On-chip metasurface and holographic coding display method based on on-chip metasurface

Abstract

The invention belongs to the technical field of micro-nano optics, and discloses an on-chip metasurface and a holographic coding display method based on the on-chip metasurface. The on-chip meta-structure surface comprises a medium substrate layer, an optical waveguide layer, a nano-structure array located on the optical waveguide layer and at least one on-chip point light source structure. The nano-structure array is composed of a plurality of nano-bricks with the same size, and the rotation angles of the plurality of nano-bricks are determined based on the target holographic image; each on-chip point light source structure is used for coupling circularly polarized light in a free space into the optical waveguide layer for transmission, and light wavefront coupled into the optical waveguide layer is converged at one point to generate an in-plane point light source; guided waves in the optical waveguide layer are transmitted to the nanostructure array from the position of the point light source, are subjected to on-chip geometric phase modulation through the nanostructure array and then are extracted to a free space. According to the invention, multi-channel point source holographic display of on-chip multi-degree-of-freedom control can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-nano optics, and more particularly relates to an on-chip super-structured surface and a holographic coded display method based on the on-chip super-structured surface. BACKGROUND

[0002] In recent years, integrating super-structured surfaces into optical waveguides to construct a compact and efficient planar light wave manipulation platform has become a research hotspot in the field of nanophotonics. Through precisely designed subwavelength nanostructures, on-chip integrated super-structured surfaces can perform high-precision control of the amplitude, phase, and polarization of extracted light, realizing various on-chip functions and applications, including directional beam control, on-chip super-lenses, vortex beam generators, AR holographic displays, and transparent screen displays. Among numerous photonic integrated devices, this technology exhibits important application prospects due to its excellent scalability and flexibility. Compared to traditional free-space optical systems, the on-chip super-structured surface scheme based on waveguide propagation not only significantly reduces the system size but also has unique advantages such as no zero-level background interference, multi-stage cascading capability, and high compatibility with other miniature on-chip devices (such as modulators, detectors, quantum light sources, etc.), greatly promoting the construction of highly integrated optical chip systems.

[0003] On the platform of waveguide-integrated super-structured surfaces, achieving multi-dimensional and multi-degree-of-freedom on-chip light parameter manipulation is increasingly becoming a key direction for promoting the evolution of integrated photonics to higher performance and stronger functions. Currently, although some research has explored strategies such as composite on-chip super-structured unit structures or algorithm optimization to achieve joint control of degrees of freedom such as detour phase and geometric phase, amplitude and phase, polarization and phase on-chip, the overall still faces limitations in the number of control degrees of freedom and channels. SUMMARY

[0004] The present application provides an on-chip super-structured surface and a holographic coded display method based on the on-chip super-structured surface, solving the problem of insufficient degrees of freedom and channel numbers in on-chip light parameter manipulation in the prior art.

[0005] The present application provides an on-chip super-structured surface, comprising: a dielectric substrate layer, an optical waveguide layer on the dielectric substrate layer, and a nanostructure array and at least one on-chip point light source structure on the optical waveguide layer; the nanostructure array is composed of a plurality of nano-bricks with the same size, and the rotation angle of the plurality of nano-bricks is determined based on a target holographic image; each on-chip point light source structure is used to couple circularly polarized light in free space into the optical waveguide layer for transmission, and the light wavefront coupled into the optical waveguide layer converges at a point to generate an in-plane point light source; the guided wave in the optical waveguide layer is transmitted from the point light source position to the nanostructure array, and is extracted to free space after on-chip geometric phase modulation by the nanostructure array.

[0006] Preferably, the on-chip point light source structure adopts a continuous curved annular grating, which is a truncated concentric circular annular grating structure.

[0007] Preferably, the on-chip point light source structure adopts a discrete array structure, which is a cylindrical array grating structure or a rectangular array grating structure.

[0008] Preferably, when the on-chip point light source structure is multiple, the multiple on-chip point light source structures are used to generate multiple point light sources located at different positions.

[0009] Preferably, the nanobrick has a subwavelength size in length and width, the dielectric substrate layer is prepared from silicon dioxide, the optical waveguide layer is prepared from silicon nitride, and the nanobrick is prepared from silicon.

[0010] In another aspect, the present application provides a holographic encoding display method based on the above-mentioned on-chip super-structured surface, which utilizes an in-plane point light source wave front for incidence, and realizes multi-channel point source holographic display by using the positional relationship between the point light source and each nanobrick in the nanobrick array, combined with on-chip geometric phase encoding, to achieve multi-degree-of-freedom manipulation on the chip.

[0011] Preferably, the total phase modulation experienced by the light wave extracted by any of the nanobricks into free space is represented as follows:

[0012] In the formula, is the total phase modulation, is the transmission phase, is the geometric phase, r is the distance between the center of the nanobrick and the point light source, is the effective refractive index of the transmitted guided wave, λ is the wavelength of the point light source; θ is the rotation angle of the nanobrick, defined as the angle between the long axis of the nanobrick and the x-axis; α is the angle between the line connecting the center of the nanobrick and the point light source and the x-axis.

[0013] Preferably, the multi-channel holographic display is realized based on the degree of freedom of the position of the point light source, including: Each point light source corresponds to a channel, and the total phase modulation corresponding to the i th channel is represented as follows:

[0014] In the formula, is the total phase modulation corresponding to the i th channel, is the distance between the center of the nanobrick and the point light source corresponding to the i th channel, is the angle between the line connecting the center of the nanobrick and the point light source corresponding to the i th channel and the x-axis; By simultaneously solving the total phase modulation under multiple channels, the phase optimization of the target holographic image of multiple channels is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0015] Preferably, the wavelength of the point light source is based on the freedom degree to realize the multi-wavelength holographic display, including: For a point light source determined for a position, the total phase modulation corresponding to the jth wavelength is represented as follows:

[0016] In the formula, is the total phase modulation corresponding to the jth wavelength, is the jth wavelength corresponding to the point light source; By simultaneously solving the total phase modulation under multiple wavelengths, the phase optimization of the target holographic image of multiple wavelengths is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0017] Preferably, the left-handed circularly polarized light component and the right-handed circularly polarized light component are based on the freedom degree of extracting light polarization to realize two-channel holographic display, including: The extracted light is divided into left-handed circularly polarized light component and right-handed circularly polarized light component, and the total phase modulations corresponding to the two are represented as follows:

[0018]

[0019] In the formula, is the total phase modulation corresponding to the left-handed circularly polarized light, is the total phase modulation corresponding to the right-handed circularly polarized light; By simultaneously solving the total phase modulation corresponding to the left-handed circularly polarized light and the right-handed circularly polarized light, the phase optimization of the target holographic image of two components is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0020] One or more technical solutions provided in the application have at least the following technical effects or advantages: The on-chip metasurface provided by the application comprises a dielectric substrate layer, an optical waveguide layer located on the dielectric substrate layer, and a nanostructure array and at least one on-chip point light source structure located on the optical waveguide layer; the nanostructure array is composed of a plurality of nano-bricks with the same size, and the rotation angle of the plurality of nano-bricks is determined based on a target holographic image; each on-chip point light source structure is used for coupling circularly polarized light in free space into transmission in the optical waveguide layer, and the light wavefront coupled into the optical waveguide layer converges at a point to generate an in-plane point light source; the guided wave in the optical waveguide layer is transmitted to the nanostructure array from the point light source position, and is extracted to free space after on-chip geometric phase modulation by the nanostructure array. The conventional on-chip metasurface relies on in-plane plane wave form guided wave incident transmission, and the application uses in-plane point light source wavefront for incidence on the basis of the above-mentioned on-chip metasurface, realizes multi-channel point source holographic display of on-chip multi-degree-of-freedom manipulation by using the positional relationship between the point light source and each nano-brick in the nanostructure array and combining on-chip geometric phase coding. The application provides a new scheme for solving the problem of insufficient on-chip light parameter manipulation degrees of freedom and channel number.

[0021] Based on the unique scattering wavefront of the point light source, the application designs several different expansion on-chip multi-degree-of-freedom coding schemes, including: (1) realizing multi-channel holographic display based on the degrees of freedom of different on-chip point light source positions; (2) realizing multi-wavelength holographic display based on the degrees of freedom of the point light source wavelength; (3) realizing two-channel holographic display of left and right circularly polarized light components based on the polarization degrees of freedom of the extracted light.

[0022] Compared with the conventional on-chip metasurface holographic display, the holographic coding based on the on-chip metasurface greatly expands the coding degrees of freedom, and subsequent multi-parameters are expected to be fused and manipulated to realize more degrees of freedom and more channel coding display. The platform has the advantages of miniaturization and integration, and is expected to be applied in the fields of next-generation wearable display devices, large-capacity information encryption storage and the like. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of a dielectric substrate layer, an optical waveguide layer and a nanostructure array in the on-chip metasurface provided by the embodiment of the application.

[0024] Figure 2 is a planar schematic diagram of on-chip point light source wavefront reaching a certain nano-brick in the nanostructure array in the on-chip metasurface provided by the embodiment of the application.

[0025] Figure 3 is a planar schematic diagram of in-plane point light source generated by a truncated concentric circular grating structure reaching the nanostructure array cascaded therewith in the embodiment of the application.

[0026] Figure 4is a side view schematic diagram of the point source generated by the truncated concentric circular grating structure reaching the nanosturcture array cascaded therewith and then being out-coupled in the embodiments of the present application.

[0027] Figure 5 is a schematic diagram of the curved annular grating that can generate the required point source after the concentric circular grating is truncated in the embodiments of the present application.

[0028] Figure 6 is a schematic diagram of the geometric relationship of the point source transmission to a certain nanobrick in the embodiments of the present application.

[0029] Figure 7 is the MATLAB simulation and FDTD simulation result of the point source holographic display obtained by the transmission of the single on-chip point source structure to the nanosturcture array in the embodiments of the present application.

[0030] Figure 8 is a schematic diagram of the geometric relationship of the point source transmission from two different positions on the chip to the same single nanobrick in the embodiments of the present application; wherein, Figure 8 (a) in the above is a schematic diagram of the point source position on the chip being P1, Figure 8 (b) in the above is a schematic diagram of the point source position on the chip being P2.

[0031] Figure 9 is the MATLAB simulation and FDTD simulation result of the double-channel holographic display obtained by the transmission of the point source from two different positions on the chip to the same nanosturcture array in the embodiments of the present application.

[0032] Figure 10 is the MATLAB simulation result of the four-channel holographic display obtained by the transmission of the point source from four different positions on the chip to the same nanosturcture array in the embodiments of the present application; wherein, Figure 10 (a) in the above is a schematic diagram of the geometric relationship of the four different point sources on the chip and the nanosturcture array, Figure 10 (b) in the above is the MATLAB simulation result of the four-channel holographic display.

[0033] Figure 11 is a conceptual schematic diagram of the double-channel holographic display obtained by the transmission of the point source from the same position on the chip but having two different wavelengths to the same nanosturcture array in the embodiments of the present application; wherein, Figure 11 (a) in the above is a top view, Figure 11 (b) in the above is a side view.

[0034] Figure 12 is the MATLAB simulation and FDTD simulation result of the double-channel holographic display obtained by the transmission of the point source from the same position on the chip but having two different wavelengths to the same nanosturcture array in the embodiments of the present application.

[0035] Figure 13 is the MATLAB optimization result of the conceptual implementation of the point light source with three different wavelengths at the same position on the chip in the embodiment of the present application, which is transmitted to the same nanostructure array to obtain a three-channel holographic display.

[0036] Figure 14 is the conceptual schematic diagram of the point light source at the same position on the chip in the embodiment of the present application, which is transmitted to the same nanostructure array to obtain a two-channel holographic display with different circular polarizations.

[0037] Figure 15 is the MATLAB optimization and FDTD simulation result of the point light source at the same position on the chip in the embodiment of the present application, which is transmitted to the same nanostructure array to obtain a two-channel holographic display with different circular polarizations.

[0038] Figure 16 is the structure design of the point light source generated by the curved circular grating in the embodiment of the present application and the FDTD simulation result of the point source focusing under the incidence of free space wavelength circularly polarized light at different wavelengths.

[0039] Figure 17 is the schematic diagram of several methods for generating in-plane point light sources designed in the embodiment of the present application; wherein, Figure 17 (a) in is a continuous curved circular grating, Figure 17 (b) in is a cylindrical array grating structure, Figure 17 (c) in is a rectangular array grating structure. DETAILED DESCRIPTION

[0040] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0041] Embodiment 1: Embodiment 1 provides an on-chip metasurface, referring to Figures 1 to 4 , comprising: a dielectric substrate layer, an optical waveguide layer located on the dielectric substrate layer, and a nanostructure array and at least one on-chip point light source structure located on the optical waveguide layer; the nanostructure array is composed of a plurality of nano-bricks with the same size, and the rotation angle of the plurality of nano-bricks is determined based on a target holographic image; each on-chip point light source structure is used to couple circularly polarized light in free space to transmission in the optical waveguide layer, and the optical wavefront coupled into the optical waveguide layer converges at a point to generate an in-plane point light source; the guided wave in the optical waveguide layer is transmitted from the point light source position to the nanostructure array, and is extracted to free space after geometric phase modulation on the chip via the nanostructure array.

[0042] The on-chip point light source structure can adopt a continuous curved annular grating, which is a truncated concentric circular annular grating structure, as shown in Figure 5 The on-chip point light source structure can also adopt a discrete array structure, which is a cylindrical array grating structure or a rectangular array grating structure.

[0043] When the on-chip point light source structure is multiple, the multiple on-chip point light source structures are used to generate multiple point light sources located at different positions.

[0044] The length and width of the nanobrick are both subwavelength sizes, the dielectric substrate layer can be prepared from silicon dioxide, the optical waveguide layer can be prepared from silicon nitride, and the nanobrick can be prepared from silicon.

[0045] Embodiment 2: Embodiment 2 provides a holographic coded display method based on the on-chip metasurface as described in embodiment 1, which utilizes an in-plane point light source wave front for incidence, and realizes multi-channel point source holographic display with on-chip multi-degree-of-freedom manipulation by utilizing the positional relationship between the point light source and each nanobrick in the nanobrick array, combined with on-chip geometric phase coding.

[0046] The total phase modulation experienced by the light wave extracted by any nanobrick to the free space is represented as follows:

[0047] In the formula, is the total phase modulation, is the transmission phase, is the geometric phase, r is the distance between the center of the nanobrick and the point light source, is the effective refractive index of the transmitted guided wave, λ is the wavelength of the point light source; θ is the rotation angle of the nanobrick, which is defined as the included angle between the long axis of the nanobrick and the x-axis; α is the included angle between the line connecting the center of the nanobrick and the point light source and the x-axis.

[0048] The multi-degree-of-freedom manipulation of the present application includes the following: (1) Realize multi-channel holographic display based on the degree of freedom of the position of the point light source.

[0049] Each point light source corresponds to a channel, and the total phase modulation corresponding to the i th channel is represented as follows:

[0050] In the formula, is the total phase modulation corresponding to the i th channel, is the distance between the center of the nanobrick and the point light source corresponding to the i th channel, The included angle between the line connecting the center of the nano brick and the point light source corresponding to the i-th channel and the x-axis; By simultaneously solving the total phase modulation under multiple channels, the phase optimization of the target holographic image of multiple channels is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0051] (2) Based on the wavelength freedom of the point light source, multi-wavelength holographic display is realized.

[0052] For a point light source determined at a position, the total phase modulation corresponding to the j-th wavelength is represented as follows:

[0053] In the formula, The total phase modulation corresponding to the j-th wavelength is represented as follows: The j-th wavelength corresponding to the point light source; By simultaneously solving the total phase modulation under multiple wavelengths, the phase optimization of the target holographic image of multiple wavelengths is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0054] (3) Based on the freedom of extracting light polarization, left-handed circularly polarized light component and right-handed circularly polarized light component two-channel holographic display is realized.

[0055] The extracted light is divided into left-handed circularly polarized component and right-handed circularly polarized component, and the total phase modulations corresponding to the two are represented as follows:

[0056]

[0057] In the formula, The total phase modulation corresponding to the left-handed circularly polarized light is represented as follows: The total phase modulation corresponding to the right-handed circularly polarized light is represented as follows: By simultaneously solving the total phase modulation corresponding to the left-handed circularly polarized light and the right-handed circularly polarized light, the phase optimization of the two-component target holographic image is carried out, and the rotation angle of all nano bricks in the nano structure array is obtained.

[0058] The present application realizes multi-freedom on-chip multi-channel point source holographic coding by utilizing the positional relationship between the point light source and each nano brick in the nano structure array, and combining on-chip geometric phase coding.

[0059] The present application will be further illustrated by combining parameters.

[0060] The carefully arranged nano structure array is selected to form an on-chip superstructure together with other structures. Figure 1The structure of the on-chip metasurface medium substrate layer (i.e. substrate), optical waveguide layer (i.e. waveguide) and nanostructure array is schematically illustrated, which can be regarded as being composed of a plurality of unit structures, each unit structure including a substrate, a waveguide and a nanostructure (i.e. nano brick), and the nanostructure is established in the direction parallel to the two edges of the working surface of the optical waveguide layer xoy coordinate system, respectively, as x axis and y axis, the rotation angle of the nano brick is θ; the long axis of the nano brick is L , the short axis is W , the periods of the nano brick in the directions of x and y are respectively and ; the nano brick is located on the top of the Si3N4 planar waveguide (thickness =220 nm) (refractive index n is about 2.05), and the SiO2 substrate (thickness is about 500 μm) is below; the height of the nano brick is 380 nm.

[0061] The working principle of the on-chip metasurface provided by the application is based on the special scattering wave front characteristics of the point light source of the waveguide in-plane transmission, as shown in Figure 2 , the relative position of the point source and the nano brick in the unit structure above the waveguide is used, combined with the on-chip geometric phase modulation, to code and optimize the multi-channel holographic phase.

[0062] As shown in Figure 3 and Figure 4 , in order to generate the required point light source at different positions of the in-plane waveguide, the cascade design of the incident curved coupling grating is carried out according to the position of the point light source, so that the required in-plane point light source incidence condition is generated at different positions in the waveguide plane under the incidence of circularly polarized light in free space, and finally different holographic images are generated. Figure 4 In the above, the circularly polarized light in free space is incident on the coupling grating to generate an in-plane point light source.

[0063] Specifically, the expression of the point light source light field U in the waveguide is: (1) wherein, λ is the wavelength of the point light source, r is the distance from the point light source to the nano brick, is the effective refractive index of the transmission guide wave.

[0064] For example, the circularly polarized light in free space can be coupled into the waveguide for transmission by designing a curved ring grating structure. The curved ring grating structure can be regarded as a part of a plurality of circular ring gratings after being cut off, as shown in Figure 5As shown, the centers of all the rings are the same point, thus ensuring that the light wavefront coupled into the waveguide converges at this center. Therefore, when the light wave at the center continues to propagate backward, it can be considered that the wavefront of the point source emitted from the center continues to propagate to the subsequent nanostructure array.

[0065] The nanostructure array is designed with geometric phase encoding, meaning the nanobricks have different rotation angles θ (relative to the x-axis). To further illustrate the encoding process of the geometric phase metasurface, such as... Figure 6 As shown, taking a unit structure in a nanostructure array as an example, the point light source is located at (x0, y0), the nanobrick is located at (x, y), and the rotation angle of the nanobrick is θ (relative to the x-axis); the distance between the center (N) of the nanobrick and the point light source (M) is r, and the line connecting them is MN. Then r satisfies Let MN make an angle α with the x-axis. Then, what is the transmission phase experienced by the guided wave as it travels from the point light source to the location of the nanobrick? Then, the guided wave is extracted into free space via the nanobrick, during which it undergoes on-chip geometric phase modulation. It can be seen that the angle between the major axis of the nanobrick and the x-axis is θ, and the angle between this major axis and MN (i.e., the propagation direction of the guided wave) is θ-α. Therefore, the geometric phase modulation corresponding to this nanobrick is... Ultimately, the single nanobrick extracts the light wave guided into free space, undergoing phase modulation. For transmission phase With geometric phase The superposition of modulation, i.e. (2) Where r is the distance between the center (N) of the nanobrick and the point light source (M), and α is the angle between the line connecting the center (N) of the nanobrick and the point light source M and the x-axis.

[0066] Similarly, the phase modulation relationship of all nanobricks in the array is calculated using the same method, and the holographic encoding design can then be carried out based on this relationship.

[0067] Next, the letter "H" is selected as the target holographic image. Using formula (2) and the optimized Gerchberg-Saxton (GS) algorithm, the target holographic image is reconstructed, ultimately obtaining the rotation angle distribution of the nanobrick (based on the relationship that the geometric phase is twice the rotation angle). Next, verification is performed in FDTD simulation. The waveguide mode of the point source incident can be directly selected and set, such as... Figure 7 As shown, the simulated result of the letter "H" was successfully obtained in the simulation. Due to limitations such as simulation time, the number of pixels in the selected metasurface array was only 80×80, resulting in a poor holographic effect. This can be improved by increasing the number of array pixels.

[0068] Furthermore, it can be seen from formula (2) that for a certain nanobrick in the same array (the angle θ between its major axis and the x-axis), when the wavelength... λ When unchanged ( (and also unchanged), if the position of the point light source changes, that is, both r and α in formula (2) will change. For example Figure 8 As shown, there are two on-chip point light sources, denoted as P1(x1, y1) and P2(x2, y2) respectively. Figure 8 (a) in the diagram is a schematic diagram when the position of the on-chip point light source is P1. Figure 8 (b) is a schematic diagram when the on-chip point light source is located at P2. Then, for the same nanobrick, the phase of the guided wave from point light source P1 after propagation is extracted to free space. It can be derived from formula (2): (3) in, The distance between the center (N) of the nanobrick and the point light source (P1) is... satisfy , Let be the angle between the line connecting the center of the nanobrick (N) and the point light source P1 and the x-axis.

[0069] Similarly, the phase of the guided wave from point source P2 is extracted into free space by the nanobrick after propagation. This can be deduced as: (4) in, The distance between the center (N) of the nanobrick and the point light source (P2) is... satisfy , Let be the angle between the line connecting the center of the nanobrick (N) and the point light source P2 and the x-axis.

[0070] At this point, by combining formulas (3) and (4), the phase optimization of the target holographic images of channels 1 and 2 under the given two point light sources can be performed, and the rotation angle distribution required for the nanobrick array can be obtained. Figure 9 As shown, the simulation verified the display of "A" and "B" holographic images for two different point light sources on the chip.

[0071] Furthermore, following the same methods and design processes, such as Figure 10 As shown in schematic (a) in the figure, a four-channel holographic display of four point light sources in four different orientations of a nanostructure array can be designed and realized. Figure 10 (b) in the figure shows the optimized simulation results of the four-channel point source hologram designed using MATLAB algorithms.

[0072] In addition, it can be seen from formula (2) that when the position of the point light source is determined, the extraction phases corresponding to different wavelengths are different. Taking red and green wavelengths as examples, the corresponding phases are and which can be given by the following formula: (5) (6) wherein, and are two wavelengths corresponding to the point light source.

[0073] Thus, by simultaneously solving formula (5) and formula (6), the rotation angle distribution of the corresponding nanostructure array can be obtained by holographic optimization, and finally the dual-channel point source holographic display under different wavelengths can be realized, as shown in the conceptual diagram of Figure 11 , wherein, Figure 11 (a) in (a) is a top view, Figure 11 (b) in (b) is a side view.

[0074] Figure 12 The simulation results of two-channel point source holographic images "A" and "E" under wavelengths of 560 nm and 633 nm achieved by FDTD simulation design are shown.

[0075] Further exploration designed three-channel holographic display under three-wavelength incidence, as shown in Figure 13 , the MATLAB optimization results of three-channel holographic images "A", "E" and "N" corresponding to wavelengths of 470 nm, 560 nm and 660 nm are shown.

[0076] For TE0 mode guided waves transmitted in the waveguide, it can be regarded as linearly polarized light perpendicular to the propagation direction, and the linearly polarized light can be regarded as the superposition of left and right circularly polarized light. Therefore, the extraction light can be divided into left and right circularly polarized light components, and the geometric phase modulation thereof satisfies the conjugate relationship, and formula (2) can be further rewritten as, the phases of left and right circularly polarized light for and are (7) (8) By simultaneously solving formula (7) and formula (8), the left and right circularly polarized light components corresponding to the extraction light can be optimized to realize two-channel holographic display under the incidence of a specific point light source, Figure 14 is the corresponding schematic diagram. Figure 15 The simulation results of two-channel point source holographic images "A" and "E" corresponding to left and right circularly polarized light components achieved by FDTD simulation design are shown.

[0077] In addition, Figure 16 The simulation results of free space circularly polarized light with wavelengths of 470 nm, 560 nm and 660 nm respectively incident on the curved circular ring type coupling grating are shown, Figure 16 In the simulation, the period of the grating is 300 nm, and the width is 150 nm. It can be seen that the guided waves of different wavelengths are all focused at the same position, so the designed incident coupling grating can generate the required point light source wavefront distribution. At the same time, the continuous curved ring grating can also be replaced by other discrete structure arrays, such as Figure 17 As shown, it can be replaced by a discrete cylindrical array or a rectangular array. Among them, Figure 17 (a) in the above (a) is a continuous curved circular ring grating, Figure 17 (b) in the above (b) is a cylindrical array grating structure, Figure 17 (c) in the above (c) is a rectangular array grating structure.

[0078] In summary, the present application designs several methods to generate in-plane point light sources, including truncated ring gratings (concentric circular rings), nanocolumn arrays and rectangular nanobrick array ring gratings. The designed superstructure surface cascaded on the chip is composed of nanobrick arrays with different rotation angles, which performs on-chip geometric phase modulation. The present application utilizes the unique scattering wavefront of the on-chip point light source and designs several different expansion schemes for on-chip multi-degree-of-freedom coding, including: (1) based on the degree of freedom of the position of the on-chip point light source, multi-channel (for example, two channels, four channels) holographic display is realized; (2) based on the degree of freedom of the wavelength of the point light source, multi-wavelength (for example, two wavelengths, three wavelengths) holographic display is realized; (3) based on the polarization degree of freedom of the extracted light, two-channel holographic display of left and right circularly polarized light components is realized. Holographic optimization and verification are carried out through FDTD simulation and MATLAB software. The holographic coding display scheme based on the on-chip superstructure surface proposed in the present application greatly expands the degree of freedom of coding compared with the traditional on-chip superstructure surface holographic display.

[0079] Finally, it should be explained that the above specific embodiments are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. An on-chip metasurface, characterized in that, The application relates to a holographic display device, which comprises a medium substrate layer, an optical waveguide layer on the medium substrate layer, and a nanostructure array and at least one on-chip point light source structure on the optical waveguide layer; the nanostructure array is composed of a plurality of nano-bricks with the same size, and the rotation angles of the plurality of nano-bricks are determined based on a target holographic image; each of the on-chip point light source structures is used for coupling circularly polarized light in free space into transmission in the optical waveguide layer, and a light wave front coupled into the optical waveguide layer converges at a point to generate an in-plane point light source; guided waves in the optical waveguide layer are transmitted to the nanostructure array from the point light source position, and are extracted to free space after on-chip geometric phase modulation via the nanostructure array. The on-chip point light source structure adopts a continuous curved ring grating, and the curved ring grating is a truncated concentric circular ring grating structure.

2. The metasurface-on-chip of claim 1, wherein, The on-chip point light source structure adopts a discrete array structure, and the discrete array structure is a cylindrical array grating structure or a rectangular array grating structure.

3. The on-chip metasurface of claim 1, wherein, When the on-chip point light source structure is multiple, the multiple on-chip point light source structures are used for generating multiple point light sources at different positions.

4. The metasurface-on-chip of claim 1, wherein, The nano-bricks have subwavelength sizes in length and width, the medium substrate layer is prepared from silicon dioxide, the optical waveguide layer is prepared from silicon nitride, and the nano-bricks are prepared from silicon.

5. The on-chip metasurface of claim 1, wherein, The in-plane point light source wave front is used for incidence, the position relationship between the point light source and each nano-brick in the nanostructure array is utilized, and on-chip geometric phase coding is combined to realize multi-degree-of-freedom on-chip multi-channel point source holographic display.

6. A holographic coded display method based on the metasurface-on-chip according to any one of claims 1-5, characterized in that, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1.

7. The metasurface-based on-chip holographic coded display method of claim 6, wherein, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. wherein, is the total phase modulation, is the transmission phase, is the geometric phase, r is the distance between the center of the nanobrick and the point light source, is the effective refractive index of the guided wave, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. is the wavelength of the point light source; θ is the rotation angle of the nanobrick, which is defined as the angle between the long axis of the nanobrick and the x-axis; and α is the angle between the line connecting the center of the nanobrick and the point light source and the x-axis.

8. The metasurface-based on-chip holographic coded display method of claim 7, wherein, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. wherein, is the total phase modulation corresponding to the i-th channel, is the distance between the center of the nano-brick and the point light source corresponding to the i-th channel, is the angle between the line connecting the center of the nano-brick and the point light source corresponding to the i-th channel and the x-axis; The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1.

9. The metasurface-based on-chip holographic coded display method of claim 7, wherein, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. In the formula, is the total phase modulation corresponding to the jth wavelength, is the jth wavelength corresponding to the point light source; The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1.

10. The metasurface-based on-chip holographic coded display method of claim 7, wherein, The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. wherein is the total phase modulation for left-handed circularly polarized light, is the total phase modulation for right-handed circularly polarized light; The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the nanostructure array is represented as follows: Formula 1. The total phase modulation experienced by the light wave extracted by any nano-brick to free space in the

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