Geometric-phase Meta-optics

We develop a flat optics technology (4th–generation optics) enabled by the geometric-phase (GP) effect grounded on the Pancharatnam-Berry phase in polarization-state transformation processes. In GP optical elements, desired refractive properties are obtainable by appropriately distributing optically anisotropic domains in a flat mm-thick film. Such GP elements can be easily embedded entirely within conventional refractive optic structures and, thereby, provide desired additional refractive-power properties in absence of any diffractive surface patterns.

The basis of GP modulation lies in spatially controlling the local orientation of anisotropic molecules in retardation film. Varying the angle f of anisotropic orientation makes a 2f phase change in circularly polarized incidence. This GP modulation is physically continuous throughout the spatially variant retardation film due to the unbound nature of GP. Thin anisotropic films are continuous down to sub-nanometer scale and can be deposited in multiple layers, ensuring clear, haze-less optics without compromising efficiency and transmittance. This is advantageous over the discontinuous surface corrugations of most conventional optics. With conventional optics, GP layers with spatially variant anisotropy axes can be additionally realized using nanostructured metasurfaces or liquid crystal polymers. UV-curable liquid crystal polymers used in our research are particularly attractive because they can be foldable and made at low cost.