Light unmanned aerial vehicle carried long-wave infrared athermalization optical system and design method thereof

Abstract

The invention provides a light unmanned aerial vehicle carried long-wave infrared athermalization optical system and a design method thereof, and relates to the technical field of optical instruments, and the optical system comprises an object plane, a first lens, a diaphragm, a second lens, a third lens and a detector image plane which are sequentially arranged from a light source to a detector in the propagation direction of incident light; the first lens and the third lens are meniscus negative lenses with negative focal power, and the second lens is a biconvex positive lens with positive focal power; wherein the front surface of the first lens is a diffraction surface, and the rear surface of the first lens is a spherical surface; the front surface of the second lens is an even-order aspheric surface, and the rear surface is a spherical surface; the front and rear surfaces of the third lens are spherical surfaces. According to the optical system, the high resolution, the large relative aperture and the optical passive athermalization function are achieved, light weight and non-toxicity of materials can be achieved under the condition that the large aperture is considered, the flight time of the unmanned aerial vehicle is prolonged, the resolution is improved, and the adaptive environment temperature is high.

Description

Technical Field

[0001] The present invention relates to the technical field of optical instruments, and particularly to a lightweight unmanned aerial vehicle (UAV) - carried long - wave infrared athermalized optical system and its design method. Background Art

[0002] The lightweight UAV - carried athermalized long - wave infrared lens has night vision function and can quickly identify targets in foggy days. However, the traditional airborne long - wave infrared lens has few requirements for athermalization, large system volume and weight, complex structure, and is greatly affected by temperature and atmospheric pressure. The lightweight UAV - carried athermalized long - wave infrared lens system reduces the volume and mass of the system, and can also improve the endurance and flight time.

[0003] Currently, there are three commonly used athermalization design methods: electromechanical active type, mechanical passive type, and optical passive type. Among them, the electromechanical active type and electromechanical passive type methods cannot correct aberration imbalance, have complex structures, high requirements for processing, installation and adjustment, and are not suitable for lightweight design. For example, the Chinese patent with the authorization announcement number CN103018884B discloses a technical solution named "a long - wave infrared optical system". This solution provides an idea of achieving a large relative aperture and miniaturization within a large field of view with two lenses, but the focal length is only 9 mm and there is no thermal aberration correction. For another example, the Chinese patent with the publication number CN118884685A discloses a technical solution named "a long - wave infrared continuous zoom optical system". This solution realizes the design of a long - wave infrared zoom lens. The system uses 5 lenses, has a complex structure, and is large in both weight and volume.

[0004] Therefore, how to develop a lightweight UAV - carried long - wave infrared athermalized optical system has become an important research direction for those skilled in the art. Summary of the Invention

[0005] In view of this, in order to solve the above - mentioned deficiencies. The purpose of the present invention is to provide a lightweight UAV - carried long - wave infrared athermalized optical system and its design method, which can achieve lightweight and non - toxic materials while taking into account large aperture conditions, and improve the flight time, resolution, and strong adaptability to environmental temperature of the UAV.

[0006] To achieve the above - mentioned purpose, the present invention provides the following technical solutions: For the above purposes, in a first aspect, the present invention provides a lightweight unmanned aerial vehicle (UAV)-mounted long-wave infrared athermalized optical system, including an object surface, a first lens, a diaphragm, a second lens, a third lens, and a detector image surface arranged in sequence from the light source to the detector along the propagation direction of the incident light; the first lens and the third lens are meniscus negative lenses with negative optical power, and the second lens is a biconvex positive lens with positive optical power; wherein, the front surface of the first lens is a diffractive surface and the rear surface is a spherical surface; the front surface of the second lens is an even aspherical surface and the rear surface is a spherical surface; the front and rear surfaces of the third lens are both spherical surfaces.

[0007] As a further aspect of the present invention, the materials of the first lens and the third lens are IRG25; the material of the second lens is zinc sulfide crystal (ZnS).

[0008] As a further aspect of the present invention, the focal length of the optical system is 32, the F-number of the optical system is [F-number value not provided in the original], the field of view angle is 12°, and it is adapted to a long-wave infrared detector with 640×512 pixels and 12 μm.

[0009] As a further aspect of the present invention, the thicknesses of the lenses and the air gaps in the first lens, the second lens, and the third lens in the optical system are in the ranges of: The thickness of the first lens is 7.9 mm to 8.2 mm, the air gap between the rear surface of the first lens and the front surface of the diaphragm is 15.1 mm to 15.5 mm, and the air gap between the rear surface of the diaphragm and the front surface of the second lens is 14.8 mm to 15.1 mm; The thickness of the second lens is 7.3 mm to 7.9 mm, and the air gap between the rear surface of the second lens and the front surface of the third lens is 2.8 mm to 3.1 mm; The thickness of the third lens is 4.8 mm to 5.1 mm, and the air gap between the rear surface of the third lens and the detector image surface is 8.9 mm to 9.3 mm.

[0010] As a further aspect of the present invention, the radii of curvature of the front and rear surfaces of the first lens are 48.9 mm to 49.1 mm and 61.7 mm to 62.8 mm respectively; the radii of curvature of the front and rear surfaces of the third lens are 20.4 mm to 20.5 mm and 12.2 mm to 12.8 mm respectively.

[0011] As a further aspect of the present invention, the surface type parameters of the diffractive surface on the front surface of the first lens are: The range of the fourth-order coefficient: -1.05×10 -6 ~ -1.04×10 -6 ; The range of the sixth-order coefficient: -7.15×10 -10 ~ -7.13×10 -10 ; Range of the coefficient of the eighth-order term: -2.58×10 -12 ~-2.55×10 -12 .

[0012] As a further solution of the present invention, in the surface equation of the even aspheric surface on the front surface of the second lens, the conic coefficient k is equal to 1.

[0013] As a further solution of the present invention, an antireflection film is coated on the rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens to eliminate stray light.

[0014] Second, the present invention also provides a design method for a lightweight unmanned aerial vehicle carrying an uncooled long-wave infrared optical system, including the following steps: S1. Gaussian design: Determine the numerical aperture of the optical system according to the resolution and the lateral magnification. S2. Athermal design: Solve the system of equations by combining the conditions of the total optical power, achromatism, and athermalization. S3. Initial structure design: Based on the athermalization conditions, use the PW method or the tangent calculation method to determine the lens curvature radius, thickness, and spacing. S4. Optimal design of the system structure: Set the evaluation function, and use optical software to optimize the even aspheric coefficient and the diffractive surface parameters to obtain a lightweight unmanned aerial vehicle carrying an uncooled long-wave infrared optical system that can achieve clear imaging at -60°C to 100°C.

[0015] As a further solution of the present invention, the lateral magnification is calculated based on the detector size and the object field of view:

[0016] The resolution is calculated according to the working central wavelength and the index value:

[0017] where represents the lateral magnification; represents the image height; represents the object height; represents the resolution; represents the working central wavelength; represents the numerical aperture value.

[0018] As a further solution of the present invention, the condition of the total optical power in the athermal design is:

[0019] The condition of achromatism is:

[0020] The condition for eliminating thermal difference is as follows:

[0021] In the formula: is the Abbe number of the i-th lens; is the linear expansion coefficient of the barrel material; represents the first lens; represents the last lens; represents the optical power of the i-th lens; represents the total optical power; represents the partial derivative formula of the optical power of the i-th lens with respect to the focal length displacement at temperature T; represents the temperature focal length displacement number.

[0022] As a further solution of the present invention, when optimizing the design of the system structure, an evaluation function is set according to the requirements of the working distance, the shape of the components, the temperature, and the quality; among them, the even aspheric equation is:

[0024] wherein, R is the surface vertex radius, K is the conic coefficient, A, B, and C are the polynomial coefficients of the even aspheric surface, y is the radial distance from the optical axis, and z is the sag value corresponding to the y value.

[0025] Compared with the prior art, a lightweight unmanned aerial vehicle-mounted long-wave infrared athermalized optical system proposed by the present invention has the following beneficial effects: 1. The first lens, the second lens, and the third lens of the present invention are combined with materials of different refractive indices, and are combined with even aspheric surfaces and diffractive surfaces, reducing the number of lenses, simplifying the structure, reducing the weight, and lowering the cost; by distributing the focal lengths and refractive index materials of the first lens, the second lens, and the third lens, an efficient material combination is achieved, and aberration correction is performed by using rotationally symmetric even aspheric surfaces and diffractive surfaces, thereby achieving high imaging quality.

[0026] 2. The first lens, the second lens, and the third lens of the present invention are made of different materials respectively. When the ambient temperature changes, the refractive indices of the lenses change to different degrees, which can compensate for the offset of the focal plane caused by temperature changes, thereby achieving optical athermalization; by selecting optical glass materials with high refractive index and low dispersion, and combining with rotationally symmetric even aspheric surfaces, an athermalized design of an optical system with a large aperture is jointly achieved, and clear imaging can be achieved within the temperature range of -60°C to 100°C. Compared with traditional athermalized systems, the number of lenses is reduced, and the use of diffractive surfaces simplifies the structure, reduces the weight, and at the same time achieves the purpose of making the optical system lightweight and miniaturized, and reduces the cost.

[0027] 3. The lightweight unmanned aerial vehicle (UAV)-borne long-wave infrared athermalized optical system provided by the present invention has a relatively wide tolerance limit. It can ensure that 90% of the samples in the amplitude modulation transfer function are greater than 33% within a radius, thickness, and eccentricity range of 0.02 mm, and the difference from the best image quality is 0.02%. Moreover, an antireflection film is coated on the rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens, which can effectively eliminate stray light.

[0028] These aspects or other aspects of the present application will be more clearly understood in the following description of the embodiments. It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and do not limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the related art, the following briefly introduces the drawings required for the description of the exemplary embodiments or the related art. The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation to the present invention. In the drawings: Figure 1 It is a schematic diagram of the optical structure layout of the long-wave infrared athermalized lens optical system carried by the lightweight UAV provided by the present invention.

[0030] Figure 2 It is a graph of the amplitude modulation transfer function at -60°C of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0031] Figure 3 It is a spot diagram at -60°C of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0032] Figure 4 It is a graph of the amplitude modulation transfer function at 20°C of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0033] Figure 5 It is a spot diagram at 20°C of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0034] Figure 6 It is a graph of the amplitude modulation transfer function at 100°C of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0035] Figure 7 It is a spot diagram at 100°C of the field of the long-wave infrared athermalized optical system carried by the lightweight UAV provided by the present invention.

[0036] Figure 8Field curvature diagram of the athermalized long-wave infrared optical system carried by the light UAV provided by the present invention.

[0037] Figure 9 Distortion diagram of the athermalized long-wave infrared optical system carried by the light UAV provided by the present invention.

[0038] Figure 10 Initial stray light analysis diagram of the athermalized long-wave infrared optical system carried by the light UAV provided by the present invention.

[0039] Figure 11 Coating stray light analysis diagram of the athermalized long-wave infrared optical system carried by the light UAV provided by the present invention.

[0040] Reference numerals: 1, object surface; 2, first lens; 3, aperture; 4, second lens; 5, third lens; 6, detector image surface. Detailed implementation manners

[0041] Next, in combination with the accompanying drawings and specific implementation manners, the present application will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0042] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the embodiments of the present invention in detail with reference to specific embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0043] It should be noted that all the expressions using "first" and "second" in the embodiments of the present invention are used to distinguish two non-identical entities or non-identical parameters with the same name. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units inherently includes other steps or units.

[0044] Next, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0045] The flowcharts shown in the accompanying drawings are only illustrative examples, and do not necessarily include all contents and operations / steps, nor do they necessarily need to be executed in the described order. For example, some operations / steps can be decomposed, combined, or partially merged, so the actual execution order may change according to the actual situation.

[0046] The following will describe in detail some embodiments of the present application with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0047] See Figures 1 to 11 As shown, an embodiment of the present invention provides a lightweight unmanned aerial vehicle (UAV) - mounted long - wave infrared athermalized optical system, which includes an object surface, a first lens, a diaphragm, a second lens, a third lens, and a detector image surface arranged in sequence from the light source to the detector along the propagation direction of the incident light. Among them, the first lens and the third lens are meniscus negative lenses with negative optical power, and the second lens is a biconvex positive lens with positive optical power; among them, the front surface of the first lens is a diffractive surface and the rear surface is a spherical surface; the front surface of the second lens is an even - numbered aspherical surface and the rear surface is a spherical surface; the front and rear surfaces of the third lens are both spherical surfaces.

[0048] In this embodiment, the materials of the first lens and the third lens are IRG25; the material of the second lens is ZnS. The focal length of this optical system is 32, the F - number of the optical system is, the field of view angle is 12°, and it is adapted to a long - wave infrared detector with 640×512 pixels and 12μm.

[0049] In this embodiment, the thicknesses of each lens and the air intervals in the first lens, the second lens, and the third lens in the optical system are in the ranges of: The thickness of the first lens is 7.9 mm to 8.2 mm, the air interval between the rear surface of the first lens and the front surface of the diaphragm is 15.1 mm to 15.5 mm, and the air interval between the rear surface of the diaphragm and the front surface of the second lens is 14.8 mm to 15.1 mm; The thickness of the second lens is 7.3 mm to 7.9 mm, and the air interval between the rear surface of the second lens and the front surface of the third lens is 2.8 mm to 3.1 mm; The thickness of the third lens is 4.8 mm to 5.1 mm, and the air interval between the rear surface of the third lens and the detector image surface is 8.9 mm to 9.3 mm.

[0050] In this embodiment, the curvature radii of the front and rear surfaces of the first lens are 48.9 mm to 49.1 mm and 61.7 mm to 62.8 mm respectively; the curvature radii of the front and rear surfaces of the third lens are 20.4 mm to 20.5 mm and 12.2 mm to 12.8 mm respectively.

[0051] Among them, the surface type parameters of the diffractive surface on the front surface of the first lens are as follows: Coefficient range of the fourth-order term: -1.05×10 -6 ~-1.04×10 -6 ; Coefficient range of the sixth-order term: -7.15×10 -10 ~-7.13×10 -10 ; Coefficient range of the eighth-order term: -2.58×10 -12 ~-2.55×10 -12 .

[0052] In this embodiment, in the surface type equation of the even aspheric surface on the front surface of the second lens, the conic quadratic curve coefficient k is equal to 1. Among them, an antireflection film is coated on the rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens to eliminate stray light.

[0053] The present invention also provides a design method for a lightweight unmanned aerial vehicle (UAV)-mounted long-wave infrared athermalized optical system, including the following steps: S1. Gaussian design: Determine the numerical aperture of the optical system according to the resolution and the lateral magnification.

[0054] S2. Athermalization design: Solve the simultaneous equations through the conditions of the total optical power, achromatism, and athermalization.

[0055] S3. Initial structure design: Based on the athermalization conditions, use the PW method or the tangent calculation method to determine the lens curvature radius, thickness, and interval.

[0056] S4. Optimization design of the system structure: Set the evaluation function, and use optical software to optimize the even aspheric surface coefficients and diffractive surface parameters to obtain a lightweight UAV-mounted long-wave infrared athermalized optical system that can achieve clear imaging at -60°C to 100°C.

[0057] In this step S1, the lateral magnification is calculated based on the detector size and the object field of view:

[0058] The resolution is calculated based on the working central wavelength and the exponent value:

[0059] Among them, represents the lateral magnification; represents the image height; represents the object height; represents the resolution; represents the working central wavelength; represents the numerical aperture value.

[0060] In the athermal design of step S2, the condition for the total optical power is as follows:

[0061] The condition for achromatism is as follows:

[0062] The condition for apochromatism is as follows:

[0063] In the formula: is the Abbe number of the i-th lens; is the linear expansion coefficient of the barrel material; represents the first lens; represents the last lens; represents the optical power of the i-th lens; represents the total optical power; represents the partial derivative formula of the optical power of the i-th lens with respect to the focal length displacement at temperature T; represents the temperature focal length displacement number.

[0064] In the initial structure design of step S3, the initial structure of the system can be obtained by the PW method or the tangent calculation method in combination with the athermal conditions of step S2. The initial structure parameters are shown in Table 1 below: Table 1 Optical structure parameter table of the initial structure of the long-wave infrared optical system carried by a light UAV

[0065] In the optimized design of the system structure in step S4, the structure calculated in step S3 is input into the optical design software, and the evaluation function is set according to the requirements of the working distance, the shape of the components, the temperature, and the mass; among them, the even aspheric equation is:

[0066] where R is the surface vertex radius, K is the conic coefficient, A, B, and C are the polynomial coefficients of the even aspheric surface, y is the radial distance from the optical axis, and z is the sagitta value corresponding to the y value.

[0067] By optimizing the even aspheric coefficients and diffractive surface parameters using the optical software, a light UAV-mounted long-wave infrared athermal optical system that satisfies clear imaging from -60°C to 100°C is obtained. Among them, the optical structure parameters are shown in Table 2, the aspheric coefficients of surface 5 are shown in Table 3, and the diffractive coefficients of surface 2 are shown in Table 4.

[0068] Table 2 Optical structure parameter table of the initial structure of the long-wave infrared optical system carried by a light UAV

[0069] Table 3 Aspherical Coefficient Table of Surface 5

[0070] Table 4 Diffraction Coefficient Table of Surface 2

[0071] See Figures 2 to 11 as shown Figures 2 to 11 is the optical characteristic curve graph of the corresponding embodiment Figure 2 and Figure 4 and Figure 6 are the amplitude modulation transfer function MTF at each temperature of the optical system, representing the comprehensive resolution level of the optical system. It is required to achieve a resolution of 42 line pairs with a 640*480 12μm detector. From Figure 2 and Figure 4 and Figure 6 it can be seen that the system has met the requirements. Figure 3 and Figure 5 and Figure 7 are the spot diagrams at each temperature, which is an analysis tool for the imaging quality of the optical system. The smaller the RMS radius, the better the imaging quality.

[0072] Figure 2 In it, the abscissa represents the spatial frequency, unit: line pairs per mm; the ordinate represents the value of the amplitude modulation transfer function MTF. From Figure 2 it can be seen that the values of each curve are close to each other. When the spatial frequency is 42, the MTF is greater than 0.3 and the imaging quality is good. From the picture in Figure 3 it can be seen that the RMS radius is very small and the imaging quality is very good. Figure 4 In it, the abscissa represents the spatial frequency, unit: line pairs per mm; the ordinate represents the value of the amplitude modulation transfer function MTF. From Figure 4 it can be seen that the values of each curve are close to each other. When the spatial frequency is 42, the MTF is greater than 0.3 and the imaging quality is good. From the picture in Figure 5 it can be seen that the RMS radius is very small and meets the requirements, and the imaging quality is good. Figure 6 In it, the abscissa represents the spatial frequency, unit: line pairs per mm; the ordinate represents the value of the amplitude modulation transfer function MTF. From Figure 6 it can be seen that the values of each curve are close to each other. When the spatial frequency is 42, the MTF is greater than 0.3 and the imaging quality is good. From the picture in Figure 7 it can be seen that the RMS radius is very small and meets the requirements, and the imaging quality is good.

[0073] Figure 8 is the field curvature graph of the long-wave infrared carried by the light unmanned aerial vehicle. It can be seen that the field curvature is between -0.0034 and -0.00024. Among them, Figure 8The abscissa represents: the percentage of field curvature value; the ordinate: the size of the field of view Y, from Figure 8 As can be seen from the field curvature value corresponding to the curve in Figure 8 , the field curvature value of the system is small and the imaging quality is good. The field area is small and meets the requirements. Figure 9 This is the distortion diagram of the optical system of this embodiment. Among them, the abscissa represents: the percentage of distortion value; the ordinate: the size of the Y field of view, from Figure 9 As can be seen from the distortion value corresponding to the curve in Figure 9 , the distortion is less than 0.0081%, the system value is small, the imaging quality is good, and it meets the system requirements. Figure 10 This is the original stray light diagram of the system. It can be seen that the stray light is very large and needs to be eliminated, otherwise it will affect the imaging quality. According to Figure 10 As can be seen from the detector image plane in Figure 10 , the number of stray light is very large, which affects the imaging quality and needs to be eliminated. Figure 11 The stray light diagram obtained through the analysis of the lens coating shows that the stray light is basically eliminated. From Figure 11 It can be seen that after coating the lens and analyzing the stray light, an image plane diagram with basically eliminated stray light can be obtained.

[0074] The first lens, the second lens and the third lens of the present invention adopt a combination of materials with different refractive indices, and are combined with even aspherical surfaces and diffractive surfaces, reducing the number of lenses, simplifying the structure, reducing the weight, and reducing the cost; by allocating the focal lengths and refractive index materials of the first lens, the second lens and the third lens, an efficient material combination is achieved, and aberration correction is achieved by using rotationally symmetric even aspherical surfaces and diffractive surfaces, thereby achieving high imaging quality.

[0075] The first lens, the second lens and the third lens of the present invention respectively adopt different materials. When the environmental temperature changes, the refractive indices of the lenses change to different degrees, which can compensate for the offset of the focal plane caused by temperature changes, thereby achieving optical athermalization; by selecting optical glass materials with high refractive index and low dispersion, and combining with rotationally symmetric even aspherical surfaces, the athermal design of an optical system with a large aperture is jointly achieved, and clear imaging can be achieved within the temperature range of -60°C to 100°C. Compared with traditional athermal systems, the number of lenses is reduced, and the use of diffractive surfaces simplifies the structure, reduces the weight, and at the same time achieves the purpose of making the optical system light and small, and reduces the cost.

[0076] The lightweight unmanned aerial vehicle-mounted long-wave infrared athermal optical system provided by the present invention has a relatively wide tolerance limit. It can be within a radius, thickness, and eccentricity range of 0.02 mm, and 90% of the samples in the amplitude modulation transfer function can be greater than 33%. The difference from the best image quality is 0.02%; moreover, antireflection films are coated on the rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens, which can effectively eliminate stray light.

[0077] The foregoing are exemplary embodiments disclosed by the present invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments disclosed by the present invention as defined by the claims. The functions, steps, and / or actions of the method claims according to the disclosed embodiments herein need not be performed in any particular order. In addition, although the elements disclosed by the embodiments of the present invention may be described or claimed in individual form, they can also be understood as plural unless explicitly limited to the singular form.

[0078] It should be understood that, as used herein, unless the context clearly supports exceptions, the singular form "a" is also intended to include the plural form. It should also be understood that the "and / or" used herein refers to any and all possible combinations of one or more of the related listed items. The foregoing serial numbers of the disclosed embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0079] Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention disclosed (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features between the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included in the protection scope of the embodiments of the present invention.

Claims

1. A lightweight unmanned aerial vehicle (UAV) - mounted long - wave infrared athermalized optical system, characterized in that, It includes an object surface, a first lens, a diaphragm, a second lens, a third lens, and a detector image surface that are arranged in sequence from the light source to the detector along the propagation direction of the incident light ray. The first lens and the third lens are meniscus negative lenses with negative focal power, and the second lens is a biconvex positive lens with positive focal power. Among them, the front surface of the first lens is a diffractive surface, and the rear surface is a spherical surface; the front surface of the second lens is an even aspherical surface, and the rear surface is a spherical surface; the front and rear surfaces of the third lens are both spherical surfaces.

2. The long-wave infrared athermalized optical system carried by the light unmanned aerial vehicle according to claim 1, wherein The materials of the first lens and the third lens are IRG25; the material of the second lens is zinc sulfide crystal.

3. The long-wave infrared athermalized optical system carried by the light unmanned aerial vehicle according to claim 2, wherein The focal length of the optical system is 32, the F-number of the optical system is, the field of view angle is 12°, and it is adapted to a long-wave infrared detector with 640×512 pixels and 12μm.

4. The long-wave infrared athermalized optical system carried by the light unmanned aerial vehicle according to claim 1, wherein The thicknesses and air spacings of the lenses in the first lens, the second lens, and the third lens in the optical system are as follows: The thickness of the first lens is 7.9 mm to 8.2 mm, the air spacing between the rear surface of the first lens and the front surface of the diaphragm is 15.1 mm to 15.5 mm, and the air spacing between the rear surface of the diaphragm and the front surface of the second lens is 14.8 mm to 15.1 mm; The thickness of the second lens is 7.3 mm to 7.9 mm, and the air spacing between the rear surface of the second lens and the front surface of the third lens is 2.8 mm to 3.1 mm; The thickness of the third lens is 4.8 mm to 5.1 mm, and the air spacing between the rear surface of the third lens and the detector image surface is 8.9 mm to 9.3 mm.

5. The long-wave infrared athermalized optical system carried by the light UAV according to claim 4, characterized in that, The curvature radii of the front and rear surfaces of the first lens are 48.9 mm to 49.1 mm and 61.7 mm to 62.8 mm respectively; the curvature radii of the front and rear surfaces of the third lens are 20.4 mm to 20.5 mm and 12.2 mm to 12.8 mm respectively.

6. The long-wave infrared athermalized optical system carried by the light UAV according to claim 5, wherein The surface type parameters of the diffractive surface on the front surface of the first lens are: Coefficient range of the quartic term: -1.05×10 -6 ~-1.04×10 -6 ; Coefficient range of the sixth term: -7.15×10 -10 ~-7.13×10 -10 ; Coefficient range of the eighth term: -2.58×10 -12 ~-2.55×10 -12 .

7. The long-wave infrared athermalized optical system carried by the light UAV according to claim 6, characterized in that, In the surface type equation of the even aspherical surface on the front surface of the second lens, the conic quadratic curve coefficient k is equal to 1.

8. The long-wave infrared athermalized optical system carried by the light UAV according to claim 7, characterized in that, Antireflection films are coated on the rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens.

9. A design method for a lightweight unmanned aerial vehicle (UAV)-mounted long-wave infrared athermalized optical system as described in any one of claims 1-8, characterized in that, It includes the following steps: S1. Gaussian design: Determine the numerical aperture of the optical system according to the resolution and the lateral magnification. S2. Athermal design: Solve the system of equations by the conditions of the total focal power, achromatism, and athermalization. S3. Initial structure design: Based on the athermalization conditions, use the PW method or the tangent calculation method to determine the curvature radii, thicknesses, and spacings of the lenses. S4. Optimization design of the system structure: Set the evaluation function, and use optical software to optimize the even aspherical surface coefficients and diffractive surface parameters to obtain a lightweight UAV-mounted long-wave infrared athermal optical system that can achieve clear imaging from -60°C to 100°C.

10. The design method of the lightweight unmanned aerial vehicle (UAV) - carried long - wave infrared athermalized optical system as claimed in claim 9, wherein, The lateral magnification is calculated based on the size of the detector and the object space field of view: ; the resolution is calculated according to the central wavelength and the exponential value of the operation: ; wherein, represents the transverse magnification; represents the image height; represents the object height; represents the resolution; represents the central wavelength of operation; represents the numerical aperture value.

Images