Monopole probe fed by coupling gold rods

In this paper, we investigate the characteristic of near-field localization and enhancement in the coupling metallic structures. Then we combine a cylindrical monopole probe with the basic structures aforementioned. The excited strong fields on the resonant coupling rods inspire the resonance of the probe analogous to a traditional radio frequency monopole antenna. With that, the dimension of the localized optical hot spot is reduced to about a half. Simultaneously, the enhancement of near field increases to about twice, and the optical background is greatly suppressed. Detailed studies of the structure show that the E field along the probe (including the amplitude and the phase), excited by the basic structure, plays a key role in the enhancement of the structure. This gives a guidance to design relevant devices to further improve the performance of localization and enhancement. For comparison, the case of a single-rod feeding monopole probe is also studied.