Biomedical Engineering Reference
In-Depth Information
(even mode) or anti-symmetric (odd mode) with respect to the
waveguide axis. The near-field patterns of the electric and magnetic
fields of the odd SPP mode are plotted in Figs. 8.4c and 8.4d,
respectfully, and the time-averaged optical powerflow is shown in
Fig. 8.4e. Similar to the case of a single metal-dielectric interface,
the time-averaged power inside and outside the dielectric slot
waveguide flows in opposite directions. The recycling of energy
between the backward and forward flow channels is achieved
via coupling of circulating powerflows around each interface,
which is revealed in the instantaneous Poynting vector distribution
plotted in Fig. 8.4f. Figure 8.5 illustrates the same characteristics
of the even-coupled SPP mode of the plasmon slot waveguide,
which corresponds to the higher-energy branch in the waveguide
dispersion characteristics (see Fig. 8.5b). The differences in the
coupling mechanism underlying formation of even and odd modes
are illustrated in Figs. 8.4f and 8.5f. The instantaneous Poynting
vector field of the odd-coupled SPP mode is characterized by
merging of the circulating powerflows formed on each material
interface (Fig. 8.4f). In contrast, the circulating powerflows of the
even SPP mode collide at the slot waveguide center (Fig. 8.5f),
whichresultsintheblue-shiftofthecorrespondingdispersioncurve
(Fig. 8.5b).
8.4 Hyperbolic Metamaterials: Global Field Topology
Defined by Local Topological Features
Even more interesting optical effects can be engineered via near-
field optical coupling between SPP waves formed on multiple
stacked M-I interfaces. The resulting anisotropic nanostructured
metal-dielectric material is schematically shown in Fig. 8.6a.
Mutual electromagnetic coupling of SPP modes across multiple M-
I interfaces results in the formation of several SPP branches in the
dispersion characteristics of such anisotropic structures (shown in
Fig.8.6b).Hereandinthefollowingfigures,thethicknessesoftheAg
andTiO
2
layersare9nmand22nm,respectively,andthedissipative
losses in Ag are fully accounted for. The presence of multiple high-k
branchesseeninFig.8.6bincreasesthebandwidthoftheplasmonic-
