3d optical data

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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

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    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".

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    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.

    http://en.wikipedia.org/wiki/File:3D_optical_storage_cross-section.svg
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    The active part of 3D optical storage media is usually an organic polymer either

    doped or grafted with the photo chemically active species. Alternatively, crystallineand sol-gel materials have been used.

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    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 viewof portability and convenience, but would be of a lower capacity than a disc.

    Crystal, Cube or Sphere: Severalscience 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.

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    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.

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    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 formfactor 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:

    LaserVariable spherical aberration correction

    Optical system

    Detection

    Data tracking

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    In addition to the academic research, several companies have been set up tocommercialize 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.

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    Despite the highly attractive nature of 3D optical data storage, the

    development of commercial products has taken a significantlength of time. This results from limited financial backing in the

    field, as well as technical issues, including:

    Destructive reading

    Thermodynamic stability

    Media sensitivity

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    Rapidly growing applications of PBG structures have alreadyresulted in an impressive progress in the development of

    theoretical approaches for the analysis of the properties of light

    in such structures.

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    The channeling of a light beam was observed regardlessof the period , indicating that the effects described

    above do not result from the interference

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    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.

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    Optical data storage system requires certain important materials for its datastorage and retrieval processes. The important components required for the

    optical data storage are:

    Laser

    Lens and MirrorsSpatial Light Modulators (SLM)

    Photosensitive materials

    Charge Coupled Devices (CCD)

    Phase masks for encryption

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    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.

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    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

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    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. Thecomputer sends binary data to the SLM.

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    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.

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    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).

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    The charge-coupled device is, by far, the most common mechanism for

    converting optical images to electrical signals. CCDs 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 msquare. Current CCDs have formats orresolution better than 2048 *2048 pixels, with a size of about 25mm square.

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    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