A broadband holographic generation device with arbitrary wavelength coding and design method

Abstract

The present invention discloses a broadband holographic generation device with arbitrary wavelength coding and a design method, which relate to the field of metasurface holographic imaging. The design method comprises: iteratively generating the phase distribution of an arbitrary wavelength-coded pure phase Fresnel hologram through a Fienup algorithm; generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-coded pure phase Fresnel hologram; loading the phase of the pure phase Fresnel hologram onto a P-B phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength-coded holography; the device manufactured by the above method has the advantages of flexible wavelength coding, high resolution, high capacity, large viewing angle, low loss, and the like.

Description

Technical Field

[0001] The present invention relates to the field of metasurface holographic imaging, and in particular to a broadband holographic generation device with arbitrary wavelength coding and a design method thereof. Background Art

[0002] Metasurface holography is a new holographic implementation method that combines computational holography with a metasurface platform. Compared with traditional holography, it has the advantages of high resolution, large viewing angle, low loss, and no need for reference light assistance. In addition, by utilizing the metasurface's ability to control different dimensions of light and combining the phase with other physical dimensions to further expand it, the holographic information capacity and encryption capabilities can be effectively improved. Among them, polarization and orbital angular momentum have been widely used in holographic multiplexing due to their mode orthogonality. Similarly, wavelengths are also orthogonal, and encoding holograms into different wavelengths can effectively increase their information capacity. Therefore, it is of great significance to study the independent control of light of different wavelengths to achieve wavelength-encoded metasurface holography.

[0003] In recent years, several methods for wavelength-encoded metasurface holography have been proposed, and to some extent, wavelength encoding has been achieved. However, these methods still face some challenges. For example, supramolecular metasurfaces composed of multiple microstructures can only achieve encoding at a fixed number of wavelengths due to the limited number of microstructures, and the phase mutation between adjacent pixels can generate significant crosstalk. Similarly, holograms generated by double-layer metasurfaces with optimized structures also face unsatisfactory resolution and contrast. While methods combining K-space engineering technology with multi-degree-of-freedom metasurfaces can achieve relatively ideal holographic images, they also generate redundant diffraction orders. Therefore, we need to explore a broadband holographic generation device and design method with arbitrary wavelength encoding. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of this application is to provide a broadband holographic generation device and design method with arbitrary wavelength coding, aiming to solve the problem of how to achieve flexible wavelength coding, high resolution, high capacity, large viewing angle and low loss of the device.

[0005] To solve the above technical problems, a first aspect of the embodiments of the present application provides a design method for a broadband holographic generation device with arbitrary wavelength coding, the method comprising:

[0006] Iteratively generating a phase distribution of an arbitrary wavelength-encoded pure phase Fresnel hologram through a Fienup algorithm, and generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram;

[0007] The phase of the pure phase Fresnel hologram is loaded onto the PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography.

[0008] As a further improved technical solution, the iterative generation of the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram by the Fienup algorithm and the generation of the pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram include:

[0009] calculating Fresnel forward diffraction of a plurality of first complex amplitudes to obtain a plurality of second complex amplitudes, and adding all of the second complex amplitudes to obtain a total complex amplitude;

[0010] Calculating the Fresnel back diffraction of the total complex amplitude to obtain a third complex amplitude, combining the phase of the third complex amplitude with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude, thereby completing the first iteration;

[0011] The fourth complex amplitude is used as the first complex amplitude of the next iteration and the iterative process is repeated until the number of iterations reaches a preset value or the holographic imaging error reaches a specified threshold, completing the iteration, and the phase of the total complex amplitude of the last iteration is used as the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram. A pure phase Fresnel hologram is generated based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram.

[0012] As a further improved technical solution, the phase of the pure phase Fresnel hologram is loaded onto the PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography, which includes:

[0013] Calculating the nanostructure rotation angle of the PB phase metasurface based on the pure phase Fresnel hologram;

[0014] A PB phase metasurface is constructed based on the rotation angle of the nanostructure to obtain a target PB phase metasurface, and the target PB phase metasurface is used as a broadband holographic generation device.

[0015] As a further improved technical solution, several first complex amplitudes are obtained by combining several target amplitudes with random phases respectively.

[0016] As a further improved technical solution, the step of calculating the Fresnel forward diffraction of a plurality of first complex amplitudes to obtain a plurality of second complex amplitudes, and adding all of the second complex amplitudes to obtain a total complex amplitude includes:

[0017] calculating Fresnel forward diffraction of a plurality of first complex amplitudes at a preset wavelength and a preset diffraction distance respectively to obtain a plurality of second complex amplitudes;

[0018] All the second complex amplitudes are added together to obtain the total complex amplitude.

[0019] As a further improved technical solution, the Fresnel back diffraction of the total complex amplitude is calculated to obtain a third complex amplitude, and the phase of the third complex amplitude is combined with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude. Completing the first iteration includes:

[0020] Calculating the Fresnel back-diffraction of the total complex amplitude at a preset wavelength and a preset diffraction distance to obtain a third complex amplitude corresponding to the wavelength;

[0021] The feedback amplitude is obtained based on the third complex amplitude through a feedback function, and the phase of the third complex amplitude is combined with the feedback amplitude to form a fourth complex amplitude, thereby completing the first iteration.

[0022] As a further improved technical solution, the holographic imaging error reaching a specified threshold includes:

[0023] The holographic imaging error is obtained by calculating the sum of the squares of the differences between the amplitudes of several first complex amplitudes in each iteration and the target amplitude and dividing it by the number of the first complex amplitudes. The holographic imaging error is compared with a specified threshold. If the holographic imaging error is greater than or equal to the specified threshold, the holographic imaging error reaches the specified threshold.

[0024] A second aspect of the embodiments of the present application provides a broadband holographic generation device with arbitrary wavelength encoding, the device comprising:

[0025] A target PB phase metasurface comprises a substrate and a unit structure array arranged on the substrate, wherein the unit structure array is a plurality of rectangular nano unit structure arrays with different rotation angles.

[0026] As a further improved technical solution, the target PB phase metasurface also includes a dielectric layer, which is located between the substrate and the unit structure array.

[0027] As a further improved technical solution, the target PB phase metasurface composed of the substrate and the unit structure array, the substrate is made of silicon dioxide material, and the unit structure array is made of titanium dioxide material; the target PB phase metasurface formed by stacking the substrate, the dielectric layer and the unit structure array from bottom to top, the substrate is made of gold material, the dielectric layer is made of silicon dioxide material, and the unit structure array is made of gold material.

[0028] Beneficial effects: Compared with the prior art, the design method of the broadband holographic generation device with arbitrary wavelength coding of the present invention includes: iteratively generating the phase distribution of the arbitrary wavelength-coded pure phase Fresnel hologram through the Fienup algorithm, generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-coded pure phase Fresnel hologram; loading the phase of the pure phase Fresnel hologram onto the PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength-coded holography; the device made by the above method of the present invention has the advantages of flexible wavelength coding, high resolution, high capacity, large viewing angle, low loss, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural diagram of the broadband holographic generation device with arbitrary wavelength coding of the present invention.

[0030] Figure 2 This is a partially enlarged view of the broadband holographic generating device with arbitrary wavelength coding of the present invention.

[0031] Figure 3 It is a schematic diagram of the use of the broadband holographic generation device with arbitrary wavelength coding of the present invention.

[0032] Figure 4 It is a schematic diagram of the Fienup algorithm based on Fresnel diffraction arbitrary wavelength encoding of the present invention.

[0033] Figure 5 This is a flow chart of the Fienup algorithm based on Fresnel diffraction arbitrary wavelength encoding of the present invention.

[0034] Figure 6 It is a phase diagram of the wavelength-coded pure phase Fresnel hologram of three wavelengths of the present invention.

[0035] Figure 7 The present invention uses circularly polarized light of different wavelengths to enter the PB phase metasurface and produces diffraction patterns at preset spatial positions.

[0036] Figure 8 It is a flow chart of the design method of the broadband holographic generating device with arbitrary wavelength coding of the present invention.

[0037] Reference numerals:

[0038] 1. Substrate; 2. Unit structure array; 3. Dielectric layer.

[0039] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0040] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art will appreciate the application of other processes and / or the use of other materials.

[0043] It should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections; they may refer to direct connections or indirect connections through an intermediate medium; they may refer to internal communication between two components or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0044] After research, the inventors found that the existing technology has the following problems:

[0045] (1) There are still some problems with the existing wavelength-coded metasurface holographic methods. For example, the supramolecular metasurface composed of multiple microstructures can only be encoded at a few fixed wavelengths due to the number of microstructures, and the phase mutation between adjacent pixels will cause large crosstalk; the holograms produced by the double-layer metasurface with optimized structure also face the problem of unsatisfactory resolution and contrast; and the method of combining K-space engineering technology with multi-degree-of-freedom metasurface can achieve relatively ideal holographic images, but it will produce redundant diffraction orders.

[0046] In order to solve the above problems, various non-limiting implementation methods of the present application are described in detail below with reference to the accompanying drawings.

[0047] like Figure 1 As shown, the embodiment of the present application provides a design method for a broadband holographic generation device with arbitrary wavelength encoding, comprising the following steps:

[0048] S1, iteratively generating a phase distribution of an arbitrary wavelength-encoded pure phase Fresnel hologram through a Fienup algorithm, and generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram;

[0049] Specifically, the phase distribution of an arbitrary wavelength-encoded pure phase Fresnel hologram is iteratively generated by the Fienup algorithm. Based on the wavelength dependence of Fresnel diffraction, the algorithm iteratively diffracts multiple different images at different wavelengths in the forward and backward directions, and finally combines them into a pure phase Fresnel hologram. The phase of the pure phase Fresnel hologram is loaded onto a PB phase (Pancharatnam–Berry phase) metasurface to achieve holographic phase generation. Different wavelength light sources emit linearly polarized light, which is modulated into circularly polarized light and then incident on the metasurface. The transmitted light will generate a hologram corresponding to the wavelength at a preset spatial position, realizing the reproduction of the hologram. The pure phase Fresnel hologram is based on the wavelength dependence of Fresnel diffraction, and is formed by iterative Fresnel diffraction of multiple different images at different wavelengths. The so-called Fresnel hologram based on the wavelength dependence of Fresnel diffraction can be described as a Fresnel hologram encoded with a specified wavelength can only be reproduced at a specified position by a specified wavelength beam, while when reproduced by a non-specified wavelength beam, only a stray light spot can be presented at the specified position.

[0050] The Fienup algorithm is an arbitrary wavelength-encoded Fienup algorithm based on Fresnel diffraction. The Fienup algorithm is also called a wavelength-encoded holographic phase generation method. The Fresnel diffraction process can be described as follows:

[0051]

[0052] where f0 and f d Represent the complex amplitudes of the hologram plane and the object plane respectively, k is the wave vector, (x0, y0) and (x, y) are the coordinates of the hologram plane and the object plane, z is the reconstruction distance, F is the fast Fourier transform, and in the algorithm, we use FrT to represent the Fresnel diffraction process.

[0053] The iterative generation of the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram by the Fienup algorithm and the generation of the pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram include the following steps:

[0054] S101, calculating Fresnel forward diffraction of a plurality of first complex amplitudes to obtain a plurality of second complex amplitudes, and adding all of the second complex amplitudes to obtain a total complex amplitude;

[0055] S102, calculating the Fresnel back-diffraction of the total complex amplitude to obtain a third complex amplitude, combining the phase of the third complex amplitude with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude, thereby completing the first iteration;

[0056] S103, using the fourth complex amplitude as the first complex amplitude of the next iteration and repeating the iterative process until the number of iterations reaches a preset value or the holographic imaging error reaches a specified threshold, completing the iteration, using the phase of the total complex amplitude of the last iteration as the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram, and generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram.

[0057] Wherein, a plurality of first complex amplitudes are obtained by combining a plurality of target amplitudes with random phases respectively.

[0058] The step of calculating the Fresnel forward diffraction of a plurality of first complex amplitudes to obtain a plurality of second complex amplitudes, and adding all of the second complex amplitudes to obtain a total complex amplitude comprises the following steps:

[0059] S1011, respectively calculating Fresnel forward diffraction of a plurality of first complex amplitudes at a preset wavelength and a preset diffraction distance to obtain a plurality of second complex amplitudes;

[0060] S1012: Add all the second complex amplitudes to obtain the total complex amplitude.

[0061] Specifically, first, N target amplitudes With random phase Combine to get N first complex amplitudes At this time, the number of iterations k = 0; calculate the N first complex amplitudes f respectively. i k ,i=0,1,2KN at wavelength λ i And the Fresnel forward diffraction with a diffraction distance of z, we get N second complex amplitudes The wavelength and distance of diffraction can be freely set according to the requirements, and the total complex amplitude G is obtained by summing up all the second complex amplitudes. k .

[0062] The step of calculating the Fresnel back diffraction of the total complex amplitude to obtain a third complex amplitude, and combining the phase of the third complex amplitude with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude, and completing the first iteration includes:

[0063] S1021, calculating the Fresnel back-diffraction of the total complex amplitude at a preset wavelength and a preset diffraction distance to obtain a third complex amplitude corresponding to the wavelength;

[0064] S1022 : Based on the third complex amplitude and using a feedback function to obtain the feedback amplitude, the phase of the third complex amplitude is combined with the feedback amplitude to form a fourth complex amplitude, thereby completing the first iteration.

[0065] Specifically, the total complex amplitude is subjected to the wavelength λ i The Fresnel back diffraction with the diffraction distance z gives a new third complex amplitude f corresponding to the wavelength. i k+1 ,i=0,1,2K N, and there is Then based on the third complex amplitude and using the feedback function of amplitude replacement The feedback amplitude is obtained by replacing the amplitude, where K is the feedback coefficient, and the phase of the feedback amplitude and the third complex amplitude is Combined into the fourth complex amplitude f i k+1 , complete the first iteration and return to step S101, and the number of iterations k=k+1, use the fourth complex amplitude as the first complex amplitude of the next iteration and repeat the iterative process until the number of iterations reaches a preset value or the holographic imaging error reaches a specified threshold, complete the iteration, use the phase H of the total complex amplitude of the last iteration as the phase distribution of the hologram, and generate a pure phase Fresnel hologram based on the phase distribution of the hologram.

[0066] The holographic imaging error reaching a specified threshold value includes:

[0067] The holographic imaging error is obtained by calculating the sum of the squares of the differences between the amplitudes of several first complex amplitudes in each iteration and the target amplitude and dividing it by the number of the first complex amplitudes. The holographic imaging error is compared with a specified threshold. If the holographic imaging error is greater than or equal to the specified threshold, the holographic imaging error reaches the specified threshold.

[0068] S2, loading the phase of the pure phase Fresnel hologram onto the PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography.

[0069] The process of loading the phase of the pure phase Fresnel hologram onto a PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography comprises the following steps:

[0070] S201, calculating the nanostructure rotation angle of the PB phase metasurface based on the pure phase Fresnel hologram;

[0071] S202, constructing a PB phase metasurface based on the rotation angle of the nanostructure to obtain a target PB phase metasurface, and using the target PB phase metasurface as a broadband holographic generation device.

[0072] Specifically, the nanostructure rotation angle θ of the PB phase metasurface is related to the additional phase relationship The nanostructure rotation angle of the PB phase metasurface is calculated, and the PB phase metasurface is constructed based on the nanostructure rotation angle to obtain the target PB phase metasurface. The target PB phase metasurface is used as a broadband holographic generation device, so that the phase H of the total complex amplitude of the last iteration can be loaded onto the PB phase metasurface with broadband response. Light sources of different wavelengths emit linearly polarized light, which is modulated into circularly polarized light and then incident on the metasurface. The transmitted light will generate a hologram corresponding to the wavelength at a preset spatial position to achieve arbitrary wavelength-encoded holographic imaging.

[0073] The metasurface described in the present invention is a TiO2-SiO2 type metasurface, which is composed of multiple unit structure arrays on the same plane. Through parameter optimization, the unit structure has a high transmittance in multiple working bands and can perform phase modulation from 0 to 2π on left-handed circularly polarized light or right-handed circularly polarized light.

[0074] Compared with the prior art, the design method of the broadband holographic generation device with arbitrary wavelength coding of the present invention includes: iteratively generating the phase distribution of the arbitrary wavelength-coded pure phase Fresnel hologram through the Fienup algorithm, generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-coded pure phase Fresnel hologram; loading the phase of the pure phase Fresnel hologram onto the PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength-coded holography; the device made by the above method of the present invention has the advantages of flexible wavelength coding, high resolution, high capacity, large viewing angle, low loss, etc.

[0075] Based on the above-mentioned design method of a broadband holographic generation device with arbitrary wavelength encoding, this embodiment provides a broadband holographic generation device with arbitrary wavelength encoding, including:

[0076] A target PB phase metasurface includes a substrate 1 and a unit structure array 2 arranged on the substrate 1, wherein the unit structure array 2 is a plurality of rectangular nano unit structure arrays 2 with different rotation angles.

[0077] Preferably, the target PB phase metasurface further includes a dielectric layer 3 , and the dielectric layer 3 is located between the substrate 1 and the unit structure array 2 .

[0078] Preferably, the target PB phase metasurface composed of the substrate 1 and the unit structure array 2, the substrate 1 is made of silicon dioxide material, and the unit structure array 2 is made of titanium dioxide material; the target PB phase metasurface formed by stacking the substrate 1, the dielectric layer 3 and the unit structure array 2 from bottom to top, the substrate 1 is made of gold material, the dielectric layer 3 is made of silicon dioxide material, and the unit structure array 2 is made of gold material.

[0079] Specifically, there are two groups of implementation methods of the target PB phase metasurface. The target PB phase metasurface of the first implementation method is composed of a substrate 1 and a unit structure array 2. The target PB phase metasurface of the second implementation method is formed by stacking the substrate 1, the dielectric layer 3 and the unit structure array 2 from bottom to top. The second implementation method has one more dielectric layer 3 than the first implementation method, and the materials used in the two implementation methods are different. The process difficulty of using metal materials to manufacture the target PB phase metasurface is relatively low. Furthermore, the unit structure array 2 is a plurality of rectangular nano-unit structure arrays 2 with different rotation angles, and the rotation angle of each rectangular nano-unit structure is calculated based on the pure phase Fresnel hologram.

[0080] In the experiment, we used red (633nm), green (532nm), and blue (473nm) of visible light as coding wavelengths to achieve wavelength-coded holography of three wavelengths.

[0081] Specifically, a laser, polarizer, wave plate, and beam combiner are placed in sequence as the light input section. The laser is used to emit light beams of different wavelengths, the polarizer and wave plate are used to generate circularly polarized light, and the beam combiner is used to combine light of different wavelengths into a coaxial beam. In this way, circularly polarized light sources of different wavelengths are prepared.

[0082] Behind the metasurface, the receiving end consists of an objective lens, wave plate, polarizer, sleeve lens and CCD. The metasurface is a device that generates holograms. When circularly polarized light of different wavelengths is incident on the metasurface, a holographic image corresponding to the wavelength will be generated at the preset spatial position behind it; the objective lens is used to amplify the hologram generated by the metasurface; the wave plate and polarizer are used to filter out unnecessary polarized light; the sleeve lens and objective lens are matched to facilitate the insertion of devices between the two; the CCD is used to collect light intensity. This setting realizes the reproduction of holograms encoded at any wavelength.

[0083] It should be pointed out that in the description of the present invention, it should be understood that the terms "thickness", "up", "down", "inside" and "outside" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0084] Throughout this specification, reference to terms such as "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the exemplary descriptions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0085] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A design method for a broadband holographic generation device with arbitrary wavelength encoding, characterized in that: include: Iteratively generating a phase distribution of an arbitrary wavelength-encoded pure phase Fresnel hologram through a Fienup algorithm, and generating a pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram; The phase of the pure phase Fresnel hologram is loaded onto a PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography; The iterative generation of the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram by the Fienup algorithm, and the generation of the pure phase Fresnel hologram based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram include: calculating Fresnel forward diffraction of a plurality of first complex amplitudes to obtain a plurality of second complex amplitudes, and adding all of the second complex amplitudes to obtain a total complex amplitude; Calculating the Fresnel back diffraction of the total complex amplitude to obtain a third complex amplitude, combining the phase of the third complex amplitude with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude, thereby completing the first iteration; The fourth complex amplitude is used as the first complex amplitude of the next iteration and the iterative process is repeated until the number of iterations reaches a preset value or the holographic imaging error reaches a specified threshold, completing the iteration, and the phase of the total complex amplitude of the last iteration is used as the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram. A pure phase Fresnel hologram is generated based on the phase distribution of the arbitrary wavelength-encoded pure phase Fresnel hologram.

2. The method for designing a broadband holographic generation device with arbitrary wavelength coding according to claim 1, characterized in that: The method of loading the phase of the pure phase Fresnel hologram onto a PB phase metasurface to obtain a broadband holographic generation device for realizing arbitrary wavelength encoded holography comprises: Calculating the nanostructure rotation angle of the PB phase metasurface based on the pure phase Fresnel hologram; A PB phase metasurface is constructed based on the rotation angle of the nanostructure to obtain a target PB phase metasurface, and the target PB phase metasurface is used as a broadband holographic generation device.

3. The method for designing a broadband holographic generation device with arbitrary wavelength coding according to claim 2, characterized in that: A plurality of first complex amplitudes are obtained by combining a plurality of target amplitudes with random phases respectively.

4. The method for designing a broadband holographic generation device with arbitrary wavelength coding according to claim 3, characterized in that: The calculating of the Fresnel forward diffraction of the plurality of first complex amplitudes to obtain the plurality of second complex amplitudes, and adding all the second complex amplitudes to obtain the total complex amplitude includes: calculating Fresnel forward diffraction of a plurality of first complex amplitudes at a preset wavelength and a preset diffraction distance respectively to obtain a plurality of second complex amplitudes; All the second complex amplitudes are added together to obtain the total complex amplitude.

5. The method for designing a broadband holographic generation device with arbitrary wavelength coding according to claim 4, characterized in that: The calculating of the Fresnel back diffraction of the total complex amplitude to obtain a third complex amplitude, combining the phase of the third complex amplitude with the feedback amplitude obtained by the feedback function to form a fourth complex amplitude, and completing the first iteration includes: Calculating the Fresnel back-diffraction of the total complex amplitude at a preset wavelength and a preset diffraction distance to obtain a third complex amplitude corresponding to the wavelength; The feedback amplitude is obtained based on the third complex amplitude through a feedback function, and the phase of the third complex amplitude is combined with the feedback amplitude to form a fourth complex amplitude, thereby completing the first iteration.

6. The method for designing a broadband holographic generation device with arbitrary wavelength coding according to claim 5, characterized in that: The holographic imaging error reaching a specified threshold includes: The holographic imaging error is obtained by calculating the sum of the squares of the differences between the amplitudes of several first complex amplitudes in each iteration and the target amplitude and dividing it by the number of the first complex amplitudes. The holographic imaging error is compared with a specified threshold. If the holographic imaging error is less than or equal to the specified threshold, the holographic imaging error reaches the specified threshold.

7. A broadband holographic generation device with arbitrary wavelength coding, applied to the design method of a broadband holographic generation device with arbitrary wavelength coding according to claim 6, characterized in that: The device includes a target PB phase metasurface, which includes a substrate and a unit structure array arranged on the substrate. The unit structure array is a plurality of rectangular nano unit structure arrays with different rotation angles.

8. The broadband holographic generation device with arbitrary wavelength coding according to claim 7, characterized in that: The target PB phase metasurface further includes a dielectric layer, which is located between the substrate and the unit structure array.

9. The broadband holographic generation device with arbitrary wavelength coding according to claim 8, characterized in that: The target PB phase metasurface composed of the substrate and the unit structure array, the substrate is made of silicon dioxide material, and the unit structure array is made of titanium dioxide material; the target PB phase metasurface formed by stacking the substrate, the dielectric layer and the unit structure array from bottom to top, the substrate is made of gold material, the dielectric layer is made of silicon dioxide material, and the unit structure array is made of gold material.

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