Lens for thermal imaging and thermal imaging device comprising the same

Abstract

This application provides a lens for thermal imaging and a thermal imaging device including the same, belonging to the technical field of thermal imaging. The lens for thermal imaging includes a first superlens and a second superlens arranged sequentially from the object side to the image side; wherein the first superlens is a compensation lens, and the second superlens is a modulation lens. This lens suppresses the influence of ambient temperature changes on lens performance.

Description

Technical Field

[0001] This disclosure relates to the technical field of thermal imaging, and more specifically, to lenses for thermal imaging and thermal imaging apparatuses incorporating the same. Background Technology

[0002] Thermal imaging works by receiving infrared radiation from a target through a lens and converting the target's temperature distribution field into a visible image using photoelectric conversion and other technologies. Thermal imaging technology is widely used in security monitoring, industrial automation, and consumer electronics.

[0003] However, due to the thermal instability of optical materials, changes in ambient temperature alter the curvature, thickness, refractive index, and inter-lens distance of the lens elements, resulting in changes in the lens's focal length and image plane displacement. Consequently, lens performance deteriorates sharply and image quality worsens with temperature variations. Current technologies typically employ two or more materials with different thermal coefficients, such as germanium, zinc selenide, and chalcogenide glass, as lens materials to overcome the effects of ambient temperature on lens performance. However, this design only meets the requirements for temperature ranges from -20°C to +40°C.

[0004] Therefore, there is an urgent need for lenses that can be used in a wider range of temperature differences. Summary of the Invention

[0005] To address the problem that lens performance in the prior art is limited by ambient temperature, this application provides a lens for thermal imaging and a thermal imaging device including the lens.

[0006] In a first aspect, this application provides a lens for thermal imaging, the lens for thermal imaging comprising a first superlens and a second superlens arranged sequentially from the object side to the image side;

[0007] Wherein, the first superlens is a compensation lens, and the second superlens is a modulation lens. Optionally, the first superlens and the second superlens also satisfy:

[0008] f1 ≥ 10.8 mm;

[0009] f2≤0.58mm;

[0010]

[0011] f1 is the focal length of the first superlens, f2 is the focal length of the second superlens, and d is the distance between the first superlens and the second superlens.

[0012] Optionally, the lens for thermal imaging also satisfies:

[0013]

[0014] Where f is the effective focal length of the lens used for thermal imaging; f1 is the focal length of the first superlens; f2 is the focal length of the second superlens; and d is the distance between the first superlens and the second superlens.

[0015] Optionally, the lens for thermal imaging also satisfies:

[0016] f2 <b<f;

[0017] Wherein, b is the back focal length of the lens used for thermal imaging; f is the effective focal length of the lens used for thermal imaging; and f2 is the focal length of the second superlens.

[0018] Optionally, each of the first and second superlenses includes a substrate and a plurality of nanostructures periodically arranged on one side of the substrate.

[0019] Optionally, the phases of each of the first and second superlenses satisfy at least one of the following relationships:

[0020]

[0021]

[0022]

[0023] Where r is the distance from the center of the substrate to the center of any of the nanostructures; x and y are the coordinates of the nanostructure on the substrate; f ML λ is the focal length of the first or second superlens; λ is the center wavelength of the incident beam. Let a be the initial phase of the incident beam. i represents the phase coefficients of each order; i is an integer greater than or equal to 1.

[0024] Optionally, the phase of each of the first and second superlenses satisfies the following constraint:

[0025]

[0026] Δneff≤C;

[0027] Wherein, neff is the equivalent refractive index of the first or second superlens; k is the wave vector of the incident beam; Hd is the height of the nanostructure; Δneff is the difference between the maximum and minimum neff of the first or second superlens; C is a constant; r is the distance from the center of the substrate (11) to the center of any of the nanostructures (12); and λ is the center wavelength of the incident beam.

[0028] Optionally, the substrate material includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide.

[0029] Optionally, the material of the nanostructure includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide.

[0030] Optionally, the nanostructure is a polarization-insensitive structure.

[0031] Optionally, the nanostructure is a polarization-sensitive structure.

[0032] Secondly, embodiments of this application also provide a thermal imaging device, which includes a lens and an infrared sensor for thermal imaging as provided in any of the above embodiments;

[0033] The infrared sensor is disposed on the image plane of the lens used for thermal imaging.

[0034] The technical solution provided in this application has achieved at least the following technical effects:

[0035] The lens for thermal imaging provided in this application overcomes the influence of ambient temperature changes on lens performance by using a first superlens and a second superlens arranged sequentially from the object side to the image side, wherein the first superlens is a compensation lens and the second superlens is a modulation lens. Attached Figure Description

[0036] The accompanying drawings are provided to further understand this application and are incorporated in and form a part of this specification. The drawings illustrate embodiments of this application and, together with the following description, serve to explain the principles of this application.

[0037] Figure 1 A schematic diagram of an optional structure of a lens for thermal imaging provided in an embodiment of this application is shown;

[0038] Figure 2 This illustration shows an optional structural diagram of the superlens provided in an embodiment of this application;

[0039] Figure 3 This illustration shows an optional structural diagram of the superlens provided in an embodiment of this application;

[0040] Figure 4 This illustration shows an optional structural diagram of the nanostructure of the superlens provided in an embodiment of this application;

[0041] Figure 5This illustration shows another optional structural schematic of the nanostructure of the superlens provided in the embodiments of this application;

[0042] Figure 6 This illustration shows an optional arrangement of the nanostructure of the superlens provided in an embodiment of this application;

[0043] Figure 7 This illustration shows another alternative arrangement of the nanostructure of the superlens provided in the embodiments of this application;

[0044] Figure 8 This illustration shows another alternative arrangement of the nanostructure of the superlens provided in the embodiments of this application;

[0045] Figure 9 This paper shows a phase distribution diagram of a superlens provided in an embodiment of the present application without phase coefficient constraints.

[0046] Figure 10 The diagram shows the phase distribution of the phase coefficient constrained by the superlens provided in this application embodiment;

[0047] Figure 11 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of -40°C.

[0048] Figure 12 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of -12°C.

[0049] Figure 13 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of 16°C.

[0050] Figure 14 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of 44°C.

[0051] Figure 15 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of 72°C.

[0052] Figure 16 The image shows a modulation transfer function (MTF) image of an optional structure of a lens for thermal imaging provided in an embodiment of this application at an ambient temperature of 100°C.

[0053] Figure 17 The diagram shows a comparative example of the structure provided in the embodiments of this application;

[0054] Figure 18 The image shows a modulation transfer function image of a comparative example provided in this application at an ambient temperature of -40°C;

[0055] Figure 19 The image shows a modulation transfer function image of a comparative example provided in this application at an ambient temperature of -12°C;

[0056] Figure 20 The image shows a modulation transfer function image of a comparative example provided in this application at an ambient temperature of 16°C;

[0057] Figure 21 The image shows a modulation transfer function image of a comparative example provided in this application at an ambient temperature of 44°C;

[0058] Figure 22 The image shows a modulation transfer function image of a comparative example provided in this application at an ambient temperature of 72°C;

[0059] Figure 23 The image shows the modulation transfer function of a comparative example provided in this application at an ambient temperature of 100°C.

[0060] The reference numerals in the figure represent:

[0061] 1-First superlens; 2-Second superlens; 11-Substrate; 12-Nanostructure; 13-Filling material; 14-Antireflective coating. Detailed Implementation

[0062] The present application will now be described more fully below with reference to the accompanying drawings, in which various embodiments are illustrated. However, the present application may be implemented in many different ways and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present application will be exhaustive and complete, and will fully convey the scope of the present application to those skilled in the art. The same reference numerals denote the same parts throughout the drawings. Furthermore, in the drawings, the thickness, proportions, and dimensions of parts are enlarged for clarity.

[0063] The terminology used herein is for descriptive purposes only and is not intended to be limiting. Unless the context clearly indicates otherwise, the terms “a,” “an,” “the,” and “at least one” as used herein are not intended to limit the quantity but are intended to include both singular and plural forms. For example, unless the context clearly indicates otherwise, “a component” has the same meaning as “at least one component.” “At least one” should not be construed as limited to the quantity “a.” “Or” means “and / or.” The term “and / or” includes any and all combinations of one or more of the associated listed items.

[0064] Unless otherwise specified, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art. Terms defined in commonly used dictionaries shall be interpreted as having the same meaning as in the relevant technical context, and shall not be construed as having a formal meaning in an idealized or overly formal sense unless expressly defined in the specification.

[0065] The meaning of “includes” or “contains” specifies a nature, quantity, step, operation, component, part, or combination thereof, but does not exclude other natures, quantities, steps, operations, components, parts, or combinations thereof.

[0066] This document describes embodiments with reference to cross-sectional views as idealized implementations. Thus, variations in shape relative to the illustrations are anticipated as a result of, for example, manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the regions shown herein, but should include deviations in shape due to, for example, manufacturing processes. For example, regions shown or described as flat may typically have rough and / or non-linear characteristics. Furthermore, acute angles shown may be rounded. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to show precise shapes of the regions and are not intended to limit the scope of the claims.

[0067] In the following description, exemplary embodiments according to this application will be described with reference to the accompanying drawings.

[0068] This application provides a lens for thermal imaging, such as... Figure 1 As shown, the lens includes a first superlens 1 and a second superlens 2. The second superlens 2 is a modulation lens, which plays a major role in deflecting the incident infrared light; the first superlens 1 is a compensation lens, which provides phase compensation for the entire lens and further improves aberrations during lens imaging.

[0069] A superlens is a metasurface, which is a subwavelength artificial nanostructure film. Unlike traditional refractive lenses that alter optical path difference, superlenses modulate the amplitude, phase, and polarization of incident light through nanostructure units. It should be noted that a nanostructure can be understood as a subwavelength structure containing all-dielectric or plasma particles capable of causing phase abrupt changes, while a nanostructure unit is a structural unit centered on each nanostructure obtained by dividing the superlens. Traditional lenses typically have thicknesses in the millimeter or even centimeter range, and temperature variations causing changes in lens thickness and surface shape have a significant impact on optical path difference. However, the nanostructures in a superlens are subwavelength structures, typically nanometer-sized, and temperature changes are insufficient to affect the phase abrupt changes induced by the nanostructures, thus having a negligible impact on the superlens's optical performance. Therefore, the lens for thermal imaging provided in this application embodiment can adapt to a wider range of temperature variations compared to lenses using traditional lenses.

[0070] According to embodiments of this application, each of the first superlens 1 and the second superlens 2 includes a substrate 11 and a plurality of nanostructures 12 periodically arranged on one side of the substrate 11. For ease of description, the first superlens 1 and the second superlens 2 will be collectively referred to as superlenses below. Figure 2 A schematic diagram of an optional structure of the superlens provided in an embodiment of this application is shown. Figure 3 This illustration shows another optional structural diagram of the superlens provided in an embodiment of this application.

[0071] Exemplary, the nanostructure 12 provided in this application embodiment can be a polarization-independent structure, such a structure imposing a propagation phase on the incident light. According to embodiments of this application, the nanostructure 12 can be a positive structure or a negative structure. For example, the shape of the nanostructure 12 includes a cylinder, a hollow cylinder, a square prism, a hollow square prism, etc. Figure 4 A schematic diagram of the nanostructure unit when nanostructure 12 is a cylinder is shown.

[0072] For example, the nanostructure 12 can be a polarization-dependent structure, which imposes a geometric phase on the incident light. The nanostructure 12 can be a positive or negative structure. For example, the nanostructure 12 can be an elliptical cylinder, a nanofin, or other structure. Figure 5 A schematic diagram of the nanostructure unit when nanostructure 12 is a nanofin is shown.

[0073] Furthermore, in the superlens, nanostructures are periodically arranged on the substrate, with each period containing nanostructures forming a superstructure unit. This superstructure unit is a close-packed pattern, such as a regular square or hexagon. Each period contains a set of nanostructures, and the vertices and / or centers of the superstructure unit may contain nanostructures. When the superstructure unit is a regular hexagon, at least one nanostructure is located at each vertex and center. Alternatively, when it is a square, at least one nanostructure is located at each vertex and center. Ideally, the superstructure unit should be a hexagon with nanostructures arranged at the vertices and center, or a square with nanostructures arranged at the vertices and center. It should be understood that in actual products, due to the limitations of the superlens shape, there may be missing nanostructures at the edges of the superlens, preventing it from satisfying the complete hexagon / square shape requirement. Specifically, for example... Figure 6 , Figure 7 and Figure 8 As shown, the above-mentioned superstructure units are composed of nanostructures arranged in a regular pattern, and several superstructure units are arranged in an array to form a metasurface structure.

[0074] like Figure 6 In one embodiment shown, the superstructure unit includes a central nanostructure and six peripheral nanostructures equidistant from it. The peripheral nanostructures are evenly distributed along the circumference to form a regular hexagon, which can also be understood as multiple nanostructures forming an equilateral triangle combined with each other.

[0075] like Figure 7 In one embodiment shown, the superstructure unit comprises a central nanostructure and four peripheral nanostructures equidistant from it, forming a square.

[0076] Superstructure units and their densely packed / arrayed forms can also be arranged in a circumferentially in a sector shape, such as... Figure 8 The sector shown can include two curved sides, or it can be a sector with only one curved side, such as... Figure 8 Nanostructures are set at the intersection of the sides of the fan-shaped area in the lower left corner and at the center.

[0077] For the sake of simplicity and clarity, only the nanostructures at the center of the superstructure unit are shown in the accompanying drawings of the embodiments. It should be understood that nanostructures are also provided at the vertices / intersections of the hexagonal, square, and sector outlines in the drawings.

[0078] According to embodiments of this application, optionally, the arrangement period of the nanostructures is greater than or equal to 0.3λ. c And less than or equal to 2λ c ; where λ c The wavelength is the center wavelength of the operating band. Optionally, according to an embodiment of this application, the height of the nanostructure is greater than or equal to 0.3λ.c And less than or equal to 5λ c ; where λ c The wavelength is the center wavelength of the operating band. According to an embodiment of this application, exemplarily, the feature size of the nanostructure is greater than or equal to 0.2λ. c And less than or equal to 0.8λ c ;λ c The center wavelength of the incident radiation is denoted as λ. Optionally, the thickness of the substrate 11 is less than or equal to 0.3 mm.

[0079] According to the method of this application, the material of the substrate 11 includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide. Optionally, the material of the nanostructure 12 includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide. The material of the nanostructure 12 may be the same as or different from the material of the substrate 11.

[0080] In some alternative implementations, such as Figure 3 As shown, the superlens provided in this embodiment further includes an antireflection coating 14. The antireflection coating is disposed on the side of the substrate 11 away from the nanostructure 12; or, the antireflection coating 14 is disposed on the side of the nanostructure 12 adjacent to air. The function of the antireflection coating 14 is to cause destructive interference of reflected light, thereby increasing transmittance and reducing reflection of incident radiation.

[0081] According to the embodiments of this application, such as Figure 3 , Figure 4 and Figure 5 As shown, the superlens also includes a filling material 13, which fills the spaces between the nanostructures 12, and the extinction coefficient of the filling material 13 for the operating wavelength is less than 0.01. Optionally, the filling material 13 may include air or other materials that are transparent or translucent in the operating wavelength. According to embodiments of this application, the absolute value of the difference between the refractive index of the filling material and the refractive index of the nanostructure 12 should be greater than or equal to 0.5.

[0082] It should be noted that the superlens provided in this application embodiment can be processed by semiconductor technology, and has the advantages of light weight, thin thickness, simple structure and process, low cost and high mass production consistency.

[0083] Furthermore, the phase of the superlens provided in the embodiments of this application satisfies at least any one of the following formulas (1-1) to (1-3):

[0084]

[0085]

[0086]

[0087] Where r is the distance from the center of substrate 11 to the center of any nanostructure 12; x and y are the coordinates of nanostructure 12 on substrate 11; f ML λ is the focal length of the superlens; λ is the center wavelength of the incident beam. Let a be the initial phase of the incident beam. i Let f be the phase coefficients for each order, where i is an integer greater than or equal to 1. For the first superlens 1, f ML Let f1 be the focal length of the first superlens; for the second superlens 2, f ML f2 is the focal length of the second superlens.

[0088] For a superlens that satisfies formulas (1-1) to (1-3) above, its design freedom is relatively high. For the same modulation capability, there may be multiple solutions for the phase coefficients, some of which will lead to changes in the phase distribution of the superlens, such as... Figure 9 The dramatic changes shown are theoretically possible in superlenses with such drastic phase distribution variations, which could be used in the lenses provided in the embodiments of this application. However, in reality, such phase oscillations are difficult, if not impossible, to fabricate using conventional superlens processing techniques.

[0089] More advantageously, in order for the superlens to meet both the imaging performance requirements of the lens and the requirements of the manufacturing process, the superlens provided in the embodiments of this application also needs to meet the following requirements:

[0090]

[0091] Δneff≤C;(2-2)

[0092] Wherein, neff is the equivalent refractive index of the superlens; k is the wave vector of the incident beam; Hd is the height of the nanostructure 12; Δneff is the difference between the maximum and minimum neff of the superlens; C is a constant; r is the distance from the center of the substrate 11 to the center of any of the nanostructures 12; and λ is the center wavelength of the incident beam. The value of C is determined by the target phase of the superlens, which is determined by the design parameters of the lens for thermal imaging provided in this application. For the first superlens 1, neff and Δneff are the equivalent refractive index and the difference between the maximum and minimum neff of the first superlens 1, respectively; for the second superlens 2, neff and Δneff are the equivalent refractive index and the difference between the maximum and minimum neff of the second superlens 2, respectively. Figure 10 The phase of the superlens provided in this application embodiment is shown after optimization and constraint by formulas (2-1) and (2-2). Figure 10The phase distribution of the superlens optimized by formulas (2-1) and (2-2) is better than that of the previous one. Figure 9 The phase distribution of the superlens shown is simpler and easier to manufacture.

[0093] Furthermore, in order to ensure that the lens for thermal imaging provided in this application can stably obtain clear images between an ambient temperature of -60°C and 80°C, the lens also satisfies formulas (3-1) to (3-3):

[0094] f1 ≥ 10.8 mm; (3-1)

[0095] f2≤0.58mm;(3-2)

[0096]

[0097] Where f1 is the focal length of the first superlens 1, f2 is the focal length of the second superlens 2, and d is the distance between the first superlens 1 and the second superlens 2.

[0098] Furthermore, the lens for thermal imaging provided in this application embodiment also satisfies formula (4):

[0099]

[0100] Where f is the effective focal length of the lens used for thermal imaging; f1 is the focal length of the first superlens 1, f2 is the focal length of the second superlens 2; and d is the distance between the first superlens 1 and the second superlens 2.

[0101] According to the embodiments of this application, the back focal length of the lens (i.e., the distance between the second superlens 2 and the image plane of the lens) satisfies: f2 <b<f;(5)

[0102] In formula (5), b is the back focal length of the lens used for thermal imaging; f is the effective focal length of the lens used for thermal imaging; and f2 is the focal length of the second superlens 2.

[0103] Example

[0104] This application provides an exemplary lens for thermal imaging, such as... Figure 1 As shown, the lens includes a first superlens 1 and a second superlens 2. The first superlens 1 is a compensation lens, and the second superlens 2 is a modulation lens. In this exemplary embodiment, the system parameters of the lens for thermal imaging are specifically shown in Table 1-1. The surface properties of each surface in the lens from the object side to the image side are shown in Table 1-2.

[0105] Table 1-1 Lens Specific Parameters

[0106] Lens parameters numerical values Operating wavelength 10μm Field of view 60° entrance pupil diameter 3.6mm Effective focal length 3.6mm F# 1

[0107] Table 1-2 Surface properties of the lens

[0108]

[0109]

[0110] It should be noted that when the radius of curvature of the sphere is infinite in Table 1-2, the sphere can be considered as a plane. In the lens structures exemplified in Table 1-2, the side surface of the first superlens 1 with the nanostructure faces the image plane, while the side surface of the second superlens 2 with the nanostructure faces away from the image plane. This allows the nanostructure of the superlens to be located within the internal space of the lens, preventing damage to the nanostructure during installation and use.

[0111] In this example, the modulation transfer function (MTF) of the lens used for thermal imaging at different ambient temperatures (-40℃, -12℃, 16℃, 44℃, 72℃, 100℃) is as follows: Figures 11 to 16 As shown. Figures 11 to 16 The vertical axis represents the modulation transfer function, and the horizontal axis represents the spatial cutoff frequency. T and S represent the curves in the sagittal and meridional directions, respectively. (Comparison) Figures 11 to 16 It can be seen that the modulation transfer function of this lens is the same under different ambient temperatures. See [link / reference] Figures 11 to 16 The modulation transfer function (MTF) of this lens is close to the diffraction limit under different fields of view. This means that the lens used for thermal imaging exhibits excellent image quality. Table 1-3 shows the MTF at different temperatures corresponding to a spatial cutoff frequency of 50 lp / mm and a field of view of 0.8. As can be seen from Table 1-3, the MTF remains consistent between -40℃ and +100℃. In other words, changes in ambient temperature between -40℃ and +100℃ have no impact on the lens's imaging performance.

[0112] Table 1-3 MTF of the lenses provided in the examples at different temperatures

[0113]

[0114]

[0115] Comparative Example

[0116] This application also provides comparative examples of the above examples. Comparative Example Lens parameters and Example The lens parameters in the comparative example are the same, as shown in Table 1-1. To meet the parameter requirements in Table 1-1, the lens in the comparative example includes three refractive lenses arranged sequentially from the object side to the image side, and its structure is as follows: Figure 17As shown. The modulation transfer function of the lens at different temperatures is provided by this comparison. Figures 18 to 23 As shown. Figures 18 to 23 The modulation transfer functions of the lens provided in this comparative example are shown in Table 2-1 at ambient temperatures of -40℃, -12℃, 16℃, 44℃, 72℃, and 100℃. The modulation transfer functions of the lens provided in this comparative example at different temperatures corresponding to a spatial cutoff frequency of 50 lp / mm and a field of view of 0.8 are also shown in Table 2-1. Figures 18 to 23 Both Table 2-1 and Table 2-1 show that the imaging performance of the modulation transfer function provided by this comparative example is unstable at different temperatures. Figures 18 to 23 As shown in Table 2-1, when the ambient temperature is between 16°C and 44°C, the image quality of the lens provided in this comparative example is close to that of the lens provided in the embodiment of this application; while at ambient temperatures outside of 16°C to 44°C, the image quality of the lens provided in this comparative example is significantly reduced.

[0117] Table 2-1 shows the MTF of the lenses provided for comparison at different temperatures.

[0118]

[0119] Secondly, this application also provides a thermal imaging device, which includes a lens for thermal imaging and an infrared sensor provided in any of the above embodiments. The infrared sensor is disposed on the image plane of the lens and is capable of converting received infrared signals into electrical signals.

[0120] In summary, the lens for thermal imaging provided in this application overcomes the influence of ambient temperature changes on lens performance by using a first superlens and a second superlens arranged sequentially from the object side to the image side, with the first superlens being a compensation lens and the second superlens being a modulation lens. This application also ensures stable image quality under different ambient temperatures by setting the focal lengths of the first and second superlenses and the distance between them. Furthermore, the lens provided in this application makes the superlenses easier to manufacture by constraining their phase.

[0121] The above description is merely a specific implementation of the embodiments of this application, but the protection scope of the embodiments of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the protection scope of the embodiments of this application. Therefore, the protection scope of the embodiments of this application should be determined by the protection scope of the claims.

Claims

1. A lens for thermal imaging, characterized in that, The lens for thermal imaging includes a first superlens (1) and a second superlens (2) arranged sequentially from the object side to the image side; the lens for thermal imaging has two lenses with optical power. Wherein, the first superlens (1) is a compensation lens, and the second superlens (2) is a modulation lens; The lens used for thermal imaging satisfies: ； Wherein, b is the back focal length of the lens used for thermal imaging; f is the effective focal length of the lens used for thermal imaging; and f2 is the focal length of the second superlens (2).

2. The lens for thermal imaging according to claim 1, characterized in that, The first superlens (1) and the second superlens (2) also satisfy: ； ； ； f1 is the focal length of the first superlens (1), f2 is the focal length of the second superlens (2), and d is the distance between the first superlens (1) and the second superlens (2).

3. The lens for thermal imaging according to claim 1, characterized in that, The lens used for thermal imaging also satisfies: ； Where f is the effective focal length of the lens used for thermal imaging; f1 is the focal length of the first superlens (1), f2 is the focal length of the second superlens (2); and d is the distance between the first superlens (1) and the second superlens (2).

4. The lens for thermal imaging according to any one of claims 1 to 3, characterized in that, Each of the first superlens (1) and the second superlens (2) includes a substrate (11) and a plurality of nanostructures (12) periodically arranged on one side of the substrate (11).

5. The lens for thermal imaging according to claim 4, characterized in that, The phase of each of the first superlens (1) and the second superlens (2) satisfies at least one of the following relationships: ； ； ； Where r is the distance from the center of the substrate (11) to the center of any of the nanostructures (12); x and y are the coordinates of the nanostructure (12) on the substrate (11); f ML λ is the focal length of the first superlens (1) or the second superlens (2); λ is the center wavelength of the incident beam. The initial phase of the incident beam. represents the phase coefficients of each order; i is an integer greater than or equal to 1.

6. The lens for thermal imaging according to claim 4, characterized in that, The phase of each of the first superlens (1) and the second superlens (2) satisfies the following constraint: ； ； Wherein, neff is the equivalent refractive index of the first superlens (1) or the second superlens (2); k is the wave vector of the incident beam; Hd is the height of the nanostructure (12); ∆neff is the difference between the maximum and minimum neff of the first superlens (1) or the second superlens (2); C is a constant; r is the distance from the center of the substrate (11) to the center of any of the nanostructures (12); and λ is the center wavelength of the incident beam.

7. The lens for thermal imaging according to claim 4, characterized in that, The material of the substrate (11) includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide.

8. The lens for thermal imaging according to claim 4, characterized in that, The material of the nanostructure (12) includes any one or more of silicon nitride, titanium oxide, gallium nitride, gallium phosphide, hydrogenated amorphous silicon, amorphous silicon, crystalline silicon, crystalline germanium, zinc sulfide, and zinc selenide.

9. The lens for thermal imaging according to claim 4, characterized in that, The nanostructure (12) is a polarization-insensitive structure.

10. The lens for thermal imaging according to claim 4, characterized in that, The nanostructure (12) is a polarization-sensitive structure.

11. A thermal imaging device, characterized in that, The thermal imaging device includes a lens and an infrared sensor for thermal imaging as described in any one of claims 1 to 10; The infrared sensor is disposed on the image plane of the lens used for thermal imaging.

Images