Blocking Lasers Produces DVDs with Petabyte Storage Capacity

A team of Australian researchers may have brought the cost-effective but logistically troublesome DVD into the 21st century with a technique that boosts the capacity of a single DVD from 4.7GB to a full petabyte.

The technique could not only make DVDs a more practical storage media for datacenter-size storage jobs, but also paves the way for the three-dimensional laser imprinting of data, limited only by the mechanical strength of the disks themselves, according to a paper published Wednesday in the journal Nature Communications.

Rewritable optical discs were once the medium of choice for long-term, low-cost data storage, but fell out of vogue as the cost of hard disks and other magnetic media dropped.

Magnetic media are faster than storing data on CDs and DVDs, and far more convenient. DVD storage capacity maxes out at 4.7GB, which means any storage or archiving job involving a petabyte of data would require approximately 223,000 DVDs.

That many disks obviously makes DVDs impractical as a solution for large-scale storage; reducing the number required to store a petabyte from 223,000 DVDs to one could change that equation dramatically. The key to increasing the capacity of DVDs (or any other optical storage medium) is to reduce the size of the dots burned by lasers on the surface of the disk to represent either a binary 1 or 0, according to authors Zongsong Gan, Yaoyu Cao, Richard A. Evans and Min Gu, of the Centre for Micro-Photonics and CUDOS, Faculty of Engineering and Industrial Sciences at Swinburne University of Technology in Hawthorn, Victoria, Australia.

Dots correspond to the size of the wavelength of the light in the laser that burns them. A beam of light cannot create a dot any smaller than one-half the distance of its own wavelength—a hard physical limit described by Abbe’s law of limited resolution.

Abbe’s law prevents DVD-drive manufacturers from continually shrinking the size of the physical imprint of data on the surface of their product, as semiconductor manufacturers do. But while it’s impossible to violate the physical law describing limitations on the behavior of light, it is possible to get around it: Rather than trying to shrink the width of a single beam of light, the Swinburne University team used two beams of different shapes, each of a shade that would cancel out the other.

The first beam produces an ordinary circle of light. The other is doughnut shaped—a toroid that is empty in the middle, like an inflated inner tube. When the two beams overlap, the doughnut-shaped beam cancels out the portion of the round beam, preventing it from writing any data to a disk—but only in the doughnut-shaped area covered by the second beam. The result is a circle of light a fraction the size of the beam that produced it—a focal spot nine nanometers in diameter rather than the 800nm diameter of the original beam.

The nano-beam can also be used to create three-dimensional dot images, multiplying the number of dots and the capacity of the disk itself even more. That would allow nano-beams (or, more properly, “three-dimensional deep sub-diffraction optical beam lithography”) to be used to shape or carve shapes in other material to produce freestanding nanowires that can be used to build three-dimensional nano-scale structures, according to the authors.

The most immediate use for the technique may be to revive the large-scale storage potential for DVDs, but the longer-term impact may be advances in techniques to build nano-size devices for semiconductors or other uses.


Image: Zongsong Gan, Yaoyu Cao, Richard A. Evans, Min Gu, Centre for Micro-Photonics and CUDOS, Swineborne University of Technology

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