  Metasurfaces are planar structures that locally modify the polarization,
phase, and amplitude of light in reflection or transmission, thus enabling
lithographically patterned flat optical components with functionalities
controlled by design. Transmissive metasurfaces are especially important, as
most optical systems used in practice operate in transmission. Several types of
transmissive metasurfaces have been realized, but with either low transmission
efficiencies or limited control over polarization and phase. Here we show a
metasurface platform based on high-contrast dielectric elliptical nano-posts
which provides complete control of polarization and phase with sub-wavelength
spatial resolution and experimentally measured efficiency ranging from 72% to
97%, depending on the exact design. Such complete control enables the
realization of most free-space transmissive optical elements such as lenses,
phase-plates, wave-plates, polarizers, beam-splitters, as well as polarization
switchable phase holograms and arbitrary vector beam generators using the same
metamaterial platform.
