Gold bow-tie shaped aperture nanoantenna: Wide band near-field resonance and far-field radiation

In this paper, the optical bow-tie shaped aperture nanoantenna excited by a plane wave is numerically investigated based on the finite integration technique (FIT) where both near-field resonant properties, and far-field radiation characteristics are studied. Different from conventional metallic antennas used in the radio frequency range, gold aperture nanoantenna with a dimension of tens of nanometers is capable of producing a localized enhanced field. The enhanced filed is equivalent to a strong light spot which can lead to the resolution improvement of the microscopy and optical lithography, thus increasing the optical data storage capacity. Compared with previous studies, the present work improves calculations in terms of broader bands specially in optical range, where the nanoantenna's surface plasmon resonance is appositely described in terms of properly chosen frequency dependent permittivity. It is found from our observation that in the near-field, the bow-tie shaped aperture nanoantenna possesses strong resonant properties. These properties, dependent on the polarization directions of the excitation source and the geometrical parameters of nanoantenna, are studied in detail. In addition, the far-field characteristics of the nanoantenna such as directivity and gain are studied for the first time via computed aperture nanoantenna's pattern. The promising results of this study may have useful potential applications in near-field sample detection, optical microscopy, etc.