Infrared dual-wavelength bifocal focusing superlens and construction method thereof

Abstract

The application belongs to the technical field of micro-nano optics, and discloses an infrared dual-wavelength dual-focus focusing superlens and a construction method thereof. The application firstly constructs a unit structure, the unit structure comprising a substrate and a nano brick of a central symmetric structure; then two working wavelengths are designed, respectively belonging to a middle-wave infrared and a long-wave infrared band; after that, a plurality of groups of unit structures are optimally designed; the unit structure of each group adds the same phase to different incident polarized light of a single working wavelength and adds different phases to different working wavelengths; under the same working wavelength, the unit structures of different groups add different phases; the two focal lengths of the superlens under the two working wavelengths are designed, and the phase distribution of the superlens is determined; finally, for each pixel point, a group of unit structures with the closest phase distribution to the phase distribution of the superlens are selected from the unit structures of the plurality of groups to arrange. The superlens obtained by the application can realize dual-wavelength dual-grade zoom in the infrared band.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics technology, and more specifically, relates to an infrared dual-wavelength dual-focal focusing superlens and its construction method. Background Technology

[0002] Superlenses are optical devices based on metasurfaces that can flexibly control incident electromagnetic waves. They can overcome the inherent disadvantages of traditional optical lenses, such as large size, high processing requirements, and limited resolution, and can achieve functions such as subwavelength focusing. These characteristics are in line with the current trend of miniaturization and integration of optical systems.

[0003] Superlenses, which utilize metasurfaces to manipulate the amplitude, phase, and polarization of light waves to achieve focusing and other functions, have attracted widespread attention. While researchers have successfully implemented many single-focal lenses in recent years, research on bifocal lenses is relatively limited, and research on dual-wavelength bifocal lenses is even less so. Existing dual-wavelength bifocal superlenses are constrained by the polarization state of the incident light, making them difficult to apply in natural environments. Furthermore, achieving polarization-insensitive dual-wavelength bifocal superlenses in both the mid-infrared and long-infrared wavelengths remains a gap, failing to meet the application needs of fields such as defense. Summary of the Invention

[0004] The purpose of this invention is to provide an infrared dual-wavelength dual-focus superlens and its construction method to achieve dual-wavelength dual-range zoom in the infrared band.

[0005] This invention provides a method for constructing an infrared dual-wavelength dual-focal focusing superlens, comprising the following steps:

[0006] Step 1: Construct a unit structure for forming a superlens, the unit structure including a substrate and nanobricks disposed on the working surface of the substrate, the nanobricks being centrosymmetric structures;

[0007] Step 2: Design the first and second working wavelengths. The first working wavelength belongs to the mid-wave infrared band, and the second working wavelength belongs to the long-wave infrared band. Through electromagnetic simulation, optimize the design of multiple group-type unit structures. For each group-type unit structure, the same phase is added to different incident polarized light of a single working wavelength, and different phases are added to different working wavelengths. Under the same working wavelength, different group-type unit structures are added with different phases.

[0008] Step 3: Design the first focal length of the superlens under the first working wavelength illumination and the second focal length of the superlens under the second working wavelength illumination, and determine the phase distribution of the superlens;

[0009] Step 4: Treat each unit structure as a pixel. For each pixel, select the unit structure from multiple groups of unit structures whose additional phase is closest to the phase distribution of the superlens and arrange them. When the light wave of the first working wavelength is incident on the superlens, a focal point is generated at the first focal length of the superlens. When the light wave of the second working wavelength is incident on the superlens, a focal point is generated at the second focal length of the superlens.

[0010] Preferably, in step 1, the x-axis and y-axis are set as the two sides parallel to the working surface of the substrate, respectively, to establish an xoy coordinate system; the cross section of the nanobrick parallel to the working surface of the substrate is a solid centrally symmetrical shape or a centrally symmetrical shape with a hollow structure.

[0011] Preferably, in step 2, the height of the nanobricks in the unit structures of different groups is the same, and the dimensional parameters of the cross-section of the nanobrick parallel to the working surface of the substrate are recorded as cross-sectional parameters. The cross-sectional parameters are characterized by at least one of length, width, and radius. The cross-sectional parameters of the nanobricks in the unit structures of different groups are different.

[0012] Preferably, when optimizing the design of multiple group-type unit structures, the height of the nanobrick and the distance between the center points of adjacent nanobricks are first determined. Then, electromagnetic simulation software is used to scan the cross-sectional parameters of the nanobrick at the working wavelength, and the phase change diagrams corresponding to the incident light polarized along the x-axis direction on nanobricks with different cross-sectional parameters at the first working wavelength and the second working wavelength are simulated respectively.

[0013] Preferably, when scanning the cross-sectional parameters of the nanobrick, one of the symmetry center lines of the nanobrick is parallel to the x-axis, and periodic boundary conditions are used, with a scanning range of 0.3 μm to 1.1 μm and a step size of 40 nm.

[0014] Preferably, when scanning the cross-sectional parameters of the nanobrick using electromagnetic simulation software at the working wavelength, the transmittance diagrams of the nanobrick for x-axis polarized light are also simulated at the first working wavelength and the second working wavelength, respectively; the transmittance of the optimized design of multiple group types of unit structures is higher than the transmittance threshold.

[0015] Preferably, the transmittance threshold is 50%.

[0016] Preferably, in step 3, the phase distribution of the superlens is determined using the following formula:

[0017]

[0018]

[0019] Where x and y are the position coordinates on the superlens, λ1 is the first working wavelength, λ2 is the second working wavelength, f1 is the first focal length, and f2 is the second focal length. This refers to the additional phase required for a certain position coordinate on the superlens at the designed first operating wavelength and first focal length. This refers to the additional phase required for a certain position coordinate on the superlens at the designed second working wavelength and second focal length.

[0020] On the other hand, the present invention provides an infrared dual-wavelength dual-focus focusing superlens, which is obtained by the above-described method for constructing an infrared dual-wavelength dual-focus focusing superlens.

[0021] Preferably, both the substrate of the superlens and the nanobrick are made of single-crystal silicon.

[0022] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0023] The nanobricks in the unit structure of this invention are centrosymmetric. This invention optimizes the design of multiple isotropic unit structures. Based on the two designed operating wavelengths and corresponding focal lengths, the required phase is designed at different positions of the superlens, enabling the constructed dual-wavelength, dual-focal-length focusing superlens to produce a corresponding focal point at each of the two designed focal lengths under infrared operating wavelength and arbitrary polarized light incidence. The superlens provided by this invention achieves polarization insensitivity under dual wavelengths and can be used in natural environments. Furthermore, this invention fills the gap in infrared dual-wavelength, dual-focal-length focusing superlenses. The superlens provided by this invention has a compact structure, can achieve dual-wavelength, dual-range zoom in the infrared band, and also has the advantages of small size and light weight, showing great industrialization potential in military, defense, encryption, and information multiplexing fields. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a unit structure in an infrared dual-wavelength dual-focus superlens provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the unit structure of multiple group classes in this invention;

[0026] Figure 3 A schematic diagram of the arrangement of nanobricks in an infrared dual-wavelength dual-focus superlens provided in an embodiment of the present invention;

[0027] Figure 4 This invention provides an embodiment of an infrared dual-wavelength dual-focus superlens that achieves dual-wavelength dual-range zoom in the infrared band; wherein, Figure 4(a) in the figure shows the effect of creating a focal point 1 mm away from the superlens under 4.2 μm laser irradiation; Figure 4 (b) in the figure shows the effect of creating a focal point at a distance of 2 mm from the superlens under 10 μm laser irradiation. Detailed Implementation

[0028] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0029] This embodiment provides a method for constructing an infrared dual-wavelength dual-focal focusing superlens, including the following steps:

[0030] Step 1: Construct a unit structure for forming a superlens. The unit structure includes a substrate and nanobricks disposed on the working surface of the substrate. The nanobricks are centrosymmetric structures.

[0031] The xoy coordinate system is established by setting the directions of the two sides parallel to the working surface of the substrate as the x-axis and y-axis, respectively; the cross section of the nanobrick parallel to the working surface of the substrate is a solid centrally symmetrical shape or a centrally symmetrical shape with a hollow structure.

[0032] Step 2: Design the first working wavelength and the second working wavelength. The first working wavelength belongs to the mid-wave infrared band, and the second working wavelength belongs to the long-wave infrared band. Through electromagnetic simulation, optimize the design of multiple group-type unit structures. For each group-type unit structure, the same phase is added to different incident polarized light of a single working wavelength, and different phases are added to different working wavelengths. Under the same working wavelength, different group-type unit structures are added with different phases.

[0033] That is, the optimized design yields a unit structure that is functionally equivalent to multiple groups of waveplates with different delays at two different operating wavelengths.

[0034] The mid-wave infrared band has a wavelength of 3-5 μm, and the long-wave infrared band has a wavelength of 7-14 μm. The height of the nanobricks is the same in different group types of unit structures. The dimensional parameters of the cross-section of the nanobrick parallel to the working surface of the substrate are denoted as cross-sectional parameters. These cross-sectional parameters are characterized by at least one of length, width, and radius. The cross-sectional parameters of the nanobricks differ in different group types of unit structures.

[0035] When optimizing the design of multiple group-type unit structures, the height of the nanobrick and the distance between the center points of adjacent nanobricks are first determined. Then, electromagnetic simulation software is used to scan the cross-sectional parameters of the nanobricks at the working wavelength. The phase change diagrams corresponding to polarized light incident along the x-axis direction on nanobricks with different cross-sectional parameters at the first working wavelength and the second working wavelength are simulated respectively.

[0036] For example, when scanning the cross-sectional parameters of nanobricks, one of the symmetry center lines of the nanobricks is made parallel to the x-axis, and periodic boundary conditions are used. The scanning range is 0.3 μm to 1.1 μm, and the step size is 40 nm.

[0037] Furthermore, when scanning the cross-sectional parameters of the nanobrick using electromagnetic simulation software at the working wavelength, the transmittance diagrams of the nanobrick for x-axis polarized light can be simulated and obtained at both the first and second working wavelengths. The transmittance of the optimized unit structures of multiple groups is higher than the transmittance threshold. For example, the transmittance threshold is 50%. The multiple unit structures obtained by this preferred scheme not only conform to the specific phase distribution at the two working wavelengths but also have high transmittance, resulting in superior superlens performance.

[0038] Step 3: Design the first focal length of the superlens under the first working wavelength illumination and the second focal length of the superlens under the second working wavelength illumination, and determine the phase distribution of the superlens.

[0039] Specifically, the phase distribution of the superlens is determined using the following formula:

[0040]

[0041]

[0042] Where x and y are the position coordinates on the superlens, λ1 is the first working wavelength, λ2 is the second working wavelength, f1 is the first focal length, and f2 is the second focal length. This refers to the additional phase required for a certain position coordinate on the superlens at the designed first operating wavelength and first focal length. This refers to the additional phase required for a certain position coordinate on the superlens at the designed second working wavelength and second focal length.

[0043] The above formula can be used to determine the additional phase required for each pixel (i.e., each position coordinate) on the superlens at the corresponding design working wavelength and focal length.

[0044] Step 4: Treat each unit structure as a pixel. For each pixel, select the unit structure from multiple groups of unit structures whose additional phase is closest to the phase distribution of the superlens and arrange them. When the light wave of the first working wavelength is incident on the superlens, a focal point is generated at the first focal length of the superlens. When the light wave of the second working wavelength is incident on the superlens, a focal point is generated at the second focal length of the superlens.

[0045] Step 4: Select the unit structure from different groups of unit structures whose additional phase is closest to the phase distribution required by the infrared dual-wavelength dual-focus focusing superlens, and arrange them to obtain an isotropic superlens that can achieve dual-wavelength dual-focus focusing.

[0046] The infrared dual-wavelength dual-focal focusing superlens obtained using the above construction method includes a substrate layer and periodically arranged nanobricks on top of the substrate layer. The superlens can be considered as being composed of several unit structures. Figure 1 The unit structure includes a square-section substrate 120 and nanobricks 110 disposed on the working surface of the substrate 120. The nanobricks 110 have a centrosymmetric structure. The period of the substrate 120 is denoted as CS, the distance between the center points of adjacent nanobricks is also CS, and the height of the nanobricks is denoted as H. Both the substrate 120 and the nanobricks 110 are subwavelength in size, and both the substrate 120 and the nanobricks 110 can be made of single-crystal silicon.

[0047] The following explanation uses two operating wavelengths, 4.2µm and 10µm.

[0048] Each of the nanobricks (or unit structures) corresponds to a superlens pixel, and nanobricks of different sizes add phase to incident light with a wavelength of 4.2 μm. Add phase to incident light with a wavelength of 10 μm By arranging the positions of nanobricks of different sizes in a reasonable manner, it is possible to generate two different focal points under two different working wavelengths of incident light.

[0049] The principle behind the different phases added to incident light by nanobricks of different sizes is as follows: When incident light is incident on nanobricks of different sizes, there are different boundary conditions. Therefore, different refractive indices can be obtained by solving Maxwell's equations. The phase added to a light wave with a certain wavelength when it propagates in a medium depends on the refractive index and the propagation distance. The height of the nanobricks is constant, and the nanobricks designed in this invention are isotropic structures. Therefore, nanobricks of different sizes will produce different refractive indices for the same polarization component of the incident light wave, thus adding different phases. Therefore, it is only necessary to select the structure according to the phase requirements of different pixels.

[0050] When designing the dimensions of the nanobricks, one of their symmetrical center lines is parallel to the x-axis. The phase added by the nanobricks to x-axis polarized light is scanned, resulting in multiple additional phase combinations under irradiation with mid-infrared light (4.2 μm) and far-infrared light (10 μm). Simultaneously, the transmittance of the nanobrick structure to infrared light of wavelengths 4.2 μm and 10 μm is scanned. To reduce the number of nanobricks selected (i.e., reduce the total number of unit structure groups), the superlens designed in this invention has a 4-step phase distribution under both working wavelengths of incident light. Based on the transmittance, a total of 16 unit structure groups are selected.

[0051] Since isotropic nanobricks of a single shape cannot meet the phase requirements of the lens designed in this invention, a total of 10 different shaped nanobricks were designed, such as... Figure 2 As shown, the unit structure numbers of multiple groups are labeled in the lower right corner of the figure, and their dimensional parameters are determined by the length L, width W, and radius R labeled within the figure. The designed nanobricks have different cross-sectional shapes and sizes, but they all have the same height H, the same distance CS between the center points of adjacent unit structures (i.e., the period of the unit structure), and are all centrosymmetric structures satisfying the isotropic properties of nanobricks.

[0052] When optimizing the design of multiple group-type unit structures, first determine the height H of the nanobrick and the distance CS between the center points of adjacent nanobricks. Then, use electromagnetic simulation software to scan the cross-sectional parameters of the nanobricks at the working wavelength to simulate and obtain the phase change diagrams corresponding to polarized light incident along the x-axis direction on nanobricks with different cross-sectional parameters at the first working wavelength and the second working wavelength.

[0053] Taking a 50*50 pixel superlens as an example, the two working wavelengths are 4.2µm and 10µm. The selected nanobrick has a height H of 9µm and a period CS of 2.5µm. The CST DESIGN ENVIRONMENT electromagnetic simulation software was used to scan the three dimensions L, W, and R of the nanobrick at the two working wavelengths, using periodic boundary conditions. The scanning range was 0.3µm-1.1µm, with a step size of 40nm, and limitations were imposed. Figure 2 The hollow region of the graphic will not exceed the boundary of the nanobrick. Simulations were used to obtain the additional phase and transmittance changes of polarized light incident on nanobricks (or unit structures) of different sizes along the x-axis. A total of 16 structures were selected. The serial number, size parameters and corresponding transmittance parameters of the cross-sectional shape (i.e., unit structure group) of the 16 structures are given here, as shown in Table 1.

[0054] Table 1. Structural parameters of sixteen different group types of unit structures

[0055]

[0056] T1 in Table 1 The unit cell representing the corresponding structural number and size has transmittance and additional phase for 4.2µm light waves incident along the x-axis polarized direction, T2. The transmittance and additional phase of the unit structure corresponding to the structural number and size when 10µm light waves are incident along the x-axis polarized light.

[0057] The additional phase required for the unit structure under 4.2µm light incidence is obtained by focusing the phase using a converging lens. And the additional phase required under incident light waves with a wavelength of 10µm. Where λ1 = 4.2 μm, λ2 = 10 μm, and f1 and f2 are the focal lengths designed for incident light at λ1 and λ2, respectively, for example, 1 mm and 2 mm. The unit structure at each pixel of the superlens is selected to meet the required phase distribution, so as to generate two independent focal points under two different working wavelengths and arbitrary polarization light incident light.

[0058] Based on the principle of minimizing the phase difference between the required phase distribution of the infrared dual-wavelength dual-focus focusing superlens and the phase difference added by the selected 16 structures at two working wavelengths, the nano-bricks (or unit structures) corresponding to each pixel point on the superlens are selected. Figure 3 This is a schematic diagram of the arrangement of nanobricks in a superlens.

[0059] See Figure 4 When the incident light wavelength is 4.2 μm, parallel light with arbitrary vibration direction will be incident on the superlens, and a bright spot will be observed at a distance of 1 mm from the superlens. See [link to relevant documentation]. Figure 4 (a) In the diagram, when the incident light wavelength is 4.2 μm, incident parallel light with arbitrary vibration direction will be observed as a bright spot at a distance of 2 mm from the superlens when it is incident on the superlens. See also: Figure 4 (b) in the middle.

[0060] In summary, this invention utilizes the phase modulation properties of metasurfaces to propose a method for constructing an isotropic infrared dual-wavelength dual-focusing superlens based on a metasurface, as well as the superlens itself. Various nanobricks of different shapes are designed to meet the phase modulation requirements. By arranging and designing these nanobricks, a metasurface is constructed to produce different focal points under illumination at different wavelengths. This invention has significant industrialization potential in military, encryption, and information multiplexing applications.

[0061] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for constructing an infrared dual-wavelength dual-focal focusing superlens, characterized in that, Includes the following steps: Step 1: Construct a unit structure for forming a superlens, the unit structure including a substrate and nanobricks disposed on the working surface of the substrate, the nanobricks being centrosymmetric structures; Step 2: Design the first and second working wavelengths. The first working wavelength belongs to the mid-wave infrared band, and the second working wavelength belongs to the long-wave infrared band. Through electromagnetic simulation, optimize the design of multiple group-type unit structures. For each group-type unit structure, the same phase is added to different incident polarized light of a single working wavelength, and different phases are added to different working wavelengths. Under the same working wavelength, different group-type unit structures are added with different phases. When optimizing the design of multiple group-type unit structures, the height of the nanobricks and the distance between the center points of adjacent nanobricks are first determined. Then, electromagnetic simulation software is used to scan the cross-sectional parameters of the nanobricks at the working wavelength, and the simulation results are obtained at the first working wavelength and the second working wavelength, respectively. x Phase change diagrams of axially polarized light incident on nanobricks with different cross-sectional parameters; Step 3: Design the first focal length of the superlens under the first working wavelength illumination and the second focal length of the superlens under the second working wavelength illumination, and determine the phase distribution of the superlens; The phase distribution of the superlens is determined using the following formula: in, x , y Here are the position coordinates on the superlens. λ 1 is the first operating wavelength. λ 2 is the second operating wavelength. f 1 represents the first focal length. f 2 is the second focal length. This refers to the additional phase required for a certain position coordinate on the superlens at the designed first operating wavelength and first focal length. This refers to the additional phase required for the coordinates of a certain position on the superlens at the designed second working wavelength and second focal length; Step 4: Treat each unit structure as a pixel. For each pixel, select the unit structure from multiple groups of unit structures whose additional phase is closest to the phase distribution of the superlens and arrange them. When the light wave of the first working wavelength is incident on the superlens, a focal point is generated at the first focal length of the superlens. When the light wave of the second working wavelength is incident on the superlens, a focal point is generated at the second focal length of the superlens.

2. The method for constructing an infrared dual-wavelength dual-focal focusing superlens according to claim 1, characterized in that, In step 1, the directions of the two sides parallel to the working surface of the base are respectively set as x shaft and y Axis, Establish xoy Coordinate system; the cross-section of the nanobrick parallel to the working surface of the substrate is a solid, centrally symmetrical shape or a centrally symmetrical shape with a hollow structure.

3. The method for constructing an infrared dual-wavelength dual-focal focusing superlens according to claim 2, characterized in that, In step 2, the height of the nanobricks is the same in the unit structures of different groups. The dimensional parameters of the cross section of the nanobrick parallel to the working surface of the substrate are recorded as cross section parameters. The cross section parameters are characterized by at least one of length, width, and radius. The cross section parameters of the nanobricks are different in the unit structures of different groups.

4. The method for constructing an infrared dual-wavelength dual-focal focusing superlens according to claim 1, characterized in that, When scanning the cross-sectional parameters of the nanobrick, one of the symmetry center lines of the nanobrick is aligned with... x The axes are parallel, and periodic boundary conditions are used. The scanning range is 0.3um to 1.1um, with a step size of 40nm.

5. The method for constructing an infrared dual-wavelength dual-focal focusing superlens according to claim 1, characterized in that, When scanning the cross-sectional parameters of the nanobricks at the working wavelength using electromagnetic simulation software, the effects of the nanobricks on the working wavelengths were also simulated at the first and second working wavelengths, respectively. x Transmittance diagram of axially polarized light; the transmittance of the optimized unit structures of multiple groups is higher than the transmittance threshold.

6. The method for constructing an infrared dual-wavelength dual-focal focusing superlens according to claim 5, characterized in that, The transmittance threshold is 50%.

7. An infrared dual-wavelength dual-focal focusing superlens, characterized in that, It is obtained by constructing an infrared dual-wavelength dual-focus superlens as described in any one of claims 1-6.

8. The infrared dual-wavelength dual-focal focusing superlens according to claim 7, characterized in that, The substrate of the superlens and the nanobricks are both made of single-crystal silicon.

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