Rare-earth sandwiches offer nonstop digital movies

日期:2017-06-23 05:56:32 作者:言沔蔡 阅读:

By Barry Fox THE DIGITAL Versatile Disc format is meant to replace videotape for home recording. But there’s a problem: there is not enough space on one side of a standard DVD to record an entire movie, so you have to flip it over halfway through. This lack of space is one of the reasons why no one has yet made consumer DVD player-recorders. Now Matsushita of Japan says it has beaten the problem with a novel “sandwich” technology that puts two layers of an erasable recording material on one side of a 12-centimetre DVD. This creates 8.5 gigabytes of storage space, enough to record 6 hours of continuous video. Each recording layer is made up of an alloy of germanium, antimony and tellurium. When heated with a recording laser, the material switches between crystalline and amorphous phases, which are optically different and can be read by a playback laser. The top layer works like a two-way mirror. Only 7 nanometres thick, it passes half the light to the lower layer, which is separated from it by 40 micrometres of transparent resin. The laser can quickly switch its focus from one layer to the other to create a seamless recording. As with video or audio tape, old recordings are erased as new ones are made. Matsushita expects viewers to welcome a recorder that allows instant replay without rewinding,