AsianScientist (Nov. 14, 2016) – Holograms just got five times better and a whole lot more colorful. In a paper published in Science Advances, researchers from China and Singapore describe how a single layer of nanostructured metal enables full-color meta-holography with wide viewing angles.
Most people would be familiar with rainbow holograms on their bank notes and credit cards where they play a role in authentication, but holograms are also used in beam shaping and the entertainment industry. However, traditional holograms are limited by large pixel sizes and the difficulty of modulating the phases of light, resulting in restricted viewing angles and poor color reproduction.
Taking a nanotechnology approach, a team of researchers led by Professor Luo Xiangang from the Institute of Optics and Electronics, Chinese Academy of Sciences, and Professor Hong Minghui from the National University of Singapore, have created a metamaterial that can increase the viewing angle by 40 times or more across the full color spectrum.
They used a chromium film studded with nano-rectangular holes to achieve a pixel size of 200×200 nm2, which is much smaller than the wavelength of visible light. Unlike typical spatial light modulators with pixel sizes of at least 8×8μm2, the new method allows holographic projections of greater than 90 degrees.
By adjusting the spatial orientation of the nano-rectangular holes, the researchers were able to modulate the phase of light across the entire visible color range.
To overcome the problem of cross-talk between different colors that plagues current metasurface holography, they introduced an off-axis illumination method to shift the holographic image in different colors and successfully reconstructed all visible colors in the imaging area. This method leads to a remarkable image quality, with a signal-to-noise ratio five times better than those of the previous meta-hologram designs.
According to the researchers, their work enables the creation of new meta-hologram devices that can be used in data storage, security and authentication.
The article can be found at: Li et al. (2016) Multicolor 3D Meta-Holography by Broadband Plasmonic Modulation.
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Source: Chinese Academy of Sciences.
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