High contrast optical film and devices including the same
Optical films are disclosed that include a plurality of interference layers. Each interference layer reflects or transmits light primarily by optical interference. The total number of the interference layers is less than about 1000. For a substantially normally incident light in a predetermined wavelength range, the plurality of interference layers has an average optical transmittance greater than about 85% for a first polarization state, an average optical reflectance greater than about 80% for an orthogonal second polarization state, and an average optical transmittance less than about 0.2% for the second polarization state.
1. An optical stack comprising a reflective polarizer bonded to, and substantially co-extensive with, an absorbing polarizer, such that for a substantially normally incident light and a visible wavelength range disposed between about 400 nm to about 700 nm:
the reflective polarizer has an average optical transmittance Ta and an average optical reflectance Ra for a first polarization state, and an average optical transmittance Tb and an average optical reflectance Rb for an orthogonal second polarization state, Tb/Rb less than about 0.002 and Ra/Ta less than about 0.17; and
the absorbing polarizer has an average first optical transmittance for the first polarization state, an average optical absorption of greater than about 50% for the second polarization state, and an average second optical transmittance for the second polarization state, a ratio of the average second optical transmittance to the average first optical transmittance greater than about 0.01.
2. The optical stack of claim 1 , wherein the ratio of the average second optical transmittance to the average first optical transmittance is greater than about 0.1.
3. The optical stack of claim 1 , wherein the reflective polarizer has a plurality of alternating different first and second polymeric layers numbering less than 800 in total.
4. The optical stack of claim 1 , wherein for light incident at an incidence angle of about 30 degrees, the reflective polarizer has an average optical transmittance of greater than about 85% for the first polarization state, an average optical reflectance of greater than about 80% for the second polarization state, and an average optical transmittance of less than about 0.2% for the second polarization state.
5. The optical stack of claim 1 , wherein T a /T b is greater than about 425.
6. The optical stack of claim 1 , wherein R b /R a is greater than about 6.7.
7. The optical stack of claim 1 , wherein the reflective polarizer has a thickness of less than about 60 μm.