r & d BREAKING DOWN TECH —PRESENT AND FUTURE
54 MAXIMUMPC APRIL 2007
M
any of us got our fi rst taste of hologra-
phy when pint-size R2-D2 projected a
grainy 3D video of a desperate Princess Leia
pleading for Obi-Wan’s help in the fi rst Star
Wars movie. But holographic technology has
a fi rmer footing in reality than you might think:
Scientists have been researching the concept
since the late 1940s, and it could deliver the
next quantum leap in data storage.
Apply holography to digital storage and
you’ll be writing and reading data to and from
the interior dimensions of discs, instead of
just their surfaces. And one disc will have the
capacity to house the entire Star Wars col-
lection—bonus content and all—with room
to spare. With space for two to four terabytes
of data—or even more—holographic stor-
age could eventually replace not only opti-
cal drives, but magnetic hard drives, fl ash
memory, tape, and every other storage media
in use today, assuming the fi nal roadblocks to
the technology can be cleared.LIGHT READING
With today’s optical disc drives, a beam
of light generated by a laser passes
through a layer of clear protective plastic
to reach the surface of a spinning disc.
The data stored on the disc is arranged
in a continuous spiral of aberrations (pits
and lands or opaque and refl ective spots,
depending on the technology) representing
ones and zeros. An optical pickup monitors
and interprets these transitions.
Holography can produce a three-dimen-
sional image of an object using patterns of
light produced by a split beam of laser-gener-
ated light. Applying the concept to the stor-
age of bits requires an input device called a
spatial light modulator (SLM). SLMs are similar
in function to LCDs, but they’re many times
smaller. They produce an image reminiscent
of the static-fi lled TV screen from Poltergeist.
Examine the image closely, however, and
you’ll discern a structured checkerboard pat-
tern in which bright pixels (which allow light to
pass through) and dark pixels (which block the
passage of light) represents ones and zeros.
To create this image, the laser light is split
into a signal beam and a reference beam. The
signal beam passes through the SLM and
toward a photosensitive storage medium. The
reference beam is directed onto a mirrored
surface and bounced back toward the signal
beam. When the two beams intersect, they
create an interference pattern consisting of
light and dark regions. This interference pat-
tern instigates chemical and/or physical altera-
tions within the storage medium, producing a
tiny holographic image.Holographic storage achieves its stagger-
ing capacity by utilizing the depth of the stor-
age medium in addition to its two-dimensional
coordinates. By making minute changes in the
angle between the signal and reference beams
or by tweaking the laser’s wavelength, the drive
can store additional images at the exact same
X and Y coordinates but at different Z coordi-
nates. Researchers at IBM believe the theoreti-
cal limit of holographic storage approaches the
tens of terabits per cubic centimeter.
Only the reference beam is needed to
retrieve data. The light shines on the hologram
and projects an image of it to an optical detec-
tor, which reconstructs the pattern of ones and
zeros and converts them back into data.ALL THAT AND SPEED, TOO?
All that capacity would be useless if it took
an eternity to stash and retrieve data to andWhite Paper: Holographic Storage
HOW IT WORKS Holographic technology stores data in intricate patterns
BY GORD GOBLE1 RECORDING 2 RECORDING 3 RECORDING 4 READING
The intersection of two beams creates an
interference pattern of bright and dark regions.A photosensitive medium records the interference
pattern.Light from one beam shining on the hologram
reconstructs the data pattern.The hologram is the image
of the interference pattern
stored within the medium.InPhase Technologies’
first-generation holo-
graphic disc drive.Impossible dream or inex-
orable future? Holographic
storage could one day
deliver terabytes of storage
on a single optical disc.