Metasurface, design method thereof, method for realizing dynamic holographic display, and application

Abstract

The application belongs to the technical field of micro-nano optics, and discloses a metasurface, a design method thereof, a method for realizing dynamic holographic display, and application. The application integrates on-chip double-atom nano bricks above a waveguide by design, independently controls the phase and polarization of extracted light waves by designing the overall displacement, rotation angle of the double-atom nano bricks and the local displacement between the double-atom nano bricks, synchronously controls the arbitrary polarization and phase of the out-coupled light waves, obtains a multi-channel full-polarization vector hologram in combination with spatial multiplexing, and actively and real-timely switches holographic images floating in a real-world scene in combination with an electrically-driven liquid crystal device, so that dynamic holographic display is realized. The application has practical dynamic control capability, simplifies the structure, and can be applied to fields such as wearable augmented reality devices, multi-channel information storage or encryption, intelligent dynamic display and the like.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optical technology, and more specifically, relates to a metasurface and its design method, a method for realizing dynamic holographic display, and its application. Background Technology

[0002] As an emerging research field in nanophotonics, incorporating metasurfaces onto optical waveguides has attracted widespread attention as a compact platform for manipulating and guiding in-plane guided waves. Recently, researchers have achieved various functions and applications by carefully patterning subwavelength nanostructures on waveguides, including directional beam control, on-chip metalenses, vortex beam generation, on-chip metasurface holography, and transparent screen displays. This also provides new avenues for developing advanced optical display devices with chip integration and miniaturization, such as for augmented reality (AR). In particular, compared to traditional free-space metasurfaces, on-chip metasurface-based displays offer unique advantages; for example, due to the on-chip propagation, the observer is not affected by zero-order background interference.

[0003] However, for next-generation wearable smart optical display devices, most previous on-chip metasurfaces only operated in a static state, lacking practical dynamic control capabilities, thus severely limiting their application in real-world scenarios. Although some active tuning strategies based on thermal, mechanical, liquid wetting, optical, and electro-driven approaches have been studied and used to manipulate free-space light, a practical solution for achieving dynamic tuning of on-chip optics remains undiscovered. On the other hand, while some on-chip integrated metasurfaces have achieved waveguide-driven metasurface holographic displays, they are still limited by the number of available polarization states and require the design of complex nanostructures of different sizes, which also cannot meet the multifunctional requirements of on-chip metasurfaces in practical applications. Therefore, looking to the future, achieving dynamic switchability based on full polarization vector wavefront control in on-chip integrated solutions is crucial. Summary of the Invention

[0004] This invention addresses the problems of existing on-chip metasurfaces lacking practical dynamic control capabilities, having a limited number of usable polarization states, or having complex structures by providing metasurfaces and their design methods, methods for realizing dynamic holographic displays, and applications.

[0005] In a first aspect, the present invention provides a method for designing metasurfaces, comprising:

[0006] A metasurface is constructed using a unit structure comprising a substrate layer, an optical waveguide layer above the substrate layer, and diatomic nanobricks disposed on the working surface of the optical waveguide layer, wherein the diatomic nanobricks are arranged orthogonally; the metasurface contains a plurality of the diatomic nanobricks forming a nanobrick structure array, and all the diatomic nanobricks contained in the metasurface are of the same size;

[0007] The overall displacement D of the diatomic nanobrick, the local displacement S between the diatomic nanobricks, and the rotation angle θ of a certain nanobrick in the diatomic nanobrick are used as adjustment parameters. Combined with the vector holographic image, the arrangement of several diatomic nanobricks is designed by designing the adjustment parameters, and the vector holographic image is encoded into the metasurface.

[0008] Preferably, the light waves extracted from each nanobrick in the diatomic nanobricks are represented as follows:

[0009]

[0010] In the formula, E1 and E2 are the electric fields of the light waves extracted by each nanobrick in the diatomic nanobrick, respectively; S x Let P be the spacing of the diatomic nanobricks along the x-direction, representing the local displacement; θ is the rotation angle of one nanobrick in the diatomic nanobrick set; and P is the rotation angle of one nanobrick in the diatomic nanobrick set. x The period of the diatomic nanobrick along the x-direction;

[0011] In the aforementioned diatomic nanobrick, the transmission phase difference along the x-direction between the two orthogonal components parallel to the long axis of each nanobrick is expressed as follows:

[0012]

[0013] In the formula, The transmission phase difference between the two orthogonal components.

[0014] Preferably, the target operating wavelength is selected as λ, and the period P of the diatomic nanobrick along the x-direction is calculated from the propagation constant β of the waveguide. x and the period P of the two-atom nanobrick along the y-direction y The spacing of the diatomic nanobricks along the y-direction is P. y / 2.

[0015] Preferably, taking the leftmost point in the x-direction within the unit structure as the baseline, the diatomic nanobrick is treated as a whole, and its distance from the baseline is denoted as the overall displacement D of the diatomic nanobrick; the overall displacement D of the diatomic nanobrick is calculated using the following formula:

[0016]

[0017] In the formula, For the target phase distribution, P x Let be the period of the diatomic nanobrick along the x-direction.

[0018] Preferably, the phase distribution map of the vector holographic image with multiple polarization states is retrieved using the GS iterative algorithm. By assigning different preset polarization states to the phase distribution maps corresponding to different target images, the overall displacement D of the diatomic nanobricks, the local displacement S between the diatomic nanobricks, and the rotation angle θ of a certain nanobrick in the diatomic nanobricks corresponding to each polarization channel are retrieved, thereby realizing independent manipulation of the phase and polarization of the extracted light wave. Combined with spatial multiplexing, the fully polarized vector holographic image is encoded into the metasurface.

[0019] Secondly, the present invention provides a metasurface obtained by the above-described metasurface design method.

[0020] Thirdly, the present invention provides a method for realizing dynamic holographic display, comprising:

[0021] A waveguide with the target operating wavelength λ is incident along the x-direction, and after passing through the aforementioned metasurface, a vector holographic image is captured using a camera.

[0022] By placing a linear or circular polarization analyzer between the camera and the metasurface, different target images can be obtained sequentially, thus achieving dynamic holographic display.

[0023] Preferably, the metasurface is combined with an electrically driven liquid crystal device, and the preset polarization state of the light wave extracted by the metasurface is adjusted by regulating the voltage of the liquid crystal device.

[0024] Preferably, the liquid crystal device functions as a cross-polarization converter for output light when inputting a low voltage below a first preset voltage; the liquid crystal device does not perform polarization conversion when inputting a high voltage above a second preset voltage.

[0025] Fourthly, the present invention provides applications of metasurfaces, namely, applying the metasurfaces to wearable augmented reality devices, multi-channel information storage or encryption, or intelligent dynamic display fields.

[0026] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0027] 1. This invention integrates on-chip diatomic nanobricks onto a waveguide at the nanoscale. By designing the overall displacement, rotation angle, and local displacements between the diatomic nanobricks, the phase and polarization of extracted light waves can be independently manipulated. This allows for synchronous control of arbitrary polarization and phase of externally coupled light waves. Furthermore, by combining spatial multiplexing methods, up to nine-channel fully polarized vector holograms can be obtained. Moreover, all diatomic nanobricks in the metasurface of this invention have the same size. Compared to existing solutions, this invention simplifies the structure and reduces design complexity and cost.

[0028] 2. By combining with an electrically driven liquid crystal device, the integrated on-chip metasurface optical device can actively and in real time switch holographic images floating in real-world scenes, realizing dynamic AR holographic display.

[0029] 3. Due to the on-chip optical propagation scheme, the vector AR hologram of projection provided by this invention eliminates the zero-order diffraction background interference to the observer.

[0030] 4. The on-chip dynamic vector holographic display integrated with a liquid crystal platform provided by this invention can realize the miniaturization and integration of optical devices, and has great potential applications in advanced intelligent dynamic display, multi-channel information storage / encryption and next-generation wearable AR display. Attached Figure Description

[0031] Figure 1 This is a three-dimensional schematic diagram of a unit structure in a metasurface provided in an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of an on-chip periodic nanostructure array integrated onto a waveguide for extracting guided waves in an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of a unit structure in a metasurface provided in an embodiment of the present invention.

[0034] Figure 4 This is the design flow of the metasurface used to generate on-chip nine-channel vector holography in the embodiments of the present invention.

[0035] Figure 5 These are SEM images of on-chip metasurface samples used in embodiments of the present invention for characterizing on-chip vector holograms and fabrication.

[0036] Figure 6 This is an on-chip nine-channel vector holographic image captured in an embodiment of the present invention.

[0037] Figure 7 This is a schematic diagram of a method for achieving dynamic holographic display by combining a metasurface with a liquid crystal device, as provided in an embodiment of the present invention.

[0038] Figure 8 This is an experimental representation of AR display based on on-chip vector holography in an embodiment of the present invention.

[0039] Figure 9 This is the experimentally measured AR holographic display result based on on-chip metasurface in the embodiments of the present invention.

[0040] Figure 10 This is a design diagram of on-chip dynamic vector AR holographic display combined with liquid crystal in an embodiment of the present invention.

[0041] Figure 11 These are digital holographic images with different polarization states captured experimentally in embodiments of the present invention.

[0042] Figure 12 This embodiment of the invention achieves electrically adjustable vector AR holographic display results by applying different voltages to the liquid crystal. Detailed Implementation

[0043] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0044] Example 1:

[0045] Example 1 provides a method for designing metasurfaces, including:

[0046] Step 1: Construct a metasurface unit structure, which includes a substrate layer 30, an optical waveguide layer 20 located above the substrate layer 30, and two-atom nanobricks 10 disposed on the working surface of the optical waveguide layer 20. The two-atom nanobricks 10 are orthogonally arranged. (See [link to documentation]). Figure 1 The metasurface contains a plurality of the aforementioned diatomic nanobricks 10, which form a nanobrick structure array, and all the diatomic nanobricks 10 contained in the metasurface are of the same size.

[0047] Step 2: Using the overall displacement D of the diatomic nanobrick 10, the local displacement S between the diatomic nanobricks 10, and the rotation angle θ of a certain nanobrick in the diatomic nanobrick 10 as adjustment parameters, and combining them with the vector holographic image, the arrangement of several diatomic nanobricks 10 is designed by designing the adjustment parameters, and the vector holographic image is encoded into the metasurface.

[0048] The light waves extracted from each nanobrick in the dual-atom nanobrick 10 are represented as follows:

[0049]

[0050] In the formula, E1 and E2 are the electric fields of the light waves extracted by each nanobrick in the diatomic nanobrick, respectively; S x Let P be the spacing of the diatomic nanobricks along the x-direction, representing the local displacement; θ is the rotation angle of one nanobrick in the diatomic nanobrick set; and P is the rotation angle of one nanobrick in the diatomic nanobrick set. x Let be the period of the diatomic nanobrick along the x-direction.

[0051] In the aforementioned diatomic nanobrick 10, the transmission phase difference along the x-direction between the two orthogonal components parallel to the long axis of each nanobrick is expressed as follows:

[0052]

[0053] In the formula, The transmission phase difference between the two orthogonal components.

[0054] Specifically, the target operating wavelength is selected as λ, and the period P of the diatomic nanobrick 10 along the x-direction is calculated from the waveguide propagation constant β. x and the period P of the two-atom nanobrick along the y-direction y The spacing of the diatomic nanobricks 10 along the y-direction is P. y / 2.

[0055] Taking the leftmost point in the x-direction within the unit structure as the baseline, the diatomic nanobrick 10 is considered as a whole, and its distance from the baseline is denoted as the overall displacement D of the diatomic nanobrick 10. The overall displacement D of the diatomic nanobrick 10 is calculated using the following formula:

[0056]

[0057] In the formula, For the target phase distribution, P x Let be the period of the diatomic nanobrick along the x-direction.

[0058] The phase distribution map of the vector holographic image with multiple polarization states is retrieved using the GS iterative algorithm. By assigning different preset polarization states to the phase distribution maps corresponding to different target images, the overall displacement D of the diatomic nanobrick 10, the local displacement S between the diatomic nanobricks 10, and the rotation angle θ of a certain nanobrick in the diatomic nanobrick 10 corresponding to each polarization channel are retrieved, thereby realizing independent manipulation of the phase and polarization of the extracted light wave. Combined with spatial multiplexing, the fully polarized vector holographic image is encoded into the metasurface.

[0059] The present invention will now be further described.

[0060] When the TE0 mode guided wave propagates along the x-direction, it can be considered as an in-plane y-linearly polarized (y-LP) wave. Simultaneously, each nanobrick can be viewed as a dipole antenna, capable of extracting light waves polarized along the long axis of the nanobrick. See the schematic diagram of the on-chip periodic nanostructure array integrated onto the optical waveguide layer for wave extraction. Figure 2 , Figure 2 In Figure a, θ represents the rotation angle of the nanobrick, and the simulated electric field intensity distribution |E| of the periodic nanostructure array on the xoy plane is shown for two cases: θ = 0° and θ = 90°, when the TE0 mode is incident from the x direction. 2 The distribution exhibits significant field enhancement contrast. For the case of θ = 90°, it can be observed that the waveguide mode excites strong electric dipole resonances in the nanoantenna, verifying that the strongly anisotropic nanostructure responds only to light waves polarized along its long axis. Therefore, nanobricks with their long axes parallel to the y-axis can efficiently extract guided waves into free space. Figure 2 Figure b shows the optical extraction efficiency of the nanostructure array at a wavelength of 633 nm as the rotation angle θ varies from -90° to 90°. Figure 2 The value of b also includes the simulated electric field intensity distributions |E| in the yoz plane at θ = 0° and θ = 90°. 2 This demonstrates a strong modulation contrast in extraction intensity as the rotation angle changes. Specifically, the optical extraction efficiency fluctuates periodically with the rotation angle θ. It reaches a maximum value (approximately 0.3) when θ = -90° / 90° and a minimum value (approximately 0.03) when θ = 0°.

[0061] Furthermore, we numerically simulated the phase variation of the guided wave extracted by the on-chip nanostructure as a function of rotation angle under incident right-hand circularly polarized (RCP) guided waves (which can be synthesized from two TE0 guided waves propagating orthogonally along the x and y directions with an initial phase difference of π / 2) in the wavelength range of 400 nm to 800 nm. Figure 2 As shown in C and D, it can be observed that the incident RCP guided wave is extracted into free space and converted into a left-handed circularly polarized (LCP) wave, while an additional phase shift of 2θ is applied, while the unconverted RCP wave retains an almost unchanged phase shift.

[0062] A schematic diagram of the unit structure in the metasurface is shown below. Figure 1 As shown, Figure 1 The geometric parameters shown as an example include: the period P of the unit structure along the x and y directions. x =P y =440nm, the nanobrick has a cuboid structure, the length L and width W of the nanobrick are 140nm and 70nm respectively, and the height H of the nanobrick is 380nm.

[0063] To achieve on-chip full polarization and arbitrary phase control, such as Figure 3 As shown in Figure a, we use orthogonally arranged diatomic atoms instead of single nanostructures, D and S x / S y These are the overall displacement of the diatomic nanobricks and the local displacements between the diatomic nanobricks along the x / y directions, respectively. Here, we will use an interval of S... y Designed for P y / 2, to avoid the effects of near-field coupling and overlap. Figure 3 Figures b and c show the simulated in-plane electric field strength |E| at rotation angles θ = 0 and θ = π / 4. 2 The distribution indicates that the two orthogonal field components of the extracted light are parallel to each nanobrick structure. At this point, the phase difference of the propagation of the two orthogonal field components along the x-direction can be expressed as... By local displacement S x From 0 to P x / 2 (or -P) x / 2), we can get The corresponding change from 0 to π (or -π). Furthermore, the amplitudes of the two orthogonal field components can be controlled by adjusting the rotation angle θ. Therefore, we can design arbitrary polarization states for extracting light waves by changing the local displacement and rotation angle of the diatomic nanobrick. (Using S...) x =P x Taking / 4 as an example, the phase difference between the two orthogonal field components parallel to the two nanobricks is This means that the performance of the diatomic nanobrick within each unit is equivalent to that of a quarter-wave plate (QWP). Therefore, when the angle between the equivalent QWP and the in-plane y-LP wave is π / 4, circularly polarized (CP) light can be generated and extracted into free space. Figure 3 In the middle, d and e respectively simulate S x =P x / 4, θ = π / 4, and S x =P x / 4, θ=3π / 4 diatomic CP conversion. It can be seen that the light waves extracted by the two diatomic nanobrick arrangements are converted into LCP and RCP respectively, with the corresponding extraction intensity ratio of LCP (or RCP) to RCP (or LCP) being approximately 3. Overall, when the local displacement S changes, any phase difference between the two orthogonal components can be obtained, thus realizing an arbitrary phase waveplate. Therefore, arbitrary polarization state conversion of the extracted guided wave can be achieved simply by rotating the equivalent phase-type waveplate angle.

[0064] Besides arbitrary polarization control, we can further achieve phase modulation independently by designing the global displacement D of the two atoms. Based on on-chip detour phase, the diatomic displacement D can be determined according to... Provides the required phase for arbitrary wavefront modulation Ultimately, by designing the overall displacement and rotation angle of the diatomic atoms, as well as the local displacement between the diatomic nanobricks, the phase and polarization of the extracted light can be manipulated independently.

[0065] The ability of on-chip two-atom metasurfaces to manipulate arbitrary polarization and control the entire phase can realize vector holography with spatially varying polarization states. Figure 4 Figures a and b illustrate the design flow of an on-chip metasurface used to reconstruct vector holograms with multiple polarization states. Here, nine chemical element letters (“H”, “He”, “Li”, “Be”, “B”, “C”, “N”, “O”, “F”) are encoded as nine polarization channels. Nine phase maps of the nine target images are retrieved using the iterative Gerchberg-Saxton (GS) algorithm. Then, by assigning the nine different polarization states to the corresponding phase maps, tuning parameters for each channel, including S, θ, and D, are retrieved. Finally, nine different diatomic subpixels are combined into a large pixel to generate the nine polarization states. Note that the subpixels are randomly arranged within each large pixel to eliminate higher-order diffraction effects caused by periodicity increases.

[0066] We fabricated the designed on-chip metasurface sample using plasma-enhanced chemical vapor deposition (PECVD) and conventional electron beam lithography (EBL). Figure 5 Figure a shows the optical setup characterizing the vector holographic performance, where LP represents the linear polarization analyzer and PF represents the polarization analysis film. Figure 5 Image b shows a SEM image of the fabricated diatomic metasurface sample, with a scale bar of 400 nm. A polarized laser (632 nm) is coupled into the waveguide via end-fire, and the projected holographic image can be directly captured by a mobile phone camera. Using a matched polarization analyzer to block orthogonal polarization states, the corresponding chemical element letter holographic images disappear sequentially, such as... Figure 6 As shown, Figure 6 The white dashed box in the image shows the corresponding vanished holographic image. Our designed on-chip metasurface has been verified to successfully generate vector holograms with nine polarization states.

[0067] Example 2:

[0068] Example 2 provides a metasurface obtained using the metasurface design method described in Example 1.

[0069] See Figure 1The diatomic nanobricks 10 can be diatomic silicon nanobricks, which are orthogonally arranged, with their length and width both being subwavelength dimensions. The optical waveguide layer 20 can be a silicon nitride optical waveguide layer with a refractive index of approximately 2.05 and a thickness of 220 nm. The substrate layer 30 can be a silicon dioxide substrate layer with a thickness of 500 μm.

[0070] The present invention provides an on-chip two-atom vector metasurface, comprising a two-atom nanobrick structure array, and an underlying optical waveguide layer and dielectric substrate layer.

[0071] Example 3:

[0072] Example 3 provides a method for realizing dynamic holographic display, including: incident a waveguide with a target operating wavelength λ along the x-direction, passing through the metasurface as described in Example 2, and capturing a vector holographic image using a camera; by setting a linear polarization or circular polarization analyzer between the camera and the metasurface, different target images can be obtained sequentially to realize dynamic holographic display.

[0073] Furthermore, the metasurface can be combined with an electrically driven liquid crystal device, and the preset polarization state of the light waves extracted by the metasurface can be adjusted by regulating the voltage of the liquid crystal device.

[0074] Specifically, the liquid crystal device acts as a cross-polarization converter for output light when inputting a low voltage below a first preset voltage; the liquid crystal device does not perform polarization conversion when inputting a high voltage above a second preset voltage.

[0075] The following steps will further explain the method for achieving dynamic holographic display.

[0076] The method for achieving dynamic holographic display includes the following steps:

[0077] S1: A two-dimensional array of two-atom nanobrick structures is arranged above the optical waveguide.

[0078] S2: Establish an xoy coordinate system with the two sides parallel to the working surface of the optical waveguide layer, designated as the x-axis and y-axis respectively; all the diatomic nanobricks are rectangular structures, and all nanobricks have the same size; the major axes of the diatomic nanobricks are always orthogonally aligned; if the rotation angle of one nanobrick in the diatomic nanobrick is θ, then the rotation angle of the other nanobrick is θ + π / 2; select the target working wavelength as λ, and calculate the corresponding period P from the waveguide propagation constant β. x and P y The spacing of the diatomic nanobricks along the x-direction is S. x The spacing of the diatomic nanobricks along the y-direction is P. y / 2.

[0079] S3: The diatomic nanobrick can couple waveguides to free space and extract light waves polarized along the long axis of the nanobrick; the light waves extracted from each diatomic nanobrick can be represented by the following formula (1);

[0080]

[0081] Where E1 and E2 are the electric fields of the light waves extracted from each nanobrick of the diatomic array, respectively, and S x Let P be the spacing of the diatomic nanobricks along the x-direction, θ be the rotation angle of the nanobricks, and P be the spacing of the diatomic nanobricks along the x-direction. x Let be the period of the diatomic nanobrick along the x-direction.

[0082] Therefore, two orthogonal field components are obtained, each parallel to the long axis of each nanobrick. The propagation phase difference of these two orthogonal field components along the x-direction can be represented by the following equation (2).

[0083]

[0084] Among them, S x The spacing of the two-atom nanobricks along the x-direction is [missing information]. P represents the transmission phase difference between two orthogonal components. x Let be the period of the diatomic nanobrick along the x-direction.

[0085] When S x From 0 to P x / 2 (or -P) x / 2), can be obtained The corresponding change from 0 to π (or -π). Therefore, any phase difference between two orthogonal components can be obtained, thus realizing an arbitrary phase waveplate. Arbitrary polarization state conversion of the extracted guided wave can be achieved simply by rotating the equivalent phase waveplate angle.

[0086] S4: Establish an xoy coordinate system with the same direction as step S2 for each unit structure, and take the leftmost part of the x direction in the unit structure as the baseline. The diatomic nanobrick is a whole, and its distance from the baseline is D. According to the principle of detour phase, the overall displacement D of the diatomic nanobrick can be calculated by the following equation (3).

[0087]

[0088] Where D represents the overall displacement of the diatomic nanobrick within a unit period. For the target phase distribution, P x Let be the period of the diatomic nanobrick along the x-direction.

[0089] S5: Combining formulas (2) and (3) described in step S3, the overall displacement D, rotation angle θ, and local displacement S between the biatomic nanobricks are designed (specifically, S0). x It can independently manipulate the phase and polarization of extracted light waves to realize on-chip vector holography with spatially varying polarization states.

[0090] S6: The phase distribution map of the selected target image is retrieved using the GS iterative algorithm. Furthermore, by assigning different preset polarization states to the corresponding phase maps, the diatomic structure parameters S of each polarization channel are retrieved. x θ and D; finally, by combining spatial multiplexing methods, the target vector image information is encoded into the on-chip dual-atom array metasurface.

[0091] S7: A guided wave with a target wavelength of λ is incident along the x-direction. After passing through the on-chip metasurface array, a vector holographic image is captured using the camera in the mobile phone. By adding a linear polarization or circular polarization analyzer between the mobile phone and the metasurface sample, different vector holographic images can be obtained sequentially.

[0092] S8: By combining the metasurface with an electric liquid crystal platform, the predetermined polarization state of the extracted light wave can be adjusted by applying a voltage to the liquid crystal device.

[0093] Specifically, for a low input voltage of approximately 0V, the LC unit acts as a cross-polarization converter for the output light. When a higher input voltage of approximately 8V is applied, the liquid crystal molecules reorient themselves parallel to the bias direction, causing the extracted light waves to pass through the liquid crystal device without any polarization conversion. By combining linear or circular polarization analyzers, we can obtain different holographic images in experiments. Ultimately, by adjusting different high and low voltages, we can successfully capture switchable holographic images floating in the real-world environment using a mobile phone camera, achieving dynamic AR holographic displays.

[0094] The following is a further explanation with reference to the accompanying drawings.

[0095] Figure 7 This illustration demonstrates the implementation of on-chip dynamic vector holographic projection displays using an on-chip metasurface integrated onto a waveguide and a liquid crystal platform. Specifically, a TEO mode guided wave propagating along the x-direction is extracted into free space by the on-chip metasurface to project vector holograms with different predefined polarization states (e.g., the nine letters of a chemical element). By changing the geometric parameters of the diatomic nanostructure, the phase and polarization state of the externally coupled light wave can be arbitrarily customized at the nanoscale. As a proof of concept, when combined with an electrodynamic liquid crystal platform, different vector holographic images can be actively adjusted and projected onto the human eye or a smartphone to achieve dynamic AR holographic displays.

[0096] To demonstrate the actual on-chip vector AR holographic display function, this invention fabricated two different metasurface samples (labeled as sample A and sample B, i.e.) Figure 8 Sample A and Sample B are used to project floating holographic virtual images onto real-world scenes, such as... Figure 8 As shown in the conceptual diagram in section a, here, sample A and sample B are designed to generate polarization states of x-LP / y-LP and LCP / RCP, respectively. Figure 8 Figures b and c show the corresponding SEM images. Then, the holographic image "volleyball" was experimentally reconstructed by adding an x-LP analyzer between sample A and the camera, while the holographic image "basketball" was clearly reconstructed by rotating the polarization analyzer to the y-direction, as shown below. Figure 8 As shown in d. Similarly, Figure 8 The paper demonstrates how, by combining linear and circular polarization analyzers, a dual-channel switchable holographic image generated from sample B was captured, and the LCP holographic image "table lamp" and the RCP holographic image "globe" were reconstructed. Finally, to verify the AR display performance, we used a mobile phone camera to simultaneously record a mixture of floating virtual images and real-world scenes, such as... Figure 9 From middle a to Figure 9 As shown in d in the figure. Thanks to the all-dielectric architecture with good transparency and the on-chip propagation scheme, the projected AR holographic display is not affected by zero-order diffraction and has satisfactory imaging intensity, sharpness and clarity.

[0097] To achieve dynamic on-chip vector AR holographic display, we also fabricated another prototype and integrated it with an electric liquid crystal platform, with a design concept as follows: Figure 10 As shown in Figure a, by applying a voltage to the liquid crystal device, the predetermined polarization state of the extracted light wave can be adjusted. Specifically, for a lower voltage input of approximately 0V, the LC unit acts as a cross-polarization converter for the output light. When a higher voltage input of approximately 8V is applied, the liquid crystal molecules reorient themselves parallel to the electrical bias direction, causing the extracted light wave to pass through the liquid crystal device without any polarization conversion. Here, the LC platform is placed between the on-chip metasurface and the mobile phone camera for dynamic polarization modulation. As a proof of concept, different portions of a seven-segment display image are assigned to four different polarization states, including x-LP, y-LP, 45°-LP, and LCP, for encoding vector holograms (such as...). Figure 10 (as shown in b). Figure 10 Figures c and d show the SEM image and actual photograph of the fabricated device, respectively. The scale bar of the SEM image is 200 nm. By combining different polarization analyzers to block orthogonal polarization states, four polarization components can be sequentially shut off, and holographic images "0", "2", "4", and "8" were captured in the experiment, as shown below. Figure 11 As shown, Figure 11The arrows in the diagram represent the polarization states that are allowed to pass through the polarization analyzer, which exhibits excellent consistency with the design.

[0098] To verify the actual dynamic AR holographic display, we successfully captured switchable holographic images floating in the real-world environment using a mobile phone camera, such as... Figure 12 As shown in a and b. Specifically, by attaching an x-LP analyzer after the LC and dynamically adjusting the LC's driving voltage from 0V to 8V, the projected holographic image floating in the real-world background dynamically switches from image "0" to image "2" (as shown in a diagram). Figure 12 (As shown in a). When another pair of QWP and y-LP analyzers is added after the LC and an external voltage of 0V to 8V is applied, the floating image "4" in the actual field of view switches to image "8" (as shown in a diagram). Figure 12 (As shown in b).

[0099] Example 4:

[0100] Example 4 provides an application of the metasurface as described in Example 2, wherein the metasurface is applied to wearable augmented reality devices, multi-channel information storage or encryption, or intelligent dynamic display.

[0101] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for designing metasurfaces, characterized in that, include: A metasurface is constructed using a unit structure comprising a substrate layer, an optical waveguide layer above the substrate layer, and diatomic nanobricks disposed on the working surface of the optical waveguide layer, wherein the diatomic nanobricks are arranged orthogonally; the metasurface contains a plurality of the diatomic nanobricks forming a nanobrick structure array, and all the diatomic nanobricks contained in the metasurface are of the same size; The overall displacement of the biatomic nanobrick D Local displacement between the two-atom nanobricks S and the rotation angle of one of the nanobricks in the aforementioned diatomic nanobricks. θ As an adjustment parameter, combined with the vector holographic image, the adjustment parameter is designed to arrange several of the two-atom nanobricks, and the vector holographic image is encoded into the metasurface. Specifically, the GS iterative algorithm is used to retrieve the phase distribution map of the vector holographic image with multiple polarization states. By assigning different preset polarization states to the phase distribution maps corresponding to different target images, the overall displacement of the diatomic nanobrick corresponding to each polarization channel is retrieved. D Local displacement between the two-atom nanobricks S and the rotation angle of one of the nanobricks in the aforementioned diatomic nanobricks. θ This enables independent manipulation of the phase and polarization of extracted light waves; combined with spatial multiplexing, the fully polarized vector holographic image is encoded into the metasurface; the full polarization includes linear polarization, circular polarization, and elliptical polarization.

2. The metasurface design method according to claim 1, characterized in that, The light waves extracted from each nanobrick in the aforementioned diatomic nanobricks are represented as follows: In the formula, E 1 and E 2 represents the electric field of the light wave extracted from each nanobrick in the diatomic nanobrick; S x For two-atom nanobricks along x The directional intervals are considered as local displacements; θ The rotation angle of one nanobrick in a diatomic nanobrick. P x For two-atom nanobricks along x The period of direction; In the aforementioned diatomic nanobricks, two orthogonal components parallel to the long axis of each nanobrick are along... x The transmission phase difference in the direction is expressed as follows: In the formula, The transmission phase difference between the two orthogonal components.

3. The metasurface design method according to claim 1, characterized in that, Selected target operating wavelength is λ The propagation constant of the waveguide β The calculations yielded the following results along the axis of the two-atom nanobrick. x Cycle of direction P x and the aforementioned dual-atom nanobricks along y Cycle of direction P y The dual-atom nanobricks along y The directional interval is P y / 2.

4. The metasurface design method according to claim 1, characterized in that, Within the unit structure x The leftmost point in the direction is the baseline. Treating the diatomic nanobrick as a whole, its distance from the baseline is denoted as the overall displacement of the diatomic nanobrick. D The overall displacement of the two-atom nanobrick was calculated using the following formula. D : In the formula, For the target phase distribution, P x For two-atom nanobricks along x The cycle of direction.

5. A metasurface, characterized in that, The metasurface is obtained using the design method described in any one of claims 1-4.

6. A method for achieving dynamic holographic display, characterized in that, include: Will have the target operating wavelength λ waveguide along x The image is incident in a specific direction and passes through the metasurface as described in claim 5. A vector holographic image is then captured using a camera. By placing a linear or circular polarization analyzer between the camera and the metasurface, different target images can be obtained sequentially, thus achieving dynamic holographic display.

7. The method for realizing dynamic holographic display according to claim 6, characterized in that, By combining the metasurface with an electrically driven liquid crystal device, the preset polarization state of the light waves extracted by the metasurface can be adjusted by regulating the voltage of the liquid crystal device.

8. The method for realizing dynamic holographic display according to claim 7, characterized in that, The liquid crystal device acts as a cross-polarization converter for output light when inputting a low voltage below a first preset voltage; the liquid crystal device does not perform polarization conversion when inputting a high voltage above a second preset voltage.

9. The application of the metasurface as described in claim 5, characterized in that, The application is to use the metasurface in wearable augmented reality devices, multi-channel information storage or encryption, or intelligent dynamic display.

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