Experimental determination of the principal dielectric functions in silver nanowire metamaterials

The polarization dependent optical properties of silver nanowire arrays are investigated by angular resolved transmission measurements. The corresponding spectra show clear Fabry–Perot oscillations, which exhibit an unusual shift toward longer wavelengths for the extraordinary waves. From the peak shift both principal dielectric functions of the metamaterial are determined and compared with effective medium theories. Their different signs lead to a hyperbolic wave vector surface for the extraordinary waves and cause the observed peculiar peak shift.