Microsoft's recent HoloLens announcement has reignited interest in holographic displays, but the current state of affairs suggests that this technology may still be too expensive and limited to become truly widespread. Researchers at Brigham Young University (BYU) and MIT are bridging the gap with a new important step toward the next generation of high-bandwidth, color-accurate holographic video displays that could span the size of an entire room at one tenth the cost of state of the art devices.

Unlike 3D movies, which render images from the very same angle no matter where you're sitting, holograms change dynamically based on the viewer's angle and position to provide a much more realistic sense of depth. The higher level of immersion has allowed for some memorable performances on stage and could transform the worlds of computer-aided design and communications (think telepresence), but the high cost and limited capabilities of today's holographic displays have been hard to overcome.

Things might change with the help of research by assistant professor Daniel Smalley and team, who have built on some of their previous work on the subject to complete a crucial new step toward building the next generation of holographic displays.

In 2013, the same team developed a way to precisely control light with the help of surface acoustic waves. The researchers used a piezoelectric crystal featuring microscopic channels, or waveguides, to confine and direct light.

A metal electrode was then placed onto each waveguide. When a radio frequency was applied to the electrode, this generated an acoustic wave that could change the polarization of the light beam and scatter light along the crystal as needed to produce a holographic image.

This scattering process gives rise to two optical modes  –  one that follows the direction of the waveguide, and a second "leaky" mode with opposite polarization that is directed toward the bottom of the crystal, where the hologram is generated. The angle and frequency of these two modes determines the color of each of the hologram's "pixels," but the relationship between these quantities is very complex, making it difficult to control the color of the hologram. Now, Smalley and team have found a way to map which parameters correspond to each color, in an advance that could bring higher color fidelity to the world of holograms.

The scientists set a prism on a rotating platform, exposed it to red, green and blue light from different angles and then used a photodetector to scan the output color produced. With this apparatus, the researchers were able to map the relationship between the input radio frequency used on the waveguide and the angular deflection of the output light. Creating such data maps for the three primary colors allows the researchers to control the color of the hologram with a high degree of precision.

Since the same color can be obtained in more than one way, the additional degrees of freedom allow for further optimization of the holographic display's performance in terms of efficiency, bandwidth or compactness. Ultimately, this will afford a greater level of flexibility in building the next generation of holographic video displays.

"We can use this technology to make simple and inexpensive color waveguide displays  –  including inexpensive holographic video displays," says Smalley. "This can drop the cost of a holographic video display from tens of thousands of dollars to less than a thousand."

The researchers are now focusing on scaling up their technology from a laboratory sample to a display that could span the size of an entire room.

An open-access paper describing the advance appears in the journal Review of Scientific Instruments.

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