Influence of symmetry breaking in pentamers on Fano resonance and near-field energy localization

Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-disk position to study the effect of symmetry breaking in pentamers. It is found that while planar symmetric oligomers can exhibit a single Fano Resonance ( FR), an offset of the central nano-disk at a controlled gap of 3 nm from the nearest neighbor nano-disk, gives rise to the appearance of an additional dark mode that can potentially be used in localized surface plasmon resonance sensing. It is shown that this mode leads to the appearance of the second FR in the same spectrum. The simulation results are in a good agreement with experimental data. Furthermore, it is found that unique near-field energy distribution in the asymmetric pentamers can be well tuned to be localized at one, two or three of the four subwavelength gaps of the pentamer selectively by only changing the polarization orientation of a single light source. (C) 2011 Optical Society of America