By Farooq Ahmed
The 1971 Nobel Prize in physics was awarded to the Hungarian-British electrical engineer Dennis Gabor for inventing the field of holography. It wasn’t until six years later, however, that the discipline would gain widespread recognition. In 1977, the movie “Star Wars” arrived in U.S. theaters, and the robot R2-D2 projected Princess Leia Organa saying the memorable words, “Help me, Obi-Wan Kenobi. You’re my only hope.” While Leia’s projection technically was not a hologram but a volumetric light-field display (a technique used to bring back to the stage deceased entertainers such as Elvis Presley and Tupac Shakur), three-dimensional holograms have been inextricably linked with a vision of the future. Current applications in holography are poised to usher it in.
“We’ve already lost control of the term hologram, and we have George Lucas to thank!” said Dan Novy, a post-doctoral associate in the Object-Based Media group at MIT’s Media Lab. Novy spent nearly two decades working in the visual effects industry and won awards, including an Emmy, on popular television shows and films such as Red Planet, Deep Blue Sea, and Blood Diamond before joining MIT, first as a graduate student.
The Object-Based Media group is working on holographic waveguides that may make another invention of science fiction become a reality—Tony Stark’s (a.k.a. Iron Man’s) smartphone from the popular Marvel films. Stark’s phone, which appears to be an ultra-thin version of a modern smartphone but made entirely from transparent glass or plastic, both displays and projects interactive, three-dimensional images and movies. In theory, it could even display Princess Leia’s message without the need for a robot with a built-in projector.
Novy said that they “wanted to replace the big, bulky, black monolithic [smartphones] with something more elegant.” “A hologram is the only medium by which you can create an object that is a perfect replica of an object you’re interested in—a true simulacrum.”
The MIT group’s waveguide uses surface acoustic waves to alter the index of refraction. The researchers were able to create full-motion, 30 frames per second, full red-green-blue three-color holograms when they pulsed the waveguide with coherent light and then modulated that light with an acoustic chirp (1). “We can actually do color mixing in the waveguide,” Novy said. Smartphones with the waveguides could be made nearly one-third thinner than traditional devices, much like Tony Stark’s phone, because it would not require red, green, and blue phosphors.
The scientists and engineers experimented with manufacturing techniques as well. Novy said that they used traditional proton-exchange methods but also femtosecond lasers to create the waveguides from a lithium niobate substrate (2). “Femtosecond laser manufacturing is almost literally like sending a job to the printer from your computer as far as the process, but it is extremely slow—right now.”
Novy foresees holograms appearing on nearly any transparent surface to provide information, assistance, and entertainment. “Holographic heads-up displays on car windshields could be overlaid onto streets to help drivers navigate, for example,” he said.
As Novy points out, holographic techniques have the potential to transform nearly any display. This could be a boon for augmented and virtual reality devices, which have had trouble gaining widespread adoption because of a longstanding problem: Even after relatively short periods, users often experience headaches, eye strain, and nausea when wearing displays. These issues are caused by the vergence-accommodation mismatch, in which a user’s brain must reconcile the disparity between perceiving virtual objects in three-dimensions while focusing on the flat screen of the display just centimeters in front of the eyes. True holograms, Novy said, would allow the eyes to relax. “The wavefront of the virtual, perceived object would just rest directly on your retina.”