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Under Development
Three-dimensional storage
Holographic solutions could turn the world of storage on
its head, says Venkatesh Ganesh
 Imagine a
scenario where storing a hundred movies on a single disc that sits comfortably
in the palm of your hand is possible. This technology, which uses holographic
techniques to store data, is being aggressively pursued by major storage companies
across the world. Theoretical calculations suggest that it will be possible
to store a terabyte (1,000 gigabytes) of data on a CD-sized disk using holographic
techniques. Contrast this to DVDs that can store less than 20 gigabytes and
you’ll see why holographic storage is being touted as the next big thing
in data storage. This is not a futuristic situation out of an Asimov novel,
but a technology that scientists and a handful of companies are working on.
The technology that makes this happen is termed “holographic storage”.
Optical storage goes 3D
Holographic data storage is an optical method of storage, wherein data is written
as light patterns in three dimensions. Data is stored on existing media in only
two dimensions. By storing data in 3D, this technique improves storage density.
Unlike other technologies that record one data bit at a time, holography allows
a million bits of data to be written and read in parallel with a single flash
of light. This enables significantly higher transfer rates than that of current
optical storage devices. Additionally, the flexibility of this technology allows
for the development of a whole host of holographic storage products that could
range from handheld devices for consumers to storage products for the enterprise.
In addition to high storage density, holographic data storage
promises fast access times since laser beams can be moved rapidly without inertia.
Since the interference patterns are spread uniformly throughout the material,
it endows holographic storage with another advantage—reliability. While
a defect in the medium for disk or tape storage might garble critical data,
a defect in a holographic medium doesn’t wipe out information. Instead,
it only results in a dimmer hologram. These advantages give holographic storage
an edge over conventional data storage techniques. However, interest levels
have risen considerably since the recent availability of relatively low-cost
components (such as liquid crystal displays for spatial light modulators (SLM)
and solid-state camera chips from video camcorders for detector arrays).
Commercial viability is elusive
Despite efforts, a complete and general-purpose system that is commercially
viable has eluded both industrial and academic researchers. The biggest challenge
for ‘holographic storage’ to gain mass acceptance is with respect
to finding the right material for the recording medium—one that works and
is inexpensive enough to produce commercially. A research team at IBM’s
Almaden Research Center has
built a precision Photo refractive Information Storage Materials (PRISM) test
stand for evaluating photosensitive samples. Apart from this, companies such
as InPhase Technologies (a spin-off of Bell Labs) and Polight Technologies are
some companies developing solutions in this space.
Large corporations may eventually make use of this technology. It could, for
instance, reduce a 12-hour backup to half an hour, overcoming pressures on the
daily archival window. Also, tape has a low archival life whereas holographic
storage can last up to 50 years. Industry analysts opine that it will take several
more years to refine the technology to build small desktop HDSS units. If it
takes shape, holographic storage will be anything but hollow.
| Light from a single laser is split into two beams,
the signal beam (which carries the data) and the reference beam. At the
point of intersection of the reference beam and the data carrier signal
beam, the hologram is recorded in the light sensitive storage medium. A
chemical reaction occurs in the medium when the bright elements of the signal
beam intersect the reference beam, causing the hologram to be stored. This
produces a replica of the original data. By varying the reference beam angle,
wavelength, or media position many different holograms can be recorded in
the same volume of material.
In order to read the data, the reference beam deflects
off the hologram thus reconstructing the stored information. This hologram
is then projected onto a detector that reads the data in parallel. This
parallel reading-out of data provides holography with its fast transfer
rates.
The process for encoding data onto the signal beam is
attained by a device called a spatial light modulator (SLM). The SLM translates
the electronic data of 0’s and 1’s into an optical “checkerboard”
pattern of light and dark pixels. The data is arranged in an array or
page of around a million bits. The exact number of bits is determined
by the pixel count of the SLM.
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venkatesh@expresscomputeronline.com
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