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Double sided Blu-ray Discs (BiRD) Disclosure Number: IPCOM000022643D
Publication Date: 2004-Mar-22
Document File: 1 page(s) / 24K

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Double sided Blu-ray Discs (BiRD)

In optical prerecorded disc media, CD is the mainstream format with a huge installed base of CD players. Higher capacity formats like DVD have since then entered the market, mainly for video content. Market introduction of third generation discs like Blu-ray Disc (BD) has already started.

Each format is best read out by a specific laser. Because of the success of CD, next generation players should preferably be able to play CD discs. So CD still remains a very solid base for distributing content for some time. To speed up market acceptance of any new format, a disc that contains both the new and the CD format is a well known concept. From a content point of view there is no problem with supplying the identical content in different formats. However, from a replication point of view new technology is needed to produce such combi-discs.

In principle there are two solutions. A first solution is to provide different format layers at different depths in the disc, with each layer having reflection and transmission properties tuned to the associated laser wavelength. Now all lasers work at the same side of the disc. A second solution is to use the two sides of a disc for different formats. The double sided DVD disc has shown that this is feasible. Main disadvantages of such double sided discs are that the disc needs to be reversed, and that there is not much space for labels.

A DVD-CD double-sided combi-disc has been introduced, but without compliance to the CD specification, mainly due to either too large an overall disc thickness and/or too small a CD substrate thickness. The nominal thickness of substrates for CD, DVD, and BD discs are 1.2mm, 0.6mm, and 0.1mm, respectively.

The idea of combining different disc formats on different sides of a disc is fairly trivial. A number of possibilities are already known. In this paper we propose to combine BD with CD or SACD.

When we restrain ourselves to one type of layer on...