Page 466 - Introduction to Information Optics

8.4. Bit-Pattern Optical Storage 451
be applied to bacteriorhodopsin [27]. However, instead of a luminescence
output, a generated photovoltage is detected as the output signal from the 3-D
storage device [27].

8.4,5. STACKED-LAYER 3-D OPTICAL STORAGE

In contrast to photon-gating 3-D storage that uses a bulk medium without
a delineated layered structure, stacked-layer 3-D optical storage really consists
of a stack of layers. This architecture can be represented by 3-D storage based
on ET materials [34].
The concept that a stack of ET layers can form a 3-D optical storage device
is schematically depicted in Fig. 8.4. The formatted 2-D page memory can be
written by properly imaging the page composer onto a specific layer with blue
laser light at 488 nm. Similar to multilayer disks [33], it had previously been
calculated [34] that the diameter of the out-of-focus spot on the neighboring
layer would be 200 times larger and the intensity would be reduced by 40,000
times. However, when 1000 x 1000 bits are written in parallel, the out-of-focus
spot may overlap and superimpose. The superimposed spots may generate
serious cross-talk noise.
This cross-talk problem can be overcome by using the coding and decoding
technique given in Figs. 8.5(a) and (b), respectively. Since bits 1 and 0 consist
of the same number of bright and dark pixels, the blurred 1 and 0 coded

Blue
Write-In
Beam

Cladding / Cladding \ Cladding

Fig. 8.4. Architecture of 3-D optical storage using ET materials.