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HOLOGRAPHIC STORAGE TECHNOLOGY
A Technical Report submitted
in partial fulfillment of the requirement
for the award of the degree of
BACHELOR OF TECHNOLOGY
In
ELECTRONICS AND COMMUNICATION ENGINEERING
By
K.VARUN KUMAR
(09PQ1A0463)
Department of Electronics and Communication Engineering
ANURAG COLLEGE OF ENGINEERING(Approved by A.I.C.T.E New Delhi, Affiliated to J.N.T.U. Hyderabad)
Aushapur(V), Ghatkesar(M), R.R.Dist- 501301
2012-2013
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ANURAG COLLEGE OF ENGINEERING(Approved by A.I.C.T.E New Delhi, Affiliated to J.N.T.U. Hyderabad)
Aushapur(V), Ghatkesar(M), R.R.Dist- 501301
2012-2013Department of Electronics and Communication Engineering
Bonafide Certificate
This is to certify that the Technical Report entitled HOLOGRAPHIC STORAGE
TECHNOLOGY, is being submitted by KANDUKURI VARUN KUMAR bearing the
Regd. No. 09PQ1A0463 in partial fulfillment for the award of the degree of Bachelor
of Technology in ELECTRNOICS AND COMMUNICATION ENGINEERING is a
record of confide work carried out by him under my guidance and supervision during the
academic year 20122013 and it has been found worthy of acceptance according to the
requirements of the university.
Guide Head of the Department
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ACKNOWLEDGEMENT
I have successfully completed my technical report. It happens only because of some
auxiliary co-operation from some people.
K.VARUN09PQ1A0463
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ABSTRACT
Devices that use light to store and read data have been the backbone of data
storage for nearly two decades. Compact discs revolutionized data storage in the early1980s, allowing multi-megabytes of data to be stored on a disc that has a diameter of a
mere 12 centimeters and a thickness of about 1.2 millimeters.
In 1997, an improved version of the CD, called a digital versatile disc (DVD),
was released, which enabled the storage of full-length movies on a single disc. CDs and
DVDs are the primary data storage methods for music, software, personal computing and
video. A CD can hold 783 megabytes of data, which is equivalent to about one hour and
15 minutes of music, but Sony has plans to release a 1.3-gigabyte (GB) high-capacity
CD. A double-sided, double-layer DVD can hold 15.9 GB of data, which is about eight
hours of movies. These conventional storage mediums meet today's storage needs, but
storage technologies have to evolve to keep pace with increasing consumer demand.
CDs, DVDs and magnetic storage all storebits of information on the surface of
a recording medium. In order to increase storage capabilities, scientists are now working
on a new optical storage method, called holographic memory, that will go beneath the
surface and use the volume of the recording medium for storage, instead of only the
surface area. Three-dimensional data storage will be able to store more information in a
smaller space and offer faster data transfer times
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CONTENTS
1. INTRODUCTION
1.1. COMPACT DISK
1.2. DIGITAL VERSATILE DISK
1.3. BLUR-RAY DISK
2. HOLOGRAPHIC DATA STORAGE
2.1. HOLGRAPHY
2.2. DESKTOP HOLOGRAPHIC DATA STORAGE
2.3. THE HOLOGRAPHIC DATA
2.4. RECORDING OF DATA IN HOLOGRAPHIC MEMORY
SYSTEMS
2.5. RETRIEVING OF DATA IN HOLOGRAPHIC MEMORY
SYSTEMS
2.6. PAGE DATA ACCESS2.7. RECORDING ERRORS
2.8. PAGE LEVEL PARITY BITS
3. MERITS & CHALLENGES OF HOLOGRAPHIC STORAGE
3.1. MERITS OF HOLOGRAPHHIC MEMORY
3.2. CHALLENGES
4. POSSIBLE APPLICATIONS
5. CONCLUSION
6. REFERENCES
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LIST OF FIGURES
FIG 1.1 CROSS SECTION OF CD
FIG 1.2 REFLECTION OF LASER IN CD
FIG 1.3 REFLECTION OF LASER ON PIT
FIG 1.4 TRACK OF CD
FIG 1.5 TRACK OF DVD
FIG 1.6 DVD Vs. BLU-RAY CONSTRUCTION
FIG 2.1 HOLOGRAHIC DATA STORAGE SYSTEM
FIG 2.2 WRITING OF DATA
FIG 2.3 READING OF DATA
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1. INTRODUCTION
The hologram was invented in 1947 by Dennis Gabor to record images in a
medium (e.g., a crystal). It has a very unique feature, namely, any small part of the
medium contains all information about the image. Therefore, even if the medium isbroken into pieces, the entire image can still be obtained from any piece, except the
resolution is reduced.
Holographic memory offers the possibility of storing 1 terabyte (TB) of data in
a sugar-cube-sized crystal. A terabyte of data equals 1,000 gigabytes, 1 million
megabytes or 1 trillion bytes. Data from more than 1,000 CDs could fit on a holographic
memory system. Most computerhard drives only hold 80 to 160 GB of data, a small
fraction of what a holographic memory system might hold. Polaroid scientist Pieter J. van
Heerden first proposed the idea of holographic (three-dimensional) storage in the early
1960s. A decade later, scientists at RCA Laboratories demonstrated the technology by
recording 500 holograms in an iron-doped lithium-niobate crystal, and 550 holograms of
high-resolution images in a light-sensitive polymer material.
Devices that use light to store and read data have been the backbone of data
storage for nearly two decades. It started from CDs which can store 700MB and has
moderate speed. Then came DVD which can store up to 17 GB and has speed up to 10
Mbps. Recently in 2006 ,BLU-RAY disc was launched which has capacity up to 54 GB
and speed of 36 Mbps.
But looking to the future we need to go ahead and find a better way of storing
data, a easier way which is far more better in speed as well as memory. In to achieve this
scientist have proposed a new technology which uses 3-D layers instead of conventional
2-D. This technology is named HOLOGRAPHIC DATA STORAGE
1.1 COMPACT DISC(CD):
Most of a CD consists of an injection-molded piece of clear polycarbonate
plastic. During manufacturing, this plastic is impressed with microscopic bumps
arranged as a single, continuous, extremely long spiral track of data. A CD has a
single spiral track of data, circling from the inside of the disc to the outside. The
elongated bumps that make up the track are each 0.5 microns wide, a minimum of
0.83 microns long and 125 nanometers high.
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FIG 1.1CROSS SECTION OF CD
A label layer
B protection layer
C Data layer (reflection layer)D protection layer (transparent)
E Logical 0 (bump)
F Logical 1 (pit)
DATA RETRIEVAL IN CD:
The data in the cd is stored in these extremely small bumps. The data is
retrieved with the help of a red laser beam in the manner as shown.
FIG 1.2 REFLECTION OF LASER IN CD
In the first image, we see that the laser (A), reflects (Image 1) on the
bump. The reflected laser light however does not seem to reach the sensor (B). The
CD-player interprets this as a logical ZERO.
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FIG 1.3 REFLECTION OF LASER ON PIT
In the second image we see a reflection on a pit (Image 2). Here we see that the
reflected laser light DOES reach the sensor (B). This is being interpreted by the CD-
player as a logical ONE. The incredibly small dimensions of the bumps make the spiral
track on a CD extremely long. If we could lift the data track off a CD and stretch it out
into a straight line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long
1.2 DIGITAL VERSATILE DISC(DVD):
DVDs are of the same diameter and thickness as CDs, and they are made
using some of the same materials and manufacturing methods. Like a CD, the data on
a DVD is encoded in the form of small pits and bumps in the track of the disc. The
elongated bumps that make up the track are each 320 nanometers wide, a minimum of
400 nanometers long and 120 nanometers high. The biggest advantage of a DVD over
a CD is that the pits and the tracks in DVD are smaller so that it takes less space than
a DVD to store the same amount of data. Thus physically tighter spacing of pits on a
DVD increases its storing capabilities.
FIG 1.4 TRACK OF CD FIG 1.5 TRACK OF DVD
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1.3 BLU-RAY DISC:
The movie industry has set a revolution with the introduction of Blu-ray Discs
(BD) in 2006. With their high storage capacity, Blu-ray discs can hold and play back
large quantities of high-definition video and audio, as well as photos, data and other
digital content. Unlike current DVDs, which use a red laser to read and write data, Blu-
ray uses a blue laser. A blue laser has a shorter wavelength (405 nanometers) than a redlaser (650 nanometers). The smaller beam focuses more precisely, enabling it to read
information recorded in pits that are only 0.15 microns (m) long. Because of this in a
Blu-ray the track pitch has been reduced from 0.74 microns to 0.32 microns.
FIG 1.6 DVD Vs. BLU-RAY CONSTRUCTION
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2. HOLOGRAPHIC DATA STORAGE
2.1 HOLOGRAPHY:
A hologram is a block or sheet of photosensitive material which records the
interference of two light sources. To create a hologram, laser light is first split into two
beams, a source beam and a reference beam. The source beam is then manipulated and
sent into the photosensitive material. Once inside this material, it intersects the reference
beam and the resulting interference of laser light is recorded on the photosensitive
material, resulting in a hologram. Once a hologram is recorded, it can be viewed with
only the reference beam. The reference beam is projected into the hologram at the exact
angle it was projected during recording. When this light hits the recorded diffraction
pattern, the source beam is regenerated out of the refracted light. An exact copy of the
source beam is sent out of the hologram and can be read by optical sensors. For example,
a hologram that can be obtained from a toy store illustrates this idea. Precise laser
equipment is used at the factory to create the hologram. A recording material which can
recreate recorded images out of natural light is used so the consumer does not need high-
tech equipment to view the information stored in the hologram. Natural light becomes the
reference beam and human eyes become the optical sensors.
Holography was invented in 1947 by the Hungarian-British physicist Dennis
Gabor (1900-1979), who won a 1971 Nobel Prize for his invention.
DESKTOP HOLOGRAPHIC DATA STORAGE
After more than 30 years of research and development, a desktop holographic
storage system (HDSS) is close at hand. Early holographic data storage devices will have
capacities of 125 GB and transfer rates of about 40 MB per second. Eventually, these
devices could have storage capacities of 1 TB and data rates of more than 1 GB per
second -- fast enough to transfer an entireDVD movie in 30 seconds. So why has it taken
so long to develop an HDSS, and what is there left to do?
Like other media, holographic media is divided into write once (where the
storage medium undergoes some irreversible change), and rewritable media (where the
change is reversible). Rewritable holographic storage can be achieved via the
photorefractive effect in crystals.
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2.2 The HOLOGRAPHIC DATA STORAGE SYSTEM:
Prototypes developed by Lucent and IBM differ slightly, but most
holographic data storage systems (HDSS) are based on the same concept. Here are the
basic components that are needed to construct an HDSS:
Blue-green argon laser Beam splitters to spilt the laser beam
Mirrors to direct the laser beams
LCDpanel (spatial light modulator)
Lenses to focus the laser beams
Lithium-niobate crystal or photopolymer
Charge-coupled device (CCD) camera
FIG 2.1 HOLOGRAPHIC DATA STORAGE SYSTEM
When the blue-green argon laser is fired, a beam splitter creates two beams.
One beam, called the object or signal beam, will go straight, bounce off one mirror and
travel through a spatial-light modulator (SLM). An SLM is a liquid crystal display (LCD)
that shows pages of raw binary data as clear and dark boxes. The information from the
page of binary code is carried by the signal beam around to the light-sensitive lithium-
niobate crystal. Some systems use a photopolymer in place of the crystal.
A second beam, called the reference beam, shoots out the side of the beam
splitter and takes a separate path to the crystal. When the two beams meet, the
interference pattern that is created stores the data carried by the signal beam in a specific
area in the crystal -- the data is stored as a hologram .
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An advantage of a holographic memory system is that an entire page of data
can be retrieved quickly and at one time. In order to retrieve and reconstruct the
holographic page of data stored in the crystal, the reference beam is shined into the
crystal at exactly the same angle at which it entered to store that page of data. Each page
of data is stored in a different area of the crystal, based on the angle at which the
reference beam strikes it. During reconstruction, the beam will be diffracted by the
crystal to allow the recreation of the original page that was stored. This reconstructed
page is then projected onto the charge-coupled device (CCD) camera, which interprets
and forwards the digital information to a computer. The key component of any
holographic data storage system is the angle at which the second reference beam is fired
at the crystal to retrieve a page of data. It must match the original reference beam angle
exactly. A difference of just a thousandth of a millimeter will result in failure to retrieve
that page of data.
2.4 RECORDING OF DATA IN HOLOGRAPHIC MEMORY
SYSTEM
When the blue-green argon laser is fired, a beam splitter creates two beams.
One beam, called the object or signal beam, will go straight, bounce off one mirror and
travel through a spatial-light modulator (SLM). An SLM is a Liquid crystal display
(LCD) that shows pages of raw binary data as clear and dark boxes. The information
from the page of binary code is carried by the signal beam around to the light-sensitive
lithium-niobate crystal. Some systems use a photopolymer in place of the crystal. A
second beam, called the reference beam, shoots out the side of the beam splitter and takes
a separate path to the crystal. When the two beams meet, the interference pattern that is
created stores the data carried by the signal beam in a specific area in the crystal - the
data is stored as a hologram.
FIG. 2.2 WRITING OF DATA
2.5 RETRIEVAL OF DATA FROM HOLOGRAPHIC MEMORY
SYSTEM
An advantage of a holographic memory system is that an entire page of data
can be retrieved quickly and at one time. In order to retrieve and reconstruct the
holographic page of data stored in the crystal, the reference beam!
s shined into thecrystal at exactly the same angle at which it entered to store that oage of data. Each page
of data is stored in a different area of the crystal, based on the angle at which the
reference beam strikes it. During reconstruction, the beam will be diffracted by the
crystal to allow the recreation of the original page that was stored. This reconstructed
page is then projected onto the charge-coupled device (CCD) camera, which interprets
and forwards the digital Formation to a computer.
Laser
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Recording
medium
RecoveredData
CCD is a 2-D array of thousands or millions of tiny solar cells, each of
which transforms the light from one small portion of the image into electrons. Next step
is to read the value (accumulated charge) of each cell in the image. In a CCD device, the
charge is actually transported across the chip and read at one corner of the array. An
analog-to-digital converter turns each pixel's value into a digital value. CCDs use a
special manufacturing process to create the ability to transport charge across the chip
without distortion. This process leads to very high-quality sensors in terms of fidelity and
light sensitivity. CCD sensors have been mass produced for a longer period of time, so
they are more mature. They tend to have higher quality and more pixels. The key
component of any holographic data storage system is the angle at which the second
reference beam is fired at the crystal to retrieve a page of data. It must match the original
reference beam angle exactly. A difference of just a thousandth of a millimeter will result
in failure to retrieve that page of data.
011101010101001010
FIG 2.3 READING OF DATA
2.6 PAGE DATA ACCESS
Because data is stored as page data in a hologram, the retrieval of this data must
also be in this form. Page data access is the method of reading stored data in sheets, not
serially as in conventional storage systems. It was mentioned in the introduction that
conventional storage was reaching its fundamental limits. One such limit is the way datais read in streams.
Holographic memory reads data in the form of pages instead. For example, if a
stream of 32 bits is sent to a processing unit by a conventional read head,a holographic
memory system would in turn send 32 x 32 bits, or 1024 bits due to its added dimension.
This provides very fast access times in volumes far greater than serial access methods.
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The volume could be one Megabit per page using a SLM resolution of 1024 x 1024 bits
at 15-20 microns per pixel.
2.7 RECORDING ERRORS
When data is recorded in a holographic medium, certain factors can lead to
erroneously recorded data. One major factor is the electronic noise generated by laserbeams. When a laser beam is split up ( for example, through a SLM ), the generated light
bleeds into places where light was meant to be blocked out. Areas where zero light is
desired might have minuscule amounts of laser light present which mutates its bit
representation. For example, if too much light gets recorded into this zero area
representing a binary 0, an erroneous change to a binary 1 might occur. Changes in both
the quality of the laser beam and recording material are being researched, but these
improvements must take into consideration the cost-effectiveness of a holographic
memory system. These limitations to current laser beam and photosensitive technology
are some of the main factors for the delay of practical holographic memory systems.
2.8 PAGE-LEVEL PARITY BITS
Once error-free data is recorded into a hologram, methods which read data
back out of it need to be error free as well. Data in page format requires a new way to
provide error control. Current error control methods concentrate on a stream of bits.
Because page data is in the form of a two dimensional array, error correction needs to
take into account the extra dimension of bits. When a page of data is written to the
holographic media, the page is separated into smaller two dimensional arrays. These sub
sections are appended with an additional row and column of bits. The added bits calculate
the parity of each row and column of data. An odd number of bits in a row or column
create a parity bit of 1 and an even number of bits create a 0. A parity bit where the row
and column meet is also created which is called an overall parity bit. The sub sections are
rejoined and sent to the holographic medium for recording.
3. MERITS & CHALLENGES OF HOLOGRAPHIC STORAGE
3.1 MERITS OF HOLOGRAPHIC MEMORY
Holographic memory offers storage capacity of about 1 TB. Speed of
retrieval of data in tens of microseconds compared to data access time of almost 10ms
offered by the fastest hard disk today. By the time they are available they can transfer an
entire DVD movie in 30 seconds. Information search is also faster in holographic
memory. Consider the case of large databases that are stored on hard disk today. To
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retrieve any piece of information you first provide some reference data. The data is then
searched by its address, track, sector and so on after which it is compared with the
reference data. In holographic storage entire pages can be retrieved where contents of two
or more pages can be compared optically without having to retrieve the information
contained in them. Also HDSS has no moving parts. So the limitations of mechanical
motion such as friction can be removed.
3.2 CHALLENGES
During the retrieval of data the reference beam has to be focused at exactly
the same angle at which it was projected during recording. A slight error can cause a
wrong data page to be accessed. It is difficult to obtain that much of accuracy. The crystal
used as the photographic filament must have exact optical characteristics such as high
diffraction efficiency, storage of data safely without any erasure and fast erasure on
application of external stimulus light ultra violet rays. With the repeated number of
accesses the holograms will tend to decay.
4. POSSIBLE APPLICATIONS
There are many possible applications of holographic memory.
Holographic memory systems can potentially provide the high-speed transfers and largevolumes of future computer systems. One possible application is data mining.
Data mining is the process of finding patterns in large amounts of data. Data miningis
used greatly in large databases which hold possible patterns which can.t be
distinguished by human eyes due to the vast amount of data. Some current computer
systems implement data mining, but the mass amount of storage required is pushing
the limits of current data storage systems. The many advances inaccess times and data
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storage capacity that holographic memory provides could exceed conventional storage
and speed up data mining considerably. This would result in more located patterns
in a shorter amount of time.Another possible application of holographic memory is in
petaflop computing. A petaflop is a thousand trillion floating point operations per
second. The fast access in extremely large amounts of data provided by holographic
memory systems couldbe utilized in a petaflop architecture. Clearly advances are needed
in more than memory systems, but the theoretical schematics do exist for such a
machine. Optical storage such as holographic memory provide a viable solution to the
extreme amount of data which is required for petaflop computing.
HOLOGRAPHIC MEMORY VS. CONVENTIONAL STORAGE DEVICES
Storage Medium Access Time
Data Transfer Rate
Storage Capacity
Holographic
Memory
2.4 us lOGB/s 400 Mbits/cm2
Main Memory
(RAM)
10-40 ns 5 MB/s 4.0 Mbits/cm2
Magnetic Disk 8.3 ms 5-20 MB/s 100 Mbits/cm2
5. CONCLUSION
The future of holographic memory is very promising. The page access of
data that holographic memory creates will provide a window into next generation
computing by adding another dimension to stored data. Finding holograms in
personal computers might be a bit longer off, however. The large cost of high-tech
optical equipment would make small-scale systems implemented with holographic
memory impractical. Holographicmemory will most likely be used in next
generation super computers where cost is not as much of an issue. Currentmagnetic
storage devices remain far more cost effective than any other medium on the market.
As computer systems evolve, it is not unreasonable to believe that magnetic storage
will continue to do so. As mentioned earlier, however, these improvements are not
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made on the conceptual level. The current storage in a personal computer operates on
the same principles used in the first magnetic data storage devices. The parallel nature
of holographic memory has many potential gains on serial storage
methods.However, many advances in optical technology and photosensitive
materials need to be made before we find holograms in computer systems.
6. REFERENCES
1. http://www.howstuffworks.com
2. http://[email protected]
3. http ://www. stanford.edu/~svngam/
http://www.howstuffworks.com/http://nford.edu/~svngam/http://www.howstuffworks.com/http://nford.edu/~svngam/