Curved retarder-based optical filters
View Patent ↗Curved polarization filters and methods of manufacturing such filters. The method includes laminating a planar polarization layer to a planar retarder layer at a predetermined orientation and bending the laminate to create a curved filter. The strain on the retarder layer results in stress-induced birefringence, and the predetermined orientation of the retarder substantially compensates for the stress-induced birefringence. In some embodiments, the predetermination is based on mathematical models. In some other embodiment, the predetermination is based on experimental data.
1. A method for manufacturing a curved filter having a retardation axis in a desired orientation, the method comprising:
providing a planar retarder film having an optical axis;
providing a planar polarization film;
predetermining an angle at which the planar retarder film would be laminated to the planar polarization film;
laminating the planar retarder film and the planar polarization film at the predetermined angle;
bending the laminated retarder and polarization films, whereby a stress is exerted on the retarder film, the stress causing a stress-induced birefringence in the retarder film; and
wherein the predetermined angle substantially compensates for the stress-induced birefringence and allow the optical axis of the retarder film to be in the desired orientation.
2. The method of claim 1 , wherein the predetermined angle is determined using a mathematical model.
3. The method of claim 1 , wherein the predetermined angle is determined using a chart or table, the chart or table providing a correlation between the radius of the curved filter to the predetermined angle.
4. The method of claim 1 , wherein the planar retarder film comprises a quarter-wave plate.
5. The method of claim 1 , wherein the planar retarder film comprises a multi-layer retarder stack.
6. The method of claim 1 , wherein the planar retarder film is made of cyclic olefin block copolymer or cellulose di-acetate.
7. The method of claim 1 , further comprising laminating a non-birefringent film to the planar retarder film, the planar retarder film being laminated between the non-birefringent film and the polarization film.
8. An optical filter in a curved configuration, the filter comprising:
a retarder layer coupled to a polarizer layer;
wherein the retarder layer and polarizer layer are configured to have a compound curvature,
wherein the retarder layer is made of a material having a strain optic coefficient K, a thickness of d, and a retardance of Γ, and wherein the ratio
K
·
d
·
ɛ
″
Γ
is less than 0.01, where “∈″” is the magnitude of a strain tensor induced on the filter by the compound curvature.
9. The filter of claim 8 , wherein the retarder layer is made of a material whose strain optic coefficient is between 0.001 to 0.025.
10. The filter of claim 8 , wherein the retarder layer has a thickness between 50 to 120 micron.
11. The filter of claim 8 , wherein the optical filter was thermoformed.
12. The filter of claim 8 , wherein the retarder layer is substantially made of cyclic olefin block copolymer.
13. The filter of claim 8 , the filter further comprising a substrate layer coupled to either the retarder layer of the polarizer layer.
14. The filter of claim 8 , wherein the coupling comprises lamination.
15. An optical filter in a curved configuration, the filter comprising:
a polarization layer; and
a retarder layer laminated to the polarization layer at a predetermined angle, wherein the retarder and polarization layers are bent to the curved configuration,
wherein the retarder layer has a stress-induced birefringence, and further wherein the predetermined angle substantially compensates for the stress-induced birefringence and disposes the optical axis of the retarder film in a desired orientation.
16. The filter of claim 15 , wherein an outer surface of the polarizer layer is laminated to an inner surface of the retarder layer.
17. The filter of claim 16 , further comprising a non-birefringent layer laminated to an outer surface of the retarder layer, the non-birefringent layer being operable to compensate the stress birefringence in the retarder layer.
18. The filter of claim 15 , wherein an outer surface of the retarder layer is laminated to an inner surface of the polarizer layer.
19. The filter of claim 18 , further comprising a non-birefringent layer laminated to an inner surface of the retarder layer, the non-birefringent layer being operable to compensate the stress birefringence in the retarder layer.
20. The filter of claim 15 , wherein the polarizer and retarder layers are laminated with a pressure sensitive adhesive.
21. The filter of claim 15 , wherein the retarder layer comprises a multi-layer retarder stack.
22. The filter of claim 15 , wherein the retarder layer comprises a quarter wave plate.
23. The filter of claim 15 , wherein the planar retarder film is made of cyclic olefin block copolymer or cellulose di-acetate.