Sep 19, 2013

Five-dimensional glass memory can store 360TB per disc

Scientists at the University of Southampton in the UK have succeeded in creating five-dimensional (5D), ultra-high-density storage on standard silica glass discs that, unlike DVDs or Blu-rays, seem to be capable of storing data for an unlimited period of time without a reduction in data integrity. The scientists say that 5D optical storage could allow for densities as high as 360 terabytes per disc, and unless you crush it in a vice, these discs are so non-volatile that data stored on them should “survive the human race.”
At first glance, five-dimensional storage might sound a bit like pseudoscience — but, in this case, the data really is stored on five different dimensions (surfaces, planes). There are the usual two dimensions (width, height) provided by a piece of silica glass, and depth is provided by writing at three different depths (layers) within the glass. The fourth and fifth dimensions are provided by nanostructuring the surface of the glass, so that it refracts and polarizes light in interesting ways.

To record data, spots are imprinted on the glass (pictured below) using a femtosecond laser. A femtosecond laser, in this case, produces bursts of laser light that last for just 280 femtoseconds (280 quadrillionths of a second). These spots, thanks to the nanostructuring of the surface, and some hologram cleverness, are capable of recording up to three bits of data in two “dimensions.” By varying the focus of the laser, the team are able to create layers of dots that are separated by five micrometers (0.005mm) in the z-axis (the third dimension). Then, by simply moving the laser horizontally and vertically, these tri-bits can be stored in two more dimensions, bringing the total to 5D. The image at the top of the story helps illustrate this concept.

To read these spots, an optical microscope that’s capable of untangling the polarized light reflected by the three-bit spots is used. There’s no word on whether these silica glass discs can be rewritten, but the research paper [PDF] makes it sound like this is a write-once-read-many (WORM) storage method.

As you can imagine, storing a tri-bit in a single dot, and then storing these dots in a three-dimensional medium, allows for utterly insane storage densities. The researchers say that 360 terabytes could be stored on a single 5D disc — by comparison, quad-layer Blu-ray discs that store just a single bit per pit have a total capacity of 128 gigabytes, or almost 3,000 times less. The best hard drive technology, heat-assisted magnetic recording (HAMR), which will soon make its way into commercial drives, will max out at around 20 terabytes per disc.

Furthermore, the scientists report that their glass discs are thermally stable at temperatures up to 1000 degrees Celsius, and the imprinted spots don’t seem to degrade over time. This led Peter Kazansky, the group’s supervisor, to pipe up with this particularly memorable/questionable soundbite: “It is thrilling to think that we have created the first document which will likely survive the human race. This technology can secure the last evidence of civilisation: all we’ve learnt will not be forgotten.”

Moving forward, the University of Southampton is now looking for industry partners to commercialize this technology. Obvious applications include archival storage, where the management of huge repositories of tapes and hard drives is expensive, complex, and time-consuming business. Eventually, assuming the complex laser/microscope setup can be miniaturized, these discs might offer an upgrade path from DVDs and Blu-rays.


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