Biomedical Engineering Reference
In-Depth Information
Figure 13.4
(a) Vortex-like profile of the time-averaged Poynting vector
(red arrows) in the case of
x
-polarized illumination at 1545 nm (b) and in
the case of
y
-polarized illumination at 1615 nm, respectively.
Figure 13.3c and 13.3d show the evolution of the simulated
spectra as the tail diameter of the Taiji pattern is changed; clearly,
the tail feature has a substantial influence over the resonant
behavior of the structure, especially for the second dip showing
electromagnetic energy vortex. As a result, the experimentally
determined resonance wavelengths slightly shift away from the
experimental measurement.
13.2.4
Vortex-Like Poynting Vector Profile
The electromagnetic energy vortex only exists in the near-field
regionofTaijimarkandcorrespondstodifferentswirlingdirections
for
x
-and
y
-polarized illumination. In order to understand
the vortex-like Poynting vector profile, a simple physical model,
consisted by an electric dipole perpendicular to the direction of
the surface currents in the near-field region of the Taiji marks, is
given.Thenear-fieldelectromagneticfielddistributionforthedipole
and also for the surface currents could be seen in the electrostatic
approximation. In Fig. 13.5b, the Poynting vector, the electric field
(induced by the electric dipole), and the magnetic field (induced
by the surface current) are denoted as solid red lines, dashed blue
lines, and orange symbols, respectively. It should be evident that, in
the cross-product of the electric and magnetic fields, a vortex-like
