Appeal No. 1998-1472 Page 17
Application No. 08/427,721
a presence, or (ii) an absence of a holographic grating at the
plural locations within the disk, using a plane-wave light
beam.” Accordingly, the claim requires using an electro-
optical head, with a plane-wave light beam, to read data by
detecting the presence or absence of a holographic grating at
plural locations within a disk.
Takeda teaches the limitations by including the following
disclosure.
FIG. 3 is a view showing an embodiment of the
hologram apparatus which reconstructs, for example,
voice signals from such a plurality of holograms.
Referring to the figure, numeral 2 designates a disk
whose surface is coated with a hologram recording
material. A plurality of holograms 1 are formed on
the surface. Each of the holograms 1 has a shape
which can be substantially regarded as oblong. The
holograms are closely arranged in such a manner that
the long side of the oblong extends in the radial
direction of the disk 2, while the short side
extends in a direction substantially orthogonal to
the radial direction.
A light source 3 is arranged on one side of the disk
2, and generates a laser beam 4. Shown at 12 is a
mask having a slit which is arranged between the
light source 3 and the disk 2. The size of the slit
is approximately equal to that of each hologram 1.
Each hologram is, accordingly illuminated by the
laser beam 4 through the rectangular slit of mask 12
which is substantially equal in size thereto.
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