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HOLOGRAPHIC VERSATILE DISC

MEENAKSHI YADAV

ELECTRONICS AND COMM ENGYMCA UNIVERSITYABSTRACT

In this paper we describe thedevelopment of Holographic VersatileDisc (HVD) i.e., a next generation storagedisc offering theoretical storage capacityof 3.9 Terabytes of data -- that's 800 timesmore than a single-sided DVD and 80times more than a current double-sidedBlu-ray, with a whopping 1Gbpsread/write speed. Holography is a method

of recording patterns of light to produce athree-dimensional object. The recordedpatterns of light are called a hologram. Theprocess of creating a hologram begins with afocused beam of light -- a laser beam. Thislaser beam is split into two separate beams:a reference beam, which remains unchangedthroughout much of the process, and aninformation beam, which passes through animage. When light encounters an image, itscomposition changes. In a sense, once theinformation beam encounters an image, it

carries that image in its waveforms. Whenthese two beams intersect, it creates apattern of light interference. If we recordthis pattern of light interference we areessentially recording the light pattern of theimage. To retrieve the information stored ina hologram, we shine the reference beamdirectly onto the hologram. When it reflectsoff the hologram, it holds the light pattern of

the image stored there. In this paper we alsoconcentrate on the servo mechanism whichis the key mechanism in storage of data inthe HVD.Besides having high storagecapacity & data transfer rate HVDs offersadvantage over a conventional DVD thatstores bits of information side-by-side in athin layer, while HVDs use a thicker recording layer & stores information inalmost the entire volume of the disc. An

HVD stores and retrieves an entire page of data, approximately 60,000 bits of information, in one pulse of light, while aDVD stores and retrieves one bit of data inone pulse of light. The full paper willdiscuss the various aspects of HVD in detail.

Keywords: - Holographic VersatileDisc, Holography, lightinterference, servo mechanism

INTRODUCTION:

Holographic Versatile Disc (HVD) is a nextgeneration optical storage solution that promisesthe theoretical storage capacity of 3.9 Terabytesof data -- that's 850 times more than a currentsingle-sided DVD and 80 times more than acurrent double-sided Blu-ray Disc, with awhopping 1Gbps read/write speed. HVD storesthe data in overlapping holographic patternsinstead of storing bits side-by-side as in

conventional CD/DVD(s).Current optical storagesaves one bit per pulse, and the HVD alliancehopes to improve this efficiency with capabilitiesof around 60,000 bits per pulse in an inverted,truncated cone shape that has a 200 micrometer diameter at the bottom and a 500 micrometer diameter at the top. High densities are possibleby moving these closer on the tracks: 100 GB at18 micrometers separation, 200 GB at 13micrometers, 500 GB at 8 micrometers, and most

demonstrated of 5 TB for 3 micrometers on a10 cm disc.

Basics of HolographyHolography is a method of recording patterns of light to produce a three-dimensional object. Therecorded patterns of light are called as ahologram . The process of creating a hologrambegins with a focused beam of light -- a laserbeam . This laser beam is split into two separatebeams: a reference beam , which remains

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unchanged throughout much of the process, andan information beam , which passes through animage. When light encounters an image, itscomposition changes. In a sense, once theinformation beam encounters an image, it carriesthat image in its waveforms. When these twobeams intersect, it creates a pattern of lightinterference. If you record this pattern of lightinterference in a photosensitive polymer layer of a disc, you are essentially recording the lightpattern of the image.Holographic Versatile Disc structure1. Green writing/reading laser (532 nm) 2. Redpositioning/addressing laser (650 nm)3. Hologram (data)(shown here as brown)4. Polycarbonate layer 5. Photopolymeric layer (data-containing layer) 6. Distance layers7. Dichroic layer (reflecting green light)8. Aluminum reflective layer (reflecting redlight)9. Transparent base P. Pit pattern

It can be shown that if the hologram isilluminated by the original reference beam, alight field is diffracted by the reference beamwhich is identical to the light field which wasscattered by the object or objects. Thus, if youlook into the hologram you 'see' the objects eventhough it may no longer be present.

(Viewing object in the hologram)

Just as in a hologram, we store analoginformation in terms of images; we can store the

digital information in holographic memory byencoding the information into binary data to bestored in the SLM (Spatial Light Modulator).This data is now turned into ones and zeroesrepresented as opaque or translucent areas on a"page; this page acts as the image that theinformation beam is going to pass through.

(Ones & Zeros represented by translucent or opaque areas)

Technology ComparisonVolumetric Recording : ConventionalCD/DVD(s) store the data bits on a planar surface i.e. on a thin surface of recording layer.As a result, bits are stored side by side & it limitsthe capacity of the disc to the available surfacearea. However, HVD uses a thicker recordinglayer & stores the information in entire volumeof the disc, instead of just in a single layer. Thisallows it to store upto 3.9 terabytes of data.

High data transfer rate : The high storagecapacity of the HVD demands the higher datatransfer rate so that whole disc could beread/write quickly & it has the ability to meet the

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future needs. The conventional optical devicesread 1 bit at each light pulse, thus it limits thetransfer rate to the frequency and width of lightpulse. However, in HVD data is read/written interms of one page of 60,000 bits instead of single bit. Thus, at each light pulse we get the60,000 bits. This allows HVD to support 1Gbpsdata transfer rate.

Servo data: Servo information is used to monitor the position of the read head over the disc,similar to the head, track, and sector informationon a conventional hard disk drive. On a CD or DVD this servo information is interspersedamongst the data.

The servo beam in the HVD system is at awavelength that does not photosensitize the

polymer recording medium. In the HVD testsystem, the servo data is carried in a separate redlaser at 650nm wavelength. The structure of thedisc places a thick recording layer between twosubstrates and incorporates a dichroic mirror thatreflects the blue-green light carrying theholography data but allows the red light to passthrough in order to gather servo information.

This prevents interference from refraction of thegreen laser off the servo data pits and is anadvance over past holographic storage media,which either experienced too much interference,or lacked the servo data entirely, making themincompatible with current CD and DVD drivetechnology.OPTWARE Corporation is the firstto overcome technical difficulties to produce first

prototype of HVD system. HVD systemdeveloped by OPTWARE Corp. is fullycompatible with CD/DVD technology. The size& thickness of HVD is also compatible withCD/DVD/HD-DVD disc.

Block Diagram

The block diagram shows the variouscomponents and the processing of the HVD.

Major Components :The major components of HVD system are:

Blue or green laser : The laser beam ishighly focused coherent source at532nm wavelength in test system. Thisbeam is splitted to obtain two identicalcoherent beams.

Beam splitter/merger : It separates thelaser beam into two identical beamscalled as reference beam & informationbeam. Both of them carry same energy& are in phase with each other.

Mirrors: It is used to deflect & guidethe beams along the desired path.

Spatial light modulator (SLM) : AnSLM is a liquid crystal display (LCD)that shows pages of raw binary data asclear and dark boxes. When theinformation beam is passed throughSLM, it gets modulated in accordancewith the digital bit pattern.

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CMOS sensor : It is used to detect thediffracted/reflected light from thephotopolymer.

Photopolymer recording medium

The HVD System: Writing DataThe process of writing information onto an HVDbegins with encoding the information into binarydata to be stored in the SLM. These data areencoded into ones and zeroes represented asopaque or translucent areas on a "page" of SLM.This page is the image that the information beamis going to pass through. Once the page of data iscreated, the next step is to fire a laser beam intoa beam splitter to produce two identical beams.One of the beams is directed away from the SLM-- this beam becomes the reference beam . Theother beam is directed toward the SLM andbecomes the information beam . When theinformation beam passes through the SLM,portions of the light are blocked by the opaqueareas of the page, and portions pass through thetranslucent areas. In this way, the informationbeam carries the image once it passes throughthe SLM.When the reference beam and the informationbeam rejoin on the same axis, they create apattern of light interference called asholography data . This joint beam carries theinterference pattern to the photopolymer disc

and stores it there as a hologram. There is aseparate servo laser at 650nm wavelength, whichkeeps track of servo information.

The HVD System: Reading DataTo read the data from an HVD, we need toretrieve the light pattern stored in the hologram.

(Read System 1)

(Read System 2)In the HVD read system, the laser projects a lightbeam onto the hologram, a light beam that isidentical to the reference beam (Read System1). The hologram diffracts this beam accordingto the specific pattern of light interference it'sstoring. The resulting light recreates the image of the page data that established the light-interference pattern in the first place. When thisbeam of light called as thereconstruction beam , bounces back off the disc(Read System 2), it travels to the CMOS sensor .The CMOS sensor then reproduces the image of the data. Each page of data is stored in adifferent area of the crystal, based on the angle atwhich the reference beam strikes it. Duringreconstruction , the beam will be diffracted bythe crystal to allow the recreation of the originalpage that was stored. The key component of anyholographic data storage system is the angle at

which the second reference beam is fired at thecrystal to retrieve a page of data. It must matchthe original reference beam angle exactly . Adifference of just a thousandth of a millimeter will result in failure to retrieve that page of data.ComparisonWhile HVD is attempting to revolutionize datastorage, other discs are trying to improve uponcurrent systems. Two such discs are Blu-ray andHD-DVD, deemed the next-generation of digitalstorage. Both build upon current DVDtechnology to increase storage capacity. All threeof these technologies are aiming for the high-

definition video market, where speed andcapacity count.

BLU-RAY

HD-DVD

HVD

Initial cost forrecordable disc

Approx.$18

Approx.$10

Approx.$120

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Initial cost forrecorder/player

Approx.$2,000

Approx.$2,000

Approx.$3,000

Initial storagecapacity

54 GB 30 GB 300 GB

Read/write

speed

36.5

Mbps

36.5

Mbps

1 Gbps

HVD is still in the late stages of development &may not hit the consumer market before 2010.An initial price tag of $120 per disc will be anobstacle, but the prices would come down withmass production.

Applications

Large amount of data storage for big

corporations.

High-Definition Video recording

Ultra High-Definition Video for Super High Vision TV of future.

Large data backups & restoreoperations.

Limitations High initial cost of the recorder & the

disc.

Large size of prototype recorderat 3ft*1ft.

Competing technologies

HVD is not the only technology in high-capacity, optical storage media. InPhaseTechnologies were developing a rivalholographic format called Tapestry Media ,which they claim will eventually store 1.6TB with a data transfer rate of 120 MB/s,and several companies are developing TB-level discs based on 3D optical data storage technology. Such large optical storagecapacities compete favorably with the Blu-ray Disc format. However, holographicdrives are projected to initially cost aroundUS$15,000, and a single disc aroundUS$120180, although prices are expectedto fall steadily.

Conclusion

This paper concludes that biggest challengefor HVD will be in establishing itself in thecommercial market, which as of now seemsto be a distant dream due to its higher costmargins. It is anticipated that a single HVD,when commercially available, may costanywhere between $100-120 (by 2012 year'send), and the reader will be priced anywherein the range of $10,000 to $15,000.

However, like anything else associated withtechnology, the price will soon fall as R&Dcosts are recouped and competitions lowersprofit margins.

References

1. "What's New" . 2004-08-23.Archived from the original on2004-10-09.

http://web.archive.org/web/20041009144100/http://www.optware.co.jp/english/what_040823.htm .

2. "Maxell focuses on holographic storage" . CNET News.com . 2005-11-28.http://news.com.com/Maxell+focuses+on+holographic+storage/2100-

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