Infrared refraction-super hybrid lens

Abstract

The invention discloses an infrared refraction and super hybrid lens, and relates to the technical field of infrared imaging. Comprising a first lens with negative focal power, a diaphragm, a super-structure lens and a second lens with positive focal power which are sequentially arranged from an object plane to an image plane in the optical axis direction. Positive chromatic aberration is obtained through the refraction spherical surface, negative chromatic aberration is obtained through the diffraction surface, and chromatic aberration correction is achieved through focal power distribution. The refraction element with positive and negative focal power is used for bearing large focal power, and the metasurface element is used for correcting residual chromatic aberration and spherical aberration. According to the invention, a light-weight large-field-angle large-numerical-aperture infrared imaging system is realized; by utilizing the characteristic that the super lens is insensitive to temperature, the system has an athermalization effect; and an aspherical lens is not used and the number of lenses is small, so that the weight and the cost of the lens are effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of infrared imaging, and in particular to an infrared refractive-super hybrid lens. Background Art

[0002] The use of infrared bands for target imaging and recognition has a wide range of practical applications. It can be used in areas such as human body temperature detection and civil security monitoring, and is also an important part of guidance technology. With the development of science and technology and application needs, there is a greater demand for the integration, multi-function and intelligence of devices.

[0003] There is an increasing demand for miniaturization and lightweight of optical imaging systems while ensuring image quality, that is, the imaging lens group can be smaller and lighter, while the production cost is effectively controlled. Secondly, compatibility and integration with CMOS structures will also be a major trend in the development of optical imaging systems in the future. Although high-quality imaging has been achieved using traditional block geometry optical systems, there is limited room for development in the direction of integration, which requires breakthroughs in theoretical design. In addition, in the case of large aperture and large numerical aperture, the demand for aspheric surfaces will also increase the overall cost of the system. With the deepening of research, refractive-superhybrid lenses have also been proposed to achieve miniaturization and integrated design of optical systems.

[0004] However, in the traditional refractive-meta hybrid design, the refractive element is also required to have multiple aspherical surfaces. This solution has high processing cost requirements, limits production applications, and does not give full play to the wavefront modulation capability of the meta-lens. In view of this, the present application provides a new infrared refractive-meta hybrid lens and design method, which obtains a miniaturized and low-cost infrared imaging optical system without using aspherical surfaces. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an infrared refractive-super hybrid lens. The present invention obtains positive chromatic aberration by refractive spherical surface and negative chromatic aberration by diffractive surface, and the two distribute the focal length to realize chromatic aberration correction, uses the refractive element with positive and negative focal length to bear a larger focal length, and uses the metasurface element to correct the remaining chromatic aberration and spherical aberration, giving full play to the advantages of the two elements, and obtaining high imaging quality under the technical requirements of low cost and miniaturization.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] An infrared refractive-meta hybrid lens comprises a first lens, an aperture, a metalens and a second lens arranged in sequence along the optical axis from the object plane to the image plane; wherein the first lens has a negative optical focal length and the second lens has a positive optical focal length; the metalens comprises a substrate and a microstructure arranged on the substrate, wherein the microstructure is a hole-shaped structure located on the image side of the metalens, and the microstructure is periodically arranged in an array on the substrate.

[0008] Preferably, both surfaces of the first lens are spherical, wherein the object side surface is concave and the image side surface is convex; the object side surface of the second lens is spherical and convex, and the image side surface is a plane; the object side surface of the meta-lens is a plane, and the image side surface is a diffraction surface, and the diffraction surface has equal group delay dispersion characteristics.

[0009] Preferably, the phase design method of the microstructure comprises the following steps:

[0010] S1. Construct a polynomial expression of the metasurface phase profile Φ. Based on the polynomial formula, design the phase profile of the metasurface as needed. The polynomial expression of the metasurface phase profile Φ is as follows:

[0011]

[0012] In the formula, the diffraction order of the metasurface is M, the maximum number of terms is N, the normalized radius is R, and the coefficients of the polynomial are A. i ;

[0013] S2, adjusting the arrangement period p and depth h of the microstructure, traversing the structural parameters d of each microstructure, simulating and obtaining the phase-wavelength curve of the microstructure, where 0.25≤d / p≤0.8, and calculating the group delay dispersion characteristics of the microstructure in the working band and the central wavelength phase of the microstructure;

[0014] S3, select a set of microstructure structural parameters d so that the current meta-lens meets the design requirements, wherein the central wavelength phase of each microstructure is consistent with the phase profile determined in S1, and the group delay dispersion characteristics of each microstructure are equal; if the microstructure cannot meet the design requirements, return to S2 to adjust the period and depth of the microstructure; repeat S2 until the current meta-lens meets the design requirements;

[0015] S4. According to the processing accuracy of the processing equipment, determine whether the current microstructure design can be processed. If it is determined that the microstructure cannot be processed, return to S2, change the microstructure parameters, and repeat S2-S3 until it is confirmed that the microstructure can be processed.

[0016] The beneficial effects of adopting the above technical solution are:

[0017] The present invention adopts two refractive spherical mirrors and a meta-lens to realize a lightweight infrared imaging system with a large field of view and a large numerical aperture; the temperature-insensitive property of the meta-lens is utilized to achieve an athermal effect; the present invention has no aspherical lenses and has a small number of lenses, which effectively reduces the weight and cost of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of an optical system of an infrared refractive-super hybrid lens provided by the present invention;

[0019] Figure 2 Schematic diagram of the optical path of an infrared refractive-super hybrid lens provided by an embodiment of the present invention;

[0020] Figure 3 is a schematic diagram of a meta-lens microstructure unit provided by an embodiment of the present invention;

[0021] Figure 4 yes Figure 2 MTF graph of the optical system shown;

[0022] Figure 5 yes Figure 2 Spot diagram of the optical system shown;

[0023] Figure 6 yes Figure 2 Illuminance graph of the optical system shown;

[0024] Figure 7 yes Figure 2 Phase distribution diagram of the meta-lens in the optical system shown;

[0025] Figure 8 yes Figure 2 The MTF curves of the optical system shown are at high and low temperatures.

[0026] Explanation of the reference numerals: 101 is the first surface of the first lens; 102 is the second surface of the first lens; 200 is the aperture; 301 is the first surface of the meta-lens; 302 is the second surface of the meta-lens; 401 is the first surface of the second lens; 402 is the second surface of the second lens; 500 is the window plate; 600 is the image plane. DETAILED DESCRIPTION

[0027] In order to enable researchers in the field to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention or the claims of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work should fall within the scope of protection of the present invention.

[0028] The solution of the present invention comprises: an infrared refractive super hybrid lens, referring to Figure 1 , including a first lens with negative focal length, an aperture, a meta-lens, and a second lens with positive focal length arranged in sequence along the optical axis from the object plane to the image plane. The infrared refractive-meta hybrid lens imaging is observed using a detector with a germanium window. Figure 2The light shown passes through the first lens, the aperture, the meta-lens, the second lens in sequence along the optical axis, and finally passes through the germanium window piece on the surface of the detector to converge into a clear image. In the embodiment of the present invention, a detector with a pixel size of 17um and a resolution of 160*120 is used. An infrared refractive-super hybrid lens with an F number (i.e., aperture number) of 1.08, a focal length of 3.1mm, a full field of view angle FOV greater than 60°, and a total number of lenses of 3 is achieved, and its operating band is 8μm to 12μm. By adjusting the curvature, thickness, curvature, and phase parameters of each lens, this embodiment can be used in an environment of -30℃ to 80℃, and the total length of the lens is less than 15mm. It can be seen from the above lens performance parameters that the embodiment of the present invention manufactures an infrared refractive-super hybrid short-focus wide-angle optical system.

[0029] As a preferred embodiment, Figure 1 , 2 As shown, the object side of each lens is called the first surface, and the image side is called the second surface. The first surface 101, the second surface 102 of the first lens, and the first surface 401 of the second lens are all spherical surfaces. The first lens is a meniscus lens, and its first surface 101 is a concave surface, and the second surface 402 is a convex surface; the second lens is a plano-convex lens, and the first surface 401 is a convex surface, and the second surface 402 is a plane; the first surface 301 of the meta-lens is a plane, and the second surface 302 is a diffraction surface. The meta-lens is a circular lens with uniform thickness, including a substrate and microstructures arranged on the substrate, the substrate is located on the plane side of the meta-lens, and the microstructure is located on the diffraction side, and all microstructures are arranged in an array periodically on the substrate.

[0030] As a preferred implementation, the equivalent focal length f of the infrared refractive-hybrid lens satisfies f≥3.1 mm; the distance from the first surface 101 of the first lens to the image plane is the total optical length TTL; wherein 3≤TTL / f≤5.5.

[0031] As a preferred embodiment, the material of the meta-lens is silicon with a thickness of 0.5 mm, and the materials of the first lens and the second lens are both chalcogenide glass.

[0032] Exemplarily, Table 1 describes in detail, in a preferred implementation manner, the specific optical system parameters of each lens in the infrared refractive-hybrid lens provided by an embodiment of the present invention at room temperature.

[0033] Table 1 Optical system structural parameters

[0034]

[0035] The serial numbers 0-8 respectively represent the first surface 101, the second surface 102 of the first lens, the first surface 301 (coinciding with the aperture 200), the second surface 302 of the meta-lens, the first surface 401, the second surface 402 of the second lens, the object side surface, the image side surface, and the image surface 600 of the window. The phase profile Φ of the meta-lens is designed using the following polynomial:

[0036]

[0037] Where M is the diffraction order of the metasurface, N is the maximum number of terms, R is the normalized radius, and A is i are coefficients of each polynomial; illustratively, Table 2 details the phase of the meta-lens in this embodiment, Figure 7 is the phase distribution diagram corresponding to the meta-lens, and the unit is rad / 2π.

[0038] Table 2 Metalens polynomial coefficients

[0039]

[0040] Figure 3 This is a schematic diagram of the microstructure of the meta-lens in the embodiment. The dotted line in the figure represents the invisible line. In order to achieve the equal group delay characteristics, the microstructure in this embodiment adopts a hole-type structure with a microstructure period of 4μm, and the structural parameter d of the hole (the structural parameter d of the circular hole represents the aperture, and the structural parameter d of the square hole represents the side length of the hole) is in the range of 1.5μm to 3μm, and the depth of the hole is h=12μm. Among them, the processing difficulty of the circular hole is relatively small and it is the most commonly used. This embodiment also uses a square hole type or a cross hole type to expand the phase dispersion library of the microstructure. And the use of a sub-wavelength microstructure arrangement period obtains high diffraction efficiency and improves the overall transmission efficiency. The use of a microstructure with a depth of 12μm effectively guarantees the equal group delay requirement of the center wavelength phase covering 2π.

[0041] The microstructure diffraction surface of the meta-lens has equal group delay dispersion characteristics, and the phase design method of the microstructure includes the following steps:

[0042] S1. Define the meta-lens phase profile Φ by a polynomial formula, and iteratively optimize according to the basic parameters of lens optical design to obtain the ideal phase profile Φ of the meta-lens;

[0043] S2. Adjust the arrangement period and depth of the microstructure, and calculate the group delay dispersion characteristics of the microstructure in the working band (8-12um) and the central wavelength phase of the microstructure by simulating the phase-wavelength curve of the microstructure; the arrangement period is the spacing distance of each row / column of microstructures;

[0044] S3, combining the phase profile Φ determined in S1, matching and determining the microstructures at each radius of the meta-lens, wherein each microstructure needs to satisfy the central wavelength phase and the phase profile, and the group delay dispersion characteristics of each microstructure are equal; if it is determined that the microstructure cannot fully match the phase profile requirement, return to S2, change the microstructure arrangement period and depth, and repeat S2 until the microstructure can fully match the designed phase profile;

[0045] S4. According to the matched microstructure parameter distribution, determine the microstructure layout for processing, observe the processing results to determine whether the current design can be processed, and if it is determined that the microstructure cannot be processed (such as falling off, the aperture error is too large, etc.), return to S2, change the microstructure parameters, and repeat S2-3 until it is confirmed that the microstructure can be processed.

[0046] Figure 4 It is a schematic diagram of the MTF curve of an embodiment of the present invention at room temperature, achieving a transfer function greater than 0.4 at 35mm / lp. Figure 5 This is a spot diagram of an embodiment of the present invention at room temperature. The spot diagram is concentrated and can match an uncooled long-wave infrared detector. Both the MTF curve and the spot diagram show that this embodiment is close to the diffraction limit and has high imaging quality. Figure 6 This is a point diagram illuminance curve diagram of an embodiment of the present invention at room temperature, which can meet a relative illumination of more than 95% under a 30-degree field of view.

[0047] Figure 8 The MTF curve of the embodiment of the present invention at high and low temperatures is shown in the figure. As shown in the figure, at low temperature of -30°C and high temperature of 80°C, the transfer function at 35lp / mm is basically above 0.4, which can achieve the passive heat elimination effect.

[0048] In summary, an infrared refractive metasurface hybrid lens of the present invention utilizes the positive and negative dispersion effects of the refractive spherical surface and the diffraction surface to achieve chromatic aberration correction by distributing the optical focal length between the two. A refractive element with one positive and one negative optical focal length is used to bear a larger optical focal length, and a single-sided metasurface element is used to correct the remaining chromatic aberration and spherical aberration, thereby giving full play to the advantages of the two elements, reducing the types of materials used, the number of lenses, and the number of aspheric surfaces, and effectively reducing costs. The system obtains an imaging quality close to the diffraction limit with a field of view angle of more than 60° and an F number of 1.08, and can effectively realize environmental detection in a wide range of temperature environments (-30°C to 80°C).

[0049] It should be noted that, in the description of this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0050] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations that do not depart from the essence of the present invention based on the technical inspirations disclosed by the present invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. An infrared hybrid lens, characterized in that: The invention comprises a first lens, an aperture, a meta-lens and a second lens which are arranged in sequence along the optical axis from the object plane to the image plane; wherein the first lens has a negative optical focal length and the second lens has a positive optical focal length; the meta-lens comprises a substrate and a microstructure arranged on the substrate, wherein the microstructure is a hole-shaped structure and is located on the image side of the meta-lens, and the microstructure is periodically arranged in an array on the substrate.

2. The infrared refractive super hybrid lens according to claim 1, characterized in that: Both sides of the first lens are spherical, wherein the object side surface is concave and the image side surface is convex; the object side surface of the second lens is spherical and convex, and the image side surface is a plane; the object side surface of the meta-lens is a plane, and the image side surface is a diffraction surface, and the diffraction surface has equal group delay dispersion characteristics.

3. The infrared refractive super hybrid lens according to claim 1, characterized in that: The focal length f1 of the first lens, the focal length f2 of the second lens and the equivalent focal length f of the infrared refractive-meta hybrid lens have the following relationship: -18≤f1 / f≤0, and 0≤f2 / f≤5.5; the distance between the first lens and the meta lens is ≥2mm, the distance between the meta lens and the second lens is ≥0.5mm, and the optical back focus of the lens is ≥3.5mm.

4. The infrared refractive super hybrid lens according to claim 1, characterized in that: The aperture is coincident with the object side surface of the meta-lens.

5. The infrared refractive super hybrid lens according to claim 1, characterized in that: The arrangement of the microstructure is specifically a periodic arrangement according to a tetragonal lattice. The microstructure is an open-hole structure, and the direction of the opening is parallel to the direction of the optical axis.

6. The infrared refractive super hybrid lens according to claim 5, characterized in that: The openings of the microstructure are all in the form of round holes or square holes.

7. The infrared refractive super hybrid lens according to claim 1, characterized in that: The phase design method of the microstructure comprises the following steps: S1. Construct a polynomial expression of the metasurface phase profile Φ. Based on the polynomial formula, design the phase profile of the metasurface as needed. The polynomial expression of the metasurface phase profile Φ is as follows: Where M is the diffraction order of the metasurface, N is the maximum number of terms, R is the normalized radius, and A is i are the coefficients of each polynomial; S2, adjusting the arrangement period p and depth h of the microstructure, traversing the structural parameters d of each microstructure, simulating and obtaining the phase-wavelength curve of the microstructure, where 0.25≤d / p≤0.8, and calculating the group delay dispersion characteristics of the microstructure in the working band and the central wavelength phase of the microstructure; S3, select a set of microstructure structural parameters d so that the current meta-lens meets the design requirements, wherein the central wavelength phase of each microstructure is consistent with the phase profile determined in S1, and the group delay dispersion characteristics of each microstructure are equal; if the microstructure cannot meet the design requirements, return to S2 to adjust the period and depth of the microstructure; repeat S2 until the current meta-lens meets the design requirements; S4. According to the processing accuracy of the processing equipment, determine whether the current microstructure design can be processed. If it is determined that the microstructure cannot be processed, return to S2, change the microstructure parameters, and repeat S2-S3 until it is confirmed that the microstructure can be processed.

8. The infrared refractive super hybrid lens according to claim 1, characterized in that: The equivalent focal length f of the infrared refractive-super hybrid lens satisfies f≥3.1 mm; the distance from the object side of the first lens to the image plane of the lens is the total optical length TTL, which satisfies 3≤TTL / f≤5.

5.

9. The infrared refractive super hybrid lens according to claim 1, characterized in that: The material of the meta-lens is silicon with a thickness of 0.5 mm, and the materials of the first lens and the second lens are both chalcogenide glass.

10. The hybrid long-wave infrared lens according to claim 1, characterized in that: The field of view angle FOV of the infrared refractive super hybrid lens satisfies FOV≥60°; and the operating temperature of the infrared refractive super hybrid lens is -30°C to 80°C.

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