| 摘要 |
An optical scanning device which is compatible with both multi-layer and single layer disc formats, and which alleviates lens design requirements by providing a dual lens system and by making, say, lens OL 0 compatible with DVD (as well as layer L 0 of the dual layer format) and lens OL 1 compatible with CD (as well as layer L 1 of the dual layer format). Thus the two lens designs only need to work at two different wavelengths, and the device achieves compatibility with three different optical record carrier formats, but the amount of spherical aberration in respect of each lens part only needs to be matched precisely with respect to two formats in one of a number of known ways.
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