The highest capacity we've heard of for current optical storage media is the Blu-Ray disc, whose double-layer format comes in at a monstrous 50GB capacity. That just might change in the next few years, as an ongoing research project has found a way to cram three times that capacity (150GB) into a DVD-sized disk, with plans to pump it up to a further 500GB by 2008.

The program, dubbed the Microholas Project, is under the supervision of the Institute of Optics and Optical Technologies at the Technical University of Berlin. The project team, under the direction of Dr. Susanna Orlic, managed to pull off this engineering feat by a process called microholographic recording, which they described as such on their home site:

On a microholographic disk the pit-land structure of a CD or DVD is replaced by microscopic volume gratings. These "microgratings" are holographically induced in the focal region of two counter propagating, highly focused laser beams: one beam is focused into the photosensitive layer and reflected back. The interference pattern of the incident and reflected beam results in a grating-like modulation of the refractive index of the storage medium.

In layman's terms, microholography recording creates three-dimensional holographic grids within the disk's nanostructure for storing and reading data. In comparison, traditional CD/DVD recording techniques use a two-dimensional pit-land structure that only uses the disc's surface for recording data.

Don't start turning in your HD-DVD/Blu-Ray players, though, as the Microholas Project's 150GB disk mentioned earlier is just a demonstrator of things to come. The team expects to have an even bigger 1 Terabyte disk out by 2010, with an expected read speed of 250 Mbits.