Pioneer makes a 400-gigabyte Blu-ray Disc
Pioneer, the Japanese drive manufacturer, has developed the first laboratory prototype of a Blu-ray Disc that can store 400 gigabytes on one side. Each of its 16 storage layers holds 25 gigabytes. The previous record holder, TDK, only managed to squeeze 200 gigabytes on to 6 to 8 storage layers.
Pioneer says the greatest difficulty it had to overcome was extracting a useful optical signal from the sandwiched layers. Its new lens technology however does a very good job of compensating for spherical aberration in the optical path and minimizing crosstalk and transmission losses, so the optical sensor is able to get a good signal even from the lowest layer.
The success of the prototype will probably be exploited mainly for publicity purposes. It is doubtful, given the current state of the art, that such a 16-layer Blu-ray Disc would ever go into production. Present-day Blu-ray Discs can store 50 gigabytes on two layers. The return from the production effort falls dramatically with each additional storage layer, so economically justifiable mass production still seems far off.
For a practical drive, higher transfer rates would be desirable. If a 400-gigabyte disc were written to at the normal Blu-ray transfer rate – 4.5 megabytes per second – it would take 25 hours for the burner to fill it. Because of speed restrictions, it's expected that the Blu-ray Disc will in the future be limited to being read or written at a maximum of 12X. This makes it more likely that the technology developed by Pioneer will be used in coming generations of new optical storage media, rather than in a Blu-ray device.