Reflective film combinations with output confinement in both polar and azimuthal directions and related constructions

• US 8,917,448 B2
• Filed: 11/16/2009
• Issued: 12/23/2014
• Est. Priority Date: 11/19/2008
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Weber, Michael F., Benoit, Gilles J.
• Primary Examiner(s): Allen, Stephone B
• Assistant Examiner(s): MADONNA, JEFFREY E
• Application Number:
  US13/129,513
• Publication Number:
  US 20110279997A1
• Time in Patent Office: 1,863 Days
• Field of Search: 35948301-49401, 359577-590, 35948901-4892
• US Class Current: 359/489.01
• CPC Class Codes: G02B 5/0841 comprising organic materials, e.g. polymers
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: G02B 5/3066 involving the reflection of light at a particular angle of incidence, e.g. Brewster's angle
• 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: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133545 Dielectric stack polarisers
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 1/133607 the light controlling member including light directing or refracting elements, e.g. prisms or lenses
• CPC Class Codes: G02F 1/133611 including means for improving the brightness uniformity
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/133617 Illumination with ultraviolet light; Luminescent elements or materials associated to the cell
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

A reflective film includes microlayers arranged into optical repeat units to reflect light in an extended wavelength band, with thinner and thicker ones of the optical repeat units being disposed generally towards a thin side and thick side, respectively, of the film. The microlayers are tailored to provide the film with a reflectivity, for p-polarized light incident in a first plane, that decreases by at least half from an initial value at normal incidence to a value R1 at an incidence angle θoblique. The film has a reflectivity for p-polarized light incident in a second plane of R2 at the angle θoblique, where R2>R1. A polarizer is combined with the reflective film, the combination defining an oblique transmission lobe, and the thick and thin sides of the reflective film are oriented relative to the polarizer to reduce an azimuthal width Δφ of the transmission lobe.

Claims

1. A combination, comprising:

a multilayer optical film having a plurality of microlayers arranged into optical repeat units for reflecting light over an extended wavelength band, adjacent microlayers having refractive index differences that define a first and second in-plane axis, such that the film has a reflectivity of at least 75% for all polarization states of normally incident light, the refractive index differences also being such that for p-polarized light incident on the film in a first plane of incidence that includes the first axis, the film has a reflectivity that decreases by at least half from an initial value at normal incidence to a value R1 at an incidence angle θ

oblique measured from a normal of the surface of the multilayer optical film, but for p-polarized light incident on the film in a second plane that includes the second axis, the film has a reflectivity R2>

R1 at the incidence angle θ

oblique; and

a polarizer having a pass axis and a block axis, the polarizer and the multilayer optical film being disposed to define an oblique transmission lobe;

wherein the optical repeat units have an optical thickness distribution across a thickness of the multilayer optical film, the thickness distribution defining a thin side and a thick side of the multilayer optical film, thinner ones of the optical repeat units being disposed generally towards the thin side and thicker ones of the optical repeat units being disposed generally towards the thick side; and

wherein the thin and thick sides of the multilayer optical films are oriented relative to the polarizer to reduce an azimuthal collimation Δ

φ

e of the transmission lobe, wherein the azimuthal collimation Δ

φ

e is measured in a plane parallel to the surface of the multilayer optical film.

2. The combination of claim 1, wherein the reflectivities R1 and R2 each include effects of two film/air interfaces.

3. The combination of claim 1, wherein the reflectivities R1 and R2 each include no effects of any film/air interface.

4. The combination of claim 1, wherein the extended wavelength band is the visible spectrum, and wherein the reflectivities R1 and R2 are each averages over the visible spectrum.

5. The combination of claim 1, wherein the polarizer comprises a reflective polarizer.

6. The combination of claim 1, wherein the pass axis of the polarizer is substantially aligned with the first axis of the multilayer optical film.

7. The combination of claim 1, wherein the oblique transmission lobe is one of two oblique transmission lobes defined by the multilayer optical film —

polarizer combination.

8. The combination of claim 1, wherein the oblique transmission lobe is substantially aligned in azimuthal angle with the first axis.

9. The combination of claim 1, wherein θ

oblique is at least 50 degrees, and wherein the oblique transmission lobe is associated with an incidence angle in air θ

in a range from 50 to 70 degrees.

10. The combination of claim 9, wherein the oblique transmission lobe has a minimum reflectance for p-polarized light at an incidence angle in air θ

of 60 degrees.

11. The combination of claim 1, wherein Δ

φ

e is no more than 120 degrees.

12. The combination of claim 11, wherein Δ

φ

e is no more than 90 degrees.

13. The combination of claim 12, wherein Δ

φ

e is no more than 60 degrees.

14. The combination of claim 1, wherein the thick side of the multilayer optical film faces the polarizer.

15. The combination of claim 1, wherein each optical repeat unit includes a first microlayer composed of a negatively birefringent material.

16. The combination of claim 15, wherein each optical repeat unit includes a second microlayer composed of an isotropic material.

17. The combination of claim 15, wherein each optical repeat unit includes a second microlayer composed of a positively birefringent material.

18. The combination of claim 1, wherein the film exhibits internal Brewster angles in both the first and second planes of incidence.

19. The combination of claim 1, wherein the film exhibits an internal Brewster angle in the first plane of incidence but exhibits no internal Brewster angle in the second plane of incidence.

20. The combination of claim 1, wherein the multilayer optical film and the polarizer are attached to each other with no substantial intervening air gap.

21. A lighting system comprising a lighting system comprising the combination of claim 1.

22. The system of claim 21, further comprising:

a light source extending along a length axis and disposed behind the reflective film;

wherein the reflective film is oriented such that the length axis is substantially perpendicular to the first plane of incidence.

23. The combination of claim 1, further comprising a linear prismatic film coupled to the combination, wherein the prisms extend parallel to a prism axis, and wherein the prism axis is substantially perpendicular to the first plane of incidence of the reflective film.