AAWSAP DIRD, Invisibility Cloaking Theory and Experiments, March 2010

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This idea comes from Fermat's principle
of the shortest optical path. 7 Suppose
that light travels from A to B. According
to Fermat's principle, light follows the
path that takes the shortest time. In
refractive materials, the speed of light is
modified-in most cases reduced-by the
refractive index. The time it takes for
light to pass through an infinitesimal
element of space is proportional to the
refractive index. So, if the index varies
in an optical material or in the
boundaries between materials, the
optical measure of path length varies,
which is the defining feature of a curved
geometry. To provide a simple example,
a lens focuses parallel light rays into a
point; the parallels meet there, which is
the hallmark of a non-Euclidian
geometry. So something as familiar as a
lens creates something as fantastic as a
curved geometry.
Figure 7. The Invisible Woman. Invisibility by bending
light, an inspiration for cloaking.
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