AN INTRODUCTION TO NANOCOMPUTING - Bio-Inspired and Nanoscale Integrated Computing - page 17

is seen—literally—in holography. To display a hologram, light waves are diffracted
through patterns that were previously recorded. The diffraction of light actually
reproduces all the waves of light that were originally recorded. Because of this,
visual holograms are well known to have accurate details and amazing realism.
Holography has found many other important engineering applications because
diffraction can manipulate light waves in a flexible, powerful way.
Equally important is the superposition of waves. Consider two waves that are
traveling in opposite directions (Fig. 1.12). The waves continue with the same
direction and speed, unaffected by each other. However, if desired, one could
measure the intensity of the point where both waves cross. The propagation of the
waves remains unaffected, but the intensity measured at a point where two waves
overlap would be the sum of both waves, a result of constructive or destructive
interference.
This provides a convenient way to overcome the significant limitation of
wiring: use waves for communication instead of particles. Because of super-
position, waves can cross over each other without destroying the information
being carried. In addition to guided waves, one could also use waves in free space,
removing dependence on wiring. This may seem like a small matter at first, but as
shown later in this topic, it allows for significant improvements in theoretical
algorithmic performance of computations. Note that improving algorithmic
performance is usually more beneficial than simply making a processor ''smaller
and faster.''
Figure 1.12. Visualization of how two waves cross. Unlike wires carrying an
electrical signal, waves can occupy the same space while propagating. However,
even though propagation over time remains unaffected, as they cross, the waves
do interfere.