredictable changes in the focal length of each lens in the system and cause the ideal image plane to shift, resulting in blurred images and reduced contrast, which ultimately affects the optical imaging quality and the imaging performance of the entire system. The lens material of the current infrared long-wave optical athermal lens generally uses zinc selenide material, but the price of zinc selenide material is relatively expensive, which naturally causes the product cost to be relatively high, limiting its application. In view of the limited number of infrared materials available, and thanks to the negative dispersion coefficient of the diffractive optical element, it is considered to use a combination of diffractive optical elements and ordinary glass to achieve achromatic aberration. Considering that in actual processing, chalcogenide glass can be mass-produced by molding technology, which can further reduce the cost of the system, therefore, this system uses a combination of diffractive elements and chalcogenide glass to design a new structure of the infrared system. Summary of the invention

[0004] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a 25.0mm large target infrared optical athermal lens and imaging method, which not only has a reasonable structure, but also effectively solves the problem that the existing lens will cause the optical focal length to change and the optimal ideal image plane to shift due to temperature difference, thereby reducing the imaging quality of the system.

[0005] In order to solve the above technical problem, the technical solution of the present invention is: a positive lens A, a negative lens B and a positive lens C are arranged in sequence from left to right along the incident direction of light in the lens optical system.

[0006] Furthermore, the air gap between the positive lens A and the negative lens B is 3.250 mm, and the air gap between the negative lens B and the positive lens C is 5.273 mm.

[0007] Furthermore, the air gap between the positive lens A and the negative lens B is 4.721 mm, and the air gap between the negative lens B and the positive lens C is 8.686 mm.

[0008] Furthermore, the material of the positive lens A is chalcogenide glass, and the materials of the negative lens B and the positive lens C are germanium (Ge), a common material for infrared lenses, and chalcogenide materials, respectively. Germanium is divided into single crystal germanium and polycrystalline germanium. Polycrystalline germanium has many impurities at its boundaries, which affects the non-uniformity of the refractive index. Therefore, single crystal germanium is preferred in this design.

[0009] Furthermore, the focal length of the positive lens A is f1, the focal length of the negative lens B is f2, the focal length of the positive lens C is f3, and the focal length of the system consisting of the positive lens A, the negative lens B and the positive lens C is f, and the ratio thereof satisfies: 1.5 <f1 / f<2.0;-3.5<f2 / f<-2.2;0.52<f3 / f<1.35。

[0010] Furthermore, the positive lens A and the positive lens C are aspherical lenses, and the negative lens B is a diffractive lens.

[0011] Furthermore, the distance between the positive lens C and the image plane is 9.85 mm.

[0012] The invention discloses a working method of a 25.0 mm large-target infrared optical athermal lens, which is performed according to the following steps: light rays are imaged after passing through a positive lens A, a negative lens B, a positive lens C and an image plane protection window from left to right in sequence.

[0013] Compared with the prior art, the present invention has the following beneficial effects: the lens device has a compact structure, a small size, a reasonable design, can meet the requirements of use within a larger temperature range, achieves the purpose of optical thermal aberration, is easy to carry, simple to use, and increases market application share. At the same time, the number of lenses is controlled to three, and chalcogenide glass that can be processed by a molding process is selected, thereby reducing production costs in mass production, better meeting customer expectations, and having strong practicality.

[0014] Furthermore, compared with the prior art, the focal length of the new structure system is 25.00 mm. According to the patent, it meets the following two conditions:

[0015] 1. The system is in the long wave band and meets the requirements of athermalization;

[0016] 2. Focal length range: ±2mm (i.e. 20mm-30mm);

[0017] For example, CN 206020789U matches the detector 640*512, with a full image height of 13.9mm, and the patent number CN 107092076 A / B with similar focal lengths matches the detector 384*288 with a full image height of 8.16mm, and the patent number CN 103941379 matches the detector 384*288 with a full image height of 12mm;

[0018] The 25.0 mm large target surface infrared optical athermal lens and imaging method of the present invention have the following more obvious benefits:

[0019] (1) The new structure of the present invention can meet the customer's requirements for a large imaging target surface of the system. The full image height is 15.80 mm, and the imaging target surface is larger than the conventional 640*512 17um detector.

[0020] (2) The technical difficulty has been upgraded and its applicability has been highlighted. It has the obvious advantage of a large target area that can match multiple types of detectors. It can be applied to different types of detectors at the same time and can meet the needs of infrared non-cooled detectors such as QVGA / QVGA MAX, meeting the different needs of the market. The technical advantage of being able to match multiple types of detectors provides usage space for different application fields, which is close to market demand.

[0021] (3) It can be applied to solve the problem of excessive tolerance in mass production of detectors. During the packaging process of detectors, positive and negative tolerances of the detector size often occur, which can be well adapted to mass production.

[0022] (4) The system adopts athermal achromatism, which can achieve athermalization over a large temperature range. The system imaging is more stable and reliable, and the system is small in size and compact.

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the optical structure of the first embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of MTF at room temperature of 20 degrees Celsius in Example 1 of the present invention;

[0026] Figure 3 This is a schematic diagram of low-temperature MTF at -40 degrees Celsius in Example 1 of the present invention;

[0027] Figure 4 This is a schematic diagram of the high temperature MTF of 80 degrees Celsius in Example 1 of the present invention;

[0028] Figure 5 Graphs showing distortion and aberration of the optical system according to Embodiment 1 of the present invention;

[0029] Figure 6 This is a schematic diagram of the optical structure of the second embodiment of the present invention;

[0030] Figure 7 This is a schematic diagram of MTF at room temperature of 20 degrees Celsius in Example 2 of the present invention;

[0031] Figure 8 This is a schematic diagram of low-temperature MTF of -40 degrees Celsius in Example 2 of the present invention;

[0032] Fig. 9 This is a schematic diagram of the high temperature MTF of 80 degrees Celsius in the second embodiment of the present invention;

[0033] Fig.10 Graphs showing distortion and aberration of the optical system of Embodiment 2 of the present invention; .

[0034] In the figure: 1-positive lens A, 2-negative lens B, 3-positive lens C, 4-image plane protection window. DETAILED DESCRIPTION

[0035] In order to make the above features and advantages of the present invention more clearly understood, embodiments are given below with reference to the accompanying drawings for detailed description as follows.

[0036] Embodiment 1: Figures 1 to 5 As shown, a 25.0 mm large target surface infrared optical athermal lens is provided, in which a positive lens A, a negative lens B and a positive lens C are arranged in sequence from left to right along the incident direction of light, the air gap between the positive lens A and the negative lens B is 3.250 mm, and the air gap between the negative lens B and the positive lens C is 5.273 mm.

[0037] In the embodiment of the present invention, the material of the positive lens A is chalcogenide glass, and the materials of the negative lens B and the positive lens C are germanium (Ge), a common material for infrared lenses, and chalcogenide materials, respectively. Germanium is divided into single crystal germanium and polycrystalline germanium. Polycrystalline germanium has many impurities at its boundaries, which affects the non-uniformity of the refractive index. Therefore, single crystal germanium is preferred in this design.

[0038] Among them, the germanium (Ge) material used in the negative lens B applies diffraction technology, which not only reduces the cost of lens materials, but also achieves the purpose of eliminating thermal differences in the infrared optical system under high and low temperatures.

[0039] In the embodiment of the present invention, the focal length of the positive lens A is f1, the focal length of the negative lens B is f2, the focal length of the positive lens C is f3, and the focal length of the system consisting of the negative lens A, the negative lens B and the positive lens C is f, and the ratio thereof satisfies:

[0040] 1.5 <f1 / f<2.0;

[0041] -3.5 <f2 / f<-2.2;

[0042] 0.52 <f3 / f<1.35。

[0043] When the above ratio conditions are met, the aberration of the infrared system in the wavelength range of 8 to 12 um can be reasonably corrected and balanced.

[0044] In the embodiment of the present invention, the positive lens A and the positive lens C may both be aspherical lenses, and the negative lens B may be a diffractive optical element. The diffractive element has a negative dispersion coefficient, which is exactly opposite to the dispersion coefficient of conventional materials and can correct chromatic aberration well.

[0045] In the embodiment of the present invention, the infrared optical structure formed by the positive lens A, the negative lens B and the positive lens C achieves the following optical indicators:

[0046] (1) Working band: 8um-12um;

[0047] (2) Focal length: f = 25.0 mm;

[0048] (3) Relative aperture D / f: 1 / 1.0

[0049] (4) Field of view: 2ω=34.48°;

[0050] (5) Distortion: <2%;

[0051] (6) Resolution: Can meet the requirements of QVGA / QVGA MAX and other models of infrared uncooled detectors;

[0052] (7) Maximum imaging target area of ​​the system: 15.80 mm;

[0053] (8) Total optical path length ≤ 40 mm, optical back intercept 9.85 mm.

[0054] In the embodiment of the present invention, the second surface of the positive lens A from left to right is an aspherical surface, the second surface of the negative lens B from left to right is a spherical surface, the first surface of the negative lens B from left to right is a diffraction surface, and both surfaces of the positive lens C are aspherical surfaces.

[0055] In the embodiment of the present invention, the positive lens A, the negative lens B and the positive lens C constitute a summary table of optical element parameters, as shown in the following Table 1, wherein S1, S2, S3, ... are the corresponding surface parameters of the positive lens A, the negative lens B and the positive lens C from left to right along the incident direction of the light, and the intervals are the center distances from one surface to the next surface:

[0056] Table 1

[0057]

[0058] Note: fn represents the curvature radius of positive lens A, negative lens B and positive lens C respectively, and n is 1, 2 and 3.

[0059] In the embodiment of the present invention, the aspheric surface satisfies the following formula:

[0060] Where Z is the height loss from the vertex of the aspheric surface when the aspheric surface reaches a position with a height of r along the optical axis;

[0061] c=1 / r, r represents the paraxial curvature radius of the mirror, and k is the cone coefficient;

[0062] A2, A4, A6, A8, A10, and A12 represent high-order aspheric coefficients.

[0063] The high-order aspheric coefficient table is shown in Table 2 below:

[0064] Table 2

[0065]

[0066] In the embodiment of the present invention, on the diffraction surface S3, the phase distribution function in Zemax = M(B1r2), the normalized radius is 9.475, and B1 = -35.2378789.

[0067] In an embodiment of the present invention, Figure 2-Figure 4 The MTF diagram of the image quality of the embodiment of the present invention is respectively the results of the system at room temperature, low temperature of -40 degrees Celsius and high temperature of 80 degrees Celsius. Figure 5 The performance diagram of the optical imaging lens of the first embodiment is shown, including the axial chromatic aberration diagram and the distortion curve diagram. Each chromatic aberration curve represents a wavelength. The horizontal axis is the distance of the image point from the image plane, and the vertical axis is the normalized aperture value. Generally, the closer the curve is to zero, the better the aberration correction of the lens is, and the better the performance of the lens is. It can be seen that the axial chromatic aberration of the first embodiment is less than 0.04mm. The lens has good imaging and meets customer requirements.

[0068] In the embodiment of the present invention, light rays are imaged on the detector target surface after passing through the positive lens A, the negative lens B and the positive lens C from left to right. The present invention has a simple structure and a reasonable design, can still achieve optical athermalization at high temperatures, has good stability to the temperature environment, and is highly practical.

[0069] In the embodiment of the present invention, the full image height is 15.80mm, and the large target surface that can match multiple types of detectors has obvious advantages. It can be applied to different types of detectors at the same time, meeting the different needs of the market. The large target surface provides usage space for different application fields, truly meeting the customer's usage requirements, and can be applicable to and solve the problem of excessively large tolerances in mass production of detectors.

[0070] Embodiment 2: Figures 6 to 10 As shown, a 25.0mm large target surface infrared optical athermal lens that can match multiple types of detectors is provided, and an infrared 8-12um band optical athermal lens with a diffraction surface is provided. In the lens optical system, a positive lens A, a negative lens B and a positive lens C are arranged in sequence from left to right along the incident direction of light. The air gap between the positive lens A and the negative lens B is 4.721mm, and the air gap between the negative lens B and the positive lens C is 5.273mm.

[0071] In the embodiment of the present invention, the material of the positive lens A is chalcogenide glass, and the materials of the negative lens B and the positive lens C are germanium (Ge), a common material for infrared lenses, and chalcogenide materials, respectively. Germanium is divided into single crystal germanium and polycrystalline germanium. Polycrystalline germanium has many impurities at its boundaries, which affects the non-uniformity of the refractive index. Therefore, single crystal germanium is preferred in this design.

[0072] Among them, the germanium (Ge) material used in the negative lens B applies diffraction technology, which not only reduces the cost of lens materials, but also achieves the purpose of eliminating thermal differences in the infrared optical system under high and low temperatures.

[0073] In the embodiment of the present invention, the focal length of the positive lens A is f1, the focal length of the negative lens B is f2, the focal length of the positive lens C is f3, and the focal length of the system consisting of the negative lens A, the negative lens B and the positive lens C is f, and the ratio thereof satisfies:

[0074] 1.4 <f1 / f<2.2;

[0075] -3.8 <f2 / f<-2.0;

[0076] 0.47 <f3 / f<1.61。

[0077] When the above ratio conditions are met, the aberration of the infrared system in the wavelength range of 8 to 12 um can be reasonably corrected and balanced.

[0078] In the embodiment of the present invention, the positive lens A and the positive lens C may both be aspherical lenses, and the negative lens B may be a diffractive optical element. The diffractive element has a negative dispersion coefficient, which is exactly opposite to the dispersion coefficient of conventional materials and can correct chromatic aberration well.

[0079] In the embodiment of the present invention, the infrared optical structure formed by the positive lens A, the negative lens B and the positive lens C also achieves the following optical indicators:

[0080] (1) Working band: 8um-12um;

[0081] (2) Focal length: f = 25.0 mm;

[0082] (3) Relative aperture D / f: 1 / 1.0

[0083] (4) Field of view: 2ω=34.48°;

[0084] (5) Distortion: <2%;

[0085] (6) Resolution: Can meet the requirements of QVGA / QVGA MAX and other models of infrared uncooled detectors;

[0086] (7) System maximum imaging target area: 15.80 mm.

[0087] (8) The total optical path length is ≤40 mm and the optical back intercept is greater than 8.5 mm.

[0088] On the basis of Example 1, in this Example 2, the positive lens A, the negative lens B and the positive lens C constitute a summary table of optical element parameters, as shown in Table 3, wherein S1, S2, S3, ... are the corresponding surface parameters of the positive lens A, the positive lens B and the positive lens C from left to right along the incident direction of the light, and the intervals are the center distances from the surface to the next surface:

[0089] Table 3

[0090]

[0091] Note: fn represents the curvature radius of positive lens A, negative lens B and positive lens C respectively, and n is 1, 2 and 3.

[0092] In the embodiment of the present invention, the aspheric surface satisfies the following formula:

[0093] Where Z is the height loss from the vertex of the aspheric surface when the aspheric surface reaches a position with a height of r along the optical axis;

[0094] c=1 / r, r represents the paraxial curvature radius of the mirror, and k is the cone coefficient;

[0095] A2, A4, A6, A8, A10, and A12 represent high-order aspheric coefficients.

[0096] The high-order aspheric coefficient table is shown in Table 4 below:

[0097] Table 4

[0098]

[0099] In the embodiment of the present invention, on the diffraction surface S3, the phase distribution function in Zemax = M(B1r2), the normalized radius is 8.5, and B1 = -30.568.

[0100] In an embodiment of the present invention, Figure 7-Figure 9 These are the image quality MTF diagrams of an embodiment of the present invention, which are the results of the system at room temperature, low temperature of -40 degrees Celsius, and high temperature of 80 degrees Celsius. The imaging is good and meets customer requirements.

[0101] Unless otherwise stated, if any technical solution disclosed in the present invention discloses a numerical range of the solution, then all disclosed numerical ranges are optimal parameter ranges, and any technician in the field should understand that the optimal numerical range of the solution is only a typical representative of the production effect of many feasible solutions. Since there are too many numerical values ​​to list one by one, the present invention only discloses some numerical values ​​to illustrate the technical solution of the present invention, and the numerical values ​​listed above cannot constitute a limitation on the scope of protection of the present invention.

[0102] In addition, unless otherwise stated, the terms used to indicate positional relationships or shapes in any of the technical solutions disclosed in the present invention include states or shapes that are approximate, similar, or close to them.

[0103] Any component provided by the present invention may be assembled from a plurality of separate components, or may be a separate component manufactured by an integral forming process.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, relevant technical personnel in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A 25.0 mm large target infrared optical athermal lens, characterized by: The lens optical system is provided with a positive lens A, a negative lens B and a positive lens C in sequence from left to right along the incident direction of light; The positive lens A, the negative lens B and the positive lens C constitute a summary table of optical element parameters, as shown in the following table: fn represents the curvature radius of the positive lens A, the negative lens B and the positive lens C respectively, and n is 1, 2 and 3.

2. A 25.0 mm large-target infrared optical athermal lens, wherein a positive lens A, a negative lens B and a positive lens C are arranged in sequence from left to right along the incident direction of light; The positive lens A, the negative lens B and the positive lens C constitute a summary table of optical element parameters, as shown in the following table: fn represents the curvature radius of the positive lens A, the negative lens B and the positive lens C respectively, and n is 1, 2 and 3.

3. An imaging method of a 25.0 mm large target infrared optical athermal lens, characterized in that: A 25.0 mm large-target infrared optical athermal lens as described in any one of claims 1-2 is used, and the following steps are performed: light is imaged from left to right after passing through positive lens A, negative lens B, positive lens C and image plane protection window.

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