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 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".

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 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

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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