Elastic Hologram Can Switch Images When Stretched

Image: University of Pennsylvania/American Chemical Society
Image: University of Pennsylvania/American Chemical Society

New elastic holograms can switch the images they display as they get stretched, finds a new study by scientists at the University of Pennsylvania. These holograms could have applications in virtual reality, flat-panel displays, and optical communications, researchers say.

Conventional holograms are photographs that, when illuminated, essentially turn into 2D windows looking at 3D scenes. The pixels of each hologram scatter light waves falling onto them, making the light waves interact with each other to generate an image with the illusion of depth.

Penn scientists in Philadelphia had previously created holograms made of gold rods only nanometers or billionths of a meter large embedded within elastic films of silicone rubber. These new holograms are a kind of metasurface, which manipulate light using structures smaller than wavelengths of light.

The researchers previously had developed a metasurface lens they could make zoom via stretching. They wanted to explore how a metasurface hologram might change when stretched.

First, the scientists found that stretching a hologram of the word “PENN” could make it look both larger and farther away. Next, they calculated that they could create multi-layered holograms consisting of multiple images. As each of these holograms stretches, one image appears in the place of another. “We can encode multiple holographic images on a single platform,” says study senior author Ritesh Agarwal, a materials scientist at the University of Pennsylvania.

In experiments, the scientists created two-layer holograms that switched from displaying “ONE” to “TWO” when stretched, or an unhappy face to a happy face. They also made a three-layer hologram that could switch between displaying a triangle, square, and pentagon.

The researchers suggest that holograms that each contain many different images could serve as compact ways of storing large amounts of data. Such holograms could also display 3D animations when stretched.

The scientists are now working on getting holograms to switch images using electric signals instead of stretching, research that could have applications in virtual reality. “Right now virtual reality devices are bulky because optical devices are inherently bulky,” Agarwal says. “If we can use holograms to trim virtual reality displays down to a flat thin layer, you can imagine virtual reality headsets the size of regular glasses.” Such research could also lead to advanced flat-panel displays and make optical communications networks less bulky, he adds.

Future research will also seek to incorporate multiple colors into these holograms and improve image quality during switching, Agarwal says. He and his colleagues Stephanie Malek and Ho-Seok Ee detailed their findings online May 10 in the journal Nano Letters

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