Two lasers are used to record data in the form of a 3D hologram

How quickly things change. Just as Blu-ray is starting to replace the DVDs in our homes, another technology is developed that could sound its death knell.

A dual-layer Blu-ray disc can store an impressive 50 gigabytes, but discs which can hold 20 times as much data have just taken a step closer, thanks to new materials that make reading and writing 3D holograms more reliable.

CDs and DVDs store data as pits on their surface that are read by a laser. A Blu-ray disc can hold over five times more data than a standard DVD because the pits are much smaller. Writing the data onto two layers within the disc instantly doubles the volume of data that can be stored. But writing data to the whole thickness of the disc in the form of a hologram could dramatically increase storage capacity.

A pair of laser beams is used to write data into discs of light-sensitive plastic, with both aiming at the same spot. One beam shines continuously, while the other pulses on and off to encode patches that represent digital 0s and 1s.


At the points where the lasers meet, the intense light causes molecules in the disc’s material to merge into chains, creating a physical pattern that locks the 0s and 1s into the disc. This pattern can be read back at a later date using another laser because the changed patches interact differently with light.

However, in the plastic normally used for holographic data storage, the structural changes caused by the laser also cause the material to shrink. Even though the volume change is tiny – around 0.23% – the distortion is enough to make reading the data from the disc tricky and means that the 1s and 0s can’t be burned at the highest densities.

Denser data

Craig Hawker‘s team at the University of California in Santa Barbara has now solved that problem by replacing the polymer’s small molecules with larger, branched ones. These need to make fewer bonds to create a patch of the alternate form of the material, cutting distortion to just 0.04%.

“For real-world applications, the shrinkage values should be below 0.1%,” Hawker says. Pioneering companies developing holographic data-storage devices could benefit from the new technique by squeezing at least 1000 gigabytes of data onto a standard disc.

One such company is Colorado-based InPhase Technologies, that sells bespoke products to the 20 or so companies around the world that are developing holograph-based data drives.

The company’s vice president of sales, Art Rancis, thinks Hawker’s work is promising. “We look forward to future results as [Hawker’s team] evaluates the performance of the material in an actual high-density digital recording system,” he told New Scientist.

Journal reference: Chemical Communications (DOI: 10.1039/b816298k)