Optical Data StorageOptical Data Storage
ByBy
Ken TatebeKen Tatebe
2004.11.12004.11.1
OutlineOutline
Basic TechnologyBasic Technology CD: Properties and CapabilitiesCD: Properties and Capabilities DVD: Comparison to CDDVD: Comparison to CD What’s makes DVD’s better?What’s makes DVD’s better? Comparison to other contemporary data Comparison to other contemporary data
storage technologiesstorage technologies Future directionsFuture directions
First Optical Storage TechniquesFirst Optical Storage Techniques
Writing systems Writing systems represent the first optically represent the first optically based data storage based data storage methods, replacing oral methods, replacing oral records.records.
Storage Capacity: Storage Capacity:
~ 0.01 byte / mm~ 0.01 byte / mm22
2020thth Century: The Compact Disc Century: The Compact Disc
Patented in 1970 by James T. Russell as a Patented in 1970 by James T. Russell as a means for durable audio data storage.means for durable audio data storage. First digital optical data storage; inspired by First digital optical data storage; inspired by
punch cards and magnetic storage devices.punch cards and magnetic storage devices. Mass production starts in 1985 by Philips and Mass production starts in 1985 by Philips and
Sony.Sony. Gives practical use to Reed – Solomon Error Gives practical use to Reed – Solomon Error
Correction.Correction.
Data Density: ~ 1Mbyte/mmData Density: ~ 1Mbyte/mm22
Tracking and Error CorrectionTracking and Error Correction
Diagonally astigmatic lens coupled with Diagonally astigmatic lens coupled with quadrant photocell.quadrant photocell.
Difficult to keep focus stable across all Difficult to keep focus stable across all freq.freq.
1 mm surface spot size due to high NA1 mm surface spot size due to high NA Reed - Solomon correction codesReed - Solomon correction codes
Over-sampled polynomial using data as Over-sampled polynomial using data as coefficients coefficients
DVD: Improvements to CDDVD: Improvements to CD
FeatureFeature DVDDVD CDCD
Substrate Dia./Thick.Substrate Dia./Thick. 120 x 1.2 mm120 x 1.2 mm 120 x 1.2 mm120 x 1.2 mm
SidesSides 1 or 21 or 2 11
Layers per sideLayers per side 1 or 21 or 2 11
Capacity (GB)Capacity (GB) 4.7, 8.54, 9.4, 174.7, 8.54, 9.4, 17 0.70.7
Track Pitch (micron)Track Pitch (micron) 0.740.74 1.61.6
Min pit length (micron)Min pit length (micron) 0.440.44 0.830.83
Linear scan velocityLinear scan velocity 3.6 m/s3.6 m/s 1.3 m/s1.3 m/s
Laser wavelengthLaser wavelength 635 nm635 nm 780 nm780 nm
Numerical ApertureNumerical Aperture .6.6 .45.45
ModulationModulation 8 to 168 to 16 8 to 178 to 17
Spot SizeSpot Size 1058 nm1058 nm 1733 nm1733 nm
Road to the DVDRoad to the DVD
Innovations:Innovations: Dual layerDual layer Increased numerical apertureIncreased numerical aperture Decreased depth of focusDecreased depth of focus Signal to noiseSignal to noise TrackingTracking Data Density: ~7 MByte/mmData Density: ~7 MByte/mm22
Dual Layer TechnologyDual Layer Technology
BenefitsBenefits Increased durabilityIncreased durability Increased capacityIncreased capacity
DetrimentsDetriments Decreased S/NDecreased S/N Decreased data densityDecreased data density
Numerical ApertureNumerical Aperture
NA = n sin(NA = n sin(/2)/2) Spot size = Spot size = /NA/NA
Depth of FocusDepth of Focus
DoF = DoF = /NA/NA22
Determines spacing Determines spacing of layersof layers
Affects S/N; places an Affects S/N; places an upper limit on NA.upper limit on NA.
Noise TolerancesNoise Tolerances
Coma AberrationsComa Aberrations Laser more stable at -135 db/HzLaser more stable at -135 db/Hz Eccentricity 100 micron down from 140 micronEccentricity 100 micron down from 140 micron Surface aberration of 0.033 Surface aberration of 0.033 down from 0.07 down from 0.07
Hard drivesHard drives
Future Data Disc AdvancesFuture Data Disc Advances
Non-linear UpgradesNon-linear Upgrades
2 – Photon absorption to decrease depth 2 – Photon absorption to decrease depth of field for more layers of field for more layers
Magnetic Super-Resolution: 100 nm spot Magnetic Super-Resolution: 100 nm spot size.size.
Separate layers by narrow spectral Separate layers by narrow spectral response.response.
Shorter wavelength (freq. doubled?)Shorter wavelength (freq. doubled?)
Volumetric StorageVolumetric Storage
““K – Vector” Addressing: a.k.a. K – Vector” Addressing: a.k.a. Holographic addressingHolographic addressing
2 beam intersection: issues with reaching 2 beam intersection: issues with reaching diffraction limitsdiffraction limits
Interferometer based path length Interferometer based path length addressingaddressing
ReferencesReferences Optical Data Storage. Optical Data Storage. Coufal, Hans, Geoffrey Burr: Coufal, Hans, Geoffrey Burr:
International Trends in OpticsInternational Trends in Optics, 2002., 2002. DVD Focus Control.DVD Focus Control. Lincoln, Bo: Lecture notes. Lincoln, Bo: Lecture notes. Smith, Steven W. Smith, Steven W. The Scientist and Engineer’s Guide to The Scientist and Engineer’s Guide to
Digital Signal Processing.Digital Signal Processing. San Diego: California San Diego: California Technical Publishing, 1997.Technical Publishing, 1997.
Usbyte.comUsbyte.com Pioneer.co.jpPioneer.co.jp Optical-disk.comOptical-disk.com Hecht, Eugene. Hecht, Eugene. Optics.Optics. Reading: Addison Wesley Reading: Addison Wesley
Longman, 1998.Longman, 1998. Magnetic Super Resolution: Fujitsu.Magnetic Super Resolution: Fujitsu.
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