Anomalous focusing characteristics of nanoscale metallic waveguide array under different incident wavelengths

The chromatic aberration effect of light focusing in a periodic nanoscale metallic waveguide array (NMWA) is investigated by using the coupled-mode theory and numerical simulations. The dispersion of the coupling coefficient in the periodic NMWA is calculated. The spreading angle of surface plasmon polaritons (SPPs) is derived from the distribution of the electric field density. The numerical results demonstrate that the light focusing in the periodic NMWA exhibits an anomalous chromatic property in an appropriate wavelength range compared to a conventional microlens.