Isotropic zero-order diffractive filter

A method to manufacture an embossing tool for embossing the microstructures of isotropic zero-order diffractive color filters comprising the steps of:—providing a substrate comprising microstructures,—depositing on said substrate a starting layer for an electroforming step,—electroforming an embossing tool from the substrate,—optionally removing the starting layer in an etch process,—optionally recombining the electroformed tool to realize a larger tool and/or a tool wherein the microstructures form a design, and wherein said zero-order diffractive color filter comprises diffractive microstructures and a wave-guiding layer, wherein the diffractive microstructures are ordered over a length scale x, wherein x is such that:

• 4×Λ<x<100 μm, where Λ is the period of said microstructures, and the diffractive microstructures are randomly arranged over length scales of more than 100 μm, in such a way that said zero-order diffractive color filter is isotropic and has color effects upon tilting with no color effect upon rotation.

A method to manufacture an isotropic zero-order diffractive color filter comprising the steps of:—embossing a diffractive microstructure, in an embossable substrate or a substrate with an embossable layer, and—coating the embossed substrate with a wave-guiding layer comprising a high refractive index, wherein said zero-order diffractive color filter comprises diffractive microstructures and a wave-guiding layer, wherein the diffractive microstructures are ordered over a length scale x, wherein x is such that:

• 4×Λ<x<100 μm, where Λ is the period of said microstructures, and the diffractive microstructures are randomly arranged over length scales of more than 100 μm, in such a way that said zero-order diffractive color filter is isotropic and has color effects upon tilting with no color effect upon rotation.