Sub-wavelength structures and their optical properties

We present fabrication and optical properties of some sub-wavelength structures studied in our group, including the sub-100 nm size gold and silver split ring resonators (SRRs). The sub-100-nm SRRs can have magnetic resonance entering into the visible frequency spectrum. The silver SRRs as small as ~60 nm and fundamental magnetic resonance (LC-resonance) as short as ~604 nm have been successfully demonstrated. The resonance wavelengths of the LC and plasmon modes of the sub-100-nm SRRs are found to linearly decrease with the decrease of SRR size. Excellent agreement between LC-model and experimental data is obtained when the capacitance of the sub-100-nm SRRs is interpreted as capacitance between two spheres instead of between two parallel plates. We also present fourfold rotationally symmetric SRR lattice configuration in which the electric and magnetic resonant modes can be efficiently excited under unpolarized light illumination. Furthermore, the large area sub-100 nm SRR metamaterials formed by fourfold rotationally symmetric SRR lattice can be used for sensing with refractive index sensitivity as high as ~636 nm/RIU.