Deep-subwavelength focusing and steering of light in an aperiodic metallic waveguide array

We consider an aperiodic array of coupled metallic waveguides with varying subwavelength widths. For an incident plane wave, we numerically demonstrate that a focus of as small as one-hundredth of a wavelength can be achieved for a focal distance that is much longer than the wavelength. Moreover, the focusing behavior can be controlled by changing either the incident wavelength or the angle of incidence, thus providing the capability of nanoscale beam steering. We show that the behavior of such subwavelength focusing can be understood using Hamiltonian optics.