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ABSTRACT
While many people think that Blu-ray will replace DVDs in the near future, a new
study shows that DVDs may still have a lot to offer. Researchers have designed a
five-dimensional DVD that can store 1.6 terabytes of data on a standard-size DVD,
which is the equivalent of about 30 Blu-ray discs. The 5D DVDs could also be
compatible with current DVD disc-drive technology. The researchers, led by micro-
photonics researcher James Chon from the Swinburne University of Technology in
Hawthorn, Australia, have presented the new DVD high-density data storage
technique in a recent issue of Nature. While scientists have been considering 3D
optical data storage for a while, this is the first time data has been recorded and read
in five dimensions: three dimensions of stacked layers, and two new dimensions of
wavelength (color) and polarization.
5D DVDs use a writing system that uses extremely tiny particles on which data is
written, with multiple layers that are read by three different colors of laser (rather
than only one, as is the case with DVDs and Blu-ray discs). According to the
developers, this could result in discs with a capacity of 10 terabytes, approximately
2000 times the capacity of a standard DVD, compared to Holographic Versatile Disc
technology, which has an estimated maximum disc capacity of 6 terabytes. The
similarity of disc writing would also make it easier to make 5D DVD player’s
backwards-compatible with existing CD and DVD technology.
LIST OF CONTENTS
1. Introduction
1.1. Optical Recording
1.2. Existing Technology
2. Five Dimensional Optical Recording
2.1. Dimensions of data storage
3. Design and Fabrication of Storage device
3.1. Basic Design
3.2. Gold Nanorods
3.3. SPR of Gold Nanorods
3.4. Effect of Colored Light
3.5. Effect of Polarized Light
4. Reading and Writing
4.1. Recording
4.2. Reading
5. Fields of Application
6. Advantages
7. Disadvantages
8. Future Scope and Enhancement
9. CONCLUSION
10.REFERENCES
1. INTRODUCTION
1.1 Optical Recording
The process of recording signals on a medium through the use of light, so that
the signals may be reproduced at a subsequent time. Photographic film has been
widely used as the medium, but in the late 1970s development of another medium, the
so-called optical disk, was undertaken. The introduction of the laser as a light source
greatly improves the quality of reproduced signals. Optical data storage involves
placing information in a medium so that, when a light beam scans the medium, the
reflected light can be used to recover the information. There are many forms of optical
storage media like CD, DVD, Blu Ray Disc etc, and many types of systems are used to
scan data.
1.2 Existing Technology
At present there exist so many different medium for performing optical
recording. They are
1. Floppy Disc
2. Compact Disc (CD)
3. Digital Versatile Disc (DVD)
4. Blu Ray Disc
5. Holographic Versatile Disc
In the case of CDs, DVDs and Blu Ray discs data is present on the surface of
the medium in the form of bumps and grooves which can be read from or written into
by the use of lasers. But in the case of Holographic versatile disc, memory will go
beneath the surface and use the volume of the recording medium for storage, instead
of only the surface area. But the quest for larger storage memory resulted in the
invention of Five dimensional optical recoding technique which will give rise to a new
range of optical disc.
2. FIVE DIMENSIONAL OPTICAL RECORDING
A team of researchers consisting of Dr.Min Gu, Mr. Peter Zijlstra and Prof.
James Won at the Swinburne University of Technology in Hawthorn, Australia
have tested a new type of five-dimensional optical storage medium that they estimated
might hold up to 2,000 times more data
than a conventional DVD.
The tinkering trio resorted to gold nanorods to coat the surface of an optical
disc. Nanomaterials, it seems, are photo reactive and adjust their shape according to
different colors of the visible spectrum, which were illuminated by lasers in this case.
The team then followed up by applying multiple polarizations to the same physical disc
space, effectively writing the data at different angles in the same place.
This means that data - usually written in a typical three dimensional (x, y, z)
fashion - acquired two more dimensions. So far this has already resulted in an optical
disc sample capable of storing 1.6TB of data, but as development continues,
researchers expect storage capacity to reach a whopping 10TB. Although wavelength,
polarization and spatial dimensions have all been exploited for multiplexing, these
approaches have never been integrated into a single technique which could ultimately
increase the information capacity by orders of magnitude.
2.1 Dimensions Of Data Storage
A parameter by which a single bit of data written on or read from an optical
recording device can be identified is known as a dimension of data storage. In the
case of CDs and DVDs human s have used their knowledge of two dimensional optical
recording technique to store data on a plane surface. With the invention multi layered
optical storage devices like dual layer DVDs and Holographic versatile disc we have
introduced a third spatial dimension. But the need for greater storage volume has
forced us to introduce more dimensions of data storage into the field of optical
recording.
The different dimensions of data storage used in five dimensional optical
recording are:
Three Spatial Dimensions : This include the three spatial dimensions x, y and z.
Three dimensional optical recording technique is currently being used in the many
optical storage devices.
Color dimension : Three-dimensional technology uses a single color laser beam or
light wavelength to read the data in the form of bits on
a platter. By using nanotechnology in the form of small gold rods that reflect light, the
researchers were able to create a spectral or color dimension. To create the color
dimension, the researchers inserted gold nanorods onto a disc's surface. Because
nanoparticles react to light according to their shape, this allowed the researchers to
record
information in a range of different color wavelengths on the same physical disc
location.
Polarization dimension : The polarization dimension was created when
researchers projected light waves onto the disc and the direction of the electric field
contained in the light waves aligned with the gold nanorods. That allowed the
researchers to record different layers of information at different angles. The
researchers were able to record data at two different polarization of light. One at 0°
polarization and other at 90° polarization.
3. DESIGN AND FABRICATION OF STORAGE DEVICE
3.1 Basic Design
The design of an optical device that incorporates five dimensional optical
recording technique is quite similar to digital versatile disc except in the use of gold
nanorods. They dispersed gold nanorods of three different sizes in a polymer solution,
coated thin glass films with the solution, and then used glue to assemble a stack of
three of the films, one on top of the other.
The substrate used is mainly made of polycarbonate. A substrate provides
mechanical support for the storage layer. The substrate also provides a measure of
contamination protection, because light is focused through the substrate and into the
recording layer. Dust particles on the surface of the substrate only partially obscure the
focused beam, so enough light can penetrate for adequate signal recovery.
a : The layer gold nanorods in a polymer solution and coated on a thinlayer of glass
b : The spacer between two recording layers
c : The polycarbonate substrate on which the whole system is mounted so as to get
mechanical strength to the disc
3.2 Gold Nanorods
With the advancement in nanotechnology scientists are now able to fabricate
nanoparticles of different metals in various shapes and sizes like rods, spheres, tubes
etc. During the research and development phase of five dimensional optical recording
the scientists opted for nanoparticles of gold in the shape of rods called gold nanorods
as a recording medium. Gold nanorods of different sizes are used in different recording
layers. Aqueous solutions containing a high yield of suspended gold nanorods have
been successfully synthesized via an electrochemical method.
The above picture shows the magnified image of gold nanorods under
microscope.
It is the unique properties of gold nanorods under light that made the
researchers use in five dimensional optical recording. Metallic nanoparticles/rods are
at the heart of nanotechnology revolution, due to their extraordinary optical and
electronic properties caused by quantum confinement effects. The most important
property of this new class of materials is that they are spectrum and polarization
sensitive materials which can be a full benefit to encoding in those dimensions,
providing multidimensionality.
Gold nanoparticles exhibit strong optical extinction at visible and near-infrared
wavelengths which can be tuned by adjusting the size. With recent advances in their
high-yield synthesis, stabilization, functionalization and bioconjugation, gold
nanoparticles are an increasingly applied
nanomaterial. Gold nanorods are particularly suitable for photonic, optoelectronic, and
biotechnological applications in the near-infrared
spectral region because of the strong dependence of their longitudinal plasmon
wavelength on the aspect ratio. One additional advantage of gold nanorods is that light
emitted from or scattered off gold nanorods is strongly polarized along the rod length
axis, making them an ideal orientation probe.
3.3 SPR Of Gold Nanorods
Surface plasmon resonance emerges from the interaction between an
electromagnetic wave and the conduction electrons in a metal. Under the
irradiation of light, the conduction electrons in a gold nanostructure are given by the
electric field to collectively oscillate at resonance frequency relative to the lattice of
positive ions. At this resonant frequency, the incident light interacts with the
nanostructure. Some of the photons will be released with the same frequency in all
directions and this process is known as scattering. At the same time, some of the
photons will be converted into phonons or vibrations of the lattice and this process is
referred to as absorption. In general, the SP resonance peak of a gold nanostructure
should include both scattering and absorption components.
The frequency and bandwidth of the SP resonance depends on the size and
shape of the nanoparticles as well as their dielectric constant and that of the
surrounding medium. For nanorods, the SP resonance splits into two bands: parallel
(longitudinal) and perpendicular (transverse) to the long axis of the nanorod. As the
aspect ratio of the rod increases, the energy separation between the two SP
resonance frequencies increases, the longitudinal SP resonance being lower in energy
than the transverse SP resonance.
So by explaining both parallel and perpendicular surface plasmon resonance of
gold we can explain the involvement of the two new dimensions of data storage that is
colored light and polarization.
3.4 Effect Of Colored Light
The surface plasmon resonance of gold nanorods mainly depends on
wavelength of the electromagnetic radiation that is incident on it. The
absorbance of the light which is converted into lattice vibrations is different for different
light.
The amount by which the light energy that absorbed or reflected by the gold
nanorods mainly depends on its size. That is the reason why a five dimensional optical
recording device uses gold nanorods of different sizes (mainly three different sizes are
used) to record data. Each layer of recording medium has gold nanorods of a
particular size so that they will resonate only when a particular wavelength of light.
Mainly red, green and blue colored lights are used in the recording device which
is completely different from the traditional drives that uses laser of a fixed wavelength.
The size of gold nanorods required for each coloured light is experimently decided by
the scientists and they form the different layers of the recording device
(a) (b) (c)
The above figure shows the far-field images of SPR modes of the same single
gold nano-rod for various incident laser light at (A) red (658 nm), (B) green (532 nm),
and (C) blue (488 nm) respectively.
3.4 Effect Of Polarized Light
Since light is an electromagnetic wave it consists of electric and magnetic field
components which oscillate in phase perpendicular to eachother and perpendicular to
the direction of energy propagation. Polarization is a property of waves that describes
the orientation of their oscillations. The polarization of light is described by specifying
the direction of the wave's electric field. When light travels in free space, in most cases
it propagates as a transverse wave, the polarization is perpendicular to the wave's
direction of travel. In this case, the electric field may be oriented in a single direction
(linear polarization), or it may rotate as the wave travels (circular or elliptical
polarization).
The polarization dimension was created when researchers projected light
waves onto the disc and the direction of the electric field contained in the light waves
aligned with the gold nanorods. That allowed the researchers to record different layers
of information at different angles.
The polarization can be rotated 360 degrees. Scientists were able to record at
zero degree polarization. Then on top of that, were able to record another layer of
information at 90 degrees polarization, without them interfering w ith each other.
The above figure shows how we can record different data in a same space
using laser giving out light of same wavelength but different polarization. If the gold
nanorods are aligned in the direction of polarization of the light they will get heated up
and melt into spheres while other nanorods in the neighborhood may remain in the
original shape depending on its relative positioning with the incoming light. Thus we
can perform recording techniques.
The figure given below illustrates that.
4. READING AND WRITING
4.1 Recoding
To record on the disc, the researchers focused a tunable laser onto 750-
nanometer-wide spots on a gold nanorod layer. The tiny rods have a
tendency to collapse into spheres when they absorb light and are heated to a certain
threshold. But the rods are selective. Nanorods of a specific size absorb a specific
wavelength and then only if they are aligned with the direction of the light’s
polarization. Under those conditions, the energy
waves traveling along the rods’ surface—called surface plasmons—resonate with the
light’s frequency. So when the laser beam is focused on the bits, only some of the rods
turn into spheres. Light impinging with a certain color and polarization will only target a
subpopulation of gold nanorods, leaving the remaining rods for the next recording.
That means each bit area can hold multiple bits. The scientist tested with three
different wavelengths and two different polarizations. To demonstrate the technology,
they created six patterns on each of the three nanorod layers by focusing light on a
grid of 75-by-75 bits. Reasearchers says they could have fit 1.1 terabits per cubic
centimeter on the disk. The volume of their disk is about 12 cm3, which gives a total
data capacity of 1.6 terabytes.
4.2 Reading
After writing the gold nanorods permanently changes its from rods to spheres.
Reading the bits involves focusing light from the same laser on the bits but with much
lower energy. The nanorods shine when they absorb the dim light, which must be of
the same wavelength and polarization that could change their shape during recording.
Once written its impossible to perform a re-writing procedure since its not
possible for the gold nanorods to change shape from spheres back to rods.
5. FIELDS OF APPLICATION
Even though the five dimensional optical recording system is still not available
in the commercial scale, the scientists predict its applicability in wide range of arenas.
A few of them are :
1. Medical Field
Mainly used to store information large data related to magnetic resonance
imaging scans (MRI) of a patients.
2. Military and Security Arenas
Provides a light and compact way of storing huge data corresponding to
research and development department of the military where large magnetic storage
devices are use.
3. Entertainment sector
Act as a large storage device to store super high definition or ultra high
definition videos.
4. Space research
Used to store high resolution images taken by space telescopes and it provides
a single point of data storage for the entire data produced by space satellites. Its small
size and light weight may also be an added advantage.
5. Financial Sector
Can be used as a backup storage of data produced in large financial institutions
like stock exchanges where the loss of data is very problematic.
6. ADVANTAGES
1. Large storage capacity
A disc that developed on the principle of five dimensional optical recording is to
said to have a storage capacity of 1.5 tera byte.
2. Light and Compact
A five dimensional optical recording device will have dimensions comparable to
a normal DVD, hence making light and compatible.
3. Data security
It provides a safe and secure method of data storage.
4. Compatible with existing technology
By reducing the thickness of the spacer we can reduce the thickness of the
recording device thereby making it compatible with existing technology.
5.Can be manufactured on a large scale
Once the drive for performing the reading and writing procedure is developed
the recording disc can be manufactured on a large scale according to the drive
specifications.
7. DISADVANTAGES
1. Slow writing speed
Since the data density is high the disc needs a high data transfer rate hence
writing to the disc a slow process. But the writing speed can be made comparable with
writing speed of DVD slightly reducing the data density without affecting the storage
capacity of the disc by a great deal.
2. Impracticality of using Titanium Sapphire Femtosecond Laser
Currently the researches where carried by a large titanium sapphire
femtosecond laser which is very costly process. But the developers are planning to
develop a cheaper and smaller diode laser which is compatible with the drive.
3. Re-writability
Since the Gold nanorods are altered from its natural shape during writing from
rods to spheres re writabillty is not possible.
8.FUTURE SCOPE AND ENHANCEMENT
The Australian researchers are optimistic about the technology. They say that
data recording could be done with a cheaper laser diode and that highspeed recording
and readout should be possible. The research, in the meantime, has been looked upon
up by the storage giant Samsung, which now seems destined to manufacture the
media that records every bit of stored data on the planet. The company says that this
technology should be ready within the next five to ten years. The researchers are
planning to developing discs having capacity ranging upto 10 TB by further increasing
the layers of recording medium.
9. CONCLUSION
By the introduction of two more dimensions to the existing technology of three
dimensional optical recording , that is color dimension and polarization we can
increase the data density to attain a storage capacity of 1.5 TB in a volume of 12 cm ³.
Thus five dimensional optical recording is proving to be a promising technology for the
future in the field of bulk data storage. The disc developed according to this technology
will be available in the market within the next 5 to 10 years.
10. REFERENCES
[1]. www.research.ibm.com/journal/rd/443/vettiger.html
[2]. http://en.wikipedia.org/wiki/IBM_Millipede
[3]. www.domino.research.ibm.com/comm/pr.nsf/pages/rsc.millipede.html
[4]. www.news.zdnet.co.uk/hardware/0,1000000091,39191254,00.html
[5].
www.news.cnet.com/Photos-IBMs-Millipede-packsapunch/20091015_35615611.html
[6]. www.searchstorage.techtarget.com/sDefinition/0,,sid5_gci966197,00.html