Focusing behaviors of optical nanotip antenna array based on surface plasmons

Surface plasmons, as a local electromagnetic field mode generated or stimulated at the interface between common metal and dielectric, can be used to greatly break through the optical diffraction limit and also localize the electric-field and then light energy in a sub-wavelength scale. It is already a research hotspot in recent years. As shown, several patterned metal nano-array can be utilized to produce relatively strong surface plasmon resonance, so as to achieve a nano-scaled localized light field on the surface of the functioned metal structure. In this paper, silicon dioxide materials are used as the substrate, and the common gold materials are fabricated into a metal film, and then the sub-wavelength metal nano-tip arrays with several morphology such as the cone-shaped, the triangular-pyramid-shaped, and the quadrangular-pyramid-shaped, are designed respectively. The functioned metal nano-structures are symmetric and asymmetric coating mode. The electric field distribution characteristics of the structure under the internal excitation mode of the incident light with vertical incidence are analyzed. The simulations show that the local field enhancement can be clearly observed at the nano-tip of the cone-shaped in the asymmetric case, but the symmetry is not. Analysis shows that the destructive interference occurs when the surface plasmons are excited by a linearly polarized light on both sides of a conical structure propagate to its top, so failure to produce focusing effect. Therefore, to the case of symmetrical film through adjusting the incident angle of light, different incident angles will affect the enhancement of the local field at the tip of the cone.