Patent ID: 8233218

Claim:
An article comprising: a volume of material substantially transparent over at least a portion of the visible spectrum, the volume being bounded by a substantially flat first surface and a generally convex faceted second surface; and one or more reflective diffraction gratings on the first surface, wherein: the first surface is larger in area than any facet of the second surface; each diffraction grating comprises a corresponding set of diffractive elements formed in a deformable layer attached to the first surface; the deformable layer comprises a reflective metal layer and a polymer layer between at least a portion of the first surface and at least a portion of the reflective metal layer; the reflective metal layer is arranged so as to permit only negligible transmission of light incident on the diffraction gratings; and the diffraction gratings are arranged so that corresponding input and output directions defined by the diffraction gratings lie within the volume of material.