The Tech Report writes Fujifilm is working on a new optical disc technology that can store up to 1TB on a single disc. Anticipted to be commercially available b 2015, the discs will store 25GB on each of the two sides of a layer on as many as 20 layers. The technology is theoretically scalable to up to 15TB per disc, and is anticipated to be cost-competitive with magnetic tape.
The new recording method combines a "two-photon absorption material" with "heat-mode recording." TechOn has a good summary of the official Fujifilm whitepaper (PDF) if you want more details on how it works. The recording process involves making "irreversible" changes to the media, suggesting that rewriting may not be possible. Reading the data is apparently a little complicated, as well; the reflectance of playback signals is only 0.5%, substantially lower than Blu-ray's 20%.
Fortunately, the media doesn't appear to be difficult to produce. Fujifilm says an eight-layer sample can be manufactured in less than half the time it takes to make four-layer Blu-ray disc. The material purportedly has the potential to store multiple bits, as well, raising the theoretical capacity ceiling to 15TB per disc.