The principles of optical storage

In order to show how polymer science makes an important contribution to optical data storage, it is necessary to explore some of its basic principles. 

For many years, no practical implementation of these basic principles was possible. The argon-ion or He-Ne lasers then available were too bulky, expensive and difficult to modulate. But recent developments in solid state laser diodes have provided compact (smaller than a pinhead), powerful ( 20mW), easily modulated ( lGHz), low-noise and cheap laser sources for optical disc drives. 

These lasers emit light at around 800 nm, and typically a well-focused spot will be approximately 1 pim in diameter. With such a spot size, it is possible to pack over 600 Mbytes of data onto one side of a 13 cm disc. A similar sized floppy disc can store up to 1 Mbyte per side, and a hard disc can store approximately 10 Mbytes per side. Thus optical discs have a large advantage in storage capacity. These capacities can be put into a more familiar context. If a floppy disc can hold the contents of a few pages of a book, an optical disc can hold the contents of an encyclopedia. Optical tape can store even greater quantities of data. A 12 cm reel can hold a terabyte of information, which is a million megabytes or a few thousand encyclopedias. 

The primary challenge to polymer scientists is to provide the perfect recording medium that can be written to reliably, read and if required, erased. But there are other important challenges that require further explanation. 

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