A wavelength decoupling design method based on minimalist metasurface and metasurface device

Abstract

The present invention belongs to the field of micro-nano optics technology and discloses a wavelength decoupling design method and metasurface device based on a minimalist metasurface. The basic structure of the metasurface device constructed by the present invention includes a substrate and a nanobrick array. The nanobrick array is composed of nanobricks of two sizes. The present invention determines the geometric dimensions of the metasurface device and the size arrangement and steering angle arrangement of several nanobricks in the nanobrick array based on two selected operating wavelengths and two holographic images. At the two operating wavelengths, circularly polarized light with the same rotation direction is incident and, after reflection by the metasurface device, two holographic images are obtained in the far field, achieving wavelength decoupling. The present invention can realize holographic multiplexing display under dual-wavelength incidence and has the advantages of simple design and easy processing.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optical technology, and more specifically, relates to a wavelength decoupling design method based on a minimalist metasurface and a metasurface device. Background Art

[0002] Metasurfaces, as a new type of artificial subwavelength structure, can be designed to realize a wide range of functions, such as vortex beam generators, high numerical aperture lenses, and achromatic lenses. Compared with traditional optical components, metasurfaces offer more controllable degrees of freedom, enabling the construction of multiplexed optical devices. Among these, wavelength, as a key parameter of light waves, plays a crucial role.

[0003] Current metasurface-based wavelength multiplexing solutions require a wide variety of nanostructures and are sensitive to their structural dimensions, placing extremely high demands on design and fabrication. Simplifying the design and reducing fabrication complexity are key research areas in this field. Summary of the Invention

[0004] The present invention solves the problems of complex design and high processing difficulty of wavelength multiplexing solutions based on metasurfaces in the prior art by providing a wavelength decoupling design method and metasurface device based on a minimalist metasurface.

[0005] The present invention provides a wavelength decoupling design method based on a minimalist metasurface, comprising the following steps:

[0006] Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface and comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array comprises nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of uniform size, each of which is provided with a nanobrick;

[0007] Selecting a first operating wavelength and a second operating wavelength, and selecting a first holographic image and a second holographic image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected operating wavelengths and the two holographic images, to obtain the desired metasurface device;

[0008] After obtaining the required metasurface device, circularly polarized light with the same rotation direction is incident at the first working wavelength and the second working wavelength. After reflection from the metasurface device, the first holographic image and the second holographic image are respectively obtained in the far field, thereby realizing wavelength decoupling.

[0009] Preferably, an xoy coordinate system is established with the directions of the two sides parallel to the working surface of the substrate set as the x-axis and the y-axis respectively, the nanobrick is a rectangular structure, the major axis and the minor axis of the nanobrick are parallel to the working surface of the substrate, and the lengths of the major axis and the minor axis are different; the steering angle of the nanobrick is the angle between the major axis of the nanobrick and the x-axis; the working surface of the substrate unit structure is square; the two sizes of nanobricks have the same height, different lengths and different widths.

[0010] Preferably, when determining the geometric dimensions of the metasurface device, the height of the nanobrick and the side length of the working surface of the substrate unit structure are first determined, and then the length and width dimension parameters of the nanobrick are scanned at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results at the two working wavelengths; finally, two groups of dimensions are selected as the determined dimension parameters of the nanobrick based on the transmission phase scanning results at the two working wavelengths, and the transmission phases of the two selected nanobricks at the first working wavelength are equal, and the transmission phase difference between the two sizes of nanobricks at the second working wavelength is π.

[0011] Preferably, when determining the geometric dimensions of the metasurface device, it also includes: scanning the length and width dimension parameters of the nanobrick at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the polarization conversion efficiency scanning results at the two working wavelengths; based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two sets of dimensions that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined dimension parameters of the nanobrick.

[0012] Preferably, after determining the geometric dimensions of the metasurface device, one of the substrate unit structures and a nanobrick located on its working surface is taken as a pixel point, and the phase of the reflected light passing through the metasurface device is modulated using the steering angle of the nanobrick and the transmission phase difference between two sizes of nanobricks. The size and steering angle of the nanobrick on each substrate unit structure are determined based on the first holographic image and the second holographic image.

[0013] Preferably, the Jones matrix J of the nanobrick with a steering angle of θ is expressed as: The Jones vector of circularly polarized light is expressed as: The circularly polarized light reflected by the nanobrick with a steering angle of θ is expressed as: where A and B are coefficients related to the reflectivity in the major and minor axis directions of the nanobrick, respectively.

[0014] Preferably, when the nanobrick is designed as an equivalent half-wave plate, A=-B is satisfied, and the reflected light only contains the reverse circular polarization component.

[0015] Preferably, the sizes of the base unit structure and the nanobricks are both sub-wavelength level.

[0016] Preferably, the nanobricks are made of single crystal silicon material, and the substrate is made of single crystal silicon material as a lower layer and fused quartz glass material as an upper layer.

[0017] On the other hand, the present invention provides a metasurface device, which is obtained based on the above-mentioned wavelength decoupling design method based on a minimalist metasurface; the metasurface device includes a substrate and a nanobrick array located on the working surface of the substrate, and the nanobrick array is composed of nanobricks of two sizes; at two working wavelengths, circularly polarized light with the same rotation direction is incident, and after reflection by the metasurface device, two different holographic images are obtained in the far field.

[0018] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0019] The present invention is based on a minimalist metasurface for wavelength decoupling design. The basic structure of the metasurface device (i.e., a minimalist metasurface) constructed by the present invention includes a substrate and a nanobrick array located on the working surface of the substrate. The nanobrick array is composed of nanobricks of two sizes. The substrate is divided into a number of substrate unit structures of the same size. Each substrate unit structure is provided with a nanobrick. The present invention determines the geometric dimensions of the metasurface device based on the two selected working wavelengths and two holographic images, as well as the size arrangement and steering angle arrangement of the several nanobricks in the nanobrick array to obtain the required metasurface device; after obtaining the required metasurface device, at the first working wavelength and the second working wavelength, circularly polarized light of the same rotation direction is incident. After being reflected by the metasurface device, the first holographic image and the second holographic image are respectively obtained in the far field, thereby achieving wavelength decoupling. In summary, the present invention constructs a minimalist metasurface based only on nanobricks of two sizes. The minimalist metasurface can achieve wavelength decoupling, which can greatly reduce the difficulty of processing and designing the metasurface device. It has the advantages of simple design and easy processing. The base unit structure and nanobricks are both subwavelength in size, making the metasurface device designed in this invention compact, lightweight, and highly integrated, making it suitable for miniaturization and microfabrication. The wavelength decoupling scheme proposed in this invention enables holographic multiplexing display under dual-wavelength incidence, and has promising applications in fields such as information multiplexing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a base unit structure and nanobricks located on its working surface in a wavelength decoupling design method based on a minimalist metasurface provided in Example 1 of the present invention;

[0021] Figure 2The transmission phase scanning diagram of the nanobrick at dual wavelengths in a wavelength decoupling design method based on a minimalist metasurface provided in Example 1 of the present invention; wherein, Figure 2 (a) is the transmission phase scan of the nanobrick at a wavelength of 550nm. Figure 2 (b) is the transmission phase scan of the nanobrick at a wavelength of 633 nm;

[0022] Figure 3 This is a scan diagram of the polarization conversion efficiency of nanobricks at dual wavelengths in a wavelength decoupling design method based on a minimalist metasurface provided in Example 1 of the present invention; wherein, Figure 3 (a) is a scanning diagram of the polarization conversion efficiency of nanobricks at a wavelength of 550nm. Figure 3 (b) is a scanning diagram of the polarization conversion efficiency of the nanobrick at a wavelength of 633 nm;

[0023] Figure 4 Schematic diagram of the effect of wavelength decoupling using metasurface devices. DETAILED DESCRIPTION

[0024] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0025] Example 1:

[0026] Example 1 provides a wavelength decoupling design method based on a minimalist metasurface, comprising the following steps:

[0027] Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface and comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array comprises nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of uniform size, each of which is provided with a nanobrick;

[0028] Selecting a first operating wavelength and a second operating wavelength, and selecting a first holographic image and a second holographic image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected operating wavelengths and the two holographic images, to obtain the desired metasurface device;

[0029] After obtaining the required metasurface device, circularly polarized light with the same rotation direction is incident at the first working wavelength and the second working wavelength. After reflection from the metasurface device, the first holographic image and the second holographic image are respectively obtained in the far field, thereby realizing wavelength decoupling.

[0030] Among them, see Figure 1, an xoy coordinate system is established with the directions of the two sides parallel to the working surface of the substrate set as the x-axis and y-axis respectively, the nanobrick is a rectangular parallelepiped structure, the major axis and minor axis of the nanobrick are both parallel to the working surface of the substrate, and the lengths of the major axis and the minor axis are different; the steering angle θ of the nanobrick is the angle between the major axis of the nanobrick and the x-axis; the working surface of the substrate unit structure is a square with a side length of C; the two sizes of nanobricks have the same height H, different lengths L, and different widths W.

[0031] The two sizes of nanobricks are designated as first and second nanobricks, respectively. The first nanobrick's structural dimensions include a first length L1, a first width W1, and a height H. The second nanobrick's structural dimensions include a second length L2, a second width W2, and a height H. These dimensional parameters were optimized through electromagnetic simulation based on the two selected operating wavelengths.

[0032] Specifically, when determining the geometric dimensions of the metasurface device, the height H of the nanobrick and the side length C of the working surface of the substrate unit structure are first determined, and then the length and width dimension parameters of the nanobrick are scanned at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results at the two working wavelengths; finally, two groups of dimensions are selected as the determined dimension parameters of the nanobrick based on the transmission phase scanning results at the two working wavelengths, and the transmission phases of the two selected nanobricks at the first working wavelength are equal, and the transmission phase difference between the two sizes of nanobricks at the second working wavelength is π.

[0033] In a preferred solution, when determining the geometric dimensions of the metasurface device, the length and width dimension parameters of the nanobrick are scanned respectively at the first working wavelength and the second working wavelength through electromagnetic simulation to obtain the polarization conversion efficiency scanning results at the two working wavelengths; finally, based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two sets of dimensions that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined dimensional parameters of the nanobrick.

[0034] After determining the geometric dimensions of the metasurface device, a base unit structure and a nanobrick located on its working surface are used as a pixel. The phase of the reflected light from the metasurface device is modulated using the nanobrick's steering angle and the difference in transmission phase between two sizes of nanobricks. The size and steering angle of the nanobrick on each base unit structure are determined based on the first and second holographic images. This determines which of the two sizes each nanobrick in the nanobrick array should adopt, and the magnitude of the steering angle of each nanobrick is determined.

[0035] The Jones matrix J of the nanobrick with a steering angle of θ is expressed as: The Jones vector of circularly polarized light is expressed as: The circularly polarized light reflected by the nanobrick with a steering angle of θ is expressed as: where A and B are coefficients related to the reflectivity in the major and minor axis directions of the nanobrick, respectively.

[0036] It can be seen that the reflected light consists of a co-circularly polarized component and an inversely polarized component. The phase of the inversely polarized component can be controlled by the nanobrick's steering angle θ. Furthermore, when the nanobrick is designed as an equivalent half-wave plate, that is, A = -B, the reflected light contains only the inversely polarized component, and the corresponding polarization conversion efficiency is maximized.

[0037] The sizes of the base unit structure and the nano bricks are both sub-wavelength.

[0038] In terms of materials, the nanobricks can be made of single-crystal silicon, and the substrate can be made of a single-crystal silicon lower layer and a fused silica upper layer. Because the metasurface device designed in this invention operates in a reflective mode, and the single-crystal silicon + fused silica + single-crystal silicon material exhibits high efficiency in this mode, the above-mentioned preparation method is preferred.

[0039] The wavelength decoupling design method based on a minimalist metasurface provided in Example 1 utilizes only a minimalist metasurface (i.e., a metasurface device) comprising two nanobricks of different sizes to obtain two different holographic images in the far field when circularly polarized light of the same rotation direction is incident at two working wavelengths.

[0040] The present invention will be further described below.

[0041] When light of any polarization state is incident and passes through the minimalist metasurface, the phase of the reflected light is modulated. By optimizing the arrangement of two nanobrick sizes and the steering angle θ of the minimalist metasurface, at a first operating wavelength λ1, when left-handed circularly polarized light passes through the minimalist metasurface, the phase of the reflected light is modulated, resulting in a single holographic image in the far field. At a second operating wavelength λ2, when left-handed circularly polarized light passes through the minimalist metasurface, the phase of the reflected light is modulated, resulting in a separate holographic image in the far field. The two holographic images at dual wavelengths can be designed independently, meaning that the design method of the present invention achieves wavelength decoupling.

[0042] It should be noted that the above description is based on an example of incident left-handed circularly polarized light. The present invention can also be used with incident right-handed circularly polarized light at both working wavelengths.

[0043] Taking the first working wavelength λ1 = 550nm and the second working wavelength λ2 = 633nm as an example, electromagnetic simulation software is used for modeling and simulation. With left-handed circularly polarized light incident vertically, the structural parameters of the nano-unit are scanned at the working wavelength, including the structural dimensions of the first nano-brick: L1, W1, H, the structural dimensions of the second nano-brick: L2, W2, H, and the size C of the working surface of the base unit structure. The scanning results of the transmission phase are shown in Figure 2. Figure 2 As shown, Figure 2 (a) is the transmission phase scan of the nanobrick at a wavelength of 550nm. It represents the transmission phase result of scanning at 550nm wavelength. Figure 2 (b) is the transmission phase scan of the nanobrick at a wavelength of 633nm. It shows the transmission phase results of scanning at 633nm wavelength.

[0044] Under the premise of ensuring that the transmission phases of the two sizes of nanobricks at 633nm are equal and the transmission phase difference at 550nm is π, the left-handed circularly polarized light is incident vertically, and the proportion of the right-handed circularly polarized light component in the reflected light field is optimized by the nanobricks to maximize the polarization conversion efficiency (that is, in the preferred solution, several groups of structures are selected under the premise of ensuring the phase difference, and the two structures with the highest polarization conversion efficiency are selected as the final selected structures). The polarization conversion efficiency scan results are shown as follows: Figure 3 As shown, Figure 3 (a) is the polarization conversion efficiency scan of the nanobrick at a wavelength of 550nm, E f1 It represents the polarization conversion efficiency result of scanning at 550nm wavelength. Figure 3 (b) is a scanning diagram of the polarization conversion efficiency of nanobricks at a wavelength of 633 nm, E f2 It shows the polarization conversion efficiency results scanned at 633nm wavelength.

[0045] In this example, the final determined structural parameters include: L1 = 130 nm, W1 = 230 nm, H = 220 nm, L2 = 290 nm, W2 = 220 nm, and C = 400 nm.

[0046] When circularly polarized light is incident on the minimalist metasurface, the phase of the reflected light is modulated. When left-handed circularly polarized light at 633nm is incident on the minimalist metasurface, a holographic image is obtained in the far field; when left-handed circularly polarized light at 550nm is incident on the minimalist metasurface, another holographic image is obtained in the far field. The two holographic images at dual wavelengths can be designed independently, which can achieve wavelength decoupling based on the minimalist metasurface. The effect diagram is shown in the figure below. Figure 4 shown.

[0047] Example 2:

[0048] Example 2 provides a metasurface device, obtained based on the wavelength decoupling design method based on a minimalist metasurface as described in Example 1. The metasurface device provided in Example 2 includes a substrate and a nanobrick array located on a working surface of the substrate, wherein the nanobrick array is composed of nanobricks of two sizes. At two operating wavelengths, incident circularly polarized light of the same handedness is reflected by the metasurface device, and two different holographic images are obtained in the far field.

[0049] Since the device provided in Example 2 corresponds to the design method provided in Example 1, Example 2 can be understood by referring to the description of Example 1, and will not be described in detail here.

[0050] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A wavelength decoupling design method based on a minimalist metasurface, characterized in that: The following steps are involved: Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface and comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array comprises nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of uniform size, each of which is provided with a nanobrick; Selecting a first operating wavelength and a second operating wavelength, and selecting a first holographic image and a second holographic image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected operating wavelengths and the two holographic images, to obtain the desired metasurface device; After obtaining the desired metasurface device, circularly polarized light with the same rotational direction is incident at the first operating wavelength and the second operating wavelength. After reflection from the metasurface device, the first holographic image and the second holographic image are respectively obtained in the far field, thereby achieving wavelength decoupling. The x-axis and y-axis are used to establish an xoy coordinate system, with the two sides parallel to the working surface of the substrate being respectively defined as the x-axis and the y-axis. The nanobrick is a rectangular parallelepiped structure, with the major axis and minor axis of the nanobrick both parallel to the working surface of the substrate, and the major axis and the minor axis being of different lengths. The turning angle of the nanobrick is the angle between the major axis of the nanobrick and the x-axis. The working surface of the substrate unit structure is square. The two sizes of nanobricks have the same height, different lengths, and different widths. When determining the geometric dimensions of the metasurface device, the height of the nanobrick and the side length of the working surface of the substrate unit structure are first determined. Then, the length and width dimension parameters of the nanobrick are scanned at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results and polarization conversion efficiency scanning results at the two working wavelengths. Finally, based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two groups of sizes that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined size parameters of the nanobricks. The transmission phases of the two selected nanobrick sizes at the first working wavelength are equal, and the transmission phase difference between the two nanobrick sizes at the second working wavelength is π. After determining the geometric dimensions of the metasurface device, one of the substrate unit structures and a nanobrick located on its working surface is taken as a pixel point. The phase of the reflected light passing through the metasurface device is modulated using the steering angle of the nanobrick and the transmission phase difference between two sizes of nanobricks. The size and steering angle of the nanobrick on each substrate unit structure are determined based on the first holographic image and the second holographic image.

2. The wavelength decoupling design method based on a minimalist metasurface according to claim 1, characterized in that: The steering angle is θ Jones matrix of nanobricks J Expressed as: , the Jones vector of circularly polarized light is expressed as: , the circularly polarized light is turned at an angle of θ The nanobricks are expressed after reflection as: ,in, A and B are the coefficients related to the reflectivity in the major and minor axis directions of the nanobricks, respectively.

3. The wavelength decoupling design method based on a minimalist metasurface according to claim 2, characterized in that: When the nanobrick is designed as an equivalent half-wave plate, , the reflected light only contains the reverse circular polarization component.

4. The wavelength decoupling design method based on a minimalist metasurface according to claim 1, characterized in that: The sizes of the base unit structure and the nano bricks are both sub-wavelength.

5. The wavelength decoupling design method based on a minimalist metasurface according to claim 1, characterized in that: The nano bricks are made of single crystal silicon material, and the substrate is made of single crystal silicon material as a lower layer and fused quartz glass material as an upper layer.

6. A metasurface device, characterized in that: The metasurface device is obtained based on the wavelength decoupling design method based on a minimalist metasurface as described in any one of claims 1 to 5; the metasurface device includes a substrate and a nanobrick array located on the working surface of the substrate, and the nanobrick array is composed of nanobricks of two sizes; at two working wavelengths, circularly polarized light with the same rotation direction is incident, and after reflection by the metasurface device, two different holographic images are obtained in the far field.

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