Biomedical Engineering Reference
In-Depth Information
FIGURE 14.8
(a) Optical image of the Brazilian weevil
Lamprocyphus augustus
and (b) some of its exoskeleton under white-
light illumination. (c, d) Cross-sectional SEM images of an entire scale and a section of the scale showing the photonic crystal
structure. Reproduced with permission from Ref.
54
. Copyright 2008, American Physical Society.
of materials and induce photon localization,
respectively. These ideas are based on creating
materials with an omnidirectional (or complete)
photonic band gap—a range of frequencies for
which light propagation within the photonic
crystal is classically forbidden in any direction.
In other words, this is a material for which the
optical density of states is zero across a given
frequency range while being non zero just above
and below this range.
The prospects of these exciting predictions
have motivated research into fabricating three-
dimensional photonic crystals with band gaps at
optical frequencies. The general requirements are
to create a three-dimensionally periodic structure
composed of dielectric compounds with differ-
ent refractive indices; the larger the difference,
the wider the photonic band gap. Furthermore,
the periodicities of this lattice should be nearly
the same in all directions (i.e. the Brillouin zones
