Optical film
An optical film has a major surface including a plurality of microstructures. Each microstructure includes an optical facet and a sidewall meeting the optical facet at a ridge of the microstructure. The optical facet and the sidewall define an oblique angle therebetween. For each microstructure in at least a majority of the microstructures, an optically absorptive layer is disposed on the sidewall. The optical film can include a polymeric layer having a microstructured surface at least partially coated with an inorganic optically transparent layer. The optically absorptive layer can an average thickness t where 100 nm<t<1 micrometer. A first layer can be disposed between the sidewall and the optically absorptive layer where the first layer has a lower extinction coefficient than the optically absorptive layer.
1. An optical film comprising a polymeric layer comprising a microstructured surface conformally coated with an inorganic optically transparent layer, the conformally coated microstructured surface comprising a plurality of microstructures, each microstructure comprising an optical facet and a sidewall meeting the optical facet at a ridge of the microstructure, the optical facet and the sidewall defining an oblique angle therebetween, wherein for each microstructure in at least a majority of the microstructures:
an optically absorptive layer is disposed on and substantially covers the sidewall, the optically absorptive layer comprising a first polyelectrolyte; and
the optical facet has a mean deviation surface roughness Ra<50 nm.
2. The optical film of claim 1 , wherein the optically absorptive layer comprises a second polyelectrolyte, the first and second polyelectrolytes having opposite charges.
3. The optical film of claim 1 , wherein the optically absorptive layer comprises a light absorbing material ionically bonded to the first polyelectrolyte.
4. The optical film of claim 1 , wherein the plurality of microstructures defines a Fresnel lens.
5. The optical film of claim 4 , wherein the Fresnel lens comprises a plurality of linear Fresnel elements extending longitudinally along a first direction.
6. The optical film of claim 1 , wherein for each microstructure in at least the majority of the microstructures, the optically absorptive layer has an average thickness t, 100 nm<t<1 micrometer.
7. The optical film of claim 6 , wherein for each microstructure in at least the majority of the microstructures, the sidewall of the microstructure has a height H from a base of an adjacent microstructure to the ridge of the microstructure, H/t>15.
8. The optical film of claim 1 , wherein for each microstructure in at least the majority of the microstructures, a first layer is disposed between the sidewall and the optically absorptive layer.
9. The optical film of claim 8 , wherein the first layer has a concentration C 1 of light absorbing material and the optically absorptive layer has a concentration C 2 of light absorbing material, C 2 >C 1 .
10. The optical film of claim 1 , wherein the plurality of microstructures has an extinction coefficient k 0 <0.05, and wherein for each microstructure in at least a majority of the microstructures:
a first layer is disposed between the sidewall and the optically absorptive layer, the first layer having an extinction coefficient k 1 , wherein k 1 >k 0 ; and
the optically absorptive layer has an extinction coefficient k 2 , wherein k 2 −k 1 >0.05.
11. The optical film of claim 1 , wherein the inorganic optically transparent layer is a monolithic layer directly contacting the microstructured surface of the polymeric layer and comprising an outermost major surface of the optical film.