Metastructure holographic device and design method and imaging method thereof

Abstract

The invention discloses a super-structure holographic device and a design method and an imaging method thereof, and belongs to the technical field of micro-nano photonics, and the design method of the super-structure holographic device comprises the steps: obtaining the phase regulation and control quantity of a to-be-designed target super-structure holographic device for diffracted light of each level, and then calculating the displacement distribution delta x (x, y) of a super-structure unit in the x direction, the displacement distribution delta y (x, y) along the y direction; displacement is carried out on all the super-structure units according to the displacement distribution (delta x (x, y) and delta y (x, y)) in the x direction and the y direction to obtain a two-dimensional nano-structure array, then the two-dimensional nano-structure array is arranged on the preset surface of the transparent substrate, and the multi-channel imaging super-structure holographic device is obtained. The super-structure holographic device has a wide working bandwidth, and multi-channel holographic imaging is realized through multiplexing of a plurality of diffraction orders under the irradiation of incident light with different wavelengths and preset total reflection angles.

Description

Technical Field

[0001] The present invention belongs to the field of micro - nano photonics, and more specifically, relates to a metasurface holographic device, a design method thereof, and an imaging method thereof. Background Art

[0002] A metasurface is a planar optical element with a thickness close to the wavelength, composed of an array of sub - wavelength structures. By precisely arranging the sub - wavelength structures, flexible control of the characteristics of electromagnetic waves (including light waves), such as phase, amplitude, polarization, etc., has been achieved in recent years, attracting wide attention in the field of optical design and applications.

[0003] Compared with traditional holographic devices, holographic devices based on metasurfaces exhibit unique advantages in terms of system size, imaging quality, working bandwidth, and working efficiency. For example, traditional holographic devices usually require a large volume and a complex optical layout, while metasurface holographic devices can significantly reduce the system volume, and at the same time improve the imaging quality and efficiency. In recent years, researchers have been able to achieve a wide working bandwidth and multifunctional integration by carefully designing the micro - nano structures of metasurfaces, which have important application values in fields such as holographic display, information storage, and security anti - counterfeiting.

[0004] However, current metasurface holographic devices still face challenges such as few imaging channels, which limits their further applications in fields such as complex light field control, waveguide display, image encryption, and information storage. Summary of the Invention

[0005] In view of the above - mentioned defects or improvement requirements of the prior art, the present invention provides a metasurface holographic device, a design method thereof, and an imaging method thereof, aiming to solve the problem of few imaging channels in current metasurface holographic devices.

[0006] To achieve the above object, according to one aspect of the present invention, a design method of a metasurface holographic device is provided, including:

[0007] S1: Obtain the phase distribution of each order of diffracted light after being modulated by the target metasurface holographic device to be designed represents the phase modulation amount of each order of diffracted light in the x - direction; represents the phase modulation amount of each order of diffracted light in the y - direction; l is the diffraction secondary order number, l ∈ [1, m], and m is the highest diffraction order number;

[0008] S2: Use and to calculate the required displacement distribution (Δ x (x, y), Δ y (x, y)) of the target two - dimensional nanostructure array in the target metasurface holographic device, where the displacement distribution Δ x(x, y) and the displacement distribution Δ in the y direction y (x, y); P is the period of the original two-dimensional nanostructure array with periodic distribution along the x and y directions;

[0009] S3: Displace each meta-unit in the original two-dimensional nanostructure array according to the displacement distribution (Δ x (x, y), Δ y (x, y)) to obtain the target two-dimensional nanostructure array;

[0010] S4: Set the target two-dimensional nanostructure array on a transparent substrate to obtain the target metasurface holographic device; When incident light is incident on the transparent substrate along the x direction and / or y direction and propagates to the target two-dimensional nanostructure array at a specific total reflection angle θ l propagates to the target two-dimensional nanostructure array, it will be modulated and diffracted into free space, and the diffracted light of orders (l, 0) and (0, l) forms holographic images corresponding to each diffraction order after propagating a certain distance.

[0011] Further, obtaining the diffraction light phase modulation amount of each diffraction order in the x direction for the target metasurface holographic device to be designed in S1 includes:

[0012] S101: Randomly generate a phase distribution According to Calculate the initial light field of each diffraction channel where j represents the imaginary unit;

[0013] S102: Based on each of the initial light fields Calculate the diffraction light field of each diffraction order on the target imaging plane Furthermore, determine the root mean square errors RMSE1, RMSE2,..., RMSE of the normalized intensity distribution of each diffraction light field and the normalized intensity distribution of the corresponding target image m ; On the imaging plane, replace the amplitude distribution of each diffraction light field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase value, to obtain a new light field distribution Use the new light field distribution Calculate the light field distribution on the holographic plane

[0014] S103: Calculate the new phase distribution through the formula Calculate the new phase distribution ω l is the weight factor of each diffraction channel in the x direction; k l is an integer parameter introduced by phase unwrapping;

[0015] S104: According to the new phase distribution Update the light field distribution on the holographic plane And return to S103 until the calculated by S103 converges. When it converges, corresponding is assigned to Finally, the phase modulation amount of the diffracted light at each order in the x direction is obtained

[0016] Furthermore, ω l is the weight factor of each diffraction channel in the x direction and is calculated by ; k l is calculated by Calculate.

[0017] Furthermore, obtaining the phase modulation amount of the diffracted light at each order in the y direction for the target metasurface holographic device to be designed in S1 includes: Including:

[0018] S111: Randomly generate a phase distribution According to Calculate the initial light field of each diffraction channel

[0019] S112: Based on each of the initial light fields Calculate the diffracted light fields at each order on the target imaging plane Furthermore, determine the root mean square errors RMSE'1, RMSE'2,..., RMSE' of the normalized intensity distribution of each diffracted light field and the normalized intensity distribution of the corresponding target image m ; On the imaging plane, replace the amplitude distribution of each diffracted light field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase value, to obtain a new light field distribution Use the new light field distribution Calculate the light field distribution on the holographic plane

[0020] S113: Pass through Calculate the new phase distribution ω' l is the weight factor of each diffraction channel in the y direction; k' l is an integer parameter introduced by phase unwrapping;

[0021] S114: According to the new phase distribution Update the light field distribution on the holographic plane And return to S113 until the tends to converge, and when it converges the corresponding is assigned to Finally, the diffraction light phase modulation amounts of each diffraction order in the y direction are obtained

[0022] Furthermore, ω' l is the weight factor of each diffraction channel in the y direction, and is calculated by ; and is calculated by obtained by calculation.

[0023] Furthermore, the method further includes: in the diffraction channels with diffraction orders of (l,0) and (0,l), setting the vacuum wavelength λ of the incident light l and the total reflection angle θ of the incident light when propagating in the transparent substrate l to satisfy: where n sub refers to the refractive index of the substrate.

[0024] Furthermore, the method further includes: setting the total reflection angle θ of the incident light when propagating in the transparent substrate in the diffraction channels with diffraction orders of (l,0) and (0,l) l to satisfy: n sub sinθ l ≥ln0; where n sub refers to the refractive index of the substrate, and n0 is the refractive index of air.

[0025] According to another aspect of the present invention, a metasurface holographic device is provided, which is designed by using the design method of the metasurface holographic device.

[0026] According to another aspect of the present invention, a four-channel imaging method for a metasurface holographic device is provided, including:

[0027] Controlling the incident light with a vacuum wavelength of λ1 in the first channel to be incident along the x direction onto the transparent substrate and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ1, and being regulated and diffracted into free space. The diffracted light with a diffraction order of (1,0) forms a first monochromatic holographic image after propagating for a certain distance;

[0028] Controlling the incident light with a vacuum wavelength of λ2 in the second channel to be incident along the x direction onto the transparent substrate and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ2, and being regulated and diffracted into free space. The diffracted light with a diffraction order of (2,0) forms a second monochromatic holographic image after propagating for a certain distance;

[0029] When controlling the incident light with a vacuum wavelength of λ1 in the third channel to be incident on the transparent substrate along the y direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ1, it will be regulated and diffracted into free space. The diffracted light with an order of (0, 1) forms the third monochromatic holographic image after propagating a certain distance;

[0030] When controlling the incident light with a vacuum wavelength of λ2 in the fourth channel to be incident on the transparent substrate along the y direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ2, it will be regulated and diffracted into free space. The diffracted light with an order of (0, 2) forms the fourth monochromatic holographic image after propagating a certain distance.

[0031] According to another aspect of the present invention, a two-channel color holographic imaging method for a metaholographic device is provided, including:

[0032] When controlling the first red incident light with a vacuum wavelength of λ'1 to propagate in the substrate along the x direction at a specific total reflection angle θ'1 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (1, 0) forms the first R component of the first color holographic image after propagating a certain distance; when controlling the first green incident light with a vacuum wavelength of λ'2 to propagate in the substrate along the x direction at a specific total reflection angle θ'2 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (2, 0) forms the first G component of the first color holographic image after propagating a certain distance; when controlling the first blue incident light with a vacuum wavelength of λ'3 to propagate in the substrate along the x direction at a specific total reflection angle θ'3 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (3, 0) forms the first B component after propagating a certain distance; when the first red incident light, the first green incident light, and the first blue incident light are simultaneously incident along the x direction at their respective specific incident angles, the first R component, the first G component, and the first B component will form the first color holographic image;

[0033] When controlling the second red incident light with a vacuum wavelength of λ'1 to propagate in the substrate along the y direction at a specific total reflection angle θ'1 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,1) forms a second R component after propagating a certain distance; when controlling the second green incident light with a vacuum wavelength of λ'2 to propagate in the substrate along the y direction at a specific total reflection angle θ'2 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,2) forms a second G component after propagating a certain distance; when controlling the second blue incident light with a vacuum wavelength of λ'3 to propagate in the substrate along the y direction at a specific total reflection angle θ'3 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,3) forms a second B component after propagating a certain distance; when the second red incident light, the second green incident light, and the second blue incident light are simultaneously incident along the y direction at their respective specific incident angles, the second R component, the second G component, and the second B component form a second color holographic image.

[0034] Generally speaking, compared with the prior art by the above technical solutions conceived in the present invention, the following beneficial effects can be achieved:

[0035] (1) The present invention provides a design method for a metasurface holographic device, which calculates the displacement distribution (Δx(x,y), Δy(x,y)) of metasurface units by obtaining the phase modulation amount of diffracted light of each order for the target metasurface holographic device to be designed. Furthermore, each metasurface unit in the original two-dimensional nanostructure array with a periodic distribution is displaced according to the displacement distribution (Δ x (x,y), Δ y (x,y)) to obtain the target two-dimensional nanostructure array, and then the target two-dimensional nanostructure array is disposed on a transparent substrate to obtain the target metasurface holographic device. This metasurface holographic device has a high working bandwidth, and under the irradiation of different wavelengths and preset total reflection angles, through the multiplexing of multiple diffraction orders, multi-channel holographic imaging is realized; furthermore, it can also selectively project a monochromatic holographic image or a color holographic image.

[0036] (2) In this solution, the light field distribution on the holographic surface is updated according to the new phase distribution and iterated cyclically until the calculated tends to converge, and the corresponding to the convergence is assigned to when converging and assigned to The advantage of this method is that multi-channel holographic imaging with diffraction order multiplexing can be achieved by optimizing the holographic phase in the x direction, thereby increasing the information capacity.

[0037] (3) In this solution, according to the new phase distribution update the light field distribution on the holographic plane and iterate cyclically until the calculated tends to converge, and when it converges the corresponding is assigned to With such a design, the advantage is that multi-channel holographic imaging with diffraction order multiplexing can be achieved by optimizing the holographic phase in the y direction, thereby increasing the information capacity.

[0038] (4) In this solution, use to calculate the weight factors of each diffraction channel in the x direction, and use to calculate the weight factors of each diffraction channel in the y direction. With such a design, the advantage is that the reconstructed image quality of each diffraction channel can be balanced.

[0039] (5) In this solution, use to calculate the integer parameter k introduced by phase unwrapping l , and use to calculate the integer parameter k' introduced by phase unwrapping l . With such a design, the advantage is that it can solve the problem of non-convergence of algorithm iteration caused by phase folding of the light field during the diffraction propagation calculation.

[0040] (6) In this solution, set the vacuum wavelength λ of the incident light in the diffraction channels with diffraction orders (l, 0) and (0, l) l and the total reflection angle θ of the incident light when it propagates in the transparent substrate l to satisfy: With such a design, the diffracted light of the target order can be controlled to exit along the normal of the device.

[0041] (7) In this solution, set the total reflection angle θ of the incident light when it propagates in the transparent substrate in the diffraction channels with diffraction orders (l, 0) and (0, l) l to satisfy: n sub sinθ l ≥ln0; With such a design, crosstalk between channels can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flowchart of the design method of the multi-channel display metasurface holographic device provided in Embodiment 1 of the present invention;

[0043] Figure 2Schematic diagram of the meta - holographic device with multi - channel display provided in Embodiment 2 of the present invention;

[0044] Figure 3 Schematic diagrams of several common meta - units provided in Embodiment 2 of the present invention, where 1 refers to the two - dimensional nanostructure array and 2 refers to the transparent substrate;

[0045] Figure 4 Flowchart of the pure - phase holographic algorithm used in the design of the multi - channel meta - holographic device provided in Embodiment 1 of the present invention;

[0046] Figure 5 Meta - holographic device in the first implementation form provided in Embodiment 3 of the present invention;

[0047] Figure 6 Shows Figure 5 Schematic diagram of the imaging result of the meta - holographic device;

[0048] Figure 7 Meta - holographic device in the first implementation form provided in Embodiment 4 of the present invention;

[0049] Figure 8 Shows Figure 7 Schematic diagram of the imaging result of the meta - holographic device. Detailed implementation manners

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] Embodiment 1

[0052] As Figure 1 shown, this embodiment provides a design method of a meta - holographic device, including: S1 - S4. Among them, S1: Obtain the phase modulation amount of the diffracted light of each order for the target meta - holographic device to be designed represents the phase modulation amount of the diffracted light of each order in the x - direction; represents the phase modulation amount of the diffracted light of each order in the y - direction; l is the diffraction secondary order number, l ∈ [1, m], and m is the highest diffraction order number; among them, the wave vector component direction of the diffracted light of each order along the grating plane is opposite to the grating vector direction; S2: Use and to calculate the required displacement distribution (Δ x(x,y), Δ y The displacement distribution Δ in the x - direction in (x,y)) x The displacement distribution Δ in the x - direction and y - direction in (x,y) y (x,y); P is the period of the original two - dimensional nanostructure array with periodic distribution along the x - and y - directions; S3: Displace each meta - unit in the original two - dimensional nanostructure array according to the displacement distribution (Δ x (x,y), Δ y (x,y)) to obtain the target two - dimensional nanostructure array; S4: Set the target two - dimensional nanostructure array on a transparent substrate to obtain the target metasurface holographic device; When incident light is incident on the transparent substrate along the x - direction and / or y - direction and propagates to the target two - dimensional nanostructure array at a specific total reflection angle θ l propagates, it will be regulated and diffracted into free space, and the diffracted light with orders (k,0) and (0,l) forms holographic images corresponding to each diffraction order after a certain distance of propagation. Among them, the structure of the metasurface holographic device is as shown in Figure 2 shown, and the structure of the meta - unit in the metasurface holographic device is as shown in Figure 3 shown.

[0053] To achieve multi - channel holographic display, the principle of detour phase modulation is used to achieve phase encoding, and the target phase is encoded in each diffraction order through a phase optimization algorithm to achieve high - resolution imaging. For an original two - dimensional nanostructure array with periodic distribution, if a displacement distribution Δ x (x,y) is applied to each unit structure therein, the diffracted light with diffraction order (l,0) diffracted from this unit structure into free space will be introduced with a phase modulation amount distribution P is the period of the original two - dimensional nanostructure array with periodic distribution along the x - and y - directions. Through Figure 4 the phase optimization algorithm shown, multi - channel diffraction order multiplexing of diffraction orders (1,0), (2,0), …, (m,0) can be achieved. By selecting appropriate parameters such as the material, the wavelength of the illumination light, the total reflection angle of the illumination light, and the unit period, monochromatic holographic imaging of m channels can be achieved. Similarly, if a displacement distribution Δ y (x,y) is applied to each unit structure in the x - direction, multi - channel diffraction order multiplexing of diffraction orders (0,1), (0,2), …, (0,m) can also be achieved. According to the present invention, for an original two - dimensional nanostructure array with periodic distribution, the required displacement distribution (Δ x (x,y), Δ y (x,y)) is applied to the nanostructures in each unit structure, and the obtained detour - phase - type metasurface holographic device, combined with Figure 4 the phase optimization algorithm shown, can achieve high - resolution holographic imaging of 2m channels. The following expandsFigure 4 Specific implementation of the phase optimization algorithm shown

[0054] As an alternative implementation, the process is specifically as Figure 4 shown, in S1, obtaining the diffraction light phase regulation amounts for each diffraction order in the x direction of the target metasurface holographic device to be designed including: S101: Randomly generating a phase distribution According to Calculating the initial light field of each diffraction channel where j represents the imaginary unit; S102: Based on each of the initial light fields Calculating the diffraction light fields of each diffraction order on the target imaging plane Furthermore, determining the root mean square errors RMSE1, RMSE2,..., RMSE between the normalized intensity distributions of each diffraction light field and the normalized intensity distribution of the corresponding target image m ; On the imaging plane, replacing the amplitude distribution of each diffraction light field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase value, to obtain a new light field distribution Using the new light field distribution Calculating the light field distribution on the holographic plane S103: Through the formula Calculating a new phase distribution ω l is the weight factor of each diffraction channel in the x direction; k l is an integer parameter introduced by phase unwrapping; S104: According to the new phase distribution Updating the light field distribution on the holographic plane And returning to S103 until the calculated by S103 tends to converge, and when it converges corresponding is assigned to Finally obtaining the diffraction light phase regulation amounts of each order in the x direction l where ω is the weight factor of each diffraction channel in the x direction, calculated by l As an alternative implementation, k is calculated by

[0055] As an alternative implementation, in S1, obtaining the diffraction light phase regulation amounts for each order in the y direction of the target metasurface holographic device to be designed Including: S111: Randomly generate a phase distribution According to Calculate the initial optical field of each diffraction channel S112: Based on each of the initial optical fields Calculate the diffracted optical fields of each order on the target imaging plane Furthermore, determine the root mean square errors RMSE'1, RMSE'2,..., RMSE' between the normalized intensity distributions of each diffracted optical field and the normalized intensity distribution of the corresponding target image m ; On the imaging plane, replace the amplitude distribution of each diffracted optical field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase value, to obtain a new optical field distribution Utilize the new optical field distribution Calculate the optical field distribution on the holographic plane S113: Through Calculate a new phase distribution ω' l is the weight factor of each diffraction channel in the y direction; k' l is an integer parameter introduced by phase unwrapping; S114: According to the new phase distribution Update the optical field distribution on the holographic plane And return to S113 until the calculated by S113 tends to converge, and when it converges corresponding is assigned to Finally, obtain the diffraction optical phase modulation amount of each diffraction order in the y direction l where ω' is the weight factor of each diffraction channel in the y direction, calculated by l By Calculated.

[0056] As an optional implementation manner, the design method further includes: setting the vacuum wavelength λ of the incident light in the diffraction channels with diffraction orders (l,0) and (0,l) l and the total reflection angle θ when the incident light propagates in the transparent substrate l Satisfy: where n sub refers to the refractive index of the substrate. Further, the design method further includes: setting the total reflection angle θ when the incident light propagates in the transparent substrate in the diffraction channels with diffraction orders (l,0) and (0,l) l Satisfy: nsub sinθ l ≥ln0; where n sub refers to the refractive index of the substrate, and n0 is the refractive index of air.

[0057] Specifically, by reasonably selecting system parameters and materials, it is possible to selectively achieve the vertical emission of a single target diffraction order into free space, thereby achieving the effect of crosstalk-free holographic imaging. Specifically, the condition and n sub sinθ l ≥ln0 (l = 1, 2, 3…). Where n sub refers to the refractive index of the substrate, θ l refers to the total reflection angle when the light beam propagates in the substrate, λ l is the vacuum wavelength of the diffracted light with diffraction orders (l, 0) and (0, l), P is the period of the unit structure, and n0 is the refractive index of air. Obviously, if one wants to achieve crosstalk-free holographic imaging with the multiplexing of four diffraction orders (1, 0), (2, 0), (0, 1), and (0, 2), then at least n sub ≥2.0 should be satisfied. If a suitable substrate material with a higher refractive index can be found, it is also possible to achieve multi-channel crosstalk-free holographic imaging with the multiplexing of more diffraction orders. On the other hand, if appropriate parameters are selected under the condition that λ1, λ2, and λ3 correspond to the red, green, and blue bands respectively, and the equation is satisfied, the multiplexing of the diffraction orders (1, 0), (2, 0), (3, 0) or (0, 1), (0, 2), (0, 3) can be achieved, and color holographic display can be realized.

[0058] Example 2

[0059] This example provides a metasurface holographic device designed by the design method of the above metasurface holographic device. Figure 2 Composed of Figure 3 The corresponding metasurface holographic device structure shown by the and metasurface units, including the arrangement of nanocolumns with the same size but different positions. This implementation method utilizes the method of detour phase modulation. The phase modulation is usually applied to the diffracted light in the transmission direction, and the applied phase modulation amount can be expressed as x (x, y), Δ y (x, y)), it is possible to achieve precise phase modulation on the diffracted light with diffraction orders (l, 0) and (0, l).

[0060] The metasurface holographic device with multi-channel display in this embodiment includes a plurality of periodically arranged metasurface units (meta-atoms). The meta-atoms are artificial sub-wavelength structures made of materials that are transparent or have low absorption rates in the target optical band. The metasurface holographic device with multi-channel display can selectively project high-resolution crosstalk-free monochromatic holographic images or high-resolution color holographic images in the normal direction of the device under the illumination of incident light with different wavelengths and different total reflection angles.

[0061] The columnar structure includes a square column with a rectangular bottom surface and an (elliptical) cylinder with an elliptical bottom surface, which are made of materials that are transparent or have low absorption rates in the visible light band. P is the period of the metasurface unit, L is the side length of the bottom surface, H is the height of the nanocolumn, and D1 and D2 are the sizes of the short axis and the long axis respectively. It should be noted that in principle, the present invention does not require the unit structure to be anisotropic or isotropic, that is, the given size parameters D1 and D2 can take equal values or unequal values. Similarly, the present invention does not impose any requirements on the polarization state of the incident light. The above-given unit structure parameters and the polarization state of the incident light only affect the magnitude of the diffraction efficiency, as long as the diffraction efficiency is ensured to be large enough to achieve clear imaging. To maintain the working efficiency in the target working band, the metasurface holographic device is composed of a dielectric material with high refractive index and low loss in the target band.

[0062] Preferred materials include titanium dioxide (TiO2), silicon nitride (SiN x ), silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and hafnium dioxide (HfO2), etc. By designing a reasonable shape and structure parameters of the metasurface unit, a high diffraction efficiency is achieved, and accurate phase modulation is achieved by designing the position distribution of the nanocolumn array.

[0063] Example 3

[0064] This embodiment provides a four-channel crosstalk-free imaging method for a metasurface holographic device, as Figure 5 and Figure 6As shown, it includes: when controlling the first incident light with a vacuum wavelength of λ1 to be incident on the transparent substrate along the x-direction and propagate to the two-dimensional nanostructure array at a specific total reflection angle θ1, it will be regulated and diffracted into free space, and the diffracted light with an order of (1,0) forms the first monochromatic holographic image after propagating a certain distance; when controlling the second incident light with a vacuum wavelength of λ2 to be incident on the transparent substrate along the x-direction and propagate to the two-dimensional nanostructure array at a specific total reflection angle θ2, it will be regulated and diffracted into free space, and the diffracted light with an order of (2,0) forms the second monochromatic holographic image after propagating a certain distance; when controlling the third incident light with a vacuum wavelength of λ1 to be incident on the transparent substrate along the y-direction and propagate to the two-dimensional nanostructure array at a specific total reflection angle θ1, it will be regulated and diffracted into free space, and the diffracted light with an order of (0,1) forms the third monochromatic holographic image after propagating a certain distance; when controlling the fourth incident light with a vacuum wavelength of λ2 to be incident on the transparent substrate along the y-direction and propagate to the two-dimensional nanostructure array at a specific total reflection angle θ2, it will be regulated and diffracted into free space, and the diffracted light with an order of (0,2) forms the fourth monochromatic holographic image after propagating a certain distance.

[0065] Figure 5 This is the first implementation mode of multi-channel imaging of a multi-channel metasurface holographic device, which can achieve multi-channel monochromatic metasurface holographic imaging. The device includes a transparent substrate and a two-dimensional nanostructure array. When the incident light propagates in the substrate to the two-dimensional nanostructure array along the x-direction at a specific total reflection angle, it will be regulated and diffracted into free space, and the diffracted light with an order of (1,0) forms the first high-resolution holographic image after propagating a certain distance; when the incident light propagates in the substrate to the two-dimensional nanostructure array along the x-direction at a specific total reflection angle, it will be regulated and diffracted into free space, and the diffracted light with an order of (2,0) forms the second high-resolution holographic image after propagating a certain distance; when the incident light propagates in the substrate to the two-dimensional nanostructure array along the y-direction at a specific total reflection angle, it will be regulated and diffracted into free space, and the diffracted light with an order of (0,1) forms the third high-resolution holographic image after propagating a certain distance; when the incident light propagates in the substrate to the two-dimensional nanostructure array along the y-direction at a specific total reflection angle, it will be regulated and diffracted into free space, and the diffracted light with an order of (0,2) forms the fourth high-resolution holographic image after propagating a certain distance.

[0066] Based on the above analysis, a four-channel crosstalk-free metaholographic monochromatic display device operating at the target wavelengths of λ1 = 671 nm and λ2 = 405 nm is designed, which consists of a nanocolumn array with a period of P = 405 nm. The target images are designed in four diffraction orders of (1,0), (2,0), (0,1), and (0,2) respectively. The substrate is high-refractive-index glass Schott P-SF68 (the refractive index is close to 2.1 near 405 nm), and the corresponding total reflection angles of the light beams with wavelengths of λ1 = 671 nm and λ2 = 405 nm in the substrate are θ1 = 56.4° and θ2 = 72.4°. Based on the Fourier transform, computational imaging analysis is performed on the designed device. Figure 6 The far-field imaging results for each target diffraction order.

[0067] Example 4

[0068] This example provides a two-channel color holographic imaging method for a metaholographic device, as Figure 7 and Figure 8As shown, it includes: when controlling the first red incident light with a vacuum wavelength of λ'1 to propagate in the substrate along the x direction at a specific total reflection angle θ'1 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (1,0) forms the first R component of the first color holographic image after propagating a certain distance; when controlling the first green incident light with a vacuum wavelength of λ'2 to propagate in the substrate along the x direction at a specific total reflection angle θ'2 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (2,0) forms the first G component of the first color holographic image after propagating a certain distance; when controlling the first blue incident light with a vacuum wavelength of λ'3 to propagate in the substrate along the x direction at a specific total reflection angle θ'3 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (3,0) forms the first B component after propagating a certain distance; when the first red incident light, the first green incident light, and the first blue incident light are incident simultaneously along the x direction at their respective specific incident angles, the first R component, the first G component, and the first B component will form the first color holographic image; when controlling the second red incident light with a vacuum wavelength of λ'1 to propagate in the substrate along the y direction at a specific total reflection angle θ'1 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,1) forms the second R component after propagating a certain distance; when controlling the second green incident light with a vacuum wavelength of λ'2 to propagate in the substrate along the y direction at a specific total reflection angle θ'2 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,2) forms the second G component after propagating a certain distance; when controlling the second blue incident light with a vacuum wavelength of λ'3 to propagate in the substrate along the y direction at a specific total reflection angle θ'3 to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,3) forms the second B component after propagating a certain distance; when the second red incident light, the second green incident light, and the second blue incident light are incident simultaneously along the y direction at their respective specific incident angles, the second R component, the second G component, and the second B component form the second color holographic image.

[0069] Figure 7As the second implementation of multi-channel imaging of the multi-channel metaholographic device, for example, when the red incident light beam 3 propagates in the substrate along the x direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (1,0) forms the R component in the first high-resolution color holographic image 4 after propagating a certain distance; when the green incident light beam 5 propagates in the substrate along the x direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (2,0) forms the G component in the first high-resolution color holographic image 4 after propagating a certain distance; when the blue incident light beam 6 propagates in the substrate along the x direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (3,0) forms the B component in the first high-resolution color holographic image 4 after propagating a certain distance; when the red incident light beam 7 propagates in the substrate along the y direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (0,1) forms the R component in the second high-resolution color holographic image 8 after propagating a certain distance; when the green incident light beam 9 propagates in the substrate along the y direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (0,2) forms the G component in the second high-resolution color holographic image 8 after propagating a certain distance; when the blue incident light beam 10 propagates in the substrate along the y direction at a specific total reflection angle to reach the two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light of order (0,3) forms the B component in the second high-resolution color holographic image 8 after propagating a certain distance.

[0070] Furthermore, a dual-channel metaholographic color display device operating at target wavelengths of λ'1 = 671 nm, λ'2 = 532 nm, and λ'3 = 405 nm is designed, which consists of a nanocolumn array with a period of P = 600 nm. The R, G, and B components of each of the two color target images are designed in six diffraction channels of (1,0), (2,0), (3,0), (0,1), (0,2), and (0,3) respectively. The substrate is high-refractive-index glass Schott P-SF68, and the corresponding total reflection angles of the light beams with wavelengths of λ'1 = 671 nm, λ'2 = 532 nm, and λ'3 = 405 nm in the substrate are θ'1 = 34.20°, θ'2 = 61.34°, and θ'3 = 74.81° respectively. Based on the Fourier transform, computational imaging analysis is performed on this designed device. Figure 8 They are the far-field imaging results for each target diffraction order.

[0071] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A design method of a metaholographic device, characterized in that, Comprising: S1: Obtain the phase modulation amount of the diffracted light of each order for the target metasurface holographic device to be designed represents the phase modulation amount of the diffracted light of each order in the x direction; represents the phase modulation amount of the diffracted light of each order in the y direction; l is the diffracted secondary order number, l ∈ [1, m], and m is the highest diffracted order number; S2: Exploitation and The displacement distribution (Δ x (x,y),Δ y The displacement distribution Δ in the x direction in (x,y) x (x, y) and displacement distribution in the y direction Δ y (x, y); P is the period of the original two-dimensional nanostructure array along the x and y directions; S3: Displace each meta-unit in the original two-dimensional nanostructure array according to the displacement distribution (Δ x (x, y), Δ y (x, y)) to obtain the target two-dimensional nanostructure array; S4: Place the target two-dimensional nanostructure array on a transparent substrate to obtain the target metasurface holographic device; when incident light is incident on the transparent substrate along the x-direction and / or y-direction and propagates to the target two-dimensional nanostructure array at a specific total reflection angle θ l the light will be modulated and diffracted into free space. The diffracted light with orders (l, 0) and (0, l) forms holographic images corresponding to each diffraction order after propagating a certain distance.

2. The design method of the metasurface holographic device according to claim 1, characterized in that Obtaining the diffraction light phase regulation amount of each diffraction order in the x direction for the target metasurface holographic device to be designed in S1 including: S101: Randomly generate a phase distribution According to Calculate the initial optical field of each diffraction channel where j represents the imaginary unit; S102: Based on each of the initial optical fields Calculate the diffracted optical fields of each diffraction order on the target imaging plane Furthermore, determine the root mean square errors RMSE1, RMSE2, …, RMSE between the normalized intensity distributions of each diffracted optical field and the normalized intensity distributions of the corresponding target images m ; On the imaging plane, replace the amplitude distribution of each diffracted optical field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase values, to obtain a new optical field distribution Utilize the new optical field distribution Calculate the optical field distribution on the hologram plane S103: Calculate the new phase distribution through the formula ω l is the weight factor of each diffraction channel in the x direction; k l is the integer parameter introduced by phase unwrapping;​ S104: According to the new phase distribution Update the light field distribution on the holographic plane And return to S103 until the calculated by S103 tends to converge. When it converges, the corresponding is assigned to Finally, the phase modulation amount of the diffracted light at each order in the x direction is obtained 3. The design method of the metaholographic device according to claim 2, characterized in that, ω l is the weight factor of each diffraction channel in the x direction, which is calculated by k l is calculated by and obtained.

4. The design method of the metasurface holographic device according to claim 1, characterized in that Obtaining the phase modulation amount of the diffracted light of each order in the y direction for the target metaholographic device to be designed in S1 including: S111: Randomly generate a phase distribution According to Calculate the initial optical field of each diffraction channel S112: Based on each of the initial optical fields calculate the diffracted optical fields of each order on the target imaging plane and then determine the root mean square errors RMSE'1, RMSE'2, …, RMSE' between the normalized intensity distributions of the respective diffracted optical fields and the normalized intensity distributions of the corresponding target images m ; on the imaging plane, replace the amplitude distribution of each diffracted optical field with the square root distribution of the normalized intensity of each target image in the x direction, while retaining the phase value, to obtain a new optical field distribution Use the new optical field distribution to calculate the optical field distribution on the hologram plane S113: By calculating a new phase distribution ω' l is the weight factor of each diffraction channel in the y direction; k' l is an integer parameter introduced by phase unwrapping; S114: According to the new phase distribution Update the light field distribution on the holographic plane And return to S113 until the result calculated by S113 Tends to converge. When it converges The corresponding Is assigned to Finally, the diffraction light phase modulation amount of each diffraction order in the y direction is obtained 5. The design method of the metasurface holographic device according to claim 4, characterized in that, ω' l is the weight factor of each diffraction channel in the y direction, which is calculated by ; k' l is calculated by .

6. The design method of the metaholographic device according to claim 1, characterized in that The method further includes: setting the vacuum wavelength λ of the incident light in diffraction channels with diffraction orders (l, 0) and (0, l) l and the total reflection angle θ of the incident light when propagating in the transparent substrate l to satisfy:[[]] where n sub refers to the refractive index of the substrate.

7. The design method of the metasurface holographic device according to claim 1, characterized in that, The method further includes: setting a total reflection angle θ of the incident light when propagating in the transparent substrate in diffraction channels with diffraction orders of (l, 0) and (0, l). l Satisfying: n sub sinθ l ≥ln0; where n sub refers to the refractive index of the substrate, and n0 is the refractive index of air.

8. A metaholographic device, characterized in that, Designed by using the design method of the metasurface holographic device according to any one of claims 1-7.

9. A four-channel imaging method for the metasurface holographic device according to claim 8, characterized in that, Comprising: When controlling the incident light with a vacuum wavelength of λ1 in the first channel to be incident on the transparent substrate along the x direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ1, it is modulated and diffracted into free space, and the diffracted light with an order of (1,0) forms the first monochromatic holographic image after propagating a certain distance; When controlling the incident light with a vacuum wavelength of λ2 in the second channel to be incident on the transparent substrate along the x direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ2, it is modulated and diffracted into free space, and the diffracted light with an order of (2,0) forms the second monochromatic holographic image after propagating a certain distance; When controlling the incident light with a vacuum wavelength of λ1 in the third channel to be incident on the transparent substrate along the y direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ1, it is modulated and diffracted into free space, and the diffracted light with an order of (0,1) forms the third monochromatic holographic image after propagating a certain distance; When controlling the incident light with a vacuum wavelength of λ2 in the fourth channel to be incident on the transparent substrate along the y direction and propagate to the target two-dimensional nanostructure array at a specific total reflection angle θ2, it is modulated and diffracted into free space, and the diffracted light with an order of (0,2) forms the fourth monochromatic holographic image after propagating a certain distance.

10. A two-channel color holographic imaging method for the metasurface holographic device according to claim 8, characterized in that Comprising: When controlling the first red incident light with a vacuum wavelength of λ'1 to propagate in the substrate along the x direction at a specific total reflection angle θ'1 to the target two-dimensional nanostructure array, it is modulated and diffracted into free space, and the diffracted light with an order of (1,0) forms the first R component of the first color holographic image after propagating a certain distance; when controlling the first green incident light with a vacuum wavelength of λ'2 to propagate in the substrate along the x direction at a specific total reflection angle θ'2 to the target two-dimensional nanostructure array, it is modulated and diffracted into free space, and the diffracted light with an order of (2,0) forms the first G component of the first color holographic image after propagating a certain distance; when controlling the first blue incident light with a vacuum wavelength of λ'3 to propagate in the substrate along the x direction at a specific total reflection angle θ'3 to the target two-dimensional nanostructure array, it is modulated and diffracted into free space, and the diffracted light with an order of (3,0) forms the first B component; when the first red incident light, the first green incident light, and the first blue incident light are simultaneously incident at their respective specific incident angles along the x direction, the first R component, the first G component, and the first B component will form the first color holographic image; When the second red incident light with a vacuum wavelength of λ'1 propagates along the y direction in the substrate at a specific total reflection angle θ'1 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,1) forms a second R component after propagating a certain distance; when the second green incident light with a vacuum wavelength of λ'2 propagates along the y direction in the substrate at a specific total reflection angle θ'2 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,2) forms a second G component after propagating a certain distance; when the second blue incident light with a vacuum wavelength of λ'3 propagates along the y direction in the substrate at a specific total reflection angle θ'3 to the target two-dimensional nanostructure array, it will be regulated and diffracted into free space. The diffracted light with an order of (0,3) forms a second B component after propagating a certain distance; when the second red incident light, the second green incident light, and the second blue incident light are incident simultaneously along the y direction at their respective specific incident angles, the second R component, the second G component, and the second B component form a second color holographic image.

Images