Scientists Create New Holographic Video Technique
Lee Rannals for redOrbit.com – Your Universe Online
Researchers are using this new technique to build a prototype color holographic-video display with a resolution similar to that of a standard-definition TV that can update video images 30 times a second. The heart of the display features an optical chip that resembles a microscopic slide.
“Everything else in there costs more than the chip,’ says Michael Bove, a principal research scientist at the MIT Media Lab and head of its Object-Based Media Group. “The power supplies in there cost more than the chip. The plastic costs more than the chip.”
As light strikes an object with an irregular surface, it bounces off at a variety of angles. In a hologram, a beam of light passes through a “diffraction fringe,” which bends the light so that it emerges at a host of different angles.
Stephen Benton, an MIT Media Lab professor who died in 2003, created one of the first holographic-video displays by using a technique known as acousto-optic modulations. With this technique, sound waves are sent through a piece of transparent material.
“The waves basically squeeze and stretch the material, and they change its index of refraction,” Bove says. “So if you shine a laser through it, [the waves] diffract it.”
The new technique uses smaller crystals of a material known as lithium niobate. Beneath the surface of materials he creates microscopic channels known as waveguides, which confines the light traveling through them. He also deposits a metal electrode onto each waveguide, which produces an acoustic wave.
Each of these waveguides corresponds to one row of pixels in the first image. The chip allows the waveguides and their individual electrodes to be packed more micrometers apart from each other. Beams of different colored light are sent down each waveguide, and the frequencies of the acoustic wave passing through the crystal determine which colors pass through and which are filtered out.
“What’s most exciting about [the new chip] is that it’s a waveguide-based platform, which is a major departure from every other type of spatial light modulator used for holographic video right now,” said Daniel Smalley, a graduate student in the Media Lab and first author on the new paper who created the chip.
“One of the big advantages here is that you get to use all the tools and techniques of integrated optics,” Smalley added. “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.”
Pierre Blanche, an assistant research professor at the University of Arizona who is also researching holographic video, said the MIT team’s research has potential to be a game changer.
“The SB product is the product between the number of pixels and their spatial frequency – the inverse of their size,” he says. “So we are looking for a large number of very small pixels. To have a large number of pixels is not really helpful if they are large.”