Three inventors have filed a patent application for an optical disc capable of holding not only Blu-ray Disc data but also HD DVD-formatted information. In fact, the system would allow disc makers to mix and match any two optical disc formats.

The application, spotted by New Scientist magazine, was originally filed in December 2005 but revised last month. It describes a multi-layer disc containing two data-bearing layers, each of different optical disc formats.

Take the Blu-ray Disc example. The disc would contain a plastic substrate on which would be placed the BD data layer, 0.1mm from the surface. A special material would then be sandwiched between the BD data and the HD DVD - or DVD, for that matter - data layer 0.6mm from the surface. The boundary layer would be sufficiently reflective to allow the disc to be read by a BD player, but transparent enough to allow not only the HD DVD read laser to shine through and focus on the 0.6mm-deep data layer but to allow light to pass back to the optical pick-up head.

If such a material can be found - and it's cheap enough - it clearly stands to benefit both the HD DVD and BD camps, but particularly the latter. Even if the two don't come together on a single disc, the would-be patent would permit content makers to ship a BD with backwardly-compatible DVD content on board.

The application even moots a triple-format disc: a dual BD/HD DVD disc of the kind outlined above with a DVD bonded on the flip-side.

Interestingly, two of the inventors - Alan Bell and Lewis Ostrover - are said by New Scientist to be Warner Bros employees, putting the studio in a strong position to combine its BD and HD DVD offerings. Of course, it first has to construct such a disc, ensure it works as predicted and establish that shipping product would be cheaper to make than two separate HD DVD and BD units.

More to the point, perhaps, the patent doesn't appear to consider the need for dual-layer HD DVD and BD media - it discusses the "case of programmes of one hour or less". ®