Optical passive athermalization long-wave infrared refractive-diffractive hybrid optical system

Abstract

The invention discloses an optical passive athermalization long-wave infrared refractive-diffractive hybrid optical system which comprises a meniscus negative lens, a biconvex positive lens, a first meniscus positive lens and a second meniscus positive lens which are sequentially arranged from an object plane to an image plane, the front surface and the rear surface of the meniscus negative lens adopt aspheric surfaces, the front surface of the biconvex positive lens adopts an aspheric surface, and the rear surface of the biconvex positive lens adopts an aspheric surface. The rear surface of the biconvex positive lens adopts a spherical surface, the front surface of the first meniscus positive lens adopts a diffraction aspheric surface, the rear surface of the first meniscus positive lens adopts a spherical surface, the front surface of the second meniscus positive lens adopts a spherical surface, and the rear surface of the second meniscus positive lens adopts an aspheric surface; the relative aperture of the optical passive athermalization long-wave infrared refractive-diffractive hybrid optical system is 1, the circular field angle is 100 degrees, and the distortion is not greater than 3%. The optical system realizes the functions of high resolution, large relative aperture, large field of view, optical passive athermalization and the like. In addition, the optical system is simple and compact in structure, good in manufacturability, easy to process and wide in applicability.

Description

Technical Field

[0001] The invention relates to the field of optical technology, and in particular to an optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system. Background Art

[0002] In recent years, with the continuous development of infrared devices, in addition to its military applications such as night vision, guidance, and remote sensing, it has also been widely used in civilian fields such as vehicle assisted driving, medicine, temperature measurement, security monitoring, and food safety testing. Compared with cooled infrared devices, uncooled infrared devices not only have the advantages of small size, light weight, and low price, but also the performance of the devices is gradually improving. At present, the resolution can reach up to 1920×1080, the minimum pixel is only 6μm, and the noise equivalent temperature difference is as low as 20mk. Therefore, uncooled infrared devices are increasingly recognized by the market. For civilian vehicle assisted driving infrared camera systems, the working environment conditions are extremely complex and harsh. Drastic temperature changes will cause changes in the curvature, thickness, and refractive index of the infrared optical system lens. If there are no subsequent compensation measures, these factors will often seriously affect the performance of the optical system, thereby reducing the performance of the entire system.

[0003] At present, there are five main athermalization technologies for infrared optical systems: mechanical active, mechanical passive, electromechanical passive, hybrid and optical passive. Among them, the optical passive type has the characteristics of simple structure, small size, light weight, no power supply and good reliability. It is in line with the requirements of miniaturization, lightweight and low cost of modern civilian optoelectronic payloads, and thus has become the main way to eliminate thermal differences in infrared optical systems.

[0004] However, existing athermalized infrared optical systems have relatively small apertures, small field of view angles, large distortion, low resolution, and a narrow athermalization temperature range, so their applicability is poor. Summary of the invention

[0005] The present invention provides an optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system to solve the technical problems of the prior art athermalized infrared optical system such as small relative aperture, small field of view, large distortion and low resolution.

[0006] To achieve the above objectives, an embodiment of the present invention provides an optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system, comprising a meniscus negative lens, a biconvex positive lens, a first meniscus positive lens, and a second meniscus positive lens, which are sequentially arranged from an object plane to an image plane, the front and rear surfaces of the meniscus negative lens are both aspherical, the front surface of the biconvex positive lens is an aspherical, the rear surface of the biconvex positive lens is a spherical, the front surface of the first meniscus positive lens is a diffractive aspherical, the rear surface of the first meniscus positive lens is a spherical, the front surface of the second meniscus positive lens is a spherical, and the rear surface of the second meniscus positive lens is an aspherical; The relative aperture of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system is 1, the circular field of view is 100°, and the distortion is no more than 3%.

[0007] Furthermore, the hybrid optical system has a focal length of 6.4 mm, a circular field of view of 100°, and a total length of 25 mm.

[0008] Optionally, the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system also includes a protective glass and an image plane of the detector, wherein the protective glass of the detector is located on a side of the meniscus positive lens away from the meniscus negative lens, and the image plane is located on a side of the protective glass of the detector away from the meniscus positive lens.

[0009] Optionally, the meniscus negative lens and the first meniscus positive lens are made of germanium material, and the double convex positive lens and the second meniscus positive lens are made of chalcogenide glass IRG206.

[0010] Optionally, the distance between the front surface and the rear surface of the meniscus negative lens is 1.8 mm, the distance between the rear surface of the meniscus negative lens and the front surface of the biconvex positive lens is 2.8 mm, the distance between the front surface and the rear surface of the biconvex positive lens is 3.1 mm, the distance between the rear surface of the biconvex positive lens and the front surface of the first meniscus positive lens is 2.7 mm, the distance between the front surface and the rear surface of the first meniscus positive lens is 2.2 mm, the distance between the rear surface of the first meniscus positive lens and the front surface of the second meniscus positive lens is 3.3 mm, the distance between the front surface and the rear surface of the second meniscus positive lens is 3.2 mm, and the distance between the rear surface of the second meniscus positive lens and the protective glass of the detector is 6 mm.

[0011] Optionally, the maximum number of ring zones of the diffractive aspheric surface is 5, the groove depth is 3.33 μm, and the minimum ring zone interval corresponding to the diffractive aspheric surface is 0.33 mm.

[0012] The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided by the present invention has the following beneficial effects: The optical system adopts a reasonable optical system structure and reasonably matches aspheric surfaces and diffractive aspheric surfaces on different glass materials, thereby achieving high resolution, large relative aperture, large field of view, and optical passive athermalization. In addition, the optical system has a simple and compact structure, good processability, is easy to process, and has a wide range of applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 A schematic diagram of the structure of an optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in an embodiment of the present application; Figure 2 A phase distribution diagram of a diffractive aspheric surface provided in an embodiment of the present application; Figure 3 The MTF curve of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in the embodiment of the present application at a temperature of -60°C; Figure 4 The MTF curve of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in the embodiment of the present application at a temperature of +20°C; Figure 5 The MTF curve of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in the embodiment of the present application at a temperature of +100°C; Figure 6 A point diagram of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in an embodiment of the present application at a temperature of -60°C; Figure 7 A point diagram of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in an embodiment of the present application at a temperature of +20°C; Figure 8 A point diagram of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in an embodiment of the present application at a temperature of +100°C; Fig. 9 The distortion curve of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in the embodiment of the present application at a temperature of +20°C; Fig.10 This is a grid distortion diagram of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system provided in an embodiment of the present application at a temperature of +20°C.

[0015] Description of reference numerals: 1. Meniscus negative lens; 2. Double convex positive lens; 3. First meniscus positive lens; 4. Second meniscus positive lens; 5. Protective glass of the detector; 6. Image plane. DETAILED DESCRIPTION

[0016] 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.

[0017] See also Figure 1The present invention provides an optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system, comprising a meniscus negative lens 1, a biconvex positive lens 2, a first meniscus positive lens 3, and a second meniscus positive lens 4, which are arranged in sequence from an object plane to an image plane, wherein the front and rear surfaces of the meniscus negative lens 1 are both aspherical, the front surface of the biconvex positive lens 2 is an aspherical, the rear surface of the biconvex positive lens 2 is a spherical, the front surface of the first meniscus positive lens 3 is a diffractive aspherical, the rear surface of the first meniscus positive lens 3 is a spherical, the front surface of the second meniscus positive lens 4 is a spherical, and the rear surface of the second meniscus positive lens 4 is an aspherical; The relative aperture of the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system is 1, the circular field of view is 100°, and the distortion is no more than 3%.

[0018] Furthermore, the optical system has a focal length of 6.4mm, a relative aperture of 1, a circular field of view of 100°, a distortion of no more than 3%, and a total length of 25mm. When the spatial frequency is 42lp / mm and the temperature is within the range of -60℃~+100℃, the MTF value of the 0 field of view is greater than 0.46, and the MTF value of the 1 field of view is greater than 0.2, realizing an optical passive athermal design within a wide temperature range.

[0019] The specific parameters of the optical system are shown in Table 1.

[0020] Table 1

[0021] The optical system adopts a reasonable optical system structure and reasonably matches aspheric surfaces and diffractive aspheric surfaces on the above-mentioned different glass materials, thereby achieving functions such as high resolution, large relative aperture, large field of view, and optical passive athermalization. In addition, the optical system has a simple and compact structure, good processability, is easy to process, and has a wide range of applicability.

[0022] Optical passive athermal design uses the principles of offsetting the thermal expansion coefficients of optical and structural materials, offsetting the temperature refractive index gradients, and reasonable distribution of positive and negative optical powers to achieve clear imaging at different temperatures. The optical system is not only simple in structure, but also reliable. According to aberration theory and the principle of optical passive athermal design, if chromatic aberration, secondary spectrum and athermalization are to be corrected simultaneously, the following three equations need to be satisfied at the same time: Power distribution: (1) Achromatic: (2) Heat elimination: (3) In the above formula: is the height of the first paraxial ray in each lens group; is the focal power of each lens group; is the total optical power of the system; is the dispersion factor of each optical element; is the coefficient of photothermal expansion; is the linear expansion coefficient of the mechanical structure; is the length of the mechanical structure.

[0023] The temperature characteristics of optical elements are expressed by the thermal expansion coefficient. The thermal expansion coefficient of a refractive lens is (4) The optical thermal expansion coefficient of the diffractive lens is (5) In the above formula: is the linear expansion coefficient of the component material; n is the refractive index of the component material; n0 is the refractive index of the medium in which the component is located; dn / dt is the refractive index temperature coefficient of the component material; dn0 / dt is the refractive index temperature coefficient of the medium in which the component is located; From equations (4) and (5), it can be seen that the temperature characteristics of the refractive lens are determined by the expansion coefficient of the material and the refractive index coefficient of the material, while the temperature characteristics of the diffractive lens are only determined by the expansion coefficient of the material and have nothing to do with the refractive index temperature coefficient of the material. In addition, the diffractive lens has negative dispersion characteristics, which is reasonably matched with the traditional lens and can achieve achromatic ability.

[0024] The expression of diffraction aspheric surface is (6) Where Z(r) is the distance from the point on the surface to the vertex along the axis; c is the curvature; r is the radial coordinate in the direction perpendicular to the optical axis; k is the quadratic constant; A is the fourth-order aspheric coefficient; B is the sixth-order aspheric coefficient; HOR is the diffraction order; C1 and C2 are the diffraction surface coefficients; λ is the design center wavelength; and n is the lens refractive index.

[0025] In a possible embodiment, the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system also includes a protective glass 5 and an image plane 6 of the detector, wherein the protective glass 5 of the detector is located on a side of the second meniscus positive lens 4 away from the meniscus negative lens 1, and the image plane 6 is located on a side of the protective glass 5 of the detector away from the fourth meniscus positive lens 4.

[0026] The detector is a 1024×768 uncooled vanadium oxide detector with a pixel size of 12μm×12μm. It should be noted that the detector is not shown in the drawings of this application. The detector only indicates that the light finally converges to the image plane. Its main technical indicators are shown in Table 2 below.

[0027] Table 2

[0028] In a possible embodiment, the meniscus negative lens 1 and the first meniscus positive lens 3 are made of germanium material, and the biconvex positive lens 2 and the second meniscus positive lens 4 are made of chalcogenide glass IRG206.

[0029] Specifically, the material of the meniscus negative lens 1 is germanium. On the one hand, the high refractive index of germanium is used to reduce aberrations. On the other hand, germanium material is relatively hard. As the first lens, a diamond-like film can be coated on the outer surface to increase the scratch resistance level, and better adapt to severe wind, sand, smoke, dust, rain and snow weather, thereby improving the reliability of the system; the material of the first meniscus positive lens 3 is germanium, and aspheric and diffractive surfaces are used on the front surface, which increases the design freedom, further reduces the thermal difference and chromatic aberration of the system, and makes the system simpler and more compact; the double convex positive lens 2 and the second meniscus positive lens 4 are both made of chalcogenide glass IRG206 to correct the residual aberration and distortion of the system, ultimately ensuring that the temperature of the refractive-diffractive hybrid optical system is in the range of -60℃~+100℃, and the imaging quality is close to the diffraction limit, meeting the optical passive athermal design within a wide temperature range.

[0030] Furthermore, the temperature coefficient of refractive index of germanium is 396×10 -6 / ℃. When the temperature changes greatly, the imaging quality is affected by the change of the material's refractive index. Compared with germanium, the refractive index temperature coefficient of chalcogenide glass material is about 1 / 10 of that of germanium, and the refractive index temperature coefficient of IRG206 is only 32×10 -6 / ℃, so the optical thermal difference coefficient caused by using chalcogenide glass will be smaller. At the same time, chalcogenide glass has the characteristics of wide wavelength transmission range and low cost. Therefore, the present application uses chalcogenide glass for athermal design.

[0031] In addition, temperature changes will also affect the air gap between lenses in the lens barrel. Therefore, the present application also considers the change of air gap with temperature. Usually, the lens barrel is made of conventional aluminum alloy material, and its thermal expansion coefficient is 23.6×10 -6 / ℃. The hybrid refractive optical system in this paper adopts the combination of negative optical power germanium, positive optical power chalcogenide glass IRG206, positive optical power germanium and positive optical power chalcogenide glass IRG206 to realize the optical passive athermal design. This structural form can not only better correct primary and higher-order aberrations, but also can more easily achieve the design requirements of large field of view.

[0032] In a possible embodiment, referring to Table 1, the distance between the front surface and the rear surface of the meniscus negative lens 1 is 1.8 mm, the distance between the rear surface of the meniscus negative lens 1 and the front surface of the biconvex positive lens 2 is 2.8 mm, the distance between the front surface and the rear surface of the biconvex positive lens 2 is 3.1 mm, the distance between the rear surface of the biconvex positive lens 2 and the front surface of the first meniscus positive lens 3 is 2.7 mm, the distance between the front surface and the rear surface of the first meniscus positive lens 3 is 2.2 mm, the distance between the rear surface of the first meniscus positive lens 3 and the front surface of the second meniscus positive lens 4 is 3.3 mm, the distance between the front surface and the rear surface of the second meniscus positive lens 4 is 3.2 mm, and the distance between the rear surface of the second meniscus positive lens 4 and the protective glass of the detector is 6 mm.

[0033] In a possible embodiment, the maximum number of rings of the diffractive aspheric surface is 5, the groove depth is 0.33 μm, and the minimum ring interval corresponding to the diffractive aspheric surface is 0.33 mm, which can be processed by a diamond lathe. The phase distribution of the diffractive surface is as follows: Figure 2 shown.

[0034] Specifically, this embodiment generates arbitrary wavefronts by adjusting the number, position, and groove depth of the diffractive lens, thereby increasing the degree of freedom in design. This not only makes it easier to achieve optical passive athermal design, but also makes the system structure simpler and more compact.

[0035] In addition, reference Figure 3-Figure 4 In this application, the optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system is evaluated by modulation transfer function (MTF) and diffuse speckle. Figure 3 , Figure 4 and Figure 5 The MTF curves of the optical system at -60℃, +20℃, and +100℃ are shown. It can be seen from the figure that the MTF values ​​of 0 field of view at the characteristic frequency of 42lp / mm at different temperatures are all greater than 0.46, and the MTF values ​​of 1 field of view are all greater than 0.2, which are close to the diffraction limit; Figure 6 , Figure 7 and Figure 8 The spot diagrams are respectively for the optical system at -60℃, +20℃, and +100℃. As can be seen from the figure, the root mean square diffuse spot diameter at different temperatures is close to the pixel size of the detector. This shows that the system has achieved the requirements of optical passive athermalization design in a wide temperature range and has good imaging quality.

[0036] The distortion value of a large field of view optical system is an important indicator to measure the system performance. Fig. 9 and Fig.10The distortion value of the optical system at +20℃ is given in different expressions. The distortion values ​​of the optical system at 60℃ and +100℃ are basically consistent with those at +20℃. It can be seen from the figure that the maximum distortion value of the full field of view is 3%, which can effectively meet the needs of different applications, especially in pure vision vehicle assisted driving systems with higher distortion requirements, further increasing the applicability of the system.

[0037] The optical passive athermalization long-wave infrared refractive-diffractive hybrid optical system uses two infrared materials, germanium and chalcogenide glass IRG206, and a combination of aspheric and diffractive aspheric surfaces to achieve optical passive athermalization in a wide temperature range of -60°C to +100°C. It can be used in harsh working environments of extreme cold and extreme heat with good imaging quality. In addition, the optical system has a simple and compact structure, good processability, and is easy to process. It can be widely used in infrared camera systems such as vehicle assisted driving, security monitoring, and food safety testing.

[0038] Finally, it should be noted that the above embodiments are only specific implementation methods of the present application, which are used to illustrate the technical solutions of the present application, rather than to limit them. The protection scope of the present application is not limited thereto. Although the present application is described in detail with reference to the above embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above embodiments within the technical scope disclosed in the present application, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes 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 application, and should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

[0039] In addition, although the operations of the method of the present application are described in a specific order in the drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

Claims

1. An optically passive athermalized long-wave infrared refractive-diffractive hybrid optical system, It is characterized in that The invention comprises a meniscus negative lens (1), a biconvex positive lens (2), a first meniscus positive lens (3) and a second meniscus positive lens (4) which are arranged in sequence from the object plane to the image plane, wherein the front and rear surfaces of the meniscus negative lens (1) are both aspherical surfaces, the front surface of the biconvex positive lens (2) is an aspherical surface, the rear surface of the biconvex positive lens (2) is a spherical surface, the front surface of the first meniscus positive lens (3) is a diffractive aspherical surface, the rear surface of the first meniscus positive lens (3) is a spherical surface, the front surface of the second meniscus positive lens (4) is a spherical surface, and the rear surface of the second meniscus positive lens (4) is an aspherical surface; The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system has a relative aperture of 1, a circular field angle of 100°, and a distortion of no more than 3%.

2. The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system according to claim 1, It is characterized in that Also includes: A protective glass (5) of the detector is located on a side of the second meniscus positive lens (4) away from the meniscus negative lens (1); An image plane (6) is located on a side of the protective glass (5) of the detector away from the second meniscus positive lens (4).

3. The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system according to claim 1, It is characterized in that The meniscus negative lens (1) and the first meniscus positive lens (3) are made of germanium material, and the double convex positive lens (2) and the second meniscus positive lens (4) are made of chalcogenide glass IRG206.

4. The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system according to claim 1, It is characterized in that The distance between the front surface and the rear surface of the meniscus negative lens (1) is 1.8 mm, the distance between the rear surface of the meniscus negative lens (1) and the front surface of the biconvex positive lens (2) is 2.8 mm, the distance between the front surface and the rear surface of the biconvex positive lens (2) is 3.1 mm, the distance between the rear surface of the biconvex positive lens (2) and the front surface of the first meniscus positive lens (3) is 2.7 mm, the distance between the front surface and the rear surface of the first meniscus positive lens (3) is 2.2 mm, the distance between the rear surface of the first meniscus positive lens (3) and the front surface of the second meniscus positive lens (4) is 3.3 mm, the distance between the front surface and the rear surface of the second meniscus positive lens (4) is 3.2 mm, and the distance between the rear surface of the second meniscus positive lens (4) and the protective glass of the detector is 6 mm.

5. The optical passive athermalized long-wave infrared refractive-diffractive hybrid optical system according to claim 1, It is characterized in that The maximum number of ring zones of the diffractive aspheric surface is 5, the groove depth is 3.33 μm, and the minimum ring zone interval corresponding to the diffractive aspheric surface is 0.33 mm.

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