Devices that use light to store and read
have been the backbone of data storage
for almost three decades.
CDs revolutionized data storage in
1980s followed by an improved version
of CDs, DVD, around 1997.
CDs and DVDs are the primary storage
media for music, software, personal
computing and video.
A CD can hold approximately 783
megabytes of data whereas a doublesided, double-layered DVD can hold up
to 15.9GB of data.
Although conventional storage mediums meet
today's storage needs, storage technologies have to
evolve to keep pace with increasing consumer
Today’s user requires such storage media that
provides faster data access ,huge storage capacity
but in a small package. To achieve this, scientists
are now working on a new optical storage method
called “Holographic Memory”.
Polaroid scientist Pieter J. vanHeerden
first proposed the idea of holographic
storage in the 1960s.
The Defence Advanced Research
Projects Agency (DARPA) and high-tech
giants IBM and Lucent's Bell Labs have
led the resurgence of holographic
Holographic Data Storage is an
advanced data storage concept that
stores information in the form of
Holographic Data Storage is a
volumetric approach of storing data.
An HDSS can store 1-4 TB of data on a
sugar-cube sized crystal.
The technology uses holograms which
are created when a light from a single
laser beam is split into two beams.
Uses a reference beam and a data beam
to create an interference pattern.
While writing :
The intersection of the two beams causes a
change, which is then stored.
Action of the reference beam and
interference pattern is used to recreate the
Blue-green argon laser is split into two
One is known as the object or signal
beam, and the other as the reference
Interference pattern created by these
two beams creates hologram.
SLM is a 1024 * 1024 array of light or
The array represents the data to be
stored, and is usually implemented by a
set of pixels on an LCD.
An SLM can be refreshed at rates of
about 1000 frames per second.
It is used to allow the laser beam to access
different pages in the hologram.
• Two types of multiplexing is used- shift and
• Shift multiplexing uses a rotating disc to vary
the angle of laser beam so as to access a
different view of the hologram, used in reading
• Angular multiplexing uses mirrors to change the
angle at which the laser strikes the crystal, used
in recording data.
There are mainly two storage mediums
• Lithium-niobate crystal, and
CCD is an array of sensors which corresponds to
the pixels on the SLM.
The CCD is used to read the interference pattern
from the reference beam, and also to read the
information from the hologram.
The matrix construction of the CCD allows it to
read1Mb data at once.
Typical CCD dimensions are one square
centimeter, and typical access rates are 1000
frames / second, or 1 Gigabit / second.
When the blue-green argon laser is fired, a beam
splitters creates two beams.
The object or signal beam travels straight and
bounces off one mirror and travels straight
through SLM(Spatial-Light Modulator).
The signal beam passes through a SLM, that
stores pages of raw binary data.
The information from the page is carried by the
signal beam to light-sensitive lithium-niobate
the reference beam shoots out the side of beam
splitters and takes a separate path to the
When the two beams meet ,the interference
pattern created stores the data in a specific area
in the crystal.
HDS contains information using an optical
interference pattern within a thick, photosensitive
Light from a single beam is divided into two separate
optical patterns of dark and light pixels.
By adjusting the reference beam angle, wavelength, or
media position, a multitude of holograms can be
stored on a single volume.
The stored data is read through the reproduction of
the same reference beam used to create the hologram.
The reference beam’s light is focused on the
photosensitive material, illuminating the appropriate
interference pattern, the light diffracts on the
interference pattern, and projects the pattern onto a
The detector is capable of reading the data in parallel,
over one million bits at once, resulting in the fast data
Files on the holographic drive can be accessed in less
than 0.2 seconds.
The word Hologram is derived from a Greek
word “holos” meaning whole and “gram”
A hologram contains the information about
size, shape, brightness and contrast of object
It is a 3-D image formed by the interference of
light beams from a laser or other coherent
Amplitude and phase modulation
Transmission and reflection holograms
Increased storage capacity
Increase read/write speed due to
Longer storage life
The challenge is to find the right
recording material-a photosensitive
substance that is both stable and cheap
enough to use commercially.
Problems with parallel recording.
Cross-talk noise, as it is known, causes
faint images all of the files recorded to
be called up even when only one is
Spatial light modulators in a low cost
Holographic recording is also very data
sensitive. You have to keep the data
streaming. It’s not appropriate for
The future of holographic memory is very promising.
The holographic storage provide high data density. It
can easily store 1000GB of data in a small cubic
centimeter crystal reducing the cost on the other hand.
It may offer high data transfer rate.
But even then the holographic way of storing data is
still at the base stage and it may take another couple
of years for this technique to hit desktop with a real life
data storage solution.
However this technology itself is dazzling and aims to
light up the desktop experienences.