Appeal No. 1998-1472 Page 19
Application No. 08/427,721
the data. By illuminating the holograms 1, which are on the
disk 2, Takeda teaches detecting the presence or absence of a
holographic grating at plural locations within a disk.
By using the laser beam 4 from the mask 12 to illuminate
the holograms 1, the reference teaches using a plane-wave
light beam to read data by detecting the presence or absence
of a holographic grating at plural locations within a disk.
It is true that Figure 3 of Takeda depicts the light from the
light source 3 diverging as it travels toward the mask 12.
More specifically, the light is drawn as expanding radially.
The figure, however, also shows the laser beam 4 emerging from
the slit in the mask 12 as a plane-wave light beam. Rather
than diverging, the beam is shown as comprising parallel
planes. Fig. 3.
In view of these teachings and showings, we are persuaded
that the reference discloses the claimed limitations of
“reading data elements using an electro-optical head by
detecting one of (i) a presence, or (ii) an absence of a
holographic grating at the plural locations within the disk,
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