Presented by:
CHENNA AVINASH

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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.
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.