Reverse-order crossed pancake lens with a shaped polarizer
In various embodiments, a pancake lens block including a shaped reflective polarizer is described. In an embodiment, the shaped reflective polarizer may include an optical element that may be configured to transmit at least a portion of light from a light source. Further, the shaped reflective polarizer may include a wire-grid polarizer that comprises (i) a bolstering substrate, (ii) a wire-grid substrate coupled to the bolstering substrate, and (iii) wire-grids disposed on the wire-grid substrate. The shaped reflective polarizer may be spaced from the optical element by a distance, which may include a cavity filled with a material (such as air or a nanovoided material).
1. A pancake lens block, comprising:
an optical element configured to transmit at least a portion of radiation from a radiation source;
a shaped reflective polarizer spaced at a distance from the optical element, wherein:
the shaped reflective polarizer is configured to provide achromatic optical reflection of the portion of radiation within the pancake lens block; and
the shaped reflective polarizer comprises:
a curved lens having a radius of curvature and at least one convex-shaped surface; and
a wire-grid polarizer shaped in two axes, the wire-grid polarizer comprising:
a wire-grid film;
a wire grid disposed on the wire-grid film, wherein the wire grid comprises a set of wires packed together on a concave-shaped surface of the wire-grid film; and
a bolstering substrate having a concave-shaped surface shaped to the convex-shaped surface of the curved lens and being coupled to the wire-grid film, wherein the bolstering substrate is configured to:
provide mechanical support to the wire-grid film to prevent the wire-grid film from buckling during a lamination process in which the wire-grid polarizer is coupled to the convex-shaped surface of the curved lens such that the wire grid is oriented toward the curved lens and the concave-shaped surface of the wire-grid film is oriented toward the curved lens; and
maintain a polarization state of the portion of radiation transmitted by the optical element; and
a nanovoided material positioned between the optical element and the shaped reflective polarizer.
2. The pancake lens block of claim 1 , wherein the optical element comprises:
a first retarder having a first axis of orientation, where the first retarder is configured to selectively transmit the portion of radiation from the radiation source;
a partial reflector that receives the portion of radiation from the first retarder and transmits the portion of radiation; and
a second retarder having a surface and being at the distance from the shaped reflective polarizer, where the second retarder is oriented to a second axis of orientation that is substantially orthogonal to the first axis of orientation, and where the second retarder transmits the portion of radiation from the partial reflector.
3. The pancake lens block of claim 2 , wherein the shaped reflective polarizer is configured to reflect the portion of radiation transmitted by the second retarder back to the partial reflector through the second retarder, where the partial reflector reflects a second portion of the radiation from the second retarder back to the shaped reflective polarizer.
4. The pancake lens block of claim 1 , wherein the bolstering substrate comprises a tri-acetyl cellulose (TAC) material or a poly-methyl methacrylate (PMMA) material.
5. The pancake lens block of claim 1 , wherein the wire-grid polarizer is thermoformed and the bolstering substrate has a glass transition temperature characterized by an associated rate of change with temperature being below a threshold.
6. The pancake lens block of claim 1 , wherein the wire-grid film comprises a TAC material or a PMMA material.
7. The pancake lens block of claim 1 , wherein the wire grid comprise a TAC material.
8. The pancake lens block of claim 1 , wherein:
the distance is configured to provide additional optical path length in the pancake lens block.
9. The pancake lens block of claim 1 , wherein each wire included in the set of wires has at least one dimension that is less than a micron.
10. A head mounted display (HMD) comprising:
an electronic display configured to emit light; and
a pancake lens block comprising:
an optical element configured to transmit at least a portion of the light emitted by the electronic display;
a shaped reflective polarizer spaced at a distance from the optical element, wherein:
the shaped reflective polarizer is configured to provide achromatic optical reflection of the portion of light within the pancake lens block; and
the shaped reflective polarizer comprises:
a curved lens having a radius of curvature and at least one convex-shaped surface; and
a wire-grid polarizer shaped in two axes, the wire-grid polarizer comprising:
a wire-grid film;
a wire grid disposed on the wire-grid film, wherein the wire grid comprises a set of wires are packed together on a concave-shaped surface of the wire-grid film; and
a bolstering substrate having a concave-shaped surface shaped to the convex-shaped surface of the curved lens and being coupled to the wire-grid film, wherein the bolstering substrate is configured to:
provide mechanical support to the wire-grid film to prevent the wire-grid film from buckling during a lamination process in which the wire-grid polarizer is coupled to the convex-shaped surface of the curved lens such that the wire grid is oriented toward the curved lens and the concave-shaped surface of the wire-grid film is oriented toward the curved lens; and
maintain a polarization state of the portion of light emitted by the electronic display; and
a nanovoided material positioned between the optical element and the shaped reflective polarizer.
11. The HMD of claim 10 , wherein the optical element comprises:
a first retarder having a first axis of orientation, where the first retarder is configured to selectively transmit the portion of the light emitted by the electronic display;
a partial reflector that receives the portion of light from the first retarder and transmits the portion of light; and
a second retarder having a surface and being at the distance from the shaped reflective polarizer, and where the second retarder is oriented to a second axis of orientation that is substantially orthogonal to the first axis of orientation, and where the second retarder transmits the portion of light from the partial reflector.
12. The HMD of claim 11 , wherein the shaped reflective polarizer is configured to reflect the portion of light transmitted by the second retarder back to the partial reflector through the second retarder, where the partial reflector reflects a second portion of the light from the second retarder back to the shaped reflective polarizer.
13. The HMD of claim 10 , wherein the bolstering substrate comprises a tri-acetyl cellulose (TAC) material or a poly-methyl methacrylate (PMMA) material.
14. A method of assembling a pancake lens block, the method comprising:
configuring an optical element to transmit at least a portion of radiation from a radiation source;
spacing a shaped reflective polarizer from the optical element by a distance, wherein:
the shaped reflective polarizer is configured to provide achromatic optical reflection of the portion of radiation within the pancake lens block; and
the shaped reflective polarizer comprises:
a curved lens having a radius of curvature and at least one convex-shaped surface; and
a wire-grid polarizer shaped in two axes, the wire-grid polarizer comprising:
a wire-grid film;
a wire grid disposed on the wire-grid film, wherein the wire grid comprises a set of wires packed together on a concave-shaped surface of the wire-grid film; and
a bolstering substrate having a concave-shaped surface shaped to the convex-shaped surface of the curved lens and being coupled to the wire-grid film, wherein the bolstering substrate is configured to:
provide mechanical support to the wire-grid film to prevent the wire-grid film from buckling during a lamination process in which the wire-grid polarizer is coupled to the convex-shaped surface of the curved lens such that the wire grid is oriented toward the curved lens and the concave-shaped surface of the wire-grid film is oriented toward the curved lens; and
maintain a polarization state of the portion of radiation transmitted by the optical element; and
positioning a nanovoided material between the optical element and the shaped reflective polarizer.