Thick film multilayer reflector with tailored layer thickness profile

• US 20060232863A1
• Filed: 04/18/2005
• Published: 10/19/2006
• Est. Priority Date: 04/18/2005
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Ouderkirk, Andrew J., Nevitt, Timothy J.
• Granted Patent: US 7,385,763 B2
• Time in Patent Office: Days
• US Class Current: 359/586
• CPC Class Codes: B32B 7/023 Optical properties
• CPC Class Codes: G02B 5/0816 Multilayer mirrors, i.e. having two or more reflecting layers G02B5/0883, G02B5/0891 take precedence

Abstract

A multilayer reflector useable to reflect or transmit light over the visible wavelength range includes optically thick constituent layers. The optical thickness of the constituent layers through the thickness of the reflector defines a layer thickness profile. The layers are arranged so that the thickness profile has a tailored non-uniform distribution, such as a graded distribution or a randomized distribution. The layers desirably have an optical thickness in a range from about one to five or one to ten design wavelengths. The reflector can be a polarizer, reflecting only one normally incident polarization state, or a mirror, reflecting two normally incident orthogonal polarization states.

Claims

1. A multilayer reflector that substantially reflects light over the visible spectrum for at least one polarization state, the reflector comprising:

a stack of light-transmissive polymer layers comprising at least a first and second alternating polymer material, the first and second materials having different refractive indices along at least one in-plane axis, the polymer layers having an average optical thickness of at least about (5/4)λ

₀, where λ

₀ is a visible wavelength of interest, the polymer layers contributing substantially to the reflectivity of the multilayer reflector;

wherein the polymer layers in the stack have a non-uniform distribution of optical thicknesses along a thickness axis of the reflector.

2. The reflector of claim 1, wherein the distribution of optical thicknesses is selected to decrease variability in reflection or transmission over visible light wavelengths.

3. The reflector of claim 1, wherein the distribution of optical thicknesses is selected to decrease variability in reflection of normally incident light of the at least one polarization state over visible light wavelengths.

4. The reflector of claim 1, wherein the non-uniform distribution includes a graded distribution.

5. The reflector of claim 1, wherein the non-uniform distribution includes a randomized distribution.

6. The reflector of claim 1, wherein the polymer layers have an average optical thickness of about 10λ

₀ or less.

7. The reflector of claim 6, wherein the polymer layers have an average optical thickness of about 5λ

₀ or less.

8. The reflector of claim 1, wherein the first polymer material is substantially birefringent and the second polymer material is substantially isotropic.

9. The reflector of claim 8, wherein the polymer layers of the first material are thinner than the polymer layers of the second material.

10. The reflector of claim 1, wherein the refractive index difference along an in-plane x-axis is Δ

n_x and a refractive index difference along an in-plane y-axis perpendicular to the x-axis is Δ

n_y, and where |Δ

n_x|≈

|Δ

n_y|.

11. The reflector of claim 1, wherein the refractive index difference along an in-plane x-axis is Δ

n_x and a refractive index difference along an in-plane y-axis perpendicular to the x-axis is Δ

n_y, and where |Δ

n_x|>

|Δ

n_y|.

12. The reflector of claim 11, wherein |Δ

n_y| is 0 or no greater than 0.01.

13. The reflector of claim 12, wherein the refractive index difference along a z-axis perpendicular to both the x- and y-axes is Δ

n_z, and |Δ

n_z| is 0 or no greater than 0.01.

14. The reflector of claim 12, wherein the refractive index difference along a z-axis perpendicular to both the x- and y-axes is Δ

n_z, and |Δ

n_z|>

|Δ

n_y|.

15. The reflector of claim 14, wherein the distribution of optical thicknesses is selected to decrease variability in transmission of p-polarized light obliquely incident in the y-z plane over visible light wavelengths.

16. The reflector of claim 1, wherein the reflector has an overall thickness of less than 1 mm.

17. The reflector of claim 1, wherein the reflector has an overall thickness of at least 1 mm.

18. The reflector of claim 1 in combination with at least one light source illuminating the reflector, the light source emitting light in at least one narrow emission peak.

19. A display comprising the reflector of claim 1.

20. The display of claim 19, wherein the reflector is a reflective polarizer.