Double Fano resonant characteristics are investigated in planar plasmonic structure by embedding a metallic nanorod in symmetric U-shaped split ring resonators, which are caused by a strong interplay between a broad bright mode and narrow dark modes. The bright mode is resulted from the nanorod electric dipole resonance while the dark modes originate from the magnetic dipole induced by LC resonances. The overlapped dual Fano resonances can be decomposed to two separate ones by adjusting the coupling length between the nanorod and U-shaped split ring resonators. Fano resonances in the designed structure exhibit high refractive-index sensing sensitivity and figure of merit, which have potential applications in single or double-wavelength sensing in the near-infrared region.

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A broad-band perfect absorber composing a two-dimensional periodic metal-dielectric-metal sandwiches array on dielectric/metal substrate is designed and numerically investigated. It is shown that the nearly-perfect absorption with a bandwidth of about 50 nm in visible region can be achieved by overlapping of two plasmon resonances: one originating from the coupling of electric dipoles between adjacent unit cells and another arising from magnetic dipole plasmon resonances. A capacitor-inductor circuit description is introduced to explain the dependence of resonance frequencies and band-width on geometrical parameters.

A novel planar plasmonic metamaterial for electromagnetically induced transparency and slow light characteristic is presented in this paper, which consists of nanoring and nanorod compound structures. Two bright modes in the metamaterial are induced by the electric dipole resonance inside nanoring and nanorod, respectively. The coupling between two bright modes introduces transparency window and large group index. By adjusting the geometric parameters of metamaterial structure, the transmittance of EIT window at 385 THz is about 60%, and the corresponding group index and Q factor can reach up to 1.2 × 10³ and 97, respectively, which has an important application in slow-light device, active plasmonic switch, SERS and optical sensing.

Dual-band perfect absorbers involving an array of gold nanoellipsoids or nanoellipsoid dimers near a gold film are designed and their resonance absorptions and field enhancements are numerically investigated. It is shown that the multilayer structures combining gold nanoparticles and gold film enable dual-band higher absorption and larger field enhancement than the structures without the metal film, due to the strong coupling between the localized surface plasmon resonance from the particles or particle dimers and the surface plasmon polaritons from the gold film. A field enhancement factor (|E|/|E0|) of more than 102 is achieved at the positions of 2.5 nm from the particle tip at two distinct wavelengths in the surface-plasmon-coupled nanoellipsoid dimer structure. The results suggest that the coupling of the localized surface plasmon resonance and the surface plasmon polaritons excited in the plasmonic metamaterials may have potential applications for multifrequency absorbers, emitters and SERS substrates as well as sensing.