- Researchers have developed a free-space volumetric display technique based on photophoretic optical trapping.
- It can produce image geometries that are currently unachievable with holograms and light-field technologies.
- So far, they have projected colorful 3D prism, butterfly, rings that wraps around an arm, and more.
You might remember the R2D2 projecting an image of Princess Leia in Star Wars movie. Well the sci-fi moment is now closer to reality. Researchers at Brigham Young University have created a 3D projection technology that can produce image in “thin air”.
What shown in Star Wars is not a hologram. It’s a 3D image (of Princess Leia) floating in air, which you can see from all angles. This is called volumetric image, and it has been featured in many Hollywood movies, including Avatar (big image-projecting table) and Ironman (3D displays Tony Stark interacts with).
The team has developed a free-space volumetric display technique based on photophoretic optical trapping. It is capable of projecting colorful, aerial volumetric images with 10 micron image points by vision persistence. Let’s dig deeper and find out what actually they’ve developed and how did they do it.
Holograms Vs. Volumetric Display
Hologram is a photographic recording of a light field that scatters light in two dimensional surface. It’s a light field encoding as an interference pattern of random variations in the density, opacity, or surface profile of the photographic medium. In order to see the 3D picture, you need to directly look at the scattering surface. Holograms can be used to store, retrieve and process data optically.
Volumetric display, on the other hand, forms a visual representation of an object in three physical dimensions. It creates 3D imagery through emission, scattering or relaying of illumination from 3D coordinates. It has little scattering surfaces scattered throughout a three dimensional space (the space occupied by the 3D picture).
This means, if a person is looking at the picture, he/she is also looking at the scatters. That is why, the display can be seen from all angles.
Projecting 3D Image Into Thin Air
The researchers used a laser beam to trap a particle. This beam can be steered around to change the location of particles and form the image. To understand it better, you can think it as a 3D printer for light – you are printing an object (3D image) in space with these tiny particles.
Optical Trap Display
The system works by isolating a cellulose particle in a photophoretic trap formed by astigmatic and spherical aberrations. These particles are then scanned via display volume while being illuminated with RGB light.
This results in a 3D image in free-space with a big color gamut and low apparent speckle. The platform is named Optical Trap Display, and it can produce image geometries that are currently unachievable with holograms and light-field technologies like tall sandtables, long-throw projections and ‘wrap around’ displays.
Projected Butterfly and Prism viewable from different angles
Limitations
The strength of trapping and holding particle varies greatly due to the wide distribution of the particle shapes and sizes, as well as the presence of multiple axial trapping sites of different quality and sizes. A particle may hop from one site to another under poor trapping conditions. The maximum achievable velocity and acceleration of particles depend on these variable conditions.
Once the optical particle and trap morphologies are identified and isolated, a clearer upper bound on the complexity of single-particle photo could be obtained.
Also, particles are sensitive to airflow. Under better trapping environments, trapped particles are robot to low airflow levels, including airflow produced by hand gestures and breathing.
Reference: Nature | doi:10.1038/nature25176 | BYU
However, it’s unlikely that the platform would work perfectly outdoors without an enclosure unless particles were much strongly confined or steps were taken to refresh trapped particles on a regular basis.
What’s Next?
Tall sandtable and vector rings that wraps around and arm
This is the first research team to use optical trapping and color effectively. So far, they have projected a 3D prism, butterfly, rings that wraps around an arm, stretch-Y BYU logo, a tall sandtable and a person crouched in a position very much similar to Princess Leia. All these projections have been small but colorful. With multiple beams and more work, they could achieve bigger projections.
Read: Transparent Materials Can Absorb Light | An Unusual Optical Effect
3D volumetric image of Erich Nygaard, mimicking the Princess Leia hologram
The technique could one day be used in entertainment purposes and to guide medical procedures. However, it is still years away from everyday use.
