Patent ID: 8335034

Claim:
Optical device comprising a pair of plate-like diffractive optical elements (DOEs) with transmission functions T 1 (r,θ)=exp[iΦ 1 (r,θ)] and T 2 (r, θ)=exp[iΦ 2 (r,θ)] where r and θ are polar coordinates, r being the radius and θ being the polar angle, and Φ 1,2 (r,θ) are phase profiles within 0 and 2π imprinted on the DOEs, the two DOEs being successively arranged in parallel to each other with a sufficiently small separation between them that the combination of the two adjacent DOEs corresponds optically to one single DOE with a transmission function of T combi =T 1 *T 2 , one (or both) of the DOEs being adapted to be rotated relative to the other around an axis perpendicular to the surface, so that the pair of DOEs acts as a DOE with the transmission function T combi = T 1 ( r ,θ)* T 2 ( r ,θ−φ)=exp[ iΦ 1 ( r ,θ)]*exp[ iΦ 2 ( r ,θ−φ)]==exp[i{Φ 1 ( r,θ)+Φ 2 (r,θ−φ)}] where φ is the relative angle of rotation, wherein the phase profiles Φ 1,2 of the two DOEs are given by Φ 1 ( r ,θ)=mod 2π {[ F ( r )θ+ m phas θ+ a spir θ 2 ]+[ G offs ( r )/2]+ a div r 2 } and Φ 2 ( r ,θ)=mod 2π {−[ F ( r )θ+ m phas θ+ a spir θ 2 ]+[ G offs ( r )/2]− a div r 2 }, where mod 2π {. . . } means the modulo 2π operation, where m phas is an integer number or zero, where the coefficients a spir and a div are real numbers or zero and where F(r) and G offs (r) are real functions depending on r but not on θ, F(r) and G(r) chosen so that each of the corresponding transfer functions T F (r)=exp[iF(r)] and T G (r)=exp[iG offs (r)] respectively is the transfer function of either a (rotationally symmetrical) Lens or of a (rotationally symmetrical) axicon or of an arbitrary superposition thereof, wherein G offs (r) may also be zero for all values of r and wherein F(r) may also be zero for all values of r, yet under the condition that in this case (i.e. F(r)=0) at least one of the coefficients m phas or a spir , is not zero.