A passive, athermalized long-wavelength infrared refraction-diffraction hybrid optical system

Abstract

This invention discloses a passive, athermalized long-wavelength infrared refractive-diffraction hybrid optical system, comprising a meniscus negative lens, a biconvex positive lens, a first meniscus positive lens, and a second meniscus positive lens arranged sequentially from the object plane to the image plane. The front and rear surfaces of the meniscus negative lens are aspherical; the front surface of the biconvex positive lens is aspherical, and the rear surface is spherical; the front surface of the first meniscus positive lens is a diffractive aspherical, and the rear surface is spherical; the front surface of the second meniscus positive lens is spherical, and the rear surface is aspherical. The passive, athermalized long-wavelength infrared refractive-diffraction hybrid optical system has a relative aperture of 1, a circular field of view of 100°, and a distortion of no more than 3%. This optical system achieves high resolution, a large relative aperture, a large field of view, and passive, athermalized optical performance. Furthermore, the optical system has a simple and compact structure, good manufacturability, is easy to manufacture, and has wide applicability.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a passive, calorimetric long-wave infrared refraction-diffraction hybrid optical system. Background Technology

[0002] In recent years, with the continuous development of infrared devices, in addition to their military applications such as night vision, guidance, and remote sensing, they have also been widely used in civilian fields such as vehicle driver assistance, medicine, temperature measurement, security monitoring, and food safety testing. Compared with cooled infrared devices, uncooled infrared devices not only have advantages such as small size, light weight, and low price, but their performance is also gradually improving. Currently, the highest resolution can reach 1920×1080, the smallest pixel is only 6μm, and the noise equivalent temperature difference is as low as 20mK. Therefore, uncooled infrared devices are gaining increasing market recognition. For civilian vehicle driver assistance infrared camera systems, the working environment is 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] Currently, there are five main types of calorimetric technologies for infrared optical systems: mechanical active, mechanical passive, electromechanical passive, hybrid, and optical passive. Among them, optical passive technology has the characteristics of simple structure, small size, light weight, no power supply required, and high reliability. It is very much in line with the requirements of miniaturization, light weight, and low cost of modern civilian optoelectronic payloads, and has therefore become the main approach to calorimetric elimination in infrared optical systems.

[0004] However, existing anechoic infrared optical systems have relatively small apertures, small field of view, large distortion, low resolution, and a narrow applicable temperature range, resulting in poor applicability. Summary of the Invention

[0005] This invention provides a passive, athermalized long-wavelength infrared refractive-diffraction hybrid optical system. This addresses the technical problems of existing athermalized infrared optical systems, such as relatively small aperture, small field of view, large distortion, and low resolution.

[0006] To achieve the above objectives, embodiments of the present invention provide an optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system, comprising a meniscus negative lens, a biconvex positive lens, a first meniscus positive lens, and a second meniscus positive lens arranged sequentially from the object plane to the image plane. The front and rear surfaces of the meniscus negative lens are both aspherical, the front surface of the biconvex positive lens is aspherical, and the rear surface of the biconvex positive lens is spherical. The front surface of the first meniscus positive lens is a diffractive aspherical, and the rear surface of the first meniscus positive lens is spherical. The front surface of the second meniscus positive lens is spherical, and the rear surface of the second meniscus positive lens is aspherical.

[0007] The relative aperture of the passive, athermalized long-wave infrared refractive-diffraction hybrid optical system is 1, the circular field of view is 100°, and the distortion is no greater than 3%.

[0008] Furthermore, the hybrid optical system has a focal length of 6.4mm, a circular field of view of 100°, and a total length of 25mm.

[0009] Optionally, the optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system also includes a protective glass for the detector and an image plane, wherein the protective glass for the detector is located on the side of the meniscus positive lens away from the meniscus negative lens, and the image plane is located on the side of the protective glass for the detector away from the meniscus positive lens.

[0010] Optionally, the meniscus negative lens and the first meniscus positive lens are made of germanium, while the biconvex positive lens and the second meniscus positive lens are made of chalcogenide glass IRG206.

[0011] Optionally, the distance between the front and rear surfaces 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 and rear surfaces 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 and rear surfaces 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 and rear surfaces 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.

[0012] Optionally, the maximum number of rings on the diffractive aspheric surface is 5, the groove depth is 3.33 μm, and the minimum ring spacing corresponding to the diffractive aspheric surface is 0.33 mm.

[0013] The present invention provides an optical passive athermalized long-wave infrared refraction-diffraction hybrid optical system, which has the following beneficial effects:

[0014] This optical system achieves high resolution, large relative aperture, large field of view, and passive, calorimetric optical properties by employing a rational optical system structure and appropriately combining aspherical and diffractive aspherical surfaces on different glass materials. Furthermore, the optical system is simple, compact, and easy to manufacture, making it widely applicable. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic diagram of the structure of the optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application;

[0017] Figure 2 A phase distribution diagram of a diffractive aspherical surface provided for an embodiment of this application;

[0018] Figure 3 MTF curve of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of -60°C;

[0019] Figure 4 MTF curve of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of +20°C;

[0020] Figure 5 MTF curve of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at +100°C;

[0021] Figure 6 A dot plot of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of -60°C;

[0022] Figure 7 A dot plot of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of +20°C;

[0023] Figure 8 A dot plot of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of +100°C;

[0024] Figure 9 Distortion curve of the optical passive calorimetric long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at +20°C;

[0025] Figure 10 The grid distortion diagram of the optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system provided in the embodiments of this application at a temperature of +20°C.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Meniscus negative lens; 2. Biconvex positive lens; 3. First meniscus positive lens; 4. Second meniscus positive lens; 5. Protective glass of the detector; 6. Image plane. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Please see Figure 1 This invention provides a passive, athermalized long-wave infrared refractive-diffraction 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 arranged sequentially from the object plane to the image plane. The front and rear surfaces of the meniscus negative lens 1 are both aspherical. The front surface of the biconvex positive lens 2 is aspherical, and the rear surface of the biconvex positive lens 2 is spherical. The front surface of the first meniscus positive lens 3 is a diffractive aspherical, and the rear surface of the first meniscus positive lens 3 is spherical. The front surface of the second meniscus positive lens 4 is spherical, and the rear surface of the second meniscus positive lens 4 is aspherical.

[0030] The relative aperture of the passive, athermalized long-wave infrared refractive-diffraction hybrid optical system is 1, the circular field of view is 100°, and the distortion is no greater than 3%.

[0031] Furthermore, the optical system has a focal length of 6.4mm, a relative aperture of 1, a circular field of view of 100°, distortion of no more than 3%, and a total length of 25mm. At a spatial frequency of 42lp / mm and a temperature range of -60℃ to +100℃, the MTF value for the 0 field of view is greater than 0.46, and the MTF value for the 1 field of view is greater than 0.2, achieving a passive, calorimetric optical design over a wide temperature range.

[0032] The specific parameters of the optical system are shown in Table 1 below.

[0033] Table 1

[0034]

[0035] This optical system achieves high resolution, large relative aperture, large field of view, and passive, calorimetric optical properties by employing a reasonable optical system structure and combining aspherical and diffractive aspherical surfaces on different glass materials. Furthermore, the optical system is simple, compact, and easy to manufacture, making it widely applicable.

[0036] Passive optical pyrography utilizes principles such as the cancellation of thermal expansion coefficients of optical and structural materials, the cancellation of temperature refractive index gradients, and the rational distribution of positive and negative optical power to achieve clear imaging at different temperatures. The optical system is not only simple in structure but also highly reliable. Based on aberration theory and the principles of passive optical pyrography, to simultaneously correct chromatic aberration, secondary spectral density, and pyrography, the following three equations must be satisfied:

[0037] Optical power allocation:

[0038] (1)

[0039] Color difference elimination:

[0040] (2)

[0041] Heat dissipation difference:

[0042] (3)

[0043] In the above formula: The height of the first paraxial ray in each lens group; The optical power of each lens group; The total optical power of the system; The dispersion factor of each optical element; It is the coefficient of photothermal expansion; The coefficient of linear expansion of the mechanical structure; This refers to the length of the mechanical structural component.

[0044] The temperature characteristics of optical components are expressed using the coefficient of photothermal expansion. The coefficient of photothermal expansion of a refractive lens is...

[0045] (4)

[0046] The coefficient of photothermal expansion of a diffractive lens is

[0047] (5)

[0048] In the above formula: dn / dt 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 temperature coefficient of refractive index of the component material; dn0 / dt is the temperature coefficient of refractive index of the medium in which the component is located;

[0049] As can be seen from equations (4) and (5), the temperature characteristics of a refracting lens are determined by the coefficient of thermal expansion and the refractive index of the material, while the temperature characteristics of a diffractive lens are determined only by the coefficient of thermal expansion and are independent of the temperature coefficient of refractive index. In addition, diffractive lenses have negative dispersion characteristics, and when properly matched with traditional lenses, they can achieve chromatic aberration reduction.

[0050] The expression for diffraction aspheric surfaces is:

[0051] (6)

[0052] In the formula, Z(r) is the axial distance from a point on the surface to the vertex; c is the curvature; r is the radial coordinate in the direction perpendicular to the optical axis; k is the quadratic curve constant; A is the fourth-order aspherical coefficient; B is the sixth-order aspherical 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.

[0053] In one possible embodiment, the optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system further includes a protective glass 5 for the detector and an image plane 6, wherein the protective glass 5 is located on the side of the second meniscus positive lens 4 away from the meniscus negative lens 1, and the image plane 6 is located on the side of the protective glass 5 for the detector away from the meniscus fourth positive lens 4.

[0054] 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 accompanying drawings; the detector only indicates that the light ultimately converges onto the image plane. Its main technical specifications are shown in Table 2 below.

[0055] Table 2

[0056]

[0057] In one possible embodiment, the negative meniscus lens 1 and the first positive meniscus lens 3 are made of germanium, and the biconvex positive lens 2 and the second positive meniscus lens 4 are made of chalcogenide glass IRG206.

[0058] Specifically, the meniscus negative lens 1 is made of germanium. On the one hand, germanium's high refractive index reduces aberrations. On the other hand, germanium is relatively hard, and as the first lens, a diamond-like carbon coating can be deposited on its outer surface to increase scratch resistance and better adapt to harsh weather conditions such as wind, sand, dust, rain, and snow, thereby improving the system's reliability. The first meniscus positive lens 3 is also made of germanium, and aspherical and diffractive surfaces are used on its front surface, increasing design freedom and further reducing thermal and chromatic aberrations, while making the system simpler and more compact. The biconvex positive lens 2 and the second meniscus positive lens 4 are both made of chalcogenide glass IRG206 to correct residual aberrations and distortions in the system. Ultimately, this ensures that the imaging quality of the hybrid refractive-diffractive optical system is close to the diffraction limit within a temperature range of -60℃ to +100℃, meeting the requirements of passive, anechoic optical design over a wide temperature range.

[0059] Furthermore, the temperature coefficient of refractive index of germanium is 396 × 10⁻⁶. -6 / ℃, when the temperature changes significantly, the image quality is affected by the change in the refractive index of the material; compared with germanium, the refractive index temperature coefficient of chalcogenide glass materials 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, this application uses chalcogenide glass for calorimetric design.

[0060] Furthermore, temperature changes also affect the air gap between lenses in the lens barrel; therefore, this application also considers the variation of air gap with temperature. Typically, the lens barrel is made of conventional aluminum alloy, which has a coefficient of thermal expansion of 23.6 × 10⁻⁶. -6 / ℃. The hybrid optical system described in this paper adopts a combination of negative optical power germanium, positive optical power chalcogenide glass IRG206, positive optical power germanium, and positive optical power chalcogenide glass IRG206 to achieve passive and calorimetric optical design. This structure can not only correct primary and higher-order aberrations well, but also more easily meet the requirements of large field of view design.

[0061] In one possible embodiment, referring to Table 1, the distance between the front and rear surfaces 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 and rear surfaces 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 and rear surfaces 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 and rear surfaces 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.

[0062] In one possible embodiment, the maximum number of rings on the diffractive aspheric surface is 5, the groove depth is 0.33 μm, and the minimum ring spacing corresponding to the diffractive aspheric surface is 0.33 mm. It can be machined using a diamond lathe. The phase distribution of the diffraction surface is specifically as follows: Figure 2 As shown.

[0063] Specifically, this embodiment generates arbitrary wavefronts by adjusting the number, position, and groove depth of the diffractive lenses, increasing design freedom. This not only makes it easier to achieve passive, calorimetric optical design, but also results in a simpler and more compact system structure.

[0064] In addition, refer to Figures 3-4 This application evaluates the optical passive athermalized long-wave infrared refractive-diffraction hybrid optical system by modulation transfer function (MTF) and speckle pattern. Figure 3 , Figure 4 and Figure 5 The figures show the MTF curves of the optical system at temperatures of -60℃, +20℃, and +100℃. It can be seen from the figures that at different temperatures, the MTF value at the characteristic frequency of 42 lp / mm at 0 field of view is greater than 0.46, and the MTF value at 1 field of view is greater than 0.2, approaching the diffraction limit. Figure 6 , Figure 7 and Figure 8 The figures show the dot plots of the optical system at temperatures of -60℃, +20℃, and +100℃. As can be seen from the figures, the root mean square (RMS) speckle diameter at each temperature is close to the pixel size of the detector. This indicates that the system achieves the requirements of a wide-temperature-range passive, calorimetric optical design and possesses good imaging quality.

[0065] The distortion value of a large field-of-view optical system is an important indicator for evaluating system performance. Figure 9 and Figure 10 The distortion values ​​of the optical system at +20℃ are given in different ways. The distortion values ​​of the optical system at 60℃ and +100℃ are basically the same as those at +20℃. As can be seen from the figure, 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 driver assistance systems with high distortion requirements, further increasing the applicability of the system.

[0066] This passively athermalized long-wave infrared refractive-diffractive hybrid optical system employs a combination of germanium and chalcogenide glass IRG206 infrared materials with aspherical and diffractive aspherical surfaces to achieve passive athermalization over a wide temperature range of -60℃ to +100℃. This allows for use in extremely cold and hot environments while maintaining excellent image quality. Furthermore, the system boasts a simple, compact structure, excellent manufacturability, and ease of fabrication, making it widely applicable in infrared camera systems for vehicle driver assistance, security monitoring, and food safety detection.

[0067] Finally, it should be noted that the above embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

[0068] Furthermore, although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

Claims

1. An optically passive athermalized long-wave infrared catadioptric hybrid optical system, characterized in that, It comprises four lenses arranged in order along the object plane to the image plane, and the four lenses are arranged in order according to the sequence of the meniscus negative lens (1), the biconvex positive lens (2), the first meniscus positive lens (3) and the second meniscus positive lens (4) and form a closed loop, the front and back surfaces of the meniscus negative lens (1) are aspherical, the front surface of the biconvex positive lens (2) is aspherical, the back surface of the biconvex positive lens (2) is spherical, the front surface of the first meniscus positive lens (3) is diffractive aspherical, the back surface of the first meniscus positive lens (3) is spherical, the front surface of the second meniscus positive lens (4) is spherical, and the back surface of the second meniscus positive lens (4) is aspherical; The relative aperture of the optical passive athermal long-wave infrared catadioptric hybrid optical system is 1, the circular field angle is 100°, and the distortion is not greater than 3%; The system further comprises a protective glass (5) of a detector, which is located on the side of the second meniscus positive lens (4) away from the meniscus negative lens (1); The meniscus negative lens (1) and the first meniscus positive lens (3) are made of germanium, and the biconvex positive lens (2) and the second meniscus positive lens (4) are made of chalcogenide glass IRG206; The front surface and the back surface of the meniscus negative lens (1) are spaced apart by 1.8 mm, the back surface of the meniscus negative lens (1) and the front surface of the biconvex positive lens (2) are spaced apart by 2.8 mm, the front surface and the back surface of the biconvex positive lens (2) are spaced apart by 3.1 mm, the back surface of the biconvex positive lens (2) and the front surface of the first meniscus positive lens (3) are spaced apart by 2.7 mm, the front surface and the back surface of the first meniscus positive lens (3) are spaced apart by 2.2 mm, the back surface of the first meniscus positive lens (3) and the front surface of the second meniscus positive lens (4) are spaced apart by 3.3 mm, the front surface and the back surface of the second meniscus positive lens (4) are spaced apart by 3.2 mm, and the back surface of the second meniscus positive lens (4) and the protective glass (5) of the detector are spaced apart by 6 mm; The range of the curvature radius R of the image side surface of the meniscus negative lens (1) is 10 < R < 30 mm, and the range of the curvature radius R of the object side surface of the meniscus negative lens (1) is 30 < R < 50 mm; The range of the curvature radius R of the object side surface of the biconvex positive lens (2) is 20 < R < 40 mm, and the range of the curvature radius R of the image side surface of the meniscus negative lens (1) is -50 < R < -100 mm; The range of the curvature radius R of the object side surface of the first meniscus positive lens (4) is -25 < R < -5 mm, and the range of the curvature radius R of the image side surface of the meniscus negative lens (1) is -30 < R < -10 mm; The range of the curvature radius R of the object side surface of the second meniscus positive lens (4) is -40 < R < -20 mm, and the range of the curvature radius R of the image side surface of the meniscus negative lens (1) is -30 < R < -10 mm.

2. The optically passive athermalized long-wave infrared catadioptric hybrid optical system of claim 1, wherein, Further comprising: An image plane (6) located on the side of the protective glass (5) of the detector away from the second meniscus positive lens (4).

3. The optically passive athermalized long-wave infrared catadioptric hybrid optical system of claim 1, wherein, The diffraction aspheric surface has 5 rings of maximum annular zones, a groove depth of 3.33 μm, and a minimum annular zone interval of 0.33 mm. The diffraction aspheric surface has 5 rings of maximum annular zones, a groove depth of 3.33 μm, and a minimum annular zone interval of 0.33 mm.

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