Transcript Laser Focus of a CD Player

How
CD’s
Work
Speros Shepherd
2005
The Anatomy of a CD
• Piece of simple plastic- 4/100 of an inch
thick
• Injection-molded, clear, polycarbonate
piece of plastic
• Has microscopic bumps arranged in an
extremely long spiral track
Complex CD
Layers
The Anatomy of a CD
• Thin, reflective, aluminum layer
covers the bumps.
• Thin acrylic layer is used to protect
the aluminum layer
Simple Layers of a CD
The Spiral of the CD
• Spiral data track
always starts in
the center
• 0.5 microns wide
• 1.6 microns
separating the
individual tracks
• Micron= millionth
of a meter
The Basic CD Spiral
The Bumps on a CD
• Bumps make track long because
of the small dimensions
• If stretched out track would be 0.5
microns wide and 3.5 miles long
CD Bumps Magnified
The Bumps on a CD
• Bumps- 0.5
microns wide,
0.83 microns
long, 125
nanometers high
• Nanometerbillionth of a
meter
• Bumps look like
pits on the
aluminum side.
CD Bumps Magnified
CD Player Components
• Drive motor
spins the CD
• Drive motor
rotates between
200-500
rotations per
minute
• Laser moves at
micron
resolutions
Parts of a CD Player
CD Player Components
• Laser and
lens system
focuses in on
and reads the
bumps
• The tracking
mechanism
moves the
laser.
CD Player
Laser Focus of a CD Player
• The technology forms data into
understandable blocks (on an Audio or
CD-ROM)
• CD player- focuses laser on the data
track
Different Focuses of a CD Laser
Laser Focus of a CD Player
•“lands”- aluminum layer
•opto-electronic sensor:
detects change in reflectivity
CD
Player
Lasers
Laser Focus of a CD Player
The electronics in the drive interpret the
reflectivity changes to read bits that make
up the bytes. Laser stages: passes
through polycarbonate layer, reflects off
aluminum layer, hits opto-electronic
device that detects changes in light.
How a Laser
Focuses on a
CD
CD Player Tracking
• spindle motor
slows the
speed of the
CD so that the
bumps travel
past the laser
at a constant
speed. (data
comes off at a
constant rate)
•Laser beam centered
on data track system
continually moves the
laser outwards.
CD Data Formats
• 2 most common:
CD-DA (audio
CD), CD-ROM
(computer
data).These are
both widely
used. Data is
converted into
electrical pulses
by laser
reflections.
A CD-RW (can be edited)
CD Data Formats
• modifications to
the CD have to
be made for you
to burn data on it.
(CD-RW have no
bumps)
A CD-RW (can be edited)
CD Data Formats
A clear dye layer covers the CD’s
mirror.The laser that writes the data to the
disc heats up the dye layer to make it
opaque.
A CD-R (cannot
be edited, just
read)
CD Data Formats
• The dye layer
must become
transparent for
data to be
written. The
data can be
changed or
rewritten when
heated or
cooled.
A CD-R (cannot
be edited, just
read)
Speros
• I am 13 years old
and in the
seventh grade.
• I like playing and
watching football
• I am Greek.
• I like going to
parties, but NOT
dancing.
Bibliography
• Brain, Marshall. How CD’s Work. How Stuff
Works. 25 April 2005.
<http://electronics.howstuffworks.com/cd1.htm>
.
• How Do Cd’s Work. CDMan Disc
Manufacturing. 28 April 2005.
<http://www.cdman.com/technical/howdocdswo
rk1.html>.
• How Do CD-RW’s Work? How Stuff Works. 2
May 2005
<http://electronics.howstuffworks.com/question6
55.htm