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Optical Data StorageLena Lopatina, 4/26/2006

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Outline

1. Analog and digital recording

2. CD Drive and CD Anatomy

3. CD Player construction

4. Data encoding and decoding

5. Types of optical discs: Audio CD, CD-R, CD-RW, DVD, Blu Ray, Dual Layer

6. Bonus: Lightscribe

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Analog and digital recording

Analog sound wave of a spoken word ‘Hello’

Analog wave converted to digital format

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In a typical optical-disk drive, an infrared beam from an aluminum gallium laser passes through a series of optical elements, is focused onto the disk, reflects back along its original path, and it’s diverted to a photodetector.

Two voice-coil motors adjust the focus of the objective lens and keep the beam locked onto the data track. Other motors spin the disk and shift the entire head along rails to find different tracks.

Drive anatomy

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CD anatomy basics

Cross-section of a CD

CD surface: bumps and the land

Spiral recording

Total length of the spiral on a CD: ~5.5 km

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CD player

1. Disc drive system 2. Laser pickup system 3. Servo system (auto-focusing and auto-tracking)4. Data decoding5. Control and display system

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Disc drive system

• The purpose of this system is to spin the CD at the correct speed. Unlike records, (which spin at a constant rate) CD's spin at different rates depending on where the laser beam is located. The speed of the CD varies from 500 revolutions per min (rev/min), on the inside, to 200 (rev/min) on the outside. This allows the data to be picked up by the laser system at a constant rate.

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Laser pickup system

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Reading the pit

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Servo system: auto-focusing

Too close

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Servo system: auto-focusing

Too far

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Servo system: auto-focusing

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Servo system: auto-tracking

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Servo system: auto-tracking

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Data encoding

• Analog music is converted to a digital signal via an analog-to-digital converter.

• The left and right channels are combined to one digital data string via a multiplexer.

• The digital data string is encoded with error detection and correction algorithms.

• The encoded data string is prepared for storage on the CD.

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Data decodingThe CD player can be called a decoder because it basically reverses the encoding process. Data read from the CD must be:

• Demodulated

• Decoded

• Demultiplexed

• Converted from digitalto analog using a digital-to-analog converter

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Control and display system

Control system: •what the present track is,•the time left on the track, the time left on the CD,•and the time left in the memory program,•interface with the control buttons and knobs on the CD player.

Subcode:•how many tracks are on the CD

•what track it is presently on,

•time left on the song, or time left on the CD, so on.

Features:•random memory programming,

•manual searches,

•random playback,

•and pausing.

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Types of optical discsAudio CD and CD-ROM: stamped,

not re-writable

1.Mastering Process: First, in a clean room, a glass master is prepared by coating a perfectly flat piece of half inch thick circular glass with a layer of nickel and burning pits in nickel layer.

2. Stamper Process: Next the glass master is used to create nickel stampers using an electroplating technique. Multiple stampers can be made from one glass master.

3. Pressing CD is pressed using up to 40 tons of pressure

4. Printing and Packaging

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Types of optical discs

CD-RA “blank” CD-R is not “empty”:

has a pregroove with a wobble,contains information about the CD-R manufacturer, and the dye used and media information

Materials used: cyanine dye CD-R – is green, is unstable(few years),azo dye CD-R – is dark blue, has lifetime of decadesphthalocyanine dye – usually silver, gold or light

green, and is stable, good for decades

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Types of optical discs

CD-RW

contains a phase-change alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium.

An infra-red laser beam is employed to selectively heat and melt the crystallized recording layer into an amorphous state or to anneal it at a lower temperature back to its crystalline state. The different reflectance of the resulting areas make them appear like the pits and lands of a prerecorded CD.

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Types of optical discsDVD and Blu Ray

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Types of optical discs

Dual Layer

Single-sided dual layer recordable discs are constructed by one dummy polycarbonate platter base and the other one that contains a single organic recording layer.

Dual layer recordable discs contain two organic dye recording layers (termed L0 and L1, respectively) between dual polycarbonate bases and semi-reflective metal layers separated by a transparent spacing layer.

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Light ScribeLightScribe is an optical disc recording technology that utilizes specially coated recordable CD and DVD media to produce laser-etched labels.

The surface of a LightScribe disc is coated with a reactive dye that changes color when it absorbs 780nm infrared laser light. The etched label lasts approximately 9 months under indoor lighting without fading.

LightScribe labels burn in concentric circles, moving outward from the center of the disc. Currently LightScribe is monochromatic, a grey etch on a gold looking surface.

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References[1] EE 498 Class Notes by y Professor Kelin Kuhn of the University of Washington (

http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm)

[2] HowStuffWorks.com (http://www.howstuffworks.com/)

[3] Burnworld.com (http://burnworld.com/)

[4] Wikipedia (http://www.wikipedia.org/)

[5] Chip's CD Media Resource Center (http://www.chipchapin.com/CDMedia/index.php3)

THANK YOU!