Optical film stack with retardance layer having in-plane retardance of greater than 2.0 microns
Optical film stacks are disclosed. The optical film stacks can include a first reflective polarizer, a second reflective polarizer, and a retardance layer disposed between the first reflective polarizer and the second reflective polarizer.
1. An optical film stack, comprising:
a first reflective polarizer having a pass axis;
a second reflective polarizer; and
a stretched polymeric retardance layer having a fast axis disposed between the first reflective polarizer and the second reflective polarizer, the retardance layer having a thickness, d, and having in-plane index of refraction values n x and n y and an index of refraction n z in a direction orthogonal to the plane of the film, wherein
0.04<|( n x −n y )/(0.5( n x +n y )− n z )|<1.00, and
2.0 microns< d ×|( n x −n y )|<75 microns;
wherein the pass axis of the first reflective polarizer is within 20 degrees of parallel with the fast axis of the retardance layer.
2. The optical film stack of claim 1 , wherein 0.12<|(n x −n y )/(0.5(n x +n y )−n z )|<0.50.
3. The optical film stack of claim 1 , wherein 2.0 microns<d×(n x −n y )|<25 microns.
4. The optical film stack of claim 1 , further comprising a diffuser plate, the diffuser plate being attached to the first reflective polarizer on a side opposite the retardance layer.
5. The optical film stack of claim 4 , wherein the diffuser plate and the first reflective polarizer are optically coupled by an optical coupling layer, the optical coupling layer having an index of refraction of less than 1.2.
6. The optical film stack of claim 1 , wherein light traveling through the film stack has an optical gain of at least 1.5.
7. The optical film stack of claim 1 , wherein a pass axis of the first reflective polarizer is substantially parallel to a pass axis of the second reflective polarizer.
8. The optical film stack of claim 1 , wherein the first reflective polarizer and the second reflective polarizer are linear polarizers.
9. The optical film stack of claim 1 , wherein the retardance layer comprises a first and second retardance sublayer.
10. The optical film stack of claim 9 , wherein the first retardance sublayer has a first fast axis and the second retardance sublayer has a second fast axis, the first and second fast axes being substantially parallel.
11. The optical film stack of claim 9 , wherein the first retardance sublayer has a first fast axis and the second retardance sublayer has a second fast axis, the first and second fast axes being substantially orthogonal.
12. An optical film stack, comprising:
a first reflective polarizer having a pass axis;
a second reflective polarizer; and
a stretched polymeric retardance layer having a fast axis disposed between the first reflective polarizer and the second reflective polarizer, the retardance layer having a thickness, d, and having orthogonal in-plane index of refraction values n x and n y , and an index of refraction, n z , in a direction orthogonal to the plane of the film, wherein
0.04<|( n x −n y )/(0.5( n x +n y )− n z )|<1.00, and
2.0 microns< d ×|( n x −n y )|<75 microns;
a brightness enhancement film having a first and second major surface, the first major surface being a smooth surface attached to the second reflective polarizer on a side opposite the retardance layer, and the second major surface being a structured surface that comprises a plurality of prismatic structures;
wherein the pass axis of the first reflective polarizer is within 20 degrees of parallel with the fast axis of the retardance layer.
13. The optical film stack of claim 12 , wherein 0.12<|(n x −n y )/(0.5(n x +n y )−n z )|<0.50.
14. The optical film stack of claim 12 , wherein 2.0 microns<d×|(n−n y )|<25 microns.
15. The optical film stack of claim 12 , further comprising a diffuser plate, the diffuser plate being attached to the first reflective polarizer on a side opposite the retardance layer.
16. The optical film stack of claim 15 , wherein the diffuser plate and first reflective polarizer are optically coupled by an optical coupling layer, the optical coupling layer having an index of refraction of less than 1.2.
17. The optical film stack of claim 12 , wherein each prismatic structure of the plurality of prismatic structures has two facets that meet at a peak, the peak having a peak angle of approximately 90 degrees.
18. The optical film stack of claim 12 , wherein light traveling through the film stack has an optical gain of greater than 1.5.
19. The optical film stack of claim 12 , wherein the retardance layer comprises a first and second retardance sublayer.
20. The optical film stack of claim 19 , wherein the first retardance sublayer has a first fast axis and the second retardance sublayer has a second fast axis, the first and second fast axes being substantially parallel.
21. The optical film stack of claim 19 , wherein the first retardance sublayer has a first fast axis and the second retardance sublayer has a second fast axis, the first and second fast axes being substantially orthogonal.
22. The optical film stack of claim 12 , wherein a pass axis of the first reflective polarizer is substantially parallel to a pass axis of the second reflective polarizer.
23. The optical film stack of claim 12 , further comprising an adhesive layer attaching the first major surface of the brightness enhancement film and the second reflective polarizer, the adhesive layer having an index of refraction of less than 1.2.