Multicolor holography technology could enable extremely compact 3D displays

The new multicolor holography technique is based on computer-generated holograms. Unlike traditional holography, which requires a physical object and laser beams to create the interference pattern necessary to form a holographic image, computer-generated holography generates interference patterns digitally.

Computer generated holograms provide high-resolution 3D images, but it has proven difficult to create them in more than one color. The Duke team overcame this challenge by fabricating a grating -- a series of fringes -- and a binary hologram in a waveguide made of a light-sensitive material known as photoresist. They developed a way to integrate the interference patterns for red, green and blue into a single binary hologram pattern.

"One of the difficult parts of making a multicolor display is combining the colors and then precisely separating them to generate a full color image," said Zhiqin Huang, first author of the paper. "With our approach this is all done all in one step on a single surface without any beam splitters or prisms. This makes it extremely amenable to integration into portable devices."

Another important achievement was creating the holographic device in a waveguide structure. "Others who have tried to create multicolor computer-generated holograms didn't use a waveguide, which makes it a challenge to integrate the structure into a device," said David R. Smith, leader of the research team. "Our design offers easier and more flexible integration with a form factor small enough for augmented reality and other displays."

Single-step color images

The researchers used their new holography method to encode interference patterns for static multicolor holograms of an apple, a flower and a bird. The resulting holographic images all matched well with theoretical predictions. Although they fabricated very small holograms for the demonstration, the researchers say that the technique could be easily scaled up to create larger displays. They also believe their approach could be incorporated with existing technologies -- such as those used to make liquid crystal displays -- to create dynamic images.

The researchers are now working to optimize the technology by reducing the light lost by the structures that encode the holograms. They also point out that incorporating the structures into a single integrated device with lasers would be necessary to make the technique practical.