Patent ID: 8270050

Claim:
A security device comprising: a homogeneous zero-order diffractive microstructure to display a colour change on tilting or rotating the homogenous zero-order diffractive microstructure, the homogenous zero-order diffractive microstructure being buried within a substrate and comprising spaced lines of material, with spacing between the lines in a range of 100 nm to 900 nm, and wherein the zero-order diffractive microstructure has an index of refraction higher than an index of refraction of the substrate, the zero-order diffractive microstructure configured to act as a waveguide; and a further structure comprising a plurality of spherical or aspherical micro-lenses formed on a surface of the substrate over the homogeneous zero-order diffractive microstructure, the plurality of micro-lenses being sufficiently small that when viewed by a user an average of different colours will be observed, and wherein the further structure is configured such that the plurality of micro-lenses reduces the colour change produced by the zero-order microstructure upon the device being tilted.