In a groundbreaking development, scientists have made significant strides in generating meta-holograms across the visible and ultraviolet spectra, surpassing previous limitations. They have achieved this by encoding two distinct holographic phase profiles onto a single metasurface, leveraging the properties of polarization and liquid crystal. These advancements have promising applications in security technologies. Image credit: Nanoscale Horizons
The prefix “meta” denotes the idea of transcending or going beyond. When applied to materials, it signifies “metamaterials,” which are artificially created substances that possess properties not found in nature.
Metasurfaces, renowned for their lightweight and slim characteristics, have garnered considerable attention as potential components for incorporating holographic generation into mobile augmented reality (AR) and virtual reality (VR) devices.
However, it is crucial to note that metasurfaces have inherent limitations. For instance, they have a restricted capacity to store information and are only capable of generating holograms within the visible spectrum.
A research team led by Professor Junsuk Rho from the Department of Mechanical Engineering and the Department of Chemical Engineering, along with Joohoon Kim from the Department of Mechanical Engineering at Pohang University of Science and Technology (POSTECH), has successfully developed meta-holograms applicable to both the visible and ultraviolet spectra.
(Left) When an electric field is not applied, the liquid crystal cells align linearly, causing the light to spin clockwise. Conversely, when an electric field is applied, the arrangement of the liquid crystal cells becomes non-linear, resulting in the light spinning in a different direction. (Right) The new approach facilitates the generation of two distinct holograms by designing them to be responsive to the direction of the light. Image credit: POSTECH
The research findings have been published in Nanoscale Horizons, a prestigious international journal, and occupy the inside front cover.
The constraint of hologram generation to the visible spectrum has largely been attributed to the light absorption exhibited by most objects in the ultraviolet range.
Nevertheless, the research team has effectively addressed this challenge by incorporating a thin layer of specially formulated gas compositions into the metasurfaces, resulting in significant improvements in holographic transmission efficiency across both the visible and ultraviolet ranges.
Moreover, the team has achieved the encoding of two distinct holographic phase profiles onto a single metasurface. The propagation of light through space is governed by its polarization characteristics.
Capitalizing on this phenomenon, the team’s approach enables the provision of holographic information for both clockwise and counter-clockwise circularly polarized light, effectively doubling the amount of encoded information on metasurfaces.
To facilitate practical implementation, the team utilized liquid crystal, a commonly employed component in cellphones and LCD displays, which allows convenient manipulation of the light’s spin direction. Experimental results have demonstrated that in the absence of an electric field, the light exhibits clockwise spinning, resulting in the generation of a type A hologram.
Conversely, the application of an electric field induces a different direction of light spinning, leading to the creation of a type B hologram. Essentially, the research team has engineered a device capable of presenting distinct holograms based on the presence or absence of an electric field.
Professor Junsuk Rho, who spearheaded the research, emphasized the significance of this breakthrough, stating, “This study is significant in that it overcomes the limitations associated with meta-holograms limited to the visible spectrum alone, and we have achieved the concurrent generation of meta-holograms in both the visible and ultraviolet domains.” He further added, “This proposed metasurface holds promise for applications in security technologies, such as anti-counterfeiting measures, identifications, and passports.”
Reference: “Spin-isolated ultraviolet-visible dynamic meta-holographic displays with liquid crystal modulators” by Aqsa Asad, Joohoon Kim, Hafiz Saad Khaliq, Nasir Mahmood, Jehan Akbar, Muhammad Tariq Saeed Chani, Yeseul Kim, Dongmin Jeon, Muhammad Zubair, Muhammad Qasim Mehmood, Yehia Massoud and Junsuk Rho, 18 April 2023, Nanoscale Horizons.
The study received support from the STEAM Research Program (Center for Nano-optics-based Smart Data Security Technology) of the National Research Foundation of Korea, funded by the Ministry of Science and ICT, as well as a program from POSCO’s Industry-Academic Integrated Research Center.
Frequently Asked Questions (FAQs) about metamaterials
What are metamaterials?
Metamaterials are artificially created substances that possess properties not found in nature. They go beyond the limitations of conventional materials and exhibit unique characteristics.
What are metasurfaces?
Metasurfaces are thin and lightweight surfaces that have gained attention for their potential integration into augmented reality (AR) and virtual reality (VR) devices. They facilitate holographic generation and offer advantages in terms of their physical properties.
What limitations do metasurfaces have?
Metasurfaces have inherent limitations such as restricted information storage capacity and the ability to generate holograms only within the visible spectrum. They were previously unable to extend holography into the ultraviolet spectrum.
How did the research team overcome the limitations of metasurfaces?
The research team incorporated a specially formulated gas composition into the metasurfaces, allowing for significant improvements in holographic transmission efficiency in both the visible and ultraviolet spectra. This breakthrough addressed the previous limitations.
How did the team encode two distinct holographic phase profiles?
By leveraging the polarization characteristics of light and utilizing liquid crystal, the team encoded two distinct holographic phase profiles onto a single metasurface. This approach effectively doubled the amount of information that could be encoded onto metasurfaces.
What are the potential applications of these meta-holograms?
The meta-holograms generated through this research have promising applications in security technologies. They can be used for anti-counterfeiting measures, identification purposes, and in passports, among other applications.
What is the significance of this research?
This research is significant as it expands the possibilities of meta-holograms beyond the visible spectrum and enables the concurrent generation of meta-holograms in both the visible and ultraviolet domains. It opens up new avenues for holography and has practical implications for various fields.
More about metamaterials
- Nanoscale Horizons
- STEAM Research Program
- POSTECH Department of Mechanical Engineering
- POSTECH Department of Chemical Engineering
- POSTECH Official Website