Holographic seminar documentation

HOLOGRAPHIC MEMORY BCA

COLLEGE 1

INTRODUCTION


COLLEGE 2

1. INTRODUCTION

Holographic VersatileDisc (HVD) system using collinear holographic technologies is one of

the best candidates for the ultra-high density and ultra-high speed removable storage media.

The HVD structure and its unique selectable recording capacity format are proposed to assure

data interchangeability as well as upward and downward capability. Holographic information

storage systems (HISS) have been a good candidate for a volumetric recording

technology,due to their large storage capacities and high transfer rates Recently, retrieval of

activity in HISS has resulted from the dramatic developments in the requisite components for

such a system, such alaser technology, spatial light modulators(SLM) and complementary

metal oxide semiconductor(CMOS)image sensors. Holographic Versatile Disc(HVD) system

using collinear technology, a new technology for HISS, proposed and demonstrated by

OPTWARE corporation. This technology can produce a small, practical HISS more easily

than conventional 2-axis holography.

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 a single-layer Blu-ray discs. The HVD also has a transfer rate of 1

gigabit/s.

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.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 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 more information in a smaller space and

offer faster data transfer times.


COLLEGE 3

HOLOGRAPHY

A hologram is a block or sheet of photosensitive material which records the interference of

two light sources. To create a hologram, laser light is first split into two beams, a source

beam and a reference beam. The source beam is then manipulated and sent into the

photosensitive material. Once inside this material, it intersects the reference beam and the

resulting interference of laser light is recorded on the photosensitive material, resulting in a

hologram. Once a hologram is recorded, it can be viewed with only the reference beam. The

reference beam is projected into the hologram at the exact angle it was projected during

recording.

When this light hits the recorded diffraction pattern, the source beam is regenerated out of the

refracted light. An exact copy of the source beam is sent out of the hologram and can be read

by optical sensors.


COLLEGE 4

IMPLEMENTATION


COLLEGE 5

2. IMPLEMENTATION

The components of Holographic data storage system is composed of

Blue-green argon laser

Beam splitters to spilt the laser beam

Mirrors to direct the laser beams

LCD panel (spatial light modulator)

Lenses to focus the laser beams

Lithium-neonate crystal or photopolymer

Charge coupled device camera

They can be classified into three sections namely recording medium, optical recording

system and photo detector array. The laser is used because it provides monochromatic light.

Only the interference pattern produced by the monochromatic beam of light is stable in time.

Lithium neonate crystal is used as photosensitive material on which hologram is

recorded. It has certain optical characteristics that make it behave as photosensitive material.

CCD camera detects the information in the light, converts to digital information and forwards

it to computer.


COLLEGE 6

CREATING HOLOGRAM

Fig:2.1

RETRIEVING HOLOGRAM

Fig:2.2


COLLEGE 7

2.1 APPLICATION TO BINARY

In order for holographic technology to be applied to computer systems, it must store data in a

form that a computer can recognize. In current computer systems, this form is binary. In the

previous section, it was mentioned that the source beam is manipulated. In common

holograms, this manipulation ;s the creation of an optical image such as a ball or human face.

In computer applications, this manipulation is in the form of bits. The next section explains

the spatial light modulator, a device that converts laser light into binary data.

2.2 SPATIAL LIGHT MODULATOR (SLM)

A spatial light modulator is used for creating binary information out of laser light. The SLM

is a 2D plane, consisting of pixels which can be turned on and off to create binary 1.s and

O.s. An illustration of this is a window and a window shade. It is possible to pull the shade

down over a window to block incoming sunlight. If sunlight is desired again, the shade can be

raised. A spatial light modulator contains a two-dimensional array of windows which are only

microns wide. These windows block some parts of the incoming laser light and let other parts

go through. The resulting cross section of the laser beam is a two dimensional array of binary

data, exactly the same as what was represented in the SLM. After the laser beam is

manipulated, it is sent into the hologram to be recorded. This data is written into the

hologram as page form. It is called this due to its representation as a two dimensional plane,

or page of data. Spatial light modulator is a Liquid Crystal Display panel that consists of clear

and dark areas corresponding to the binary information it represent.

Spatial light modulator is actually that device which makes holography

applicable to computers. Sort is one of the important components of Holographic Data

Storage System.


COLLEGE 8

Fig:2.3

Laser


COLLEGE 9

WORKING


COLLEGE 10

3.WORKING

3.1 RECORDING OF DATA IN HOLOGRAPHIC MEMORY SYSTEM

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 created stores the data carried by the signal beam

in a specific area in the crystal - the data is stored as a hologram.

3.2 RETRIEVAL OF DATA FROM HOLOGRAPHIC MEMORY

SYSTEM

An advantage of a holographic memory system is that an entire page of data can be retrieved

quickly and at one time. In order to retrieve and reconstruct the holographic page of data

stored in the crystal, the reference beam !s shined into the crystal at exactly the same angle at

which it entered to store that age of data. Each page of data is stored in a different area of the

crystal, based on the angle at which the reference beam strikes it. During reconstruction, the

beam will be diffracted by the crystal to allow the recreation of the original page that was

stored. This reconstructed page is then projected onto the charge-coupled device (CCD)

camera, which interprets and forwards the digital “Formation” to a computer.

CCD is a 2-D array of thousands or millions of tiny solar cells, each of

which transforms the light from one small portion of the image into electrons. Next step is

to read the value (accumulated charge) of each cell in the image. In a CCD device, the

charge is actually transported across the

chip and read at one corner of the array. An analog-to-digital converter turns each pixel's

value into a digital value. CCDs use a special manufacturing process to create the ability

to transport charge across the chip without distortion. This process leads to very high-

quality sensors in terms of fidelity and light sensitivity. CCD sensors have been mass


COLLEGE 11

produced for a longer period of time, so they are more mature. They tend to have higher

quality and more pixels.

The key component of any holographic data storage system is the angle at which the second

reference beam is fired at the crystal to retrieve a page of data. It must match the original

reference beam angle exactly. A difference of just a thousandth of a millimeter will result in

failure to retrieve t hat page of data.

Fig:3.1

3.3 PAGE DATA ACCESS

Because data is stored as page data in a hologram, the retrieval of this data must also be in

this form. Page data access is the method of reading stored data in sheets, not serially as in

conventional storage systems. It was mentioned in the introduction that conventional storage

was reaching its fundamental limits. One such limit is the way data is read in streams.

Holographic memory reads data in the form of pages instead. For example, if a stream of 32

bits is sent to a processing unit by a conventional read head,a holographic memory system

would in turn send 32 x 32 bits, or 1024 bits due to its added dimension. This provides very

fast access times in volumes far

greater than serial access methods. The volume could be one Megabit per page using a SLM

resolution of 1024 x 1024 bits at 15-20 microns per pixel.

3.4 MULTIPLEXING

Once one can store a page of bits in a hologram, an interface to a computer can be made. The

problem arises, however, that storing only one page of bits is not beneficial. Fortunately, the

properties of holograms provide a unique solution to this dilemma. Unlike magnetic storage

mechanisms which store data on their surface, holographic memories store information

throughout their whole volume. After a page of data is recorded in the hologram, a small


COLLEGE 12

modification to the source beam before it reenters the hologram will record another page of

data in the same volume. This method of storing multiple pages of data in the hologram is

called multiplexing. The thicker the volume becomes, the smaller the modifications to the

source beam can be.

3.5 ANGULAR MULTIPLEXING

When a reference beam recreates the source beam, it needs to be at the same angle it was

during recording. A very small alteration in this angle will make the regenerated source beam

disappear. Harnessing this property, Angular multiplexing changes the angle of the source

beam by very minuscule amounts after each page of data is recorded. Depending on the

sensitivity of the recording material, thousands of pages of data can be stored in the same

hologram, at the same point of laser beam entry. Staying away from conventional data access

systems which move mechanical matter to obtain data, the angle of entry on the source beam

can be deflected by high-frequency sound waves in solids.

Fig:3.2

3.6 WAVELENGTH MULTIPLEXING

Used mainly in conjunction with other multiplexing methods, wavelength multiplexing alters

the wavelength of source and reference beams between recordings. Sending beams to the

same point of origin in the recording medium at different wavelengths allows multiple pages

of data to be recorded. Due to the small tuning range of lasers, however, this form of

multiplexing is limited on its own.


COLLEGE 13

3.7 SPATIAL MULTIPLEXING

Spatial multiplexing is the method of changing the point of entry of source and reference

beams into the recording medium. This form tends to break away from the non-mechanical

paradigm because either the medium or recording beams must be physically moved. Like

wavelength multiplexing, this is combined with other forms of multiplexing to maximize the

amount of data stored in the holographic volume. Two commonly used forms of spatial

multiplexing are per strophic multiplexing and shift multiplexing

.

Holographic Cube

Fig:3.3

3.8 PHASE-ENCODED MULTIPLEXING

The form of multiplexing farthest away from using mechanical means to record many pages

in the same volume of a holograph is called phase-encoded multiplexing. Rather than

manipulate the angle of entry of a laser beam or rotate or translate the recording medium,

phase-encoded multiplexing changes the phase of individual parts of a reference beam. The

main reference beam is split up into many smaller partial beams which cover the same area as

the original reference beam. This smaller beam lets vary by phase which changes the state of

the reference beam as a whole. The reference beams intersects the source beam and records

the diffraction relative to the different phases of the beam lets. The phase of the beam lets can

be changed by non-mechanical means, therefore speeding up access times.

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COLLEGE 14

Fig:3.4

3.9 RECORDING ERRORS

When data is recorded in a holographic medium, certain factors can lead to erroneously

recorded data. One major factor is the electronic noise generated by laser beams. When a

laser beam is split up (for example, through a SLM), the generated light bleeds into places

where light was meant to be blocked out. Areas where zero light is desired might have

minuscule amounts of laser light present which mutates its bit representation. For example, if

too much light gets recorded into this zero area representing a binary 0, an erroneous change

to a binary 1 might occur. Changes in both the quality of the laser beam and

recordingmaterial are being researched, but these improvements must take into consideration

the cost effectiveness of a holographic memory system. These limitations to current laser

beam and photosensitive technology are some of the main factors for the delay of practical

holographic memory systems.

3.10 PAGE-LEVEL PARITY BITS

Once error-free data is recorded into a hologram, methods which read data back out of it need

to be error free as well. Data in page format requires a new way to Provide error control.

Current error control methods concentrate on a stream of bits. Because page data is in the

form of a two dimensional array, error correction needs to take into account the extra

dimension of bits. When a page of data is written to the holographic media, the page is

separated into smaller two dimensional arrays. These sub sections are appended with an

additional row and column of bits.

The added bits calculate the parity of each row and column of data. An odd

number of bits in a row or column create a parity bit of 1 and an even number of bits create a


COLLEGE 15

0. A parity bit where the row and column meet is also created which is called an overall

parity bit. The sub sections are rejoined and sent to the holographic medium for recording.


COLLEGE 16

APPLICATIONS


COLLEGE 17

4. APPLICATIONS

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

can potentially provide the high-speed transfers and large volumes of future computer

systems. One possible application is data mining. Data mining is the process of finding

patterns in large amounts of data. Data mining is used greatly in large databases which hold

possible patterns which can't be distinguished by human eyes due to the vast amount of data.

Some current computer systems 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 speed up data mining considerably. This would result in more

located patterns in a shorter amount of time.

Another possible application of holographic memory is in petaflop computing.

A pet flop is a thousand trillion floating point operations per second. The fast access in

extremely large amounts of data provided by holographic memory systems could be utilized

in pet flop architecture. Clearly advances are needed 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 pet

flop computing.

Holographic memory can be used as extended DRAM with 10ns access time,

Hard disk drives ,CD ROMs of large storage capacity and rockmounted (combining

numerous DASDs) of petabytes storage capacity.

Fig:4.1


COLLEGE 18

4.1 RECENT DEVELOPMENTS

The research on holographic memory is taking place in well-guarded and rich companies like

IBM, ROCKWELL and In Phase. In Phase claims to have developed a holographic memory

of size slightly larger than a DVD. It has a capacity of about 100GB. They are trying to push

it upto1tb.IBM and ROCKWELL claims to have developed a recording medium less

sensitive than lithium niobate crystals.

4.2 HOLOGRAPHIC MEMORY VS CONVENTIONAL STORAGE

DEVICES

Comparing the access times holographic memory lies midway between that of main memory

and magnetic disk. Data transfer rate is 10GB/s which is higher than that of other storage

devices and, and a storage capacity that is higher than both main memory and magnetic disk.

Certainly if the issues of hologram decay and interference are resolved, then holographic

memory could become a part of the memory hierarchy, or take the place of magnetic disk

much as magnetic disk has displaced magnetic tape for most applications.


COLLEGE 19

ADVANTAGES


COLLEGE 20

5. ADVANTAGES OF HOLOGRAPHIC MEMORY

Holographic memory offers storage capacity of about 1 TB. Speed of retrieval of data in tens

of microseconds compared to data access time of almost 10ms offered by the fastest hard disk

today. By the time they are available they can transfer an entire DVD movie in 30 seconds.

Information search is also faster in holographic memory. Consider the case of large databases

that are stored on hard disk today. To retrieve any piece of information you first provide

some reference data. The data is then searched by its address, track, sector and so on after

which it is compared with the reference data. In holographic storage entire pages can be

retrieved where contents of two or more pages can be compared optically without having to

retrieve the information contained in them. Also HDSS has no moving parts. So the

limitations of mechanical motion such as friction can be removed.

For theoretical exhibitors, HVDs 1Gbps bandwidth means that d-cinema

presentations can be played directly from the disc. This is a critical point as theatre operators,

studio executives, and video on demand executives quickly realize that the digital delivery of

gargantuan movie files via FTP is impractical and unreliable even at the proposed modest 2:1

compression level. HVD offers not only the efficiency and reliability of delivering a 2K or

4K resolution movie overnight in a FedExenvelope; it can do so with absolute security –a

vital concern to Hollywood and high profile content owners. HVDs security is delivered in

part from the one million possible keys per page of data. Bearing in mind that 22,000 such

pages can be written every second, each with its own unique key, One can see how DVD can

easily embrace a virtually unbreakable security scheme. Looking at HVD slightly differently,

the media contains no readable data until a hologram actually forms, and this can only happen

if the correct key or keys are present.


COLLEGE 21

DISADVANTAGES


COLLEGE 22

6. DISADVANTAGES OF HOLOGRAPHIC DATA STORAGE

Not a guaranteed market leader.

If another technology becomes the industry standard then read/write equipment will

be hard to find.

Expensive development.

Existing technology is becoming better and cheaper.

It is difficult to market a product that is more expensive per GB of storage.


COLLEGE 23

FUTURE SCOPE


COLLEGE 24

7. FUTURE SCOPE

During the retrieval of data the reference beam has to be focused at exactly the same angle at

which it was projected during recording. A slight error can cause a wrong data page to be

accessed. It is difficult to obtain that much of accuracy. The crystal used as the photographic

filament must have exact optical characteristics such as high diffraction efficiency, storage of

data safely without any erasure and fast erasure on application of external stimulus light ultra

violet rays. With the repeated number of accesses the holograms will tend to decay.


COLLEGE 25

CONCLUSION


COLLEGE 26

8. CONCLUSION In conclusion, Holographic Storage has the advantage overother storage mediums as it relates

to:

Storage Capacity

Transfer Rate

Backup

Its main disadvantage is its cost of ownership.

Keep in mind, when Blu-ray was Introduced in 2006, a 25-gigabyte disc cost nearly $1 a

gigabyte. It is about half the cost now. Overtime, the overall cost of holographic data storage

should decrease to an acceptable amount.

Collinear technologies will make commercialization of HVD drive systems

economically feasible. It has been proved that system margins are wide enough to produce a

small, practical, and low-cost HVD system. Atheoretical discussion has been proposed

regarding why collinear holographic storage systems have significant advantages compared

with other HISSs. The new standards of HVD will be submitted to ISO for fast-tracking

processing. In the future , collinear technology will not only be compatible with existing disk

storage system, like CD, DVD, and next-generation optical disk(Blu-ray disc and HD,DVD),

but also enable its applications into other optical information storage systems.


COLLEGE 27

APPENDIX


COLLEGE 28

9. APPENDIX

Figure Name Figure No Page No

Create Hologram 2.1 6

Retrieving Hologram 2.2 6

Spatial Light Modulator 2.3 8

Retrieval of Data 3.1 11

Angular Multiplexing 3.2 12

Holographic Cube 3.3 13

Phase Encoded Multiplexing 3.4 14

Application 4.1 16


COLLEGE 29

REFERENCES


COLLEGE 30

9. REFERENCES

1. D Psaltis and F. Mok, “Holographic Memories,” Scientific American, Nov. 1995.

2. J.H. Hong et al.,” Volume Holographic Memory Systems: Techniques and

Architectures,” OpticalEng.,Aug.

1995,pp.2,193-203.

3. J.F. Heanue, M.CBashaw,and L. Hesselink,”Volume

Holographic Storage and Retrival of Digital data,”Science,

Agu.1994,pp.749-752.

4. Selected papers on Holographics Storage ,G.T Sincerbox,

ed.,SPIE Milestone Series ,vol MS 95,SPIE,

Bellinghing,wish.,1994

5. A.Pu.and D.Psalits,”High-Density Recording in photopolymer based Holographic

Three-dimensional disk,”AppliedOptics ,May 1996, pp.2,389-2,398.

6. G.Barbastathis,M.Levene,and D.psaltis,”Shift Multiplexing with spherical

Reference Wave,”Applied

Optics may 1996,pp.2,403-2,417.

7. G.W.burr, Volume Holographics storage using the

90 degree Geomatry,doctoraldissertation,californiainstitite of

Technology,pasadena,calif.,1996

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Holographic seminar documentation

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