Matsushita (better known as Panasonic) announced yesterday that it has developed a rewritable optical disc with a capacity of 50GB.

A blue laser stores the data on a dual layer optical disc 120mm in diameter, said Matsushita spokesman Yoshinari Takemura.

Until now this dual layer approach, which allows one side of a disc to hold two recording layers, was only possible using red lasers. Currently, 850 nanometre red lasers are used for optical discs.

But a laser beam with a shorter wavelength can register smaller dots on a disc, meaning more data can be stored. A blue laser has a 425 nanometre wavelength and can record five times more data on to an optical disc than a red laser, which can store up to 4.7GB on one layer. Blue lasers can make discs with two layers, each of which can store around 25GB of data on a 120mm disc, according to the company.

Matsushita developed a material called GeSbTe (germanium antimony tellurium) film for the recording layer of the disc which can record information at the high densities possible with blue lasers, Takemura said.

The disc records and retrieves data at up to 33Mbps (megabits per second), making it three times faster than 'conventional' DVD (digital versatile disc) technology, the company said.

According to Matsushita, the dual layer blue laser-written disc’s speed and capacity make it possible for a 50GB disc to record more than four hours of high-definition digital TV pictures, which transfer data at 25Mbps.

The company hopes the new optical disc will be used as a recording medium for high-definition digital TV programs and hopes to have the product on the market by the time Japan starts broadcasting such programs in about 2003, Takemura said.

The new optical disc will be unveiled on Friday at the International Symposium on Optical Memory in Taipei, Taiwan.