Arm-edge conditions in plasmonic folded dipole nanoantennas

Silver folded dipoles consisting of two parallel nanowires may operate as efficient transmitting and receiving nanoantennas in the optical domain in both cases of silver-nanowire-terminated arm-edges and open-terminated arm-edges, in contrast to their conventional radio-frequency (RF) counterparts that only operate efficiently when they are short-wire-terminated arm-edges. The mode decomposition analysis with the equivalent circuit reveals that the difference of the wave numbers between the common and the differential modes allows this feature for the optical folded dipole nanoantenna under both arm-edge conditions. The analysis also estimates the efficiency of the folded dipoles via the equivalent radius of nanowires for the common mode. These folded nanostructures may exhibit the enhanced efficiency with the maintained radiation patterns, where the efficiency of folded dipoles is the same as that of the effective single dipole at resonance. (C) 2011 Optical Society of America