Patent ID: 8339566

Claim:
A polarization grating, comprising: a first polarization grating layer comprising a molecular structure that is twisted according to a first twist sense over a first thickness defined between opposing faces of the first polarization grating layer such that respective relative orientations of molecules of the first polarization grating layer are rotated by a first twist angle over the first thickness throughout the first polarization grating layer; and a second polarization grating layer on the first polarization grating layer, the second polarization grating layer comprising a molecular structure that is twisted according to a second twist sense opposite the first twist sense over a second thickness defined between opposing faces of the second polarization grating layer such that respective relative orientations of molecules of the second polarization grating layer are rotated by a second twist angle over the second thickness throughout the second polarization grating layer, wherein the second twist angle is about +70 degrees, and wherein the first twist angle is about −70 degrees.