Immersed reflective polarizer with high off-axis reflectivity
A film construction ( 320 ) includes a broad band reflective polarizing film ( 312 ) that may be immersed in an ultra low refractive index medium ( 322, 324 ). The reflecting polarizing film is characterized by a pass axis and a block axis, and its reflectivity for white light of the pass state polarization increases with increasing incidence angle to provide a compressed or narrowed viewing cone in one or two planes.
1. A film construction, comprising:
a plurality of microlayers configured to selectively transmit and reflect light as a function of angle and polarization over an extended wavelength region including visible wavelengths, the microlayers defining a pass axis for normally incident visible light of a first polarization and a block axis for normally incident visible light of a second polarization, the microlayers also characterized by increased a pass axis reflectivity at oblique angles that is greater than a pass axis reflectivity for normally incident light so as to transmit visible light of the first polarization in a compressed viewing cone;
an optically thick low index layer having a refractive index, averaged over visible wavelengths, in a range from 1.1 to 1.3 coupled to the microlayers; and
a first and second optically thick layer arranged such that the optically thick low index layer and the plurality of microlayers are both disposed between the first and second optically thick layers;
wherein the first and second optically thick layers have higher refractive indices than that of the optically thick low index layer.
2. The construction of claim 1 , wherein the plurality of microlayers has a pass axis, a block axis, and a normal axis, and
wherein the plurality of microlayers has an average internal reflectivity over visible wavelengths, as a function of propagation angle θ, of: RPpass(θ) for p-polarized light incident in a pass plane containing the pass axis and the normal axis; RSblock(θ) for s-polarized light incident in the pass plane; RPblock(θ) for p-polarized light incident in a block plane containing the block axis and the normal axis; and RSpass(θ) for s-polarized light incident in the block plane;
wherein Rblock(θ) is an average of RSblock(θ) and RPblock(θ), and Rpass(θ) is an average of RSpass(θ) and RPpass(θ);
wherein the plurality of microlayers has an average internal transmission over visible wavelengths, as a function of the propagation angle θ, of: TPpass(θ) for p-polarized light incident in the pass plane; TSblock(θ) for s-polarized light incident in the pass plane; TPblock(θ) for p-polarized light incident in the block plane; and TSpass(θ) for s-polarized light incident in the block plane; and
wherein Tblock(θ) is an average of TSblock(θ) and TPblock(θ), and Tpass(θ) is an average of TSpass(θ) and TPpass(θ).
3. The construction of claim 2 , wherein Tblock(0) is less than 10%, and wherein Tpass(0) is in a range from 55% to 75%.
4. The construction of claim 3 , wherein the propagation angle θ is an angle θ air measured in air, and wherein Tpass(θ air =60°)<0.85*Tpass(0).
5. The construction of claim 3 , wherein the propagation angle θ is an angle θ low index measured in the optically thick low index layer, and wherein Tpass(θ low index =90°)<0.6* Tpass(0).
6. The construction of claim 1 , wherein the first optically thick layer comprises a light guide.
7. The construction of claim 1 , wherein the first optically thick layer comprises a diffusing layer.
8. The construction of claim 1 , wherein the first optically thick layer comprises a display panel.