Abstract

The metallodielectric Yagi antenna showed high directivity in the visible range as compared with all dielectric nanoantennas. In this paper, two different configurations have been introduced and analyzed: slanted nanowire optical Yagi antenna and asymmetric core-shell nanoantenna. Both designs have an Ag core and Si shell. The numerical results are obtained using the 3D FDTD technique. The proposed nanoantennas show ultradirective radiation in the direction of propagation. It has been shown that, by varying the angle $\mathrm{\Theta }$ of the slanted nanowire directors, the directivity of the nanoantenna is enhanced, and the beam width becomes narrow in the desired direction. The directivity is improved to 21.23 when $\mathrm{\Theta }=18°$, and the radiation efficiency is enhanced to 54% at a wavelength of 500 nm. Additionally, the asymmetric core-shell Yagi design enhanced the directivity to 22.4 at a wavelength of 500 nm, with an enhancement of 30% over the symmetric design. This improvement is attributed to the near-field intensity enhancement of the asymmetric core-shell design. The variation of the silver core position may be beneficial for various applications, including surface-enhanced Raman spectroscopy, energy harvesting, photodetection, and photovoltaics.

© 2017 Optical Society of America

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