CDs set for leap into the blue: A new laser diode will offer compact discs added playing time, writes Dan Houston
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Your support makes all the difference.A SOLID-STATE laser which emits blue light has just been demonstrated in Japan by Sony. It holds the promise of revolutionising the technology of compact discs.
The blue light is produced by a semiconducting component known as a laser diode. Diode lasers are incorporated in all compact disc machines, with the low-powered beam of laser light reading the digital information encoded on the disc.
Previously, the lasers have all emitted reddish light, which has a longer wavelength than Sony's new diode produces.
The ability to use blue laser light could increase threefold the data that can be stored on all optical disc media. It is seen as a major advance in both the computer and home entertainment industries. On a compact disc it increases potential playing time to three and a half hours, compared with the present 74 minutes.
It also means that conventional CDs of 'super sound quality' could be produced, containing much more musical information than is currently possible.
Other media which will benefit from blue-laser technology include computers which use CD-ROM (read only memory) drives, CD-Interactive and CD-Video conventional 12cm discs. It could also benefit surgeons who need a smaller and more efficient local light source for internal surgery.
The worldwide drive to develop a blue laser diode began five years ago, according to Professor David Phillips, of Imperial College, London. 'Blue light has a much shorter wavelength in the spectrum than the red light currently used by lasers in CD players,' he says.
'The shorter wavelength means that a blue laser can be focused far more efficiently, so it is easier to discriminate between the microscopic pits on a CD.' Sony's blue laser has a wavelength of just 447 nanometres (a nanometre measures a billionth of one metre).
In developing its blue laser diode, Sony has come up with a 'new' semiconductive material - selenic blende, which is sandwiched with zinc selenide. For the first demonstration the diode was cooled with liquid nitrogen to minus 196C.
Work is now under way refining the system to work at room temperatures - something experts believe will be a fairly straightforward task. But Sony sees the system's commercial application as being at least five years away.
While blue lasers may spawn a new generation of compact discs, whether for audio, video or computing, Sony is keen to keep the development compatible with existing technology. 'If you took a disc which was recorded using a blue laser, it wouldn't be possible for a red laser to read it, the information pits would be just too small,' says Eric Kingdon, a spokesman for Sony UK.
'But then there's no reason why you can't design a blue laser system that could read both types of disc. The exciting thing is that there are so many possibilities that are now open to us.'
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