Abstract

Plasmonic nanostructures can serve as model systems for a variety of fascinating classical oscillator physics. For example, in nanostructures with broken symmetry, Fano resonances can arise due to the interaction of narrow dark modes with broad bright modes. We have recently identified non-concentric ring/disk cavities as a system with a highly tunable Fano resonance and exceptionally large refractive index sensitivity and localized surface plasmon resonance figure of merit [1]. Using numerical electromagnetic simulations, Zhang and coworkers have further shown that for dolmen-shaped slab structures with optimized geometries a full plasmonic- induced optical transparency can develop [2]. This constitutes a classical analogue [3] to the well-known phenomenon of electromagnetically induced transparency (EIT). Here we present an experimental demonstration of Fano resonances in two plasmonic systems: firstly the dimer/monomer dolmen slab structure proposed by Zhang et al [2], and secondly for a side-by-side arrangement of a Au ring and a Au disk (ring near disk cavity, RNDC), both fabricated using e-beam lithography. We analyze the dependence of the Fano lineshapes on the polarization of the incident light, and of the strength of the feature on the separation between individual nanoscale sub-units. We further show that for significantly broad dipolar modes, multiple Fano resonances can arise.

© 2009 IEEE