Birefringent reflectors using isotropic materials and form birefringence

• US 6,590,707 B1
• Filed: 03/31/2000
• Issued: 07/08/2003
• Est. Priority Date: 03/31/2000
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Weber, Michael F.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Curtis, Craig
• Application Number:
  US09/541,463
• Time in Patent Office: 1,194 Days
• Field of Search: 359/359, 359/485, 359/487, 359/488, 359/493-494, 359/498, 359/500, 359/577, 359/580, 359/587, 359/589, 428/212
• US Class Current: 359/361
• CPC Class Codes: G02B 5/3041 comprising multiple thin layers, e.g. multilayer stacks
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree

Abstract

Multilayer thin film reflectors, such as mirrors and reflective polarizers, are described in which form birefringent optical layers are incorporated into a plurality of optical repeat units in the film. The form birefringent layers exhibit birefringence as a result of microscopic structures that have a dimension that is small compared to the wavelength of light but large compared to molecular distances. The optical layers within the optical repeat units have out-of-plane indices of refraction that are tailored to produce desired effects as a function of incidence angle for p-polarized light. The multilayer reflectors can be made by conventional vacuum deposition techniques using known inorganic optical materials, but can also be made entirely with polymeric materials by co-extrusion or other processes.

Claims

1. A multilayer reflector having a plurality of optical repeat units arranged to reflect one or more desired wavelengths of light, wherein at least some of the optical repeat units comprise:

a uniaxial form birefringent optical layer.

2. The reflector of claim 1, wherein the form birefringent optical layer has an in-plane index of refraction, and an out-of-plane index of refraction that is greater than the in-plane index of refraction.

3. The reflector of claim 1, wherein the form birefringent optical layer has an in-plane index of refraction, and an out-of-plane index of refraction that is less than the in-plane index of refraction.

4. The reflector of claim 1, wherein the at least some of the optical repeat units further comprise:

an isotropic optical layer.

5. The reflector of claim 1, wherein the at least some of the optical repeat units further comprise:

a second uniaxial form birefringent optical layer.

6. The reflector of claim 1, wherein the plurality of optical repeat units are arranged to form a device selected from the group consisting of a mirror and a polarizer.

7. The reflector of claim 3, wherein the form birefringent optical layer comprises at least three microlayers.

8. The reflector of claim 3, wherein the form birefringent optical layer has a bottom microlayer and a top microlayer composed of the same material.

9. The reflector of claim 3, wherein the form birefringent optical layer consists essentially of an odd number of microlayers.

10. The reflector of claim 5, wherein the first form birefringent optical layer is positive uniaxial and the second form birefringent optical layer is negative uniaxial.

11. A multilayer reflector having a plurality of optical repeat units arranged to reflect one or more desired wavelengths of light, wherein at least some of the optical repeat units comprise:

an isotropic optical layer; and

a form birefringent optical layer.

12. The reflector of claim 11, wherein the form birefringent optical layer is selected from the group consisting of a positive uniaxial optical layer, a negative uniaxial optical layer, and a biaxial optical layer.

13. The reflector of claim 11, wherein the form birefringent optical layer comprises at least three microlayers.

14. The reflector of claim 13, wherein the form birefringent optical layer has a top microlayer and a bottom microlayer composed of the same material.

15. A multilayer reflector having a plurality of optical repeat units arranged to reflect one or more desired wavelengths of light, wherein at least some of the optical repeat units comprise:

an intrinsically birefringent optical layer; and

a form birefringent optical layer.

16. A multilayer reflector having a plurality of optical repeat units arranged to reflect one or more desired wavelengths of light, wherein at least some of the optical repeat units comprise a form birefringent optical layer and another optical layer, and wherein a relationship between the out-of-plane refractive indices of the form birefringent optical layer and the another optical layer produces a desired reflectivity of p-polarized light as a function of incidence angle.

17. The reflector of claim 16, wherein the out-of-plane refractive indices differ by an amount less than about 80% of the largest in-plane index differential between the form birefringent optical layer and the another optical layer.

18. The reflector of claim 16, wherein the out-of-plane refractive indices differ by an amount that is opposite in sign to at least a first in-plane index differential between the form birefringent optical layer and the another optical layer.

19. The reflector of claim 16, wherein the out-of-plane refractive indices differ by an amount that is of the same sign as a second in-plane index differential between the form birefringent optical layer and the another optical layer.

20. The reflector of claim 17, wherein the out-of-plane refractive indices differ by an amount less than about 50% of the largest in-plane index differential between the form birefringent optical layer and the another optical layer.

21. The reflector of claim 20, wherein the out-of-plane refractive indices differ by an amount less than about 20% of the largest in-plane index differential between the form birefringent optical layer and the another optical layer.

22. The reflector of claim 21, wherein the first in-plane differential is greater in magnitude than the second in-plane differential.

23. A mirror comprising a plurality of form birefringent optical layers.

24. The mirror of claim 23, wherein the form birefringent optical layers are arranged with at least a second plurality of optical layers to form a plurality of optical repeat units.

25. The mirror of claim 24, wherein the second plurality of layers are substantially isotropic optical layers.

26. The mirror of claim 24, wherein the second plurality of layers are intrinsically birefringent optical layers.

27. The mirror of claim 24, wherein the second plurality of layers are form birefringent optical layers.

28. The mirror of claim 24, wherein the form birefringent optical layers each comprise at least 3 microlayers.

29. The mirror of claim 24, wherein the form birefringent optical layers comprise inorganic material.

30. The mirror of claim 24, wherein the form birefringent optical layers comprise polymeric material.