Nanotech helps scientists create high definition colour holograms

Scientists for the first time have created a technology that can display true, high resolution colour holograms but Hollywood holograms are still a way off

By carefully arranging nanoblocks to display pixels on a metasurface, researchers have demonstrated that they can manipulate incoming visible light in just the right way to create a colour hologram, known as a "Meta Hologram" and the new technique could lead to true, high definition colour holograms that  that have applications for various types of 3D colour holographic displays and achromatic planar lenses.

Fig 1. A Nanoblock creating a meta-hologram

The researchers, Bo Wang et al., from Peking University and the National Center for Nanoscience and Technology, both in China, have published a paper on the new type of hologram in a recent issue of Nano Letters.

The pixels on the new metasurface consist of three types of silicon nanoblocks whose precise dimensions correspond to the wavelengths of three different colors: red, green, and blue. To enhance the efficiency for the blue light, two identical nanoblocks corresponding to the blue light are arranged in each pixel, along with one nanoblock for red light and one for green light.

The researchers explain that each pixel of light can be thought of as a "meta-molecule" and that hese meta-molecules let the metasurface control light in ways that aren't possible without nanoscale design so when red, green, and blue lasers illuminate the hologram, each nanoblock manipulates the phase of its corresponding colour. The researchers explain that a key achievement of the study was to minimize the interactions between nanoblocks so that the nanoblocks function almost independently of each other. Then by orienting the nanoblocks in different ways, the researchers could change the light's phase manipulation, resulting in different holographic images.

"Our work provides an approach for realizing the almost independent manipulation of phased light for different visible wavelengths," said coauthor Yan Li, at Peking University.

The researchers demonstrated that the nanoblock approach can be used to create two different types of holograms. In an achromatic hologram, the entire reconstructed image is in one colour and by balancing the relative input of the three colours, they could achieve a wide variety of colours. In the second type of hologram, called a highly dispersive hologram, different parts of the reconstructed image have different colours - for example, a red flower, green stem, and blue container.

The new colour hologram has a variety of potential applications where this type of light manipulation is useful, such as 3D colour holograms, achromatic lenses, and anti-conterfeiting products. The researchers plan to pursue these applications in future work.

"Based on this idea and approach, novel real planar optical devices may be fabricated to realize many novel or extra functions in the future," Weiguo Chu at the National Center for Nanoscience and Technology said.