Study Of Optical Drive Under Two Photon Optical Data Storage

1843 words - 8 pages

[Need to modify: copied from thesis Robust and Fault Tolerant Control of CD-players]
In 1972 Philips announced a technique to store data on an optical disc. First in 1981 Philips and Sony proposed the Compact Disc Digital Audio standard (CD-DA) which was coded in the so-called Red Book [Philips and Sony Corporation, 1991]. The development of this technique revolutionized the audio world by introducing truly digital technology for the first time. It was in the year 1982 that Philips and Sony launched the first players and discs on the market. The CD became the music carrier of choice by 1991, when sales exceeded those of audio-cassettes.
Another widely available optical disc technology is ...view middle of the document...

The surface of the disc is coated with an ultra thin layer of reflective material such as aluminium, silver, gold or copper. They cannot be re-recorded.
WORM Discs
WORM discs, consisting of a recordable CD (CD-R) and a recordable DVD (DVD-R), are very similar to the first group except that they have a layer of photosensitive dye covered by a reflective metallic layer. Recording is performed by burning the photosensitive compounds in the dye by a laser. Once a recording has been made, it cannot be changed or erased.
Rewritable Optical Discs
The rewritable optical discs resembleWORM discs except that the dye layer is replaced by a special phase-change compound. The states of this compound can be altered according to the amount of applied energy by the laser. The rewritable CD and DVD (CD-RW, DVD-RW and DVD+RW) can be re-recorded around a thousand times while DVD-RAM discs can be re-recorded up to 100,000 times. MiniDiscs (MD) belong also to this group of rewritable optical discs. The principles behind a MD are based on magnetic-optic principles and are not described here. The interested reader is referred to [Watkinson, 2001].
There is a wide variety of optical discs on the market and winners in the rewritable DVD race have not yet been determined. It is even more unclear to predict the winner among the high capacity optical discs as their standards have not been completely established yet. However, optical discs, whether it be a CD, a DVD or a higher capacity optical disc, they rely in similar optical principles [Milster, 2003] which are described in the subsequent sections.
2.4.2 Optical Disc Construction
[Need to modify: copied from thesis Robust and Fault Tolerant Control of CD-players]
Common for the CD and DVD is that they are discs of 120 mm in diameter. Data is stored in the form of microscopic pits; see Figure 2.2, forming a clockwise spiral track which starts at the center of the disc. The length of the pits and the distance between them form the recorded information. The layer which holds the data, called information layer, is divided in three parts. Starting from the center of the disc, the first area is the lead-in area, which contains a table of contents (TOC). The TOC contains information on the contents of the disc, such as number of selections, the starting point of each selection and duration. The information interesting to the user is contained in the program area. The end of the program area is defined by the lead-out area.
The optical discs are basically constituted by inexpensive polycarbonate plastic in which an information layer and a reflective coat are placed. Viewed from the readout side, the laser is focused through a layer of polycarbonate plastic. This layer is also called optical transmittance protection layer as it protects the information layer from being damaged by sharp objects or by parts of the optical disc drive such as the optical pickup. The information layer has poor reflection properties; therefore it is...

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