DETAILS OF THE ACHIEVEMENT
| Optical properties of gradient subwavelength structures |
| Vladimír Kuzmiak, Ph.D. |
| Year: 2007 |
We studied dielectric layers characterized by gradient dielectric
function which leads to a non-local dispersion with a cutoff frequency
that separates frequency ranges supporting traveling and evanescent
waves. For realistic values of the modulation of the refractive index
the system supports evanescent s-waves while for p-waves predicts
traveling regime, i.e. in contrast to photonic barrier with a
homogeneous profile the tunneling becomes polarization-depentent. By
using exactly solvable model we examined the effect of concave profile
that characterizes photonic barrier on the reflectance and
transmittance of a single and double layer for both s- and p-wave
incidenting with arbitrary angle. We have shown that by increasing of
the modulation depth of the refractive index our model predicts in the
regime of reflectionless tunneling the existence of the transmittance
peaks for s-waves – see Fig. 1.We proved that unlike in the case of
the square barrier with constant refraction index the cancellation of
the reflected wave occurs due to the interference between the
reflected wave and transmitted part of the evanescent wave at the
interface between the gradient layer and vacuum. The effect of
nonattenuated tunneling is analogous to the superlensing phenomenon in
which evanescent waves contribute to the perfect image of the objects
by means of negative refractive index medium and represent an
alternative concept of energy transfer that employs evanescent waves
and may be useful in design of subwavelength devices. Using different
profiles opens a possibility of design of new class of metamaterials
in which spatial distribution implies resonant behavior of the
permittivity that is in contrast to metallic negative index medium not
accompanied with a sizable absorption.
Transmittance of gradient and homogeneous layers |
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