An optical element, an infrared optical system, and an infrared camera module

Abstract

This invention discloses an optical element, an infrared optical system, and an infrared camera module. The optical element includes a substrate, one side of which has a convex surface, and the other side of which has a subwavelength metasurface. The substrate is made of single-crystal silicon. The convex surface on one side of the substrate is fabricated using a photolithography-etched semiconductor process, and the subwavelength metasurface on the other side of the substrate is fabricated using a photolithography-etched semiconductor process. This invention utilizes a spherical surface and a metasurface to form an independent optical element. This structural approach combines the advantages of both surface types to efficiently utilize the optical element, achieving light focusing and aberration control, improving image quality, reducing cost, decreasing system weight, and shrinking system size.

Description

Technical Field

[0001] This invention relates to the field of infrared optical imaging technology, and in particular to an optical element, an infrared optical system, and an infrared camera module. Background Technology

[0002] Infrared optics technology utilizes infrared light for optical imaging and measurement, and is widely used in fields such as thermal imaging, remote sensing, and medical diagnostics. With the rapid development of infrared technology, infrared cameras can achieve excellent imaging results at night and in harsh environments, leading to increasing market demand. Besides its widespread application in the military field, in recent years, with the popularization of infrared detection technology, significant breakthroughs have been achieved in important areas such as security monitoring, surveying and remote sensing, non-contact temperature measurement, outdoor sports, industrial inspection, and smart homes. Infrared optical lenses are a crucial component in this field. The development of infrared imaging optical systems has become a key factor in the development of infrared detection technology, requiring the miniaturization and thinning of infrared imaging equipment, which necessitates limitations on the number and structure of lenses in optical imaging systems; it also demands increasingly lower costs and higher resolution and performance for infrared imaging equipment, representing a need for lower-cost, more cost-effective solutions for optical systems.

[0003] In related infrared imaging technologies, long-wave infrared lenses mainly use traditional methods to process optical components, such as cold processing, single-point machining, or molding, with germanium single crystals and chalcogenide materials as the main materials.

[0004] Optical components manufactured using the above methods employ traditional design schemes, requiring each lens to possess a certain optical power, i.e., a certain curvature and thickness. When the optical power distribution is insufficient or the aberration correction capability is inadequate, the number of lenses needs to be further increased, thus hindering the realization of lightweight miniaturization and failing to effectively reduce size and weight. Furthermore, traditional design schemes have both high material and processing costs, and production capacity is strictly limited by processing capabilities, which restricts the cost from being reduced to a level suitable for widespread application, thus limiting the application of infrared imaging technology in the civilian consumer market. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes an optical element, an infrared optical system and an infrared camera module. The optical element of the present invention can reduce the size of the lens and reduce the manufacturing cost.

[0006] The technical solution of the present invention is implemented as follows: The present invention discloses an optical element, including a substrate, one side of the substrate having a convex surface, and the other side of the substrate having a subwavelength structure metasurface.

[0007] Furthermore, the phase distribution of the subwavelength metasurface satisfies the following expression:

[0008]

[0009] Where ρ is the radial coordinate of the metasurface, R is the normalized radius, and A, B, C, D, E, F, G, H, and I are the coefficients of the quadratic, quartic, hexagram, octagonal, decagram, twelfth, fourteenth, sixteenth, and eighteenth order terms of the phase abrupt change of the metasurface, respectively.

[0010] Furthermore, the subwavelength structure metasurface includes an array of nanopillars, which consists of several nanopillars with a fixed period T and a height h.

[0011] Furthermore, the substrate material is monocrystalline silicon.

[0012] Furthermore, the convex and / or subwavelength metasurface is coated with an antireflective film.

[0013] The present invention also discloses an infrared optical system, including a first optical element and a second optical element arranged sequentially along the optical axis propagation direction. The first optical element and the second optical element adopt the optical elements described above. The object side of the first optical element has a convex surface, the image side of the first optical element has a subwavelength structure metasurface, the object side of the second optical element has a subwavelength structure metasurface, and the image side of the second optical element has a convex surface.

[0014] Furthermore, the first optical element has negative or positive optical power, and the second optical element has positive optical power.

[0015] Furthermore, the effective convex aperture of the first optical element is D2, and the effective convex aperture of the second optical element is D3;

[0016] The object-side elevation of the first optical element is Sag1, and the image-side elevation of the second optical element is Sag2.

[0017] 27.36≤D2 / |Sag1|≤54.55, 15.16≤D3 / |Sag2|≤18.63.

[0018] Furthermore, the aspect ratio of the subwavelength metasurface ranges from 9.6 to 41.7.

[0019] Furthermore, the convex surface and subwavelength metasurface of the first and second optical elements are coated with an antireflection film.

[0020] Furthermore, the infrared optical system of the present invention also includes an aperture stop, a detector protection window, and a focal plane, wherein the aperture stop, the first optical element, the second optical element, the detector protection window, and the focal plane are arranged sequentially along the optical axis propagation direction.

[0021] The present invention also discloses an infrared camera module, which employs the infrared optical system described above.

[0022] The present invention has at least the following beneficial effects:

[0023] This invention uses a spherical surface and a metasurface to form an independent optical element. This structure can combine the advantages of the two surface types to efficiently utilize the optical element, achieve light focusing and aberration control, and improve imaging quality.

[0024] This invention employs a structure consisting of a spherical surface and a metasurface, which allows for ample design freedom while leveraging the ability of the spherical surface to be coated with a hard protective film. This facilitates placement at the outermost end, preventing damage to the relatively fragile subwavelength structure of the metasurface that could affect image quality and effectively improving the lens's environmental adaptability.

[0025] This invention directly utilizes standard single-crystal silicon wafers and employs photolithography etching semiconductor processes to precisely design and fabricate metasurfaces at the microscopic level, exhibiting extremely high reproducibility. Spherical surface processing also employs photolithography etching semiconductor processes, ensuring compatibility with metasurface fabrication techniques. This enables efficient production and application of optical components. This approach not only guarantees imaging performance but also significantly reduces production costs and facilitates mass production by fully leveraging photolithography technology. Through an innovative optical architecture, this invention allows the use of a single optical element combining a spherical surface and a metasurface to replace a monolithic metasurface optical element and a traditional optical element, or to replace an optical assembly composed of multiple traditional optical elements. This design overcomes the current limitations in the metasurface lens field, such as the constraints between bandwidth, large aperture, and high image quality. This solution not only guarantees imaging performance but also significantly reduces production costs and system weight.

[0026] The infrared camera temperature measurement device composed of optical elements with this architecture can greatly reduce its size and weight, making it easier to expand and integrate this device into consumer-grade application scenarios that focus on cost-effectiveness. This solution can not only ensure imaging performance, but also significantly reduce user costs and product experience. Attached Figure Description

[0027] Figure 1 A schematic diagram of an infrared optical system provided in one embodiment of the present invention;

[0028] Figure 2 A spherical elevation diagram of an optical element provided in one embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the nanopillar parameters of an optical element provided in one embodiment of the present invention;

[0030] Figure 4 A schematic diagram of the aspect ratio of a nanopillar for an optical element provided in one embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the nanopillar distribution period of an optical element provided in one embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the assembly of an infrared camera module provided in one embodiment of the present invention;

[0033] Figure 7 An exploded view of an infrared camera module provided in one embodiment of the present invention;

[0034] Figure 8 This is a schematic diagram of the distortion of an infrared optical system provided in one embodiment of the present invention.

[0035] In the attached diagram, 1 is the aperture stop, 2 is the first optical element, 21 is the object-side surface of the first optical element, 22 is the image-side surface of the first optical element, 3 is the second optical element, 31 is the object-side surface of the second optical element, 32 is the image-side surface of the second optical element, 4 is the detector protection window, 5 is the focal plane, 6 is the lens barrel, 7 is the spacer, 8 is the lens mount, 9 is the infrared detector, 10 is the ceramic substrate, and 11 is the FPC. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. In the description of this invention, unless otherwise stated, "a plurality" or "several" means two or more. Similarly, "an," "a," or "the," and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0038] In the various figures, the same elements are represented by similar reference numerals. For clarity, not all parts in the figures are drawn to scale. Furthermore, some well-known parts may not be shown in the figures.

[0039] Many specific details of the invention, such as the structure, materials, dimensions, processing methods, and techniques of the components, are described below to provide a clearer understanding of the invention. However, as those skilled in the art will understand, the invention may be implemented without following these specific details.

[0040] Example 1

[0041] See Figures 1 to 5 The present invention discloses an optical element comprising a substrate, one side of which has a convex surface and the other side of which has a subwavelength structure metasurface.

[0042] Furthermore, the convex surface can be spherical or aspherical. Since it is currently difficult to guarantee the surface quality when processing aspherical surfaces, affecting the final imaging effect, it is preferable that the convex surface of this invention is spherical. This invention primarily uses spherical surfaces for design and development.

[0043] The optical element of this invention adopts a spherical-supersurface combination. Compared with an optical system composed of pure metasurfaces, the optical element of this invention with the addition of a spherical surface has two advantages: First, most of the optical power is concentrated on the spherical surface, and the metasurface only needs to undertake a small amount of focusing function, which reduces the influence of the metasurface's own chromatic aberration on the system's chromatic aberration. Second, because a spherical surface with a design curvature that can be varied is added, the metasurface can vary a wider range in wavefront control, and the phase distribution is more free, which plays a greater role in correcting aberrations.

[0044] This invention can obtain the phase change characteristics of metasurface units of different sizes and shapes at different wavelengths within the working band by scanning, forming a metasurface unit library. Based on the dispersion characteristics requirements of the metasurface at each location given by the optical system, the required metasurface units are selected from the library.

[0045] Furthermore, the phase distribution of the subwavelength metasurface satisfies the following expression:

[0046]

[0047] Where ρ is the radial coordinate of the metasurface, R is the normalized radius, and A, B, C, D, E, F, G, H, and I are the coefficients of the quadratic, quartic, hexagram, octagonal, decagram, twelfth, fourteenth, sixteenth, and eighteenth order terms of the phase abrupt change of the metasurface, respectively.

[0048] Furthermore, the subwavelength structure metasurface includes a nanopillar array, which consists of several nanopillars with a fixed period T and height h. That is, the subwavelength structure metasurface of this invention is arranged with a nanopillar array of period T and height h. The nanopillar array is arranged in a quadrilateral or hexagonal periodic arrangement. Besides quadrilateral and hexagonal periodic arrangements, other shapes and arrangements of nanopillar arrays also exist.

[0049] The nanopillars of this invention can be in various shapes, such as circular, annular, square, or square annular, to meet the requirements for width dispersion control of different metasurfaces.

[0050] Regarding the morphology selection of the metasurface unit, the height h of the metasurface unit can be selected to be between 5 and 15 μm, and the period can be selected to be between 2.5 and 3.5 μm. The aspect ratio of the metasurface unit is less than or equal to 50.

[0051] The aspect ratio is the ratio of the height perpendicular to the machined surface to the smaller feature size on the machined surface. For example, the aspect ratio can be the ratio of the height of a nanopillar to its diameter, or the height of a nanopillar to the spacing between nanopillar mirrors.

[0052] Further, see Figure 5 The nanopillars are arranged in a periodic pattern T, and the diameter of the nanopillars is D. n The air gap between the nanopillars is d. n And T = d n +D n n is a positive integer, i.e., 1, 2, 3...i. The minimum column spacing d1 = 0.3 μm, and the nanopillar height h = 12.5 μm. The maximum column spacing d... i =1.3μm, nanopillar height h=12.5μm.

[0053] Furthermore, the aspect ratio of the subwavelength metasurface is in the range of h / maximum column spacing d. i (e.g. 9.6) to h / minimum column spacing d1 (e.g. 41.7).

[0054] Furthermore, the substrate material for the optical element is monocrystalline silicon.

[0055] Furthermore, the optical element is formed by photolithography and etching of a whole silicon wafer.

[0056] Furthermore, the surfaces of the optical elements are all fabricated using semiconductor processes such as photolithography or nanoimprinting.

[0057] Furthermore, the convex surface on one side of the substrate is fabricated using a photolithography semiconductor etching process, and the subwavelength metasurface on the other side of the substrate is fabricated using a photolithography semiconductor etching process.

[0058] This invention, through an innovative optical architecture and photolithographic etching semiconductor process, allows the use of a single optical element combining a spherical surface and a metasurface to replace a monolithic metasurface optical element and a traditional optical element, or to replace an optical assembly composed of multiple traditional optical elements. This design overcomes the current limitations in the field of metasurface lenses, such as the constraints between bandwidth, large aperture, and high image quality. This solution not only ensures imaging performance but also significantly reduces production costs and system weight.

[0059] Furthermore, the convex and / or subwavelength metasurface is coated with an antireflective film.

[0060] Example 2

[0061] See Figures 1 to 5 This invention discloses an infrared optical system, including a propagation direction along the optical axis I (e.g., Figure 1 The first optical element 2, which has negative or positive optical power, and the second optical element 3, which has positive optical power, are arranged sequentially from left to right. The first optical element 2 and the second optical element 3 adopt the optical elements described in Embodiment 1. The object side 21 of the first optical element 2 has a convex surface (a convex surface in the region near the optical axis), and the image side 22 of the first optical element 2 has a subwavelength structure metasurface. The object side 31 of the second optical element 3 has a subwavelength structure metasurface, and the image side 32 of the second optical element 3 has a convex surface (a convex surface in the region near the optical axis).

[0062] Preferably, the convex surface of the object side 21 of the first optical element 2 is a spherical surface.

[0063] Preferably, the convex surface of the image side 32 of the second optical element 3 is a spherical surface.

[0064] Furthermore, the phase distributions φ1 and φ2 of the subwavelength metasurfaces of the first optical element 2 and the second optical element 3 satisfy the following expressions:

[0065]

[0066] Where ρ is the radial coordinate of the metasurface, R is the normalized radius, and A1, B1, C1, D1, E1, F1, G1, H1, and I1 are the coefficients of the quadratic, quartic, septic, octogenetic, decadal, twelfth, fourteenth, sixteenth, and eighteenth order phase transitions of the metasurface of the image-side surface 22 of the first optical element 2, respectively. A2, B2, C2, D2, E2, F2, G2, H2, and I2 are the coefficients of the quadratic, quartic, septic, octogenetic, decadal, twelfth, fourteenth, sixteenth, and eighteenth order phase transitions of the metasurface of the object-side surface 31 of the second optical element 3, respectively. The metasurface coefficients of the three embodiments are shown in Tables 1, 2, and 3.

[0067] Table 1 Metasurface Coefficients of the First Embodiment

[0068]

[0069] Table 2 Metasurface Coefficients of the Second Embodiment

[0070]

[0071] Table 3 Metasurface Coefficients of the Third Embodiment

[0072]

[0073] Furthermore, the effective convex aperture of the first optical element 2 is D2, and the effective convex aperture of the second optical element 3 is D3; the sagitta of the object side 21 of the first optical element 2 is Sag1, and the sagitta of the image side 32 of the second optical element 3 is Sag2.

[0074] 27.36≤D2 / |Sag1|≤54.55,15.16≤D3 / |Sag2|≤18.63;

[0075] When the above relationship is out of range, it will cause a sharp increase in processing difficulty and a sharp decrease in production yield, which is not conducive to cost reduction.

[0076] Furthermore, the convex surface and subwavelength metasurface of the first optical element 2 and the second optical element 3 are coated with antireflection films. Multiple layers of antireflection films are applied to the convex (or spherical) surface and the metasurface to achieve higher transmittance, reduce reflection and scattering losses, and improve the imaging quality of the system.

[0077] The object-side surface of the first optical element 2 is spherical, assuming part of the optical power to focus light rays at various field-of-view angles. The image-side surface of the second optical element 3 is spherical, assuming part of the optical power, and effectively improving the ability of edge beams to be incident on the detector focal plane 5.

[0078] The image-side surface of the first optical element 2 and the object-side surface of the second optical element 3 are metasurfaces. By adjusting the periodic size and height of the nanopillars, the phase of each field of view light is modulated so that the dispersion characteristics in the 8-12μm working band are nearly consistent, and spherical aberration, coma, field curvature and astigmatism are corrected.

[0079] The focal length of the first optical element 2 is f1, and the focal length of the second optical element 3 is f2, wherein f1<0 or f1>0, and f2>0.

[0080] Furthermore, the infrared optical system of the present invention also includes an aperture stop 1, a detector protection window 4, and a focal plane 5, wherein the aperture stop 1, the first optical element 2, the second optical element 3, the detector protection window 4, and the focal plane 5 are arranged sequentially along the propagation direction of the optical axis I.

[0081] Furthermore, multiple such optical elements are arranged according to the designed optical system sequence and spacing, and fixed by a precision positioning device to form an optical system. The metasurface coefficients of one embodiment are shown in Tables 2, 3, and 4, and its distortion diagram is shown below. Figure 8 As shown.

[0082] Table 2 shows the optical system parameters of the first embodiment.

[0083]

[0084] Where, Sag1 = 0.022, Sag2 = -0.107, f1 = -61.03, f2 = 1.229

[0085] D2 / |Sag1|=54.55; D3 / |Sag2|=17.6; TTL / f=2.336

[0086] Table 3 shows the optical system parameters for the second embodiment.

[0087]

[0088] Where, Sag1 = 0.0199, Sag2 = -0.105, f1 = 3.11, f2 = 1.125

[0089] D2 / |Sag1|=50.75; D3 / |Sag2|=15.16; TTL / f=2.863

[0090] Table 4 shows the optical system parameters for the third embodiment.

[0091]

[0092]

[0093] Where, Sag1 = 0.044, Sag2 = -0.109, f1 = -3.711, f2 = 0.907

[0094] D2 / |Sag1|=27.36; D3 / |Sag2|=18.63; TTL / f=2.408

[0095] Example 3

[0096] See Figures 1 to 7 An infrared camera module employs the infrared optical system described in Embodiment 2.

[0097] The infrared camera module includes a lens mount 8, a lens barrel 6, and a substrate. The lens mount 8 is fixed on the substrate, and an infrared detector 9 is disposed on the substrate. The lens barrel 6 is fixedly connected to the upper end of the lens mount 8. The first optical element 2 and the second optical element 3 of the infrared optical system are fixed inside the lens barrel 6 and located directly above the infrared detector 9. The substrate is connected to the FPC 11. The substrate is a ceramic substrate 10.

[0098] The lens barrel 6 is provided with a spacer 7, which is located between the first optical element 2 and the second optical element 3.

[0099] The focal length of the optical lens is f, and the total length of the optical lens is TTL, and 2.3 <TTL / f<2.9。

[0100] This invention reduces costs, as detailed below: Through innovative architecture and photolithography techniques, this invention utilizes semiconductor processing on standard wafers, significantly reducing mass production costs while maintaining imaging performance. This is because the spherical and metasurface surfaces used in this invention are achieved using process-compatible semiconductor processing technologies, and the metasurface technology greatly enhances the design freedom of optical devices, enabling functions that traditional optical components cannot achieve. This reduces the need for complex optical components and lowers production costs.

[0101] This invention reduces system weight, as detailed below: By employing a spherical surface and a metasurface to construct an independent optical element, this invention significantly reduces system weight. This is because metasurface technology allows for flexible control over the phase, amplitude, and polarization characteristics of light, thereby enabling more flexible optical element design, reducing the number of traditional optical elements used, and ultimately lowering system weight.

[0102] This invention reduces the system size, as detailed below: The infrared imaging temperature measurement device composed of optical elements with this structure can significantly reduce its physical size. This is because metasurface technology greatly improves the design freedom of optical devices, allowing traditionally thick spherical lenses to be replaced by extremely thin silicon wafers, enabling a more rational spatial distribution of optical elements and reducing the system size.

[0103] This invention expands the application scenarios, as detailed below: Through the improvements in the above three aspects, this invention enables infrared optical systems to meet the requirements of miniaturization and lightweighting while ensuring imaging performance, thereby expanding into more consumer-grade application scenarios that focus on cost-effectiveness.

[0104] Due to its advanced nature, this invention has wide applications in optical lens design, metasurface technology, and infrared optics. First, through innovative structural methods and photolithography, it significantly reduces mass production costs and greatly lightens system weight while maintaining imaging performance, which is of significant practical value in optical lens design. Second, the metasurface technology of this invention greatly enhances the design freedom of optical devices, enabling functions that traditional optical components cannot achieve, which has important research and application value in the field of metasurface technology. Finally, the infrared optical system of this invention can maintain imaging performance while achieving miniaturization and weight reduction, which has significant application prospects in the field of infrared optics. Furthermore, with technological advancements and increasing consumer demands for product performance, the demand for lightweight, compact, and high-performance optical devices is growing, making the application prospects of this invention very broad.

[0105] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An infrared optical system, characterized in that: It includes a first optical element and a second optical element arranged sequentially along the optical axis propagation direction. The object side of the first optical element has a convex surface, and the image side of the first optical element has a subwavelength structure metasurface. The object side of the second optical element has a subwavelength structure metasurface, and the image side of the second optical element has a convex surface. The effective convex aperture of the first optical element is D2, and the effective convex aperture of the second optical element is D3. The object-side elevation of the first optical element is Sag1, and the image-side elevation of the second optical element is Sag2. 27.36≤D2 / |Sag1|≤54.55,15.16≤D3 / |Sag2|≤18.

63.

2. The infrared optical system according to claim 1, characterized in that: The phase distribution of the subwavelength structure metasurface satisfies the following expression: ； in, ρ Let R be the radial coordinate of the metasurface, and R be the normalized radius. A, B, C, D, E, F, G, H, and I are the coefficients of the quadratic, quartic, hexagram, octagonal, decimal, twelfth, fourteenth, sixteenth, and eighteenth order terms of the phase abrupt change of the metasurface, respectively.

3. The infrared optical system according to claim 1, characterized in that: Subwavelength structured metasurfaces include nanopillar arrays, which consist of several nanopillars with a fixed period T and height h.

4. The infrared optical system according to claim 1, characterized in that: The substrate material for both the first and second optical elements is monocrystalline silicon.

5. The infrared optical system according to claim 1, characterized in that: The first optical element has negative or positive optical power, and the second optical element has positive optical power.

6. The infrared optical system according to claim 1, characterized in that: The aspect ratio of the subwavelength metasurface ranges from 9.6 to 41.

7.

7. The infrared optical system according to claim 1, characterized in that: It also includes an aperture stop, a detector protection window, and a focal plane, wherein the aperture stop, the first optical element, the second optical element, the detector protection window, and the focal plane are arranged sequentially along the optical axis propagation direction.

8. An infrared camera module, characterized in that: The infrared optical system described in any one of claims 1 to 7 is employed.

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