Multilayer optical thin film structure

Patent metadata

Field	Value
Publication number	US-12055740-B2
Application number	US-201917045005-A
Country	US
Kind code	B2
Filing date	Apr 3, 2019
Priority date	Apr 5, 2018
Publication date	Aug 6, 2024
Grant date	Aug 6, 2024

Abstract

There is described a multilayer optical thin film structure comprising multiple optically absorbing layers and multiple optically non-absorbing layers. The optically absorbing layers and the optically non-absorbing layers are configured such that light incident on the structure is reflected with a red colour at a first angle, and light incident on the structure is reflected with a yellow colour at a second angle. There is also described an item having applied thereto such a multilayer structure.

First claim

The invention claimed is:

1. A multilayer optical thin film structure comprising:
multiple optically absorbing layers; and
multiple optically non-absorbing layers,
wherein the optically absorbing layers and the optically non-absorbing layers are configured such that visible light incident on the structure is reflected with a red colour at a first angle relative to a normal to a plane defined by the structure, and visible light incident on the structure is reflected with a yellow colour at a second angle relative to the normal to the plane defined by the structure, and
wherein the first angle is smaller than the second angle.

2. The optical thin film structure of claim 1 , wherein the optically absorbing layers comprise semiconducting layers.

3. The optical thin film structure of claim 1 , wherein the optically absorbing layers comprise one or more of a metal, a metal alloy, a metalloid, a nitride, amorphous silicon, germanium, and tantalum.

4. The optical thin film structure of claim 1 , wherein the optically non-absorbing layers comprise one or more of silicon oxide, aluminium oxide, magnesium fluoride, an oxide, and a fluorite.

5. The optical thin film structure of claim 1 , further comprising a bonding layer for bonding the structure to a substrate.

6. The optical thin film structure of claim 1 , wherein the structure comprises at least three optically absorbing layers and at least three optically non-absorbing layers.

7. The optical thin film structure of claim 1 , wherein the optically absorbing layers and the optically non-absorbing layers are arranged in alternating order.

8. The optical thin film structure of claim 1 , further comprising an optically absorbing and reflecting layer.

9. The optical thin film structure of claim 8 , wherein the optically absorbing and reflecting layer comprises one or more of a metal, a metal alloy, aluminium, silver, gold, chromium, nickel, and tantalum.

10. The optical thin film structure of claim 8 , wherein the structure comprises at least three optically non-absorbing layers.

11. The optical thin film structure of claim 8 , wherein the optically absorbing layers and the optically non-absorbing layers are arranged to form a stack, and wherein the optically absorbing and reflecting layer is arranged at an end of the stack.

12. The optical thin film structure of claim 11 , wherein one of the optically absorbing layers comprises the optically absorbing and reflecting layer.

13. The optical thin film structure of claim 8 , wherein the optically absorbing layers and the optically non-absorbing layers are positioned on one side of the optically absorbing and reflecting layer and form a set of layers, and wherein the structure further comprises an identical set of layers positioned on an opposite side of the optically absorbing and reflecting layer.

14. The optical thin film structure of claim 1 , wherein at least one of the optically absorbing layers comprises amorphous silicon and at least one of the optically non-absorbing layers comprises silicon dioxide.

15. The optical thin film structure of claim 1 , wherein at least one of the optically absorbing layers comprises germanium and at least one of the optically non-absorbing layers comprises silicon dioxide.

16. The optical thin film structure of claim 8 , wherein the optically absorbing and reflecting layer comprises aluminium, at least one of the optically absorbing layers comprises tantalum, and at least one of the optically non-absorbing layers comprises silicon dioxide.

17. The optical thin film structure of claim 8 , wherein the optically absorbing and reflecting layer comprises aluminium, at least one of the optically absorbing layers comprises a nitride, and at least one of the optically non-absorbing layers comprises silicon dioxide.

18. The optical thin film structure of claim 8 , wherein the optically absorbing and reflecting layer comprises aluminium, at least one of the optically absorbing layers comprises germanium, and at least one of the optically non-absorbing layers comprises silicon dioxide.

19. The optical thin film structure of claim 8 , wherein the optically absorbing and reflecting layer comprises chromium, at least one of the optically absorbing layers comprises amorphous silicon, and at least one of the optically non-absorbing layers comprises silicon dioxide.

20. The optical thin film structure of claim 1 , wherein the first angle is comprised between about 0 degrees relative to the normal to the plane defined by the structure, and about 28 degrees relative to the normal, and wherein the second angle is comprised between about 45 degrees relative to the normal, and about 80 degrees relative to the normal.

21. The optical thin film structure of claim 1 , wherein the optically absorbing layers and the optically non-absorbing layers are further configured such that, as an angle of reflection of visible light incident on the structure varies from the first angle to the second angle, a degree of yellow in the reflected light increases and a degree of red in the reflected light decreases.

22. The optical thin film structure of claim 1 , wherein the optically non-absorbing layers comprise dielectric layers.

23. A method of securing an item so as to inhibit or prevent counterfeiting of the item, comprising applying to the item a multilayer optical thin film structure according to claim 1 .

24. An item having applied thereto a multilayer optical thin film structure according to claim 1 , wherein the item comprises one or more of a bank note, a document, a passport, an identification card, a bank card, and a valuable good.

25. The optical thin film structure of claim 1 , wherein the red colour is in a red colour region of a 1931 CIE chromaticity diagram.

Assignees

• Nat Res Council Canada

Inventors

• Ma Penghui

Classifications

• G02B5/22

  Absorbing filters {(G02B5/201 - G02B5/208 take precedence)} · CPC title

• B42D25/36

  comprising special materials · CPC title

• B42D25/29

  Securities; Bank notes · CPC title

• G02B5/26

  Reflecting filters (G02B5/28 takes precedence) · CPC title

• G02B5/207

  comprising semiconducting materials · CPC title