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Abstract
The optical property of optical antennas is studied by three-dimensional electromagnetic calculation at visible and near-infrared wavelengths. The simulations for gold nanorod and ellipsoid illuminated by plane wave polarized along the antenna axis are performed. All calculations predict the same general trends of response and dependences on geometry. The influence of geometrical parameters of the antenna on the field enhancement and the spectral response are discussed. The antenna can excite huge electric field enhancement at the ends. For monopole antennas, electric field enhancements are found to be dependent on length, radius and shape. The electric field enhancement of ellipsoid antenna is stronger than that of nanorod antenna. And for dipole antennas, electric field enhancements are found to be dependent on gap size, length and radius. The electric field enhancements of both antennas are almost the same. The spectral position of the electric field enhancement peak red shifts to near infrared, as length increases or radius decreases for all antennas.