Polarization direction multiplexing gray near-field display method and element based on metasurface

Abstract

The invention provides a polarization direction multiplexing gray near-field display method and element based on a metasurface, and belongs to the technical field of micro-nano optics. The polarization direction multiplexing gray near-field display method based on the metasurface comprises the following steps: selecting four target images, and respectively carrying out graying and size processing on the four target images; based on the nanoscale interference and diffraction principle of light, the arrangement positions of the two nanometer blocks in each subunit are determined, the deflection angles of the nanometer blocks in each subunit are determined, the deflection angles of the two nanometer blocks in the same subunit are the same, and the deflection angles of the nanometer blocks in the two diagonal subunits in the pixel unit are different; the incident direction of incident ray polarized light is adjusted to be parallel to the x axis or the y axis, so that a near-field grayscale image with two polarization states is generated under the condition of each incident direction. According to the invention, the control dimension of the metasurface and the number of display channels of the optical image can be improved, and the corresponding information capacity is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of micro-nano optical technology, and in particular to a polarization direction multiplexing grayscale near-field display method and element based on a metasurface. Background Art

[0002] Metasurfaces are an emerging class of optical components that interact with light at the micro- and nanoscale, leveraging the interference and diffraction properties of light to control parameters such as amplitude, phase, and polarization. By combining these micro- and nanostructures into arrays, they enable functions such as beam deflection, focusing, and computational holography. Metasurfaces offer advantages not found in conventional optical components, such as ultrathinness and ease of integration, subwavelength control precision, and independent control of multiple optical parameters. The control effects of metasurfaces in related technologies typically focus on individual control of grayscale, phase, and amplitude.

[0003] However, the limited control freedom and number of channels of these methods limit the effectiveness of micro-nano optical near-field displays. For applications in high-density optical information storage and multi-dimensional encryption, dynamic augmented reality displays, and wearable optical devices, metasurface technology urgently needs new control schemes to expand the number of channels. Summary of the Invention

[0004] This disclosure provides a polarization-direction multiplexed grayscale near-field display method and element based on a metasurface, which can increase the control dimension of the metasurface and the number of display channels of optical images, thereby increasing the corresponding information capacity. The technical solution includes at least the following solutions: On the one hand, a polarization direction multiplexing grayscale near-field display method based on a metasurface is provided, wherein the metasurface includes an optical waveguide layer and a plurality of subunits arranged in a square periodic arrangement on the optical waveguide layer, each of the subunits has two nanoblocks, and the nanoblocks are of the same size. Four of the subunits are spatially multiplexed to form a square pixel unit, and the two adjacent vertical sides of the metasurface are the x-axis and the y-axis respectively. The method comprises: selecting four target images and performing grayscale and size processing on them respectively, and each of the four subunits of the pixel unit corresponds to a target image. The pixel points after image grayscale and sizing; based on the principle of nanoscale interference and diffraction of light, the arrangement position of the two nanoblocks in each subunit is determined, and the deflection angle of the nanoblocks in each subunit is determined, the deflection angle of the two nanoblocks in the same subunit is the same, and the deflection angle of the nanoblocks in the two diagonal subunits in the pixel unit is different; by adjusting the incident direction of the incident linear polarized light to be parallel to the x-axis or the y-axis, a near-field grayscale image with two polarization states is generated under each incident direction condition, and the two diagonal subunits are used to encode the near-field grayscale image generated under the same incident direction condition.

[0005] Optionally, determining the arrangement positions of the two nano-blocks in each sub-unit based on the principle of nanoscale interference and diffraction of light includes: designing the first distance and the second distance between the two nano-blocks in each sub-unit, and the center point position of the line connecting the centers of the two nano-blocks, pixel by pixel based on the principle of nanoscale interference and diffraction of light; under any of the incident direction conditions, in the sub-unit used for encoding and generating the corresponding near-field grayscale image, the distance between the two nano-blocks in the incident direction is the first distance, and the distance between the two nano-blocks in the direction perpendicular to the incident direction is the second distance.

[0006] Optionally, the nanoblock is used to extract the secondary diffracted light to generate the corresponding near-field grayscale image, and the first distance between two nanoblocks in each subunit is designed pixel by pixel according to the following formula: I=E0 2 ×[2×cos(β×D1+π)+2] Wherein, I is the light intensity of the pixel point corresponding to the target image after grayscale and resizing, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

[0007] Optionally, the nanoblock is used to extract first-order diffraction light to generate the corresponding near-field grayscale image, and the first distance between two nanoblocks in each subunit is designed pixel by pixel according to the following formula: I=E0 2 ×[2×cos(β×D1)+2] Wherein, I is the light intensity of the pixel point corresponding to the target image after grayscale and resizing, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

[0008] Optionally, the second distance is P / 2, where P is the arrangement period of the subunits.

[0009] Optionally, each of the sub-units is located in a square area on the optical waveguide layer, and the center point of a line connecting the centers of two nano-blocks in each sub-unit is located in the center of the square area.

[0010] Optionally, the deflection angle of the nanoblock is 45° to 135°.

[0011] Optionally, the near-field grayscale image with two polarization states includes linearly polarized light of 45° to 135°.

[0012] Optionally, the material of the optical waveguide layer includes a silicon compound, and the material of the nanoblock includes silicon.

[0013] On the other hand, a polarization direction multiplexing grayscale near-field display element based on a metasurface is provided, which adopts any of the aforementioned polarization direction multiplexing grayscale near-field display methods based on a metasurface for display.

[0014] The beneficial effects of the technical solutions provided by the embodiments of the present disclosure include at least: In the disclosed embodiment, four target images are selected and grayscaled and sized respectively, the arrangement positions of the two nanoblocks in the sub-units of the spatially multiplexed pixel units in the metasurface and the deflection angles of the nanoblocks are designed, and the incident direction of the incident linearly polarized light is adjusted. A near-field grayscale image with two polarization states can be generated under the conditions of two incident directions parallel to the x-axis and the y-axis, respectively, to obtain a metasurface that can store and display four grayscale images, thereby increasing the control dimension of the metasurface and the number of display channels of the optical image, and increasing the corresponding information capacity, so that the metasurface can be better applied to high-density optical information storage and multi-dimensional encryption, dynamic augmented reality display, wearable optical devices and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 Schematic diagram of the principle of polarization direction multiplexing grayscale near-field display based on metasurface provided by an embodiment of the present disclosure; Figure 2 is a top view of the arrangement of pixel units provided by an embodiment of the present disclosure; Figure 3 is a schematic structural diagram of a subunit provided in an embodiment of the present disclosure; Figure 4 is a schematic diagram of a target image provided by an embodiment of the present disclosure; Figure 5 This is a MATLAB simulation diagram of the extracted light intensity of first-order diffraction and second-order diffraction at different nanoblock distances provided by an embodiment of the present disclosure; Figure 6 Schematic diagram of the relationship between the operating wavelength and the sine value of the diffraction angle at an arrangement period of 800 nm for the subunits provided in an embodiment of the present disclosure; Figure 7 Schematic diagram of the relationship between the operating wavelength and the sine value of the diffraction angle at 380 nm for the arrangement period of the subunits provided in an embodiment of the present disclosure.

[0017] Reference numerals: 10: optical waveguide layer; 20: subunit; 201: nanoblock; 21: pixel unit. DETAILED DESCRIPTION

[0018] Unless otherwise defined, the technical or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present disclosure belongs. The words “first”, “second”, “third” and similar terms used in the patent application specification and claims of the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as “a” or “an” do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as “include” or “comprising” mean that the elements or objects appearing before “include” or “comprising” cover the elements or objects listed after “include” or “comprising” and their equivalents, and do not exclude other elements or objects. “Up”, “down”, “left”, “right” and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. A and / or B means that there are three situations: A, B, and A and B.

[0019] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0020] Example 1: Figure 1 It is a schematic diagram of the principle of polarization direction multiplexing grayscale near-field display based on metasurface provided in an embodiment of the present disclosure. Figure 2 3 is a top view of the arrangement of pixel units provided in an embodiment of the present disclosure. Figure 3 It is a structural diagram of the subunit provided in an embodiment of the present disclosure. Figure 4 is a schematic diagram of a target image provided by an embodiment of the present disclosure. Figures 1 to 4 The metasurface includes an optical waveguide layer 10 and a plurality of subunits 20 arranged in a square periodic pattern on the optical waveguide layer 10. Each subunit 20 contains two nanoblocks 201 of identical size. Four subunits 20 are spatially multiplexed to form a square pixel unit 21. The two adjacent vertical edges of the metasurface are the x-axis and the y-axis, respectively. The polarization-direction-multiplexed grayscale near-field display method based on the metasurface includes the following steps: In step S1, four target images are selected and grayscaled and resized respectively.

[0021] In the four subunits 20 of the pixel unit 21 , each subunit 20 corresponds to a pixel point of the target image after grayscale conversion and resizing.

[0022] In step S2 , based on the principle of nanoscale interference and diffraction of light, the arrangement positions of the two nanoblocks in each subunit are determined, and the deflection angle of the nanoblock in each subunit is determined.

[0023] The deflection angles θ of the two nano-blocks 201 in the same sub-unit 20 are the same, and the deflection angles θ of the nano-blocks 201 in the two diagonal sub-units 20 in the pixel unit 21 are different.

[0024] In step S3 , the incident direction of the incident linearly polarized light is adjusted to be parallel to the x-axis or the y-axis, so as to generate a near-field grayscale image with two polarization states under each incident direction condition.

[0025] The two diagonal subunits 20 are used to encode the near-field grayscale image generated under the same incident direction.

[0026] In the disclosed embodiment, four target images are selected and grayscaled and sized respectively, the arrangement positions of the two nanoblocks 201 in the subunit 20 that spatially multiplexes the pixel unit 21 in the metasurface and the deflection angle θ of the nanoblocks 201 are designed, and the incident direction of the incident linearly polarized light is adjusted. A near-field grayscale image with two polarization states can be generated under the conditions of two incident directions parallel to the x-axis and the y-axis, respectively, to obtain a metasurface that can store and display four grayscale images, thereby increasing the control dimension of the metasurface and the number of display channels of the optical image, and increasing the corresponding information capacity, so that the metasurface can be better applied to high-density optical information storage and multi-dimensional encryption, dynamic augmented reality display, wearable optical devices and other fields.

[0027] Exemplarily, the incident direction of the incident linearly polarized light includes a first incident direction and a second incident direction, the first incident direction is parallel to the x-axis, and the second incident direction is parallel to the y-axis. Figure 2 In the figure, the upper left and lower right subunits 20 are used to encode the near-field grayscale image generated under the first incident direction, and the upper right and lower left subunits 20 are used to encode the near-field grayscale image generated under the second incident direction. The polarization state of the near-field grayscale image is determined by the deflection angle θ of the nanoblock 201.

[0028] For example, in the above step S1, four target images may be selected, and grayscale, resized, and normalized are performed on them respectively to determine the light intensity of each corresponding pixel.

[0029] Figure 2In the pixel unit 21 shown, the sub-unit 20 in the upper left corner can correspond to the pixel points of the first target image after grayscale and resizing, that is, the pixel points of grayscale image one; the sub-unit 20 in the lower right corner can correspond to the pixel points of the second target image after grayscale and resizing, that is, the pixel points of grayscale image two; the sub-unit 20 in the upper right corner can correspond to the pixel points of the third target image after grayscale and resizing, that is, the pixel points of grayscale image three; the sub-unit 20 in the lower left corner can correspond to the pixel points of the fourth target image after grayscale and resizing, that is, the pixel points of grayscale image four.

[0030] Optionally, in the above step S2, the arrangement positions of the two nano-blocks 201 in each sub-unit 20 are determined based on the principle of nanoscale interference and diffraction of light, including: based on the principle of nanoscale interference and diffraction of light, designing the first distance D1 and the second distance D2 between the two nano-blocks 201 in each sub-unit 20 on a pixel-by-pixel basis, as well as the center point position of the line connecting the centers of the two nano-blocks 201.

[0031] Under any incident direction condition, in the subunit 20 for encoding and generating the corresponding near-field grayscale image, the distance between the two nanoblocks 201 in the incident direction is a first distance D1, and the distance between the two nanoblocks 201 in the direction perpendicular to the incident direction is a second distance D2. Figure 4 The subunits in can be represented by Figure 2 In the upper left corner of the subunit 20, the first distance D1 is the distance between the two nanoblocks 201 in the direction parallel to the x-axis, and the second distance D2 is the distance between the two nanoblocks 201 in the direction perpendicular to the x-axis. In other subunits 20 for encoding and generating corresponding near-field grayscale images under another incident direction condition, for example Figure 2 In the subunit 20 in the upper right corner, the first distance D1 is the distance between the two nanoblocks 201 in the direction parallel to the y-axis, and the second distance D2 is the distance between the two nanoblocks 201 in the direction perpendicular to the y-axis.

[0032] Figure 5 This is a matlab simulation diagram of the extracted light intensity of the first and second diffraction at different nanoblock distances provided by the embodiment of the present disclosure. Figure 5 As shown in Figure 1, at different nanoblock distances, the first-order diffraction and second-order diffraction extracted light intensity transformations are opposite, and there is a phase difference of π in the images. Here, the nanoblock distance refers to the distance between the two nanoblocks in the incident direction, that is, the first distance D1.

[0033] The following is an exemplary description of a metasurface that utilizes polarization direction multiplexing of secondary diffraction and can store and display four grayscale images.

[0034] In this embodiment, the nanoblocks 201 are used to extract the secondary diffracted light to generate the corresponding near-field grayscale image. The first distance D1 between two nanoblocks 201 in each subunit 20 can be designed pixel by pixel according to the following formula (1): I=E0 2 ×[2×cos(β×D1+π)+2](1) Wherein, I is the light intensity of the corresponding pixel point after the target image is grayscaled and resized, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

[0035] Exemplarily, the propagation constant β of the waveguide satisfies the following formula (2): β=2×π×n eff / λ(2) Among them, n eff is the effective refractive index of the metasurface, and λ is the operating wavelength of the incident linearly polarized light.

[0036] Exemplarily, the operating wavelength λ of the incident linearly polarized light is 560 nm, and the arrangement period P of the subunits 20 is 800 nm.

[0037] Figure 6 Schematic diagram of the relationship between the working wavelength and the sine value of the diffraction angle at 800nm ​​for the arrangement period of the subunits provided in the embodiment of the present disclosure. Figure 6 As shown, since the numerical aperture (NA) of the commonly used objective lens is 0.45, this embodiment requires that the secondary diffraction light is within the objective lens and the primary diffraction light is outside the objective lens. Therefore, the sine value of the secondary diffraction angle needs to be between ±0.45. Under the condition of different sub-unit arrangement periods P, the diffraction angle can be determined according to the following formula (3): sinθ=n eff ×k0-n×λ / P(3) Where θ is the diffraction angle, n eff is the effective refractive index of the metasurface, k0 is the wave vector in air, n is the diffraction order, λ is the operating wavelength of the incident linearly polarized light, and P is the arrangement period of the subunits.

[0038] See also Figures 4 to 6 When the operating wavelength λ of incident linearly polarized light is 560 nm and the arrangement period P of the subunits 20 is 800 nm, the first distance D1 between two nanoblocks 201 in each subunit 20 can range from P / 4 to P / 2. This results in a metasurface that utilizes polarization direction multiplexing by secondary diffraction and can store and display four grayscale images.

[0039] It should be noted that the above-mentioned operating wavelength λ of the incident linearly polarized light and the arrangement period P of the subunits 20 are only used as an example. In other embodiments, the operating wavelength λ of the incident linearly polarized light and the arrangement period P of the subunits 20 can also be adjusted according to actual needs, and the present disclosure does not limit this.

[0040] Optionally, the second distance D2 is P / 2, where P is the arrangement period of the subunits 20 . Figure 2 In the figure, the upper left and lower right subunits 20 encode the near-field grayscale image generated under the first incident direction, while the upper right and lower left subunits 20 encode the near-field grayscale image generated under the second incident direction. The polarization state of the near-field grayscale image is determined by the deflection angle θ of the nanoblock 201. Because the intensity of the extracted light is related to the distance between the two nanoblocks 201, the second distance D2 of P / 2 ensures that the near-field grayscale images extracted under different incident directions do not affect each other.

[0041] For example, Figure 2 In the two subunits 20 in the upper left and lower right corners, the distance between the two nanoblocks 201 in the direction parallel to the x-axis is the calculated first distance D1, and the distance between the two nanoblocks 201 in the direction parallel to the y-axis is the second distance D2 = P / 2. In the subunits 20 in the upper right and lower left corners, the distance between the two nanoblocks 201 in the direction parallel to the y-axis is the calculated first distance D1, and the distance between the two nanoblocks 201 in the direction parallel to the x-axis is the second distance D2 = P / 2.

[0042] See also Figure 1 and Figure 2 When the incident direction of the incident linear polarized light is the first incident direction parallel to the x-axis, the polarization states of the near-field grayscale images obtained by extracting the light are respectively Figure 2 The deflection angles θ of the nanoblocks 201 in the subunit 20 in the upper left corner and the subunit 20 in the lower right corner correspond to each other. By performing polarization analysis on the extracted light, two grayscale images of the target image (grayscale image 1 and grayscale image 2) can be obtained. Under this first incident direction condition, in the subunit 20 in the upper right corner and the subunit 20 in the lower left corner, the distance between the two nanoblocks 201 in the direction parallel to the x-axis is P / 2, and the extracted light intensity is 0, so it will not affect the extraction of the two grayscale images.

[0043] Similarly, when the incident direction of the incident linear polarized light is the second incident direction parallel to the y-axis, the polarization states of the near-field grayscale images obtained by extracting the light are respectively Figure 2The deflection angles θ of the nanoblocks 201 in the subunit 20 in the upper right corner and the subunit 20 in the lower left corner correspond to each other. By performing polarization analysis on the extracted light, the grayscale images of the other two target images (grayscale image three and grayscale image four) can be obtained. Under this second incident direction condition, in the subunit 20 in the upper left corner and the subunit 20 in the lower right corner, the distance between the two nanoblocks 201 in the direction parallel to the y-axis is P / 2, and the extracted light intensity is 0, so it will not affect the extraction of the two grayscale images.

[0044] See also Figures 1 to 4 Each subunit 20 is located in a square area on the optical waveguide layer 10, and the center point of the line connecting the centers of two nanoblocks 201 in each subunit 20 is located at the center of the square area. The arrangement period P of the above subunits 20 is also the side length of the square area.

[0045] Exemplarily, the nanoblock 201 is in the shape of a cuboid, the orthographic projection of the nanoblock 201 on the optical waveguide layer 10 is a rectangle, and the deflection angle θ is the angle between the long axis of the rectangle and the x-axis.

[0046] Optionally, the deflection angle θ of the nanoblock 201 is between 45° and 135°. Exemplarily, the near-field grayscale image with two polarization states includes linearly polarized light at 45° to 135°. For example, the nanoblocks 201 in two diagonal subunits 20 have two deflection angles θ of 45° and 135°, respectively. The near-field grayscale image with two polarization states includes linearly polarized light at 45° and linearly polarized light at 135°. This can reduce interference between grayscale images with different polarization states and improve modulation efficiency. Figure 2 , the deflection angle θ of the nanoblock 201 in the upper left subunit 20 and the nanoblock 201 in the upper right subunit 20 is 45°, and the deflection angle θ of the nanoblock 201 in the lower left subunit 20 and the nanoblock 201 in the lower right subunit 20 is 135°.

[0047] In other embodiments, the deflection angle θ of the nano-block 201 may also be adjusted according to actual needs, and the present disclosure does not impose any limitation thereto.

[0048] Optionally, the length L of the nanoblock 201 is 120 nm, the width W of the nanoblock 201 is 60 nm, and the height H of the nanoblock 201 is 380 nm.

[0049] It should be noted that the specific size of the nano block 201 is only an example. In other embodiments, the size of the nano block 201 may also be adjusted according to actual needs, and the present disclosure does not impose any limitation on this.

[0050] Optionally, the material of the optical waveguide layer 10 includes a silicon compound, and the material of the nanoblocks 201 includes silicon.

[0051] In other embodiments, the material of the optical waveguide layer 10 may also be selected from other materials according to actual needs, and the present disclosure does not limit this.

[0052] Example 2: The difference between this embodiment and embodiment 1 is that this embodiment uses a metasurface that utilizes polarization direction multiplexing of first-order diffraction and can store and display four grayscale images.

[0053] In this embodiment, the nanoblocks 201 are used to extract the first-order diffracted light to generate the corresponding near-field grayscale image. The first distance D1 between two nanoblocks 201 in each subunit 20 can be designed pixel by pixel according to the following formula (4): I=E0 2 ×[2×cos(β×D1)+2](4) Wherein, I is the light intensity of the corresponding pixel point after the target image is grayscaled and resized, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

[0054] Exemplarily, the operating wavelength λ of the incident linearly polarized light is 560 nm, and the arrangement period P of the subunits 20 is 380 nm.

[0055] Figure 7 Schematic diagram of the relationship between the operating wavelength and the sine value of the diffraction angle at 380 nm for the arrangement period of the subunits provided in the embodiment of the present disclosure. Figure 4 、 Figure 5 and Figure 7 This embodiment requires that the first-order diffracted light be within the objective lens, while the second-order diffracted light be outside the objective lens. Therefore, the sine of the first-order diffraction angle must be between ±0.45. When the operating wavelength λ of the incident linearly polarized light is 560 nm and the period P of the subunits 20 is 380 nm, the first distance D1 between two nanoblocks 201 in each subunit 20 can range from 0 to P / 2. This results in a metasurface that utilizes polarization direction multiplexing of first-order diffraction to store and display four grayscale images.

[0056] It should be noted that the arrangement of the subunits 20, the size and deflection angle θ of the nanoblocks 201, and the second distance D2 between two nanoblocks 201 in each subunit 20 in this embodiment can be referred to in the above embodiment 1 and will not be repeated here.

[0057] The embodiments of the present disclosure also provide a polarization direction multiplexing grayscale near-field display element based on a metasurface, which uses any of the aforementioned polarization direction multiplexing grayscale near-field display methods based on a metasurface for display.

[0058] The above description is merely an optional embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the scope of protection of the present disclosure.

Claims

1. A polarization-direction multiplexing grayscale near-field display method based on a metasurface, characterized in that: The metasurface includes an optical waveguide layer and a plurality of subunits arranged in a square periodic pattern on the optical waveguide layer, each of the subunits having two nanoblocks of the same size, and a square pixel unit is formed by spatial multiplexing of four subunits, wherein two adjacent vertical sides of the metasurface are the x-axis and the y-axis, respectively. The method includes: Selecting four target images and performing grayscale and resizing processing on them respectively, wherein each of the four subunits of the pixel unit corresponds to a pixel point of the target image after grayscale and resizing; Based on the principles of nanoscale interference and diffraction of light, the arrangement positions of the two nanoblocks in each subunit are determined, and the deflection angle of the nanoblocks in each subunit is determined. The deflection angles of the two nanoblocks in the same subunit are the same, while the deflection angles of the nanoblocks in the two diagonal subunits in the pixel unit are different. By adjusting the incident direction of the incident linear polarized light to be parallel to the x-axis or the y-axis, a near-field grayscale image with two polarization states is generated under each incident direction condition, and the two subunits of the diagonal line are used to encode the near-field grayscale image generated under the same incident direction condition.

2. The polarization direction multiplexing grayscale near-field display method based on metasurface according to claim 1, characterized in that: The method of determining the arrangement positions of the two nanoblocks in each subunit based on the principle of nanoscale interference and diffraction of light includes: Based on the principles of nanoscale interference and diffraction of light, the first and second distances between two nanoblocks in each subunit, as well as the center point position of the line connecting the centers of the two nanoblocks, are designed pixel by pixel. Under any of the incident direction conditions, in the subunit used to encode and generate the corresponding near-field grayscale image, the distance between the two nanoblocks in the incident direction is the first distance, and the distance between the two nanoblocks in the direction perpendicular to the incident direction is the second distance.

3. The polarization direction multiplexing grayscale near-field display method based on metasurface according to claim 2, characterized in that: The nanoblock is used to extract the secondary diffraction light to generate the corresponding near-field grayscale image. The first distance between two nanoblocks in each subunit is designed pixel by pixel according to the following formula: I=E0 2 ×[2×cos(β×D1+π)+2] Wherein, I is the light intensity of the pixel point corresponding to the target image after grayscale and resizing, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

4. The polarization direction multiplexing grayscale near-field display method based on metasurface according to claim 2, characterized in that: The nanoblock is used to extract the first-order diffraction light to generate the corresponding near-field grayscale image. The first distance between two nanoblocks in each subunit is designed pixel by pixel according to the following formula: I=E0 2 ×[2×cos(β×D1)+2] Wherein, I is the light intensity of the pixel point corresponding to the target image after grayscale and resizing, E0 is the electric field amplitude of the incident linearly polarized light, β is the propagation constant of the waveguide, and D1 is the first distance.

5. The polarization direction multiplexing grayscale near-field display method based on metasurface according to claim 2, characterized in that: The second distance is P / 2, where P is the arrangement period of the subunits.

6. The polarization direction multiplexing grayscale near-field display method based on a metasurface according to any one of claims 2 to 5, characterized in that: Each of the sub-units is located in a square area on the optical waveguide layer, and the center point of the line connecting the centers of two nano-blocks in each sub-unit is located in the center of the square area.

7. The polarization direction multiplexing grayscale near-field display method based on a metasurface according to any one of claims 1 to 5, characterized in that: The deflection angle of the nanoblock is 45° to 135°.

8. The polarization direction multiplexing grayscale near-field display method based on metasurface according to claim 7, characterized in that: The near-field grayscale image with two polarization states includes linearly polarized light ranging from 45° to 135°.

9. The polarization direction multiplexing grayscale near-field display method based on a metasurface according to any one of claims 1 to 5 and claim 8, characterized in that: The material of the optical waveguide layer includes a silicon compound, and the material of the nanoblock includes silicon.

10. A polarization-direction multiplexing grayscale near-field display element based on a metasurface, characterized in that: Display is performed using the polarization direction multiplexing grayscale near-field display method based on a metasurface as described in any one of claims 1 to 9.

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