Download 3D Optical Data Storage CONTENTS

CONTENTS
›
Introduction
›
Overview
›
Media design
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Media form factor
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Media manufacturing
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Commercial development
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Development issue
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Method of simulation
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Defect modes and light localization in 2d pbg structures
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Three-dimensional photonic-crystal optical-memory systems
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Basic component
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Advertisements AND dis advertisements
› Conclusion
› References
INTRODUCTION
›
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
DVD-sized 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".
OVERVIEW
• 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.
MEDIA DESIGN
• 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 solgel materials have
been used.
MEDIA FORM FACTOR
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.
MEDIA MANUFACTURING
›
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.
DRIVE DESIGN
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
COMMERCIAL DEVLOPMENT
› 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
METHOD OF SIMULATION
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.
Defect modes and light localization in 2D PBG
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.
THREE-DIMENSIONAL PHOTONIC-CRYSTAL
OPTICAL-MEMORY SYSTEMS
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.
BASIC COMPONENTS
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:
›
›
›
›
›
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Laser
Lens and Mirrors
Spatial Light Modulators (SLM)
Photosensitive materials
Charge Coupled Devices (CCD)
Phase masks for encryption
LASER
›
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.
LENS AND MIRROR
›
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
SPATIAL LIGHT MODULATOR
› 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.
PHOTOSENSITIVE MATERIALS
› Photorefractive crystals
› Photopolymers
PHOTO REFLECTIVE CRYSTAL
› 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.
PHOTO POLYMER
› 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 DVDROM 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).
Charge Coupled Devices(CCD)
› 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.
PHASE MASK FOR ENCRYPTION
 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.
ADVANTAGES
› 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 read-many,
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
DISADVANTAGES
› 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.
CONCLUSION
In this presentation, 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.
REFERENCES
›
Hunter, S., Kiamilev, F., Esener, S., et al., 1990, Appl. Opt., 29, 2058.
›
Parthenopoulos, D.A and Rentzepis, P.M., 1989, Science, 245, 643.
›
Dvornikov, A.S., Cokgor, I., McCormick, F.B., et al., 1996, Opt. Commun.,
128, 205.
›
Wang, M.M., Esener, S.C., McCormick, F.B., et al., 1997, Opt. Lett., 22,
558.
›
Akimov, D.A., Zheltikov, A.M., Koroteev, N.I., et al., 1996, Kvantovaya
Elektron., 23, 871.