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3-D Pits Boost Optical Storage

Photonics Spectra
Jul 1997
Michael D. Wheeler

EMERYVILLE, Calif. -- Two researchers have developed an encoding technique that could revolutionize the world of CD-ROMs and digital video discs, essentially tripling their storage capacity. To consumers, especially those eyeing the trend toward high-definition television, discs storing an entire movie on one side could be on the market in less than two years.
The new method -- dubbed pit depth modulation -- has a number of distinct advantages. Probably most important is that it has proved compatible with current CD-ROMs and will soon be compatible with digital video disc systems. Pit depth modulation technology also uses current CD mastering and replicating equipment, requiring only minor modifications. The additional integrated circuits required to run these discs cost between $20 and $40 for the end user, according to company estimates.
The discovery came as a result of work by Terrence Wong and Michael O'Neill on laser feedback interferometry at the University of California at Berkeley. After receiving several patents, the pair left Berkeley to form Calimetrics Inc. and to continue their research. They found that tinkering with the development of the photoresistant material used in making CDs caused different pit depths to emerge. Instead of two depths on a standard CD, there were now between eight and 16 depths. This enabled them to store more than three times the amount of sound and picture data on a disc and moved CD-ROM technology from the two-dimensional to the three-dimensional realm. At the same time, the rate that the data could be read also increased. For instance, a standard CD-ROM disc holds 0.68 GB and transfers data at a speed of 1.2 Mb/s. However, on a disc encoded using pit depth modulation, the storage capacity is 2.2 GB and the data transfer rate is 3.9 Mb/s. Similar capacity increases hold true for digital video discs -- up from 4.7 GB to 15 GB.

Commercial interest
The potential commercial applications of a revamped disc were obvious to Wong and O'Neill. With private investments and funding from the US Advanced Technology Program and the California Trade and Commerce Agency, the company began looking to the large-scale manufacture of these discs.
To that end, Calimetrics is targeting a number of initial markets and customers. In the high-performance CD- and DVD-ROM-drive market, the company is looking at customers such as Sony, Toshiba and Hitachi. Wong said Calimetrics hopes to introduce the first digital video discs that contain an entire high-definition TV feature-length movie on a single side in 1998.

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