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.