This paper discusses holographic data storage as an option for high-density data storage. It describes the technology and its benefits

Desmarais, Norman

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DigitalCommons@Providence

Providence CollegeDigitalCommons@ProvidenceLibrary Faculty and Staff papers Phillips Memorial LibraryJune 20023D Data StorageNorman DesmaraisProvidence College, normd@providence.eduFollow this and additional works at: http://digitalcommons.providence.edu/facstaff_pubsThis Article is brought to you for free and open access by the Phillips Memorial Library at DigitalCommons@Providence. It has been accepted forinclusion in Library Faculty and Staff papers by an authorized administrator of DigitalCommons@Providence. For more information, please contactmcaprio1@providence.edu, hposey@providence.edu.Desmarais, Norman, "3D Data Storage" (2002). Library Faculty and Staff papers. 19.http://digitalcommons.providence.edu/facstaff_pubs/1984 Against the Grain / Special Reprint — June 2002 <http://www.against-the-grain.com>continued on page 85SPECIAL REPRINTVOLUME 14,  NUMBER 3 JUNE 2002“Linking Publishers, Vendors and Librarians”ISSN: 1043-2094c/o Katina Strauch209 Richardson AvenueMSC 98, The CitadelCharleston, SC 29409™Innovations Affecting Us — 3-D Data Storageby Norman Desmarais  (Acquisitions Librarian, Phillips Memorial Library, Providence College)<normd@postoffice.providence.edu>DVD superseded CD-ROM. Holographic datastorage will eventually replace DVD. Demand forhigh-density data storage proceeds unabated; soengineers continue to search for ways to pack moredata into increasingly smaller spaces.  CD-ROMspacked 650MB of data onto a single layered disc.DVD found a way to put two layers on the sameside of a disc. In addition to doubling capacity, itwas the first three-dimensional storage medium.By putting two layers on each side, DVD can de-liver up to 9GB of data. Holography promises toincrease the number of information layers to tenand, eventually, to 100 or more.  Holographic datastorage differs from conventional storage tech-niques in that it uses the entire volume of the re-cording medium, rather than just the surface,thereby greatly increasing potential data density.A hologram is created by splitting a laser beamin two. One portion of the beam illuminates anobject with coherent light in which all the wavestravel in phase with one another. The other portionof the same beam, called the reference beam, isdirected at the photographic plate simultaneously,but it is reflected by a mirror or prism. Because thetwo beams take different paths, they are no longerin phase with each other when they reach the filmand interfere. This interference pattern is recordedon the film and constitutes the  hologram. To re-construct (view) the image requires illuminatingthe hologram with a light shining from the samedirection as the reference beam. The interferencepattern (hologram) diffracts this light to reconstructthe light patterns from the original scene, render-ing the original surface pattern of the object in threedimensions.This works fine for images of objects; but digi-tal data is nota three-di-mensional object; so how can it can be recorded inholographic images? The data is usually repre-sented as bright and dark spots, analogous to theones and zeroes or charged and non-charged par-ticles of conventional binary storage devices.The Big PictureA single hologram can store a very largeamount of data because each “page” is recordedat a different angle relative to the plate. To readeach page requires illuminating the hologramwith a laser beam focused at the same wave-length, angle and polarization as the originalreference beam. In other words, the address ofthe data is the angle and frequency of the refer-ence beam. Rotating the beam slightly — as littleas 1000th of a degree — allows recording a fresh“page” in the same hologram.Holograms have a particular advantage in thatthey allow information retrieval with only partialinformation about the original content. The read-ing mechanism retrieves and transfers an entire“page” of data from the storage medium at a singletime. A beam with only a partial image is suffi-cient to reconstruct a reference beam that can pro-vide the address of the stored information contentthat corresponds most closely with the partial in-put information. This is significant for image-baseddata sets because they are difficult to process us-ing relational database techniques. Holographypermits searching a large volume of data simul-taneously resulting in very fast data search rates.Rates of up to 100GB/s have been demonstratedunder experimental conditions.Developers have focused on two types of stor-age material. One approach uses a photorefractiveferro-electric crystal (lithium niobate). The otheruses azobenzene polyesters in the form of an amor-phous or liquid crystal. However, both the photo-polymer and crystal methods have their prob-lems. The material must be sensitive enough fora low-powered laser to read and write on it butnot so sensitive that the laser does not obliteratedata in the retrieval process. The photopolymersenjoy high photosensitivity, high dynamic range,and ease of processing for display;  but they havea shorter “shelf life” than crystals. The crystals, onthe other hand, must be “fixed” so that the readinglaser does not destroy the information during thereading process. Holographic storage media havea projected life expectancy of up to a hundred yearsbecause they are more resistant to temperature fluc-tuations, water, acid, and electrical fields than tra-ditional storage media.Fluorescent Multilayer DiscsOne effort at holographic data storage uses fluo-rescent multilayer discs (FMD) developed by Con-stellation 3D Inc. (C3D) in New York. FMD tech-nology uses fluorescent dye instead of the reflectiveand semi-reflective coatings used by CD-ROMsand DVDs. They  can support up to ten informa-tion layers on each side of a disc and match thedensity and transfer speeds of DVD.The fluorescent dye allows the laser beam totravel deeper into the medium with less noise(stray light) and interference in the return sig-nal because when the focused laser strikes a piton one of the information layers, the fluores-cent light that’s reflected has a higher wave-length than the laser. In other optical media,more layers produce more stray light, making itdifficult to distinguish the signal from the noise,particularly if the noise is the same wavelength asthe signal. With fluorescent multilayer discs, thefluorescent light carries the information; and theread device filters out the stray light and only readsthe signal. This configuration permits the use ofmore information layers because it’s better able todistinguish the signal from the noise.While the cost of a single FMD will probablybe higher than that of other storage media, the costper gigabyte should be considerably lower if theFMDs now in development can hold the projected140GB of data. In contrast, the next-generation ofDVDs are expected to contain 20GB.InPhase has a prototype hologram disc the sizeof a CD that can hold up to 400GB of data andretrieve it at the rate of about 30MB per second.Against the Grain / Special Reprint — June 2002 <http://www.against-the-grain.com>   85Uncommon ...Against the Grain is your key tothe latest news about libraries,publishers, book jobbers, andsubscription agents. ATG is aunique collection of reports on theissues, literature, and people thatimpact the world of books, journals,and electronic information.Unconventional ...ATG is published six times a year, inFebruary, April, June, September,November, and December/January. Asix issue subscription is available foronly $40 U.S. ($50 Canada, $70foreign), making it an uncommonlygood buy for all that it covers. Makechecks payable to Against the Grain,LLC and mail to:Katina Strauch209 Richardson AvenueMSC 98, The CitadelCharleston, SC 29409“Linking  Publishers, Vendors    and Librarians”Name___________________________________________________Address______________________________________________________________________________________________________CityStateZip___________________________________________________CompanyPhone___________________________________________________Email___________________________________________________○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○Innovations Affecting Usfrom page 84That’s roughly equivalent to downloading a DVDmovie in about thirty seconds. IBM is developinga system that stores 250GB in a hologram no largerthan a square inch. Another approach proposes to usea photosensitive crystal the size and shape of a sugarcube to store 1 terabyte of data.The Photorefractive Information StorageMaterials consortium (PRISM) and the Holo-graphic Data Storage System consortium(HDSS), under the aegis of the Defense AdvancedResearch Projects Agency (DARPA) have beenexperimenting with the development of new andimproved holographic media, spatial light modu-lators, and detector arrays, as well as the opto-me-chanical components needed for high performancesystem implementations.Blue Light SpecialsAll of the technologies discussed so far usered lasers. Scientists have also been working todevelop devices that use blue lasers that haveshorter wavelengths and, consequently, greaterstorage capabilities. The blue lasers would burnsmaller pits to cram more data onto the storagemedium. That would be comparable to shrink-ing car sizes and parking them closer togetherto increase the capacity of a parking lot. How-ever, blue-laser devices haven’t made it out ofthe laboratory because they remain too unwieldyfor commercial applications. The main problemis that the heat they generate makes blue lasersvery difficult to function reliably at room tem-perature; but Jan Oosterveld, a member ofPhilips Electronics NV’s group managementcommittee says: “We are not so far away fromproducing blue-laser DVDs in mass quantities.”Sony, Matsushita Electric Industrial,Hitachi, Pioneer, Sharp, Samsung Electron-ics, LG Electronics, and Thomson Multime-dia have recently agreed on uniform standardsfor next-generation blue-laser DVDs which mayappear as early as next year. These new discspromise capacities of up to 27GB on one side ofa single 12cm disc — enough to store more thantwo hours of digital high-definition motionvideo. That’s nearly six times the 4.7GB capac-ity of current DVDs.The key factors that will determine the suc-cess of a holographic data storage system are:useful capacity, transfer rate, and access time.A holographic data storage system also has tobe cost-competitive at the same time it deliversimproved performance over other conventionaloptical and magnetic drives.Crystal BallHolographic data storage has a bright future assmaller and more powerful lasers get developed.It can expect competition from other optical stor-age technologies, particularly DVD, which mayemploy some kind of volumetric storage scheme.This could entail the use of multilayer discs or evena holographic approach to increase data-storagecapacity. Data transfer rates of multilayer technolo-gies are much lower than those of holographic sys-tems; so DVD may rely on blue-laser technology,holography, or a combination of both.Holographic data storage will require a new andcostly manufacturing infrastructure to meet mar-ket demands for competitively priced products insufficient quantity and quality. Polymer-based sys-tems may be the first on the market because theyleverage the existing manufacturing infrastructurebetter than the crystal-based, all-solid-state devices.They also allow write speeds 100 to 1,000 timesfaster than those using crystals.Holographic devices may eventually appear inall kinds of small portable appliances and electronicdevices, such as mobile phones, handheld com-puters, video recorders, PCs, digital cameras, andhigh-definition TVs. They also offer great portabil-ity as they permit storing gigabytes of data on adisc the size and shape of a credit card.  ReferencesBuderi, Robert.  Data holograms. Upside.11:6 Jun 1999 p.146.High density, high performance optical datastorage via volume holography: viability atlast?Wilson, W. L.; Curtis, K.; Harris, A., et al.Optical and Quantum Electronics. 32: 3,2000 pp. 393-404.Matlis, Jan. Fluorescent multilayer discspromise to provide 1406B of storage in thespace of a CD. Computerworld. 35:15 pp.56 ss.Orlov, Sergei S. Volume holographic datastorage. Association for Computing Machin-ery. Communications of the ACM. 43:11(Nov, 2000), pp. 47-54.

3D Data Storage

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3D Data Storage

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