Researchers at MIT’s Media Lab discovered
a new approach to generate holograms that could lead to color holographic-video
displays that are much cheaper to manufacture than today’s experimental,
monochromatic displays. The same technique could also increase the resolution
of conventional 2D displays. Using the new technique, researchers are building
a prototype color holographic-video display whose resolution is roughly that of
a standard-definition TV and which can update video images 30 times a second,
fast enough to produce the illusion of motion. The heart of the display is an
optical chip, resembling a microscope slide for about $10. When light strikes
an object with an irregular surface, it bounces off at a huge variety of
angles, so that different aspects of the object are disclosed when it’s viewed
from different perspectives. In a hologram, a beam of light passes through a
so-called diffraction fringe, which bends the light so that it, too, emerges at
a host of different angles.
One way to produce holographic
video is to create diffraction fringes from patterns displayed on an otherwise
transparent screen. The problem with that approach is that the pixels of the
diffraction pattern have to be as small as the wavelength of the light they’re
bending, and most display technologies don’t happily shrink down that much. The
team used a small crystal of a material called lithium niobate. Just beneath
the surface of the crystal microscopic channels (known as waveguides) are
created, which confine the light traveling through them. Each waveguide
corresponds to one row of pixels in the final image. Beams of red, green and
blue 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. Combining, say, red and blue to produce purple doesn’t
require a separate waveguide for each color; it just requires a different
acoustic-wave pattern.
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