1VISHVESHWARAIAH TECHNOLOGICAL UNIVERSITYS.D.M COLLEGE OF ENGINEERING AND TECHNOLOGYA seminar report onHolographic Data StorageSubmitted bySharath H N (2SD06CS092)8th semesterDEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING2009-102VISHVESHWARAIAH TECHNOLOGICAL UNIVERSITYS.D.M COLLEGE OF ENGINEERING AND TECHNOLOGYCERTIFICATECertified that the seminar work entitled “HOLOGRAPHIC DATASTORAGE” is a bonafide work presented by SHARATH H N bearingUSN 2SD06CS092 in a partial fulfillment for the award of degree ofBachelor of Engineering in COMPUTER SCIENCE ANDENGINEERING branch, under Visveswaraya Technological University,Belgaum during the year 2009-10. The seminar report has been approvedas it satisfies the academic requirements with respect to seminar workpresented for the Bachelor of Engineering Degree.Staff in charge H.O.DName: Sharath H N USN: 2SD06CS0923

HOLOGRAPHIC DATA STORAGEBy,Sharath H NRoll no 100CSE ‘B’ Devision.4INDEX1. Abstract……………………………………………………………………………52. Introduction………………………………………………………………………..53. Different types of data storage systems……………………………………………53.1. Magnetic data storage system……………………………………………53.1.1. Magnetic disk…………………………………………………..53.1.2. Floppy disk……………………………………………………..83.2. Optical data storage system……………………………….……………...83.2.1 CD technology………………………………………………….83.2.2 DVD technology…………...……………………………………9

4. Holographic data storage systems…………………………………………...……104.1. Theory behind holographic data storage systems……………………….104.2. Advantages of holographic data storage systems……………………….124.3. Working…………………………………………………………………124.3.1. Spatial Light Modular (SLM)…………………………………124.3.2 The components involved……………………………………...134.3.3. writing……….………………………………………………...134.3.4. Reading………………………………………………………..144.3.5. Multiplexing…………………………………………………...144.3.6. Errors…………………………………………………………..174.4. Holographic Versatile Disk…………………………………………174.4.1. Some features………………………………………………….174.4.2. Disk structure…………………………….................................184.4.3. Limitations of HVD…………………………………………...184.4.4. Comparison of HVD…………………………………………..195. Future development and challenges……………………………………………..196. Conclusion……………………………………………………………………….207. References………………………………………………...…………………….1451. ABSTRACT:This paper provides a description of different type of data storage systems along withexamples. Later it introduces the concept holographic data storage system(HDSS), a three dimensional data storage system which has afundamental advantage over previously mentioned conventional read/write memorysystems.The theory behind HDSS and working is seen, which is followed by some advantagesof HDSS with respect to other systems are discussed. Later the working is seen whichdiscusses reading, writing and some multiplexing techniques. Then HolographicVersatile Disk (HVD) is discussed.The future development and challenges of holographic memory is then presented,followed by conclusion.2. INTRODUCTION:It is estimated that until now people have produced more than 5 exabytes (5 billiongigabytes) of data, the majority of which is in digital form. Since this figure is alwaysgrowing and analogue media is constantly being converted to digital, new methods ofstoring this data are needed. Currently the two main storage methods i.e. magnetic andoptical are just about keeping ahead of these needs; unfortunately this is not alwaysgoing to be the case.Holographic data storage is a potential replacement technology in the area of highcapacitydata storage currently dominated by magnetic and conventional optical datastorage.3. Different types of Data storage systemsThey are• Magnetic Data storage• Optical data storage3.1. Magnetic data storage

Magnetic storage and magnetic recording are terms from engineering referring to thestorage of data on a magnetized medium. Magnetic storage uses different patternsof magnetization in a magnetizable material to store data and is a form of non-volatilememory. [1]Some of the major storage devices that comes under magnetic data storage systemsare• Magnetic disk• & Floppy disk63.1.1 Magnetic Disk:Hard disks were invented in the 1950s. They started as large disks up to 20 inches indiameter holding just a few megabytes. Magnetic disk is a plastic disk coated withmagnetic material and used for storing computer programs and data as a series ofmagnetic spots. Most computers contain a hard disk unit for general storage. Hardmagnetic disks can store larger amounts of data and come in cartridges that slot into aspecial drive unit. [2]Structure and workingOn a hard disk (magnetic disk), data is stored in the magnetic coating of the disk’splatters. The platter is a flat disk of either alloy or glass, with a spindle at the centre.Modern platters generally have a diameter of 3.5” in desktops or 2.5” in laptops,although smaller drives are available for devices that require a micro-drive.The spindle is rotated by an electric motor, and this cause the platter to spin. Thespeed at which the platter spins is measured in RPM and a higher speed is usuallyreflective of a higher performance, disk, in terms of data writing and reading.The magnetic media holds the binary data as with tapes and floppy disks. The data isread from the surface of the platter by a set of ‘heads’ which are fixed so that they canonly move between the centre of the platter and the outside edge. The heads are heldjust above the magnetic media by actuator arms that facilitate this movement acrossthe disk’s platter surface. The heads are not designed to touch the platter surface asphysical contact can cause damage to the magnetic media. Each platter has a top sideand an underside, and there is usually a head for both. Therefore, a hard disk drivewith 5 platters would have 10 heads.When the disk is not in use, the heads are ‘parked’, usually at the outside edge of theplatter.Data in the magnetic media is organized into cylinders - concentric tracks on themedia that are further divided into sectors. A sector is the smallest allocatable logicalunit on a drive and usually, but not always, is 512 bytes in size. [3]Next, the drive moves the heads over the appropriate track on a platter. The time ittakes to move the heads is called the seek time. Once over the correct track, the drivewaits while the platters rotate the desired sector under the head. The amount of timethat takes is called the drive's latency. The shorter the seek time and latency, the fasterthe drive can do its work.When the drive electronics determine that a head is over the correct sector to write thedata, the drive sends electrical pulses to that head. The pulses produce a magneticfield that alters the magnetic surface of the platter. The variations recorded there nowrepresent the data.

Reading data complements the recording process. The drive positions the read portionof the head over the correct track, and then waits for the correct sector to orbit around.When the particular magnetic specks that represent your data in the right sector andtrack pass under the read head, the drive's electronics detect the small magneticchanges and convert them back into bits. Once the drive checks the bits for errors andfixes any it sees, it sends the data back to the operating system. [3]Below is the diagram of the hard disk with platters, spindle and the head.73.1.2 Floppy disksFloppy disks are smaller, simpler, and cheaper disk units that consist of flexible, removable,plastic, diskette coated with the magnetic material. The diskette is enclosed in plastic jacket,which has an opening where the read/write head makes contacts with diskette. A hole in thecentre allows a spindle mechanism in the disk drive to position and rotate the diskette.Information recorded on floppy disks by combining the clock and data information along eachtrack using Manchester encoding. Disks encoded in this way are said to have single destiny.The main features of floppy disks are small physical size and low cost. But this is offset bysmaller storage capacity longer acess time and higher failure than hard disk.The floppy diskshave been superseded by the emergence of rewritable compact disks having higher capacities.[1]83.2. Optical data storageToday's meaning of optical data storage refers to storage systems that use light forrecording and retrieval of information. Optical recording systems potentially havemuch greater reliability than magnetic recording systems since there is a much largerdistance between the read/write element and the moving media. Therefore, there is nowear associated with repeated use of the optical systems. Another advantage of theoptical recording systems over the best performing magnetic recording systems - harddrives - is their removability.The main disadvantage of optical storage when compared to magnetic is slowerrandom data access. This partially comes from the design of the relatively large (andheavy) optical heads. [4]Optical drives of all kinds operate on the same principle of detecting variations in theoptical properties of the media surface. CD and DVD drives detect changes in thelight intensity, MO drives - changes in the light polarization. All optical storagesystems work with reflected light.[4]Some of the major optical data storage technologies are• CD Technology.• DVD Technology.• Blue ray disk Technology.• & Holographic data storage technology.3.2.1 CD Technology:The first generation of CD was developed by sony and Philips corporations, for audio systems.To provide high quality audio production and reproduction, 16-bit samplesOf the analog signals are taken at 44100 samples per second. The CDs were required to hold atleast an hour of music. [1]Structure of a CD

A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch(1.2 mm) thick. During manufacturing, this material is impressed with microscopicbumps arranged as a single, continuous, extremely long spiral track of data. Laterathin, reflective aluminium layer is sputtered onto the disc, covering the bumps. TheCD can store up to 600Mbs of data.[5]9The read laser passes through the polycarbonate underside of the disc to the reflectivealuminium layer underneath, reflecting the laser light from the pits and bumps —which represent the binary data on the disc. Note that recordable CDs use a differentstructure with a 'dye' that can be changed by a laser, thus allowing tracks to be burnedon a disc.3.2.2 The DVD technologyThe quest for greater storage capacity resulted in the development of digital versatiledisk(DVD) technology in 1996.The structure of DVDThe size of a DVD disk is same as that of the CD, whereas the storage capacity is increasedbecause of the change made in design process, as mentioned below.The pits are smaller having minimum length of 0.4 micron.The tracks are placed more closer, the distance between the tracks are 0.74 micron.A red light laser with a wavelength of 635nm is used instead of infrared light (780nm) laserused in CDs. The above improvements lead to DVD capacity of 4.74 GBs.[1]The Multi-Layer Storage of DVDTo increase the storage capacity even more, a DVD can have up to four layers, two oneach side. The laser that reads the disc can actually focus on the second layer throughthe first layer. It can be single sided, single layered (capacity-)or single sided, double layeredor double sided, double layered.The below diagram shows double layered, single sided DVD.10Here is a list of the capacities of different forms of DVDs:Format Capacity Approx. Movie TimeSingle-sided/single-layer 4.38 GB 2 hoursSingle-sided/double-layer 7.95 GB 4 hoursDouble-sided/single-layer 8.75 GB 4.5 hoursDouble-sided/double-layer 15.9 GB Over 8 hoursThe capacity of a DVD doesn't double when a whole second layer is added to the disc.This is because when a disc is made with two layers, the pits have to be a little longer,on both layers, than when a single layer is used. This helps to avoid interferencebetween the layers, which would cause errors when the disc is played.[5]4. Holographic Data storageHolographic data storage is the methodology that comes under Optical data storage.When magnetic and optical data storage devices are considered, they rely onindividual bits being stored as distinct magnetic or optical changes on the surface ofthe recording medium.In order to increase storage capabilities, a new optical storage method is beingconsidered called holographic memory that will go beneath the surface and use thevolume of the recording medium for storage, instead of only the surface area.

4.1Theory behind holographic data storageHolograms are photographic images that are three-dimensional and appear to havedepth. Holograms work by creating an image composed of two superimposed 2-dimensional pictures of the same object seen from different reference points.Holography requires the use of light of a single exact wavelength, so lasers must beused. In reflection holograms, the kind of holography that can be viewed in normallight, two laser beams and a photographic plate are used to take an image of theobject.Holography is a method of recording patterns of light to produce a three dimensionalobject. The patterns of light are called a hologram. The process of creating a hologrambegins with a focused beam of light -- a laser beam. This laser beam is split into twoseparate beams: a reference beam, which remains unchanged throughout much of theprocess, and an information beam, which passes through an image. When lightencounters an image, its composition changes and the image is captured in itswaveforms. When these two beams intersect, it creates a pattern of light interference.If this pattern of light interference in a layer of a disc is recorded then the lightpattern of the image is recorded.11To retrieve the information stored, the reference beam is applied directly onto thehologram. When it reflects off the hologram, it holds the light pattern of the imagestored there. The holographic memory systems use holograms to store digital insteadof analog information. [6]124.2 Some of the Advantages of HDSS with respect other data storage methods• Three-dimensional data storage will be able to store more information in asmaller space and offer faster data transfer times.• Unlike other technologies that record one data bit at a time, holographyrecords and reads more than a million bits of data with a single flash of light.• This enables significantly higher transfer rates than current optical storagedevices.• High storage densities and fast transfer rates, combined with durable, reliable,low-cost media, mean that holography is poised to become a compellingchoice for next-generation storage.• In addition, the flexibility of the technology allows a wide variety ofholographic storage products to be developed, ranging from handheld devicesfor consumers to storage products for enterprises.• IT can be imagined having 50 hours of high-definition video on a single disc,50 000 songs on a postage stamp, or 500 000 X-rays on a credit card.[7]4.3 Working of Holographic Data Storage System4.3.1 Spatial Light Modulator (SLM)A spatial light modulator is used for creating binary information out of laser light. TheSLM is a 2D plane, consisting of pixels which can be turned on and off to createbinary 1.s and 0.s. An illustration of this is a window and a window shade. It ispossible to pull the shade down over a window to block incoming sunlight. If sunlightis desired again, the shade can be raised. A spatial light modulator contains a twodimensionalarray of windows which are only microns wide. These windows block

some parts of the incoming laser light and let other parts go through. The resultingcross section of the laser beam is a two dimensional array of binary data, exactly thesame as what was represented in the SLM. After the laser beam is manipulated, it issent into the hologram to be recorded. This data is written into the hologram as pageform. It is called this due to its representation as a two dimensional plane, or page, ofdata[10].134.3.2 The components involved :• The holographic memory system is made up of the following basiccomponents:• a charge-coupled device• lenses to focus the laser beams• an LCD panel• a photopolymer or lithium niobate crystal• mirrors to direct the laser light• beam splitters• and an argon laser.4.3.3 WritingThe light from the argon laser is split in two by the beam splitter. The signal or objectbeam will bounce off a mirror and pass through a spatial light modulator or SLM (andLCD showing raw binary data as dark and clear boxes). The signal or object beamwill then carry the information from the SLM to the crystal. The second beam or thereference beam, on the other hand, takes another course towards the crystal and uponhitting it along with the object beam, creates an interference pattern that will be usedto store the information relayed by the object beam in a certain location in the crystal.144.3.4 Retrieving:The interference pattern induces modulations in the refractive index of the recordingmaterial yielding diffractive volume gratings. The reference beam is used duringreadout to diffract off of the recorded gratings, reconstructing the stored array of bits.The reconstructed array is projected onto a pixelated detector that reads the data inparallel. This parallel readout of data provides holography with its fast data transferrates (10's to 100's of MBytes/second). The readout of data depends sensitively uponthe characteristics of the reference beam. By varying the reference beam, for exampleby changing its angle of incidence or wavelength, many different data pages can berecorded in the same volume of material and read out by applying a reference beamidentical to that used during writing. This process of multiplexing data yields theenormous storage capacity of holography. [5][7]4.3.5 MultiplexingOnce one can store a page of bits in a hologram, an interface to a computer can bemade. The problem arises, however, that storing only one page of bits is notbeneficial. Fortunately, the properties of holograms provide a unique solution to thisdilemma. Unlike magnetic storage mechanisms which store data on their surface,holographic memories store information throughout their whole volume. After a pageof data is recorded in the hologram, a small modification to the source beam before itreenters 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. Thethicker the volume becomes, the smaller the modifications to the source beam can be.There are five types of multiplexing• Angular Multiplexing• Wavelength Multiplexing• Spatial Multiplexing• Peristrophic Multiplexing• Shift Multiplexing• Phase-Encoded Multiplexing15Angular MultiplexingWhen a reference beam recreates the source beam, it needs to be at the same angle itwas during recording. A very small alteration in this angle will make the regeneratedsource beam disappear. Harnessing this property, angular multiplexing changes theangle of the source beam by very minuscule amounts after each page of data isrecorded (see figure 2). Depending on the sensitivity of the recording material,thousands of pages of data can be stored in the same hologram, at the same point oflaser beam entry[10]. Staying away from conventional data access systems whichmove mechanical matter to obtain data, the angle of entry on the source beam can bedeflected by high-frequency sound waves in solids[10]. The elimination ofmechanical access methods reduces access times from milliseconds to microseconds.Wavelength MultiplexingUsed mainly in conjunction with other multiplexing methods, wavelengthmultiplexing alters the wavelength of source and reference beams between recordings.Sending beams to the same point of origin in the recording medium at differentwavelengths allows multiple pages of data to be recorded. Due to the small tuningrange of lasers, however, this form of multiplexing is limited on its own.Spatial MultiplexingSpatial multiplexing is the method of changing the point of entry of source andreference beams into the recording medium. This form tends to break away from thenon-mechanical paradigm because either the medium or recording beams must bephysically moved. Like wavelength multiplexing, this is combined with other formsof multiplexing to maximize the amount of data stored in the holographic volume.Two commonly used forms of spatial multiplexing are peristrophic multiplexing andshift multiplexing.16Peristrophic MultiplexingThis form of spatial multiplexing rotates the recording medium as the light sourcebeams remain in fixed positions[10]. For instance, a holographic cube could berotated so each of its six sides could take in a source beam. This would provide sixtimes the number of pages which could be stored in the volume. Certain problemsarise when implementing this method of multiplexing. The rotational axes needs to bepositioned in a way which does not interfere with the laser beams. As with all spatialmultiplexing, bringing the recording media back to its original position for dataretrieval would need to be very precise. This is much easier to maintain when themedia remains static.

Shift MultiplexingShift multiplexing alters the point of entry on one surface of the recording media. Therecording optics or media could be repositioned to allow the source beam to entermultiple positions on a surface. Depending on the size of the laser beam andthesensitivity of the recording media, the points of entry the source beam takes into itcan be immense[10]. This form of multiplexing combined with peristrophicmultiplexing could cover a very large percentage of the hologram.Phase-Encoded MultiplexingThe form of multiplexing farthest away from using mechanical means to record manypages 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/translate therecording medium, phase-encoded multiplexing changes the phase of individual partsof a reference beam. The main reference beam is split up into many smaller partialbeams which cover the same area as the original reference beam. These smallerbeamlets vary by phase which changes the state of the reference beam as a whole. Thereference beams intersects the source beam and records the diffraction relative to thedifferent phases of the beamlets. The phase of the beamlets can be changed bynonmechanical means, therefore speeding up access times.[10]17Combining Multiplexing MethodsNo single multiplexing method by itself is the best way to pack a hologram full ofinformation. The true power of multiplexing is brought out in the combination of oneor more methods. Hybrid wavelength and angular multiplexing systems have beentested and the results are promising. Recent tests have also been formed on spatialmultiplexing methods which create a hologram the size of a compact disc, but whichhold 500 times more data[10].4.3.6 ErrorsWhen data is recorded in a holographic medium, certain factors can lead toerroneously recorded data. One major factor is the electronic noise generated by laserbeams. When a laser beam is split up (for example, through a SLM ), the generatedlight bleeds into places where light was meant to be blocked out. Areas where zerolight is desired might have minuscule amounts of laser light present which mutates itsbit representation. For example, if too much light gets recorded into this zero arearepresenting a binary 0, an erroneous change to a binary 1 might occur.4.4 A holographic data storage device: Holographic versatile disk (HVD)(Holographic Versatile Disc) A high-capacity optical disc is the one that combinessingle beam holographic storage and DVD technologies to provide cartridgecapacities reaching 1TB and beyond.Hence the holographic Versatile Disk offer far more storage and transfer capacitythan CDs and DVDs and even "next-generation" DVDs like Blu-ray.[8]4.4.1 Some of the features of HVD• Unlike current CD and the DVD drive technology the HVDs have the capacityto hold up to 300 gigaabytes of information.• The holographic versatile disc has a transfer rate of 1 Gbit/s.• Working of HVD is almost similar to the holographic data storage mechanism.

[9]184.4.2 Holographic Versatile Disc – Disc StructureThe figure below the right shows the cross section of an HVD disc.As seen in this diagram, holographic recording layer is formed on top of a reflectivelayer. The simple optical setup of Collinea Technology has allowed the HVD disc tohave a reflective layer on the substrate and address pits formed on this layer. Thisconfiguration is the key to apply Collinear™ Technology to commercial HVDproducts. These address pits and the servo technology to read them guarantee theinterchangeability of HVD discs, ruggedness against vibration in the realenvironment, wide system margin against variety of HVD discs from differentmanufacturers. Of course the servo information also make random access easy.The servo technology and the address pits are, in fact, not different from those usedin the current CD and DVD players and disks. The laser which is used to read addresspits is 650nm red laser, also common with DVD players in the market.Another layer called “Dichroic Mirror Layer_Eis placed between the holographicrecording layer and the substrate to block the green or blue laser, which are used toread/write holographic information, to reach address pits, thus eliminates noise.In short, HVD is a disc the holographic recording layer of which is formed on top of aconventional optical disk.[9]4.4.3. Some of the limitations of HVD• Holographic consumer products need to be very cheap in order to competewith DVD drives, which currently cost much higher, because of the muchhigher complexities in working and development. [9 ]• Holographic memory discs have been notably thicker than CDs and DVDs. [5]• Since HVDs are composed of very complex mechanisms and an investment ofover $100 m (778 m) is typically required to develop a new platform. [5]194.4.4 ComparisonWhile HVD is attempting to revolutionize data storage, other discs are trying toimprove upon current systems. Two such discs are Blu-ray and HD-DVD, deemed thenext-generation of digital storage. Both build upon current DVD technology toincrease storage capacity. All three of these technologies are aiming for the highdefinitionvideo market, where speed and capacity count.Blu-ray HD-DVD HVDInitial cost for recordabledisc Approx. $18 Approx. $10 Approx.$120Initial cost forrecorder/playerApprox.$2,000Approx.$2,000Approx.$3,000

Initial storage capacity 54 GB 30 GB 300 GBRead/write speed 36.5 Mbps 36.5 Mbps 1 GbpsHVD is still in the late stages of development and it has probably noticed that theprojected introductory price for an HVD is a bit steep. An initial price of about $120per disc will probably be a big obstacle to consumers. However, this price might notbe so insurmountable to businesses, which are HVD developers' initial targetaudience. Optware and its competitors will market HVD's storage capacity andtransfer speed as ideal for archival applications, with commercial systems available assoon as late 2006. Consumer devices could hit the market around 2010.[5]5. Future development and challenges:In the past, the realization of holographic data storage has been frustrated by the lackof availability of suitable system components, the complexity of holographicmultiplexing strategies, and perhaps most importantly, the absence of recordingmaterials that satisfied the stringent requirements of holographic data storage.Recently the development of practical components for holographic systems hasrekindled interest in this technology. While the development of the neededcomponents has been accomplished for non holographic markets, the volume of thesemarkets is expected to lead to low-cost, reliable components for holographic datastorage. DVD-R (red 680nm) and DVD-B (blue 405-407nm) have been developed forthe optical storage market place. These recording sources have the desiredcharacteristics for holographic storage and are attractive due to their small size,ruggedness, and low cost.The InPhase Technology team has invented several multiplexing techniques thatyielded a simple, easily implementable architecture for holographic storagesystems.[5]Changes in both the quality of the laser beam and recording material are beingresearched, but these improvements must take into consideration the cost20effectiveness of a holographic memory system. These limitations to current laserbeam and photosensitive technology are some of the main factors for the delay ofpractical holographic memory systems.[10]6. ConclusionMay be one day one of these scenarios with data stored in holograms materializes andbecome reality in the foreseeable future. In collaboration and competition with a largenumber of scientists from around the globe, the study on the technical feasibility ofholographic storage and memory devices with parameters that are relevant for realworldapplications should be continued. Whether this research will one day lead toproducts depends on the insights that leads to gain into these technical issues and howwell holography can compete with established techniques in the marketplace.References :1. Computer organisation by Carl hamacher.2. www.softpedia.com.3. http://www.riedelit.com/Data_Recovery_Technical_Guide.html4. http://www.usbyte.com/common/optical_data_storage_systems.html5. www.howstuffworks.com/6. www.mediastoragedevices.com/holographic-versatile-disc.html7. Kevin Kurtis from Iphase technologies.

8. http://www.answers.com/topic/holographic-versatile-disc9. http://www.hvd-forum.org/abouthvd/technology.html10. Holographic memory, by John Sand.21