# US 8,542,442 B2 · Isotropic zero-order diffractive filter

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- Number: US 8,542,442 B2
- Document ID: US8542442B2
- Status: Granted
- Kind: B2
- Application number: 12/116,233
- Filed: 2008-05-07
- Published: 2008-11-13
- Granted: 2013-09-24
- Earliest claimed: 2007-05-07
- Assignees: Centre Suisse d'Electronique et de Microtechnique SA—Recherche et Developpement
- Applicants: Nicolas Blondiaux; Mickaël Guillaumee; Raphaël Pugin; Ross Stanley; Alexander Stuck; Harald Walter
- Inventors: Nicolas Blondiaux; Mickaël Guillaumee; Raphaël Pugin; Ross Stanley; Alexander Stuck; Harald Walter
- Web page: https://patentgrep.com/patent/US8542442B2

## CPC

- G02B 5/203: {having holographic or diffractive elements (diffraction gratings per se G02B5/18; holographic elements per se G02B5/32; generating the spectrum using diffraction elements G01J3/18)}
- G02B 5/1809: {with pitch less than or comparable to the wavelength}
- G02B 5/1847: {Manufacturing methods}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The present invention relates to an isotropic zero-order diffractive color filter, to a method to manufacture an embossing tool and to a method to manufacture such a filter. The zero-order diffractive color filter comprises diffractive microstructures and a wave-guiding layer, wherein the diffractive microstructures possess a short range ordering over at least four times the period of the microstructures, and the diffractive microstructures possess a long range disordering over length scales of more than 100 μm.

## Claims

### Claim 1

A zero-order diffractive color filter, comprising: 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.

### Claim 2 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein x is such that:
10×Λ<x<25 μm.

### Claim 3 (depends on 2)

The zero-order diffractive colour filter according to claim 2, wherein the period of the microstructure Λ is comprised between 150 and 2000 nm.

### Claim 4 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein the period of the microstructure Λ is comprised between 150 and 2000 nm.

### Claim 5 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein a depth of said microstructures is comprised between 30 and 700 nm.

### Claim 6 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein said microstructures are obtained from beads made of a material selected from the group comprising silica, polystyrene and melamine.

### Claim 7 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein said microstructures are obtained from self-assembly structures of polymers or block copolymers.

### Claim 8 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein said microstructures are obtained by etching through a mask comprising such microstructures.

### Claim 9 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein said microstructures are obtained by embossing a substrate by means of an embossing tool comprising such microstructures.

### Claim 10 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein the wave-guiding layer has a thickness comprised between 30 and 500 nm.

### Claim 11 (depends on 1)

A pigment containing isotropic zero-order diffractive colour filters according to claim 1.

### Claim 12 (depends on 1)

A security device, in particular for banknotes or passports, containing isotropic zero-order diffractive colour filters according to claim 1.

### Claim 13 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein x is such that:
10×Λ<x<10 μm.

### Claim 14 (depends on 1)

The zero-order diffractive colour filter according to claim 1, wherein a period of the microstructure Λ is comprised between 250 and 1200 nm.

### Claim 15

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.

### Claim 16 (depends on 15)

The method according to claim 15, wherein said structures are microstructures formed by a bead layer.

### Claim 17 (depends on 15)

The method according to claim 15, wherein said structures are microstructures obtained by using polymer demixing or block-copolymer phase separation.

### Claim 18 (depends on 15)

The method according to claim 15, wherein said structures are micro- and nano-structures obtained by the combination of polymer demixing with block-copolymer phase separation.

### Claim 19 (depends on 15)

The method according to claim 15, wherein said structures are obtained by etching the substrate through a mask comprising such structures.

### Claim 20

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.