Holograms You Can Touch

The holographic display is a technology that has seemingly been on the way for decades, but that still has not yet arrived. There are a number of workable technologies in existence, and some of them have even been made available commercially, but for one reason or another, there are still factors that prevent their widespread adoption. This is a shame, because science fiction has been teasing us with the possibilities of holographic displays for many years, and most technophiles would love to get their hands on one.

Speaking of getting your hands on one, a team of researchers at the Public University of Navarre in Spain is preparing for a future in which holographic displays are not only practical, but also interactive. That is like leap-frogging straight from a static “Help me, Obi-Wan Kenobi. You're my only hope” three-dimensional video message to a full-blown holodeck. The researchers’ tech may not be anywhere near that level just yet, but it does appear to be a meaningful step toward that goal.

The team’s system is called FlexiVol, a new kind of volumetric display that allows users to physically reach into the 3D graphics it projects. Unlike traditional volumetric displays that rely on rigid optical diffusers — surfaces that scatter light to form 3D images — FlexiVol uses elastic, flexible diffusers. These stretchable materials enable users to interact directly with the rendered content by penetrating the display volume with their hands.

In standard volumetric displays, images are produced by projecting a series of rapid 2D “slices” onto a surface that moves back and forth quickly, creating the illusion of a floating 3D object. The challenge is that the rigid diffusing surface makes physical interaction impractical and even dangerous. With FlexiVol’s soft, flexible diffusers, users can safely reach through the projection area to grab, move, or manipulate objects, with real-time visual feedback that matches the spatial location of their hand.

To make this possible, the team modified both off-the-shelf and custom-built volumetric displays, including the commercially available Voxon VX1, and incorporated elastic diffuser materials such as stretchable films and strip arrays. These diffusers are mounted on oscillating frames driven by actuators — often repurposed speaker components — that vibrate in sync with high-speed projectors. These projectors render image slices at rates exceeding 2,800 frames per second, ensuring the resulting 3D image is stable and fluid.

Because flexible diffusers can deform as users interact with them, the system must also compensate for distortions. The researchers developed a correction algorithm that adjusts the projection in real time, ensuring the 3D graphics maintain their intended shape even when the diffuser is stretched or pushed.

Since this technology made it possible for a user to reach into the display, the researchers also explored the interactions it makes possible. Inspired by multi-touch gestures on flat screens, they identified a range of intuitive hand movements that work well in 3D, such as grabbing, docking, and tracing. In a user study, participants performed tasks using both a traditional 3D mouse and FlexiVol’s reach-through interaction. The results showed that FlexiVol enabled faster task completion, lower cognitive load, and higher satisfaction, although with a slight drop in precision.

Though still in the prototype stage, FlexiVol is a significant step toward truly immersive holographic interfaces. By making the 3D content not only visible but also physically interactive, it pushes the boundaries of what a graphical display can be — and brings us just a little bit closer to making science fiction a reality.