Passive and Active Nano-Antenna Systems - Singular and Chiral Nanoplasmonics - page 436

Figure 14.12 Directivity for the lossless and passive ( κ = 0) and super-
resonant ( κ =− 0.245) Ag-based CNP excited by a z -oriented EHD located
inside the nano-core at 12 nm along the positive x -axis. The E-plane ( xz -
plane) pattern is shown in (a), and the H-plane ( xy -plane) pattern is shown
in (b).
EHD.Inparticular,becauseitradiatesasanelectricallysmalldipole,
its value remains around 1.5. There is a complete symmetry in the
CNP and, consequently, no preferred axis. Thus, as in the passive
spherical case treated in [55], the dipolar resonance excited inside
the active spherical CNPs does not modify the directivity pattern
of the exciting Hertzian dipole; to this end, the higher-order modes
need to be excited inside the CNPs. Apart from the flipping of the E
and H-plane patters by 90 ◦ , the same results hold true for the case
of x -oriented EHD excitation of the currently investigated CNPs.
14.3.4.3 Influence of EHD orientation
The super-resonances in Fig. 14.10b are not restricted for the EHD
locations inside the nano-core of the CNP. Figure 14.13 shows the
NRR as a function of the EHD distance r s from the center of the
super-resonant Ag-based CNP, as well as the corresponding Au and
Cu-based CNPs, for a z -oriented (Fig. 14.13a) and x -oriented (Fig.
14.13b) EHDs—from these results, it is clear that large NRR values
are also obtained for the EHD locations inside the nano-shell and
outside the CNP.