Appeal No. 1998-1472 Page 2
Application No. 08/427,721
compact disk-read only memory (CD-ROM). Although this storage
capacity suffices for some audio and computer applications, it
does not suffice for high-resolution video applications.
The inventive optical disk drive stores and reads data by
creating and detecting, respectively, the presence of
holographic gratings in an optical disk. A holographic
grating is an interference pattern created in a holographic
medium forming all or part of the optical disk. Specifically,
a plane-wave beam and a counter-propagating, focused beam are
used to create the holographic gratings in the medium.
In one embodiment of the invention, the presence of a
holographic grating within a data storage location of the disk
indicates a first binary state, whereas the absence of such a
grating indicates the second binary state. In other
embodiments, the holographic gratings are created with varying
diffraction efficiencies. The variance in diffraction
efficiency distinguishes holographic gratings associated with
the same point of focus. This in turn allows the holographic
gratings to represent “n-ary” or analog-valued data.
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