Optical properties of metamaterials based on asymmetric double-wire structures.

We performed theoretical and experimental investigations of the magnetic properties of metamaterials based on asymmetric double-wire structures. Using the multipole model for the description of metamaterials, we investigated the influence of the geometrical asymmetry of the structure on the macroscopic effective parameters. The results show that the larger wire in the system dominates the dynamics of the structure and defines the orientation and the strength of the microscopic currents. As a result the magnetization of the structure can be significantly enhanced for certain asymmetric configurations of the double-wire structure.

Single and multilayer metamaterials fabricated by nanoimprint lithography.

We demonstrate for the first time a fast and easy nanoimprint lithography (NIL) based stacking process of negative index structures like fishnet and Swiss-cross metamaterials. The process takes a few seconds, is cheap and produces three-dimensional (3D) negative index materials (NIMs) on a large area which is suitable for mass production. It can be performed on all common substrates even on flexible plastic foils. This work is therefore an important step toward novel and breakthrough applications of NIMs such as cloaking devices, perfect lenses and magnification of objects using NIM prisms. The optical properties of the fabricated samples were measured by means of transmission and reflection spectroscopy. From the measured data we retrieved the effective refractive index which is shown to be negative for a wavelength around 1.8 µm for the fishnet metamaterial while the Swiss-cross metamaterial samples show a distinct resonance at wavelength around 1.4 µm.

Polarization-independent negative-index metamaterial in the near infrared.

We present and evaluate theoretically and experimentally a design for a negative-index metamaterial that is termed the "Swiss cross" structure. Compared with the established fishnet structure, the proposed design eliminates the drawback of polarization-dependent effective optical parameters. The new design is fabricated by means of e-beam technology and experimentally analyzed using spectroscopic techniques. The thorough comparison with numerical simulations reveals an effective refractive index of n=-1.9 at an operational wavelength of 1400 nm that is independent of the incident polarization. The resonances of the system are comprehensively discussed.