A Second Wind for Red-Laser DVD Technology?

Idea could disrupt plans for transition to blue-laser optical disks

Din-ping Tsai, a physicist at the National Taiwan University (NTU) in Taipei, claims to have proved in principle that his novel adaptation of red-laser technology will make possible superdense DVDs with 100 GB of information—more than 20 times the density of the 4.7-GB red-laser disks currently on the market and four times the density of the first-generation blue-laser disks generally expected to supplant red-laser technology in a few years.

Lin Wei-chih, a doctoral student of Din-ping Tsai, tunes the red-laser system that he has designed for superdense DVDs, exploiting near-field optical effects.

Tsai says the concept depends on exploiting near-field optical effects occurring at distances shorter than a wavelength. Near-field effects allow light to behave as if it had a much shorter wavelength, but they are extremely sensitive to minute changes in distance from the light source. Previously, attempts to use the effect focused on ways to keep the disk drive's laser very close to the disk with very high precision.

Tsai's team coats a regular DVD or CD with two extra layers: a transparent spacing medium above the recording layer and, on top of that, a "near-field active" layer in which near-field effects come into play when reading from or writing to the disk. The spacing layer finesses the problem of how to keep the light source in constant relation to the targets. The upshot is that pits as small as 100 nm in diameter can be written and read, as compared to 400 nm on today's DVDs and 900 nm on CDs.

Members of Tsai's team delivered academic papers describing the system at conferences last summer, and at the beginning of August NTU received a five-year NT $166 million grant from Taiwan's Ministry of Economic Affairs and NT $22.5 million from the National Science Council—US $5.5 million in all—to pursue work on recording technologies using nano-optics and nanomagnetics. Taiwan's Ritek Corp., the world's largest maker of optical disks, has supported the team's work and currently is moving it from laboratory to factory to evaluate its potential for mass production.

—Yu-Tzu Chiu

PHOTO: NATIONAL TAIWAN UNIVERSITY