Page 469 - Introduction to Information Optics

454 8. Information Storage with Optics

(c)

Fig. 6. Continued.

8.4.6. PHOTOCHEMICAL HOLE-BURNING 3-D STORAGE

In photochemical hole-burning optical storage [23,28,29], the third dimen-
sion is frequency instead of depth or thickness. Thus, the storage may look like
an ordinary single-layer optical disk or photographic plate, but the storage
capacity can be as high as 1000 times that of single-layer disks. Currently, the
media should be kept at a very low temperature, typically less than 100 K. This
makes it impractical at present. The application of photochemical hole burning
to optical storage is somewhat like the change from black-and-white to color
photography. Consequently, low-cost and stable semiconductor lasers would
be needed that must be tunable over a fairly large frequency range and must
operate in single mode. Lasers fulfilling these requirements are still under
development. Nevertheless, holography in photochemical hole-burning media
has also been proposed recently [36].

8.5. HOLOGRAPHIC OPTICAL STORAGE

In optical signal processing [2,4], it is widely known that an image can be
recorded either directly on a photographic plate or in a hologram. The
hologram records the interference pattern generated by the image and a
reference beam. The hologram can then be reconstructed to produce the