A thermal tuning nano-printing method based on liquid crystal tunable metasurface

Abstract

A kind of thermal tuning nano printing method based on liquid crystal adjustable super surface, it is characterized in that: light beam deflection super surface and incident angle multiplexing nano printing super surface vertical cascade, by integrating high birefringence liquid crystal into double-layer super surface, the device can realize the dynamic thermal switching of pre-encoded nano printing image. In order to realize light beam deflection and incident angle multiplexing nano printing image display, silicon nanoblock with different arrangement mode is established, and the interval layer between the two super surfaces is composed of silicon dioxide. For the super surface with beam guiding function, twelve-element gradient super unit periodic arrangement composed of silicon nanoblock integrated with high birefringence liquid crystal is used, high transmission characteristics and 2π phase modulation are introduced in super surface resonance. For angle multiplexing nano printing super surface, by exploring and screening the geometric size of unit cell, the unit structure with different amplitude response is designed under two different illumination angles, so as to produce independently controlled double-channel nano printing image. Finally, the cascaded double-layer super surface can actively modulate nano printing image by combining the thermal driven liquid crystal tuning scheme, which can provide a way for preparing effective optical encryption platform. The present application has high information security and multiplexing, and can be widely used in new generation miniaturized optical encryption platform and anti-counterfeiting technology, multifunctional optical equipment, dynamic display.

Description

Technical Field

[0001] This invention relates to a thermally tunable nanoprinting method based on a liquid crystal tunable metasurface. Specifically, it relates to achieving near-field multi-channel display through vertical cascading of metasurfaces with beam deflection and nanoprinting functions under liquid crystal orientation modulated by different external temperatures. This method can be applied to the technical fields of next-generation optical encryption platforms, high-security identification systems, and multifunctional optical devices. Background Technology

[0002] The revolutionary advancements in digital technology have permeated all aspects of daily life, record management, and military applications, making the security and capacity of information storage in digital devices an increasingly important concern. Given the multiple degrees of freedom of light in terms of polarization, phase, and amplitude, optical encryption strategies with specific decryption methods and high capacity have become mainstream solutions. Prior art includes an anti-counterfeiting image display optical system and method based on a light polarization angle-sensitive metasurface, as described in the Chinese invention patent "Dual-channel color-coded anti-counterfeiting image display metasurface and its design method," patent number: CN202010014612.1. This optical encryption method has many advantages, such as low cost and the ability to achieve dynamic modulation; however, it still has some fundamental shortcomings: 1) The polarization of the incident light relies on additional optical equipment such as a rotating polarizer, requiring a larger working size and hindering the development of next-generation miniaturized and compact devices; 2) Because polarization-based encryption design procedures are relatively mature and frequently used, the encoded information is easily decrypted, thus reducing the security of the encrypted information. Therefore, developing a small integrated optical system with dynamically adjustable characteristics to achieve high-security, high-capacity optical encryption and identification technology has been a persistent goal in practical applications. Here, we propose a thermally tunable nanoprinting technique based on a high-refractive-index liquid crystal integrated bilayer metasurface to generate dual-channel nanoprinted images with enhanced security for application in the field of optical information encryption. By cascading a thermally switchable beam-polarizing metasurface with another angle-multiplexed nanoprinted metasurface, the proposed optical system avoids additional optical elements to control the incident angle, thereby achieving dynamic tunability of the ultracompact metasurface structure. By utilizing the liquid crystal orientation at different temperatures to control the deflection angle of the incident light, and by exploring and screening the geometry of the unit cell, the angle-multiplexed nanoprinted metasurface is designed. This method allows for the generation of independently controlled dual-channel images at different temperatures. In summary, this invention envisions that cascaded bilayer metasurfaces can actively modulate nanoprinted images by combining a thermally driven liquid crystal tuning scheme, which can serve as an effective thermally tunable optical encryption platform. Summary of the Invention

[0003] To overcome the aforementioned deficiencies of existing technologies, this invention discloses a thermally tunable nanoprinting method based on a liquid crystal tunable metasurface. By vertically cascading a liquid crystal-integrated beam deflection metasurface with another angle-multiplexed nanoprinted metasurface separated by a silicon dioxide spacer layer, the dynamic tuning characteristics of thermal and angle multiplexing can be combined into an ultra-compact and lightweight optical system without the need for additional optical components. We successfully manipulated the wave vector of transmitted light by controlling the temperature around the metasurface, enabling it to propagate in a straight line or with a deflection angle of 10.9°. Furthermore, based on the angle-multiplexed metasurface, two angle-dependent nanoprinted images can be generated, introducing new degrees of freedom for angle control at 0° and 11°. This invention can generate dynamic nanoprinted images by changing the temperature to achieve a novel method for encrypted transmission of optical information.

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a thermally tunable nanoprinting method based on a liquid crystal tunable metasurface, comprising the following steps: A compact two-layer metasurface structure is constructed: the metasurface consists of a three-layer structure, including a silicon dioxide spacer layer in the middle and rectangular nanopillar structural units arranged in an array at both ends of the spacer layer; the rectangular nanopillars are made of high-refractive-index single-crystal silicon material; the function of the metasurface is achieved by a two-dimensional planar cascade composed of two layers of multiple periodically arranged unit structures; wherein, each independent planar unit structure has a fixed height, and the geometric dimensions of the unit structure along the major and minor axes can be independently selected; Realization of beam deflection function: A metasurface with beam deflection function was designed. A twelve-element phase gradient supermonomer composed of silicon nanopillars was used as one period. Specifically, in the interaction between the metasurface and light, high light transmission was achieved and phase modulation was introduced, so that the twelve nanopillars based on Huygens' principle achieved a gradient change in the 2π phase range, thereby realizing the beam deflection function. Realization of incident angle multiplexing nanoprinting function: A metasurface with incident angle multiplexing nanoprinting function was designed. Four silicon nanopillars with appropriate geometric dimensions were selected so that they would generate different resonant electric field excitations under two different incident angles, resulting in different amplitude responses for each array. The amplitude responses are low amplitude transmitted light close to 0 and high amplitude transmitted light close to 1, respectively, thus generating different nanoprinted images through different incident angles. The finite-difference time-domain method was used to simulate silicon nanoblocks of different sizes: silicon nanopillars of different sizes along the long and short axes were scanned to obtain the amplitude and phase response of silicon nanopillars of different sizes under the incident x-polarized light. A thermally tunable miniaturized encryption platform integrating high-refractive-index liquid crystal: By integrating a designed metasurface with high-refractive-index liquid crystal, the liquid crystal layer can be subjected to a specific temperature to perform phase compensation on each unit structure of the metasurface with beam deflection function, so as to control the beam deflection angle. Finally, a miniaturized optical encryption platform with dynamically tunable light amplitude can be realized by adjusting the temperature around the device.

[0005] Secondly, a thermally tunable nanoprinting method based on a liquid crystal tunable metasurface is characterized by: vertically cascading a beam deflection metasurface and an angle-multiplexing nanoprinted metasurface by screening and coupling the characteristics of unit cells, separated by a dielectric layer. High birefringence liquid crystal is integrated into the bilayer metasurface, and the cascaded optical system can achieve dynamic thermal switching of pre-encoded nanoprinted images. The amplitude of transmitted light can be switched by adjusting the external temperature, and this can be applied to optical encryption technology.

[0006] Thirdly, the present invention provides a thermally tunable nanoprinting technique based on a liquid crystal tunable metasurface designed as described above, which can be widely applied in the fields of next-generation miniaturized optical encryption platforms and anti-counterfeiting technology, multifunctional optical devices, and dynamic displays.

[0007] Compared with the prior art, the advantages and positive effects of the present invention are: 1. Due to the temperature-tunable orientation of liquid crystal molecules, different nanoprinted patterns can be displayed at different temperatures. This dynamically tunable metasurface with multiplexing strategy has potential applications in next-generation optical encryption platforms.

[0008] 2. By vertically cascading liquid crystal-integrated beam deflection metasurfaces and angle-multiplexed nanoprinted metasurfaces, the dynamic tuning characteristics of thermal multiplexing and angle multiplexing can be combined into an ultra-compact and lightweight optical system without the need for additional optical components.

[0009] 3. Through the carefully designed nanostructure, the encoded information has robustness against repetition, thus enabling high-precision nanoscale image display that is not easily copied or decrypted. This is crucial for developing a new generation of high-security optical encryption devices. Attached Figure Description

[0010] Figure 1 This is a functional diagram of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention to realize the dynamically adjustable beam deflection function. The angle of incident light is controlled by adjusting the temperature to regulate the liquid crystal orientation. Figure 3 This is a schematic diagram of the structure of the present invention to realize the nanoprinting function of incident angle reuse; different amplitudes of transmitted light are controlled by adjusting the angle of incident light. Figure 4This invention relates to the amplitude response of metasurfaces of different structural sizes at different incident angles; Figure 5 This invention implements the reverse encoding design of dual-channel nanoprinted images. Detailed Implementation

[0011] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, these embodiments are not intended to limit the present invention. Any similar structures and similar variations of the present invention should be included in the protection scope of the present invention.

[0012] A thermally tunable nanoprinting method based on a liquid crystal tunable metasurface is disclosed. Specific parameters of the embodiment are as follows: the spacing between each unit of the beam deflection metasurface is 190 nm; the height of the nanopillars is 400 nm; a deflection unit consists of twelve nanopillars; the geometric dimensions of each nanopillar along its major and minor axes are: 60 nm × 60 nm, 75 nm × 75 nm, 85 nm × 85 nm, 94 nm × 94 nm, 100 nm × 100 nm, 108 nm × 108 nm, 115 nm × 115 nm, 124 nm × 124 nm, 131 nm × 131 nm, 145 nm × 145 nm, 151 nm × 151 nm, and 160 nm × 160 nm; the intermediate spacer layer is made of silicon dioxide; the height of the nanopillars on the nanoprinted metasurface is 110 nm; and the lengths (with equal geometric dimensions along the major and minor axes) of the four different amplitude response structural units are 275 nm, 345 nm, and 275 nm, respectively. The nanopillars are 365 nm, 275 nm, and 365 nm, with corresponding periods of 215 nm, 230 nm, 160 nm, and 100 nm, respectively. The nanopillars are single-crystal silicon high-refractive-index materials, with a refractive index of 3.87.

[0013] Figure 1 The diagram shows the functional characteristics of the present invention, which allows for the control of incident light at different temperatures to achieve the switching display of dual-channel nanoprinted images.

[0014] Figure 2This is a schematic diagram illustrating the structure by which the present invention achieves dynamically adjustable beam deflection. The dynamic switching of beam deflection is achieved by manipulating the interaction between the liquid crystal and the silicon nanopillar metasurface through controlling the ambient temperature. At room temperature (approximately 25°C), the liquid crystal exhibits anisotropy and is pre-aligned through a multi-step, partially overlapping exposure process. When the temperature rises to the clean point of the liquid crystal (150°C), the alignment of the liquid crystal shifts to isotropy. When x-polarized light is normally incident on the beam-guiding metasurface at two different ambient temperatures, at 25°C, the incident light is directly transmitted without deflection; at 150°C, the beam diffraction is switched from the zeroth order to the first order, with a deflection of 10.9°. Therefore, dynamic beam deflection can be achieved by adjusting the ambient temperature. Figure 3 This is a schematic diagram of the structure for realizing the incident angle multiplexing nanoprinting function of the present invention. The metasurface array exhibits an angle-dependent transmission response, wherein at the incident angle of... θ 1 and θ 2. The transmission through the metasurface has different amplitudes, respectively | A 1| and | A 2|. Figure 4 This study demonstrates the amplitude response of nanoprinted metasurfaces of different structural sizes at various incident angles. The amplitude contrast at specific wavelengths and illumination angles is represented by binary digital values ​​"0" (low amplitude of transmitted light) and "1" (high amplitude of transmitted light), with the four metasurfaces corresponding to the states "00", "10", "01", and "11", respectively. Ultimately, any two nanoprinted images can be simultaneously encoded into two angular channels using pixel combinations of "00", "10", "01", and "11". Figure 5 This invention achieves reverse encoding design of dual-channel nanoprinted images by combining the amplitude requirements of the printed patterns "M" and "U" to reverse design a nanoprinted metasurface. This invention successfully utilizes a liquid crystal tunable bilayer metasurface to switch between two nanoprinted images by manipulating the ambient temperature.

Claims

1. A thermally tunable nanoprinting method based on a liquid crystal tunable metasurface, characterized in that: Includes the following steps: S1: Constructing a compact two-layer metasurface structure: This metasurface consists of a three-layer structure, including a silicon dioxide spacer layer in the middle and rectangular nanopillar structure units arranged in an array at both ends of the spacer layer; the rectangular nanopillars are made of high-refractive-index single-crystal silicon material; the function of this metasurface is achieved by cascading two-dimensional planes composed of two layers of multiple periodically arranged unit structures; wherein, each independent plane unit structure has a fixed height, and the geometric dimensions of the unit structure along the major and minor axes can be independently selected; S2: Realization of beam deflection function: A metasurface with beam deflection function was designed. A twelve-element phase gradient supermonomer composed of silicon nanopillars was used as one period. In the interaction between the metasurface and light, high light transmission was achieved and phase modulation was introduced, so that the twelve nanopillars based on Huygens' principle achieved a gradient change in the 2π phase range, thereby realizing the beam deflection function. S3: Realization of incident angle multiplexing nanoprinting function: A metasurface with incident angle multiplexing nanoprinting function was designed. Four silicon nanopillars with appropriate geometric dimensions were selected so that they would generate different resonant electric field excitations under two different incident angles, resulting in different amplitude responses for each array. The amplitude responses are low amplitude transmitted light close to 0 and high amplitude transmitted light close to 1, respectively, thus generating different nanoprinted images through different incident angles. S4: Simulation of silicon nanoblocks of different sizes using the finite-difference time-domain method: Scanning silicon nanopillars of different sizes along the long and short axes to obtain the amplitude and phase response of silicon nanopillars of different sizes under x-polarized light incident. S5: Thermally Tunable Miniaturized Encryption Platform with Integrated High-Refractive-Index Liquid Crystal: The designed metasurface is integrated with a high-refractive-index liquid crystal. The liquid crystal layer can be subjected to a specific temperature to perform phase compensation on each unit structure of the metasurface with beam deflection function, so as to control the beam deflection angle. Finally, by adjusting the temperature around the device, a miniaturized optical encryption platform with dynamically adjustable light amplitude can be realized.

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