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INTRODUCTION
OVERVIEW
MEDIA DESIGN
MEDIA FORM FACTOR
MEDIA MANUFACTURING
COMMERCIAL DEVLOPMENT
DEVELOPMENT ISSUE
METHOD OF SIMULATION
DEFECT MODES AND LIGHT LOCALIZATION IN 2D PBG STRUCTURES
THREE-DIMENSIONAL PHOTONIC-CRYSTAL OPTICAL-MEMORY SYSTEMS
BASIC COMPONENT
ADVERTISEMENTS AND DIS ADVERTISEMENTS
CONCLUSION
REFERENCES
 3D optical data storage is the term given to any form of optical data storage in
which information can be recorded and/or read with three dimensional resolution
(as opposed to the two dimensional resolution afforded, for example, by CD).
This innovation has the potential to provide byte-level mass storage on DVDsized disks. Data recording and read back are achieved by focusing lasers within
the medium.
No commercial product based on 3D optical data storage has yet arrived on
the mass market, although several companies are actively developing the
technology and claim that it may become available "soon".
Current optical data storage media, such as the CD and DVD store data as a series of
reflective marks on an internal surface of a disc. In order to increase storage capacity, it
is possible for discs to hold two or even more of these data layers, but their number is
severely limited since the addressing laser interacts with every layer that it passes
through on the way to and from the addressed layer.
The active part of 3D optical storage media is usually an organic polymer either
doped or grafted with the photo chemically active species. Alternatively, crystalline
and sol-gel materials have been used.
Media for 3D optical data storage have been suggested in several form
factors:
 Disc: A disc media offers a progression from CD/DVD, and allows reading
and writing to be carried out by the familiar spinning disc method.
 Card: A credit card form factor media is attractive from the point of view
of portability and convenience, but would be of a lower capacity than a disc.
 Crystal, Cube or Sphere: Several science fiction writers have suggested
small solids that store massive amounts of information, and at least in
principle this could be achieved with 3D optical data storage.
The simplest method of manufacturing - the molding of a disk in one piece
is a possibility for some systems.
A more complex method of media manufacturing is for the media to be
constructed layer by layer.
This is required if the data is to be physically created during manufacture.
However, layer-by-layer construction need not mean the sandwiching of many
layers together.
A drive designed to read and write to 3D optical data storage media
may have a lot in common with CD/DVD drives, particularly if the form
factor and data structure of the media is similar to that of CD or DVD.
However, there are a number of notable differences that must be taken into
account when designing such a drive, including:
Laser
Variable spherical aberration correction
Optical system
Detection
Data tracking
In addition to the academic research, several companies have been set up to
commercialize 3D optical data storage and some large corporations have also
shown an interest in the technology.
However, it is not yet clear whether the technology will succeed in the
market in the presence of competition from other quarters such as hard drives,
flash storage, and holographic storage.
Examples of 3D optical data storage media.
Top row - Written Call/Recall media; Mempile media.
Middle row - FMD; D-Data DMD and drive.
Bottom row - Landauer media; Microholas media in action.
Despite the highly attractive nature of 3D optical data storage, the
development of commercial products has taken a significant
length of time. This results from limited financial backing in the
field, as well as technical issues, including:
Destructive reading
Thermodynamic stability
Media sensitivity
Rapidly growing applications of PBG structures have already
resulted in an impressive progress in the development of
theoretical approaches for the analysis of the properties of light
in such structures.
The channeling of a light beam was observed regardless
of the period Λ , indicating that the effects described
above do not result from the interference
Different modifications of 3D optical memory units based on photonic
band-gap structures can be proposed, depending on the arrangement of
writing and reading beams in space, as well as on whether a one-, two-,
or multiphoton process is used to produce the luminescence readout
signal.
Optical data storage system requires certain important materials for its data
storage and retrieval processes. The important components required for the
optical data storage are:
 Laser
 Lens and Mirrors
 Spatial Light Modulators (SLM)
 Photosensitive materials
 Charge Coupled Devices (CCD)
 Phase masks for encryption
Laser is a device for the generation of coherent, nearly monochromatic and
highly directional electromagnetic radiation emitted, somewhere in the range
from sub-millimeter through ultraviolet and X-ray wavelengths.
More than two hundred types of lasers have been fabricated which range in
power, size, performance, use and cost.
Mirrors are used to reflect laser beams to the desired direction. Lenses are
usually used to converge the laser to a point.
A special type of lens is used in the case of optical recording called the
Fourier lens.
The lens has the property of obtaining the Fourier transform and the
inverse transform system is described below:
lens as a Fourier transform system
SLM is an optical device that is used to convert the real image or data into a
single beam of light that will intersect with the reference beam during
recording.
It basically consists of an array of pixels which are usually microscopic
shutters or LCD displays. These can be controlled by a computer. The
computer sends binary data to the SLM.
There are two main classes of materials used for the holographic storage
medium. These are photo refractive crystals and photo polymers. The
recording medium usually used is a photo refractive crystal such as LiNbO3
or BaTiO3 that has certain optical characteristics.
These characteristics include high diffraction efficiency, high resolution,
permanent storage until erasure, and fast erasure on the application of external
stimulus such as UV light.
Photo refractive crystals are suitable for random access memory with
periodic refreshing of data, and can be erased and written to many times.
Photopolymers have been developed that can also be used as a
holographic storage medium.
Typically the thickness of the photopolymers is much less than the
thickness of photo refractive crystals because the photopolymers are limited
by mechanical stability and optical quality.
example :
A photopolymer is a 100 m thickness, which is greater than DVD-ROM
by a factor of two. Stored holograms are permanent and do not degrade over
time or by read out of the hologram, so photopolymers are suited for read
only memory (ROM).
The charge-coupled device is, by far, the most common mechanism for
converting optical images to electrical signals. CCD’s are silicon devices,
which contain an array of potential wells created through a series of column,
implants (for vertical confinement).
Each pixel is typically 15 to 30 μm square. Current CCD’s have formats or
resolution better than 2048 *2048 pixels, with a size of about 25mm square.
There is wide spread interest in the development of encryption systems,
which operate in the optical domain.
The advantages inherent in the optical approach to encryption, such as a
high space-bandwidth product, the difficulty of accessing, copying or
falsification and the possibility of including biometrics are widely recognized.
In an encryption system, we wish to encode information in such a fashion
that even if it is viewed or copied only the application of the correct key will
reveal the original information.
Durability. With proper care, optical media can last a long time,
depending on what kind of optical media you choose.
Great for archiving. Several forms of optical media are write-once readmany, which means that when data is written to them, they cannot be reused.
This is excellent for archiving because data is preserved permanently with
no possibility of being overwritten.
Transportability. Optical media are widely used on other platforms,
including the PC. For example, data written on a DVD-RAM can be read on
a PC or any other system with an optical device and the same file system.
Random access. Optical media provide the capability to pinpoint a
particular piece of data stored on it, independent of the other data on the
volume or the order in which that data was stored on the volume
Reusable. The write-once read-many (WORM) characteristic of some
optical media makes it excellent for archiving, but it also prevents you
from being able to use that media again.
Writing time. The server uses software compression to write
compressed data to your optical media. This process takes considerable
processing unit resources and may increase the time needed to write and
restore that data.
In this paper, we applied the finite-difference time domain
technique to analyze light localization and channeling in a defect mode
of a two-dimensional PBG structure. This analysis shows that a light
field in such a structure can be localized in a sub wavelength-size area,
suggesting a new way of arranging three-dimensional optical-memory
devices.
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