Philips has demonstrated the world's highest ever recording speed of recordable DVD (DVD+R) in an experimental set-up built at Philips Research. The system is able to record 16 times faster (16x) than the normal playing speed of video DVDs, allowing to burn a DVD+R with video or data up to the maximum capacity in less than 6 minutes. This recording speed is close to the highest possible speed, which means that this represents the ultimate performance of any DVD recording system. The results were presented at the International Symposium on Optical Memory (ISOM, Nara, Japan, 3-7 November) and received the best-poster award there. The Philips technology will form the basis for the 16x DVD+R recording standard to be defined by the DVD+RW Alliance in the course of 2004.
A key aspect in realizing higher recording speeds is the development of a suitable 'writing strategy' - the timing and power of the laser pulses in such a way that marks (representing digital zeros and ones) of the correct length are created in the organic dye that forms the active layer of recordable DVDs. Doing this well becomes increasingly difficult at higher recording speeds, because the available time to heat up and cool down the dye at the position of a mark becomes ever shorter. Especially avoiding that post-heating partly erases a written mark when a neighbouring mark is written is a challenging task. Philips has developed an efficient write strategy that not only results in accurate recording results, but in addition needs only a limited number of parameters to realize it, allowing disc-drive manufacturers to implement the algorithm in a straightforward manner.
Besides the write strategy, improvements on the recorder set-up were needed to realize recording at 16x speed. Especially the design of an accurate and stable system for tracking and focusing the laser beam to the right position on the disc was challenging. Another demanding task was the development of fast laser driving electronics, which runs at a 420 MHz clock at 16x DVD speed. Last but not least, a prototype high-power laser was utilized to achieve the recording power needed.
The results mark a next step in the speed race for recordable DVD. It is generally agreed that the now achieved recording speed is close to the ultimate limit, which is set by the highest safe rotational velocity of the polycarbonate discs. A higher disc velocity would require so much additional energy to be pumped into the disc that it would start resonating and eventually break. At the currently reached 16x recording speed, a disc makes 180 rotations per second, corresponding to a linear velocity of 56 meters per second (over 200 km/h), while marks are burned with a precision of less than 0.05 micrometer!