Holographic Data Storage
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computer science crazy
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21-09-2008, 10:41 AM


Mass memory systems serve computer needs in both archival and backup needs. There exist numerous applications in both the commercial and military sectors that require data storage with huge capacity, high data rates and fast access. To address such needs 3-D optical memories have been proposed. Since the data are stored in volume, they are capable of much higher storage densities than existing 2-D memory systems. In addition this memory system has the potential for parallel access. Instead of writing or reading a sequence of bits at each time, entire 2-D data pages can be accessed at one go. With advances in the growth and preparation of various photorefractive materials, along with the advances in device technologies such as spatial light modulators(SLM), and detector arrays, the realizations of this optical system is becoming feasible.

A hologram is a recording of the optical interference pattern that forms at the intersection of two coherent optical beams. Typically, light from a single laser is split into two paths, the signal path and the reference path.. The beam that propagates along the signal path carries information, whereas the reference is designed to be simple to reproduce. A common reference beam is a plane wave: a light beam that propagates without converging or diverging. The two paths are overlapped on the holographic medium and the interference pattern between the two beams is recorded. A key property of this interferometric recording is that when it is illuminated by a readout beam, the signal beam is reproduced. In effect, some of the light is diffracted from the readout beam to "reconstruct" a weak copy of the signal beam. If the signal beam was created by reflecting light off a 3D object, then the reconstructed hologram makes the 3D object appear behind the holographic medium. When the hologram is recorded in a thin material, the readout beam can differ from the reference beam used for recording and the scene will still appear.

Volume Holograms
To make the hologram, the reference and object beams are overlapped in a photosensitive medium, such as a photopolymer or inorganic crystal. The resulting optical interference pattern creates chemical and/or physical changes in the absorption, refractive index or thickness of the storage media, preserving a replica of the illuminating interference pattern. Since this pattern contains information about both the amplitude and the phase of the two light beams, when the recording is illuminated by the readout beam, some of the light is diffracted to "reconstruct" a weak copy of the object beam .If the object beam originally came from a 3-D object, then the reconstructed hologram makes the 3-D object reappear. Since the diffracted wave front accumulates energy from throughout the thickness of the storage material, a small change in either the wavelength or angle of the readout beam generates enough destructive interference to make the hologram effectively disappear through Bragg selectivity.

As the material becomes thicker, accessing a stored volume hologram requires tight tolerances on the stability and repeatability of the wavelength and incidence angle provided by the laser and readout optics. However, destructive interference also opens up a tremendous opportunity: a small storage volume can now store multiple superimposed holograms, each one distributed throughout the entire volume. The destructive interference allows each of these stored holograms to be independently accessed with its original reference beam. To record a second, angularly multiplexed hologram, for instance, the angle of the reference beam is changed sufficiently so that the reconstruction of the first hologram effectively disappears. The new incidence angle is used to record a second hologram with a new object beam. The two holograms can be independently accessed by changing the readout laser beam angle back and forth. For a 2-cm hologram thickness, the angular sensitivity is only 0.0015 degrees. Therefore, it becomes possible to store thousands of holograms within the allowable range of reference arm angles (typically 20-30 degrees). The maximum number of holograms stored at a single location to date7 is 10,000.
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gani021974
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22-01-2012, 06:36 PM

pls send me the full report of holographic data storage(electronics)
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seminar addict
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23-01-2012, 11:03 AM

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bhavana n
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09-02-2012, 12:36 AM

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seminar addict
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09-02-2012, 10:17 AM

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seminar flower
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17-08-2012, 03:55 PM

Holographic Data Storage


.ppt   Data-Storage-Technology.ppt (Size: 1.33 MB / Downloads: 20)

What is Holographic System

Leverages More Data Storage
1500 CDs or 200 DVDs Data in Single DVD.
Optical Storage Method
Data Stored as Optical Interference Pattern known as holograms

How it Works

Laser beams splits into 2 beams.
Beams works as object beam and Reference beam.
To read the stored data, the media is illuminated by original reference beam.
Thousands of Holograms can be stored in the same location by simply changing angle of reference.
Multiple Data Recording is possible by Using Light at Different angles

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seminar flower
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20-09-2012, 12:18 PM

Holographic data storage



.docx   Holographic data storage.docx (Size: 44.32 KB / Downloads: 13)

Holographic data storage is a potential technology in the area of high-capacity data storage currently dominated by magnetic and conventional optical data storage. Magnetic and optical data storage devices rely on individual bits being stored as distinct magnetic or optical changes on the surface of the recording medium. Holographic data storage overcomes this limitation by recording information throughout the volume of the medium and is capable of recording multiple images in the same area utilizing light at different angles.
Additionally, whereas magnetic and optical data storage records information a bit at a time in a linear fashion, holographic storage is capable of recording and reading millions of bits in parallel, enabling data transfer rates greater than those attained by traditional optical storage.

Recording data

Holographic data storage contains information using an optical interference pattern within a thick, photosensitive optical material. Light from a single laser beam is divided into two separate optical patterns of dark and light pixels. By adjusting the reference beam angle, wavelength, or media position, a multitude of holograms (theoretically, several thousand) can be stored on a single volume.

Reading data

The stored data is read through the reproduction of the same reference beam used to create the hologram. The reference beam’s light is focused on the photosensitive material, illuminating the appropriate interference pattern, the light diffracts on the interference pattern, and project and implimentations the pattern onto a detector. The detector is capable of reading the data in parallel, over one million bits at once, resulting in the fast data transfer rate. Files on the holographic drive can be accessed in less than 200 milliseconds.[2]

Longevity

Holographic data storage can provide companies a method to preserve and archive information. The write-once, read many (WORM) approach to data storage would ensure content security, preventing the information from being overwritten or modified. Manufacturers[who?] believe this technology can provide safe storage for content without degradation for more than 50 years, far exceeding current data storage options[dubious – discuss]. Counterpoints to this claim are that the evolution of data reader technology has – in the last couple of decades – changed every ten years. If this trend continues, it therefore follows that being able to store data for 50–100 years on one format is irrelevant, because you would migrate the data to a new format after only ten years. However, claimed longevity of storage has, in the past, proven to be a key indicator of shorter-term reliability of storage media. Current optical formats – such as CD – have largely lived up to the original longevity claims (where reputable media makes are used) and have proved to be more reliable shorter-term data carriers than the floppy disc and DAT tape media they displaced

Effect of annealing

For a doubly doped lithium niobate (LiNbO3) crystal there exists an optimum oxidation/reduction state for desired performance. This optimum depends on the doping levels of shallow and deep traps as well as the annealing conditions for the crystal samples. This optimum state generally occurs when 95 – 98% of the deep traps are filled. In a strongly oxidized sample holograms cannot be easily recorded and the diffraction efficiency is very low. This is because the shallow trap is completely empty and the deep trap is also almost devoid of electrons. In a highly reduced sample on the other hand, the deep traps are completely filled and the shallow traps are also partially filled. This results in very good sensitivity (fast recording) and high diffraction efficiency due to the availability of electrons in the shallow traps. However during readout, all the deep traps get filled quickly and the resulting holograms reside in the shallow traps where they are totally erased by further readout. Hence after extensive readout the diffraction efficiency drops to zero and the hologram stored cannot be fixed.

Development and marketing

At the National Association of Broadcasters 2005 (NAB) convention in Las Vegas, InPhase conducted public demonstrations of the world’s first prototype of a commercial storage device at the Maxell Corporation of America booth.
The three main companies involved in developing holographic memory, as of 2002, were InPhase and Polaroid spinoff Aprilis in the United States, and Optware in Japan.[5] Although holographic memory has been discussed since the 1960s,[6] and has been touted for near-term commercial application at least since 2001,[7] it has yet to convince critics that it can find a viable market.[8] As of 2002, planned holographic products did not aim to compete head to head with hard drives, but instead to find a market niche based on virtues such as speed of access


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