Method for realizing metasurface hologram

Abstract

The invention provides a method for realizing a metasurface hologram, and the method comprises the steps: presetting three kinds of nanometer unit structures which are different in geometric dimension and geometric shape, and each kind of nanometer unit structure comprises nanometer bricks; according to a preset target near field pattern, performing array periodic arrangement on the three nano unit structures on a preset substrate; encoding the phase information of the processed target far-field hologram into the nano brick rotation angle of each nano unit structure after arrangement to complete the construction of the metasurface; polarized light with different wavelengths is arranged to be incident to the metasurface, and a color hologram is achieved in a far-field area of the metasurface. According to the method, near-field nano-imprinting and far-field color holography are simultaneously realized on the same metasurface in a simple coding mode, and complete decoupling is realized, so that two channels have no crosstalk.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optical technology, and in particular to a method for realizing a supersurface hologram. Background Art

[0002] Metasurface is an artificial two-dimensional material composed of subwavelength unit structures. It has a strong ability to control electromagnetic waves. It can control the amplitude, phase and electric field strength of the electromagnetic field by optimizing the shape, size and arrangement of the unit structure. Traditional optical components mainly accumulate light paths through materials with different refractive indices, and then modulate, manipulate and convert the frequency of the light beam, such as optical lenses, half-wave plates, nonlinear crystals, etc. This control method has great limitations in tiny and precise optical systems, and optical metasurfaces are expected to become a breakthrough in solving this problem. On the other hand, metasurfaces can effectively control the wavefront of light within the subwavelength scale, which is conducive to the integration of optical systems.

[0003] With the advent of the information age, holographic technology has developed into computational holography. This technology combines computers with holographic technology. It does not require an actual interference optical path. It directly uses a computer to calculate the amplitude and phase distribution of the hologram corresponding to the target image, and then uses a coding device to control the wavefront. Since metasurfaces are relatively simple to prepare and have super-strong modulation capabilities for electromagnetic waves, metasurfaces are widely used as coding devices in holographic technology.

[0004] However, traditional metasurface holographic technology has disadvantages such as small number of channels, low holographic efficiency, and complex encoding. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings, the main purpose of the present invention is to provide a method for realizing metasurface holograms. This method uses a simple encoding method to enable the same metasurface to simultaneously realize near-field nanoimprinting and far-field color holography, and is completely decoupled, with no crosstalk between the two channels, thereby reducing the process steps and processes.

[0007] (II) Technical solution

[0008] In order to achieve the above-mentioned purpose, the present invention provides a method for realizing a metasurface hologram, comprising: presetting three nanounit structures, wherein the three nanounit structures have different geometric sizes and geometric shapes, and each nanounit structure includes a nanobrick; according to a preset target near-field image, the three nanounit structures are periodically arranged in an array on a preset substrate; encoding the phase information of the processed target far-field hologram into the rotation angle of the nanobricks of each arranged nanounit structure to complete the construction of the metasurface; and realizing a color hologram in the far-field region of the metasurface by setting polarized light of different wavelengths to be incident on the metasurface.

[0009] In the above scheme, by setting polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface, and also includes: realizing color nanoimprinting in the near-field region of the metasurface.

[0010] In the above scheme, three nano-unit structures are preset, and the method further includes: scanning each nano-unit structure, and determining the geometric size and geometric shape of the nano-bricks in each nano-unit structure according to the polarization conversion rate of the nano-unit structure to the incident light.

[0011] In the above scheme, when three colors of light are incident, each of the three nano-unit structures only produces high reflectivity reflection for a certain monochromatic light, and does not reflect the incident light of the other two colors.

[0012] In the above scheme, the phase information of the processed target far-field hologram is encoded into the rotation angle of the nanobrick in each nanounit structure to complete the construction of the metasurface, including: extracting the phase information of the preset target far-field hologram, and performing regional division and sampling processing on the phase information; encoding the phase information of the processed target far-field hologram into the rotation angle of the nanobrick in each nanounit structure to construct the metasurface.

[0013] In the above scheme, by setting polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface, wherein; the polarization type of the incident light is left-handed circularly polarized light; and the working area of ​​the metasurface is a reflection area.

[0014] In the above scheme, by setting polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface, including: modulating the amplitude of the incident light through anisotropic nanobricks to realize color nanoimprinting; and modulating the phase of the incident light to realize a color hologram.

[0015] In the above scheme, the metasurface includes a substrate and three nanounit structures distributed on the substrate in a periodic arrangement.

[0016] In the above scheme, the substrate of the super surface includes an Al thin film bottom layer and a SiO2 top layer; and the nanobricks include Al and Ag.

[0017] In the above scheme, nanobricks of different sizes have different reflection spectra; and when white light is incident, nanobricks of different sizes display different colors.

[0018] (III) Beneficial effects

[0019] The technical solution of the embodiment of the present invention has at least the following beneficial effects:

[0020] (1) This method uses metal materials to form three nano-unit structures. The geometric size, shape and metal material of the unit structure are used as the amplitude factors for modulating the near field, and the rotation angle of the unit structure is used as the phase factor for modulating the far field. This method can enable the same metasurface to simultaneously achieve near-field nanoimprinting and far-field color holography, and is completely decoupled without crosstalk between the two channels.

[0021] (2) This method can achieve color holography in a simple encoding manner and increase information storage density; the nanobrick structure is simple and large arrays are easy to produce, which greatly reduces the process steps and processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart schematically shows a method for realizing a metasurface hologram according to an embodiment of the present invention;

[0023] Figure 2 Schematically shows a target pattern of color nano-printing and color holography according to an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the structure of a super surface according to an embodiment of the present invention is shown;

[0025] Figure 4a Schematically showing the change of cross-polarized light reflectivity of three unit cell structures at different rotation angles according to an embodiment of the present invention;

[0026] Figure 4b Schematically showing the change diagram of phase mutation of three unit cell structures at different rotation angles according to the embodiments of the present invention;

[0027] Figure 5 A schematic diagram of a process for realizing color nanoimprinting and color hologram according to an embodiment of the present invention is shown;

[0028] Figure 6 The far-field result diagram and the near-field result diagram according to an embodiment of the present invention are schematically shown. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0030] Figure 1 A flow chart of a method for realizing a metasurface hologram according to an embodiment of the present invention is schematically shown.

[0031] like Figure 1 As shown, in an embodiment of the present invention, the method for realizing a metasurface hologram further includes operations S1 to S4.

[0032] In operation S1 , three nano unit structures are preset, wherein the three nano unit structures have different geometrical sizes and geometrical shapes, and each nano unit structure includes a nano brick.

[0033] In an embodiment of the present invention, three nano unit structures are firstly preset. For example, three nano unit structures with different geometric sizes and geometric shapes can be designed by using a MIM (metal-dielectric-metal) structure.

[0034] Further, each nano-unit structure is scanned, and the geometric size and geometric shape of the nano-brick in each nano-unit structure are determined according to the polarization conversion rate of the nano-unit structure to the incident light. Exemplarily, when using the simulation method, the target metasurface simulation unit structure, that is, the nano-unit structure, is first determined, and then the geometric size of the nano-brick is scanned, and the appropriate geometric shape and geometric size of the nano-brick is selected according to its polarization conversion rate to the incident light.

[0035] In the embodiment of the present invention, for three different nano unit structures, when three colors of light are incident, each of the three nano unit structures generates high reflectivity reflection only for a certain monochromatic light, and does not reflect the incident light of the other two colors.

[0036] In an embodiment of the present invention, nanobricks of different sizes have different reflection spectra; and when white light is incident, nanobricks of different sizes display different colors.

[0037] Specifically, nanobricks of different sizes have different reflection spectra. When white light is incident, the wavelengths of the strongest points of the reflection spectra of nanobricks of different sizes are different, causing the nanobricks to display different colors.

[0038] In operation S2, three nanometer unit structures are periodically arranged in an array on a preset substrate according to a preset target near-field pattern.

[0039] In operation S3, the phase information of the processed target far-field hologram is encoded into the rotation angle of the nanobricks of each arranged nanounit structure to complete the construction of the metasurface.

[0040] Exemplarily, the large array periodic arrangement of three nanobrick unit structures on the substrate is determined according to a preset target near-field pattern.

[0041] Specifically, the phase information of the preset target far-field hologram is first extracted, and the phase information is divided into regions and sampled. Then, the phase information of the processed target far-field hologram is encoded into the rotation angle of the nanobrick in each nanounit structure to complete the construction of the metasurface.

[0042] Figure 2 Schematically illustrates target patterns of color nano-printing and color holography according to an embodiment of the present invention.

[0043] like Figure 2 As shown, the metasurface is constructed based on the preset color nanoprinting and color holographic target graphics. Figure 2 As shown in FIG. 1 , the target patterns of color nanoprinting and color holography are both composed of the three primary colors of RGB. Figure 2 The graph shown in a is divided into three pictures according to the three primary colors, so that each picture is composed of only one of the three primary colors, and the picture pixel size is adjusted to 100 × 100. A nanobrick of the corresponding color is filled in the pixels of the picture with the graph, so the size of the nanobrick array is also 100 × 100.

[0044] Further, the target hologram (such as Figure 2 The phase information contained in (b) is obtained by Fourier transform and inverse Fourier transform to obtain the phase information of the metasurface, and half of the phase information is the angle between the metasurface unit and the z-axis.

[0045] In an embodiment of the present invention, the super surface includes a substrate and three nano unit structures distributed on the substrate in a periodic arrangement. The substrate of the super surface includes an Al film bottom layer and a SiO2 top layer; the nano bricks include Al and Ag, for example, the nano bricks are composed of Al or Ag.

[0046] Figure 3 The structure of a super surface according to an embodiment of the present invention is schematically shown.

[0047] like Figure 3 As shown, Figure 3 The invention comprises three supersurfaces including different nano-unit structures, namely, supersurface 31, supersurface 32 and supersurface 33.

[0048] Please continue reading Figure 3The metasurface 31 is stacked from bottom to top with a substrate 311 and a nanobrick 312, wherein the substrate 311 is stacked from bottom to top with an Al layer and a transparent optical material SiO2 layer. The working wavelength of the metasurface 31 is 632nm; the shape of the nanobrick 312 is a parallelogram column, and the angle between the two adjacent sides is 45° or 135°; the material of the nanobrick 312 is Al, which is embedded in the SiO2 layer, and the upper surface of the nanobrick 312 is flush with the upper surface of the SiO2 layer.

[0049] Please continue reading Figure 3 The metasurface 32 is stacked from bottom to top as a substrate 321 and a nanobrick 322, wherein the substrate 321 is stacked from bottom to top as an Al layer and a transparent optical material SiO2 layer. The working wavelength of the metasurface 32 is 576nm; the shape of the nanobrick 322 is a rectangular column; the material of the nanobrick 322 is Al, which is embedded in the SiO2 layer, and the upper surface of the nanobrick 322 is flush with the upper surface of the SiO2 layer.

[0050] Please continue reading Figure 3 The metasurface 33 is stacked from bottom to top with a substrate 331 and a nanobrick 332, wherein the substrate 331 is stacked from bottom to top with an Al layer and a transparent optical material SiO2 layer. The working wavelength of the metasurface 33 is 476nm; the shape of the nanobrick 332 is a parallelogram column, and the angle between the two adjacent sides is 45° or 135°; the material of the nanobrick 332 is Al, which is embedded in the SiO2 layer and located on the SiO2 layer.

[0051] Figure 4a The diagram schematically shows the change of the cross-polarized light reflectivity of three unit cell structures at different rotation angles according to the embodiments of the present invention. Figure 4b The diagram schematically shows the change of phase mutation of three unit cell structures at different rotation angles according to the embodiments of the present invention.

[0052] As shown in FIG. 4 , FIG. 4 is a diagram showing the changes in the cross-polarized light reflectivity and phase mutation of the three unit cell structures used in the examples of the present invention at different rotation angles. Figure 4a As shown, in order to select a suitable nanobrick unit cell structure (a metasurface unit structure containing only a single nanobrick), the thickness of the substrate layer is fixed, for example, the thickness of the Al layer is determined to be 40nm, and the thickness of the silicon dioxide layer is determined to be 200nm. By scanning the length and width of the nanobrick, the values ​​with the highest incident light reflectivity and cross-polarization conversion efficiency are selected as the nanobrick unit cell structure, and finally the unit cell size is determined.

[0053] Furthermore, by changing the angle between the long axis of the nanobrick and the z-axis, the phase mutation value of the nanobrick to polarized light passing through the metasurface is calculated, such as Figure 4bAs shown, the phase mutation value changes linearly with the rotation angle of the nanobrick and meets the PB phase modulation requirements, where each nanobrick pattern corresponds to one of the three primary colors.

[0054] In operation S4, by setting polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface.

[0055] It should be noted that by setting polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface, which also includes: realizing color nanoimprinting in the near-field region of the metasurface.

[0056] Figure 5 A schematic diagram of a process for realizing color nanoimprinting and color hologram according to an embodiment of the present invention is shown.

[0057] like Figure 5 As shown, in an embodiment of the present invention, the polarization type of the incident light is left-handed circularly polarized light; and the working area of ​​the metasurface is a reflective area.

[0058] Exemplarily, three types of left-handed circularly polarized light of different wavelengths are used to illuminate the metasurface and simulate the metasurface model. The reflected light will cause a colorful nanoimprint pattern to appear on the metasurface, and a colorful holographic image will be displayed on the designed distance plane.

[0059] Specifically, by adjusting the rotation angle of the nanounit structure and modulating the amplitudes of three left-handed circularly polarized lights of different wavelengths through anisotropic nanobricks, color nanoimprinting is achieved in the near-field region, and the two channels are crosstalk-free and independent of each other; and by modulating the phase of the incident light, a color hologram is achieved in the far-field region of the metasurface.

[0060] Figure 6 The far-field result diagram and the near-field result diagram according to an embodiment of the present invention are schematically shown.

[0061] like Figure 6 As shown in the figure, the metasurface constructed by the above steps contains information about the far-field and near-field target graphics. By irradiating the metasurface with a laser of the working wavelength, the far-field and near-field light fields can be reconstructed. Figure 6 As shown, the far field is the simulation result at a distance of 0.3 mm from the metasurface, and the near field is the simulation result at a distance of one wavelength from the metasurface.

[0062] Through the disclosed embodiment, a double-layer metasurface hologram based on PB phase to realize color holography and nanoimprint is realized. Three nano-unit structures are formed by metal materials. The geometric size, shape and metal materials of the unit structure and other factors constituting the nanobrick are used as the amplitude factors for modulating the near field, and the rotation angle of the unit structure is used as the phase factor for modulating the far field. The same metasurface can realize near-field nanoimprint and far-field color holography at the same time, and the two channels are completely decoupled without crosstalk. This method can realize color holography and increase information storage density in a simple encoding method; the nanobrick structure is simple, and large arrays are easy to manufacture, which greatly reduces the process steps and processes.

[0063] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for realizing a metasurface hologram, characterized in that: The method comprises: Three nano-unit structures are preset, wherein the three nano-unit structures have different geometric sizes and geometric shapes, and each of the nano-unit structures includes a nano-brick; According to a preset target near-field diagram, the three nanounit structures are periodically arranged in an array on a preset substrate; Encoding the processed phase information of the target far-field hologram into the rotation angle of the nanobricks of each of the arranged nanounit structures to complete the construction of the metasurface; By arranging polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface.

2. The method for realizing a metasurface hologram according to claim 1, characterized in that: The method of realizing a color hologram in a far-field region of the metasurface by arranging polarized light of different wavelengths to be incident on the metasurface further includes: Color nanoimprinting is achieved in the near-field region of the metasurface.

3. The method for realizing a metasurface hologram according to claim 1, characterized in that: The three preset nano unit structures also include: Each nanometer unit structure is scanned, and the geometric size and geometric shape of the nanobricks in each nanometer unit structure are determined according to the polarization conversion rate of the incident light by the nanometer unit structure.

4. The method for realizing a metasurface hologram according to claim 1 or 3, characterized in that: When three colors of light are incident, each of the three nano unit structures generates high reflectivity reflection only for a certain monochromatic light, and does not generate reflection for the incident light of the other two colors.

5. The method for realizing a metasurface hologram according to claim 1 or 3, characterized in that: The step of encoding the processed phase information of the target far-field hologram into the rotation angle of the nanobricks in each of the nanounit structures to complete the construction of the metasurface includes: Extracting phase information of a preset target far-field hologram, and performing area division and sampling processing on the phase information; The phase information of the processed target far-field hologram is encoded into the rotation angle of the nanobricks in each of the nanounit structures to construct a metasurface.

6. The method for realizing a metasurface hologram according to claim 1, characterized in that: By arranging polarized light of different wavelengths to be incident on the metasurface, a color hologram is realized in the far-field region of the metasurface, wherein; The polarization type of the incident light is left-handed circularly polarized light; and The metasurface working area is a reflection area.

7. The method for realizing a metasurface hologram according to claim 2 or 6, characterized in that: The method of realizing a color hologram in a far-field region of the metasurface by setting polarized light of different wavelengths to be incident on the metasurface comprises: Color nanoimprinting is achieved by modulating the amplitude of incident light through anisotropic nanobricks; and Color holograms are achieved by modulating the phase of the incident light.

8. The method for realizing a metasurface hologram according to claim 5, characterized in that: The super surface includes a substrate and three nano unit structures distributed on the substrate and arranged periodically.

9. The method for realizing a metasurface hologram according to claim 8, characterized in that: The substrate of the super surface includes an Al thin film bottom layer and a SiO2 top layer; and The nanobrick includes Al and Ag.

10. The method for realizing a metasurface hologram according to claim 3, characterized in that: Nanobricks of different sizes have different reflectance spectra; and When white light is incident, nanobricks of different sizes display different colors.

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