An anti-counterfeiting smart label and security platform that makes counterfeiting fundamentally impossible has been proposed. The device accomplishes this by monitoring a variety of information about light, including color, phase, and polarization in a single optical device.
A POSTECH research team – led by Professor Junsuk Rho from the Departments of Mechanical and Chemical Engineering, Dr Inki Kim and Ph.D. candidates Jaehyuck Jang and Gyeongtae Kim – developed a hologram printing platform encryption that works in both natural light and laser light using the metasurface, an ultra-thin optical material one thousandth of a human hair thick. The label printed with this technology can produce a holographic color image that maintains a specific polarization. The researchers called this a “vector hologram”. The results of this study were recently published in Natural communications.
The metasurface devices reported so far can only modulate a single property of light such as color, phase or polarization. To overcome this limitation, the researchers designed a pixelated bifunctional metasurface by grouping several metasurfaces.
Within the unitary structure that is the basis of the metasurface, the research team designed a device that uses its size to control color, orientation angles to control phase, and the relative angle difference and group ratio – which generates circularly polarized light for left-handed and right-handed people within the pixelated group – to express all polarizations of light. To freely modulate the different degrees of freedom of light and maximize its efficiency at the same time, the metasurface acts as a resonator1 and an optical waveguide2 at the same time.
The vector hologram label designed in this way displays QR codes that contain a variety of colors to the naked eye or when scanned with a camera. Simultaneously, under laser illumination, polarization-encoded 3D holographic images are rendered. This holographic image has a special state of polarization for each part of the image, which sets it apart from previously reported holograms.
The vector holographic color printing technology developed in this research is an optical approach to the two-level encrypted one-time password (OTP) security mechanism that generates a password required to access the current banking system that verifies the ‘user. First, when a user scans the QR code of the meta-optical device with a smartphone, the first password consisting of random numbers is generated. When this password is applied to the meta-optical device as a voltage value, the secondary password is displayed as an encrypted holographic image.
“This vector holographic color printing platform is more advanced than the metasurface devices reported so far and has demonstrated that varying degrees of freedom of light can be modulated with a single optical device,” Prof. Junsuk explained. Rho. “This is a highly advanced optical OTP device that promises to be a novel optical encryption technology applicable to the design and analysis of meta atoms.”
The research team has carried out cutting-edge research on optical metasurface devices over the past five years and the device under development this time has great commercialization potential in the fields of optical sensors, holographic displays, security and anti-counterfeiting applications.
This study is funded by the Samsung Research Funding & Incubation Center for Future Technology grant funded by Samsung Electronics.
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Material provided by Pohang University of Science and Technology (POSTECH). Note: Content can be changed for style and length.