High contrast optical film having specified transmittance and reflectance of polarized light
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 film comprising:
a plurality of interference layers, each interference layer reflecting or transmitting light primarily by optical interference, a total number of the interference layers less than about 1000, such that for a substantially normally incident light in a predetermined wavelength range extending from about 400 nm to about 700 nm, the plurality of interference layers has an average optical transmittance over the predetermined wavelength range greater than about 95% for a first polarization state, an average optical reflectance over the predetermined wavelength range greater than about 80% for an orthogonal second polarization state, and an average optical transmittance over the predetermined wavelength range less than about 0.2% for the second polarization state.
2. The optical film of claim 1 , such that for light incident on the optical film at an incidence angle of about 30 degrees in the predetermined wavelength range, the plurality of interference layers has an average optical transmittance greater than about 85% for the first polarization state, an average optical reflectance greater than about 80% for the second polarization state, and an average optical transmittance less than about 0.2% for the second polarization state.
3. The optical film of claim 1 , wherein the plurality of interference layers comprises a plurality of alternating first and second polymeric layers, for each pair of adjacent first and second layers: in a plane of the first layer, the first layer has a maximum index of refraction n1x along an x-direction; the second layer has an index of refraction n2x along the x-direction; and a difference between n1x and n2x is greater than about 0.24.
4. The optical film of claim 3 , wherein a maximum angular range of the x-directions of the first layers is less than about 2 degrees.
5. The optical film of claim 1 , wherein an optical power of the plurality of the interference layers per interference layer is greater than −0.0012*N+1.46, where N is the total number of the interference layers.
6. The optical film of claim 1 , wherein for a plurality of non-overlapping groups of sequentially arranged layers in the plurality of interference layers, the layers in each group numbered from one to m, m greater than 25, for each non-overlapping group a fitted curve is a best-fit regression applied to a layer thickness of the group as a function of layer number, wherein in a region extending from the first layer in the group to the mth layer in the group, the fitted curve has an average slope such that, a maximum difference between the average slopes of the fitted curves in the plurality of non-overlapping groups is less than 0.70 nm/layer.