A meta-holographic device and its design and imaging methods

Abstract

This invention discloses a metaholographic device and its design and imaging methods, belonging to the field of micro-nano photonics technology. The design method of the metaholographic device includes: obtaining the phase modulation amount of the target metaholographic device to be designed for each order of diffraction light, and then calculating the displacement distribution Δ of the metaunit along the x-direction. x (x,y) and displacement distribution Δ along the y direction y (x,y); each of the superunits is distributed according to the displacement along the x and y directions (Δ). x (x,y),Δ y A two-dimensional nanostructure array is obtained by displacement of (x, y), and then the two-dimensional nanostructure array is placed on the preset surface of the transparent substrate to obtain a meta-holographic device for multi-channel imaging. This meta-holographic device has a wide operating bandwidth and achieves multi-channel holographic imaging by multiplexing multiple diffraction orders under incident light of different wavelengths and preset total reflection angles.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano photonics, and more specifically, relates to a meta-holographic device and its design and imaging methods. Background Technology

[0002] Metasurfaces are planar optical elements composed of subwavelength structure arrays with a thickness close to the wavelength. By precisely arranging the subwavelength structures, they enable flexible control of the phase, amplitude, polarization, and other characteristics of electromagnetic waves (including light waves), and have attracted widespread attention in the field of optical design and application in recent years.

[0003] Compared to traditional holographic devices, metasurface-based holographic devices exhibit unique advantages in system size, imaging quality, bandwidth, and efficiency. For example, traditional holographic devices typically require large volumes and complex optical layouts, while metasurface holographic devices can significantly reduce system size while improving imaging quality and efficiency. In recent years, researchers have achieved wide bandwidth and multifunctional integration through the careful design of micro- and nano-structures of metasurfaces, which have significant application value in fields such as holographic displays, information storage, and security and anti-counterfeiting.

[0004] However, current metaholographic devices still face challenges such as a limited number of imaging channels, which restricts their further application in fields such as complex light field manipulation, waveguide display, image encryption, and information storage. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a meta-holographic device and its design method and imaging method, which aims to solve the problem of the limited imaging channels of current meta-holographic devices.

[0006] To achieve the above objectives, according to one aspect of the present invention, a design method for a meta-holographic device is provided, comprising:

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

[0008] S2: Utilize and The displacement distribution (Δ) required for the target two-dimensional nanostructure array in the target metaholographic device was calculated. x (x,y),Δ y Displacement distribution Δ in the x-direction of (x,y) xDisplacement distribution Δ in (x,y) and 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: Arrange each metaunit in the original two-dimensional nanostructure array according to the displacement distribution (Δ) x (x,y),Δ y The target two-dimensional nanostructure array is obtained by displacement of (x,y)).

[0010] S4: The target two-dimensional nanostructure array is disposed on a transparent substrate to obtain the target meta-holographic device; when incident light is incident on the transparent substrate along the x-direction and / or y-direction with a specific total internal reflection angle θ l When propagated to the target two-dimensional nanostructure array, the light will be modulated and diffracted into free space. The diffracted light of orders (l,0) and (0,l) will form holographic images corresponding to each diffraction order after propagating over a distance.

[0011] Furthermore, in S1, the phase modulation amount of the diffraction light at each diffraction order in the x-direction of the target metaholographic device to be designed is obtained. include:

[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 field of each diffraction order on the target imaging plane. Then, the root mean square errors RMSE1, RMSE2, ..., RMSE of the normalized intensity distribution of each diffracted light field and the corresponding normalized intensity distribution of the target image are determined. m On the imaging plane, the amplitude distribution of each diffracted light field is replaced with the normalized square root intensity distribution of each target image in the x-direction, while retaining the phase value, to obtain a new light field distribution. Utilizing the new light field distribution Calculate the light field distribution on the holographic surface

[0014] S103: Through formula Calculate the new phase distribution ω l It is the weighting factor for each diffraction channel in the x-direction; k l It is an integer parameter introduced by phase unwrapping;

[0015] S104: Based on the new phase distribution Update the light field distribution on the holographic surface And return to S103, until the result calculated by S103 is obtained. It tends to converge, and when it converges corresponding Assign to Finally, the phase modulation of the diffracted light at each order in the x-direction is obtained.

[0016] Furthermore, ω l It is the weighting factor of each diffraction channel in the x-direction, derived from... Calculated; k l Depend on Calculated.

[0017] Furthermore, in S1, the phase modulation of the diffracted light at each order in the y-direction of the target metaholographic device to be designed is obtained. include:

[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 diffraction field of each order on the target imaging plane. Then, the root mean square errors RMSE'1, RMSE'2, ..., RMSE' of the normalized intensity distribution of each diffracted light field and the corresponding normalized intensity distribution of the target image are determined. m On the imaging plane, the amplitude distribution of each diffracted light field is replaced with the normalized square root intensity distribution of each target image in the x-direction, while retaining the phase value, to obtain a new light field distribution. Utilizing the new light field distribution Calculate the light field distribution on the holographic surface

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

[0021] S114: Based on the new phase distribution Update the light field distribution on the holographic surface And return to S113, until the result calculated by S113 is obtained. It tends to converge, and when it converges corresponding Assign to Finally, the phase modulation of the diffraction light at each diffraction order in the y-direction is obtained.

[0022] Furthermore, ω' l It is the weighting factor of each diffraction channel in the y-direction, derived from... Calculated; by Calculated.

[0023] Furthermore, the method further includes: setting the incident light vacuum wavelength λ in the diffraction channel with diffraction orders of (l,0) and (0,l). l The total internal reflection angle θ of the incident light as it propagates in the transparent substrate l satisfy: Where, n sub This refers to the refractive index of the substrate.

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

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

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

[0027] When the incident light with a vacuum wavelength of λ1 in the first channel is incident on the transparent substrate along the x direction and propagates to the target two-dimensional nanostructure array at a specific total reflection angle θ1, it is modulated and diffracted into free space. The diffracted light with an order of (1,0) propagates over a distance to form the first monochromatic holographic image.

[0028] When the incident light with a vacuum wavelength of λ2 in the second channel is incident on the transparent substrate along the x-direction and propagates to the target two-dimensional nanostructure array at a specific total internal reflection angle θ2, it will be modulated and diffracted into free space. The diffracted light with an order of (2,0) propagates over a distance to form a second monochromatic holographic image.

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

[0030] When the incident light with a vacuum wavelength of λ2 in the fourth channel is incident along the y direction onto the transparent substrate and propagates to the target two-dimensional nanostructure array at a specific total reflection angle θ2, it will be modulated and diffracted into free space. The diffracted light with an order of (0,2) propagates over a distance to form the fourth monochrome holographic image.

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

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

[0034] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0035] (1) This invention provides a design method for a metaholographic device, which obtains the phase modulation amount of the diffracted light at each order of the target metaholographic device to be designed. Then, the displacement distribution (Δx(x,y), Δy(x,y)) of the metaunits is calculated; and each metaunit in the periodically distributed original two-dimensional nanostructure array is arranged according to the displacement distribution (Δx(x,y), Δy(x,y)). x (x,y),Δ y The target two-dimensional nanostructure array is obtained by displacement (x, y), and then the target two-dimensional nanostructure array is placed on a transparent substrate to obtain the target metaholographic device. This metaholographic device has a high operating bandwidth, and under illumination at different wavelengths and preset total reflection angles, it can achieve multi-channel holographic imaging by multiplexing multiple diffraction orders; furthermore, it can selectively project monochrome holographic images or color holographic images.

[0036] (2) Based on the new phase distribution in this scheme Update the light field distribution on the holographic surface And iterate repeatedly until the result is obtained. It tends to converge, and when it converges corresponding Assign to The advantage of this method is that it can achieve diffraction-order multiplexing multi-channel holographic imaging by optimizing the holographic phase in the x-direction, thereby increasing the information capacity.

[0037] (3) Based on the new phase distribution in this scheme Update the light field distribution on the holographic surface And iterate repeatedly until the result is obtained. It tends to converge, and when it converges corresponding Assign to The advantage of this design is that it can achieve diffraction-order multiplexing multichannel holographic imaging by optimizing the holographic phase in the y-direction, thereby increasing the information capacity.

[0038] (4) This plan utilizes Calculate the weighting factor of each diffraction channel in the x-direction, using... Calculate the weighting factor of each diffraction channel in the y-direction. The advantage of this design is that it can balance the image quality of each diffraction channel.

[0039] (5) This plan utilizes Integer parameter k introduced by calculating phase unwrapping l ,use Integer parameter k' introduced by calculating phase unwrapping l The advantage of this design is that it can solve the problem of algorithm iteration non-convergence caused by phase folding of the light field during diffraction propagation calculation.

[0040] (6) In this scheme, the vacuum wavelength λ of the incident light in the diffraction channel with diffraction order (l,0) and (0,l) is set. l The total internal reflection angle θ of the incident light as it propagates in the transparent substrate l satisfy: This design allows for control over the diffracted light of the target order to exit along the device normal.

[0041] (7) The total internal reflection angle θ of the incident light propagating in the transparent substrate in the diffraction channels with diffraction orders (l,0) and (0,l) in this scheme. l Satisfy: n sub sinθ l ≥ln0; This design can avoid crosstalk between channels. Attached Figure Description

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

[0043] Figure 2This is a schematic diagram of the multi-channel display metaholographic device provided in Embodiment 2 of the present invention;

[0044] Figure 3 This is a schematic diagram of several commonly used meta-units provided in Embodiment 2 of the present invention, wherein 1 refers to a two-dimensional nanostructure array and 2 refers to a transparent substrate;

[0045] Figure 4 The flowchart of the pure phase holography algorithm used in the design of the multi-channel metaholographic device provided in Embodiment 1 of the present invention is shown.

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

[0047] Figure 6 Showing Figure 5 A schematic diagram of the imaging results of the meta-holographic device;

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

[0049] Figure 8 Showing Figure 7 A schematic diagram of the imaging results of the meta-holographic device. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0051] Example 1

[0052] like Figure 1 As shown, this embodiment provides a design method for a metaholographic device, including: S1-S4. Wherein, S1: Obtain the phase modulation amount of the target metaholographic device to be designed for each order of diffraction light. This represents the amount of phase modulation of the diffracted light at each order in the x-direction; S1 represents the phase modulation amount of the diffracted light at each order in the y direction; l is the diffraction order number, l∈[1,m], and m is the highest diffraction order number; wherein, the wave vector component of each order of diffracted light along the grating plane is opposite to the grating vector direction; S2: using and The displacement distribution (Δ) required for the target two-dimensional nanostructure array in the target metaholographic device was calculated. x(x,y),Δ y Displacement distribution Δ in the x-direction of (x,y) x Displacement distribution Δ in (x,y) and y direction y (x,y); P is the period of the original two-dimensional nanostructure array along the x and y directions; S3: The metaunits in the original two-dimensional nanostructure array are arranged according to the displacement distribution (Δ). x (x,y),Δ y S4: The target two-dimensional nanostructure array is obtained by displacement (x, y); S5: The target two-dimensional nanostructure array is placed on a transparent substrate to obtain the target meta-holographic device; When incident light is incident on the transparent substrate along the x and / or y directions and with a specific total internal reflection angle θ l When propagated to the target two-dimensional nanostructure array, the light is modulated and diffracted into free space. The diffracted light of orders (k,0) and (0,l) propagates over a distance to form holographic images corresponding to each diffraction order. The structure of the metaholographic device is as follows: Figure 2 As shown, the structure of the meta-unit in the meta-holographic device is as follows: Figure 3 As shown.

[0053] To achieve multi-channel holographic display, phase encoding is implemented using the principle of detour phase modulation. A phase optimization algorithm is then used to encode the target phase in each diffraction order to achieve high-resolution imaging. For a periodically distributed original two-dimensional nanostructure array, if a displacement distribution Δ in the x-direction is applied to each unit structure... x (x,y), then the diffracted light of order (l,0) diffracted from this unit structure into free space will be introduced into the phase modulation distribution. P represents the period of the original two-dimensional nanostructure array with the said periodic distribution along the x and y directions. Through Figure 4 The phase optimization algorithm shown can achieve multi-channel diffraction order multiplexing with diffraction orders (1,0), (2,0), ..., (m,0). By selecting appropriate materials, wavelengths of illumination light, total reflection angles of illumination light, and unit cell periods, monochromatic holographic imaging with m channels can be achieved. Similarly, if a displacement distribution Δ in the x-direction is applied to each unit cell structure... y Similarly, (x,y) can achieve multi-channel diffraction order reuse with diffraction orders of (0,1), (0,2), ..., (0,m). According to this invention, for a periodically distributed original two-dimensional nanostructure array, the required displacement distribution (Δ) is applied to the nanometers in each unit structure. x (x,y),Δ y (x,y)), the resulting detour-phase metaholographic device, combined with Figure 4 The phase optimization algorithm shown can achieve high-resolution holographic imaging with 2m channels. (Further details follow.) Figure 4 The specific implementation of the phase optimization algorithm shown is illustrated.

[0054] As an optional implementation method, the process is as follows: Figure 4 As shown, in step S1, the phase modulation of the diffraction light at each diffraction order in the x-direction is obtained for the target metaholographic device to be designed. Includes: S101: Randomly generate a phase distribution according to Calculate the initial light field of each diffraction channel. Where j represents the imaginary unit; S102: Based on each of the initial light fields Calculate the diffraction field of each diffraction order on the target imaging plane. Then, the root mean square errors RMSE1, RMSE2, ..., RMSE of the normalized intensity distribution of each diffracted light field and the corresponding normalized intensity distribution of the target image are determined. m On the imaging plane, the amplitude distribution of each diffracted light field is replaced with the normalized square root intensity distribution of each target image in the x-direction, while retaining the phase value, to obtain a new light field distribution. Utilizing the new light field distribution Calculate the light field distribution on the holographic surface S103: Through formula Calculate the new phase distribution ω l It is the weighting factor for each diffraction channel in the x-direction; k l These are integer parameters introduced by phase unwrapping; S104: based on the new phase distribution Update the light field distribution on the holographic surface And return to S103, until the result calculated by S103 is obtained. It tends to converge, and when it converges corresponding Assign to Finally, the phase modulation of the diffracted light at each order in the x-direction is obtained. Where, ω l It is the weighting factor of each diffraction channel in the x-direction, derived from... Calculated. As an optional implementation, k l Depend on Calculated.

[0055] As an optional implementation, in step S1, the phase modulation of the diffracted light at each order in the y-direction of the target metaholographic device to be designed is obtained. Includes: S111: Randomly generate a phase distribution according to Calculate the initial light field of each diffraction channel. S112: Based on each of the initial light fields Calculate the diffraction field of each order on the target imaging plane. Then, the root mean square errors RMSE'1, RMSE'2, ..., RMSE' of the normalized intensity distribution of each diffracted light field and the corresponding normalized intensity distribution of the target image are determined. m On the imaging plane, the amplitude distribution of each diffracted light field is replaced with the normalized square root intensity distribution of each target image in the x-direction, while retaining the phase value, to obtain a new light field distribution. Utilizing the new light field distribution Calculate the light field distribution on the holographic surface S113: Pass Calculate the new phase distribution ω' l It is the weighting factor of each diffraction channel in the y-direction; k' l These are integer parameters introduced by phase unwrapping; S114: based on the new phase distribution Update the light field distribution on the holographic surface And return to S113, until the result calculated by S113 is obtained. It tends to converge, and when it converges corresponding Assign to Finally, the phase modulation of the diffraction light at each diffraction order in the y-direction is obtained. Where, ω' l It is the weighting factor of each diffraction channel in the y-direction, derived from... Calculated. As an optional implementation, k' l Depend on calculate.

[0056] As an optional implementation, the design method further includes: setting the vacuum wavelength λ of the incident light in the diffraction channel with diffraction orders of (l,0) and (0,l). l The total internal reflection angle θ of incident light propagating in a transparent substrate l satisfy: Where, n sub This refers to the refractive index of the substrate. Furthermore, this design method also includes: setting the total internal reflection angle θ of incident light propagating in the transparent substrate in diffraction channels with diffraction orders of (l,0) and (0,l). l Satisfy: nsub sinθ l ≥ln0; where n sub This refers to the refractive index of the substrate, where n0 is the refractive index of air.

[0057] Specifically, by rationally selecting system parameters and materials, it is possible to selectively achieve vertical emission of individual target diffraction orders into free space, thereby achieving crosstalk-free holographic imaging. Specifically, the following conditions must be met. And n sub sinθ l ≥ln0 (l=1,2,3…). Where n sub This refers to the substrate refractive index, θ l λ refers to the total internal reflection angle of a light beam propagating in a substrate. l Let be the vacuum wavelength of the diffracted light with diffraction orders (l,0) and (0,l), P be the period of the unit cell structure, and n0 be the air refractive index. Clearly, to achieve crosstalk-free holographic imaging that reuses four diffraction orders (1,0), (2,0), (0,1), and (0,2), at least n0 must be satisfied. sub ≥2.0. If a suitable substrate material with a higher refractive index can be found, multi-channel crosstalk-free holographic imaging with multiple diffraction orders can also be achieved. On the other hand, if suitable parameters are selected such that λ1, λ2, and λ3 correspond to the red, green, and blue bands respectively, the equation can be satisfied. This allows for the reuse of diffraction orders (1,0), (2,0), (3,0) or (0,1), (0,2), (0,3) to achieve color holographic display.

[0058] Example 2

[0059] This embodiment provides a meta-holographic device, which is designed using the above-described design method for meta-holographic devices. Figure 2 For the reason Figure 3 The meta-holographic device structure shown comprises meta-units arranged in different positions, including nanopillars of the same size. This implementation utilizes a roundabout phase modulation method, where phase modulation is typically applied to the diffracted light in the transmission direction. The applied phase modulation amount can be expressed as... and By designing the positional distribution (Δ) of the nanopillar array x (x,y),Δ y (x,y)) can achieve precise phase modulation of diffracted light with diffraction orders (l,0) and (0,l).

[0060] The multi-channel display metaholographic device in this embodiment includes multiple periodically arranged metaunits (metaatoms). The metaatoms are artificial subwavelength structures made of materials that are transparent or have low absorption in the target light band. Under illumination by incident light of different wavelengths and different total reflection angles, the multi-channel display metaholographic device can selectively project high-resolution, crosstalk-free monochrome holographic images or high-resolution color holographic images along the device's normal direction.

[0061] The columnar structure is made of a material that is transparent or has low absorption in the visible light band, with either a rectangular base (square column) or an elliptical base ((ellipsoidal) cylinder). P is the metacellular unit period, L is the side length of the base, H is the height of the nanopillar, and D1 and D2 are the sizes of the minor and major axes, respectively. It is worth noting that this invention does not mandate anisotropic or isotropic unit structures in principle; that is, the given dimensional parameters D1 and D2 can have equal or unequal values. Similarly, this invention does not impose any requirements on the polarization state of the incident light. The unit structure parameters and the polarization state of the incident light only affect the diffraction efficiency; as long as the diffraction efficiency is high enough to achieve clear imaging, it is acceptable. To maintain operating efficiency in the target wavelength band, the metaholographic device is constructed from a dielectric material with both high refractive index and low loss in the target wavelength band.

[0062] Preferred materials include titanium dioxide (TiO2) and silicon nitride (SiN). x Materials include silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and hafnium dioxide (HfO2). High diffraction efficiency is achieved by designing appropriate metaunit shapes and structural parameters, and accurate phase modulation is achieved by designing the positional distribution of nanopillar arrays.

[0063] Example 3

[0064] This embodiment provides a four-channel crosstalk-free imaging method for metaholographic devices, such as... Figure 5 and Figure 6As shown, the process includes: when a first incident light with a vacuum wavelength of λ1 is incident along the x-direction onto a transparent substrate and propagates to a two-dimensional nanostructure array at a specific total internal reflection angle θ1, it will be modulated and diffracted into free space. The diffracted light of order (1,0) propagates over a distance to form a first monochromatic holographic image; when a second incident light with a vacuum wavelength of λ2 is incident along the x-direction onto a transparent substrate and propagates to a two-dimensional nanostructure array at a specific total internal reflection angle θ2, it will be modulated and diffracted into free space. The diffracted light of order (2,0) propagates over a distance to form a second monochromatic holographic image. When a third incident light with a vacuum wavelength of λ1 is incident along the y-direction onto a transparent substrate and propagates to a two-dimensional nanostructure array at a specific total internal reflection angle θ1, it will be modulated and diffracted into free space. The diffracted light of order (0,1) propagates over a distance to form a third monochromatic holographic image. When a fourth incident light with a vacuum wavelength of λ2 is incident along the y-direction onto a transparent substrate and propagates to a two-dimensional nanostructure array at a specific total internal reflection angle θ2, it will be modulated and diffracted into free space. The diffracted light of order (0,2) propagates over a distance to form a fourth monochromatic holographic image.

[0065] Figure 5 This is a first embodiment of multi-channel imaging for a multi-channel metaholographic device, enabling multi-channel monochromatic metaholographic imaging. The device comprises 1 transparent substrate and 2 two-dimensional nanostructure arrays. When incident light 3 propagates along the x-direction at a specific total internal reflection angle in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (1,0) propagates over a distance to form the first high-resolution holographic image 4. When incident light 5 propagates along the x-direction at a specific total internal reflection angle in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (2,0) propagates over a distance to form the second high-resolution holographic image 6. When incident light 7 propagates along the y-direction at a specific total internal reflection angle in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (0,1) propagates over a distance to form the third high-resolution holographic image 8. When incident light 9 propagates along the y-direction at a specific total internal reflection angle in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (0,2) propagates over a distance to form the fourth high-resolution holographic image 10.

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

[0067] Example 4

[0068] This embodiment provides a two-channel color holographic imaging method for metaholographic devices, such as... Figure 7 and Figure 8As shown, the process includes: when a first red incident light with a vacuum wavelength of λ'1 propagates along the x-direction at a specific total internal reflection angle θ'1 in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (1,0) propagates over a distance to form the first R component of the first color holographic image; when a first green incident light with a vacuum wavelength of λ'2 propagates along the x-direction at a specific total internal reflection angle θ'2 in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (2,0) propagates over a distance to the first R component of the first color holographic image. The propagation over a distance forms the first G component of the first color holographic image; when the first blue incident light with a vacuum wavelength of λ'3 propagates along the x-direction at a specific total internal reflection angle θ'3 in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (3,0) propagates over a distance to form the first B component; 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... The first color holographic image will be formed. When the second red incident light, with a vacuum wavelength of λ'1, propagates along the y-direction at a specific total reflection angle θ'1 in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (0,1) propagates a certain distance to form the second R component. Similarly, when the second green incident light, with a vacuum wavelength of λ'2, propagates along the y-direction at a specific total reflection angle θ'2 in the substrate to the two-dimensional nanostructure array, it will be modulated and diffracted into free space. The diffracted light of order (0,2) propagates a certain distance to the second R component. The propagation of the second blue incident light with a vacuum wavelength of λ'3 along the y-direction at a specific total internal reflection angle θ'3 in the substrate will form the second G component. When the second blue incident light is propagated to the two-dimensional nanostructure array along the y-direction at a specific total internal reflection angle θ'3, it will be modulated and diffracted into free space. The diffracted light with an order of (0,3) will propagate over a distance to form the second B component. 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 specific incident angles, the second R component, the second G component, and the second B component will form the second color holographic image.

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

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

[0071] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of designing a superstructured holographic device, characterized in that, Comprising: S1: obtaining phase control amount (Δφ x, l (x,y),Δφ y, l (x, y)) of each order of diffraction light of the target metasurface holographic device to be designed; Δφ x, l (x, y) represents the phase control amount of each order of diffraction light in the x direction; Δφ y, l (x, y) represents the phase control amount of each order of diffraction light in the y direction; l is the diffraction order number, l ∈ [1, m], and m is the highest diffraction order number. S2: using and The displacement distribution (Δ x (x, y), Δ y (x, y)) in the x direction and the displacement distribution (Δ x (x, y) and the displacement distribution (Δ y (x, y) in the y direction of the target two-dimensional nanostructure array in the target metasurface holographic device are calculated. P is the period of the original two-dimensional nanostructure array along the x and y directions. S3: displacing each superunit 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: disposing the target two-dimensional nanostructure array on a transparent substrate to obtain the target super-structured holographic device; when incident light is incident on the transparent substrate along the x direction and / or the y direction and at a specific total reflection angle propagating to the target two-dimensional nanostructure array, being modulated and diffracted into free space, the diffraction order being and the diffracted light of the diffraction order corresponding to a holographic image formed after a distance of propagation; The S1 obtains the phase control amount Δφ of the target metaholographic device to be designed for the diffraction light of each diffraction order in the x direction x, l (x, y), comprising: S101: Randomly generate a phase distribution , according to calculating the initial light field of each diffraction channel , , , where j represents the imaginary unit; S102: calculating the diffraction light field of each diffraction order on the target imaging surface based on each of the initial light fields , , , , , , , , , ; replacing the amplitude distribution of each diffraction light field on the imaging surface with the normalized intensity square root distribution of each target image in the x direction while retaining the phase value to obtain a new light field distribution , , , ; calculating the light field distribution on the holographic surface using the new light field distribution , , , , , , ;​​​ S103: Calculate the new phase distribution by the formula ; ; is the weight factor of each diffraction channel in the x direction; is the integer parameter introduced by phase unwrapping. S104: According to the new phase distribution updating the light field distribution on the holographic surface , , , , and returning to S103 until the S103 calculated tends to converge, and when converging the corresponding l is assigned to Δφ x, l (x, y), and finally the x-direction diffraction light phase control amount Δφ x, l (x, y) of each order is obtained; The S1 obtains the phase control amount Δφ of each order of diffracted light in the y direction of the target metasurface holographic device to be designed y, l (x, y), comprising: S111: Randomly generate a phase distribution Calculate initial light field of each diffraction channel ;​​​​​ S112: calculating the diffraction light field of each order on the target imaging plane based on each of the initial light fields , , , , , , , , , ; replacing the amplitude distribution of each diffraction light field on the imaging plane with the normalized intensity square root distribution of each target image in the x direction while retaining the phase value to obtain a new light field distribution , , , ; calculating the light field distribution on the holographic plane using the new light field distribution , , , , , , ;​​​ S113: by calculating a new phase distribution ; is a weight factor for each diffraction channel in the y-direction; is an integer parameter introduced by phase unwrapping; S114: according to the new phase distribution updating the light field distribution on the holographic surface , , , , and returning to S113 until the S113 calculation tends to converge, and when converging the corresponding l is assigned to Δφ y, l (x, y), and finally the diffraction light phase control amount Δφ y, l (x, y) of each diffraction order in the y direction is obtained.

2. The design method of a superstructured holographic device according to claim 1, wherein are the weight factors for each diffraction channel in the x direction, calculated from are calculated from are calculated from​ 3. The design method of a superstructured holographic device according to claim 1, wherein are the weight factors for each diffraction channel in the y direction, calculated from are calculated from are calculated from​ 4. The design method of a superstructured holographic device according to claim 1, wherein, The method further comprises: setting the incident light vacuum wavelength and the diffraction order of the diffraction channel to satisfy: and the total reflection angle of the incident light when propagating in the transparent substrate satisfy: ; wherein, refers to the substrate refractive index.

5. The design method of a superstructured holographic device according to claim 1, wherein The method further comprises setting the total reflection angle of the incident light in the transparent substrate when propagating in the diffraction order and of the diffraction channel satisfies: ; wherein is the substrate refractive index, is the air refractive index.

6. A meta-holographic device, characterized in that The design method of the super-structured holographic device according to any one of claims 1-5.

7. A four-channel imaging method of the superstructured holographic device of claim 6, characterized in that, Comprising: The vacuum wavelength of the control first channel is incident light of the wavelength of propagates to the target two-dimensional nanostructure array, is modulated and diffracted into free space, and the order of the diffracted light is After a distance of propagation, a first amplitude monochromatic holographic image is formed. The vacuum wavelength of the second channel is incident light with wavelength of propagating to the target two-dimensional nanostructure array will be manipulated and diffracted into free space with order of The diffracted light with wavelength of propagates for a distance to form a second monochromatic holographic image. The vacuum wavelength of the third channel is incident light of the wavelength of is incident to the transparent substrate along the y direction and at a specific total reflection angle propagates to the target two-dimensional nanostructure array, is modulated and diffracted into free space, and the order of the diffracted light is The third monochromatic holographic image is formed after a distance of propagation. The vacuum wavelength of the fourth channel is incident light of the wavelength of is incident to the transparent substrate along the y direction and is totally reflected at a specific angle to the target two-dimensional nanostructure array, is modulated and diffracted into free space, and the order of the diffracted light is The fourth monochromatic holographic image is formed after a distance of propagation.

8. A two-channel color holographic imaging method of the superstructured holographic device of claim 6, characterized in that, Comprising: a first red incident light with a vacuum wavelength of is controlled to propagate along the x direction at a certain total reflection angle to the target two-dimensional nanostructure array in the substrate, and is diffracted into free space, the diffraction order being a first R component of the first color holographic image is formed after a distance of propagation of the diffracted light; a first green incident light with a vacuum wavelength of is controlled to propagate along the x direction at a certain total reflection angle to the target two-dimensional nanostructure array in the substrate, and is diffracted into free space, the diffraction order being a first G component of the first color holographic image is formed after a distance of propagation of the diffracted light; a first blue incident light with a vacuum wavelength of is controlled to propagate along the x direction at a certain total reflection angle to the target two-dimensional nanostructure array in the substrate, and is diffracted into free space, the diffraction order being a first B component is formed after a distance of propagation of the diffracted light; when the first red incident light, the first green incident light and the first blue incident light are incident simultaneously, the first R component, the first G component and the first B component form the first color holographic image. The control vacuum wavelength of the second red incident light is The second red incident light is controlled to propagate in the substrate along the y direction at a specific total reflection angle When propagating to the target two-dimensional nanostructure array, the second red incident light is regulated and diffracted into free space, and the diffraction light with an order of propagates for a distance to form a second R component; the control vacuum wavelength of the second green incident light is The second green incident light is controlled to propagate in the substrate along the y direction at a specific total reflection angle When propagating to the target two-dimensional nanostructure array, the second green incident light is regulated and diffracted into free space, and the diffraction light with an order of propagates for a distance to form a second G component; the control vacuum wavelength of the second blue incident light is The second blue incident light is controlled to propagate in the substrate along the y direction at a specific total reflection angle When propagating to the target two-dimensional nanostructure array, the second blue incident light is regulated and diffracted into free space, and the diffraction light with an order of propagates for a distance to form a second B component; 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 a specific incident angle respectively, the second R component, the second G component, and the second B component form a second full-color holographic image.

Images