We’re all familiar with the famous Star Wars scene, no?
R2D2 projects an image of Princess Leia, who then initiates one of the most famous distress calls in movie history: “Help me, Obi Wan Kenobi. You’re my only hope.”
Brigham Young University electrical and computer engineering professor and holography expert Daniel Smalley has long had the goal of creating the same type of 3D image projection.
In the edited Q&A below, Smalley tells Tech Briefs about his “Princess Leia” project – and why his lab’s volumetric display has a number of advantages over screen-based 3D.
For one, the volumetric image – not a hologram, says the BYU researcher – floats in mid-air, allowing a viewer to see the object from any angle.
Tech Briefs: What is the difference between the volumetric image that you create and a hologram?
Prof. Daniel Smalley: A hologram scatters light from a 2D surface that later converges in space to form 3D images. In a volumetric display, the light scattering surface is distributed in the 3D volume. So, material objects form the image – not merely the convergence of light.
Tech Briefs: I’ve heard this technology compared to additive manufacturing. How is the display a “3D printer for light?”
Smalley: A 3D printer moves a print head, or the focus of a laser, to every x,y,z location of an object, and deposits something at that location – whether it be a bit of extruded plastic or a bit of cured epoxy. Our display also places a bit of material, a small particle of paper, at every image point location, if only briefly. When you look at our image, you are looking at a physical object, albeit one that only exists at one point at a time.
Tech Briefs: Take me through the platform from a technology perspective. What does it look like?
Smalley: To look at our display, you would see a lens, a few large moving mirrors, and a particle that looks like a glowing dust mote. The speck moves through space as if held by an invisible force. As the dust mote moves more and more quickly, it blurs to form a line and then an image.
The invisible force at work is really a tractor beam, created by a violet laser that is especially difficult to see. The laser's focus has a dark pocket that the particle is trapped in. The mirrors move the pocket around, and the particle is moved with it. As the speck moves, red, green, and blue light illuminate the particle to form an image in 3D space.
Tech Briefs: What are the advantages of a volumetric display?
Smalley: Volumetric displays have a number of advantages over screen-based 3D. They can be seen from every angle. The displays also provide excellent focus cues; your eye can focus on the image points in the same way they would focus on any real object. Additionally, a volumetric system can have very low bandwidth requirements when compared to holograms – if the scene is sparse, as would be the case for air-traffic control, for example.
Tech Briefs: Are there disadvantages?
Smalley: They do have a couple of disadvantages: Free-space volumetric images to-date have been limited to “ghosts and “hulls”: one part of the image does not eclipse, or occlude, another part. I do not believe this to be a fundamental limitation, and I think we may see occlusion-capable freespace volumetric displays.
Also, volumetric images produce “real images” – that is, images that exist in real space. You could not, for example, draw a window and then look through that window into a virtual world. With holography, however, these types of “virtual image windows” are the norm.
Finally, our particular approach is a little fragile. You can knock the particle out of the trap if you so desire. Thankfully, it is easy enough to pick another particle up and keep going. We've automated this process and feel like there are so many opportunities for redundancy that this is unlikely to present much of a problem in a refined display.
Tech Briefs: What is most exciting to you about this volumetric display?
Smalley: If the technology is scaled up to a useful size, it will literally be able to create the 3D display we see in Star Wars, Iron Man, and Avatar. As we walked around these images, they float in air and behave much like we expect them to.
Tech Briefs: What’s next regarding the development of the technology?
Smalley: First, we will optimize our traps and particles, with the goal achieving a 3x improvement in robustness. Next, we’ll use diffractive optical elements and spatial light modulators to allow us to trap and illuminate multiple particles at once. Multiple particles will mean a 10x, 100x, or 1000x increase in size and/or image sophistication.
What do you think? Would you be excited to use a volumetric display? Share your thoughts below.