The same filters used in 3D movie glasses could be used to view two completely different pictures. Image courtesy of Wikimedia.
Imagine looking at a picture through a transparent filter and then rotating the filter to reveal something entirely different. Researchers have developed a printed image that can do just that, by encoding two colours within each pixel.
The pixel design uses an array of nanoscale posts that reflect light at two different colours and polarizations, dependent on their dimensions and positions. By using filters to only let certain polarizations pass through, the two images can be independently viewed.
Polarization is a directional property of light – the same one used to produce 3D effects in modern movies. Without the glasses, viewers see two images projected simultaneously on the screen. Although it’s impossible to identify with the naked eye, each projection has a different polarization and can only be seen through one of the glasses’ lenses. The difference is similar to being blocked by a horizontal bar, but being able to pass if you roll underneath.
Researchers from the A*Star Institute, National University of Singapore and Singapore University of Technology and Design developed two geometries capable of encoding double images through separate polarizations, each with certain advantages.
The first design used elliptical posts, with the long axes positioned at right angles to each other to produce the two polarizations. The dimensions could be tuned to a wide range of colours, but the array faced challenges of colour mixing when viewed.
The second geometry used pairs of square nanoposts. In this design, the spacing between the two posts determined the colours and polarizations reflected and resulted in lower cross-talk. However, the pairs reflected a much narrower spectrum of colours and were more challenging to pattern.
The researchers have used the pixels to demonstrate a three-dimensional stereoscopic image. Potential applications include anti-counterfeiting measures, data storage and high-resolution 3D displays.
Their next steps will be increasing the pixel density to three or more images within the same area.
For more information, visit the A*Star Institute website or the Nature Communications article.