Metasurface structure based on high-order topological vector beam multiplexing and method for increasing holographic multiplexing channel number

Abstract

The application discloses a kind of based on high-order topological vector beam multiplexing metasurface structure and the method for improving holographic multiplexing channel number.The metasurface structure includes substrate, medium microstructure, vector polarized light beam;The medium microstructure is established on substrate;The medium microstructure is the metasurface array structure formed by several high reflectivity medium metasurface units periodic arrangement, the high reflectivity medium metasurface unit is the cube of geometric shape, and vector polarized light beam is vertically incident on the metasurface array structure.The present application mainly overcomes the defects of existing based on orbital angular momentum multiplexing holographic technology, it uses the topological orthogonal characteristics of vector vortex light beam itself to improve the selection isolation degree between different parameters of vector vortex light, realizes the technology of not dependent on orbital angular momentum selection, without the assistance of spatial dot array filter plate, can carry out target holographic imaging.

Description

Technical Field

[0001] This invention relates to the technical field of metasurface-based optical field manipulation, specifically to high-dimensional multi-channel holography relying on the topological orthogonality of vector beams, and particularly to a metasurface structure based on high-order topological vector beam multiplexing and a method for increasing the number of holographic multiplexing channels. Background Technology

[0002] Dielectric metasurfaces are optical components composed of subwavelength-scale nanostructures capable of scattering light. By precisely controlling parameters such as the material, structure, shape, and orientation of each unit, dielectric metasurfaces can achieve precise manipulation of optical signals. Due to their extremely small size, dielectric metasurfaces can be designed to perform multiple functions such as spatial multiplexing, polarization multiplexing, and wavelength multiplexing, all within a much smaller footprint than traditional optical components. This miniaturization allows them to perform complex optical operations within very limited spaces. Dielectric metasurfaces offer significant advantages in terms of multifunctionality, compactness, small size, light weight, and high integration. Furthermore, they are compatible with traditional nanofabrication processes, making them easier to integrate into existing systems in practical applications. These characteristics make dielectric metasurfaces extremely promising and valuable for the design of mid-infrared enhanced imaging optical systems, especially in applications requiring miniaturization and high efficiency. Orbital angular momentum, as one of the characteristic dimensions of light, gives light a helical phase. Due to its physically infinite orthogonal helical modes, it becomes a method for carrying high-capacity information transmission channels. Numerous studies have demonstrated the potential of the singular Hall effect in optical vector modes, opening new avenues for the design and application of future multifunctional optical devices. Starting with the orbital angular momentum dimension of light, the development of high-capacity holographic multiplexing techniques has gradually taken shape, subsequently leading to multi-dimensional joint multiplexing techniques combining different dimensions of light with the orbital angular momentum dimension. However, all of these require spatial frequency sampling of the digital hologram in momentum space to preserve the orbital angular momentum characteristics of the incident light and selectively present holographic images with matching orbital angular momentum. However, this phase-only hologram does not consider the precise convolution during the propagation of the orbital angular momentum spiral wavefront, resulting in extremely strong crosstalk during orbital angular momentum multiplexing. Therefore, a filter needs to be added to the imaging plane to achieve perfect imaging. Summary of the Invention

[0003] The purpose of this invention is to provide a metasurface structure based on high-order topological vector beam multiplexing and a method for increasing the number of holographic multiplexing channels. It mainly overcomes the defects of existing orbital angular momentum multiplexing holographic technology. It utilizes the topological orthogonality of the vector vortex beam itself to improve the selectivity and isolation between vector vortex beams with different parameters, and realizes a technology that can perform target holographic imaging without relying on orbital angular momentum selectivity and without the assistance of spatial lattice filter plates.

[0004] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0005] A metasurface structure based on high-order topological vector beam multiplexing is characterized in that it comprises a substrate, a dielectric microstructure, and a vector polarized beam.

[0006] The dielectric microstructure is built on a substrate; the dielectric microstructure is a metasurface array structure formed by a periodic arrangement of several high-transmittance dielectric metasurface units, the high-transmittance dielectric metasurface units are cubes in geometric shape, and a vector-polarized beam is incident perpendicularly on the metasurface array structure.

[0007] The metasurface structure based on high-order topological vector beam multiplexing is characterized in that: the substrate is made of silicon, the dielectric microstructure is made of silicon, and the wavelength of the vector polarized beam is 3-5 micrometers.

[0008] The metasurface structure based on high-order topological vector beam multiplexing is characterized in that: the cube of geometric shape is an elliptical cylinder, the major axis diameter and minor axis diameter of the elliptical cylinder are variables, while the period of each elliptical cylinder and the height of the elliptical cylinder remain equal.

[0009] The metasurface structure based on high-order topology vector beam multiplexing is characterized in that: the elliptical cylinder is periodically extended along two mutually perpendicular directions, which are defined as the x-axis and y-axis, respectively, and the two extension directions are mutually perpendicular; when a plane wave with polarization direction along the x-axis is irradiated along the z-axis in the positive direction, it will carry the phase distribution determined by the major axis dimension of the elliptical cylinder; when a plane wave with polarization direction along the y-axis is irradiated along the z-axis in the positive direction, it will carry the phase distribution determined by the minor axis dimension of the elliptical cylinder. Combined with the high-dimensional degree of freedom information carried by the vector polarized beam (3), a low crosstalk and high-channel information carrier can be realized.

[0010] The metasurface structure based on high-order topological vector beam multiplexing is characterized in that: the major axis diameter and minor axis diameter of the elliptical cylinder vary from 300 nanometers to 1200 nanometers, its unit period is 1.5 micrometers to 2 micrometers, the number of elliptical cylinders is 1200×1200, and the total length is 1800 micrometers×1800 micrometers.

[0011] The metasurface structure based on high-order topological vector beam multiplexing is characterized in that the height of the elliptical cylinder is 4 micrometers.

[0012] A method for increasing the number of holographic multiplexing channels using a metasurface structure based on high-order topological vector beam multiplexing, characterized by comprising the following steps:

[0013] Step A: Select appropriate substrate and dielectric microstructure materials based on the incident light wavelength of the vector polarized beam;

[0014] Step B: Based on the selected material, simulate the changes in phase and intensity of incident plane light as it passes through cells of different sizes, creating a database of these changes.

[0015] Step C: Use the gradient descent algorithm to obtain the required metasurface array phase information, then find the corresponding elements in the database, and obtain the simulation results through simulation calculation;

[0016] Step D: Fabricate the metasurface array structure;

[0017] Step E: Conduct experimental testing on the designed metasurface array structure. If the results do not meet the requirements, return to step B, adjust and optimize the metasurface parameters, and repeat steps DE until the experimental results meet the requirements.

[0018] The method is characterized in that: in step D, electron beam lithography, dry etching, or wet etching is used to process the metasurface array structure.

[0019] The method is characterized in that: after step D and before step E, the surface of the metasurface array structure is cleaned with ultraviolet ozone.

[0020] When a specified incident vector-polarized light beam illuminates the metasurface structure of this high-order vector topology multiplexing, the holographic image presented by the outgoing beam in the Fourier plane closely matches the preset image. Changing the incident beam produces different images, achieving the effect of vector polarization multiplexing. Its outstanding feature is that the image does not depend on the sampling of the spatial lattice, which greatly reduces the size of the metasurface and opens up the possibility of manipulating infrared polarized light at the subwavelength scale.

[0021] Based on spatially structured vector vortex beams, this invention investigates a metasurface holography in the mid-infrared band based on high-order vector topology multiplexing. The design utilizes three different vector vortex multiplexing techniques to create metasurface holograms with a total of 12 independently controllable holographic channels.

[0022] This invention primarily aims to overcome the shortcomings of existing orbital angular momentum multiplexing holographic techniques by providing a metasurface holographic multiplexing device structure and fabrication based on a high-order topological superimposed vector beam. By overcoming the limitation of previous orbital angular momentum multiplexing holographic techniques requiring spatial frequency sampling of the digital hologram in momentum space to preserve the orbital angular momentum characteristics of the incident light and selectively present orbital angular momentum-matched holographic images, this invention achieves metasurface holograms that do not require frequency space sampling, thus eliminating reliance on orbital angular momentum selectivity and enabling target holographic imaging without the aid of a filter. This significantly simplifies the optical path system and design process, promoting the development of integrated and miniaturized optical devices. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the metasurface structure based on high-order topological vector beam multiplexing of the present invention;

[0024] Figure 2 This invention provides a database of x-direction phase and x-direction transmittance of superatoms, as well as a database of y-direction phase and x-direction transmittance.

[0025] Figure 3 This is a flowchart illustrating the design process of the metasurface structure of this invention;

[0026] Figure 4 This is a schematic diagram of the metasurface holographic results of three different vector beam multiplexing provided in the embodiments of the present invention, where l represents the topological charge value. Detailed Implementation

[0027] Please see Figure 1 This invention discloses a metasurface structure based on high-order topological vector beam multiplexing, which includes a substrate 1, a dielectric microstructure 2, and a vector polarized beam 3. The dielectric microstructure 2 is built on the substrate 1. The dielectric microstructure 2 is a metasurface array structure formed by a periodic arrangement of several high-transmittance dielectric metasurface units. The high-transmittance dielectric metasurface units are cubic in shape. The vector polarized beam 3 is incident perpendicularly on the metasurface array structure.

[0028] In this invention, the substrate 1 is made of silicon or other high-refractive-index dielectric material, and its thickness can be considered semi-infinite. The dielectric microstructure 2 is made of silicon or other materials with high transmittance to mid-infrared light, and its thickness is 4 micrometers. The wavelength of the vector-polarized beam 3 is 3-5 micrometers.

[0029] In this invention, the cube of geometric shape can be an elliptical cylinder. The major axis diameter and minor axis diameter of the elliptical cylinder are variables, while the period and height of each elliptical cylinder remain equal.

[0030] Furthermore, the elliptical cylinder is periodically extended along two mutually perpendicular directions, defined as the x-axis and y-axis, respectively, with the two extension directions being mutually perpendicular. When a plane wave with a polarization direction along the x-axis irradiates the high-transmittance medium metasurface unit along the z-axis, it will carry the phase distribution determined by the major axis dimension of the elliptical cylinder. When a plane wave with a polarization direction along the y-axis irradiates the high-transmittance medium metasurface unit along the z-axis, it will carry the phase distribution determined by the minor axis dimension of the elliptical cylinder. Combined with the high-dimensional degree of freedom information carried by the vector polarized beam 3 itself, a low-crosstalk, high-channel information carrier can be realized.

[0031] Furthermore, the major and minor axis diameters of the elliptical cylinder vary from 300 nanometers to 1200 nanometers, its unit period is 1.5 micrometers to 2 micrometers, the number of elliptical cylinders is 1200 × 1200, and the total length is 1800 micrometers × 1800 micrometers. The height of the elliptical cylinder is 4 micrometers.

[0032] This invention also discloses a method for increasing the number of holographic multiplexing channels using a metasurface structure based on high-order topological vector beam multiplexing, which includes the following steps:

[0033] Step A: Select appropriate materials for substrate 1 and dielectric microstructure 2 based on the incident light band of vector polarized beam 3;

[0034] Step B: Based on the selected material, simulate the changes in phase and intensity of incident plane light as it passes through 50×50 cells of different sizes, ranging from 300 nm to 1200 nm in the x and y directions, and compile a database (e.g., ...) Figure 2 );

[0035] Step C: Gradient descent algorithm is used to obtain phase information. Given the incident light information, the target image is presented at a specified spatial position through optical diffraction. During iteration, the loop exits when the loss function is less than a specified value. After obtaining the metasurface array phase information, the corresponding unit is searched in the database, and simulation results are obtained through simulation calculations (e.g., ...). Figure 3 );

[0036] Step D: Fabricate the metasurface array structure;

[0037] Step E: Conduct experimental testing on the designed metasurface array structure. If the results do not meet the requirements, return to step B, adjust and optimize the metasurface parameters, and repeat steps DE until the experimental results meet the requirements.

[0038] In step D, the metasurface array structure is fabricated using electron beam lithography, dry etching, or wet etching.

[0039] After step D and before step E, the surface of the metasurface array structure is cleaned with ultraviolet ozone.

[0040] The present invention will be further described below with reference to embodiments and accompanying drawings. Example

[0041] Step 1: First, it is necessary to scan and obtain the x-polarized target phase and y-polarized target phase that high-transmittance dielectric metasurface units (or: superatoms) of different sizes can generate. In this embodiment, the working wavelength of the light wave is 4 micrometers, the material of the superatoms and the substrate is silicon, and the geometry of the superatoms is cubic, such as... Figure 1 As shown, the period P = 1.5 micrometers, the height H = 4 micrometers, and the length and width range from 300 nanometers to 1200 nanometers. Fifty points of equal length and width were selected for each superatom, resulting in 2500 superatoms of different geometric dimensions. The superatoms were irradiated with linearly polarized light of three target wavelengths, one x-polarized and one y-polarized, respectively, to obtain their ability to manipulate light waves with a wavelength of 4 micrometers. Figure 2 The two images at the top show the x-direction phase and x-direction transmittance databases for superatoms, while the two images at the bottom show the y-direction phase and x-direction transmittance databases. In each database, the x-polarization phase and y-polarization target phase achieve full coverage from -π to +π, and the transmittance is above 65%.

[0042] Step 2: Apply the gradient descent algorithm for iterative calculation to obtain the phase distribution information of each target pattern, such as... Figure 3 In this implementation, the metasurface is designed with a pixel size of 1200 × 1200 (1800 μm × 1800 μm). First, the target pattern needs to be distributed according to different incident light vectors and diffraction distances. The digital images "A" to "L" are planned to be reproduced on the focal plane at a distance of 2000 μm from the metasurface. Then, the distance and wavelength parameters corresponding to each target image are substituted into the Rayleigh-Sommerfeld equation of the first kind to obtain the corresponding response function. Finally, iterative calculations using the gradient descent algorithm yield the required phase distribution information.

[0043] Step 3: Assign the target images to different polarization channels. Images "A", "C", "E", "G", "I", and "K" are assigned to the x-polarization-x-polarization channel, while images "B", "D", "F", "H", "J", and "L" are assigned to the y-polarization-y-polarization channel. The data from each channel are then fed into the corresponding Jones matrix function, and the x-polarization and y-polarization target phases are set as optimization variables. Finally, the required x-polarization and y-polarization phase distribution information can be obtained.

[0044] Step 4: Select superatoms based on the obtained x-polarized and y-polarized target phase distribution information and construct a metasurface. Compare the obtained x-polarized and y-polarized target phase distribution information with the corresponding wavelength's phase and transmittance databases. Specifically, for a given pixel, transform the corresponding x-polarized and y-polarized target light fields into complex functions and subtract them from the database data, taking the modulus. Since a single unit has two target phases (x-polarized and y-polarized), the results need to be added together, and the minimum value is taken to find the superatom that best meets the requirements. In this implementation case, the designed high-order topological charge vector holographic metasurface achieved holographic imaging results after vector beam incident on three different topological combinations, as shown below. Figure 4 As shown, the 12 digit patterns from “A” to “L” were reproduced on the focal plane with f=2000 micrometers.

[0045] In summary, the metasurface holography based on high-order vector topology multiplexing perfectly realizes 12 multi-dimensional multiplexed channels. This invention has very important practical significance for the research on increasing the number of multi-dimensional multiplexed channels on non-interlaced metasurfaces.

Claims

1. A metasurface structure based on high-order topological vector beam multiplexing, characterized in that: It includes a substrate (1), a dielectric microstructure (2), and a vector polarized beam (3); The medium microstructure (2) is built on the substrate (1); the medium microstructure (2) is a metasurface array structure formed by a periodic arrangement of several high-transmittance medium metasurface units, the high-transmittance medium metasurface units are cubes of geometric shape, and the vector polarized beam (3) is incident perpendicularly on the metasurface array structure. The substrate (1) is made of silicon, the dielectric microstructure (2) is made of silicon, and the wavelength of the vector polarized beam (3) is 3-5 micrometers. The cube with the described geometric shape is an elliptical cylinder. The major axis diameter and minor axis diameter of the elliptical cylinder are variables, while the period and height of each elliptical cylinder remain constant. The elliptical cylinder is periodically extended along two mutually perpendicular directions, defined as the x-axis and y-axis, respectively. The two extension directions are perpendicular to each other. When a plane wave with polarization along the x-axis is irradiated by the high-transmittance medium metasurface unit along the z-axis, it will carry the phase distribution determined by the major axis dimension of the elliptical cylinder. When a plane wave with polarization along the y-axis is irradiated by the high-transmittance medium metasurface unit along the z-axis, it will carry the phase distribution determined by the minor axis dimension of the elliptical cylinder. Combined with the high-dimensional degree of freedom information carried by the vector polarized beam (3), a low-crosstalk, high-channel information carrier can be realized. The major and minor axis diameters of the elliptical cylinder vary from 300 nanometers to 1200 nanometers, its unit period is 1.5 micrometers to 2 micrometers, the number of elliptical cylinders is 1200×1200, and the total length is 1800 micrometers×1800 micrometers.

2. The metasurface structure based on high-order topological vector beam multiplexing according to claim 1, characterized in that: The height of the elliptical cylinder is 4 micrometers.

3. A method for increasing the number of holographic multiplexing channels using a metasurface structure based on high-order topological vector beam multiplexing as described in claim 1 or 2, characterized in that: It includes the following steps: Step A: Select appropriate substrate (1) and dielectric microstructure (2) materials according to the incident light band of the vector polarized beam (3); Step B: Based on the selected material, simulate the changes in phase and intensity of incident plane light as it passes through cells of different sizes, creating a database of these changes. Step C: Use the gradient descent algorithm to obtain the required metasurface array phase information, then find the corresponding elements in the database, and obtain the simulation results through simulation calculation; Step D: Fabricate the metasurface array structure; Step E: Conduct experimental testing on the designed metasurface array structure. If the results do not meet the requirements, return to step B, adjust and optimize the metasurface parameters, and repeat steps DE until the experimental results meet the requirements.

4. The method according to claim 3, characterized in that: In step D, the metasurface array structure is fabricated using electron beam lithography, dry etching, or wet etching.

5. The method according to claim 3, characterized in that: After step D and before step E, the surface of the metasurface array structure is cleaned with ultraviolet ozone.

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