29659592 Holographic Data Storage System Seminar Report

8/3/2019 29659592 Holographic Data Storage System Seminar Report

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Project Report

On

HOLOGRAPHIC

MASS STORAGE SYSTEM

Submitted To Submitted By

Mrs. Jyoti Kaushik Ankit Bansal

ECE Dept. 11082021MMEC ECE (D2)


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Acknowledgment

Firstly I would like to express my sincere gratitude to the Almighty for His solemn presencethroughout the seminar study. I would also like to express my special thanks to the HOD Mr.

Naveen Hemrajani for providing an opportunity to undertake this seminar. I am deeply indebted to

our seminar coordinators for providing me with valuable advice and guidance during the course of

the study.

I would like to extend my heartfelt gratitude to the Faculty of the Department of Computer

Science and Engineering for their constructive support and cooperation at each and every juncture

of the seminar study.

Finally I would like to express my gratitude to Gyan Vihar College of Engineering and

Technology for providing me with all the required facilities without which the seminar studywould not have been possible.


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Table of Contents

Table of contents1.Abstract..............................................................................................................................32.Introduction........................................................................................................................43.Technical Aspect...............................................................................................................54.Holograms..........................................................................................................................85.Underlying Technology.....................................................................................................106. Working.............................................................................................................................167. Application......................................................................................................................178. Advantages & Disadvantages of HDSS..........................................................................219. Comparison.....................................................................................................................2210.HVD at a glance..............................................................................................................2311..Bibliography.....................................................................................................................25


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1.Abstract

Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which

would greatly increase storage over Blue-ray Disc and HD DVD optical disc systems. It employs

a technique known as collinear holography, whereby two lasers, one red and one blue-green, arecollimated in a single beam. The blue-green laser reads data encoded as laser interference fringes

from a holographic layer near the top of the disc while the red laser is used as the reference beam

and to read servo information from a regular CD-style aluminium layer near the bottom. Servo

information is used to monitor the position of the read head over the disc, similar to the head,

track, and sector information on a conventional hard disk drive. On a CD or DVD this servo

information is interspersed amongst the data.

A dichroic minor layer between the holographic data and the servo data reflects the blue-green

laser while letting the red laser pass through. This prevents interference from refraction of the

blue-green laser off the servo data pits and is an advance over past holographic storage media,

which either experienced too much interference, or lacked the servo data entirely, making them

incompatible with current CD and DVD drive technology. These discs have the capacity to hold

up to 3.9 terabyte(TB) of information, which is approximately 6,000 times the capacity of a CD-

ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray Discs, and

about 8 times the capacity of standard computer hard drives as of 2006. The HVD also has a

transfer rate of 1 gigabit/s. Optware has released a 200 GB disc in early June 2006 and Maxell in

September 2006 with a capacity of 300 GB and transfer rate of 20 MB/s.


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2.Introduction

With its omnipresent computers, all connected via the Internet, the Information Age has led to an

explosion of information available to users. The decreasing cost of storing data, and the increasing

storage capacities of the same small device footprint, has been key enablers of this revolution.

While current storage needs are being met, storage technologies must continue to improve in orderto keep pace with the rapidly increasing demand.

Devices that use light to store and read data have been the backbone of data storage for nearly two

decades. Compact discs revolutionized data storage in the early 1980s, allowing multi-megabytes

of data to be stored on a disc that has a diameter of a mere 12 centimeters and a thickness of about

1.2 millimeters. In 1997, an improved version of the CD, called a digital versatile disc (DVD),

was released, which enabled the storage of full-length movies on a single disc.

CDs and DVDs are the primary data storage methods for music, software, personal computing and

video. A CD can hold 783 megabytes of data. A double-sided, double-layer DVD can hold 15.9

GB of data, which is about eight hours of movies. These conventional storage mediums meet

today's storage needs, but storage technologies have to evolve to keep pace with increasing

consumer demand. CDs, DVDs and magnetic storage all store bits of information on the surface of

a recording medium. In order to increase storage capabilities, scientists are now working on a new

optical storage method called holographic memory that will go beneath the surface and use the

volume of the recording medium for storage, instead of only the surface area. Three-dimensional

data storage will be able to store more information in a smaller space and offer faster data transfer

times.

Holographic memory is developing technology that has promised to revolutionalise the storage

systems. It can store data upto 1 Tb in a sugar cube sized crystal. Data from more than 1000 CDscan fit into a holographic memory System. Most of the computer hard drives available today can

hold only 10 to 40 GB of data, a small fraction of what holographic memory system can hold.

Conventional memories use only the surface to store the data. But holographic data storage

systems use the volume to store data. It has more advantages than conventional storage systems. It

is based on the principle of holography. However, both magnetic and conventional optical data

storage technologies, where individual bits are stored as distinct magnetic or optical changes on

the surface of a recording medium, are approaching physical limits beyond which individual bits

may be too small or too difficult to store. Storing information throughout the volume of a

mediumnot just on its surfaceoffers an intriguing high-capacity alternative. Holographic data

storage is a volumetric approach which, although conceived decades ago, has made recent

progress toward practicality with the appearance of lower-cost enabling technologies, significantresults from longstanding research efforts, and progress in holographic recording materials.

In holographic data storage, an entire page of information is stored at once as an optical

interference pattern within a thick, photosensitive optical material (Figure 1). This is done by

intersecting two coherent laser beams within the storage material. The first, called the object

beam, contains the information to be stored; the second, called the reference beam, is designed to

be simple to reproducefor example, a simple collimated beam with a planar wavefront. The

resulting optical interference pattern causes chemical and/or physical changes in the

photosensitive medium: A replica of the interference pattern is stored as a change in the

absorption, refractive index, or thickness of the photosensitive medium. When the stored

interference grating is illuminated with one of the two waves that were used during recording[Figure 2(a)], some of this incident light is diffracted by the stored grating in such a fashion that


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the other wave is reconstructed. Illuminating the stored grating with the reference wave

reconstructs the object wave, and vice versa [Figure 2(b)]. Interestingly, a backward-propagating

or phase-conjugate reference wave, illuminating the stored grating from the back side,

reconstructs an object wave that also propagates backward toward its original source [Figure 2(c)].

A large number of these interference gratings or patterns can be superimposed in the same thickpiece of media and can be accessed independently, as long as they are distinguishable by the

direction or the spacing of the gratings. Such separation can be accomplished by changing the

angle between the object and reference wave or by changing the laser wavelength. Any particular

data page can then be read out independently by illuminating the stored gratings with the reference

wave that was used to store that page. Because of the thickness of the hologram, this reference

wave is diffracted by the interference patterns in such a fashion that only the desired object beam

is significantly reconstructed and imaged on an electronic camera. The theoretical limits for the

storage density of this technique are around tens of terabits per cubic centimeter.

.


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3.Technical Aspects

Like other media, holographic media is divided into write once (where the storage medium

undergoes some irreversible change), and rewritable media (where the change is reversible).

Rewritable holographic storage can be achieved via the photorefractive effect in crystals:

Mutually coherent light from two sources creates an interference pattern in the media. Thesetwo sources are called the reference beam and the signal beam.

Where there is constructive interference the light is bright and electrons can be promoted fromthe valence band to the conduction band of the material (since the light has given the electrons

energy to jump the energy gap). The positively charged vacancies they leave are

called holes and they must be immobile in rewritable holographic materials. Where there is

destructive interference, there is less light and few electrons are promoted.

Electrons in the conduction band are free to move in the material. They will experience twoopposing forces that determine how they move. The first force is the Coulomb force between

the electrons and the positive holes that they have been promoted from. This force encourages

the electrons to stay put or move back to where they came from. The second is the pseudo-

force ofdiffusion that encourages them to move to areas where electrons are less dense. If the

coulomb forces are not too strong, the electrons will move into the dark areas.

Beginning immediately after being promoted, there is a chance that a given electron willrecombine with a hole and move back into the valence band. The faster the rate of

recombination, the fewer the number of electrons that will have the chance to move into thedark areas. This rate will affect the strength of the hologram.

After some electrons have moved into the dark areas and recombined with holes there, there isa permanent space charge field between the electrons that moved to the dark spots and the

holes in the bright spots. This leads to a change in the index of refraction due to the electro-

optic effect.
http://en.wikipedia.org/wiki/Coherenthttp://en.wikipedia.org/wiki/Interference_patternhttp://en.wikipedia.org/wiki/Reference_beamhttp://en.wikipedia.org/wiki/Signal_beamhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Electronshttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Coulomb_forcehttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Refractive_indexhttp://en.wikipedia.org/wiki/Electro-optic_effecthttp://en.wikipedia.org/wiki/Electro-optic_effecthttp://en.wikipedia.org/wiki/Electro-optic_effecthttp://en.wikipedia.org/wiki/Electro-optic_effecthttp://en.wikipedia.org/wiki/Refractive_indexhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Coulomb_forcehttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Electronshttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Signal_beamhttp://en.wikipedia.org/wiki/Reference_beamhttp://en.wikipedia.org/wiki/Interference_patternhttp://en.wikipedia.org/wiki/Coherent


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When the information is to be retrieved or read out from the hologram, only the reference beam is

necessary. The beam is sent into the material in exactly the same way as when the hologram was

written. As a result of the index changes in the material that were created during writing, the beam

splits into two parts. One of these parts recreates the signal beam where the information is stored.

Something like a CCD camera can be used to convert this information into a more usable form.

Holograms can theoretically store one bit per cubic block the size of the wavelength of light in

writing. For example, light from a helium-neon laser is red, 632.8 nm wavelength light. Using

light of this wavelength, perfect holographic storage could store 4 gigabits per cubic millimeter. In

practice, the data density would be much lower, for at least four reasons:

The need to add error-correction The need to accommodate imperfections or limitations in the optical system Economic payoff (higher densities may cost disproportionately more to achieve) Design technique limitationsa problem currently faced in magnetic Hard Drives wherein

magnetic domain configuration prevents manufacture of disks that fully utilize the theoretical

limits of the technology.

Unlike current storage technologies that record and read one data bit at a time, holographic

memory writes and reads data in parallel in a single flash of light.
http://en.wikipedia.org/wiki/Hologramhttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Helium-neon_laserhttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Error-correctionhttp://en.wikipedia.org/wiki/File:Hologram_lezen.svghttp://en.wikipedia.org/wiki/Error-correctionhttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Helium-neon_laserhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/Hologram


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HOLOGRAPHIC MEMORY LAYOUT


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4.Holograms

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 aplanewave: 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 toreconstruct 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.

4.1 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 3D object, then the

reconstructed hologram makes the 3D object reappear. Since the diffracted wave front

accumulates energy from throughout the thickness of the storage material, a small change in eitherthe wavelength or angle of the readout beam generates enough destructive interference to make

the hologram effectively disappear through Bragg selectivity.


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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 2030

degrees). The maximum number of holograms stored at a single location to date is 10,000.

Figure 4

Reconstruction of an image from a hologram


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5.Underlying Technology

5.1 HOLOGRAPHY

Holographic data storage refers specifically to the use of holography to store and retrieve digitaldata. To do this, digital data must be imposed onto an optical wave front, stored holographically

with high volumetric density, and then extracted from the retrieved optical wav front with

excellent data fidelity. A hologram preserves both the phase and amplitude of an optical wave

front of interest called the object beamby recording the optical interference pattern between it

and a second coherent optical beamthe reference beam. Figure shows this process.

The reference beam is designed to be simple to reproduce at a later stage (A common reference

beam is a plane wave a light beam that propagates without converging or diverging). These

interference fringes are recorded if the two beams have been overlapped within a suitable

photosensitive media, such as a photopolymer or inorganic crystal or photographic film. The

bright and dark variations of the interference pattern create chemical and/or physical changes in

the media, preserving a replica of the interference pattern as a change in absorption, refractiveindex or thickness.


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Though holography is often referred to as 3D photography, this is a misconception. A better

analogy is sound recording where the sound field is encoded in such a way that it can later be

reproduced. In holography, some of the light scattered from an object or a set of objects falls on

the recording medium. A second light beam, known as the reference beam, also illuminates the

recording medium, so that interference occurs between the two beams. The resulting light field is

an apparently random pattern of varying intensity which is the hologram. It can be shown that if

the hologram is illuminated by the original reference beam, a light field is diffracted by the

reference beam which is identical to the light field which was scattered by the object or objects.

Thus, someone looking into the hologram "sees" the objects even though they are no longer

present. There are a variety of recording materials which can be used, including photographic

film.

5.2 Interference and diffraction

Interference occurs when one or more wavefronts are superimposed. Diffraction occurs whenever

a wavefront encounters an object. The process of producing a holographic reconstruction is

explained below purely in terms of interference and diffraction. It is somewhat simplistic, but is

accurate enough to provide an understanding of how the holographic process works.

5.3 Plane wavefronts

A diffraction grating is a structure with a repeating pattern. A simple example is a metal plate with

slits cut at regular intervals. Light rays travelling through it are bent at an angle determined by ,

the wavelength of the light and d, the distance between the slits and is given by sin = /d.

A very simple hologram can be made by superimposing two plane waves from the same light

source. One (the reference beam) hits the photographic plate normally and the other one (the

object beam) hits the plate at an angle . The relative phase between the two beams varies across

the photographic plate as 2 y sin/ where y is the distance along the photographic plate. The two

beams interfere with one another to form an interference pattern. The relative phase changes by 2

at intervals of d = /sin so the spacing of the interference fringes is given by d. Thus, the relative

phase of object and reference beam is encoded as the maxima and minima of the fringe pattern.

When the photographic plate is developed, the fringe pattern acts as a diffraction grating and when

the reference beam is incident upon the photographic plate, it is partly diffracted into the same

angle at which the original object beam was incident. Thus, the object beam has been

reconstructed. The diffraction grating created by the two waves interfering has reconstructedthe

"object beam" and it is therefore a hologram as defined above.
http://en.wikipedia.org/wiki/Sound_recordinghttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Wavefrontshttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Diffraction_gratinghttp://en.wikipedia.org/wiki/Ray_(optics)http://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Waveshttp://en.wikipedia.org/wiki/Interference_patternhttp://en.wikipedia.org/wiki/Interference_patternhttp://en.wikipedia.org/wiki/Waveshttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Ray_(optics)http://en.wikipedia.org/wiki/Diffraction_gratinghttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Wavefrontshttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Sound_recording


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5.4 Point sources

A slightly more complicated hologram can be made using a point source of light as object beamand a plane wave as reference beam to illuminate the photographic plate. An interference pattern

is formed which in this case is in the form of curves of decreasing separation with increasing

distance from the centre.

The photographic plate is developed giving a complicated pattern which can be considered to be

made up of a diffraction pattern of varying spacing. When the plate is illuminated by the reference

beam alone, it is diffracted by the grating into different angles which depend on the local spacing

of the pattern on the plate. It can be shown that the net effect of this is to reconstruct the object

beam, so that it appears that light is coming from a point source behind the plate, even when the

source has been removed. The light emerging from the photographic plate is identical to the light

that emerged from the point source that used to be there. An observer looking into the plate from

the other side will "see" a point source of light whether the original source of light is there or not.

This sort of hologram is effectively a concave lens, since it "converts" a plane wavefront into a

divergent wavefront. It will also increase the divergence of any wave which is incident on it in

exactly the same way as a normal lens does. Its focal length is the distance between the point

source and the plate.
http://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Photographic_platehttp://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Concave_lenshttp://en.wikipedia.org/wiki/Concave_lenshttp://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Photographic_platehttp://en.wikipedia.org/wiki/Plane_wavehttp://en.wikipedia.org/wiki/Point_source


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5.5 Complex objects

To record a hologram of a complex object, a laser beam is first split into two separate beams of

light using a beam splitter of half-silvered glass or a birefringent material. One beam illuminates

the object, reflecting its image onto the recording medium as it scatters the beam. The second

(reference) beam illuminates the recording medium directly.

According to diffraction theory, each point in the object acts as a point source of light. Each of

these point sources interferes with the reference beam, giving rise to an interference pattern. The

resulting pattern is the sum of a large number (strictly speaking, an infinite number) ofpoint

source + reference beam interference patterns.

When the object is no longer present, the holographic plate is illuminated by the reference beam.

Each point source diffraction grating will diffract part of the reference beam to reconstruct the

wavefront from its point source. These individual wavefronts add together to reconstruct the

whole of the object beam.

The viewer perceives a wavefront that is identical to the scattered wavefront of the object

illuminated by the reference beam, so that it appears to him or her that the object is still in place.

This image is known as a "virtual" image as it is generated even though the object is no longer

there. The direction of the light source seen illuminating the virtual image is that of the original

illuminating beam.
http://en.wikipedia.org/wiki/Beamsplitterhttp://en.wikipedia.org/wiki/Silveringhttp://en.wikipedia.org/wiki/Birefringenthttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Birefringenthttp://en.wikipedia.org/wiki/Silveringhttp://en.wikipedia.org/wiki/Beamsplitter


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This explains, albeit in somewhat simple terms, how transmission holograms work. Other

holograms, such as rainbow and Denisyuk holograms, are more complex but have similar

principles.

When the recording is illuminated by a readout beamsimilar to the original reference beam, some

of the light is diffracted to reconstruct a copy of the object beam as shown in Fig if the object

beam originally came from a 3-D object, then the reconstructed hologram makes the 3-D object

reappear.


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6.Working

A holographic data storage system consists of a recording medium, an optical recording system,

and a photodetector array. A beam of coherent light is split into a reference beam and a signal

beam which are used to record a hologram into the recording medium. The recording medium is

usually a photorefractive crystal such as LiNbO3 or BaTiO3 that has certain optical characteristics.These characteristics are high diffraction efficiency, high resolution, permanent storage until

erasure, and fast erasure on the application of external stimulus such as UV light. A hologram is

simply the three-dimensional interference pattern of the intersection of the reference and signal

beams at 90degree to each other. This interference pattern is imprinted into the crystal as regions

of positive and negative charge. To retrieve the stored hologram, a beam of light that has the same

wavelength and angle of incidence as the reference beam is sent into the crystal and the resulting

diffraction pattern is used to reconstruct the pattern of the signal beam.

Many different holograms may be stored in the same crystal volume by changing the angle of

incidence of the reference beam. One characteristic of the recording medium that limits the

usefulness of holographic storage is the property that every time the crystal is read with the

reference beam, the stored hologram at that location is disturbed by the reference beam and

some of the data integrity is lost. With current technology, recorded holograms in Fe- and Tb-

doped LiNbO3 that use UV light to activate the Tb atoms can be preserved without significant

decay for two years.

A series of spectral memory demonstration experiments have been conducted at the University of

Oregon. These experiments employ a 780-nm commercial semiconductor diode laser as the light

source, acrystal of Tm3+:YAG as the frequency selective recording material, and an avalanchephotodiode as a signal detector. The diode laser was stabilized to an external cavity containing a

grating and an electro optic crystal. The intracavity electro optic crystal provides for microsecond

timescale sweeping of the laser frequency over roughly one gigahertz. Two storage (reference and

data) beams and one reading beam, are created from the output of the single laser source using the

beam splitter and the acousto-optic modulators shown in figure. The beams are focused to a 150

m2

spot in a Tm3+:YAG crystal. The reference and data beams are simultaneous as are the read

and signal beams.


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The most common holographic recording system uses laser light, a beam splitter to divide the

laser light into a reference beam and a signal beam, various lenses and mirrors to redirect the light,

a photorefractive crystal, and an array of photodetectors around the crystal to receive the

holographic data. To record a hologram, a beam of laser light is split into two beams by a mirror.

These two beams then become the reference and the signal beams. The signal beam interacts withan object and the light that is reflected by the object intersects the reference beam at right angles.

The resulting interference pattern contains all the information necessary to recreate the image of

the object after suitable processing. The interference pattern is recorded onto the photoreactive

material and may be retrieved at a later time by using a beam that is identical to the reference

beam (including the wavelength and the angle of incidence into the photoreactive material). This

is possible because the hologram has the property that if it is illuminated by either of the beams

used to record it, the hologram causes light to be diffracted in the direction of the second beam

that was used to record it, thereby recreating the reflected image of the object if the reference

beam was used to illuminate the hologram. So, the reflected image must be transformed into a real

image with mirrors and lenses that can be sent to the laser detector array.

There are many different volume holographic techniques that are being researched. The most

promising techniques are angle-multiplexed, wavelength multiplexed, spectral, and phase

conjugate holography. Angle- and wavelength- multiplexed holographic methods are very similar,

with the only difference being the way data is stored and retrieved, either multiplexed with

different angles of incidence of the reference beam, or with different wavelengths of the reference

beam. Spectral holography combines the basic principles of volume holography using a

photorefractive crystal with a time sequencing scheme to partition holograms into their own

subvolume of the crystal using the collision of ultrashort laser pulses to differentiate between the

image and the time-delayed reference beam. Phase-conjugate holography is a technique to reducethe total volume of the system (the system includes recording devices, storage medium, and

detector array) by eliminating the need for the optical parts between the spatial light modulator

(SLM) and the detector.

The SLM is an optical device that is used to convert the real image into a single beam of light that

will intersect with the reference beam during recording. Phase-conjugate holography eliminates

these optical parts by replacing the reference beam that is used to read the hologram with a

conjugate reference beam that propagates in the opposite direction as the bam used for recording.

The signal diffracted by the hologram being accessed is sent back along the path from which itcame, and is refocused onto the SLM, which now serves as both the SLM and the detector.

There are two main classes of materials used for the holographic storage medium. These are

photorefractive crystals and photopolymers (organic films). The most commonly used

photorefractive crystals used are LiNbO3 and BaTiO3. During hologram recording, the refractive

index of the crystal is changed by migration of electron charge in response to the imprinted three

dimensional interference patterns of reference and signal beams. As more and more holograms are

superimposed into the crystal, the more decay of the holograms occurs due to interference from

the superimposed holograms. Also, holograms are degraded every time they are read out because

the reference beam used to read out the hologram alters the refractive nature of the crystal in that

region.


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7.Application

7.1 Holographic Versatile Disc

An HVD (holographic Versatile Disc), a holographic storage media, is an advanced optical discthats presently in the development stage. Polaroid scientist J. van Heerden was the first to come

up with the idea for holographic three-dimensional storage media in 1960. An HVD would be a

successor to todays Blu-ray and HDDVD technologies. It can transfer data at the rate of 1 Gigabit

per second. The technology permits over 10 kilobits of data to be written and read in parallel with

a single flash. The disc will store upto 3.9 terabyte (TB) of data on a single optical disk.

Holographic data storage, a potential next generation storage technology, offers both high storage

density and fast readout rate. In this article, I discuss the physical origin of these attractive

technology features and the components and engineering required to realize them. I conclude by

describing the current state of holographic storage research and development efforts in the context

of ongoing improvement to established storage technologies.

7.2 FEATURES

Data transfer rate: 1 gbps.The technology permits over 10 kilobits of data to be written and read in parallel with a

single flash.

Most optical storage devices, such as a standard CD saves one bit per pulse.HVDs manage to store 60,000 bits per pulse in the same place.1 HVD5800 CDs830 DVD160 BLU-RAY Discs.

7.3 STRUCTURE

HVD STRUCTURE

HVD structure is shown in fig 3.1 the following components are used in HVD.

1. Green writing/reading laser (650 nm).

2. Red positioning/addressing laser (650 nm).

3. Hologram (data).4. Polycarbon layer.

5. Photopolymeric layer (data-containing layer).

6. Distance layers.

7. Dichroic layer (reflecting green light).

8. Aluminum reflective layer (reflecting red light).

9. Transparent base.

10. PIT.


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HVD STRUCTURE

7.4 HVD READER PROTOTYPE

To read data from an HVD reader. The following components are used to make a reader.

A blue-green laser, beam splitters to split the laser beams, mirrors to direct the laser beams, LCD

panels (spatial light modulator), lenses to focus the beams, lithiumniobate crystals or

photopolymers, and charge-coupled device (CCD) cameras.

HVD READER PROTOTYPE


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RECORDING DATA

A simplified HVD system consists of the following main components:Blue or green laser (532-nm wavelength in the test system)Beam splitter/mergerMirrorsSpatial light modulator (SLM)CMOS sensorPolymer recording medium

The process of writing information onto an HVD begins with encoding the information into binary

data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or

translucent areas on a "page" -- this page is the image that the information beam is going to pass

through.

When the blue-green argon laser is fired, a beam splitter creates two beams. One beam, called the

object or signal beam, will go straight, bounce off one mirror and travel through a spatial-light

modulator (SLM). An SLM is a liquid crystal display (LCD) that shows pages of raw binary data

as clear and dark boxes.

The information from the page of binary code is carried by the signal beam around to the light-

sensitive lithium-niobate crystal. Some systems use a photopolymer in place of the crystal.

A second beam, called the reference beam, shoots out the side of the beam splitter and takes a

separate path to the crystal. When the two beams meet, the interference pattern that is createdstores the data carried by the signal beam in a specific area in the crystal -- the data is stored as a

hologram.


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8.ADVANTAGES and Disadvantages Of HDSS

8.1 Advantages Of HDSS

With three-dimensional recording and parallel data readout, holographic memories can outperform

existing optical storage techniques. In contrast to the currently available storage strategies,holographic mass memory simultaneously offers high data capacity and short data access time

(Storage capacity of about 1TB/cc and data transfer rate of 1 billion bits/second).

Holographic data storage has the unique ability to locate similar features stored within a crystal

instantly. A data pattern projected into a crystal from the top searches thousands of stored

holograms in parallel. The holograms diffract the incoming light out of the side of the crystal, with

the brightest outgoing beams identifying the address of the data that most closely resemble the

input pattern. This parallel search capability is an inherent property of holographic data storage and

allows a database to be searched by content.

Because the interference patter ns are spread uniformly throughout the material, it endows

holographic storage with another useful capability: high reliability. While a defect in the medium

for disk or tape storage might garble critical data, a defect in a holographic medium doesn't wipe

out information. Instead, it only makes the hologram dimmer. No rotation of medium is required as

in the case of other storage devices. It can reduce threat of piracy since holograms cant be easily

replicated.

8.2 DISADVANTAGES OF HDSS

Manufacturing cost HDSS is very high and there is a lack of availability of resources which areneeded to produce HDSS. However, all the holograms appear dimmer because their patterns must

share the material's finite dynamic range. In other words, the additional holograms alter a material

that can support only a fixed amount of change. Ultimately, the images become so dim that noise

creeps into the read-out operation, thus limiting the material's storage capacity.

A difficulty with the HDSS technology had been the destructive readout. The re- illuminated

reference beam used to retrieve the recorded information also excites the donor electrons and

disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the

recording. In the past, this has limited the number of reads that can be made before the signal-to -

noise ratio becomes too low. Moreover, writes in the same fashion can degrade previous writes in

the same region of the medium. This restricts the ability to use the three-dimensional capacity of aphotorefractive for recording angle-multiplexed holograms. You would be unable to locate the data

if theres an error of even a thousandth of an inch.


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9 .COMPARISON

9.1 Comparison between DVD, Blue-Ray and HVD

Parameters DVD BLU-RAY HVD

Capacity 4.7 GB 25 GB 3.9 TB

Laser wave length650 nm

(red)

405 nm

(blue)

532 nm

(green)

Disc diameter 120 mm 120 mm 120 mm

Hard coating No yes Yes

Data transfer rate

(rawdata)

11.08 mbps36 mbps 1 gbps


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10.HVD AT A GLANCE

Media type : Ultra-high density optical disc.

Encoding : MPEG-2, MPEG-4 AVC (H.264), and VC-1.

Capacity : Theoretically up to 3.9 TB.

Usage : Data storage, High-definition video, & he possibility of ultra High-definition

video.

STANDARDS

On December 9, 2004 at its 88th General Assembly the standards body Ecma International created

Technical committee 44, dedicated to standardizing HVD formats based on Optwares technology.

On June 11, 2007, TC44 published the first two HVD standards ECMA-377, defining a 200 GB

HVD recordable cartridge and ECMA-378,defining a 100 GB HVD-ROM disc. Its next stated

goals are 30 GB HVD cards and submission of these standards to the International Organization

for Standardization for ISO approval.

POSSIBLE APPLICATION FIELDS

There are many possible applications of holographic memory. Holographic memory systems can

potentially provide the high speed transfers and large volumes of future computer system. One

possible application is data mining.


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Data mining is the processes of finding patterns in large amounts of data. Data mining is used

greatly in large databases which hold possible patterns which cant be distinguished by human eyes

due to the vast amount of data. Some current computer system implement data mining, but the

mass amount of storage required is pushing the limits of current data storage systems. The many

advances in access times and data storage capacity that holographic memory provides could exceed

conventional storage and speedup data mining considerably. This would result in more locatedpatterns in a shorter amount of time.

Another possible application of holographic memory is inpetaflop computing. A petaflop is athousand trillion floating point operations per second. The fast access extremely large amounts of

data provided by holographic memory could be utilized in petaflop architecture. Clearly advances

are needed to in more than memory systems, but the theoretical schematics do exist for such a

machine. Optical storage such as holographic memory provides a viable solution to the extreme

amount of data which is required for a petaflop computing.


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11. Bibliography

www.holopc.com www.wikeipedia.com www.engeeniringseminars.com www.computer.howstuffworks.com www.tech-faq.com/hvd.shtml www.ibm.com - IBM Research Press Resources Holographic Storage

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29659592 Holographic Data Storage System Seminar Report

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