Patent ID: 7787182

Claim:
A diffractive optical device enabling special color effects viewable from a viewing direction, said diffractive optical device comprising a zero-order diffractive color filter, wherein said zero-order diffractive color filter comprises at least two materials with different indices of refraction, said at least two materials forming a diffractive structure, wherein said diffractive structure has a grating depth (t w ) between 30 nm and 500 nm, said at least two materials comprising an essentially transparent high-index layer and materials surrounding said high-index layer, said high-index layer comprising said grated structure, said high-index layer having a relative high index of refraction compared to an index of refraction of materials surrounding said high-index layer; a reflecting structure; and a spacer layer sandwiched between said zero-order diffractive color filter and said reflecting structure; wherein said reflecting structure is on the backside of said spacer layer with respect to said viewing direction and is an essentially uniform distance (d spacer ) between 50 nm and 1500 nm from said zero-order diffractive color filter; said high-index layer thus acting as a leaky waveguide for light incident thereon and making zero-order diffraction and a rotation color effect viewable from said viewing direction; and wherein said reflecting structure reflects towards said zero-order diffractive color filter at least part of light transmitted through said zero-order diffractive color filter in order to cause enhanced interference effects between light reflected from said reflecting structure and light leaking out of said leaky waveguide.