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 is a meniscus positive lens with positive focal power, the third lens is a meniscus negative lens 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 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 application relates to the technical field of optical instruments, in particular to a long-wave infrared athermal optical system carried by a light unmanned aerial vehicle and a design method thereof. BACKGROUND

[0002] The long-wave infrared athermal lens carried by the light unmanned aerial vehicle has night vision function and can quickly identify targets in foggy weather. However, the traditional long-wave infrared lens carried by an aircraft has the problems of small requirements for athermalization, large volume and weight, complex structure, and large influence of temperature and atmospheric pressure. The long-wave infrared athermal lens system carried by the light unmanned aerial vehicle reduces the volume and weight of the system, and improves the endurance and flight time.

[0003] There are three common athermal design methods at present: mechanical and electrical active type, mechanical passive type and optical passive type. Among them, the mechanical and electrical active type and the mechanical and electrical passive type cannot correct the imbalance of aberration, have complex structure, high requirements for processing and installation and adjustment, and are not suitable for light design. For example, a Chinese patent with the authorization announcement number CN103018884B discloses a technical solution named "a long-wave infrared optical system". The solution provides a thought of realizing large relative aperture and miniaturization in a large field of view range by using two lenses, but the focal length is only 9mm and the athermalization is not performed. For example, a Chinese patent with the authorization announcement number CN118884685B discloses a technical solution named "a long-wave infrared continuous zoom optical system". The solution realizes the design of a long-wave infrared zoom lens, and the system uses 5 lenses, which has complex structure, large weight and volume.

[0004] Therefore, how to develop a long-wave infrared athermal optical system carried by a light unmanned aerial vehicle has become an important research direction of the technical personnel in the field. SUMMARY

[0005] Therefore, in order to solve the above problems, the present application aims to provide a long-wave infrared athermal optical system carried by a light unmanned aerial vehicle and a design method thereof, which can realize light weight and material non-toxicity under the condition of large aperture, and improve the flight time, resolution and environmental temperature resistance of the unmanned aerial vehicle.

[0006] To achieve the above purpose, the present application provides the following technical scheme: In order to achieve the above object, the present application provides a light unmanned aerial vehicle-mounted long-wave infrared athermal optical system, which comprises, in sequence from a light source to a detector and along the propagation direction of incident light, an object plane, a first lens, an aperture, a second lens, a third lens and a detector image plane; the first lens is a meniscus positive lens with positive focal power, the third lens is a meniscus negative lens with negative focal power, and the second lens is a double-convex positive lens with positive focal power; wherein the front surface of the first lens is a diffraction surface, and the rear surface is a spherical surface; the front surface of the second lens is an even aspheric surface, and the rear surface is a spherical surface; and the front and rear surfaces of the third lens are both spherical surfaces.

[0007] As a further scheme of the present application, the material of the first lens and the third lens is IRG25, and the material of the second lens is zinc sulfide crystal (ZnS).

[0008] As a further scheme of the present application, the focal length of the optical system is 32, the F number of the optical system is 1, and the field of view angle is 12°, which is suitable for a long-wave infrared detector with 640×512 pixels and 12 μm.

[0009] As a further scheme of the present application, the thickness and air gap range of each lens 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-8.2 mm, the air gap between the rear surface of the first lens and the front surface of the aperture is 14.9 mm-15.5 mm, and the air gap between the rear surface of the aperture and the front surface of the second lens is 14.8 mm-15.1 mm; The thickness of the second lens is 7.3 mm-8.0 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-3.1 mm; The thickness of the third lens is 4.8 mm-5.1 mm, and the air gap between the rear surface of the third lens and the detector image plane is 8.9 mm-9.3 mm.

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

[0011] As a further scheme of the present application, the surface type parameters of the diffraction surface of the front surface of the first lens are as follows: The 4th order coefficient ranges from -1.05×10 -6 to -1.04×10 -6 ; The 6th order coefficient ranges from -7.15×10 -10 to -7.13×10-10 ; 8th order coefficient range: -2.58*10 -12 ~ -2.55*10 -12 .

[0012] As a further scheme of the present application, the conic quadratic curve coefficient k in the surface equation of the front surface even aspherical surface of the second lens is equal to 1.

[0013] As a further scheme of the present application, the back surface of the first lens, the front surface of the second lens and the back surface of the third lens are all coated with an anti-reflection film for eliminating stray light.

[0014] In a second aspect, the present application further provides a design method of a long-wave infrared athermal optical system carried by a light-weight unmanned aerial vehicle, comprising the following steps: S1, Gaussian design: calculating the vertical axial magnification according to the size of the detector and the object field of view; determining the resolution of the optical system according to the F number and the central wavelength; S2, athermal design: solving the equation set through the conditions of total optical power, achromatism and athermalization; S3, initial structure design: based on the conditions of athermalization, using PW method or tangent calculation method to determine the curvature radius, thickness and interval of the lens; S4, optimization design of system structure: setting evaluation function, using optical software to optimize even aspherical surface coefficient and diffraction surface parameters to obtain a light-weight unmanned aerial vehicle carrying long-wave infrared athermal optical system which can clearly image at-60℃~100℃.

[0015] As a further scheme of the present application, the vertical axial magnification is calculated according to the size of the detector and the object field of view:

[0016] The resolution is calculated according to the central wavelength and the F number:

[0017] Wherein, represents the vertical axial magnification; represents the image height; represents the object height; represents the resolution; represents the central wavelength; represents the numerical value of the F number.

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

[0019] The condition of achromatism is:

[0020] The condition of the athermalization is:

[0021] In the formula: The optical power of the i-th lens is represented by Di; The total optical power is represented by D; The first lens is represented by L1; The last lens is represented by Ln; The Abbe number of the i-th lens is represented by Vi; The partial derivative formula of the optical power of the i-th lens with respect to the focal length focal length shift at T temperature is represented by DiT; The linear expansion coefficient of the lens barrel material is represented by a; The temperature focal length shift number is represented by T;

[0022] As a further scheme of the present application, when the system structure is optimized and designed, an evaluation function is set according to the working distance requirement, the component shape, the temperature, and the mass requirement; wherein, the even aspherical surface equation is:

[0023] Wherein, R is the surface vertex radius, K is the conic coefficient, A, B, and C are the polynomial coefficients of the even aspherical surface, is the radial distance from the optical axis, is the radial distance from the optical axis, is the arc height value corresponding to the value.

[0024] Compared with the prior art, the light unmanned aerial vehicle carrying the long-wave infrared athermal optical system has the following beneficial effects: 1. The first lens, the second lens, and the third lens of the present application adopt the collocation of different refractive index materials, and collocate even aspherical surfaces and diffractive surfaces, which reduces the number of lenses, simplifies the structure, reduces the weight, and reduces the cost; by distributing the focal length and the refractive index material of the first lens, the second lens, and the third lens, efficient material collocation is realized, and by using rotationally symmetric even aspherical surfaces and diffractive surfaces for aberration correction, high imaging quality is realized.

[0025] 2. The first lens, the second lens and the third lens of the present application are made of different materials respectively, when the ambient temperature changes, the refractive index of the lens changes to different degrees, which can compensate for the shift of the focal plane caused by temperature change, so as to realize optical athermalization; by selecting high refractive, low dispersion optical glass material, and matching with rotationally symmetric even aspheric surface, the athermalization design of optical system with large aperture is realized, clear imaging can be realized in the temperature range of-60 DEG C to 100 DEG C, compared with the traditional athermalization system, the number of lenses is reduced, and the use of diffraction surface simplifies the structure, reduces the weight, realizes the purpose of small and light optical system, and reduces the cost.

[0026] 3. The long-wave infrared athermalization optical system carried by the light unmanned aerial vehicle provided by the present application has a wide tolerance limit, 90% of the sampling in the amplitude modulation transfer function can be greater than 33% within the radius, thickness and eccentricity range of 0.02mm, and the maximum like quality difference is 0.02%; in addition, the rear surface of the first lens, the front surface of the second lens and the rear surface of the third lens are coated with anti-reflection film, which can well eliminate stray light.

[0027] These aspects or other aspects of the present application will be more apparent 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 cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technical solutions, the drawings needed to be used in the exemplary embodiments or the related technical description will be briefly introduced as follows, the drawings are used to provide further understanding of the present application, and constitute a part of the specification, and are used to explain the embodiments of the present application, and do not constitute a limitation of the present application. In the drawings: Figure 1 The optical structure layout schematic diagram of the long-wave infrared athermalization lens optical system carried by the light unmanned aerial vehicle provided by the present application.

[0029] Figure 2 The-60 DEG C amplitude modulation transfer function diagram of the long-wave infrared athermalization optical system carried by the light unmanned aerial vehicle provided by the present application.

[0030] Figure 3 The-60 DEG C point column diagram of the long-wave infrared athermalization optical system carried by the light unmanned aerial vehicle provided by the present application.

[0031] Figure 4 The 20 DEG C amplitude modulation transfer function diagram of the long-wave infrared athermalization optical system carried by the light unmanned aerial vehicle provided by the present application.

[0032] Figure 5A point column diagram of 20℃ of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0033] Figure 6 A 100℃ amplitude modulation transfer function diagram of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0034] Figure 7 A point column diagram of 100℃ of the field of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0035] Figure 8 A field curvature diagram of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0036] Figure 9 A distortion diagram of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0037] Figure 10 An initial stray light analysis diagram of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0038] Figure 11 A coating stray light analysis diagram of the long-wave infrared athermal optical system carried by the light unmanned aerial vehicle provided in the present application.

[0039] Reference signs: 1, object plane; 2, first lens; 3, diaphragm; 4, second lens; 5, third lens; 6, detector image plane. DETAILED DESCRIPTION

[0040] Hereinafter, the present application will be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that the following described embodiments or technical features can be combined with each other to form new embodiments without conflict.

[0041] In order to make the objectives, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0042] It should be noted that all the expressions of "first" and "second" in the embodiments of the present application 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 used for the convenience of description and should not be understood as a limitation of the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, the process, method, system, product or device inherently includes other steps or units.

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of the present application.

[0044] The flowchart shown in the drawings is only an example and does not necessarily include all the contents and operations / steps, nor does it necessarily be executed in the described order. For example, some operations / steps can be further decomposed, combined or partially merged, so that the actual execution order can be changed according to the actual situation.

[0045] Some embodiments of the present application will be described in detail below with reference to the drawings. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0046] Referring to Figures 1 to 11 The embodiment of the present application provides a light unmanned aerial vehicle carrying a long-wave infrared athermal optical system, which comprises, in sequence from a light source to a detector and along the propagation direction of incident light, an object plane 1, a first lens 2, an aperture 3, a second lens 4, a third lens 5 and a detector image plane 6. The first lens 2 is a meniscus positive lens with positive focal power, the third lens 5 is a meniscus negative lens with negative focal power, and the second lens 4 is a double-convex positive lens with positive focal power. The front surface of the first lens 2 is a diffractive surface, and the rear surface is a spherical surface. The front surface of the second lens 4 is an even aspheric surface, and the rear surface is a spherical surface. The front and rear surfaces of the third lens 5 are both spherical surfaces.

[0047] In the embodiment, the material of the first lens 2 and the third lens 5 is IRG25, and the material of the second lens 4 is ZnS. The focal length of the optical system is 32, the F number of the optical system is 1, and the field of view angle is 12°, which is suitable for a long-wave infrared detector with 640×512 pixels and 12 μm.

[0048] In the embodiment, the thickness and air gap range of each lens in the first lens 2, the second lens 4 and the third lens 5 in the optical system are as follows: The thickness of the first lens 2 is 7.9 mm to 8.2 mm, the air gap between the rear surface of the first lens 2 and the front surface of the aperture 3 is 14.9 mm to 15.5 mm, and the air gap between the rear surface of the aperture 3 and the front surface of the second lens 4 is 14.8 mm to 15.1 mm; The thickness of the second lens 4 is 7.3 mm to 8.0 mm, and the air gap between the rear surface of the second lens 4 and the front surface of the third lens 5 is 2.8 mm to 3.1 mm; The thickness of the third lens 5 is 4.8mm-5.1mm, and the air interval between the rear surface of the third lens 5 and the image plane 6 of the detector is 8.9mm-9.3mm.

[0049] In the embodiment, the radii of curvature of the front and rear surfaces of the first lens 2 are 48.9mm-49.1mm and 61.7mm-62.8mm respectively, and the radii of curvature of the front and rear surfaces of the third lens 5 are 20.4mm-20.5mm and 12.2mm-12.8mm respectively.

[0050] The surface type parameters of the diffraction surface of the front surface of the first lens 2 are as follows: 4th order coefficient range: -1.05*10 -6 ~ -1.04*10 -6 ; 6th order coefficient range: -7.15*10 -10 ~ -7.13*10 -10 ; 8th order coefficient range: -2.58*10 -12 ~ -2.55*10 -12 .

[0051] In the embodiment, the conic quadratic curve coefficient k in the surface type equation of the even-order aspheric surface of the front surface of the second lens 4 is equal to 1. The rear surface of the first lens 2, the front surface of the second lens 4 and the rear surface of the third lens 5 are all coated with an anti-reflection film for eliminating stray light.

[0052] The application also provides a design method of a long-wave infrared athermal optical system carried by a light-weight unmanned aerial vehicle, which comprises the following steps: S1, Gaussian design: calculating the vertical axial magnification according to the size of the detector and the object field of view; determining the resolution of the optical system according to the F number and the central wavelength.

[0053] S2, athermal design: solving the equation set through the conditions of total optical power, achromatism and athermalization.

[0054] S3, initial structure design: determining the radii of curvature, thickness and interval of the lenses by using the PW method or the tangent calculation method based on the athermalization condition.

[0055] S4, optimization design of the system structure: setting an evaluation function, optimizing the even-order aspheric surface coefficient and the diffraction surface parameter by using optical software, and obtaining the long-wave infrared athermal optical system carried by the light-weight unmanned aerial vehicle which can clearly image at-60℃-100℃.

[0056] In the step S1, the vertical axial magnification is calculated according to the size of the detector and the object field of view:

[0057] The resolution is calculated according to the central wavelength of working and F number:

[0058] wherein, represents the axial magnification; represents the image height; represents the object height; represents the resolution; represents the central wavelength of working; represents the numerical value of F number.

[0059] The condition of total optical power in the athermalization design of this step S2 is:

[0060] The condition of achromatism is:

[0061] The condition of athermalization is:

[0062] wherein, is the total optical power, represents the optical power of the i-th lens; represents the first lens; represents the last lens; represents the Abbe number of the i-th lens; represents the partial derivative formula of the focal length focal displacement of the optical power of the i-th lens at T temperature; is the linear expansion coefficient of the barrel material; represents the temperature focal displacement number.

[0063] In the initial structure design of this step S3, the initial structure of the system combines the athermalization condition of the step S2, and can be obtained by the PW method or the tangent calculation method. The initial structure parameters are as shown in the following table 1: Table 1 Optical structure parameter table of initial structure of long-wave infrared optical system carried by light unmanned aerial vehicle

[0064] In the optimization design of the system structure of this step S4, the structure calculated in the step S3 is input in the optical design software, and the evaluation function is set according to the working distance requirement, the element shape, the temperature, and the mass requirement; wherein, the even aspherical surface equation is:

[0065] wherein, R is the surface vertex radius, K is the conic coefficient, A, B, and C are the polynomial coefficients of the even aspherical surface, The radial distance between the optical axis and the optical axis. To and The value corresponds to the arc height.

[0066] By optimizing the even-order aspherical coefficients and diffraction surface parameters using optical software, a lightweight UAV equipped with a long-wave infrared athermalized optical system that can achieve clear imaging at temperatures ranging from -60℃ to 100℃ was obtained. The optical structure parameters are shown in Table 2, the aspherical coefficients of surface 5 are shown in Table 3, and the diffraction coefficients of surface 2 are shown in Table 4.

[0067] Table 2 Optical structure parameters of the initial structure of a light UAV equipped with a long-wave infrared optical system

[0068] Table 3 Aspherical coefficients of surface 5

[0069] Table 4. Diffraction coefficients of surface 2

[0070] See Figures 2 to 11 As shown, Figures 2 to 11 The graph shows the optical characteristics of the corresponding embodiment. Figure 2 , Figure 4 , Figure 6 The amplitude modulation transfer function (MTF) of the optical system at various temperatures represents the overall resolution of the optical system, requiring a 42-line-pair resolution when paired with a 640*480 12μm detector. Figure 2 , Figure 4 , Figure 6 It can be seen that the system has met the requirements. Figure 3 , Figure 5 , Figure 7 A point plot at various temperatures is an analytical tool for the imaging quality of an optical system; the smaller the RMS radius, the better the imaging quality.

[0071] Figure 2 The horizontal axis represents spatial frequency, in line pairs per mm; the vertical axis represents the amplitude modulation transfer function (MTF) value, from... Figure 2 As can be seen, when the curve values ​​are close to each other, and the MTF is greater than 0.3 at a spatial frequency of 42, the image quality is good. Figure 3 The images show that the RMS radius is very small and the image quality is very good. Figure 4 The horizontal axis represents spatial frequency, in line pairs per mm; the vertical axis represents the amplitude modulation transfer function (MTF) value, from... Figure 4 As can be seen, when the curve values ​​are close to each other, and the MTF is greater than 0.3 at a spatial frequency of 42, the image quality is good.Figure 5 From the figure, it can be seen that the RMS radius is small and meets the requirements, and the imaging quality is good. Figure 6 In the figure, the horizontal coordinate represents spatial frequency, and the unit is line per mm; and the vertical coordinate represents the value of amplitude modulation transfer function (MTF), and the unit is percentage. Figure 6 From the figure, it can be seen that the values of the curves are close to each other, and when the spatial frequency is 42, the MTF is greater than 0.3, and the imaging quality is good. Figure 7 From the figure, it can be seen that the RMS radius is small and meets the requirements, and the imaging quality is good.

[0072] Figure 8 The figure is a field curvature diagram of a long-wave infrared carried by a light unmanned aerial vehicle, and it can be seen that the field curvature is between -0.0034 and 0.00024, wherein, Figure 8 In the figure, the horizontal coordinate represents field curvature value percentage; and the vertical coordinate represents Y field size, and the unit is percentage. Figure 8 From the field curvature values corresponding to the curves in the figure, it can be seen that the system field curvature value is small, the imaging quality is good, and the field area meets the requirements. Figure 9 The figure is a distortion diagram of the optical system, wherein the horizontal coordinate represents distortion value percentage; and the vertical coordinate represents Y field size, and the unit is percentage. Figure 9 From the distortion values corresponding to the curves in the figure, it can be seen that the distortion is less than 0.0081%, the system value is small, the imaging quality is good, and the system requirements are met. Figure 10 The figure is an original stray light diagram of the system, and it can be seen that the stray light is large and needs to be eliminated, otherwise the imaging quality is affected. Figure 10 From the detector image surface 6 in the figure, it can be seen that the number of stray lights is large, and the imaging quality is affected, and stray light elimination is needed. Figure 11 The figure is a stray light diagram obtained through analysis of lens coating, and it can be seen that the stray light is basically eliminated. Figure 11 It can be seen that after the lens is coated and the stray light is analyzed, an image surface diagram in which the stray light is basically eliminated can be obtained.

[0073] The first lens 2, the second lens 4 and the third lens 5 of the present application adopt collocation of different refractive index materials, and collocation of even-order aspheric surfaces and diffraction surfaces, so that the number of lenses is reduced, the structure is simplified, the weight is reduced, and the cost is reduced; by distributing the focal lengths and refractive index materials of the first lens 2, the second lens 4 and the third lens 5, efficient material collocation is realized, and by using rotationally symmetrical even-order aspheric surfaces and diffraction surfaces for aberration correction, high imaging quality is realized.

[0074] The first lens 2, the second lens 4 and the third lens 5 of the application are made of different materials, and when the ambient temperature changes, the refractive index of the lens changes to different degrees, which can compensate for the shift of the focal plane caused by the temperature change, thereby realizing optical athermalization; by selecting high-refractive and low-dispersion optical glass materials and matching the rotationally symmetric even aspheric surface, the optical system is athermalized, clear imaging can be achieved in the temperature range of-60 DEG C to 100 DEG C, compared with the traditional athermalization system, the number of lenses is reduced, and the use of the diffraction surface simplifies the structure, reduces the weight, realizes the purpose of small and light optical system, and reduces the cost.

[0075] The light unmanned aerial vehicle-mounted long-wave infrared athermalization optical system provided by the application has a wide tolerance limit, and in the 0.02mm radius, thickness and eccentricity range, 90% of the sampling in the amplitude modulation transfer function can be greater than 33%, and the most similar quality difference is 0.02%; moreover, the rear surface of the first lens 2, the front surface of the second lens 4 and the rear surface of the third lens 5 are coated with an antireflection film, which can well eliminate stray light.

[0076] The above is the exemplary embodiment disclosed by the application, but it should be noted that various changes and modifications can be made without departing from the scope of the embodiments disclosed by the application defined by the claims. The functions, steps and / or actions of the method claims described herein need not be performed in any particular order. In addition, although the elements of the embodiments disclosed by the application can be described or claimed in individual form, they can also be understood as plural unless explicitly limited as singular.

[0077] It should be understood that, unless the context clearly supports otherwise, the singular form "a", "an" and "the" as used herein are intended to include the plural forms as well. It should also be understood that "and / or" as used herein refers to any and all possible combinations of one or more of the associated listed items. The above embodiment numbers of the embodiments disclosed by the application are only for description, and do not represent the advantages and disadvantages of the embodiments.

[0078] Those skilled in the art should understand that the above discussion of any embodiment is only exemplary and is not intended to limit the scope of the embodiments disclosed by the application (including claims) to these examples; under the idea of the embodiments of the application, the technical features of the above embodiments or different embodiments can also be combined, and there are many other changes of the different aspects of the embodiments of the application as above. In order to be brief, they are not provided in detail. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made in the spirit and principle of the embodiments of the application shall be included in the protection scope of the embodiments of the application.

Claims

1. A lightweight unmanned aerial vehicle (UAV) equipped with a long-wave infrared athermalized optical system, characterized in that, It includes the object plane, the first lens, the aperture, the second lens, the third lens, and the detector image plane, arranged sequentially from the light source to the detector along the direction of the incident light propagation. The first lens is a meniscus positive lens with positive optical power, the third lens is a meniscus negative lens 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-order aspherical surface and the rear surface is a spherical surface; and both the front and rear surfaces of the third lens are spherical surfaces.

2. The lightweight UAV equipped with a long-wave infrared athermal optical system as described in claim 1, characterized in that, The first and third lenses are made of IRG25; the second lens is made of zinc sulfide crystal.

3. The lightweight UAV equipped with a long-wave infrared athermalized optical system as described in claim 2, characterized in that, The optical system has a focal length of 32, an F-number of 1, and a field of view of 12°, and is compatible with a 640×512 pixel, 12μm long-wave infrared detector.

4. The lightweight UAV equipped with a long-wave infrared athermalized optical system as described in claim 1, characterized in that, The thickness and air gap range of each lens in the first, second, and third lenses of the optical system are as follows: The thickness of the first lens is 7.9mm to 8.2mm, the air gap between the rear surface of the first lens and the front surface of the aperture is 14.9mm to 15.5mm, and the air gap between the rear surface of the aperture and the front surface of the second lens is 14.8mm to 15.1mm. The thickness of the second lens is 7.3mm to 8.0mm, and the air gap between the rear surface of the second lens and the front surface of the third lens is 2.8mm to 3.1mm. The thickness of the third lens is 4.8mm to 5.1mm, and the air gap between the rear surface of the third lens and the image plane of the detector is 8.9mm to 9.3mm.

5. The lightweight UAV equipped with a long-wave infrared athermal optical system as described in claim 4, characterized in that, 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.

6. The lightweight UAV equipped with a long-wave infrared athermalized optical system as described in claim 5, characterized in that, The surface profile parameters of the diffraction surface on the front surface of the first lens are as follows: The range of the coefficient for the fourth term is -1.05 × 10⁻⁶. -6 ~-1.04×10 -6 ; The range of coefficients for the 6th term is -7.15 × 10⁶. -10 ~-7.13×10 -10 ; The range of coefficients for the 8th term is -2.58 × 10⁸. -12 ~-2.55×10 -12 .

7. The lightweight UAV equipped with a long-wave infrared athermalized optical system as described in claim 6, characterized in that, In the surface equation of the even-order aspherical surface of the front surface of the second lens, the coefficient k of the conic quadratic curve is equal to 1.

8. The lightweight UAV equipped with a long-wave infrared athermal optical system as described in claim 7, characterized in that, The rear surface of the first lens, the front surface of the second lens, and the rear surface of the third lens are all coated with anti-reflective coatings.

9. A design method for a lightweight unmanned aerial vehicle (UAV) equipped with a long-wave infrared athermalized optical system as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Gaussian Design: Calculate the transverse magnification based on the detector size and object-side field of view; determine the resolution of the optical system based on the F-number and center wavelength; S2, Athermalization Design: Solve a system of equations based on the conditions of total optical power, achromatic aberration, and athermal aberration; S3. Initial structural design: Based on the condition of no pyrolysis, the radius of curvature, thickness and spacing of the lens are determined by the PW method or the tangent calculation method. S4. System structure optimization design: Set the evaluation function and use optical software to optimize the even-order aspherical coefficient and diffraction surface parameters to obtain a lightweight UAV equipped with a long-wave infrared athermal optical system that can achieve clear imaging from -60℃ to 100℃.

10. The design method for a lightweight unmanned aerial vehicle equipped with a long-wave infrared athermalized optical system as described in claim 9, characterized in that, The vertical magnification is calculated based on the detector size and the object-side field of view. The resolution is calculated based on the operating center wavelength and F-number. ;in, Indicates the vertical axis magnification; Indicates image height; Indicates the height of an object; Indicates resolution; Indicates the center wavelength of the operation; This represents the numerical value of the F-number.

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