Patent ID: 8279525

Claim:
A three-dimensional diffractive device, comprising: a substrate having a diffracting structure, wherein the structure further comprises: a first periodic diffracting structure having a periodicity, d x , in a first direction, and a groove depth, h x , characterized by only a single dispersing diffracting plane that supports a single propagating first-dispersing-order of light and a zero-specular order; and a second periodic structure having a periodicity, d z , in a second direction that is different than the first direction, and a groove depth, h z , that supports only a zero-specular order for the periodicity d z , wherein the device has a working spectral interval that is related to the periods d x , d z , as follows, where λ is the light wavelength, θ x is the projection of the angle of incidence on a plane parallel to the direction of the first periodicity, and θ z is the projection of the angle of incidence on a plane parallel to the direction of the second periodicity: for the existence of the first diffractive order created by the first periodicity: |sin θ x −λ/d x |<1; for the absence of higher orders created by the first periodicity: |sin θ x +λ/d x |>1; |sin θ x −2 λ/d x |>1;and for the absence of non-specular orders created by the second periodicity: |sin θ z −λ/d z |>1.