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Price Cut: Hologram-producing Chip Developed for $10 by MIT Grad Student

Jun 20, 2013 10:05 AM EDT

Father's day recently passed and while most people opted for a card, come a few short years more individuals may be sending their love via a hologram of themselves, and they would have Massachusetts Institute of Technology to thank.

Researchers at MIT reported Wednesday the development of a new approach to generating the futuristic interfaces that is far cheaper than today's experimental, monochromatic displays. And for those less interested in a "mini-me" of themselves, the researchers further stated the same technique could be used to increase the resolution of conventional 2-D displays.

Stephen Benton, an MIT professor who passed away in 2003, created one of the first holographic-video displays using an acousto-optic modulation, in which sound waves were sent through a piece of transparent material. As they did so, they squeezed and stretched it, changing the index of its refraction.

Later, a more sophisticated display, the Mark-II, was built with the help of a colleagues and applied acousto-optic modulation to a crystal of an expensive material called tellurium dioxide.

"That was the biggest piece of tellurium dioxide crystal that had ever been grown," Michael Bove, who joined in Benton's later study and acted as the thesis advisor to the current one, said in a press release. "And that wasn't TV resolution. So there was a definite scaling problem going on there."

For this reason, Daniel Smalley, a graduate student at the school's Media Lab, used a much smaller crystal of material called lithium niobate and, just beneath the surface, created microscopic channels known as waveguides, which confine the light traveling through them. Onto each waveguide, he deposited a metal electrode capable of producing an acoustic wave.

Because each waveguide corresponds to one row of pixels in the final image, the waveguides with their individual electrodes can be packed mere micrometers apart from each other, unlike the Mark-II, which demanded the tellurium dioxide crystal be big enough that the acoustic waves producing the separate lines of the hologram were insulated from each other.

Beams of red, green and blue light are then sent down each waveguide in Smalley's device, and the frequencies of the acoustic wave passing through the crystal determine what colors pass through and what colors are filtered out. This way, combining, for example, red and blue to make purple doesn't require a separate waveguide for each color; rather, it only requires a difference acoustic-wave pattern.

This, according to Bove, is the most exciting part of the new chip housing the new technology.

"Until now, if you wanted to make a light modulator for a video projector, or an LCD panel for a TV, or something like that, you had to deal with the red light, the green light and the blue light separately," he said. "If you look closely at an LCD panel, each pixel actually has three little color filters in it. There's a red subpixel, a green subpixel and a blue subpixel."

Not only is such a process inefficient given that the filters, even if they were perfect, would throw away two-thirds of the light, but it also reduces either the resolution or the speed at the modulator can operate at.

All told, the chip, which resembles a microscopic slide, was built using only MIT facilities for approximately $10.

"This has the potential to be a game-changer, and I'm really serious about that," said Pierre Blanche, an assistant research professor at the University of Arizona who is also researching holographic video. "It's a huge achievement."

Furthermore, while Blanche says the experimental holographic-video system that he and Nasser Peyghambarian, chair of photonics and lasers at Arizona, are developing boasts better image quality, the MIT system, he says, achieves video rate, which is something they lack.

According to Smalley, however, the most exciting thing about the new chip is that it's waveguide-based platform, which represents a significant departure from all other types of spatial light modulators used for holographic video currently.

"One of the big advantages here is that you get to use all the tools and techniques of integrated optics," he explained. "Any problem we're going to meet now in holographic video displays, we can feel confidence that there's a suite of tools to attack it, relatively simply."

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