3-D Projection Into Thin Air

A 3-D volumetric image of a butterfly, using a new display with an optical trap for single particles. (Source: D. Smalley Lab, BYU)

In the original Star Wars film, R2D2 projects an image of Princess Leia in distress. The iconic scene includes the line still famous 40 years later: “Help me Obi Wan Kenobi, you’re my only hope.“ BYU electrical and computer engi­neering professor and holo­graphy expert Daniel Smalley has long had a goal to create the same type of 3D image projec­tion. For this purpose, Smalley has developed a new prototype of a volumetric display. “We refer to this collo­quially as the Princess Leia project,” Smalley said. “Our group has a mission to take the 3D displays of science fiction and make them real. We have created a display that can do that.”

First things, first, Smalley says. The image of Princess Leia is not what people think it is: It’s not a hologram. A 3D image that floats in air, that you can walk all around and see from every angle, is actually called a volumetric image. Examples of volumetric images include the 3D displays Tony Stark interacts with in Ironman or the massive image-projecting table in Avatar. A holographic display scatters light only at a 2D surface. If you aren’t looking at that surface you won’t see the 3D image because you must be looking at the scattering surface to see the image. A volumetric display has little scattering surfaces scattered throughout a 3D space – the same space occupied by the 3D image – so if you are looking at the image you’re are also looking at the scatters. For this reason, a volumetric image can be seen from any angle.

Abb.: Daniel Smalley explains the details of his volumetric display. (Source: Producer Julie Walker, Cinematographer Brian Wilcox, Editor Hannah Hansen)

Smalley and his colleagues have devised a free-space volu­metric display platform, based on photo­phoretic optical trapping, that produces full-color, aerial volu­metric images with 10-micron image points by persis­tence of vision. “We’re using a laser beam to trap a particle, and then we can steer the laser beam around to move the particle and create the image,” said undergrad coauthor Erich Nygaard. Smalley said the easiest way to under­stand what they are doing is to think about the images they create like 3D-printed objects.

“This display is like a 3D printer for light,” Smalley said. “You’re actually printing an object in space with these little particles.” So far Smalley and his student researchers have 3D light printed a butterfly, a prism, the stretch-Y BYU logo, rings that wrap around an arm and an indi­vidual in a lab coat crouched in a position similar to Princess Leia as she begins her projected message. While previous researchers outside of BYU have done related work to create volu­metric imagery, the Smalley team is the first to use optical trapping and color effec­tively. Their method of trapping particles and illu­minating it with colorful lasers you can see is novel. “We’re providing a method to make a volumetric image that can create the images we imagine we’ll have in the future,” Smalley said. (Source: BYU)

Reference: D. E. Smalley et al.: A photophoretic-trap volumetric display, Nature, online 24. Januar 2018; DOI: 10.1038/nature25176

Link: Dept. of Electrical and Computer Engineering, Brigham Young University, Provo, Utah, USA

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