Waveguiding of electromagnetic waves and investigation of negative phase velocity in photonic crystals and metamaterials
Author(s)
Advisor
Özbay, EkmelDate
2012Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Electromagnetic wave propagation is characterized in periodic dielectric
and metallic structures: Photonic Crystals (PCs) and Metamaterials,
respectively. The applications of these structures are demonstrated in the
Microwave regime. In the first application, Graded Index (GRIN) PC is used to
focus the incoming waves into a small spot. Speaking in terms of PC period a,
for an incident beam with Full Width Half Maximum of 9.20a the power of the
focusing behavior is quantified by looking at the spot size conversion ratio,
which is around 3.9. PCs can act as an efficient input coupler for the PC
Waveguide (PCW). The GRIN PC has been experimentally shown to yield a
coupling efficiency of 5 dB over the single PCW at 18 GHz. This method can be
applied to provide a solution for the input coupling losses between PC structures
and other lightwave circuits. PCs can also be used to achieve dual-bandpass and
bandstop spatial filtering by proper adjustments of the lattice parameters and the
frequency range. For the plane-wave excitation, a wideband spatial filtering is
shown to exist due to the specific Fabry-Perot type resonances, which are nearly
independent on the angle of incidence. The effect of the finite angular distribution of the Gaussian-beam excitation is also demonstrated. The spatial
filtering in the incidence and observation angle domains has been discussed both
numerically and experimentally for the non-plane-wave excitations under the
light of calculated iso-frequency contours. In addition to bandstop
characteristics, the dispersion relation of the PCs can be modified with the
proper arrangement, namely by employment of the dimer layer. This surface
layer supports the surface waves and serves like a waveguide for the
electromagnetic waves. At higher frequencies above the lightline, surface waves
radiate into air in the form of backward leaky waves and frequency dependent
steering is reported from 0
º
to 70º
for the outgoing beam. The leaky wave
behavior and backward radiation is similar to that is seen in Left-Handed (LH)
Metamaterials. Metallic fishnet layers are used to demonstrate negative
refractive index (NRI) in conjunction with the left-handed behavior in this class
of metamaterial. A wedge structure formed by fishnet layers is used to measure
the NRI which was also verified by the retrieval analysis. The limits of
homogenization are discussed. The dependence of the LH properties on the
fishnet parameters is investigated parametrically. For example, the NRI changes
from -1.8 to -1.3 as the interseperation distance of the layers varies from
as=λ/10.5 (2mm) to as=λ/4.2 (4mm) at magnetic resonance frequency around
14.3 GHz (ωm). It is also shown that the fishnet layers behave as an LC
resonator as well as a TEM waveguide and a 1D transmission line at ωm.
Keywords
Photonic Crystals (PCs)Graded Index PCs
Focusing
Waveguides
Spatial Filtering
Backward Leaky Waves
Metamaterials
Negative Refractive Index