  The manipulation of light by conventional optical components such as a
lenses, prisms and wave plates involves engineering of the wavefront as it
propagates through an optically-thick medium. A new class of ultra-flat optical
components with high functionality can be designed by introducing abrupt phase
shifts into the optical path, utilizing the resonant response of arrays of
scatters with deeply-subwavelength thickness. As an application of this
concept, we report a theoretical and experimental study of birefringent arrays
of two-dimensional (V- and Y-shaped) optical antennas which support two
orthogonal charge-oscillation modes and serve as broadband, anisotropic optical
elements that can be used to locally tailor the amplitude, phase, and
polarization of light. The degree of optical anisotropy can be designed by
controlling the interference between the light scattered by the antenna modes;
in particular, we observe a striking effect in which the anisotropy disappears
as a result of destructive interference. These properties are captured by a
simple, physical model in which the antenna modes are treated as independent,
orthogonally-oriented harmonic oscillators.
