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Optical discs are one of the most popular methods of storing
data electronically on mediums such as Compact Disc (CD), Digital Versatile Disc
(DVD), and Blu-ray Disc (BD) among other formats. These discs are written to
and read by a laser inside the disc player. When the laser is writing or
burning the disc, it creates little pits and bumps on the surface. These pits
and bumps are later read by a laser in the disc player, which is translated
into the stored data.
Rise of the Optical
Disc
The first digital optical disc was created by James T. Russell in 1965. Like
many others in that day, Russell wasn't happy with the sound quality of vinyl
records. He had an idea for a new type of audio system where there was no
physical contact between the disc and the player. The best way Russell found to
achieve this was through the use of light. By using a laser to burn light and
dark marks on the disc for "on" and "off" positions, he was able to store the
data as binary code which uses only 1s and 0s. James Russell is credited for
inventing the compact disc. Although the CD is known as the first successful
optical disc, it wasn't the first.
The first commercial optical disc format was actually the
Laserdisc, which got its name from the laser used in the player. The main
difference between Laserdisc and current optical disc technologies is that
Laserdisc is the only optical disc format that stores an analog signal. Although
Laserdisc was a higher quality than VHS, two factors prevented Laserdisc from
becoming as popular.
First Generation
Optical Discs
The first and biggest limiting factor of LaserDisc is that the analog signal made
it virtually impossible for consumers to create their own discs, due to the way
the analog discs had to be written. The other limiting feature of Laserdisc was
the higher price compared to VHS tapes. In the end, consumers chose price and
ease of use over higher quality.
First generation optical discs such as CD, DVD and the short
lived Mini-disc are read using an infrared laser. CD and MiniDisc both use a
780nm laser diode, while DVD uses a laser with a shorter wavelength of 650nm.
Once optical disc technology hit the marketplace and people were able to burn
their own CDs and then DVDs, it quickly overtook magnetic storage as the leader
in portable data mediums. Magnetic storage devices such as the floppy discs and
later the zip disc were popular and relatively cheap, but the storage capacity
couldn't keep up with optical discs.
Optical Discs Today
The 2nd generation of optical discs includes Blu-ray Disc and the
now defunct HD DVD. These discs use a blue laser instead of a red laser to read
and write data. By using a blue laser with a shorter wavelength, the data can
be written closer together packing more information into the same area. That is
why a Blu-ray disc can hold 25GB in the same space a DVD can hold 4.7GB.
Although shortening the wavelength has been a great method
to increase optical disc capacity, there have been other improvements as well.
Newer lasers are capable of storing data on a separate physical layer that is "stacked"
on top of the other. Dual-layer DVDs can hold 9GB of data instead of 4.7 held
on regular DVDs. Blu-ray discs also come in single and dual layer varieties of
25GB and 50GB. No one is stopping at 2 layers though; Pioneer has recently demoed a 16 layer Blu-ray disc
capable of holding 400GB. The
problem with multilayer discs is they are prone to errors, and have a lower
yield rate in mass production. This means more "bad discs" come out of the
batch.
As can be expected, engineers are continuing their work to
improve optical disc technology with many formats and methods vying for the
next crown. Some future developments currently being worked on include
multi-layered discs, holographic discs, and photonic jets among other technologies.
Resources:
How CD Burners Work
James T. Rusell - The Digital Compact Disc
Pioneer 16-Layer Blu-ray Disc Features 400GB
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Re: Evolution of the Optical Disc
