Thin-film optical retarders
View Patent ↗An oblique angle deposition is used to provide an A-plate optical retarder having at least one dense, form-birefringent layer. According to one embodiment, the dense, form-birefringent layer(s) are deposited as part of an FBAR stack to provide an all-dielectric full-function A/−C-plate trim retarder for LCD birefringence compensation. Advantageously, the dense structure of the full-function A/−C-plate trim retarder offers high durability and/or stability, thus making it well suited for providing polarization compensation in high light flux polarization-based projection systems.
1. An optical retarder comprising: a form-birefringent layer formed using an oblique angle deposition, wherein the form-birefringent layer has a predetermined A-plate retardance, wherein the form-birefringent layer is substantially non-porous, wherein the form-birefringent layer is substantially amorphous, and wherein the form-birefringent layer lacks distinct column/void microstructure.
2. An optical retarder according to claim 1 , wherein the form-birefringent layer has a density greater than about 90% of the layer material bulk density.
3. An optical retarder according to claim 1 , wherein the form-birefringent layer comprises a dielectric thin film.
4. An optical retarder according to claim 1 , wherein form-birefringent layer comprises a metal oxide.
5. An optical retarder according to claim 1 , wherein the form-birefringent layer consists of Ta 2 O 5 .
6. An optical retarder according to claim 1 , wherein the form-birefringent layer is incorporated into an anti-reflection thin film stack.
7. An optical retarder according to claim 1 , wherein the predetermined A-plate retardance is between 1 and 30 nm at a wavelength in the visible band.
8. An optical retarder according to claim 1 , wherein the optical retarder is a trim retarder, and wherein the predetermined A-plate retardance is for compensating for the residual in-plane birefringence of a liquid crystal display panel.
9. An optical retarder according to claim 8 , comprising a form-birefringent anti-reflection stack including a first plurality of dielectric layers having first refractive index, interleaved with at least a second plurality of dielectric layers having a second refractive index, for providing −C-plate retardance for compensating the out-of-plane birefringence of the liquid crystal display panel.
10. An optical retarder according to claim 9 , wherein the form-birefringent layer and the form-birefringent anti-reflection stack are coupled to opposite sides of a substrate.
11. An optical retarder according to claim 9 , wherein the form-birefringent layer and the form-birefringent anti-reflection stack are cascaded on a same side of a substrate.
12. An optical retarder according to claim 9 , wherein the form-birefringent layer and the form birefringent anti-reflection stack are coupled to a cover plate of the liquid crystal display panel.
13. A method of fabricating an optical retarder comprising: depositing a form-birefringent layer on a surface using an oblique angle deposition, wherein the form-birefringent layer has a predetermined A-plate retardance, wherein the form-birefringent layer is substantially non-porous, wherein the form-birefringent layer is substantially amorphous, and wherein the form-birefringent layer lacks distinct column/void microstructure.
14. A method of fabricating an optical retarder according to claim 13 , wherein depositing the form-birefringent layer using the oblique angle deposition includes directing a material towards the surface at the deposition angle using an energetic process.
15. A method of fabricating an optical retarder according to claim 13 , wherein the energetic process includes an ion-assisted deposition.
16. A method of fabricating an optical retarder according to claim 13 , wherein depositing the form-birefringent layer using the oblique angle deposition includes directing a material towards the surface using a range of incident vapour flux angles.
17. A method of fabricating an optical retarder according to claim 16 , wherein the average deposition angle is less than about 40°.
18. A method of fabricating an optical retarder according to claim 16 , wherein the maximum deposition angle is less than about 40°.
19. A method of fabricating an optical retarder according to claim 16 , including using a mask to reduce the maximum deposition angle.
20. A method of fabricating an optical retarder according to claim 13 , wherein the optical retarder is a trim retarder, and wherein depositing the form-birefringent layer using the oblique angle deposition includes directing a material towards the surface at a deposition angle less than 40° until the form-birefringent layer is sufficiently thick to have the predetermined A-plate retardance, the predetermined A-plate retardance for compensating for the residual in-plane birefringence of a liquid crystal display panel.
21. A liquid crystal display based projection system comprising: a light source; a first polarizer for receiving light from the light source and transmitting a first linearly polarized light having a first linear polarization axis; a liquid crystal display panel for optically modulating the first linearly polarized light, the liquid crystal display panel having residual birefringence; a second polarizer for receiving the optically modulated light and for transmitting a second linearly polarized light having a second linear polarization axis; a projection lens for projecting the second linearly polarized light onto a screen; and a trim retarder for compensating the residual birefringence of the liquid crystal display panel, the trim retarder comprising: a form-birefringent layer deposited using an oblique angle deposition, wherein the form-birefringent layer has a predetermined A-plate retardance, wherein the form-birefringent layer is substantially non-porous, wherein the form-birefringent layer is substantially amorphous, and wherein the form-birefringent layer lacks distinct column/void microstructure.
22. A liquid crystal display based projection system according to claim 21 , wherein the trim retarder has an out-of-plane retardance of between 0 nm and −1000 nm in a wavelength range between 380 nm and 800 nm, and an in-plane retardance of between 1 nm and 30 nm in a wavelength range between 380 nm to 800 nm.
23. The liquid crystal display based projection system according to claim 21 , wherein the trim retarder is integrated with the liquid crystal display panel.
24. The liquid crystal display based projection system according to claim 21 , wherein the liquid crystal display panel is a VAN-mode LCoS microdisplay panel, and wherein the first and second polarizers are a same polarization beam splitter.
25. A method of providing polarization control comprising: inserting an optical retarder in a polarized beam of light, the optical retarder including a form-birefringent layer deposited using an oblique angle deposition, wherein the form-birefringent layer has a predetermined A-plate retardance, wherein the form-birefringent layer is substantially non-porous, wherein the form-birefringent layer is substantially amorphous, and wherein the form-birefringent layer lacks distinct column/void microstructure.
26. A method according to claim 25 , wherein inserting the optical retarder in a polarized beam of light comprises inserting the optical retarder in a polarized beam of light in a liquid crystal display based projection system, and wherein the predetermined A-plate retardance is for compensating for the residual in-plane birefringence of a liquid crystal display panel in the projection system.
27. A method according to claim 26 , wherein the optical retarder is an all-dielectric trim retarder.
28. A method according to claim 26 , wherein the predetermined A-plate retardance is sufficiently high to provide the polarization control.
29. A method according to claim 27 , comprising rotating the trim retarder about an axis substantially perpendicular to the plane thereof such that the system contrast level is increased.