optical media

8/8/2019 Optical Media

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History of optical storage media

CD-ROM, introduced in 1982

CD-R and CD-RW in 1988

DVD was rolled out in 1996

DVD-R in late 1997

DVD+R in 2002


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As of 2007, future development beyond HD DVDand Blu-ray Disc appear to be based upon one or more of the following technologies, all in varyingstages of development:

Holographic data storage.3D optical data storage.Nearfield optics.Solid immersion opticsDiscs utilizing very short wavelengths such as UV

or X-rays.Layer selection discs (LS-R).

Multi-level technology.Complex pit shapes allowing multiple channels to

be stored on one track.Wavelength multiplexing techniques.


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Optical Storage TechnologyAssociation (OSTA)

An international trade association which promotes the use of recordable opticaltechnologies and products


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RNA might be the oldest data storage medium , nowreplaced by DNA in most organisms.


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Optical disc recordingtechnologies and modes

Overburning > Buffer underrun protection > Packet writing >

CD Disc-At-Once >

CD Track-At-Once > DVD-R Disc At Once > Session At Once >


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The optical lens of a CD drive .


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Optical discflat, circular, usually polycarbonate disc

data is stored in the form of pits (or bumps)within a flat surface, usually along a singlespiral groove that covers the entire recordedsurface of the disc


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data is generally accessed when a specialmaterial on the disc (often aluminium) is

illuminated with a laser diode

pits distort the reflected laser light


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OPTICAL MEDIA TYPESLaser disc >CD> 5.1 Music disc SACD Photo CD

CD-R > CD-ROM CD-RW >


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Video CD SVCD CD+G

CD-Text CD ROM XA CD-Extra CD-i Bridge CD-i


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Mini Disc >

DVD> DVD-R DVD+R DVD-R DL DVD+R DL DVD-RW DVD+RW

DVD-RW DL DVD+RW DL DVD-RAM DVD-D >


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HD DVD >

HD DVD-R HD DVD-RW HD DVD-RAM

Blue Ray Disc (BD) > BD-R BD-RE

UDO>UMD>


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potential to provide terabyte-level massstorage on DVD-sized disksdata recording and readback are achieved

by focusing lasers within the mediumbecause of the volumetric nature of the datastructure, the laser light must travel throughother data points before it reaches the pointwhere reading or recording is desired

nonlinearity is required to ensure that theseother data points do not interfere with theaddressing of the desired point


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In order to record information on the disc alaser is brought to a focus at a particular depth in the media that corresponds to a

particular information layer When the laser is turned on it causes a

photochemical change in the mediaAs the disc spins and the read/write headmoves along a radius, the layer is written

just as a DVD-R is written

The depth of the focus may then be changedand another entirely different layer of information written


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The distance between layers may be 5 to100 micrometers, allowing >100 layers of information to be stored on a single disc


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In order to read the data back, a similar procedure is used, except this time insteadof causing a photochemical change in themedia the laser causes flourescenceThis is achieved by using a lower laser

power or a different laser wavelengthThe intensity or wavelength of thefluorescence is different depending on

whether the media has been written at that point, and so by measuring the emitted lightthe data is read


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Schematic representation of a cross-section through a 3D optical storagedisc (yellow) along a data track (orange marks). Four data layers areseen, with the laser currently addressing the third from the top. The laser

passes through the first two layers and only interacts with the third, since

here the light is at a high intensity

As the disc spins, it moves the laser beam along the track


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Examples of 3 D optical data storage media

Mempile media

D-Data DMDand drive

Microholasmedia in action

Written

Call/Recallmedia

FMD

Landauer media


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Holographic storagestores information optically inside crystalsor photopolymersnon-volatile , sequential accesseither write once or read/write storage


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Holographic Versatile Disc (HVD)an optical disc technology which wouldhold up to 3.9 terabytes (TB) of information approximately 5,500 times the capacity of a

CD-ROM 830 times the capacity of a DVD 160 times the capacity of single-layer Blue-ray

discs about 4 times the capacity of the largest

computer hard drives as of 2007

employs a technique known as collinear

holography


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Collinear HolographyTwo lasers, one red and one green, are collimatedin a single beamThe 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 thereference beam and to read servo informationfrom a regular CD-style aluminium layer near the

bottomA dichroic mirror layer between the holographicdata and the servo data reflects the green laser while letting the red laser pass through


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Picture of an HVD


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3 -D Holography Breakthrough:

Erase And Rewrite In MinutesS cience Daily (Feb. 6, 2008) Universityof Arizona optical scientists have broken atechnological barrier by making three-dimensional holographic displays that can

be erased and rewritten in a matter of

minutes.


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V iews of an automobile (top) and of a human brain (bottom) from theupdatable 3-D holographic display developed at The University of

Arizona College of Optical S ciences in collaboration with Nitto DenkoTechnical Corp., Oceanside, Calif. The 3-D images were recorded on a4-inch by 4-inch photorefractive polymer device


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OPEN TO DISCUSSION


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Overburning is the process of recording

data past the normal size limitMany disc manufacturers extend arecordable disc to leave a small margin of

extra groove at the outer edgeThis lead-out was originally intended to

provide tolerance for the read head of anaudio CD player should it overseek, by

providing a padding of up to 90 seconds of silent digital audio >


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A buffer underrun occurs during recordingif the recorder runs out of data in therecording buffer Once the laser is on, it cannot stop andresume flawlessly; thus the pause

necessitated by the underrun can cause thedata on the disc to become invalidWith buffer underrun protection, the laser is able to stop writing for any amount of time and resume when the buffer is fullagain. The gap between successive writes isextremely small >


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Packet writing is a technology that allowsoptical discs to be used in a similar manner to a floppy discPacket writing can be used both with once-writeable media and rewriteable media >


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Disc-At-Once or DAO for CD-R media is amode that masters the disc contents in one

pass, rather than a track at a time as inTrack At OnceDAO mode, unlike TAO mode, allows any

amount of audio data (or no data at all) to be written in the "pre-gaps" betweentracks >


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Track-At-Once or TAO is a recordingmode where the recording laser stops after each track is finished and two run-out

blocks are writtenOne link block and four run-in blocks are

written when the next track is recorded >


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Disc At Once recording for DVD-R mediais a mode in which all data is writtensequentially to the disc in one uninterruptedrecording sessionThe on-disk contents result in a lead-in area,

followed by the data, and closed by a lead-out area >


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Session at Once recording allows multiplesessions to be recorded and finalized on asingle discThe resulting disc can be read by computer drives, but sessions after the first are

generally not readable by CD Audioequipment >


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Laserdisc (LD ) was the first commercialoptical disc storage medium, and was used

primarily for movies for home viewing

The standard home video laserdisc is 30 cm(11.81 inches) in diameter and made up of two single-sided aluminum discs layered in

plastic and bonded with glue


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Laserdisc (left) compared to a DVD/CD (right) >


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ACompact Disc (CD ) is an optical discused to store digital data, originally

developed for storing digital audioThe technology was later adapted andexpanded to include data storage (CD-

ROM), write-once audio and data storage(CD-R), rewritable media (CD-RW),SACD, VCD, SVCD, PhotoCD, PictureCD,CD-i, and Enhanced CD. CD-ROMs andCD-Rs remain widely used technologies inthe computer industry


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A Compact Disc is made from a 1.2 mm

thick disc of almost pure polycarbonate plastic and weighs approximately 16 grams.A thin layer of aluminium or, more rarely,gold is applied to the surface to make itreflective, and is protected by a film of lacquer

Standard CDs have a diameter of 120 mmand can hold up to 80 minutes of audio


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The pits in a CD are 500 nm wide, between830 nm and 3,000 nm long and 150 nm deep .


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The spacing between the tracks, the pitch, is1.6 mA CD is read by focusing a 780 nmwavelength semiconducter laser through the

bottom of the polycarbonate layer The pits and lands themselves do notdirectly represent the zeros and ones of

binary data. Instead, Non-return-to-zero,

inverted (NRZI) encoding is used: a changefrom pit to land or land to pit indicates aone, while no change indicates a zero


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Physical size Audio CapacityCD-ROM Data

Capacity

12 cm (standard) 7480 min 650703 MB

8 cm (mini-CD) 2124 min 185210 MB

"Business card" ~6 min ~55 MB


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Double layer (DL) media have twoindependent data layers separated by asemi-reflective layer Both layers are accessible from the sameside, but require the optics to change the

laser's focus


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Traditional single layer (SL) writable media are produced with a spiral groove molded in the

protective polycarbonate layer (not in the datarecording layer), to lead and synchronize the speedof recording headDouble-layered writable media have: a first

polycarbonate layer with a (shallow) groove, afirst data layer, a semi-reflective layer, a second(spacer) polycarbonate layer with another (deep)groove, and a second data layer

The first groove spiral usually starts on the inner edge and extends outerwards, while the secondgroove starts on the outer edge and extendsinwards >


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The polycarbonate disc is coated on the pregroove side with a very thin layer of organic dyeOn top of the dye is coated a thin, reflectinglayer of silver, a silver alloy, or gold

Finally, a protective coating of a photo- polymerizable lacquer is applied on top of the metal reflector and cured with UV-lightA blank CD-R is not "empty"; the

pregroove has a wobble, which helps thewriting laser to stay on track and to writethe data to the disc at a constant rate >


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Compact Disc ReWritable (CD-RW)While a prerecorded CD has its information

permanently written onto its polycarbonate surface,a CD-RW disc contains a phase-change alloyrecording layer composed of a phase change

material, most often AgInSbTe, an alloy of silver,indium,antimony and telluriumAn infra-red laser beam is used to selectively heat

and melt, at 400 degrees (Celsius), the crystallizedrecording layer into an amorphous state or to annealit at a lower temperature back to its crystallinestate >


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AMiniDisc (MD ) is a magneto-opticaldisc-based data storage deviceThe disc is permanently housed in acartridge (68 72 5 mm) with a slidingdoor, similar to the casing of 90 mm floppy

discthe disc is a random-access mediumAt the beginning of the disc there is a table

of contents (TOC, also known as "SystemFile" area of the disc)


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Anti-skip

MiniDisc has a feature that prevents disc skippingunder all but the most extreme conditions.Older CD players had once been a source of annoyance to users as they were prone tomistracking from vibration and shock.MiniDisc solved this problem by reading the datainto a memory buffer at a higher speed than was

required before being read out to the digital-to-analog converter at the standard rate required bythe format.The size of the buffer varies by model.


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A Mini-CD is 8 centimeters in diameter >


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DVD ("Digital Versatile Disc " or "Digital Video Disc "

DVD uses 650 nm wavelength laser diodelight as opposed to 780 nm for CD. This

permits a smaller spot on the media surface

(1.32 m for DVD versus 2.11 m for CD)A DVD disk has several layers, which aremade of plastic. All layers have a thicknessof 1.2 mm. An injection used on a

polycarbonate plastic (this plastic can resistvery high and low temperatures) leads to thecreation of microscopic bumps. >


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DVD-D

DVD-D is a self-destructing disposableDVD formatIt is sold in a cardboard sleeve, and beginsto destroy itself after several hoursDVD-D now exists as one time play onlyfor movies, limited time play for video

games, and recordable DVD-D >


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H D DVD / Blu-ray disc comparison

Currently, Blu-ray discs have a higher storage capacity than HD DVD discs(50 GB vs. 30 GB)

Although HD DVD standard allows for anas-yet unused triple-layer 51 GB disc >


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Front side of an experimental Blu-ray Disc >


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U ltra Density Optical

An Ultra Density Optical disc or UDO is a5.25" ISO cartridge optical disc which canstore up to 60 GB of dataUtilises a design based on a Magneto-optical disc, but using PhaseChange

technology combined with a blue violetlaser


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U niversal Media Disc (U MD )

developed by Sony for use on thePlayStation Portablecan hold up to 1.8 gigabytes of data

Dimensions: approx. 65 mm (W) 64 mm(D) 4.2 mm (H)Maximum capacity: 1.80 GB (dual layer),900 MB (single-layer)Laser wavelength: 660 nm (red laser) >

optical media

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