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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 microphotonics 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 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

nanoparticles are an increasingly applied

and

bioconjugation,

gold

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 750nanometer-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