Patent ID: 8164721

Claim:
An optical retarder comprising: an axially-inhomogeneous element including a first plurality of layers having a first refractive index and a first thickness and a second plurality of layers having a second refractive index and a second thickness, the first plurality of layers interleaved with the second plurality of layers, the first and second thicknesses and the first and second refractive indices selected to form a zeroth order sub-wavelength grating structure that provides negative out-of plane retardance; a transversely-inhomogeneous element including a first plurality of regions having a first refractive index and a first width and a second plurality of regions having a second refractive index and a second width, the first plurality of regions interleaved with the second plurality of regions, the first and second widths and the first and second refractive indices selected to form a zeroth order sub-wavelength grating structure that provides in-plane retardance; and at least one substrate for supporting the axially-inhomogeneous and the transversely-inhomogeneous elements.