A flexible metasurface holographic optical film and a method of making the same

Abstract

The application discloses a flexible metasurface holographic optical film and a preparation method thereof. The flexible metasurface holographic optical film comprises a flexible transparent substrate and a composite nanostructure array arranged above the flexible transparent substrate. The composite nanostructure array is an integrated structure of an elliptical column and a nanocone. The long axis, the short axis and the orientation angle of the elliptical column are used to control the polarization, the propagation phase and the geometric phase respectively. The cone angle and the height of the nanocone are used to control the amplitude and the propagation direction of light. The elliptical column is used to control the polarization and the phase, and the nanocone is used to control the amplitude and the propagation direction of light, so that the four-dimensional parameters of the light field are completely decoupled. The surface of the composite nanostructure array is coated with a photochromic layer and a piezoelectric composite layer, so that the double excitation programmable is realized. The photochromic molecular conformation of the photochromic layer is controlled by ultraviolet or visible light irradiation to change the dielectric environment, so that the polarization state and the holographic pattern are switched. The phase and the beam propagation direction are controlled, so that the global programmable control is realized.

Description

Technical Field

[0001] This invention relates to the field of optical film technology, and more specifically, to a flexible metasurface holographic optical film and its preparation method. Background Technology

[0002] Current optical films capable of modulating light fields are limited by fabrication processes and control mechanisms, facing numerous insurmountable bottlenecks. Existing metasurface technologies have not yet broken free from traditional frameworks, with the following specific shortcomings: 1. Traditional optical films have extremely limited functions: multilayer interference films can only control the amplitude of light (transmittance / reflectance) and cannot achieve phase and polarization control; diffractive optical elements and holographic films can only be designed for a single wavelength and a single function, are sensitive to the incident angle, and cannot achieve multi-dimensional coordinated control, making it difficult to adapt to the needs of complex optical systems.

[0003] 2. Dynamic control technology has fatal flaws: the few schemes that attempt to achieve dynamic control can only achieve simple switching of a single dimension (such as phase or polarization), and cannot achieve full-domain control of amplitude, phase, polarization and propagation direction; moreover, they mostly rely on a single excitation method (only illumination or only electric field), resulting in low control accuracy, slow response and difficulty in achieving programmable reuse. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a flexible metasurface holographic optical film with a fully programmable light field, which realizes four-dimensional independent decoupled control of light field amplitude, phase, polarization and propagation direction. It achieves dynamic programmable switching of optical functions through dual excitation of illumination and weak voltage, and realizes high diffraction efficiency in preparation. It is suitable for multiple scenarios such as AR / VR, information encryption, and integrated optics, filling the technical gap of fully programmable flexible metasurface optical films.

[0005] The technical problem to be solved by the present invention is achieved through the following technical solution: To address the aforementioned technical problems, this invention provides a flexible metasurface holographic optical film, comprising a flexible transparent substrate and a composite nanostructure array disposed above the flexible transparent substrate. The composite nanostructure array is an integrated structure of elliptical cylinders and nanocones. The major axis, minor axis, and orientation angle of the elliptical cylinders respectively regulate polarization, propagation phase, and geometric phase. The cone angle and height of the nanocones regulate the amplitude and the direction of light propagation. The surface of the composite nanostructure array is coated with a photochromic layer and a piezoelectric composite layer. By irradiating with ultraviolet or visible light, the conformation of the photochromic molecules in the photochromic layer is regulated to achieve switching between polarization states and holographic patterns. By driving the piezoelectric composite layer to deform with a weak voltage of less than or equal to 5V, the phase and beam propagation direction are regulated.

[0006] In a preferred embodiment of the flexible metasurface holographic optical film provided by the present invention, the composite nanostructure array is a core-shell material of TiO2 and ZnO.

[0007] In a preferred embodiment of the flexible metasurface holographic optical film provided by the present invention, the refractive index of the composite nanostructure array is greater than or equal to 2.4.

[0008] As a preferred embodiment of the flexible metasurface holographic optical film provided by the present invention, the structure within the composite nanostructure array is flexibly connected.

[0009] This invention provides a method for preparing a flexible metasurface holographic optical film, which is used to prepare a flexible metasurface holographic optical film as described in any of the above claims. A photoresist layer is disposed on a flexible transparent substrate. Instead of using electron beam lithography, a master is prepared by laser direct writing. The pattern of the master is transferred to the photoresist layer of the flexible transparent substrate by nanoimprinting. The composite nanostructure array is precisely arranged by directional self-assembly technology. Then, the filling medium is filled by atomic layer deposition, and the unwanted photoresist layer is peeled off.

[0010] The present invention has the following beneficial effects: The cone angle and height of the nanocones regulate the amplitude and light propagation direction, while the elliptical cylinders regulate polarization and phase. The nanocones further control the amplitude and light propagation direction, achieving complete decoupling of the four-dimensional parameters of the light field. The surface of the composite nanostructure array is coated with a photochromic layer and a piezoelectric composite layer, enabling dual-excitation programmability. By irradiating the photochromic layer with ultraviolet or visible light, the conformation of the photochromic molecules is modulated to change the dielectric environment, achieving polarization state and holographic pattern switching. A weak voltage of less than or equal to 5V drives the piezoelectric composite layer to deform, fine-tuning the nanostructure size and controlling the phase and beam propagation direction, achieving multifunctional dynamic switching and allowing for full-domain programmable control of phase and beam propagation direction. Detailed Implementation

[0011] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0012] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0013] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. The present invention will be described in detail below with reference to embodiments, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0014] This invention provides a flexible metasurface holographic optical film, comprising a flexible transparent substrate and a composite nanostructure array disposed on the flexible transparent substrate. The composite nanostructure array is an integrated structure of elliptical cylinders and nanocones, abandoning the single nanocylinder design. The major axis, minor axis, and orientation angle of the elliptical cylinders respectively control polarization, propagation phase, and geometric phase, while the cone angle and height of the nanocones control amplitude and light propagation direction. The elliptical cylinders are responsible for controlling polarization and phase, while the nanocones are responsible for controlling amplitude and light propagation direction, achieving complete decoupling of the four-dimensional parameters of the light field. The surface of the composite nanostructure array is coated with a photochromic layer and a piezoelectric composite layer, enabling dual-excitation programmability. By irradiating with ultraviolet or visible light, the conformation of the photochromic molecules in the photochromic layer is controlled to change the dielectric environment, thereby switching the polarization state and holographic pattern. By driving the piezoelectric composite layer to deform with a weak voltage of less than or equal to 5V, the nanostructure size is finely adjusted, and the phase and beam propagation direction are controlled, achieving multifunctional dynamic switching. The phase and beam propagation direction are controlled, making it programmable across the entire domain.

[0015] Furthermore, the composite nanostructure array uses TiO2 and ZnO as its core-shell material, which improves diffraction efficiency and light field confinement capability.

[0016] Furthermore, the refractive index of the composite nanostructure array is greater than or equal to 2.4.

[0017] Furthermore, the structure within the composite nanostructure array is flexibly connected, adapting to the bending and folding of flexible transparent substrates. When the bending radius is ≤5mm, the optical performance attenuation is ≤5%. It can be directly bonded to curved surfaces and irregular structures, adapting to scenarios such as AR / VR optical waveguides, flexible displays, and curved anti-counterfeiting, without the need for additional adaptation structures.

[0018] 1. Principle of Four-Dimensional Decoupling and Control of Light Field By employing an elliptical cylinder-nanocone composite nanostructure, complete orthogonal decoupling of amplitude, phase, polarization, and propagation direction is achieved: ① The major and minor axis dimensions of the elliptical cylinder respectively control the polarization state and propagation phase, and the orientation angle controls the geometric phase (φ_g=±2θ), covering the full phase range of 0π-2π, and is suitable for wide-band applications; ② The cone angle and height of the nanocone can modulate the amplitude (transmittance / reflectance) of light. Through the cone angle gradient design, the amplitude can be continuously adjusted. ③ The density of the spatial arrangement of the composite structure controls the direction of light propagation, enabling functions such as beam deflection and focusing. The four elements are independent of each other and do not interfere with each other, thus achieving full-domain control of the light field.

[0019] 2. Dual-response programmable control principle (1) Photochromic modulation: The azobenzene derivative photochromic layer coated on the surface of the nanostructure undergoes trans→cis isomerization under ultraviolet light irradiation, and the real part of the refractive index changes by Δn≈0.15~0.25. By changing the dielectric environment around the nanostructure, the phase response of the elliptical cylinder can be precisely controlled to achieve rapid switching of holographic patterns and polarization states (response time <10ms); the trans state is restored under visible light irradiation, realizing reversible modulation.

[0020] (2) Piezoelectric control: The piezoelectric polymer layer below the photochromic layer undergoes a small deformation (deformation rate <1%) under a weak voltage (≤5V), which drives the nanocone height and elliptical cylinder size to be finely adjusted, changing the amplitude and phase delay, and realizing precise control of the beam propagation direction and focusing accuracy; after the voltage is removed, it returns to its original state, and works in synergy with the photochromic control to achieve full-domain programmability.

[0021] 3. Principle of Multiple Function Reuse Combining spatial partitioning, polarization multiplexing, and wavelength multiplexing into a three-pronged strategy: ① Spatial partitioning: The thin film is divided into multiple micro-regions, each corresponding to a basic function (such as holography, focusing); ② Polarization multiplexing: The nanostructure design of the same micro-region is adapted to incident light with different polarization states, and different polarization light incident light activates different functions; ③ Wavelength reuse: Through the design of nanostructure size gradient, it can adapt to different wavelengths of incident light and realize the function switching under multiple wavelengths; the three work together to enable the same film to realize the dynamic reuse of more than 5 optical functions without functional interference.

[0022] 4. Principle of Maintaining High Optical Performance on Flexible Transparent Substrates A core-shell nanostructure of high-refractive-index TiO2 and ZnO (n≈2.5) and a low-refractive-index flexible transparent substrate (PET, n≈1.6) are selected to form a high refractive index contrast, which effectively confines the light field inside the nanostructure and avoids the degradation of optical performance caused by the deformation of the flexible substrate. At the same time, the nanostructure adopts a flexible connection design to adapt to the bending and folding of the substrate. When the bending radius is ≤5mm, the diffraction efficiency attenuation is ≤5%, ensuring stable use in flexible scenarios.

[0023] This invention provides a method for preparing a flexible metasurface holographic optical film, which is used to prepare a flexible metasurface holographic optical film as described in any of the above claims. A photoresist layer is disposed on a flexible transparent substrate. Instead of using electron beam lithography, a master is prepared by laser direct writing. The pattern of the master is transferred to the photoresist layer of the flexible transparent substrate by nanoimprinting. The composite nanostructure array is precisely arranged by directional self-assembly technology. Then, the filling medium is filled by atomic layer deposition, and the unwanted photoresist layer is peeled off.

[0024] The process of “master copying-nanoimprinting-self-assembly” eliminates the need for electron beam lithography. First, a low-cost master is prepared by laser direct writing. Then, the pattern is transferred to the photoresist layer (PET / COP) on a flexible transparent substrate by nanoimprinting. The nanostructures are precisely arranged by directional self-assembly technology, enabling large-area (square meter level) and low-cost mass production. The preparation efficiency is more than 10 times higher than that of existing technologies.

[0025] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] Obviously, the embodiments described above are merely some embodiments of this application, not all embodiments. This application provides preferred embodiments, but does not limit the patent scope of this application. This application can be implemented in many different forms; rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification, directly or indirectly applied to other related technical fields, are similarly within the scope of patent protection of this application.

Claims

1. A flexible metasurface holographic optical film, characterized in that, It includes a flexible transparent substrate and a composite nanostructure array disposed on the flexible transparent substrate; the composite nanostructure array is an integrated structure of elliptical cylinder and nanocone, the major axis, minor axis and orientation angle of the elliptical cylinder respectively regulate polarization, propagation phase and geometric phase, and the cone angle and height of the nanocone regulate the amplitude and propagation direction of light. The surface of the composite nanostructure array is coated with a photochromic layer and a piezoelectric composite layer. The photochromic molecular conformation of the photochromic layer is regulated by ultraviolet or visible light irradiation to achieve polarization state and holographic pattern switching. The piezoelectric composite layer is deformed by a weak voltage of less than or equal to 5V to achieve phase and beam propagation direction regulation.

2. The flexible metasurface holographic optical film according to claim 1, characterized in that, The composite nanostructure array is made of TiO2 and ZnO core-shell materials.

3. The flexible metasurface holographic optical film according to claim 1, characterized in that, The refractive index of the composite nanostructure array is greater than or equal to 2.

4.

4. The flexible metasurface holographic optical film according to claim 1, characterized in that, The structures within the composite nanostructure array are flexibly connected.

5. A method for preparing a flexible metasurface holographic optical film, used to prepare the flexible metasurface holographic optical film as described in any one of claims 1 to 4, characterized in that, A photoresist layer is set on a flexible transparent substrate. Instead of electron beam lithography, a master is prepared by laser direct writing. The pattern of the master is transferred to the photoresist layer of the flexible transparent substrate by nanoimprinting. The composite nanostructure array is precisely arranged by directional self-assembly technology. Then, the medium is filled by atomic layer deposition and the unwanted photoresist layer is peeled off.