Optical disk

The invention:Anonmagnetic storage medium for computers that

can hold much greater quantities of data than similar size magnetic

media, such as hard and floppy disks.

The people behind the invention:

Klaas Compaan, a Dutch physicist

Piet Kramer, head of Philips’ optical research laboratory

Lou F. Ottens, director of product development for Philips’

musical equipment division

George T. de Kruiff, manager of Philips’ audio-product

development department

Joop Sinjou, a Philips project leader

Holograms Can Be Copied Inexpensively

Holography is a lensless photographic method that uses laser

light to produce three-dimensional images. This is done by splitting

a laser beam into two beams. One of the beams

is aimed at the object

whose image is being reproduced so that the laser light will reflect

from the object and strike a photographic plate or film. The second

beam of light is reflected from a mirror near the object and also

strikes the photographic plate or film. The “interference pattern,”

which is simply the pattern created by the differences between the

two reflected beams of light, is recorded on the photographic surface.

The recording that is made in this way is called a “hologram.”

When laser light or white light strikes the hologram, an image is created

that appears to be a three-dimensional object.

Early in 1969, Radio Corporation of America (RCA) engineers

found a way to copy holograms inexpensively by impressing interference

patterns on a nickel sheet that then became a mold from

which copies could be made. Klaas Compaan, a Dutch physicist,

learned of this method and had the idea that images could be recorded

in a similar way and reproduced on a disk the size of a phonograph

record. Once the images were on the disk, they could be

projected onto a screen in any sequence. Compaan saw the possibilities

of such a technology in the fields of training and education.

Computer Data Storage Breakthrough

In 1969, Compaan shared his idea with Piet Kramer, who was the

head of Philips’ optical research laboratory. The idea intrigued

Kramer. Between 1969 and 1971, Compaan spent much of his time

working on the development of a prototype.

By September, 1971, Compaan and Kramer, together with a handful

of others, had assembled a prototype that could read a blackand-

white video signal from a spinning glass disk. Three months

later, they demonstrated it for senior managers at Philips. In July,

1972, a color prototype was demonstrated publicly. After the demonstration,

Philips began to consider putting sound, rather than images,

on the disks. The main attraction of that idea was that the 12-

inch (305-millimeter) disks would hold up to forty-eight hours of

music. Very quickly, however, Lou F. Ottens, director of product development

for Philips’ musical equipment division, put an end to

any talk of a long-playing audio disk.

Ottens had developed the cassette-tape cartridge in the 1960’s.

He had plenty of experience with the recording industry, and he had

no illusions that the industry would embrace that new medium. He

was convinced that the recording companies would consider fortyeight

hours of music unmarketable. He also knew that any new

medium would have to offer a dramatic improvement over existing

vinyl records.

In 1974, only three years after the first microprocessor (the basic

element of computers) was invented, designing a digital consumer

product—rather than an analog product such as those that were already

commonly accepted—was risky. (Digital technology uses

numbers to represent information, whereas analog technology represents

information by mechanical or physical means.) When

George T. de Kruiff became Ottens’s manager of audio-product

development in June, 1974, he was amazed that there were no

digital circuit specialists in the audio department. De Kruiff recruited

new digital engineers, bought computer-aided design

tools, and decided that the project should go digital.

Within a few months, Ottens’s engineers had rigged up a digital

system. They used an audio signal that was representative of an

acoustical wave, sampled it to change it to digital form,

and encoded it as a series of pulses.

On the disk itself, they varied the

length of the “dimples” that were used to represent the sound so

that the rising and falling edges of the series of pulses corresponded

to the dimples’ walls. A helium-neon laser was reflected from

the dimples to photodetectors that were connected to a digital-toanalog

converter.

In 1978, Philips demonstrated a prototype for Polygram (a West

German company) and persuaded Polygram to develop an inexpensive

disk material with the appropriate optical qualities. Most

important was that the material could not warp. Polygram spent

about $150,000 and three months to develop the disk. In addition, it

was determined that the gallium-arsenide (GaAs) laser would be

used in the project. Sharp Corporation agreed to manufacture a

long-life GaAs diode laser to Philips’ specifications.

The optical-system designers wanted to reduce the number

of parts in order to decrease manufacturing costs and improve

reliability. Therefore, the lenses were simplified and considerable

work was devoted to developing an error-correction code.

Philips and Sony engineers also worked together to create a standard

format. In 1983, Philips made almost 100,000 units of optical

disks.

Consequences

In 1983, one of the most successful consumer products of all time

was introduced: the optical-disk system. The overwhelming success

of optical-disk reproduction led to the growth of a multibillion-dollar

industry around optical information and laid the groundwork

for a whole crop of technologies that promise to revolutionize computer

data storage. Common optical-disk products are the compact

disc (CD), the compact disc read-only memory (CD-ROM), the

write-once, read-many (WORM) erasable disk, and CD-I (interactive

CD).

The CD-ROM, the WORM, and the erasable optical disk, all of

which are used in computer applications, can hold more than 550

megabytes, from 200 to 800 megabytes, and 650 megabytes of data,

respectively.

The CD-ROM is a nonerasable disc that is used to store computer

data. After the write-once operation is performed, a WORM becomes

a read-only optical disk. An erasable optical disk can be

erased and rewritten easily. CD-ROMs, coupled with expert-system

technology, are expected to make data retrieval easier. The CD-ROM,

the WORM, and the erasable optical disk may replace magnetic

hard and floppy disks as computer data storage devices.