Appeal No. 2005-2750
Application 09/460,221
The figures of the original patent depict eight different embodiments of apparatus
for recording data on or reproducing data from two different types of optical discs each
having a recording layer and a substrate layer. In the “first” type of disc, depicted in
Figure 4A, the substrate has a thickness d1 of 1.2 mm. Original Patent, col. 5, ll. 66-
67.2 Nishiuchi et al. Patent 5,097,464 (“Nishiuchi”), which was applied during
prosecution of the original patent, explains that this is the commonly used substrate
thickness for optical discs. Nishiuchi, col. 1, ll. 25-28. In the “second” type of disc,
depicted in Figure 4B, the substrate has a smaller thickness d2 of, for example, 0.3 mm.
Original Patent, col. 6, l. 6. As explained at column 1, lines 21-65, the smaller
thickness of this substrate is due to the fact that it is designed to record a higher density
of information than is possible using the conventional, thicker substrate. Specifically,
higher-density recording requires a reduced spot diameter (D), which is related as
follows to the laser wavelength (λ) and the numerical aperture (NA) of the focusing lens:
D ∝ λ/NA
Thus, the recording density can be increased by increasing the numerical aperture and
thereby decreasing the spot diameter. While increasing the numerical aperture will
inherently cause an increase in coma aberration, that effect is avoided or reduced by
reducing the thickness of the substrate. Another problem is that an objective lens which
is designed for use with the thinner, high-density optical disc will suffer from an
2 All citations herein to the specification of the reissue application, which does
not include line numbers, are to the specification of the original patent, which does.
3
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