Angle-multiplexed optically encrypted metasurfaces fabricated by ultrafast laser induced spatially selective-modified nanograting structures
doi: 10.37188/CO.2022-0228
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摘要:
图案信息的光学加密在防伪、信息加密存储等方面具有广泛的应用，基于各向异性功能复用的结构色超表面得到发展。基于一维光栅衍射的光学加密超表面由于需要逐个加工掩模或单元结构，从而导致效率低下；传统激光烧蚀波纹结构(LIPSS)效率高，但所形成的结构均匀、一致性差。基于以上难题，提出了一种基于皮秒激光直写相变材料Ge2Sb2Te5得到的改性结构加工光学超表面的方法。首先，表征所制备的GST改性光栅的色散性能，结合改性光栅的偏振依赖性，设计了角度复用的信息加密超表面。实现了在自然光条件下加密，在强光条件下能够选择性解密读取并动态展示的性能。相比于传统加工方法，本方法可在一次直写过程中以同时打印的形式生成一系列光栅结构，提高了加工效率；同时加工得到的光栅结构均匀一致性好，提高了显色效果。利用取向角相差16°的改性光栅实现了无串扰的选择性信息读取，所得结构色均匀鲜艳。本文提出的加工策略在防伪、信息加密存储及可穿戴柔性显示设备等领域有深刻的应用前景。
Abstract:The optical encrypted metasurface based on one-dimensional grating diffraction requires the processing of mask or unit structure one by one, resulting in low efficiency. In addition, the poor uniformity of the structure formed by conventional ablated LIPSS can also affect device performance. Aming at the above problems, an optical metasurfaces processing method is proposed based on modified structures obtained by picosecond laser direct writing phase-change material Ge2Sb2Te5. Firstly, the dispersion properties of the prepared GST-modified gratings are first characterized, and the angle-multiplexed information encryption metasurfaces are designed by combining the polarization dependence of the modified grating, and the metasurface prepared by the proposed method is further demonstrated. In addition, the performance of encryption under natural light conditions and selective decryption reading and dynamic display under strong light conditions has been achieved. Compared to the conventional processing method, the proposed method can generate a series of grating structures in the form of simultaneous printing in a direct writing process, which improves the processing efficiency. At the same time, the grating structure obtained by processing has good uniformity and consistency, which improves the color rendering effect. A modified grating with an orientation angle difference of 16° is used to realize selective information reading without crosstalk resulting in uniform and bright structural colors. The processing strategy proposed in this paper has a profound application prospect in the fields of anti-counterfeiting, information encryption storage and wearable flexible display devices.
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Key words:
- ultrafast laser /
- phase-change material /
- information encryption /
- grating structure
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图 1 信息加密超表面的设计图。(a)激光直写后GST的性质变化；(b)激光直写GST的三种特征结构对应加工图案；(c)信息加密超表面分别在自然光和强光下的效果
Figure 1. Schematic diagram of an information-encrypting metasurface. (a) The properties of GST after direct laser writing; (b) the three characteristic structures of laser direct writing GST correspond to the processing patterns; (c) the effect of the information encryption metasurface under natural light and strong light, respectively
图 2 改性光栅结构的表征。(a)100倍光镜下的改性光栅；(b)(c)改性光栅的SEM图；(d)改性光栅的AFM结果；(e)对应图(d)的曲线图
Figure 2. Characterization of modified grating structures. (a) Modified grating under 100× optical microscope; (b)(c) SEM image of modified grating; (d) AFM results of modified grating; (e) the graph corresponding to (d)
图 3 GST 改性光栅色散特性的表征。(a)偏振与改性结构之间的关系；(b)−(e)分别在 0°、10°、30° 和 40° 激光偏振条件下的改性结构; (f)用于表征色散能力的装置示意图；(g)−(i)RGB色彩的实拍展示；(j)拍照所获得的不同角度下的色散结果
Figure 3. Characterization of the dispersion properties of GST-modified gratings. (a) Relationship between polarization and modified structure; (b)−(e) modified structure under laser polarization conditions of 0°, 10°, 30°, and 40°, respectively; (f) schematic diagram of the device used to characterize the dispersion capability; (g)−(i) real shot display of RGB color; (j) the dispersion results obtained at different angles
图 4 嵌套加工的信息加密超表面。(a)器件表面三种不同的改性结构排布方式的设计图；(b)自然光条件下加工区域的照片；(c), (d)嵌套区域和背景区域的光学显微镜图像；(e)不同视角解码的图案信息
Figure 4. Information encryption metasurfaces for nested processing. (a) Design diagrams of three different modified structure arrangements on the device surface. (b) Photograph of the processed area under natural light conditions. (c) and (d) are optical microscopy images of the nested and background regions, respectively. (e) Pattern information decoded from different views
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