Technology: New compact disc video will cram the pits


By ANDY COGHLAN NIMBUS, a British company, is to produce a long-playing compact video disc. Nimbus hopes that its disc, which will be the same size as an ordinary CD, will eventually supersede video tape. The company plans to unveil a prototype of the hour-long disc early next year. At present, the 12-centimetre discs on the market have not sold well because they play for only five minutes. The larger, 30-centimetre discs that play for an hour each side have proved difficult to manufacture, and people have not bought them because they are so bulky. Gerald Reynolds, the joint managing director and technical director of Nimbus, says that the company expects to have perfected a prototype for an hour-long, 12-centimetre CDV disc within the next few months. Like Philips and Sony, its rivals in Europe and Japan, Nimbus wants to develop a disc of the same size as the increasingly popular audio CDs. The company has already developed a prototype 12-centimetre disc that plays for 30 minutes, but its engineers still have to overcome technical constraints before they can cram an hour’s worth of information into the space. Reynolds says that the half-hour prototype carries twice as much encoded information as an ordinary, five-minute CDV disc. A disc that plays for an hour will have to carry twice as much again, he says. Nimbus will also need to develop a separate device for playing the video. In order to read such concentrated information, it must rely on lasers which produce light at ‘blue’ wavelength, which is sufficiently short to read the data. Reynolds says that the existing gas lasers, which work by exciting helium and cadmium, are too bulky and expensive for mass production. He believes that solid-state lasers, which rely on crystals rather than gases to emit their light, would be much easier to reproduce. Nimbus is collaborating with a number of Japanese companies on a laser for its video player and has produced a solid-state prototype of a laser that produces ‘blue’ light. Meanwhile, the company is working on the problem of cramming information onto the master disc – the template from which duplicates are mass-produced. One way to do this is to put more information in each pit on the disc. (The pits are the cavities that store and transmit video and audio signals.) Another approach is to use more of the space on the disc. In audio discs, pits follow a spiral track with each ‘groove’ 1.6 millimetres from the next. If an hour’s worth of video and audio information is to fit onto the same size of disc, says Reynolds, engineers will have to halve the space between grooves. Despite making progress on the prototype, Reynolds warns that it will be years rather than months before consumers can buy players and discs. Last week, the company revealed the results of a marketing survey which showed that, in the past year, sales of audio CDs around the world have risen by 54 per cent over the previous year. Conventional vinyl discs are becoming less popular, although sales of audio cassettes rose by 10 per cent. In Britain, 16 per cent of householders now have CD players,
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