Tech Page: Holostorage

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Overlapping blue lasers record holographic patterns in GE's new polycarbonate material, which has been fabricated into a disc the size of a CD, DVD or Blu-ray. This technology will allow capacities of 500 GB to 1 TB on such a disc.

Photo: Courtesy GE Research

Electronic musicians and other media mavens have an insatiable appetite for data storage. Digital audio consumes more and more as sampling rates and bit depths increase, and high-definition video is a real data hog.

Hard disks and solid-state memory are getting cheaper all the time, but what about optical discs? The best we have at the moment is Blu-ray, with 25 GB per layer and a maximum of two layers. Even when more layers become feasible, the capacity of a Blu-ray disc will probably top out at 100 or 200 GB.

If recent experiments at General Electric Research ( are any indication, the next generation of optical discs will far exceed this limit. GE scientists have developed a new material that can store data holographically, leading to a capacity of 500 GB on a disc the size of a DVD or Blu-ray. This is equivalent to the capacity of 20 single-layer Blu-ray discs or more than 100 single-layer DVDs. Even better, the GE disc can be recorded and read by optical systems that are very similar to current read/write technologies.

“GE's breakthrough is a huge step toward bringing our next-generation holographic storage technology to the everyday consumer,” says Brian Lawrence, who leads GE's holographic storage program. “Because GE's micro-holographic discs could essentially be read and played using similar optics to those found in standard Blu-ray players, our technology will pave the way for cost-effective, robust and reliable holographic drives that could be in every home. The day when you can store your entire high-definition movie collection on one disc and support high-resolution formats like 3-D television is closer than you think.”

According to GE's Website, “The average company's data-storage needs triple every 18 to 24 months, and the worldwide data-storage capacity has grown from 283,000 terabytes in 2000 to nearly 5 million terabytes in 2005. Couple that with the average person's data-storage growth of 250 megabytes per year and the fact that 75 percent of all IT spending is for data storage, and you have one enormous data-storage challenge.”

CDs, DVDs and Blu-rays store data as essentially two-dimensional “pits and lands” on the surface of the disc. Digital 1s and 0s are distinguished by a difference in reflectivity between the pits and lands. Higher storage capacities have been achieved by making the wavelength of the laser shorter, allowing smaller pits and lands and thus more data in a given area.

By contrast, holographic storage uses the entire volume of a specialized polycarbonate material that undergoes a change in refractive index when bombarded with two high-power lasers to write data as a holographic interference pattern. A low-power laser is used to detect the changes in refractive index and read the data represented in the pattern.

Even though data is stored within the entire volume of material instead of on the surface, the system still depends on differences in reflectivity. At the start of 2009, the GE material could be written with 405-nanometer (nm) blue lasers, and data areas exhibited a reflectivity of 0.005 to 0.01 percent, which is too low to enable the high capacities sought by the team. Six months later, the material has been enhanced to provide a reflectivity as high as 1 percent, which will allow capacities of 500 GB to 1 TB on a 5-inch optical disc.

GE intends to concentrate first on commercial archival applications, and such products could become available by 2012. After that, we could see consumer products such as disc players and computer drives, which would be a huge boon for media users of all types.