Scientists working at London's Imperial College have come up with a way of radically increasing the storage capacity of optical discs.

The technique is called 'Multiplexed Optical Data Storage' and essentially allows each pit in the disc's reflective data layer to store multiple values instead of just one.

The pits and peaks in today's DVDs and CDs encode a single 1 or 0. Light from a laser is reflected back on to a detector as the disc spins, generating a stream of 1s and 0s.

The base of each pit is essentially flat, but MODS pit-bases contain many faces, at an angle to each other, effectively harnessing the not-quite-flat nature of the pit's base. Angling the laser differently can reflect up to ten different data streams off each of these pit-bottom faces.

The upshot is a disc that can theoretically hold a hundred times the data than a current DVD can, though in practice the results yield a lower increase - from 4.7GB to around 250GB. Boost the number of layers within each disc, and the capacity grows even further.

Imperial College's Dr Peter Torok detailed the technique at the Asia-Pacific Data Storage Conference 2004, held in Taiwan last week. While the idea was conceived some years ago, only now has Torok and his team been able to calculate precisely the properties of the reflected light, in order to determine how much of it can be used to carry the digital signal.

That said, the team estimate that it could take five more years to perfect the technique in the lab, with further work then needed to commercialise MODS. ®

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